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Sample records for compressible mixing layer

  1. The compressible mixing layer

    NASA Technical Reports Server (NTRS)

    Vandromme, Dany; Haminh, Hieu

    1991-01-01

    The capability of turbulence modeling correctly to handle natural unsteadiness appearing in compressible turbulent flows is investigated. Physical aspects linked to the unsteadiness problem and the role of various flow parameters are analyzed. It is found that unsteady turbulent flows can be simulated by dividing these motions into an 'organized' part for which equations of motion are solved and a remaining 'incoherent' part represented by a turbulence model. Two-equation turbulence models and second-order turbulence models can yield reasonable results. For specific compressible unsteady turbulent flow, graphic presentations of different quantities may reveal complementary physical features. Strong compression zones are observed in rapid flow parts but shocklets do not yet occur.

  2. Analysis of Compressible Mixing Layers Using Dilatational Covariances Model

    NASA Technical Reports Server (NTRS)

    Thangam, S.; Zhou, Y.; Ristorcelli, J. R.

    1996-01-01

    Compressible mixing layers are analyzed using a dilatational covariances model based on a pseudo-sound constitutive relation. The calculations are used to evaluate the different physical phenomena affecting compressible mixing layers. The rate of growth of the mixing layer is retarded by both the compressible dissipation and the pressure-dilatational covariances. The pressure-dilatational, essentially a nonequilibrium effect, reduces the amount of excess production over dissipation available for the turbulence energy growth. The pseudo-sound model also includes a history dependent portion: this is also investigated. All constants in the model and used in these computations are predicted by the theory.

  3. The stability of compressible mixing layers in binary gases

    NASA Technical Reports Server (NTRS)

    Kozusko, F.; Lasseigne, D. G.; Grosch, C. E.; Jackson, T. L.

    1996-01-01

    We present the results of a study of the inviscid two-dimensional spatial stability of a parallel compressible mixing layer in a binary gas. The parameters of this study are the Mach number of the fast stream, the ratio of the velocity of the slow stream to that of the fast stream, the ratio of the temperatures, the composition of the gas in the slow stream and in the fast stream, and the frequency of the disturbance wave. The ratio of the molecular weight of the slow stream to that of the fast stream is found to be an important quantity and is used as an independent variable in presenting the stability characteristics of the flow. It is shown that differing molecular weights have a significant effect on the neutral-mode phase speeds, the phase speeds of the unstable modes, the maximum growth rates and the unstable frequency range of the disturbances. The molecular weight ratio is a reasonable predictor of the stability trends. We have further demonstrated that the normalized growth rate as a function of the convective Mach number is relatively insensitive (Approx. 25%) to changes in the composition of the mixing layer. Thus, the normalized growth rate is a key element when considering the stability of compressible mixing layers, since once the basic stability characteristics for a particular combination of gases is known at zero Mach number, the decrease in growth rates due to compressibility effects at the larger convective Mach numbers is somewhat predictable.

  4. Development of a Hybrid RANS/LES Method for Compressible Mixing Layer Simulations

    NASA Technical Reports Server (NTRS)

    Georgiadis, Nicholas J.; Alexander, J. Iwan D.; Reshotko, Eli

    2001-01-01

    A hybrid method has been developed for simulations of compressible turbulent mixing layers. Such mixing layers dominate the flows in exhaust systems of modem day aircraft and also those of hypersonic vehicles currently under development. The hybrid method uses a Reynolds-averaged Navier-Stokes (RANS) procedure to calculate wall bounded regions entering a mixing section, and a Large Eddy Simulation (LES) procedure to calculate the mixing dominated regions. A numerical technique was developed to enable the use of the hybrid RANS/LES method on stretched, non-Cartesian grids. The hybrid RANS/LES method is applied to a benchmark compressible mixing layer experiment. Preliminary two-dimensional calculations are used to investigate the effects of axial grid density and boundary conditions. Actual LES calculations, performed in three spatial directions, indicated an initial vortex shedding followed by rapid transition to turbulence, which is in agreement with experimental observations.

  5. Centrifugal instability of the wake-dominated curved compressible mixing-layers.

    NASA Astrophysics Data System (ADS)

    Lin, Li; Stephen, Sharon

    2007-11-01

    The mixing layer is an interfacial region between two moving homogeneous fluids of different density, compressibility, velocity and temperature. G"ortler instability is a type of centrifugal instability which could arise from the mixing layer system owing to the dynamical effect of centreline curvature. The linear development of G"ortler vortices at high Reynolds number within both stably and unstably curved compressible mixing layers is investigated. The purpose behind this investigation is to determine if the presence of a G"ortler mode could enhance the mixing of two fluids in certain physical situations such as the mixing between fuel and oxidizer within a scramjet engine for the propulsion of hypersonic aircraft. The investigation is made by examining the growth rate and the location of the G"ortler modes in the limit of larger G"ortler number. An analytical Gaussian wake model is first used to predict the development of the G"ortler modes. A more accurate basic wake model has also been obtained numerically to compare with the earlier prediction.

  6. Mixing and non-equilibrium chemical reaction in a compressible mixing layer. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Steinberger, Craig J.

    1991-01-01

    The effects of compressibility, chemical reaction exothermicity, and non-equilibrium chemical modeling in a reacting plane mixing layer were investigated by means of two dimensional direct numerical simulations. The chemical reaction was irreversible and second order of the type A + B yields Products + Heat. The general governing fluid equations of a compressible reacting flow field were solved by means of high order finite difference methods. Physical effects were then determined by examining the response of the mixing layer to variation of the relevant non-dimensionalized parameters. The simulations show that increased compressibility generally results in a suppressed mixing, and consequently a reduced chemical reaction conversion rate. Reaction heat release was found to enhance mixing at the initial stages of the layer growth, but had a stabilizing effect at later times. The increased stability manifested itself in the suppression or delay of the formation of large coherent structures within the flow. Calculations were performed for a constant rate chemical kinetics model and an Arrhenius type kinetic prototype. The choice of the model was shown to have an effect on the development of the flow. The Arrhenius model caused a greater temperature increase due to reaction than the constant kinetic model. This had the same effect as increasing the exothermicity of the reaction. Localized flame quenching was also observed when the Zeldovich number was relatively large.

  7. Inviscid spatial stability of a compressible mixing layer. Part 2: The flame sheet model

    NASA Technical Reports Server (NTRS)

    Jackson, T. L.; Grosch, C. E.

    1989-01-01

    The results of an inviscid spatial calculation for a compressible reacting mixing layer are reported. The limit of infinitive activation energy is taken and the diffusion flame is approximated by a flame sheet. Results are reported for the phase speeds of the neutral waves and maximum growth rates of the unstable waves as a function of the parameters of the problem: the ratio of the temperature of the stationary stream to that of the moving stream, the Mach number of the moving streams, the heat release per unit mass fraction of the reactant, the equivalence ratio of the reaction, and the frequency of the disturbance. These results are compared to the phase speeds and growth rates of the corresponding nonreacting mixing layer. We show that the addition of combustion has important, and complex effects on the flow stability.

  8. The structure of variable property, compressible mixing layers in binary gas mixtures

    NASA Technical Reports Server (NTRS)

    Kozusko, F.; Grosch, C. E.; Jackson, T. L.; Kennedy, Christipher A.; Gatski, Thomas B.

    1996-01-01

    We present the results of a study of the structure of a parallel compressible mixing layer in a binary mixture of gases. The gases included in this study are hydrogen (H2), helium (He), nitrogen (N2), oxygen (02), neon (Ne) and argon (Ar). Profiles of the variation of the Lewis and Prandtl numbers across the mixing layer for all thirty combinations of gases are given. It is shown that the Lewis number can vary by as much as a factor of eight and the Prandtl number by a factor of two across the mixing layer. Thus assuming constant values for the Lewis and Prandtl numbers of a binary gas mixture in the shear layer, as is done in many theoretical studies, is a poor approximation. We also present profiles of the velocity, mass fraction, temperature and density for representative binary gas mixtures at zero and supersonic Mach numbers. We show that the shape of these profiles is strongly dependent on which gases are in the mixture as well as on whether the denser gas is in the fast stream or the slow stream.

  9. Inviscid spatial stability of a compressible mixing layer. Part 3: Effect of thermodynamics

    NASA Technical Reports Server (NTRS)

    Jackson, T. L.; Grosch, C. E.

    1989-01-01

    The results of a comprehensive comparative study of the inviscid spatial stability of a parallel compressible mixing layer using various models for the mean flow are reported. The models are: (1) the hyperbolic tangent profile for the mean speed and the Crocco relation for the mean temperature, with the Chapman viscosity-temperature relation and a Prandtl number of one; (2) the Lock profile for the mean speed and the Crocco relation for the mean temperature, with the Chapman viscosity-temperature relation and a Prandtl number of one; and (3) the similarity solution for the coupled velocity and temperature equations using the Sutherland viscosity temperature relation and arbitrary but constant Prandtl number. The purpose was to determine the sensitivity of the stability characteristics of the compressible mixing layer to the assumed thermodynamic properties of the fluid. It is shown that the quantative features of the stability characteristics are quite similiar for all models but that there are quantitative differences resulting from the difference in the thermodynamic models. In particular, it is shown that the stability characteristics are sensitive to the value of the Prandtl number.

  10. A numerical study of a class of TVD schemes for compressible mixing layers

    NASA Technical Reports Server (NTRS)

    Sandham, N. D.; Yee, H. C.

    1989-01-01

    At high Mach numbers the two-dimensional time-developing mixing layer develops shock waves, positioned around large-scale vortical structures. A suitable numerical method has to be able to capture the inherent instability of the flow, leading to the roll-up of vortices, and also must be able to capture shock waves when they develop. Standard schemes for low speed turbulent flows, for example spectral methods, rely on resolution of all flow-features and cannot handle shock waves, which become too thin at any realistic Reynolds number. The performance of a class of second-order explicit total variation diminishing (TVD) schemes on a compressible mixing layer problem was studied. The basic idea is to capture the physics of the flow correctly, by resolving down to the smallest turbulent length scales, without resorting to turbulence or sub-grid scale modeling, and at the same time capture shock waves without spurious oscillations. The present study indicates that TVD schemes can capture the shocks accurately when they form, but (without resorting to a finer grid) have poor accuracy in computing the vortex growth. The solution accuracy depends on the choice of limiter. However a larger number of grid points are in general required to resolve the correct vortex growth. The low accuracy in computing time-dependent problems containing shock waves as well as vortical structures is partly due to the inherent shock-capturing property of all TVD schemes. In order to capture shock waves without spurious oscillations these schemes reduce to first-order near extrema and indirectly produce clipping phenomena, leading to inaccuracy in the computation of vortex growth. Accurate simulation of unsteady turbulent fluid flows with shock waves will require further development of efficient, uniformly higher than second-order accurate, shock-capturing methods.

  11. Nonlinear interactions in mixing layers and compressible heated round jets. Ph.D. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Jarrah, Yousef Mohd

    1989-01-01

    The nonlinear interactions between a fundamental instability mode and both its harmonics and the changing mean flow are studied using the weakly nonlinear stability theory of Stuart and Watson, and numerical solutions of coupled nonlinear partial differential equations. The first part focuses on incompressible cold (or isothermal; constant temperature throughout) mixing layers, and for these, the first and second Landau constants are calculated as functions of wavenumber and Reynolds number. It is found that the dominant contribution to the Landau constants arises from the mean flow changes and not from the higher harmonics. In order to establish the range of validity of the weakly nonlinear theory, the weakly nonlinear and numerical solutions are compared and the limitation of each is discussed. At small amplitudes and at low-to-moderate Reynolds numbers, the two results compare well in describing the saturation of the fundamental, the distortion of the mean flow, and the initial stages of vorticity roll-up. At larger amplitudes, the interaction between the fundamental, second harmonic, and the mean flow is strongly nonlinear and the numerical solution predicts flow oscillations, whereas the weakly nonlinear theory yields saturation. In the second part, the weakly nonlinear theory is extended to heated (or nonisothermal; mean temperature distribution) subsonic round jets where quadratic and cubic nonlinear interactions are present, and the Landau constants also depend on jet temperature ratio, Mach number and azimuthal mode number. Under exponential growth and nonlinear saturation, it is found that heating and compressibility suppress the growth of instability waves, that the first azimuthal mode is the dominant instability mode, and that the weakly nonlinear solution describes the early stages of the roll-up of an axisymmetric shear layer. The receptivity of a typical jet flow to pulse type input disturbance is also studied by solving the initial value problem

  12. On the turbulence-generated sound and control of compressible mixing layers

    NASA Astrophysics Data System (ADS)

    Kleinman, Randall Ray

    A mixing layer is a common model used to study the noise generation and mixing characteristics of the near-nozzle region of jets. This work presents three separate but related studies that investigate sound generation and active control for noise mitigation and mixing enhancement of such mixing layers. High-fidelity direct numerical simulations of temporal and spatial mixing layers are used for this in two and three dimensions. The first study investigates the role of turbulence scales in generating the radiated far-field sound from temporally-developing, Mach 0.9 mixing layers. To do this, four mixing layers were simulated, starting from the same initial conditions but with Reynolds numbers that varied by a factor of twelve. Above a momentum thickness Reynolds number of 300, all the mixing layers radiate over 85 percent of the acoustic energy of the apparently asymptotically high-Reynolds-number value we are able to compute. Wavenumber spectra of turbulence energy and pressure show the expected Reynolds number dependence: the two highest Reynolds number simulations show evidence of an inertial range and Kolmogorov scaling at the highest wavenumbers. Farfield pressure spectra all decay much more rapidly with wavenumber than the corresponding near-field spectra and show significantly less sensitivity to Reynolds number. Low wavenumbers account for nearly all of the radiated acoustic energy. Implications of these results for jet noise large-eddy simulations are discussed. The second study uses direct numerical simulations of Mach 1.3 mixing layers to characterize the physical mechanisms of flow actuation by localized arc-filament plasma actuators. A validated numerical model of the actuator is devised and placed, as in corresponding experiments, in a cavity in the nozzle near its exit. A rapid Joule heating caused by the plasma is thought to be the root mechanism of flow actuation based upon experimental observation. Simulations show that in the confined space of the

  13. Influence of external disturbances and compressibility on free turbulent mixing. [in free shear layers

    NASA Technical Reports Server (NTRS)

    Oh, Y. H.; Bushnell, D. M.

    1975-01-01

    It is shown that disturbances in external flow can significantly affect, by as much as an order of magnitude, the turbulent mixing rate in free shear layers and that the length scale of the external flow disturbances is as important as the amplitude. The difference between the effect of wide-band and narrow-band disturbances is stressed. The model for pressure fluctuation term in the kinetic energy equation is included in a two-equation model. The reduced spreading rate in high Mach number, high Reynolds number, adiabatic, free turbulent shear layers is predicted.

  14. Ignition and structure of a laminar diffusion flame in a compressible mixing layer with finite rate chemistry

    NASA Technical Reports Server (NTRS)

    Grosch, C. E.; Jackson, T. L.

    1991-01-01

    The ignition and structure of a reacting compressible mixing layer is considered using finite rate chemistry lying between two streams of reactants with different freestream speeds and temperatures. Numerical integration of the governing equations show that the structure of the reacting flow can be quite complicated depending on the magnitude of the Zeldovich number. An analysis of both the ignition a diffusion flame regimes is presented using a combination of large Zeldovich number asymptotics and numerics. This allows to analyze the behavior of these regimes as a function of the parameters of the problem.

  15. Ignition and structure of a laminar diffusion flame in a compressible mixing layer with finite rate chemistry

    NASA Technical Reports Server (NTRS)

    Grosch, C. E.; Jackson, T. L.

    1991-01-01

    The ignition and structure of a reacting compressible mixing layer is considered using finite rate chemistry lying between two streams of reactants with different freestream speeds and temperatures. Numerical integration of the governing equations show that the structure of the reacting flow can be quite complicated depending on the magnitude of the Zeldovich number. An analysis of both the ignition and diffusion flame regimes is presented using a combination of large Zeldovich number asymptotics and numerics. This allows to analyze the behavior of these regimes as a function of the parameters of the problem.

  16. Calculation of the flow field including boundary layer effects for supersonic mixed compression inlets at angles of attack

    NASA Technical Reports Server (NTRS)

    Vadyak, J.; Hoffman, J. D.

    1982-01-01

    The flow field in supersonic mixed compression aircraft inlets at angle of attack is calculated. A zonal modeling technique is employed to obtain the solution which divides the flow field into different computational regions. The computational regions consist of a supersonic core flow, boundary layer flows adjacent to both the forebody/centerbody and cowl contours, and flow in the shock wave boundary layer interaction regions. The zonal modeling analysis is described and some computational results are presented. The governing equations for the supersonic core flow form a hyperbolic system of partial differential equations. The equations for the characteristic surfaces and the compatibility equations applicable along these surfaces are derived. The characteristic surfaces are the stream surfaces, which are surfaces composed of streamlines, and the wave surfaces, which are surfaces tangent to a Mach conoid. The compatibility equations are expressed as directional derivatives along streamlines and bicharacteristics, which are the lines of tangency between a wave surface and a Mach conoid.

  17. Compressible turbulent mixing: Effects of compressibility

    NASA Astrophysics Data System (ADS)

    Ni, Qionglin

    2016-04-01

    We studied by numerical simulations the effects of compressibility on passive scalar transport in stationary compressible turbulence. The turbulent Mach number varied from zero to unity. The difference in driven forcing was the magnitude ratio of compressive to solenoidal modes. In the inertial range, the scalar spectrum followed the k-5 /3 scaling and suffered negligible influence from the compressibility. The growth of the Mach number showed (1) a first reduction and second enhancement in the transfer of scalar flux; (2) an increase in the skewness and flatness of the scalar derivative and a decrease in the mixed skewness and flatness of the velocity-scalar derivatives; (3) a first stronger and second weaker intermittency of scalar relative to that of velocity; and (4) an increase in the intermittency parameter which measures the intermittency of scalar in the dissipative range. Furthermore, the growth of the compressive mode of forcing indicated (1) a decrease in the intermittency parameter and (2) less efficiency in enhancing scalar mixing. The visualization of scalar dissipation showed that, in the solenoidal-forced flow, the field was filled with the small-scale, highly convoluted structures, while in the compressive-forced flow, the field was exhibited as the regions dominated by the large-scale motions of rarefaction and compression.

  18. Interactive calculation procedures for mixed compression inlets

    NASA Technical Reports Server (NTRS)

    Reshotko, Eli

    1983-01-01

    The proper design of engine nacelle installations for supersonic aircraft depends on a sophisticated understanding of the interactions between the boundary layers and the bounding external flows. The successful operation of mixed external-internal compression inlets depends significantly on the ability to closely control the operation of the internal compression portion of the inlet. This portion of the inlet is one where compression is achieved by multiple reflection of oblique shock waves and weak compression waves in a converging internal flow passage. However weak these shocks and waves may seem gas-dynamically, they are of sufficient strength to separate a laminar boundary layer and generally even strong enough for separation or incipient separation of the turbulent boundary layers. An understanding was developed of the viscous-inviscid interactions and of the shock wave boundary layer interactions and reflections.

  19. Advances in compressible turbulent mixing

    SciTech Connect

    Dannevik, W.P.; Buckingham, A.C.; Leith, C.E.

    1992-01-01

    This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately.

  20. A computer program for the calculation of the flow field including boundary layer effects for mixed-compression inlets at angle of attack

    NASA Technical Reports Server (NTRS)

    Vadyak, J.; Hoffman, J. D.

    1982-01-01

    A computer program was developed which is capable of calculating the flow field in the supersonic portion of a mixed compression aircraft inlet operating at angle of attack. The supersonic core flow is computed using a second-order three dimensional method-of-characteristics algorithm. The bow shock and the internal shock train are treated discretely using a three dimensional shock fitting procedure. The boundary layer flows are computed using a second-order implicit finite difference method. The shock wave-boundary layer interaction is computed using an integral formulation. The general structure of the computer program is discussed, and a brief description of each subroutine is given. All program input parameters are defined, and a brief discussion on interpretation of the output is provided. A number of sample cases, complete with data listings, are provided.

  1. A study of the topology of dissipating motions in direct numerical simulations of time-developing compressible and incompressible mixing layers

    NASA Technical Reports Server (NTRS)

    Chen, J. H.; Chong, M. S.; Soria, J.; Sondergaard, R.; Perry, A. E.; Rogers, M.; Moser, R.; Cantwell, B. J.

    1990-01-01

    A preliminary investigation of the geometry of flow patterns in numerically simulated compressible and incompressible mixing layers was carried out using 3-D critical point methodology. Motions characterized by high rates of kinetic energy dissipation and/or high enstrophy were of particular interest. In the approach the partial derivatives of the velocity field are determined at every point in the flow. These are used to construct the invariants of the velocity gradient tensor and the rate-of-strain tensor (P, Q, R, and P(sub s), Q(sub s), R(sub s) respectively). For incompressible flow the first invariant is zero. For the conditions of the compressible simulation, the first invariant is found to be everywhere small, relative to the second and third invariants, and so in both cases the local topology at a point is mainly determined by the second and third invariants. The data at every grid point is used to construct scatter plots of Q versus R and Q(sub s) versus R(sub s). Most points map to a cluster near the origin in Q-R space. However, fine scale motions, that is motions which are characterized by velocity derivatives which scale with the square root of R(sub delta), tend to map to regions which lie far from the origin. Definite trends are observed for motions characterized by high enstrophy and/or high dissipation. The observed trends suggest that, for these motions, the second and third invariants of the velocity gradient and rate-of-strain tensors are strongly correlated. The second and third invariants of the rate-of-strain tensor are related by K(-Q(sub s))(exp 3/2), which is consistent with the above scaling of velocity derivatives. The quantity K appears to depend on Reynolds number with an upper limit K = 2(the square root of 3)/9 corresponding to locally axisymmetric flow. For both the compressible and incompressible mixing layer, regions corresponding to high rates of dissipation are found to be characterized by comparable magnitudes of R(sub ij

  2. Compressible turbulent boundary layer interaction experiments

    NASA Technical Reports Server (NTRS)

    Settles, G. S.; Bogdonoff, S. M.

    1981-01-01

    Four phases of research results are reported: (1) experiments on the compressible turbulent boundary layer flow in a streamwise corner; (2) the two dimensional (2D) interaction of incident shock waves with a compressible turbulent boundary layer; (3) three dimensional (3D) shock/boundary layer interactions; and (4) cooperative experiments at Princeton and numerical computations at NASA-Ames.

  3. Anelastic Rayleigh–Taylor mixing layers

    NASA Astrophysics Data System (ADS)

    Schneider, N.; Gauthier, S.

    2016-07-01

    Anelastic Rayleigh–Taylor mixing layers for miscible fluids are investigated with a recently built model (Schneider and Gauthier 2015 J. Eng. Math. 92 55–71). Four Chebyshev–Fourier–Fourier direct numerical simulations are analyzed. They use different values for the compressibility parameters: Atwood number (the dimensionless difference of the heavy and light fluid densities) and stratification (accounts for the vertical variation of density due to gravity). For intermediate Atwood numbers and finite stratification, compressibility effects quickly occurs. As a result only nonlinear behaviours are reached. The influence of the compressibility parameters on the growth speed of the RTI is discussed. The 0.1—Atwood number/0.4—stratification configuration reaches a turbulent regime. This turbulent mixing layer is analyzed with statistical tools such as moments, PDFs, anisotropy indicators and spectra.

  4. Anelastic Rayleigh-Taylor mixing layers

    NASA Astrophysics Data System (ADS)

    Schneider, N.; Gauthier, S.

    2016-07-01

    Anelastic Rayleigh-Taylor mixing layers for miscible fluids are investigated with a recently built model (Schneider and Gauthier 2015 J. Eng. Math. 92 55-71). Four Chebyshev-Fourier-Fourier direct numerical simulations are analyzed. They use different values for the compressibility parameters: Atwood number (the dimensionless difference of the heavy and light fluid densities) and stratification (accounts for the vertical variation of density due to gravity). For intermediate Atwood numbers and finite stratification, compressibility effects quickly occurs. As a result only nonlinear behaviours are reached. The influence of the compressibility parameters on the growth speed of the RTI is discussed. The 0.1—Atwood number/0.4—stratification configuration reaches a turbulent regime. This turbulent mixing layer is analyzed with statistical tools such as moments, PDFs, anisotropy indicators and spectra.

  5. Effect of three-dimensionality on compressible mixing

    SciTech Connect

    Papamoschou, D. )

    1992-02-01

    Existing experimental data and hypotheses on the growth rates of compressible and incompressible turbulent shear layers are used to estimate the effect of three-dimensionality in the turbulent mixing enhancement in compressible shear flows that is critically important to the efficiency of scramjet powerplants. The general trend is found to be a decrease in growth rate with increasing three-dimensionality, excepting only the restricted regime, where the growth-rate increase is modest. 9 refs.

  6. Calculation methods for compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

    1976-01-01

    Calculation procedures for non-reacting compressible two- and three-dimensional turbulent boundary layers were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete boundary layer equations summarized. Alternative numerical solution procedures were examined, and both mean field and mean turbulence field closure models were considered. Physics and related calculation problems peculiar to compressible turbulent boundary layers are described. A catalog of available solution procedures of the finite difference, finite element, and method of weighted residuals genre is included. Influence of compressibility, low Reynolds number, wall blowing, and pressure gradient upon mean field closure constants are reported.

  7. 3M Coban 2 Layer Compression Therapy: Intelligent Compression Dynamics to Suit Different Patient Needs

    PubMed Central

    Bernatchez, Stéphanie F.; Tucker, Joseph; Schnobrich, Ellen; Parks, Patrick J.

    2012-01-01

    Problem Chronic venous insufficiency can lead to recalcitrant leg ulcers. Compression has been shown to be effective in healing these ulcers, but most products are difficult to apply and uncomfortable for patients, leading to inconsistent/ineffective clinical application and poor compliance. In addition, compression presents risks for patients with an ankle-brachial pressure index (ABPI) <0.8 because of the possibility of further compromising the arterial circulation. The ABPI is the ratio of systolic leg blood pressure (taken at ankle) to systolic arm blood pressure (taken above elbow, at brachial artery). This is measured to assess a patient's lower extremity arterial perfusion before initiating compression therapy.1 Solution Using materials science, two-layer compression systems with controlled compression and a low profile were developed. These materials allow for a more consistent bandage application with better control of the applied compression, and their low profile is compatible with most footwear, increasing patient acceptance and compliance with therapy. The original 3M™ Coban™ 2 Layer Compression System is suited for patients with an ABPI ≥0.8; 3M™ Coban™ 2 Layer Lite Compression System can be used on patients with ABPI ≥0.5. New Technology Both compression systems are composed of two layers that combine to create an inelastic sleeve conforming to the limb contour to provide a consistent proper pressure profile to reduce edema. In addition, they slip significantly less than other compression products and improve patient daily living activities and physical symptoms. Indications for Use Both compression systems are indicated for patients with venous leg ulcers, lymphedema, and other conditions where compression therapy is appropriate. Caution As with any compression system, caution must be used when mixed venous and arterial disease is present to not induce any damage. These products are not indicated when the ABPI is <0.5. PMID:24527315

  8. Kelvin-Helmholtz Instability in Compressible Flows and Mixing Inhibition

    NASA Astrophysics Data System (ADS)

    Karimi, Mona; Girimaji, Shararath

    2015-11-01

    It is well-established that the Kelvin-Helmholtz (KH) instability is central to shear flow mixing. Toward understanding the suppression of turbulent mixing under the influence of compressibility, we first examine the modification to KH instability in a planar mixing layer at high speeds. In this presentation, combining the outcomes of the linear stability analysis with the results of the numerical simulation, we establish that the flow domain can be classified into two main regions: the outer regions on the fast and slow sides and dilatational interface layer (DIL) in the middle. Compressibility engenders the formation of a dilatational or acoustic layer at the high-shear interface between two streams of different speeds. Within the DIL, the velocity perturbations become oscillatory. In the incompressible shear layers, the interface experiences steady vortical motion that entrains fluid from both streams leading to familiar KH behavior. In contrast, in the compressible case, the interface motion is oscillatory inhibiting vortex-merging and roll-up, thereby suppressing entrainment that leads to inhibition of the KH instability. Analysis and illustrations of the constituent mechanisms are presented.

  9. Some design considerations for supersonic cruise mixed compression inlets

    NASA Technical Reports Server (NTRS)

    Bowditch, D. N.

    1973-01-01

    A mixed compression inlet designed for supersonic cruise has very demanding requirements for high total pressure recovery and low bleed and cowl drag. However, since the optimum inlet for supersonic cruise performance may have other undesirable characteristics, it is necessary to establish trade-offs between inlet performance and other inlet characteristics. Some of these trade-offs between the amount of internal compression, aerodynamic performance and angle-of-attack tolerance are reviewed. Techniques for analysis of boundary layer control and subsonic diffuser flow are discussed.

  10. Calculation methods for compressible turbulent boundary layers, 1976

    NASA Technical Reports Server (NTRS)

    Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

    1977-01-01

    Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.

  11. Mixed Layers and Satellite Retrievals

    NASA Technical Reports Server (NTRS)

    Boers, R.

    1984-01-01

    As part of the process to determine whether it is possible to retrieve boundary layer structure with the current sounding techniques, temperature retievals were performed for radiosonde profiles that showed temperature inversions. It was found that when temperature inversions exceed 8 to 10 C a retrieval will indeed show a temperature increase with height over a limited vertical distance. For weaker inversions retrieved temperatures are generally smoothly decreasing with height. It is, however, impossible to determine the actual mixed layer height from the retrievals. Whether the water vapor channels could be used in observing mixed layer structure was investigated. Temperature inversions are accompanied by significant drops in relative humidity. While this effect is very pronounced in parts of the trade wind regimes with relative humidity drops of up to 60%, it is widespread in other areas of the ocean as well. A simulation experiment was performed in which brightness temperatures were computed for smooth temperature and humidity profiles and compared with those computed from inversion profiles.

  12. Compressible turbulent mixing: Effects of Schmidt number.

    PubMed

    Ni, Qionglin

    2015-05-01

    We investigated by numerical simulations the effects of Schmidt number on passive scalar transport in forced compressible turbulence. The range of Schmidt number (Sc) was 1/25∼25. In the inertial-convective range the scalar spectrum seemed to obey the k(-5/3) power law. For Sc≫1, there appeared a k(-1) power law in the viscous-convective range, while for Sc≪1, a k(-17/3) power law was identified in the inertial-diffusive range. The scaling constant computed by the mixed third-order structure function of the velocity-scalar increment showed that it grew over Sc, and the effect of compressibility made it smaller than the 4/3 value from incompressible turbulence. At small amplitudes, the probability distribution function (PDF) of scalar fluctuations collapsed to the Gaussian distribution whereas, at large amplitudes, it decayed more quickly than Gaussian. At large scales, the PDF of scalar increment behaved similarly to that of scalar fluctuation. In contrast, at small scales it resembled the PDF of scalar gradient. Furthermore, the scalar dissipation occurring at large magnitudes was found to grow with Sc. Due to low molecular diffusivity, in the Sc≫1 flow the scalar field rolled up and got mixed sufficiently. However, in the Sc≪1 flow the scalar field lost the small-scale structures by high molecular diffusivity and retained only the large-scale, cloudlike structures. The spectral analysis found that the spectral densities of scalar advection and dissipation in both Sc≫1 and Sc≪1 flows probably followed the k(-5/3) scaling. This indicated that in compressible turbulence the processes of advection and dissipation except that of scalar-dilatation coupling might deferring to the Kolmogorov picture. It then showed that at high wave numbers, the magnitudes of spectral coherency in both Sc≫1 and Sc≪1 flows decayed faster than the theoretical prediction of k(-2/3) for incompressible flows. Finally, the comparison with incompressible results showed that

  13. Logarithmic laws for compressible turbulent boundary layers

    SciTech Connect

    So, R.M.C.; Zhang, H.S.; Gatski, T.B.; Speziale, C.G.

    1994-11-01

    Dimensional similarity arguments proposed by Millikan are used with the Morkovin hypothesis to deduce logarithmic laws for compressible turbulent boundary layers as an alternative to the traditional van Driest analysis. It is shown that an overlap exists between the wall layer and the defect layer, and this leads to logarithmic behavior in the overlap region. The von Karman constant is found to depend parametrically on the Mach number based on the friction velocity, the dimensionless total heat flux, and the specific heat ratio. Even though it remains constant at approximately 0.41 for a freestream Mach number range of 0 to 4.544 with adiabatic wall boundary conditions, it rises sharply as the Mach number increases significantly beyond 4.544. The intercept of the logarithmic law of the wall is found to depend on the Mach number based on the friction velocity, the dimensionless total heat flux, the Prandtl number evaluated at the wall, and the specific heat ratio. On the other hand, the intercept of the logarithmic defect law is parametric in the pressure gradient parameter and all of the aforementioned dimensionless variables except the Prandtl number. A skin friction law is also deduced for compressible boundary layers. The skin friction coefficient is shown to depend on the momentum thickness Reynolds number, the wall temperature ratio, and all of the other parameters already mentioned. 26 refs.

  14. Geometric invariance of compressible turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Bi, Wei-Tao; Wu, Bin; She, Zhen-Su; Hussain, Fazle

    2015-11-01

    A symmetry based approach is applied to analyze the mean velocity and temperature fields of compressible, flat plate turbulent boundary layers (CTBL). A Reynolds stress length scale and a turbulent heat flux length scale are identified to possess the same defect scaling law in the CTBL bulk, which is solely owing to the constraint of the wall to the geometry of the wall-attached eddies, but invariant to compressibility and wall heat transfer. This invariance is called the geometric invariance of CTBL eddies and is likely the origin of the Mach number invariance of Morkovin's hypothesis, as well as the similarity of energy and momentum transports. A closure for the turbulent transport by using the invariant lengths is attainted to predict the mean velocity and temperature profiles in the CTBL bulk- superior to the van Driest transformation and the Reynolds analogy based relations for its sound physics and higher accuracy. Additionally, our approach offers a new understanding of turbulent Prandtl number.

  15. Coherent structures in compressible free-shear-layer flows

    SciTech Connect

    Aeschliman, D.P.; Baty, R.S.; Kennedy, C.A.; Chen, J.H.

    1997-08-01

    Large scale coherent structures are intrinsic fluid mechanical characteristics of all free-shear flows, from incompressible to compressible, and laminar to fully turbulent. These quasi-periodic fluid structures, eddies of size comparable to the thickness of the shear layer, dominate the mixing process at the free-shear interface. As a result, large scale coherent structures greatly influence the operation and efficiency of many important commercial and defense technologies. Large scale coherent structures have been studied here in a research program that combines a synergistic blend of experiment, direct numerical simulation, and analysis. This report summarizes the work completed for this Sandia Laboratory-Directed Research and Development (LDRD) project.

  16. Experiments on the enhancement of compressible mixing via streamwise vorticity. II - Vortex strength assessment and seed particle dynamics

    NASA Technical Reports Server (NTRS)

    Naughton, J. W.; Cattafesta, L. N.; Settles, G. S.

    1993-01-01

    The effect of streamwise vorticity on compressible axisymmetric mixing layers is examined using vortex strength assessment and seed particle dynamics analysis. Experimental results indicate that the particles faithfully represent the dynamics of the turbulent swirling flow. A comparison of the previously determined mixing layer growth rates with the present vortex strength data reveals that the increase of turbulent mixing up to 60 percent scales with the degree of swirl. The mixing enhancement appears to be independent of the compressibility level of the mixing layer.

  17. Bypass transition in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Vandervegt, J. J.

    1992-01-01

    transitional state. The effects of large free stream turbulence in compressible boundary layers at Mach numbers are examined both in the subsonic and transonic regime using direct numerical simulations. The flow is computed over a flat plate and curved surface. while many applications operate in the transonic regime. Due the nature of their numerical scheme, a non-conservation formulation of the Navier-Stokes equations, it is a non-trivial extension to compute flow fields in the transonic regime. This project aims at better understanding the effects of large free-stream turbulence in compressible boundary layers at mach number both in the subsonic and transonic regime using direct numerical simulations. The present project aims at computing the flow over a flat plate and curved surface. This research will provide data which can be used to clarify mechanisms leading to transition in an environment with high free stream turbulence. This information is useful for the development of turbulence models, which are of great importance for CFD applications, and are currently unreliable for more complex flows, such as transitional flows.

  18. Secondary instabilities in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Ng, Lian; Erlebacher, Gordon

    1990-01-01

    Secondary instabilities are examined in compressible boundary layers at Mach numbers M(sub infinity) = 0, 0.8, 1.6, and 4.5. It is found that there is a broad-band of highly unstable 3-d secondary disturbances whose growth rates increase with increasing primary wave amplitude. At M(sub infinity) is less than or equal to 1.6, fundamental resonance dominates at relatively high (2-d) primary disturbance amplitude, while subharmonic resonance is characterized by a low (2-d) primary amplitude. At M(sub infinity) = 4.5, the subharmonic instability which arises from the second mode disturbance is the strongest type of secondary instability. The influence of the inclination, theta, of the primary wave with respect to the mean flow direction on secondary instability is investigated at M(sub infinity) = 1.6 for small to moderate values of theta. It is found that the strongest fundamental instability occurs when the primary wave is inclined at 10 deg to the mean flow direction, although a 2-d primary mode yields the most amplified subharmonic. The subharmonic instability at a high value of theta (namely, theta = 45 deg) is also discussed. Finally, a subset of the secondary instability results are compared against direct numerical simulations.

  19. Martian Mixed Layer during Pathfinder Mission

    NASA Astrophysics Data System (ADS)

    Martinez, G. M.; Valero, F.; Vazquez, L.

    2008-09-01

    In situ measurements of the Martian Planetary Boundary Layer (MPBL) encompass only the sur- face layer. Therefore, in order to fully address the MPBL, it becomes necessary to simulate somehow the behaviour of the martian mixed layer. The small-scale processes that happen in the MPBL cause GCM's ([1], [2]) to describe only partially the turbulent statistics, height, convective scales, etc, of the surface layer and the mixed layer. For this reason, 2D and 3D martian mesoscale models ([4], [5]), and large eddy simulations ([4], [6], [7], [8]) have been designed in the last years. Although they are expected to simulate more accurately the MPBL, they take an extremely expensive compu- tational time. Alternatively, we have derived the main turbu- lent characteristics of the martian mixed layer by using surface layer and mixed layer similarity ([9], [10]). From in situ temperature and wind speed measurements, together with quality-tested simu- lated ground temperature [11], we have character- ized the martian mixed layer during the convective hours of Pathfinder mission Sol 25. Mean mixed layer turbulent statistics like tem- perature variance < σ? >, horizontal wind speed variance < σu,v >, vertical wind speed variance < σw >, viscous dissipation rate < ǫ >, and turbu- lent kinetic energy < e > have been calculated, as well as the mixed layer height zi, and the convective scales of wind w? and temperature θ?. Our values, obtained with negligible time cost, match quite well with some previously obtained results via LES's ([4] and [8]). A comparisson between the above obtained mar- tian values and the typical Earth values are shown in Table 1. Convective velocity scale w doubles its counterpart terrestrial typical value, as it does the mean wind speed variances < σu,v > and < σw >. On the other hand, the temperature scale θ? and the mean temperature variance < σ > are virtually around one order higher on Mars. The limitations of these results concern the va- lidity

  20. Layered compression for high-precision depth data.

    PubMed

    Miao, Dan; Fu, Jingjing; Lu, Yan; Li, Shipeng; Chen, Chang Wen

    2015-12-01

    With the development of depth data acquisition technologies, access to high-precision depth with more than 8-b depths has become much easier and determining how to efficiently represent and compress high-precision depth is essential for practical depth storage and transmission systems. In this paper, we propose a layered high-precision depth compression framework based on an 8-b image/video encoder to achieve efficient compression with low complexity. Within this framework, considering the characteristics of the high-precision depth, a depth map is partitioned into two layers: 1) the most significant bits (MSBs) layer and 2) the least significant bits (LSBs) layer. The MSBs layer provides rough depth value distribution, while the LSBs layer records the details of the depth value variation. For the MSBs layer, an error-controllable pixel domain encoding scheme is proposed to exploit the data correlation of the general depth information with sharp edges and to guarantee the data format of LSBs layer is 8 b after taking the quantization error from MSBs layer. For the LSBs layer, standard 8-b image/video codec is leveraged to perform the compression. The experimental results demonstrate that the proposed coding scheme can achieve real-time depth compression with satisfactory reconstruction quality. Moreover, the compressed depth data generated from this scheme can achieve better performance in view synthesis and gesture recognition applications compared with the conventional coding schemes because of the error control algorithm. PMID:26415171

  1. Computation of turbulent high speed mixing layers using a two-equation turbulence model

    NASA Technical Reports Server (NTRS)

    Narayan, J. R.; Sekar, B.

    1991-01-01

    A two-equation turbulence model was extended to be applicable for compressible flows. A compressibility correction based on modelling the dilational terms in the Reynolds stress equations were included in the model. The model is used in conjunction with the SPARK code for the computation of high speed mixing layers. The observed trend of decreasing growth rate with increasing convective Mach number in compressible mixing layers is well predicted by the model. The predictions agree well with the experimental data and the results from a compressible Reynolds stress model. The present model appears to be well suited for the study of compressible free shear flows. Preliminary results obtained for the reacting mixing layers are included.

  2. Lidar observation of marine mixed layer

    NASA Technical Reports Server (NTRS)

    Yamagishi, Susumu; Yamanouchi, Hiroshi; Tsuchiya, Masayuki

    1992-01-01

    Marine mixed layer is known to play an important role in the transportation of pollution exiting ship funnels. The application of a diffusion model is critically dependent upon a reliable estimate of a lid. However, the processes that form lids are not well understood, though considerable progress toward marine boundary layer has been achieved. This report describes observations of the marine mixed layer from the course Ise-wan to Nii-jima with the intention of gaining a better understanding of their structure by a shipboard lidar. These observations were made in the summer of 1991. One interesting feature of the observations was that the multiple layers of aerosols, which is rarely numerically modeled, was encountered. No attempt is yet made to present a systematic analysis of all the data collected. Instead we focus on observations that seem to be directly relevant to the structure of the mixed layer.

  3. Lidar observations of mixed layer dynamics - Tests of parameterized entrainment models of mixed layer growth rate

    NASA Technical Reports Server (NTRS)

    Boers, R.; Eloranta, E. W.; Coulter, R. L.

    1984-01-01

    Ground based lidar measurements of the atmospheric mixed layer depth, the entrainment zone depth and the wind speed and wind direction were used to test various parameterized entrainment models of mixed layer growth rate. Six case studies under clear air convective conditions over flat terrain in central Illinois are presented. It is shown that surface heating alone accounts for a major portion of the rise of the mixed layer on all days. A new set of entrainment model constants was determined which optimized height predictions for the dataset. Under convective conditions, the shape of the mixed layer height prediction curves closely resembled the observed shapes. Under conditions when significant wind shear was present, the shape of the height prediction curve departed from the data suggesting deficiencies in the parameterization of shear production. Development of small cumulus clouds on top of the layer is shown to affect mixed layer depths in the afternoon growth phase.

  4. Compression behavior of single-layer graphenes.

    PubMed

    Frank, Otakar; Tsoukleri, Georgia; Parthenios, John; Papagelis, Konstantinos; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S; Galiotis, Costas

    2010-06-22

    Central to most applications involving monolayer graphenes is its mechanical response under various stress states. To date most of the work reported is of theoretical nature and refers to tension and compression loading of model graphenes. Most of the experimental work is indeed limited to the bending of single flakes in air and the stretching of flakes up to typically approximately 1% using plastic substrates. Recently we have shown that by employing a cantilever beam we can subject single graphenes to various degrees of axial compression. Here we extend this work much further by measuring in detail both stress uptake and compression buckling strain in single flakes of different geometries. In all cases the mechanical response is monitored by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene. Despite the infinitely small thickness of the monolayers, the results show that graphenes embedded in plastic beams exhibit remarkable compression buckling strains. For large length (l)-to-width (w) ratios (> or =0.2) the buckling strain is of the order of -0.5% to -0.6%. However, for l/w < 0.2 no failure is observed for strains even higher than -1%. Calculations based on classical Euler analysis show that the buckling strain enhancement provided by the polymer lateral support is more than 6 orders of magnitude compared to that of suspended graphene in air. PMID:20496881

  5. Mixed alkaline earth effect in the compressibility of aluminosilicate glasses.

    PubMed

    Smedskjaer, Morten M; Rzoska, Sylwester J; Bockowski, Michal; Mauro, John C

    2014-02-01

    The mixed modifier effect (MME) in oxide glasses manifests itself as a non-additive variation in certain properties when one modifier oxide species is substituted by another one at constant total modifier content. However, the structural and topological origins of the MME are still under debate. This study provides new insights into the MME by investigating the effect of isostatic compression on density and hardness of mixed MgO/CaO sodium aluminosilicate glasses. This is done using a specially designed setup allowing isostatic compression of bulk glass samples up to 1 GPa at elevated temperature. A mixed alkaline earth effect is found in the compressibility and relative change of hardness, viz., a local maximum of density as a function of Mg/Ca ratio appears following compression, whereas a local minimum of hardness in the uncompressed glasses nearly disappears after compression. Moreover, the densification of these glasses is found to occur at temperatures much below the glass transition temperature, indicating that a non-viscous mechanism is at play. This is further supported by the fact that density relaxes in a stretched exponential manner upon subsequent annealing at ambient pressure with an exponent of ∼0.62. This is close to the Phillips value of 3/5 for relaxation in three dimensions when both short- and long-range interactions are activated.

  6. A random distribution reacting mixing layer model

    NASA Technical Reports Server (NTRS)

    Jones, Richard A.

    1994-01-01

    A methodology for simulation of molecular mixing and the resulting velocity and temperature fields has been developed. The ideas are applied to the flow conditions present in the NASA Lewis Planar Reacting Shear Layer (PRSL) facility, and results compared to experimental data. A gaussian transverse turbulent velocity distribution is used in conjunction with a linearly increasing time scale to describe the mixing of different regions of the flow. Equilibrium reaction calculations are then performed on the mix to arrive at a new species composition and temperature. Velocities are determined through summation of momentum contributions. The analysis indicates a combustion efficiency of the order of 80 percent for the reacting mixing layer, and a turbulent Schmidt number of 2/3. The success of the model is attributed to the simulation of large-scale transport of fluid. The favorable comparison shows that a relatively quick and simple PC calculation is capable of simulating the basic flow structure in the reacting and non-reacting shear layer present in the facility given basic assumptions about turbulence properties.

  7. A random distribution reacting mixing layer model

    NASA Technical Reports Server (NTRS)

    Jones, Richard A.; Marek, C. John; Myrabo, Leik N.; Nagamatsu, Henry T.

    1994-01-01

    A methodology for simulation of molecular mixing, and the resulting velocity and temperature fields has been developed. The ideas are applied to the flow conditions present in the NASA Lewis Research Center Planar Reacting Shear Layer (PRSL) facility, and results compared to experimental data. A gaussian transverse turbulent velocity distribution is used in conjunction with a linearly increasing time scale to describe the mixing of different regions of the flow. Equilibrium reaction calculations are then performed on the mix to arrive at a new species composition and temperature. Velocities are determined through summation of momentum contributions. The analysis indicates a combustion efficiency of the order of 80 percent for the reacting mixing layer, and a turbulent Schmidt number of 2/3. The success of the model is attributed to the simulation of large-scale transport of fluid. The favorable comparison shows that a relatively quick and simple PC calculation is capable of simulating the basic flow structure in the reacting and nonreacting shear layer present in the facility given basic assumptions about turbulence properties.

  8. A dedicated compression device for high resolution X-ray tomography of compressed gas diffusion layers

    SciTech Connect

    Tötzke, C.; Manke, I.; Banhart, J.; Gaiselmann, G.; Schmidt, V.; Bohner, J.; Müller, B. R.; Kupsch, A.; Hentschel, M. P.; Lehnert, W.

    2015-04-15

    We present an experimental approach to study the three-dimensional microstructure of gas diffusion layer (GDL) materials under realistic compression conditions. A dedicated compression device was designed that allows for synchrotron-tomographic investigation of circular samples under well-defined compression conditions. The tomographic data provide the experimental basis for stochastic modeling of nonwoven GDL materials. A plain compression tool is used to study the fiber courses in the material at different compression stages. Transport relevant geometrical parameters, such as porosity, pore size, and tortuosity distributions, are exemplarily evaluated for a GDL sample in the uncompressed state and for a compression of 30 vol.%. To mimic the geometry of the flow-field, we employed a compression punch with an integrated channel-rib-profile. It turned out that the GDL material is homogeneously compressed under the ribs, however, much less compressed underneath the channel. GDL fibers extend far into the channel volume where they might interfere with the convective gas transport and the removal of liquid water from the cell.

  9. Compressive failure of delamination-embedded layered structures

    NASA Astrophysics Data System (ADS)

    Wu, Li-Chun

    1997-11-01

    Various failure mechanisms involving both local and global deformation mechanisms of layered structures, consisting of differently oriented orthotropic laminae, are investigated with a large deformation finite element analysis. The aim of this study is to identify the dominant mode which leads to the structural failure under a given boundary condition and geometrical shape. It is assumed that these structures contain initial interlaminar flaws represented by embedded delaminations. Such flaws can play a significant role in defining overall structural integrity and deformation mechanisms. The energy release rate, mixed-mode stress intensity factors and phase angle are computed to quantify the crack driving force and used to measure likelihood of delamination growth in two-dimensional and three- dimensional composite structures. In the first part, two composite structures with distinguished shapes, consisting of four laminae are considered in two-dimensional analysis. One is a flat panel under compressive load and the other structure is a cylindrical shell subjected to external pressure. In the flat panel model, two buckling modes, a global and a local ligament, are observed under quasi-static loading conditions. The interaction of these two modes produces an unstable post-buckling behavior. It is found that the energy release rate exceeds experimentally estimated fracture toughness values only after buckling occurs. In the cylindrical shell study, lower critical buckling loads are observed for models with longer interlaminar delamination as in the flat panel model. However, unlike the flat panel case, the energy release rate surpasses the critical toughness well before the applied pressure reaches the buckling load of the flawed cylindrical shell. This behavior implies that a shell containing an embedded defect along an interface can fail by delamination growth and therefore has a failure load lower than its critical buckling load. Also for thicker cylindrical

  10. Plane mixing layer vortical structure kinematics

    NASA Technical Reports Server (NTRS)

    Leboeuf, Richard L.

    1993-01-01

    The objective of the current project was to experimentally investigate the structure and dynamics of the streamwise vorticity in a plane mixing layer. The first part of this research program was intended to clarify whether the observed decrease in mean streamwise vorticity in the far-field of mixing layers is due primarily to the 'smearing' caused by vortex meander or to diffusion. Two-point velocity correlation measurements have been used to show that there is little spanwise meander of the large-scale streamwise vortical structure. The correlation measurements also indicate a large degree of transverse meander of the streamwise vorticity which is not surprising since the streamwise vorticity exists in the inclined braid region between the spanwise vortex core regions. The streamwise convection of the braid region thereby introduces an apparent transverse meander into measurements using stationary probes. These results corroborated with estimated secondary velocity profiles in which the streamwise vorticity produces a signature which was tracked in time.

  11. Cumulus cloud venting of mixed layer ozone

    NASA Technical Reports Server (NTRS)

    Ching, J. K. S.; Shipley, S. T.; Browell, E. V.; Brewer, D. A.

    1985-01-01

    Observations are presented which substantiate the hypothesis that significant vertical exchange of ozone and aerosols occurs between the mixed layer and the free troposphere during cumulus cloud convective activity. The experiments utilized the airborne Ultra-Violet Differential Absorption Lidar (UV-DIAL) system. This system provides simultaneous range resolved ozone concentration and aerosol backscatter profiles with high spatial resolution. Evening transects were obtained in the downwind area where the air mass had been advected. Space-height analyses for the evening flight show the cloud debris as patterns of ozone typically in excess of the ambient free tropospheric background. This ozone excess was approximately the value of the concentration difference between the mixed layer and free troposphere determined from independent vertical soundings made by another aircraft in the afternoon.

  12. Modeling and diagnosing interface mix in layered ICF implosions

    NASA Astrophysics Data System (ADS)

    Weber, C. R.; Berzak Hopkins, L. F.; Clark, D. S.; Haan, S. W.; Ho, D. D.; Meezan, N. B.; Milovich, J. L.; Robey, H. F.; Smalyuk, V. A.; Thomas, C. A.

    2015-11-01

    Mixing at the fuel-ablator interface of an inertial confinement fusion (ICF) implosion can arise from an unfavorable in-flight Atwood number between the cryogenic DT fuel and the ablator. High-Z dopant is typically added to the ablator to control the Atwood number, but recent high-density carbon (HDC) capsules have been shot at the National Ignition Facility (NIF) without this added dopant. Highly resolved post-shot modeling of these implosions shows that there was significant mixing of ablator material into the dense DT fuel. This mix lowers the fuel density and results in less overall compression, helping to explain the measured ratio of down scattered-to-primary neutrons. Future experimental designs will seek to improve this issue through adding dopant and changing the x-ray spectra with a different hohlraum wall material. To test these changes, we are designing an experimental platform to look at the growth of this mixing layer. This technique uses side-on radiography to measure the spatial extent of an embedded high-Z tracer layer near the interface. Work performed under the auspices of the U.S. D.O.E. by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

  13. A defect stream function formulation for compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Barnwell, Richard W.; Wahls, Richard A.

    1990-01-01

    Progress to date on the development of a method for turbulent, wall-bounded flow which uses the defect stream function formulation in the outer layer and an analytic law of the wall and wake formulation in the inner region is reviewed. This two-formulation approach avoids the need to computationally resolve the high-gradient inner layer. One of the most appealing recent developments is the transformation of the compressible governing equation for the defect stream function into a linear, second-order differential equation which has analytic solutions for many problems of practical interest. Numerical and analytic results for incompressible and compressible flows are shown to be in excellent agreement with experimental results. In this paper the two-formulation approach is applied to primitive-variable computations. Excellent comparisons with experiment are presented for two compressible flat plate flows.

  14. Quasi 1D Modeling of Mixed Compression Supersonic Inlets

    NASA Technical Reports Server (NTRS)

    Kopasakis, George; Connolly, Joseph W.; Paxson, Daniel E.; Woolwine, Kyle J.

    2012-01-01

    The AeroServoElasticity task under the NASA Supersonics Project is developing dynamic models of the propulsion system and the vehicle in order to conduct research for integrated vehicle dynamic performance. As part of this effort, a nonlinear quasi 1-dimensional model of the 2-dimensional bifurcated mixed compression supersonic inlet is being developed. The model utilizes computational fluid dynamics for both the supersonic and subsonic diffusers. The oblique shocks are modeled utilizing compressible flow equations. This model also implements variable geometry required to control the normal shock position. The model is flexible and can also be utilized to simulate other mixed compression supersonic inlet designs. The model was validated both in time and in the frequency domain against the legacy LArge Perturbation INlet code, which has been previously verified using test data. This legacy code written in FORTRAN is quite extensive and complex in terms of the amount of software and number of subroutines. Further, the legacy code is not suitable for closed loop feedback controls design, and the simulation environment is not amenable to systems integration. Therefore, a solution is to develop an innovative, more simplified, mixed compression inlet model with the same steady state and dynamic performance as the legacy code that also can be used for controls design. The new nonlinear dynamic model is implemented in MATLAB Simulink. This environment allows easier development of linear models for controls design for shock positioning. The new model is also well suited for integration with a propulsion system model to study inlet/propulsion system performance, and integration with an aero-servo-elastic system model to study integrated vehicle ride quality, vehicle stability, and efficiency.

  15. Dynamic compressive properties of bovine knee layered tissue

    NASA Astrophysics Data System (ADS)

    Nishida, Masahiro; Hino, Yuki; Todo, Mitsugu

    2015-09-01

    In Japan, the most common articular disease is knee osteoarthritis. Among many treatment methodologies, tissue engineering and regenerative medicine have recently received a lot of attention. In this field, cells and scaffolds are important, both ex vivo and in vivo. From the viewpoint of effective treatment, in addition to histological features, the compatibility of mechanical properties is also important. In this study, the dynamic and static compressive properties of bovine articular cartilage-cancellous bone layered tissue were measured using a universal testing machine and a split Hopkinson pressure bar method. The compressive behaviors of bovine articular cartilage-cancellous bone layered tissue were examined. The effects of strain rate on the maximum stress and the slope of stress-strain curves of the bovine articular cartilage-cancellous bone layered tissue were discussed.

  16. Large-scale structure evolution in axisymmetric, compressible free-shear layers

    SciTech Connect

    Aeschliman, D.P.; Baty, R.S.

    1997-05-01

    This paper is a description of work-in-progress. It describes Sandia`s program to study the basic fluid mechanics of large-scale mixing in unbounded, compressible, turbulent flows, specifically, the turbulent mixing of an axisymmetric compressible helium jet in a parallel, coflowing compressible air freestream. Both jet and freestream velocities are variable over a broad range, providing a wide range mixing layer Reynolds number. Although the convective Mach number, M{sub c}, range is currently limited by the present nozzle design to values of 0.6 and below, straightforward nozzle design changes would permit a wide range of convective Mach number, to well in excess of 1.0. The use of helium allows simulation of a hot jet due to the large density difference, and also aids in obtaining optical flow visualization via schlieren due to the large density gradient in the mixing layer. The work comprises a blend of analysis, experiment, and direct numerical simulation (DNS). There the authors discuss only the analytical and experimental efforts to observe and describe the evolution of the large-scale structures. The DNS work, used to compute local two-point velocity correlation data, will be discussed elsewhere.

  17. Efficiency of shear induced entrainment in convectively mixed layers

    NASA Technical Reports Server (NTRS)

    Boers, Reinout

    1988-01-01

    Lidar data of mixed layer height are used to compare the model of process partitioning to that of Eulerian partitioning. It is found that the Eulerian partitioning model more closely follows the data and that the process partitioning model underpredicts the mixed layer depth. The results suggest that shear production and consumption of turbulent kinetic energy at the mixed layer top are local processes.

  18. Mixed Layer Drift Revealed by Satellite Data

    NASA Technical Reports Server (NTRS)

    Liu, Antony K.; Zhao, Yun-He; Esaias, Wayne E.; Campbell, Janet W.; Moore, Timothy; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    For the first time we are able to derive ocean currents using the wavelet algorithm for feature tracking from two different sensors (MODIS and SeaWiFS) on different satellites. Satellite ocean color data provide an important insight to the marine biosphere because of their capability to quantify certain fundamental properties (such as phytoplankton pigment concentration, marine primary production, etc.) on a global basis. The mixed layer drift can be derived because the ocean color signal bears information from a much larger depth (10 to 30 meters) as compared with the sea surface temperature data. Although the drifter data are very limited in the study area, the comparison shows a general agreement between drifter data and satellite tracking results, especially for the cases near the Gulf Stream boundary.

  19. Mixed Layer Heat Budget During Pomme Experiment

    NASA Astrophysics Data System (ADS)

    Giordani, H.; Caniaux, G.; Prieur, L.; Gavart, M.; Reverdin, G.

    A simplified 3D oceanic model derived from 1D turbulent mixing model was built in order to evaluate separately the impacts of the different processes of the mixed layer. This model is run from the hydrological networks collected during the POMME ex- periment (NE Atlantic, February to April 2001). Five simulations were performed be- tween Pomme1 (13/02) and Pomme2 (04/04), each one deduced from the previous one by adding one new physical process. The performance of the model to retrieve the final analysed fields increases with the number of the processes. A significant improvement is reached when the ageostrophic circulation (associated with the geostrophic adjust- ment of the large scale structures) is activated. In this case, the vertical heat transport has a clear signature in fronts and in some eddies present in the domain. Therefore, these local strong intensities seems well to be associated to the synoptic structures in permanent geostrophic adjustment. Thus subduction seems to be linked to the evolu- tion of the fronts and eddies.

  20. A constrained two-layer compression technique for ECG waves.

    PubMed

    Byun, Kyungguen; Song, Eunwoo; Shim, Hwan; Lim, Hyungjoon; Kang, Hong-Goo

    2015-08-01

    This paper proposes a constrained two-layer compression technique for electrocardiogram (ECG) waves, of which encoded parameters can be directly used for the diagnosis of arrhythmia. In the first layer, a single ECG beat is represented by one of the registered templates in the codebook. Since the required coding parameter in this layer is only the codebook index of the selected template, its compression ratio (CR) is very high. Note that the distribution of registered templates is also related to the characteristics of ECG waves, thus it can be used as a metric to detect various types of arrhythmias. The residual error between the input and the selected template is encoded by a wavelet-based transform coding in the second layer. The number of wavelet coefficients is constrained by pre-defined maximum distortion to be allowed. The MIT-BIH arrhythmia database is used to evaluate the performance of the proposed algorithm. The proposed algorithm shows around 7.18 CR when the reference value of percentage root mean square difference (PRD) is set to ten. PMID:26737691

  1. Finite volume solution of the compressible boundary-layer equations

    NASA Technical Reports Server (NTRS)

    Loyd, B.; Murman, E. M.

    1986-01-01

    A box-type finite volume discretization is applied to the integral form of the compressible boundary layer equations. Boundary layer scaling is introduced through the grid construction: streamwise grid lines follow eta = y/h = const., where y is the normal coordinate and h(x) is a scale factor proportional to the boundary layer thickness. With this grid, similarity can be applied explicity to calculate initial conditions. The finite volume method preserves the physical transparency of the integral equations in the discrete approximation. The resulting scheme is accurate, efficient, and conceptually simple. Computations for similar and non-similar flows show excellent agreement with tabulated results, solutions computed with Keller's Box scheme, and experimental data.

  2. Tollmien-Schlichting/vortex interactions in compressible boundary layer flows

    NASA Technical Reports Server (NTRS)

    Blackaby, Nicholas D.

    1993-01-01

    The weakly nonlinear interaction of oblique Tollmien-Schlichting waves and longitudinal vortices in compressible, high Reynolds number, boundary-layer flow over a flat plate is considered for all ranges of the Mach number. The interaction equations comprise of equations for the vortex which is indirectly forced by the waves via a boundary condition, whereas a vortex term appears in the amplitude equation for the wave pressure. The downstream solution properties of interaction equations are found to depend on the sign of an interaction coefficient. Compressibility is found to have a significant effect on the interaction properties; principally through its impact on the waves and their governing mechanism, the triple-deck structure. It is found that, in general, the flow quantities will grow slowly with increasing downstream co-ordinate; i.e. in general, solutions do not terminate in abrupt, finite-distance 'break-ups'.

  3. Lagrangian mixed layer modeling of the western equatorial Pacific

    NASA Technical Reports Server (NTRS)

    Shinoda, Toshiaki; Lukas, Roger

    1995-01-01

    Processes that control the upper ocean thermohaline structure in the western equatorial Pacific are examined using a Lagrangian mixed layer model. The one-dimensional bulk mixed layer model of Garwood (1977) is integrated along the trajectories derived from a nonlinear 1 1/2 layer reduced gravity model forced with actual wind fields. The Global Precipitation Climatology Project (GPCP) data are used to estimate surface freshwater fluxes for the mixed layer model. The wind stress data which forced the 1 1/2 layer model are used for the mixed layer model. The model was run for the period 1987-1988. This simple model is able to simulate the isothermal layer below the mixed layer in the western Pacific warm pool and its variation. The subduction mechanism hypothesized by Lukas and Lindstrom (1991) is evident in the model results. During periods of strong South Equatorial Current, the warm and salty mixed layer waters in the central Pacific are subducted below the fresh shallow mixed layer in the western Pacific. However, this subduction mechanism is not evident when upwelling Rossby waves reach the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific due to episodes of strong wind and light precipitation associated with the El Nino-Southern Oscillation. Comparison of the results between the Lagrangian mixed layer model and a locally forced Eulerian mixed layer model indicated that horizontal advection of salty waters from the central Pacific strongly affects the upper ocean salinity variation in the western Pacific, and that this advection is necessary to maintain the upper ocean thermohaline structure in this region.

  4. The compressible Gortler problem in two-dimensional boundary layers

    NASA Astrophysics Data System (ADS)

    Dando, Andrew H.; Seddougui, Sharon O.

    1993-01-01

    In this paper the authors investigate the growth rates of Gortler vortices in a compressible flow in the inviscid limit of large Gortler number. Numerical solutions are obtained for O(1) wavenumbers. The further limits of (i) large Mach number and (ii) large wavenumber with O(1) Mach number are considered. It is shown that two different types of disturbance mode can appear in this problem. The first is a wall layer mode, so named as it has its eigenfunctions trapped in a thin layer near the wall. The other mode investigated is confined to a thin layer away from the wall and termed a trapped-layer mode for large wavenumbers and an adjustment-layer mode for large Mach numbers, since then this mode has its eigenfunctions concentrated in the temperature adjustment layer. It is possible to investigate the near crossing of the modes which occurs in each of the limits mentioned. The inviscid limit does not predict a fastest growing mode, but does enable a most dangerous mode to be identified for O(1) Mach number. For hypersonic flow the most dangerous mode depends on the size of the Gortler number.

  5. Slow, Fast and Mixed Compressible Modes near the Magnetopause

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.; Maynard, N. C.; Burke, W. J.

    2003-12-01

    certification include the assignment of various portions of time-domain data streams to the compression or rarefaction phases of fast/slow modes structures, the directions of wave-power propagation in the plasma frame and relative to the magnetic field direction as well as their phase speeds with respect to the background plasma. These certifications also imply temporal trains of electric fields of the ambipolar type, including spatially varying E∥ (t), that may be the cause of some of the structured observations of E∥ that have recently been detected near the diffusion region. Along with Walén tests the new procedures enable surveys for the presence and roles of non-dispersive fast, intermediate, and slow MHD waves in geospace. Geophysical examples from the Polar satellite illustrate fast, slow and even admixtures of fast and slow magnetosonic waves retrieved through our analysis. On this experimental basis, we discuss the roles of compressible-mode structures in boundary layers associated with the magnetopause.

  6. Observation of Mix in a Compressible Plasma in a Convergent Cylindrical Geometry

    NASA Astrophysics Data System (ADS)

    Batha, Steven H.; Barnes, C. W.; Lanier, N. E.; Magelssen, G. R.; Scott, J. M.; Holmes, R. L.; Murphy, T. J.; Rothman, S.; Dunne, A. M.; Parker, K.; Youngs, D. L.

    2001-11-01

    Mixing of two materials may occur when the interface between them is shocked or accelerated. The mixing is exacerbated when the interface is imploding, highlighting the important effects of compressibility, miscibility, and convergence under strong-shock conditions. We present experiments and simulations of mix occurring in convergent cylindrical geometry. A hollow plastic 1-mm-diameter cylinder is imploded by ≈20 kJ of 351-nm laser light in a 1-ns square pulse from the OMEGA laser. The cylinder is filled with low-density foam that provides a back-pressure to the implosion. A higher density "marker layer" is placed at the interface between the plastic and foam. Both the plastic/marker and marker/foam interfaces are Richtmyer-Meshkov unstable. The marker material is chosen to produce either a large or small amount of mix. Experimentally, we measured the radial extent of the radiographically opaque marker layer. We found that the simulations were in excellent agreement in both cases with the experiments.

  7. Observation of Mix in a Compressible Plasma in a Convergent Cylindrical Geometry

    NASA Astrophysics Data System (ADS)

    Batha, Steven H.; Barnes, C. W.; Lanier, N. E.; Magelssen, G. R.; Scott, J. M.; Holmes, R. L.; Murphy, T. J.; Rothman, S.; Dunne, A. M.; Parker, K.; Youngs, D. L.

    2001-10-01

    Mixing of two materials may occur when the interface between them is shocked or accelerated. The mixing is exacerbated when the interface is imploding, highlighting the important effects of compressibility, miscibility, and convergence under strong-shock conditions. We present experiments and simulations of mix occurring in convergent cylindrical geometry. A hollow plastic 1-mm-diameter cylinder is imploded by ≈20 kJ of 351-nm laser light in a 1-ns square pulse from the OMEGA laser. The cylinder is filled with low-density foam that provides a back-pressure to the implosion. A higher density "marker layer" is placed at the interface between the plastic and foam. Both the plastic/marker and marker/foam interfaces are Richtmyer-Meshkov unstable. The marker material is chosen to produce either a large or small amount of mix. Experimentally, we measured the radial extent of the radiographically opaque marker layer. We found that the simulations were in excellent agreement in both cases with the experiments.

  8. Amplitude-dependent neutral modes in compressible boundary layer flows

    NASA Technical Reports Server (NTRS)

    Gajjar, J. S. B.

    1990-01-01

    The ideas of Benney and Bergeron (1969) and Davies (1970) on nonlinear critical layers are extended, and some new nonlinear neutral modes are computed for compressible boundary layer flow. A special case of the work is when the generalized inflexion point criterion holds. Neutral modes are found for a range of phase-speeds, dependent on the Mach number, and the properties of these are discussed. As in the linear case when the flow is relatively supersonic, multiple neutral modes exist. The behavior of the neutral amplitude in some limiting cases is also considered, and it is found that the results are significantly different from that in incompressible flow when the flow is locally supersonic.

  9. Investigation on flow and mixing characteristics of supersonic mixing layer induced by forced vibration of cantilever

    NASA Astrophysics Data System (ADS)

    Zhang, Dongdong; Tan, Jianguo; Lv, Liang

    2015-12-01

    The mixing process has been an important issue for the design of supersonic combustion ramjet engine, and the mixing efficiency plays a crucial role in the improvement of the combustion efficiency. In the present study, nanoparticle-based planar laser scattering (NPLS), particle image velocimetry (PIV) and large eddy simulation (LES) are employed to investigate the flow and mixing characteristics of supersonic mixing layer under different forced vibration conditions. The indexes of fractal dimension, mixing layer thickness, momentum thickness and scalar mixing level are applied to describe the mixing process. Results show that different from the development and evolution of supersonic mixing layer without vibration, the flow under forced vibration is more likely to present the characteristics of three-dimensionality. The laminar flow region of mixing layer under forced vibration is greatly shortened and the scales of rolled up Kelvin-Helmholtz vortices become larger, which promote the mixing process remarkably. The fractal dimension distribution reveals that comparing with the flow without vibration, the turbulent fluctuation of supersonic mixing layer under forced vibration is more intense. Besides, the distribution of mixing layer thickness, momentum thickness and scalar mixing level are strongly influenced by forced vibration. Especially, when the forcing frequency is 4000 Hz, the mixing layer thickness and momentum thickness are 0.0391 m and 0.0222 m at the far field of 0.16 m, 83% and 131% higher than that without vibration at the same position, respectively.

  10. A symmetry based approach to quantifying the compressible turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Wu, Bin; Bi, Wei-Tao; She, Zhen-Su; Hussain, Fazle

    2015-11-01

    Developing analytical description of the compressible turbulent boundary layer (CTBL) is of great importance to many technological applications and to the understanding and modeling of compressible turbulence. Here a symmetry-based approach is applied to analyze the CTBL data acquired from DNS, covering a wide range of Reynolds number (Re), Mach number (Ma) and wall temperature. The Reynolds stress length scale displays a four-layer structure in the direction normal to the wall and obeys the dilation group invariance as in the incompressible TBL. A newly-identified turbulent heat flux length scale behaves similarly, which is the classical temperature mixing length weighted by the mean temperature. A significant result is the identification of three physical parameters for each length function to characterize the adiabatic flow: a bulk flow constant, a buffer layer thickness and a boundary layer edge, which vary with Re and Ma. For the diabatic flow, the sublayer thickness and the inner layer scaling exponents vary additionally with the wall temperature. These parameters are modeled empirically, leading to a highly accurate prediction of the mean fields of the CTBL. Thus we reveal that the symmetry principle found in canonical wall-bounded flows holds also for the CTBL, and a quantitative mean field theory is viable with appropriate symmetry considerations.

  11. Linear stability analysis of three-dimensional compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Malik, Mujeeb R.; Orszag, Steven A.

    1987-01-01

    A compressible stability analysis computer code is developed. The code uses a matrix finite-difference method for local eigenvale solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used inital-value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed that may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black-box stability code. Sample stability calculations are presented for the boundary layer profiles of an LFC swept wing.

  12. Turbulent mixing layers in the interstellar medium of galaxies

    NASA Technical Reports Server (NTRS)

    Slavin, Jonathan D.; Shull, J. M.; Begelman, Mitchell C.

    1993-01-01

    It is proposed that turbulent mixing layers are common in the ISM of the Milky Way and selected external galaxies, with many layers per kiloparsec along typical lines of sight. All of the diffuse C I 1550-A background emission and a significant fraction of the diffuse H-alpha background at high latitude can be explained by mixing layers cooling at pressure of about 3000/cu cm K. These models also produce the correct ratio of semiforbidden C IV 15500 III 1663-A emission. Only 10 percent of the disk H-alpha is likely to arise from mixing layers. The observed Galactic absorption-line column densities of C IV, N V, Si IV, and O VI are roughly consistent with mixing-layer models with an intermediate temperature of about 10 exp 5.3 K and depleted abundances.

  13. Observations of mixed layer deepening during an Antarctic gale

    NASA Astrophysics Data System (ADS)

    Lane-Serff, G. F.; Stansfield, K. L.

    2013-03-01

    of mixed layer deepening made during a gale in February 2005 near an ice shelf, Fimbulisen, Antarctica, are reported. The observations were made from the RRS James Clark Ross in the lee of the ice shelf, using repeated downcasts ("yo-yo") of a conductivity-temperature-depth package, together with shipboard meteorological and other measurements. The mixed layer deepened from less than 40 m to over 120 m over the course of 27 h, with a very rapid deepening from 80 m to 120 m over a period of under 11 h. The mixed layer became both colder and fresher, with the change in salinity and heat content likely to be caused by melting ice. Oxygen isotope results suggest the source of the fresh water was melting sea ice rather than precipitation or ice shelf melt. The input of melt water at the surface stabilizes the mixed layer, so extra energy is required to deepen the mixed layer. The observations suggest that approximately 1.8% of the available "wind-work" energy was used to mix the upper water column, while the stabilizing surface buoyancy flux inhibits the turbulence in the mixed layer, limiting the mixing length to 1.6 m. The eventual depth of the mixed layer is in line with estimates based on the planetary length scale u*/f. The rate of mixed layer deepening is given by Ue/u* = 0.035. The apparent peak ice melting rate was approximately 60 mm hr-1, although this is likely to be exaggerated by convergence and downwelling.

  14. A Hybrid Numerical Method for Turbulent Mixing Layers. Degree awarded by Case Western Reserve Univ.

    NASA Technical Reports Server (NTRS)

    Georgiadis, Nicholas J.

    2001-01-01

    A hybrid method has been developed for simulations of compressible turbulent mixing layers. Such mixing layers dominate the flows in exhaust systems of modern day aircraft and also those of hypersonic vehicles currently under development. The method configurations in which a dominant structural feature provides an unsteady mechanism to drive the turbulent development in the mixing layer. The hybrid method uses a Reynolds-averaged Navier-Stokes (RANS) procedure to calculate wall bounded regions entering a mixing section, and a Large Eddy Simulation (LES) procedure to calculate the mixing dominated regions. A numerical technique was developed to enable the use of the hybrid RANS-LES method on stretched, non-Cartesian grids. Closure for the RANS equations was obtained using the Cebeci-Smith algebraic turbulence model in conjunction with the wall-function approach of Ota and Goldberg. The wall-function approach enabled a continuous computational grid from the RANS regions to the LES region. The LES equations were closed using the Smagorinsky subgrid scale model. The hybrid RANS-LES method is applied to a benchmark compressible mixing layer experiment. Preliminary two dimensional calculations are used to investigate the effects of axial grid density and boundary conditions. Vortex shedding from the base region of a splitter plate separating the upstream flows was observed to eventually transition to turbulence. The location of the transition, however, was much further downstream than indicated by experiments. Actual LES calculations, performed in three spatial directions, also indicated vortex shedding, but the transition to turbulence was found to occur much closer to the beginning of the mixing section. which is in agreement with experimental observations. These calculations demonstrated that LES simulations must be performed in three dimensions. Comparisons of time-averaged axial velocities and turbulence intensities indicated reasonable agreement with experimental

  15. Evolution of a forced stratified mixing layer

    NASA Astrophysics Data System (ADS)

    Rotter, J.; Fernando, H. J. S.; Kit, E.

    2007-06-01

    Laboratory measurements were carried out in a spatially developing stably stratified shear layer generated downstream of a splitter plate. The instabilities were controlled using a flapper spanning the entire shear layer, with the flapper forced at the fastest growing frequency of the primary [Kelvin-Helmholtz (KH)] instability. The measurements were taken as the KH instabilities roll up, break down, and degenerate into stratified turbulence. Both stratified and homogeneous shear layers were considered, the latter acting as the "baseline" case. The measurements included the streamwise and vertical velocities (made using X-wire hot film probes), which allowed calculation of the mean and rms velocities, turbulent kinetic energy (TKE) dissipation, and TKE production. The density and its gradients were measured using miniature conductivity probes. The measurements and flow visualization elicited interesting features of KH evolution, namely that KH billows may be turbulent from the onset, the TKE dissipation is largest at early stages of evolution, the production of TKE is a maximum at the breakdown of billows, the decay of turbulence to fossilized motions and concomitant formation of fine (layered) structure occur rapidly after the breakdown of billows, and episodic rebirth of (zombie) turbulence develops before a final permanently fossilized state is achieved.

  16. Numerical study of mixing viscous fluids in T-shaped micro-channels with compressibility effects

    NASA Astrophysics Data System (ADS)

    Yang, Junfeng; Matar, Omar; Harrison, Christopher; Sullivan, Matthew

    2015-11-01

    We study numerically the mixing processes of two miscible fluids in T-shaped micro-channels in the presence of compressibility effects. Three mixing modes are considered: `passive' mixing, which relies on the molecular diffusion and chaotic advection; `active' mixing relies on external disturbances, e.g. due to periodic compression; and a combination of these modes. In all cases considered, one of the fluids, fluid `A', is initially present in the dead-end region of the micro-channel. In the `passive' mixing case, the other fluid, fluid `B', flows through the open part of the channel at a constant flow rate. In the `active' case, this fluid is initially at rest but is then set in motion through pressure cycling. The combined case, involves the flow of fluid `B' in the presence of compression-decompression cycles. Numerical simulations are carried out for three different fluids, accounting for their compressibility, and their pressure-dependent e.g. density, viscosity, and diffusivity; a simple mixing rule is used to model the properties of the mixed fluids. Our results indicate that the vortices in the dead-end zone, engendered by the relative motion of the fluids leads to their mixing; the combination of mixing modes is shown to promote mixing efficiency significantly. Schlumberger-Doll Research.

  17. Spatially Developing Secondary Instabilities in Compressible Swept Airfoil Boundary Layers

    NASA Technical Reports Server (NTRS)

    Li, Fei; Choudhari, Meelan M.

    2011-01-01

    Two-dimensional eigenvalue analysis is used on a massive scale to study spatial instabilities of compressible shear flows with two inhomogeneous directions. The main focus of the study is crossflow dominated swept-wing boundary layers although the methodology can also be applied to study other type of flows, such as the attachment-line flow. Certain unique aspects of formulating a spatial, two-dimensional eigenvalue problem for the secondary instability of finite amplitude crossflow vortices are discussed, namely, fixing the spatial growth direction unambiguously through a non-orthogonal formulation of the linearized disturbance equations. A primary test case used for parameter study corresponds to the low-speed, NLF-0415(b) airfoil configuration as tested in the ASU Unsteady Wind Tunnel, wherein a spanwise periodic array of roughness elements was placed near the leading edge in order to excite stationary crossflow modes with a specified fundamental wavelength. The two classes of flow conditions selected for this analysis include those for which the roughness array spacing corresponds to either the naturally dominant crossflow wavelength, or a subcritical wavelength that serves to reduce the growth of the naturally excited dominant crossflow modes. Numerical predictions are compared with the measured database, both as indirect validation for the spatial instability analysis and to provide a basis for comparison with a higher Reynolds number, supersonic swept-wing configuration. Application of the eigenvalue analysis to the supersonic configuration reveals that a broad spectrum of stationary crossflow modes can sustain sufficiently strong secondary instabilities as to potentially cause transition over this configuration. Implications of this finding for transition control in swept wing boundary layers are examined.

  18. The difficulty in the assessment of the compression behaviour of powder mixtures: Double layer tablets versus arithmetic additivity rule.

    PubMed

    Belda, Petra M; Mielck, Jobst B

    2005-05-01

    The weighted arithmetic mean from values of a feature derived from the individual components is often used to calculate the theoretically expected compression behaviour of powder mixtures if no interparticulate interactions between the components occur. Alternatively, simulated and experimental double layer tablets are presented. The suitability of the various methods to serve as a reference for the assessment of the compression behaviour of powder mixtures shall be compared. Narrow and similar sieve fractions of maltitol and metamizol were mixed in various ratios of true volumes. Constant total true volumes of the single substances, powder mixtures, and layered powders of the same composition were compressed on an eccentric tabletting machine to a constant maximum geometric mean punch force. In addition, the compression of double layer tablets was mathematically simulated from the dynamic relative density-force data of the pure materials. At a given momentary force, the relative density of a simulated double layered powder bed is given by the harmonic mean of the relative density values of the pure materials weighted by their true volume fractions. The results show that the total, the net, and the expansion work change indeed almost linearly with the true volume fraction of the components in the double layer tablets, with the consequence that the plasticity index (=net work/total workx100) proceeds non-linearly. The slope of the Heckel plot 'at pressure' and the apparent mean yield pressure obtained from these Heckel data are non-linearly related to the true volume fraction. If the weighted arithmetic mean is used to analyse the compression behaviour of the powder mixtures, results are obtained which are incompatible or even contradictory between interrelated features. On the other hand, the double layer model provides a consistent evaluation. A good agreement between the results of the experimental and the simulated double layer tablets is found.

  19. Gradient layer entrainment in a thermohaline system with mixed layer circulation

    SciTech Connect

    Incropera, F.P.; Lents, C.E.; Viskanta, R.

    1986-11-01

    Entrainment of salt-stratified fluid into a bottom mixed layer is investigated under conditions for which mixing is driven by bottom heating and/or an imposed horizontal flow. Entrainment rate measurements and mixed layer flow visualization suggest that entrainment is strongly influenced by a shear mechanism involving both horizontal and vertical fluid velocity components. Under certain conditions, imposition of the horizontal flow inhibits the buoyancy flow and entrainment rates for combined mixing are less than those for pure buoyant mixing. Attempts to correlate entrainment rates in terms of conventional dimensionless parameters were unsuccessful.

  20. Direct numerical simulations of a reacting mixing layer with chemical heat release

    NASA Technical Reports Server (NTRS)

    Mcmurtry, P. A.; Jou, W.-H.; Metcalfe, R. W.; Riley, J. J.

    1985-01-01

    In order to study the coupling between chemical heat release and fluid dynamics, direct numerical simulations of a chemically reacting mixing layer with heat release are performed. The fully compressible equations as well as an approximate set of equations that is asymptotically valid for low-Mach-number flows are treated. These latter equations have the computational advantage that high-frequency acoustic waves have been filtered out, allowing much larger time steps to be taken in the numerical solution procedure. A detailed derivation of these equations along with an outline of the numerical solution technique is given. Simulation results indicate that the rate of chemical product formed, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release.

  1. Response of a supersonic boundary layer to a compression corner

    NASA Technical Reports Server (NTRS)

    Vandromme, D.; Zeman, O.

    1992-01-01

    On the basis of direct numerical simulations of rapidly compressed turbulence, Zeman and Coleman have developed a model to represent rapid directional compression contribution to the pressure dilatation term in the turbulent kinetic energy equation. The model has been implemented in the CFD code for simulation of supersonic compression corner flow with an extended separated region. The computational results have shown a significant improvement with respect to the baseline solution given by the standard k- epsilon turbulence model which does not contain any compressibility corrections.

  2. Three-wave mixing mediated femtosecond pulse compression in β-barium borate.

    PubMed

    Grün, A; Austin, Dane R; Cousin, Seth L; Biegert, J

    2015-10-15

    Nonlinear pulse compression mediated by three-wave mixing is demonstrated for ultrashort Ti:sapphire pulses in a type II phase-matched β-barium borate (BBO) crystal using noncollinear geometry. 170 μJ pulses at 800 nm with a pulse duration of 74 fs are compressed at their sum frequency to 32 fs with 55 μJ of pulse energy. Experiments and computer simulations demonstrate the potential of sum-frequency pulse compression to match the group velocities of the interacting waves to crystals that were initially not considered in the context of nonlinear pulse compression.

  3. Geometric Frustration in the Mixed Layer Pnictide Oxides

    SciTech Connect

    Enjalran, M.; Scalettar, R.T.; Kauzlarich, S.M.

    2000-06-06

    The authors present results from a Monte Carlo investigation of a simple bilayer model with geometrically frustrated interactions similar to those found in the mixed layer pnictide oxides (Sr{sub 2}Mn{sub 3}Pn{sub 2}O{sub 2}, Pn = As, Sb). The model is composed of two inequivalent square lattices with nearest-neighbor intra- and interlayer interactions. They find a ground state composed of two independent Neel ordered layers when the interlayer exchange is an order of magnitude weaker than the intralayer exchange, as suggested by experiment. Evidence for local orthogonal order between the layers is found, but it occurs in regions of parameter space which are not experimentally realized. Qualitatively similar results were observed in models with a larger number of layers. They conclude that frustration caused by nearest-neighbor interactions in the mixed layer pnictide oxides is not sufficient to explain the long-range orthogonal order that is observed experimentally.

  4. Numerical simulation of the non-Newtonian mixing layer

    NASA Technical Reports Server (NTRS)

    Azaiez, Jalel; Homsy, G. M.

    1993-01-01

    This work is a continuing effort to advance our understanding of the effects of polymer additives on the structures of the mixing layer. In anticipation of full nonlinear simulations of the non-Newtonian mixing layer, we examined in a first stage the linear stability of the non-Newtonian mixing layer. The results of this study show that, for a fluid described by the Oldroyd-B model, viscoelasticity reduces the instability of the inviscid mixing layer in a special limit where the ratio (We/Re) is of order 1 where We is the Weissenberg number, a measure of the elasticity of the flow, and Re is the Reynolds number. In the present study, we pursue this project with numerical simulations of the non-Newtonian mixing layer. Our primary objective is to determine the effects of viscoelasticity on the roll-up structure. We also examine the origin of the numerical instabilities usually encountered in the simulations of non-Newtonian fluids.

  5. Direct simulations of chemically reacting turbulent mixing layers, part 2

    NASA Technical Reports Server (NTRS)

    Metcalfe, Ralph W.; Mcmurtry, Patrick A.; Jou, Wen-Huei; Riley, James J.; Givi, Peyman

    1988-01-01

    The results of direct numerical simulations of chemically reacting turbulent mixing layers are presented. This is an extension of earlier work to a more detailed study of previous three dimensional simulations of cold reacting flows plus the development, validation, and use of codes to simulate chemically reacting shear layers with heat release. Additional analysis of earlier simulations showed good agreement with self similarity theory and laboratory data. Simulations with a two dimensional code including the effects of heat release showed that the rate of chemical product formation, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release. Subsequent three dimensional simulations showed similar behavior, in agreement with laboratory observations. Baroclinic torques and thermal expansion in the mixing layer were found to produce changes in the flame vortex structure that act to diffuse the pairing vortices, resulting in a net reduction in vorticity. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers were shown to result from vorticity generation by baroclinic torques.

  6. Mixing layer resonance under high-speed stream forcing

    NASA Astrophysics Data System (ADS)

    Thomassin, Jean; Mureithi, Njuki; Vo, Huu Duc

    2014-12-01

    In the majority of fluid-structure interaction problems, the biggest challenge lies in the fundamental understanding of the flow physics. Forced mixing layers is an important phenomenon found in many cases of flow-induced vibrations and acoustics. The response of a mixing layer to high-speed stream acoustic forcing is investigated with a theoretical and experimental approach. Two different experiments demonstrating the fluid mechanic phenomenon are presented. The first experiment consists of a circular jet impinging on a vibrating plate. The second experiment demonstrates the mixing layer resonance in the context of a fluidelastic instability causing high-amplitude vibrations in gas turbine high-pressure compressor rotor blades. Both the plate and the adjacent blade vibration induce an acoustic feedback that propagates within the jet and blade tip clearance flow, respectively. The resonance was found to occur when the feedback wavelength matched either the jet-to-plate or the inter-blade distance. In both experimental cases, the resonance condition has been simply modeled by the coincidence of a 1D feedback wave, which propagates upstream at reduced velocity by the high-speed flow. The coupling between the jet induced mixing layer and the feedback wave is assumed to naturally occur when one of the wave crests reaches the separation edge. The objective of this study is to improve the understanding of the coupling mechanism between an emanating shear layer and the acoustic forcing originating within a fast flow stream. The study is based on a simplified analytical model in order to enlarge the current understanding of the mixing layer receptivity to the more specific case of its response to high-speed stream forcing. To identify the mixing layer resonant modes, an analytical resonance condition is proposed. It is found that the mixing layer response becomes spatially resonant for specific source locations downstream in the high-speed flow. The study also provides an

  7. Transition and mixing in layered stratified shear flows.

    NASA Astrophysics Data System (ADS)

    Lee, Victoria; Caulfield, C. P.

    2001-11-01

    Flows with step-wise density distributions, i.e. well-mixed layers of fluid separated by narrow regions of high density gradient, are common in geophysics. We investigate numerically and theoretically the nonlinear evolution of a parallel shear flow at a moderate Reynolds number which has embedded within it a mixed layer of intermediate fluid. Linear stability theory predicts that the flow may be unstable to stationary vortical disturbances which are a generalization of an inviscid instability first considered by G. I. Taylor. We investigate the behaviour of these "Taylor waves" at finite amplitude through 3D nonlinear numerical simulations. We follow the development of primary and secondary instabilities which contribute to the eventual breakdown of the layered flow. In particular, we are interested in the mixing properties of the flow as it undergoes transition to small-scale disorder.

  8. Transient effects in unstable ablation fronts and mixing layers in HEDP

    NASA Astrophysics Data System (ADS)

    Clarisse, J.-M.; Gauthier, S.; Dastugue, L.; Vallet, A.; Schneider, N.

    2016-07-01

    We report results obtained for two elementary unstable flow configurations relevant to high energy density physics: the ablation front instability and the Rayleigh–Taylor -instability induced mixing layer. These two flows are characterized by a transience of their perturbation dynamics. In the ablative flow case, this perturbation dynamics transience takes the form of finite-durations of successive linear-perturbation evolution phases until reaching regimes of decaying oscillations. This behaviour is observed in various regimes: weakly or strongly accelerated ablation fronts, irradiation asymmetries or initial external-surface defects, and is a result of the mean-flow unsteadiness and stretching. In the case of the Rayleigh–Taylor-instability induced mixing layer, perturbation dynamics transience manifests itself through the extinction of turbulence and mixing as the flow reaches a stable state made of two stably stratified layers of pure fluids separated by an unstratified mixing layer. A second feature, also due to compressibility, takes the form of an intense acoustic wave production, mainly localized in the heavy fluid. Finally, we point out that a systematic short-term linear-perturbation dynamics analysis should be undertaken within the framework of non-normal stability theory.

  9. Method for producing a compressed body of mix-powder for ceramic

    NASA Technical Reports Server (NTRS)

    Okawa, K.

    1983-01-01

    Under the invented method, a compressed body of mix powder for ceramic is produced by mixing and stirring several raw powder materials with mixing liquid such as water, and, in the process of sending the resulted viscous material pressurized at 5 kg/cm to 7 kg/cm, using 1.5 to 2 times the pressure to filter and dehydrate, adjusting the water content to 10 to 20%.

  10. Prediction of dynamic and mixing characteristics of drop-laden mixing layers using DNS and LES

    NASA Technical Reports Server (NTRS)

    Okong'o, N.; Leboissetier, A.; Bellan, J.

    2004-01-01

    Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) have been conducted of a temporal mixing layer laden with evaporating drops, in order to assess the ability of LES to reproduce dynamic and mixing aspects of the DNS which affect combustion, independently of combustion models.

  11. Compressive epitactic layers on single-crystal components for improved mechanical durability and strength

    SciTech Connect

    Marion, J.E.; Gualtieri, D.M.; Morris, R.C.

    1987-09-01

    Compressive epitactic layers grown on single-crystal substrates are shown to substantially improve mechanical durability. In this study, neodymium-substituted gadolinium gallium garnet (GGG) layers are grown on undoped GGG substrates. The layers are found to dramatically improve the abrasion resistance of the substrates, but to have only a slight effect on strength. Abrasion treatments, which cause up to 20 times decrease in the strength of substrates without epitactic layers, do not cause a significant decrease in the strength of substrates with these compressive surface layers. This permits the high strength of specially prepared strong substrates to be retained after abrasion.

  12. LIF measurements of scalar mixing in turbulent shear layers

    NASA Technical Reports Server (NTRS)

    Karasso, Paris S.; Mungal, M. G.

    1993-01-01

    The structure of shear layer flows at high Reynolds numbers remains a very interesting problem. Straight mixing layers have been studied and yielded information on the probability density function (pdf) of a passive scalar across the layer. Konrad and Koochesfahani & Dimotakis measured the pdf of the mixture fraction for mixing layers of moderate Reynolds numbers, each about 25,000 (Re based on velocity difference and visual thickness). Their measurements showed a 'non-marching' pdf (central hump which is invariant from edge to edge across the layer), a result which is linked to the visualizations of the spanwise Kelvin-Helmholtz (K-H) instability mode, which is the primary instability for plane shear layer flows. A secondary instability mode, the Taylor-Gortler (T-G) instability, which is associated with streamwise vortical structures, has also been observed in shear layers. Image reconstruction by Jimenez et al. and volume renderings by Karasso & Mungal at low Re numbers have demonstrated that the K-H and the T-G instability modes occur simultaneously in a non-mutually destructive way, evidence that supports the quasi two-dimensional aspect of these flows and the non-marching character of the pdf at low Reynolds numbers. At higher Re numbers though, the interaction of these two instability modes is still unclear and may affect the mixing process. In this study, we perform measurements of the concentration pdf of plane mixing layers for different operating conditions. At a speed ratio of r = U(sub 1)/U(sub 2) = 4:1, we examine three Reynolds number cases: Re = 14,000, Re = 31,000, and Re = 62,000. Some other Re number cases' results, not presented in detail, are invoked to explain the behavior of the pdf of the concentration field. A case of r = 2.6:1 at Re = 20,000 is also considered. The planar laser-induced fluorescence technique is used to yield quantitative measurements. The different Re are obtained by changing the velocity magnitudes of the two streams. The

  13. Double-diffusive layering and mixing in Patagonian fjords

    NASA Astrophysics Data System (ADS)

    Pérez-Santos, Iván; Garcés-Vargas, José; Schneider, Wolfgang; Ross, Lauren; Parra, Sabrina; Valle-Levinson, Arnoldo

    2014-12-01

    Double-diffusive layering was quantified for the first time in the Chilean Patagonian fjords region (41.5-56°S). Approximately 600 temperature and salinity profiles collected during 1995-2012 were used to study water masses, quantify diffusive layering and compute the vertical diffusivity of heat. Development of 'diffusive-layering' or simply 'layering' was favored by relatively fresh-cold waters overlying salty-warm waters. Fresh waters are frequently derived from glacial melting that influences the fjord either directly or through rivers. Salty waters are associated with Modified Subantarctic (MSAAW) and Subantarctic Water (SAAW). Double-diffusive convection occurred as layering in 40% of the year-round data and as salt fingering in <1% of the time. The most vigorous layering, was found at depths between 20 and 70 m, as quantified by (a) Turner angles, (b) density ratios, and (c) heat diffusivity (with maximum values of 5 × 10-5 m2 s-1). Diffusive-layering events presented a meridional gradient with less layering within the 41-47°S northern region, relative to the southern region between 47° and 56°S. Layering occupied, on average, 27% and 56% of the water column in the northern and southern regions, respectively. Thermohaline staircases were detected with microprofile measurements in Martinez and Baker channels (48°S), showing homogeneous layers (2-4 m thick) below the pycnocline (10-40 m). Also in this area, increased vertical mixing coincided with the increased layering events. High values of Thorpe scale (LT ∼ 7 m), dissipation rate of TKE (ε = 10-5-10-3 W kg-1) and diapycnal eddy diffusivity (Kρ = 10-6-10-3 m-2 s-1) were associated with diffusive layering. Implications of these results are that diffusive layering should be taken into account, together with other mixing processes such as shear instabilities and wind-driven flows, in biological and geochemical studies.

  14. Three-dimensional plastic flow of anisotropic layer compressed by flat dies

    NASA Astrophysics Data System (ADS)

    Maksimova, Ljudmila A.

    2016-06-01

    Three-dimensional flow of anisotropic plastic layer compressed by parallel rough flat dies is considered. Ideal plastic material model with Hill anisotropic yield criterion modification of Mises isotropic model is used with associated plastic flow rule. General solution of a thin layer plastic flow problem with Prandtl linear velocity and shear stress variation in layer thickness direction is presented. Effects of contact friction force vector module and direction on the layer pressure on the dies and the layer plastic flow are considered.

  15. Internal wave energy radiated from a turbulent mixed layer

    SciTech Connect

    Munroe, James R.; Sutherland, Bruce R.

    2014-09-15

    We examine mixed-layer deepening and the generation of internal waves in stratified fluid resulting from turbulence that develops in response to an applied surface stress. In laboratory experiments the stress is applied over the breadth of a finite-length tank by a moving roughened conveyor belt. The turbulence in the shear layer is characterized using particle image velocimetry to measure the kinetic energy density. The internal waves are measured using synthetic schlieren to determine their amplitudes, frequencies, and energy density. We also perform fully nonlinear numerical simulations restricted to two dimensions but in a horizontally periodic domain. These clearly demonstrate that internal waves are generated by transient eddies at the integral length scale of turbulence and which translate with the background shear along the base of the mixed layer. In both experiments and simulations we find that the energy density of the generated waves is 1%–3% of the turbulent kinetic energy density of the turbulent layer.

  16. Mixing layers and coherent structures in vegetated aquatic flows

    NASA Astrophysics Data System (ADS)

    Ghisalberti, Marco; Nepf, Heidi M.

    2002-02-01

    To date, flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow, with vegetative drag treated as an extension of bed drag. However, recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer. This paper presents laboratory measurements, obtained from a scaled seagrass model, that demonstrate the applicability of the mixing layer analogy to aquatic systems. Specifically, all vertical profiles of mean velocity contained an inflection point, which makes the flow susceptible to Kelvin-Helmholtz instability. This instability leads to the generation of large, coherent vortices within the mixing layer (observed in the model at frequencies between 0.01 and 0.11 Hz), which dominate the vertical transport of momentum through the layer. The downstream advection of these vortices is shown to cause the progressive, coherent waving of aquatic vegetation, known as the monami. When the monami is present, the turbulent vertical transport of momentum is enhanced, with turbulent stresses penetrating an additional 30% of the plant height into the canopy.

  17. LES of Temporally Evolving Mixing Layers by an Eighth-Order Filter Scheme

    NASA Technical Reports Server (NTRS)

    Hadjadj, A; Yee, H. C.; Sjogreen, B.

    2011-01-01

    An eighth-order filter method for a wide range of compressible flow speeds (H.C. Yee and B. Sjogreen, Proceedings of ICOSAHOM09, June 22-26, 2009, Trondheim, Norway) are employed for large eddy simulations (LES) of temporally evolving mixing layers (TML) for different convective Mach numbers (Mc) and Reynolds numbers. The high order filter method is designed for accurate and efficient simulations of shock-free compressible turbulence, turbulence with shocklets and turbulence with strong shocks with minimum tuning of scheme parameters. The value of Mc considered is for the TML range from the quasi-incompressible regime to the highly compressible supersonic regime. The three main characteristics of compressible TML (the self similarity property, compressibility effects and the presence of large-scale structure with shocklets for high Mc) are considered for the LES study. The LES results using the same scheme parameters for all studied cases agree well with experimental results of Barone et al. (2006), and published direct numerical simulations (DNS) work of Rogers & Moser (1994) and Pantano & Sarkar (2002).

  18. Injectant mole-fraction imaging in compressible mixing flows using planar laser-induced iodine fluorescence

    NASA Technical Reports Server (NTRS)

    Hartfield, Roy J., Jr.; Abbitt, John D., III; Mcdaniel, James C.

    1989-01-01

    A technique is described for imaging the injectant mole-fraction distribution in nonreacting compressible mixing flow fields. Planar fluorescence from iodine, seeded into air, is induced by a broadband argon-ion laser and collected using an intensified charge-injection-device array camera. The technique eliminates the thermodynamic dependence of the iodine fluorescence in the compressible flow field by taking the ratio of two images collected with identical thermodynamic flow conditions but different iodine seeding conditions.

  19. Mixing Layer Excitation by Dielectric Barrier Discharge Plasma Actuators

    NASA Astrophysics Data System (ADS)

    Ely, Richard; Little, Jesse

    2012-11-01

    The response of a mixing layer with velocity ratio 0.28 to perturbations near the high-speed side (U2=11 m/s, ReL = 0.26 × 106) of its origin from dielectric barrier discharge plasma actuators is studied experimentally. Both alternating current (ac) and nanosecond (ns) pulse driven plasma are investigated in an effort to clarify the mechanisms associated with each technique as well as the more general physics associated with flow control via momentum-based versus thermal actuation. Ac-DBD plasma actuators, which function through electrohydrodynamic effects, are found to generate an increase in mixing layer momentum thickness that is strongly dependent on forcing frequency. Results are qualitatively similar to previous archival literature on the topic employing oscillating flaps. Ns-DBD plasma, which is believed to function through thermal effects, has no measureable influence on the mixing layer profile at similar forcing conditions. In the context of previous archival literature, these results suggest different physical mechanisms govern active control via ac- and ns-DBD plasma actuation and more generally, momentum versus thermal perturbations. Further investigation of these phenomena will be provided through variation of the boundary/mixing layer properties and forcing parameters in the context of spatially and temporally resolved experimental data. Supported by: AFOSR and Raytheon Missile Systems.

  20. Disintegration of fluids under supercritical conditions from mixing layer studies

    NASA Technical Reports Server (NTRS)

    Okong'o, N.; Bellan, J.

    2003-01-01

    Databases of transitional states obtained from Direct Numerical simulations (DNS) of temporal, supercritical mixing layers for two species systems, O2/H2 and C7H16/N2, are analyzed to elucidate species-specific turbulence aspects and features of fluid disintegration.

  1. Turbulent mixing layers in the interstellar medium of galaxies

    NASA Technical Reports Server (NTRS)

    Slavin, J. D.; Shull, J. M.; Begelman, M. C.

    1993-01-01

    We propose that turbulent mixing layers are common in the interstellar medium (ISM). Injection of kinetic energy into the ISM by supernovae and stellar winds, in combination with density and temperature inhomogeneities, results in shear flows. Such flows will become turbulent due to the high Reynolds number (low viscosity) of the ISM plasma. These turbulent boundary layers will be particularly interesting where the shear flow occurs at boundaries of hot (approximately 10(exp 6) K) and cold or warm (10(exp 2) - 10(exp 4) K) gas. Mixing will occur in such layers producing intermediate-temperature gas at T is approximately equal to 10(exp 5.0) - 10(exp 5.5) that radiates strongly in the optical, ultraviolet, and EUV. We have modeled these layers under the assumptions of rapid mixing down to the atomic level and steady flow. By including the effects of non-equilibrium ionization and self-photoionization of the gas as it cools after mixing, we predict the intensities of numerous optical, infrared, and ultraviolet emission lines, as well as absorption column densities of C 4, N 5, Si 4, and O 6.

  2. Unstable Mixing of Compressible Fluids Driven by Cylindrical Shocks

    NASA Astrophysics Data System (ADS)

    Graham, Mary Jane; Zhang, Qiang

    1996-11-01

    As an incident shock wave hits a material interface between two compressible fluids of different densities, the interface becomes unstable. Small disturbances at the interface start to grow forming spikes and bubbles. This interfacial instability is known as the Richtmyer-Meshkov (RM) instability. To date, the majority of the numerical and theoretical studies are for the RM instability in plane geometry. We present a systematic study of the RM instabiliy in cylindrical geometry with curved shocks for all four classes: shock exploding from light fluid to heavy fluid; (2) shock imploding from light fluid to heavy fluid; (3) shock exploding from heavy fluid to light fluid; and (4) shock imploding from heavy fluid to light fluid. A careful study and understanding of the effects of various physical parameters will be presented: including the curvature of the geometry, the incident shock strength, the amplitude of the perturbation as well as the number of fingers at the material interface, and the phenomenon of reshock.

  3. Suppression of Cavity-Driven Flow Separation in a Simulated Mixed Compression Inlet

    NASA Technical Reports Server (NTRS)

    Wendt, Bruce J.

    2000-01-01

    A test facility designed to simulate a bifurcated subsonic diffuser operating within a mixed compression inlet is described. The subsonic diffuser in this facility modeled a bypass cavity feature often used in mixed compression inlets for engine flow matching and normal shock control. A bypass cavity-driven flow separation was seen to occur in the subsonic diffuser without applied flow control. Flow control in the form of vortex generators and/or a partitioned bypass cavity cover plate were used to eliminate this flow separation, providing a 2% increase in area-averaged total pressure recovery, and a 70% reduction in circumferential distortion intensity.

  4. Initial development of a hypersonic free mixing layer

    NASA Technical Reports Server (NTRS)

    Harvey, W. D.; Bolton, R. L.

    1972-01-01

    A preliminary experimental investigation to establish some of the characteristics and further the understanding of the initial development of a turbulent free mixing layer for hypersonic speeds has been conducted. Mean profile data at about 6 inches downstream of the exit of a hypersonic nozzle have been obtained in nitrogen for a nominal Mach number of 19.5, total temperature of about 1670 K and Reynolds number range from about 50,000 to 110,000 per foot and have been compared with profiles upstream of the nozzle exit. Static pressure varied across the shear layer for the present tests. The outer 80 percent of the high-velocity portion of the free shear layer can be calculated by a rotational method of characteristics. However, turbulent mixing is evidently important in the low-velocity region, and effects of eddy viscosity and eddy conductivity should be included in a theoretical analysis.

  5. Vorticity-production mechanisms in shock/mixing-layer interaction problems

    NASA Astrophysics Data System (ADS)

    Tritarelli, R. C.; Kleiser, L.

    2016-04-01

    In this study, we investigate analytically the importance of different vorticity-production mechanisms contributing to the shock-induced vorticity caused by the interaction of a steady oblique shock wave with a steady, planar, supersonic, laminar mixing layer. The inviscid analysis is performed under the condition of a supersonic post-shock flow, which guarantees that the shock refraction remains regular. Special attention is paid to the vorticity production induced by a change in shock strength along the shock. Our analysis subdivides the total vorticity production into its contributions due to bulk or volumetric compression, pre-shock density gradients and variable shock strength. The latter is the only contribution dependent on the shock-wave curvature. The magnitudes of these contributions are analysed for two limiting cases, i.e., the interaction of an oblique shock wave with a constant-density shear layer and the interaction with a constant-velocity mixing layer with density gradients only. Possible implications for shock/mixing-layer interactions occurring in scramjet combustors are briefly discussed.

  6. Measurements of Molecular Mixing in a High Schmidt Number Rayleigh-Taylor Mixing Layer

    SciTech Connect

    Mueschke, N J; Schilling, O; Youngs, D L; Andrews, M

    2007-12-03

    Molecular mixing measurements are performed for a high Schmidt number (Sc {approx} 10{sup 3}), small Atwood number (A {approx} 7.5 x 10{sup -4}) buoyancy-driven turbulent Rayleigh-Taylor mixing layer in a water channel facility. Salt was added to the top stream to create the desired density difference. The degree of molecular mixing was measured as a function of time by monitoring a diffusion-limited chemical reaction between the two fluid streams. The pH of each stream was modified by the addition of acid or alkali such that a local neutralization reaction occurred as the two fluids molecularly mixed. The progress of this neutralization reaction was tracked by the addition of phenolphthalein - a pH-sensitive chemical indicator - to the acidic stream. Accurately calibrated backlit optical techniques were used to measure the average concentration of the colored chemical indicator. Comparisons of chemical product formation for pre-transitional buoyancy- and shear-driven mixing layers are given. It is also shown that experiments performed at different equivalence ratios (acid/alkali concentration) can be combined to obtain a mathematical relationship between the colored product formed and the density variance. This relationship was used to obtain high-fidelity, quantitative measures of the degree of molecular mixing which are independent of probe resolution constraints. The dependence of such mixing parameters on the Schmidt and Reynolds numbers is examined by comparing the current Sc {approx} 10{sup 3} measurements with Sc = 0.7 gas-phase and Pr = 7 liquid-phase measurements. This comparison indicates that the Schmidt number has a large effect on the bulk quantity of mixed fluid at small Reynolds numbers Re{sub h} < 10{sup 3}. At late times, all mixing parameters indicated a greater degree of molecular mixing and a decreased Schmidt number dependence. Implications for the development and quantitative assessment of turbulent transport and mixing models appropriate for

  7. Integrated random-aligned carbon nanotube layers: deformation mechanism under compression

    NASA Astrophysics Data System (ADS)

    Zeng, Zhiping; Gui, Xuchun; Gan, Qiming; Lin, Zhiqiang; Zhu, Yuan; Zhang, Wenhui; Xiang, Rong; Cao, Anyuan; Tang, Zikang

    2014-01-01

    Carbon nanotubes have the potential to construct highly compressible and elastic macroscopic structures such as films, aerogels and sponges. The structure-related deformation mechanism determines the mechanical behavior of those structures and niche applications. Here, we show a novel strategy to integrate aligned and random nanotube layers and reveal their deformation mechanism under uniaxial compression with a large range of strain and cyclic testing. Integrated nanotube layers deform sequentially with different mechanisms due to the distinct morphology of each layer. While the aligned layer forms buckles under compression, nanotubes in the random layer tend to be parallel and form bundles, resulting in the integration of quite different properties (strength and stiffness) and correspondingly distinct plateau regions in the stress-strain curves. Our results indicate a great promise of constructing hierarchical carbon nanotube structures with tailored energy absorption properties, for applications such as cushioning and buffering layers in microelectromechanical systems.Carbon nanotubes have the potential to construct highly compressible and elastic macroscopic structures such as films, aerogels and sponges. The structure-related deformation mechanism determines the mechanical behavior of those structures and niche applications. Here, we show a novel strategy to integrate aligned and random nanotube layers and reveal their deformation mechanism under uniaxial compression with a large range of strain and cyclic testing. Integrated nanotube layers deform sequentially with different mechanisms due to the distinct morphology of each layer. While the aligned layer forms buckles under compression, nanotubes in the random layer tend to be parallel and form bundles, resulting in the integration of quite different properties (strength and stiffness) and correspondingly distinct plateau regions in the stress-strain curves. Our results indicate a great promise of

  8. High-fidelity numerical simulations of compressible turbulence and mixing generated by hydrodynamic instabilities

    NASA Astrophysics Data System (ADS)

    Movahed, Pooya

    High-speed flows are prone to hydrodynamic interfacial instabilities that evolve to turbulence, thereby intensely mixing different fluids and dissipating energy. The lack of knowledge of these phenomena has impeded progress in a variety of disciplines. In science, a full understanding of mixing between heavy and light elements after the collapse of a supernova and between adjacent layers of different density in geophysical (atmospheric and oceanic) flows remains lacking. In engineering, the inability to achieve ignition in inertial fusion and efficient combustion constitute further examples of this lack of basic understanding of turbulent mixing. In this work, my goal is to develop accurate and efficient numerical schemes and employ them to study compressible turbulence and mixing generated by interactions between shocked (Richtmyer-Meshkov) and accelerated (Rayleigh-Taylor) interfaces, which play important roles in high-energy-density physics environments. To accomplish my goal, a hybrid high-order central/discontinuity-capturing finite difference scheme is first presented. The underlying principle is that, to accurately and efficiently represent both broadband motions and discontinuities, non-dissipative methods are used where the solution is smooth, while the more expensive and dissipative capturing schemes are applied near discontinuous regions. Thus, an accurate numerical sensor is developed to discriminate between smooth regions, shocks and material discontinuities, which all require a different treatment. The interface capturing approach is extended to central differences, such that smooth distributions of varying specific heats ratio can be simulated without generating spurious pressure oscillations. I verified and validated this approach against a stringent suite of problems including shocks, interfaces, turbulence and two-dimensional single-mode Richtmyer-Meshkov instability simulations. The three-dimensional code is shown to scale well up to 4000 cores

  9. Size scale dependence of compressive instabilities in layered composites in the presence of stress gradients

    NASA Astrophysics Data System (ADS)

    Poulios, K.; Niordson, C. F.

    2016-07-01

    The compressive strength of unidirectionally or layer-wise reinforced composite materials in direction parallel to their reinforcement is limited by micro-buckling instabilities. Although the inherent compressive strength of a given material micro-structure can easily be determined by assessing its stability under a uniform compressive load, this is often not sufficient for predicting failure initiation within a larger structure. In cases, where the composite material micro-structure is locally subjected to strongly non-uniform loadings, compressive instabilities depend not only on the maximum compressive stress but also on spatial stress or strain gradients, rendering failure initiation size scale dependent. The present work demonstrates and investigates the aforementioned effect through numerical simulations of periodically layered structures with notches and holes under bending and compressive loads, respectively. The presented results emphasize the importance of the reinforcing layer thickness on the load carrying capacity of the investigated structures, at a constant volumetric fraction of the reinforcement. The observed strengthening at higher values of the relative layer thickness is attributed to the bending stiffness of the reinforcing layers.

  10. Kubo-Anderson Mixing in the Turbulent Boundary Layer

    NASA Astrophysics Data System (ADS)

    Dekker, H.; de Leeuw, G.; Brink, A. Maassen Van Den

    A novel ab initio analysis of the Reynolds stress is presented in order to model non-local turbulence transport. The theory involves a sample path space and a stochastic hypothesis. A scaling relation maps the path space onto the boundary layer. Analytical sampling rates are shown to model mixing by exchange. Nonlocal mixing involves a scaling exponent ɛ≈0.58 (ɛ→∞ in the diffusion limit). The resulting transport equation represents a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process.

  11. 49 CFR 173.334 - Organic phosphates mixed with compressed gas.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 2 2010-10-01 2010-10-01 false Organic phosphates mixed with compressed gas. 173...-GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.334 Organic..., tetraethyl pyrophosphate, or other Division 6.1 organic phosphates (including a compound or mixture), may...

  12. 49 CFR 173.334 - Organic phosphates mixed with compressed gas.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 2 2014-10-01 2014-10-01 false Organic phosphates mixed with compressed gas. 173...-GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.334 Organic..., tetraethyl pyrophosphate, or other Division 6.1 organic phosphates (including a compound or mixture), may...

  13. 49 CFR 173.334 - Organic phosphates mixed with compressed gas.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 2 2013-10-01 2013-10-01 false Organic phosphates mixed with compressed gas. 173...-GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.334 Organic..., tetraethyl pyrophosphate, or other Division 6.1 organic phosphates (including a compound or mixture), may...

  14. 49 CFR 173.334 - Organic phosphates mixed with compressed gas.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 2 2012-10-01 2012-10-01 false Organic phosphates mixed with compressed gas. 173...-GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.334 Organic..., tetraethyl pyrophosphate, or other Division 6.1 organic phosphates (including a compound or mixture), may...

  15. 49 CFR 173.334 - Organic phosphates mixed with compressed gas.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 2 2011-10-01 2011-10-01 false Organic phosphates mixed with compressed gas. 173...-GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.334 Organic..., tetraethyl pyrophosphate, or other Division 6.1 organic phosphates (including a compound or mixture), may...

  16. Streamwise vortex meander in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Leboeuf, Richard L.; Mehta, Rabindra D.

    1993-01-01

    The present experimental study was conducted in order to determine the existence of streamwise vortex meander in a mixing layer, and if present, its significance on the measured properties. The dependence of the velocity cross-correlation on the fixed probe location was shown to be a good indicator of the stationarity of the streamwise vortex location. The cross-correlation measurements obtained here indicate that spanwise meander is negligible, although transverse apparent meander (normal to the plane of the mixing layer) was indicated. The transverse meander, exemplified by the elliptical shape of the mean streamwise vorticity contours, was expected, since the streamwise vorticity in the braid region is essentially inclined, with respect to the streamwise direction. These conclusions were supported by results of estimated spanwise profiles of the transverse velocity component. The balance of evidence suggests that the measured mean streamwise vorticity decay is representative of the decay of the vorticity rather than an artifact of meander.

  17. Dynamics of coherent structures in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Hussain, Fazle; Moser, R. D.; Colonius, T.; Moin, P.; Rogers, M. M.

    1988-01-01

    An incompressible, time developing 3-D mixing layer with idealized initial conditions was simulated numerically. Consistent with the suggestions from experimental measurements, the braid region between the dominant spanwise vortices or rolls develops longitudinal vortices or ribs, which are aligned upstream and downstream of a roll and produce spanwise distortion of the rolls. The process by which this distortion occurs is explained by studying a variety of quantities of dynamic importance (e.g., production of enstrophy, vortex stretching). Other quantities of interest (dissipation, helicity density) are also computed and discussed. The currently available simulation only allows the study of the early evolution (before pairing) of the mixing layer. New simulations in progress will relieve this restriction.

  18. Application of a Reynolds stress turbulence model to the compressible shear layer

    NASA Technical Reports Server (NTRS)

    Sarkar, S.; Balakrishnan, L.

    1990-01-01

    Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number.

  19. Application of large eddy interaction model to a mixing layer

    NASA Technical Reports Server (NTRS)

    Murthy, S. N. B.

    1989-01-01

    The large eddy interaction model (LEIM) is a statistical model of turbulence based on the interaction of selected eddies with the mean flow and all of the eddies in a turbulent shear flow. It can be utilized as the starting point for obtaining physical structures in the flow. The possible application of the LEIM to a mixing layer formed between two parallel, incompressible flows with a small temperature difference is developed by invoking a detailed similarity between the spectra of velocity and temperature.

  20. PDF calculation of scalar mixing layer with simple chemical reactions

    NASA Astrophysics Data System (ADS)

    Kanzaki, Takao; Pope, Stephen B.

    1999-11-01

    A joint velocity-composition-turbulent frequency PDF(JPDF) model is used to simulate reactive mixing layer in a grid-generated turbulence with the influence of second-order irreversible chemical reactions. To investigate the effects of molecular mixing, a gas flow and a liquid flow are simulated. For a gas flow, the oxidation reaction (NO+ O3 arrow NO2 +O2 ) between nitricoxide (NO) and ozone (O3 ) is used. For a liquid flow, the saponification reaction(NaOH+HCOOCH3 arrow HCOONa+CH_3OH) between sodiumhydroxide(NaOH) and methylformate(HCOOCH_3) is used. The both cases are moderately fast reactions. Therefore, reactive scalar statistics are affected by turbulent mixing. The results of caliculation are compared with experimental data of Komori et al.(1994) and Bilger et al.(1991)

  1. Irreversible Entropy Production in Two-Phase Mixing Layers

    NASA Technical Reports Server (NTRS)

    Okongo, Nora

    2003-01-01

    This report presents a study of dissipation (irreversible production of entropy) in three-dimensional, temporal mixing layers laden with evaporating liquid drops. The purpose of the study is to examine the effects of evaporating drops on the development of turbulent features in flows. Direct numerical simulations were performed to analyze transitional states of three mixing layers: one without drops, and two that included drops at different initial mass loadings. Without drops, the dissipation is essentially due to viscous effects. It was found that in the presence of drops, the largest contribution to dissipation was made by heating and evaporation of the drops, and that at large length scales, this contribution is positive (signifying that the drops reduce turbulence), while at small scales, this contribution is negative (the drops increase turbulence). The second largest contribution to dissipation was found to be associated with the chemical potential, which leads to an increase in turbulence at large scales and a decrease in turbulence at small scales. The next smaller contribution was found to be that of viscosity. The fact that viscosity effects are only third in order of magnitude in the dissipation is in sharp contrast to the situation for the mixing layer without the drops. The next smaller contribution - that of the drag and momentum of the vapor from the drops - was found to be negative at lower mass loading but to become positive at higher mass loading.

  2. Numerical investigation of algebraic oceanic turbulent mixing-layer models

    NASA Astrophysics Data System (ADS)

    Chacón-Rebollo, T.; Gómez-Mármol, M.; Rubino, S.

    2013-11-01

    In this paper we investigate the finite-time and asymptotic behaviour of algebraic turbulent mixing-layer models by numerical simulation. We compare the performances given by three different settings of the eddy viscosity. We consider Richardson number-based vertical eddy viscosity models. Two of these are classical algebraic turbulence models usually used in numerical simulations of global oceanic circulation, i.e. the Pacanowski-Philander and the Gent models, while the other one is a more recent model (Bennis et al., 2010) proposed to prevent numerical instabilities generated by physically unstable configurations. The numerical schemes are based on the standard finite element method. We perform some numerical tests for relatively large deviations of realistic initial conditions provided by the Tropical Atmosphere Ocean (TAO) array. These initial conditions correspond to states close to mixing-layer profiles, measured on the Equatorial Pacific region called the West-Pacific Warm Pool. We conclude that mixing-layer profiles could be considered as kinds of "absorbing configurations" in finite time that asymptotically evolve to steady states under the application of negative surface energy fluxes.

  3. Optical transfer function of the supersonic mixing layer.

    PubMed

    Gao, Qiong; Yi, Shihe; Jiang, Zongfu; He, Lin; Wang, Xiaohu

    2012-12-01

    The optical path difference (OPD) of the supersonic mixing layer with convective Mach number 0.5 is measured using the nanoparticle-based planar laser scattering technique, and its short-exposure optical transfer function (OTF) is computed with the proper orthogonal decomposition (POD). The OPD is analyzed from the viewpoint of structure function, and remarkable power law behavior is found. The power exponent is computed and analyzed. Taking the advantage of POD in capturing the energy of a signal, we present a model for the temporal evolution of OPD, which combines the deterministic and random factors together. With this model, the short-exposure OTF of the mixing layer is computed and analyzed. The amplitude modulation is evident at low frequencies, and it is almost negligible at high frequencies. The imaginary part of OTF for the mixing layer with developed vortex structures is of considerable amplitude, and the phase modulation becomes important for image degradation. We compare this phenomenon with the early result in aero-optics and explain it with the non-Gaussian statistics of OPD. PMID:23455913

  4. Direct simulation of high-speed mixing layers

    NASA Technical Reports Server (NTRS)

    Mukunda, H. S.; Sekar, B.; Carpenter, M. H.; Drummond, J. Philip; Kumar, Ajay

    1992-01-01

    A computational study of a nonreacting high-speed mixing layer is performed. A higher order algorithm with sufficient grid points is used to resolve all relevant scales. In all cases, a temporal free-stream disturbance is introduced. The resulting flow is time-sampled to generate a statistical cross section of the flow properties. The studies are conducted at two convective Mach numbers, three free-stream turbulence intensities, three Reynolds numbers, and two types of initial profiles-hyperbolic tangent (tanh) and boundary layer. The boundary-layer profile leads to more realistic predictions of the transition processes. The predicted transition Reynolds number of 0.18 x 10(exp 6) compares well with experimental data. Normalized vortex spacings for the boundary-layer case are about 3.5 and compare favorably with the 1.5 to 2.5 found in experimental measurements. The tanh profile produces spacings of about 10. The growth rate of the layer is shown to be moderately affected by the initial disturbance field, but comparison with experimental data shows moderate agreement. For the boundary-layer case, it is shown that noise at the Strouhal number of 0.007 is selectively amplified and shows little Reynolds number dependence.

  5. Effects of boundary layer and liquid viscosity and compressible air on sloshing characteristics

    NASA Astrophysics Data System (ADS)

    Zou, Chang-Fang; Wang, De-Yu; Cai, Zhong-Hua

    2015-07-01

    In this paper, numerical investigations for tank sloshing, based on commercial CFD package FLUENT, are performed to study effects of boundary layer grid, liquid viscosity and compressible air on sloshing pressure, wave height and rising time of impact pressure. Also, sloshing experiments for liquids of different viscosity are carried out to validate the numerical results. Through comparison of numerical and experimental results, a computational model including boundary layer grid can predict the sloshing pressure more accurately. Energy dissipation due to viscous friction leads to reduction of sloshing pressure and wave elevation. Sloshing pressure is also reduced because of cushion effect of compressible air. Due to high viscosity damping effect and compressible air effect, the rising time of impact pressure becomes longer. It is also found that liquid viscosity and compressible air influence distribution of dynamic pressure along the vertical tank wall.

  6. DNS and LES of a Shear-Free Mixing Layer

    NASA Technical Reports Server (NTRS)

    Knaepen, B.; Debliquy, O.; Carati, D.

    2003-01-01

    The purpose of this work is twofold. First, given the computational resources available today, it is possible to reach, using DNS, higher Reynolds numbers than in Briggs et al.. In the present study, the microscale Reynolds numbers reached in the low- and high-energy homogeneous regions are, respectively, 32 and 69. The results reported earlier can thus be complemented and their robustness in the presence of increased turbulence studied. The second aim of this work is to perform a detailed and documented LES of the shear-free mixing layer. In that respect, the creation of a DNS database at higher Reynolds number is necessary in order to make meaningful LES assessments. From the point of view of LES, the shear-free mixing-layer is interesting since it allows one to test how traditional LES models perform in the presence of an inhomogeneity without having to deal with difficult numerical issues. Indeed, as argued in Briggs et al., it is possible to use a spectral code to study the shear-free mixing layer and one can thus focus on the accuracy of the modelling while avoiding contamination of the results by commutation errors etc. This paper is organized as follows. First we detail the initialization procedure used in the simulation. Since the flow is not statistically stationary, this initialization procedure has a fairly strong influence on the evolution. Although we will focus here on the shear-free mixing layer, the method proposed in the present work can easily be used for other flows with one inhomogeneous direction. The next section of the article is devoted to the description of the DNS. All the relevant parameters are listed and comparison with the Veeravalli & Warhaft experiment is performed. The section on the LES of the shear-free mixing layer follows. A detailed comparison between the filtered DNS data and the LES predictions is presented. It is shown that simple eddy viscosity models perform very well for the present test case, most probably because the

  7. Investigations of Compression Shocks and Boundary Layers in Gases Moving at High Speed

    NASA Technical Reports Server (NTRS)

    Ackeret, J.; Feldmann, F.; Rott, N.

    1947-01-01

    The mutual influences of compression shocks and friction boundary layers were investigated by means of high speed wind tunnels.Schlieren optics provided a clear picture of the flow phenomena and were used for determining the location of the compression shocks, measurement of shock angles, and also for Mach angles. Pressure measurement and humidity measurements were also taken into consideration.Results along with a mathematical model are described.

  8. Design and calibration of the mixing layer and wind tunnel

    NASA Technical Reports Server (NTRS)

    Bell, James H.; Mehta, Rabindra D.

    1989-01-01

    A detailed account of the design, assembly and calibration of a wind tunnel specifically designed for free-shear layer research is contained. The construction of this new facility was motivated by a strong interest in the study of plane mixing layers with varying initial and operating conditions. The Mixing Layer Wind tunnel is located in the Fluid Mechanics Laboratory at NASA Ames Research Center. The tunnel consists of two separate legs which are driven independently by centrifugal blowers connected to variable speed motors. The blower/motor combinations are sized such that one is smaller than the other, giving maximum flow speeds of about 20 and 40 m/s, respectively. The blower speeds can either be set manually or via the Microvax II computer. The two streams are allowed to merge in the test section at the sharp trailing edge of a slowly tapering splitter plate. The test section is 36 cm in the cross-stream direction, 91 cm in the spanwise direction and 366 cm in length. One test section side-wall is slotted for probe access and adjustable so that the streamwise pressure gradient may be controlled. The wind tunnel is also equipped with a computer controlled, three-dimensional traversing system which is used to investigate the flow fields with pressure and hot-wire instrumentation. The wind tunnel calibration results show that the mean flow in the test section is uniform to within plus or minus 0.25 pct and the flow angularity is less than 0.25 deg. The total streamwise free-stream turbulence intensity level is approximately 0.15 pct. Currently the wind tunnel is being used in experiments designed to study the three-dimensional structure of plane mixing layers and wakes.

  9. Nonlinear stability of non-stationary cross-flow vortices in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Gajjar, J. S. B.

    1995-01-01

    The nonlinear evolution of long wavelength non-stationary cross-flow vortices in a compressible boundary layer is investigated and the work extends that of Gajjar (1994) to flows involving multiple critical layers. The basic flow profile considered in this paper is that appropriate for a fully three-dimensional boundary layer with O(1) Mach number and with wall heating or cooling. The governing equations for the evolution of the cross-flow vortex are obtained and some special cases are discussed. One special case includes linear theory where exact analytic expressions for the growth rate of the vortices are obtained. Another special case is a generalization of the Bassom & Gajjar (1988) results for neutral waves to compressible flows. The viscous correction to the growth rate is derived and it is shown how the unsteady nonlinear critical layer structure merges with that for a Haberman type of viscous critical layer.

  10. Evaluation of some compression aids in tableting of roller compacted swellable core drug layer.

    PubMed

    Golchert, D; Bines, E; Carmody, A

    2013-09-10

    Swellable core technology (SCT) represents a broadly applicable oral osmotic drug delivery platform for the controlled release of drugs. SCT tablets control drug delivery by using osmosis to regulate the influx of water into the tablet's core. The tablet consists of two layers; drug layer and sweller layer, with a semi-permeable membrane coating and delivery port located in the drug layer side of the tablet. The key component of SCT formulations is polyethylene oxide (PEO), which is typically wet granulated with organic solvents to prevent rapid gel hydration observed during contact with aqueous environments. However, the use of organic solvents has their own environmental and cost considerations which make this form of processing undesirable. To overcome this issue, dry granulation can be employed. However, PEO is a very plastic material and problems may be encountered during the tableting process, when work hardening occurs upon double compression. The addition of compression aids to the drug layer will help to increase the roll force when generating ribbons - reducing fines and segregation potential - while also reducing work hardening effects which impact tablet friability. The five compression aids used in this study were microcrystalline cellulose (MCC), xylitol, di-calcium phosphate (anhydrous), lactose monohydrate and starch. The work undertaken here studies the compression properties of the drug layer blends with different levels of the five compression aids as part of the formulation. Roller compaction properties are also varied to provide granules with differing solid fractions. The results of this study indicate that addition of microcrystalline cellulose in the formulation in levels between 10% and 30% significantly improve the tablet hardness at lower tablet compression forces. Further work is required to investigate the impact on dissolution. PMID:23796839

  11. Effects of viscosity variations in temporal mixing layer

    NASA Astrophysics Data System (ADS)

    Taguelmimt, N.; Danaila, L.; Hadjadj, A.

    2014-08-01

    The objective of the present investigation is to assess the effects of viscosity variations in low-speed temporally-evolving turbulent mixing layer. Direct Numerical Simulations (DNS) are performed for several viscosity ratios, Rv = vhigh/vlow, varying between 1 and 9, whereas the upper and lower streams are of equal density. The space-time evolution of Variable-Viscosity Flow (VVF) is compared with the Constant-Viscosity Flow (CVF), for which Rv = 1. The initial Reynolds number, based on the initial momentum thickness, δθ,0, is Reδθ,0 = 160 for the considered cases. The study focuses on the first stages of the temporal evolution of the mixing-layer. It is shown that in VVF (with respect to CVF): (i) the birth of turbulent fluctuations is accelerated; (ii) large-scale quantities, i.e. mean longitudinal velocity and momentum thickness, are affected by the viscosity variations, thus dispelling the myth that viscosity is a 'small-scale quantity that does not affect the large scales'; (iii) the velocity fluctuations are enhanced for VVF. In particular, the turbulent kinetic energy peaks earlier and is three times larger for VVF than CVF at the earliest stage of the mixing, and (iv) the transport equation for the turbulent kinetic energy is derived and favourably compared with simulations data.

  12. A comparison of hydrographically and optically derived mixed layer depths

    USGS Publications Warehouse

    Zawada, D.G.; Zaneveld, J.R.V.; Boss, E.; Gardner, W.D.; Richardson, M.J.; Mishonov, A.V.

    2005-01-01

    Efforts to understand and model the dynamics of the upper ocean would be significantly advanced given the ability to rapidly determine mixed layer depths (MLDs) over large regions. Remote sensing technologies are an ideal choice for achieving this goal. This study addresses the feasibility of estimating MLDs from optical properties. These properties are strongly influenced by suspended particle concentrations, which generally reach a maximum at pycnoclines. The premise therefore is to use a gradient in beam attenuation at 660 nm (c660) as a proxy for the depth of a particle-scattering layer. Using a global data set collected during World Ocean Circulation Experiment cruises from 1988-1997, six algorithms were employed to compute MLDs from either density or temperature profiles. Given the absence of published optically based MLD algorithms, two new methods were developed that use c660 profiles to estimate the MLD. Intercomparison of the six hydrographically based algorithms revealed some significant disparities among the resulting MLD values. Comparisons between the hydrographical and optical approaches indicated a first-order agreement between the MLDs based on the depths of gradient maxima for density and c660. When comparing various hydrographically based algorithms, other investigators reported that inherent fluctuations of the mixed layer depth limit the accuracy of its determination to 20 m. Using this benchmark, we found a ???70% agreement between the best hydrographical-optical algorithm pairings. Copyright 2005 by the American Geophysical Union.

  13. Slip velocity method for three-dimensional compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Barnwell, Richard W.; Wahls, Richard A.

    1988-01-01

    A slip velocity method for 2-D incompressible turbulent boundary layers was presented in AIAA Paper 88-0137. The inner part of the boundary layer was characterized by a law of the wall and a law of the wake, and the outer part was characterized by an arbitrary eddy viscosity model. In the present study for compressible flows, only a law of the wall is considered. The problem of 2-D compressible flow is treated first; then the extension to 3-D flow is addressed. A formulation for primitive variables is presented.

  14. Study on Compressibility Control of Hyperelastic Material for Homogenization Method Using Mixed Finite Element Analysis

    NASA Astrophysics Data System (ADS)

    Okada, Jun-Ichi; Hisada, Toshiaki

    It is well known that the compressibility or incompressibility of biological tissue stems from its microscopic structure, which is generally composed of material with varied compressibility, including incompressibility. This paper proposes a framework for a homogenization method in which the compressibility/incompressibility of the macrostructure properly reflects that of the microstructure. The formulation is based on the mixed variational principle with a perturbed Lagrange-multiplier. It is shown that the rate of volumetric change of the macrostructure can be controlled through the homogenization procedure by introducing the constraint on the microstructure only. A couple of numerical examples are given to demonstrate the validity of the proposed method. By comparing the numerical results with theoretical solutions, the method is also confirmed to be free from locking.

  15. Turbulence in the upper-ocean mixed layer.

    PubMed

    D'Asaro, Eric A

    2014-01-01

    Nearly all operational models of upper-ocean mixing assume that the turbulence responsible for this mixing is driven by the atmospheric fluxes of momentum, heat, and moisture and the shear imposed by the ocean circulation. This idealization is supported by historical measurements of dissipation rate within the boundary layer. Detailed measurements made recently by many investigators and supported by theoretical and numerical results have found significant deviations from this classical view attributable to the influence of surface waves. Although a review of these measurements finds strong support for the influence of waves-and, in particular, for the predictions of large-eddy simulations, including the Craik-Leibovich vortex force-there are insufficient data to give definitive support to a new paradigm.

  16. Water Vapor Turbulence Profiles in Stationary Continental Convective Mixed Layers

    SciTech Connect

    Turner, D. D.; Wulfmeyer, Volker; Berg, Larry K.; Schween, Jan

    2014-10-08

    The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program’s Raman lidar at the ARM Southern Great Plains (SGP) site in north-central Oklahoma has collected water vapor mixing ratio (q) profile data more than 90% of the time since October 2004. Three hundred (300) cases were identified where the convective boundary layer was quasi-stationary and well-mixed for a 2-hour period, and q mean, variance, third order moment, and skewness profiles were derived from the 10-s, 75-m resolution data. These cases span the entire calendar year, and demonstrate that the q variance profiles at the mixed layer (ML) top changes seasonally, but is more related to the gradient of q across the interfacial layer. The q variance at the top of the ML shows only weak correlations (r < 0.3) with sensible heat flux, Deardorff convective velocity scale, and turbulence kinetic energy measured at the surface. The median q skewness profile is most negative at 0.85 zi, zero at approximately zi, and positive above zi, where zi is the depth of the convective ML. The spread in the q skewness profiles is smallest between 0.95 zi and zi. The q skewness at altitudes between 0.6 zi and 1.2 zi is correlated with the magnitude of the q variance at zi, with increasingly negative values of skewness observed lower down in the ML as the variance at zi increases, suggesting that in cases with larger variance at zi there is deeper penetration of the warm, dry free tropospheric air into the ML.

  17. Vertical and horizontal mixing in the tropical tropopause layer

    NASA Astrophysics Data System (ADS)

    Glanville, Anne Alexandra

    Nearly all air enters the stratosphere through a single layer in the tropics. The tropical tropopause layer (TTL) is a transition region between the troposphere and stratosphere and its roles include regulating stratospheric chemistry and surface climate. Multiscale dynamics existing in the TTL range from transient convection to the hemispheric wave-driven circulation and the relative influences of these processes still remain unclear. This study pays special attention to vertical and horizontal mixing which are associated with breaking gravity waves and Rossby waves, respectively. Our study quantifies the roles of these dynamics by taking advantage of the conservative nature of water vapor in the lower stratosphere. Unable to change concentration in the lowermost stratosphere after passing through the cold point, water vapor becomes a tracer for total transport and its signal is known as the tape recorder. This tape recorder is studied using observations, reanalysis data, a chemistry-climate model (CCM), and simple idealized modeling. Modifying past methods, we are able to capture the seasonal cycle of effective transport in the TTL and we introduce seasonally-dependent dynamics to a one-dimensional model and perform a parameter-sweep to test all possible dynamical combinations. Simulating with unrealistic annual mean transports results in bimodality where either vertical advection or vertical mixing dominate. The solutions that depend on amplified vertical advection disappear when seasonally-dependent transports are used. Overall, all datasets show that vertical mixing is as important to TTL transport as vertical advection itself even during boreal winter when advection peaks. The reanalysis and CCM have increased effective transport compared to observations, however, they rely on different dynamics. The reanalysis has amplified vertical mixing while the CCM has amplified vertical advection. This hints at the possible influence of spurious diffusion from data

  18. Prediction of heat release effects on a mixing layer

    NASA Technical Reports Server (NTRS)

    Farshchi, M.

    1986-01-01

    A fully second-order closure model for turbulent reacting flows is suggested based on Favre statistics. For diffusion flames the local thermodynamic state is related to single conserved scalar. The properties of pressure fluctuations are analyzed for turbulent flows with fluctuating density. Closure models for pressure correlations are discussed and modeled transport equations for Reynolds stresses, turbulent kinetic energy dissipation, density-velocity correlations, scalar moments and dissipation are presented and solved, together with the mean equations for momentum and mixture fraction. Solutions of these equations are compared with the experimental data for high heat release free mixing layers of fluorine and hydrogen in a nitrogen diluent.

  19. Calculation of compressible boundary layer flow about airfoils by a finite element/finite difference method

    NASA Technical Reports Server (NTRS)

    Strong, Stuart L.; Meade, Andrew J., Jr.

    1992-01-01

    Preliminary results are presented of a finite element/finite difference method (semidiscrete Galerkin method) used to calculate compressible boundary layer flow about airfoils, in which the group finite element scheme is applied to the Dorodnitsyn formulation of the boundary layer equations. The semidiscrete Galerkin (SDG) method promises to be fast, accurate and computationally efficient. The SDG method can also be applied to any smoothly connected airfoil shape without modification and possesses the potential capability of calculating boundary layer solutions beyond flow separation. Results are presented for low speed laminar flow past a circular cylinder and past a NACA 0012 airfoil at zero angle of attack at a Mach number of 0.5. Also shown are results for compressible flow past a flat plate for a Mach number range of 0 to 10 and results for incompressible turbulent flow past a flat plate. All numerical solutions assume an attached boundary layer.

  20. A mixing layer theory for flow resistance in shallow streams

    NASA Astrophysics Data System (ADS)

    Katul, Gabriel; Wiberg, Patricia; Albertson, John; Hornberger, George

    2002-11-01

    A variety of surface roughness characterizations have emerged from nineteenth and twentieth century studies of channel hydraulics. When the water depth h is much larger than the characteristic roughness height ks, roughness formulations such as Manning's n and the friction factor f can be explicitly related to the momentum roughness height zo in the log-law formulation for turbulent boundary layers, thereby unifying roughness definitions for a given surface. However, when h is comparable to (or even smaller than) ks, the log-law need not be valid. Using a newly proposed mixing layer analogy for the inflectional velocity profile within and just above the roughness layer, a model for the flow resistance in shallow flows is developed. The key model parameter is the characteristic length scale describing the depth of the Kelvin-Helmholtz wave instability. It is shown that the new theory, originally developed for canopy turbulence, recovers much of the earlier roughness results for flume experiments and shallow gravel streams. This study is the first to provide such a unifying framework between canopy atmospheric turbulence and shallow gravel stream roughness characterization. The broader implication of this study is to support the merger of a wealth of surface roughness characterizations independently developed in nineteenth and twentieth century hydraulics and atmospheric sciences and to establish a connection between roughness formulations across traditionally distinct boundary layer types.

  1. Effect of mixed layer crystallinity on the performance of mixed heterojunction organic photovoltaic cells.

    PubMed

    Song, Byeongseop; Rolin, Cedric; Zimmerman, Jeramy D; Forrest, Stephen R

    2014-05-01

    Organic vapor-phase deposition (OVPD) is used to grow tetraphenyldibenzoperiflanthen (DBP):C70 mixed heterojunction photovoltaic devices. Compared with vacuum thermal evaporation (VTE), the OVPD-grown film develops nanocrystalline domains of C70. Optimized OVPD-grown OPVs have a 61% fill factor for a 100 nm active layer thickness, whereas VTE-grown devices have a 47% fill factor at the same thickness.

  2. A compressible near-wall turbulence model for boundary layer calculations

    NASA Technical Reports Server (NTRS)

    So, R. M. C.; Zhang, H. S.; Lai, Y. G.

    1992-01-01

    A compressible near-wall two-equation model is derived by relaxing the assumption of dynamical field similarity between compressible and incompressible flows. This requires justifications for extending the incompressible models to compressible flows and the formulation of the turbulent kinetic energy equation in a form similar to its incompressible counterpart. As a result, the compressible dissipation function has to be split into a solenoidal part, which is not sensitive to changes of compressibility indicators, and a dilational part, which is directly affected by these changes. This approach isolates terms with explicit dependence on compressibility so that they can be modeled accordingly. An equation that governs the transport of the solenoidal dissipation rate with additional terms that are explicitly dependent on the compressibility effects is derived similarly. A model with an explicit dependence on the turbulent Mach number is proposed for the dilational dissipation rate. Thus formulated, all near-wall incompressible flow models could be expressed in terms of the solenoidal dissipation rate and straight-forwardly extended to compressible flows. Therefore, the incompressible equations are recovered correctly in the limit of constant density. The two-equation model and the assumption of constant turbulent Prandtl number are used to calculate compressible boundary layers on a flat plate with different wall thermal boundary conditions and free-stream Mach numbers. The calculated results, including the near-wall distributions of turbulence statistics and their limiting behavior, are in good agreement with measurements. In particular, the near-wall asymptotic properties are found to be consistent with incompressible behavior; thus suggesting that turbulent flows in the viscous sublayer are not much affected by compressibility effects.

  3. Part 1 of a Computational Study of a Drop-Laden Mixing Layer

    NASA Technical Reports Server (NTRS)

    Okong'o, Nora A.; Bellan, Josette

    2004-01-01

    This first of three reports on a computational study of a drop-laden temporal mixing layer presents the results of direct numerical simulations (DNS) of well-resolved flow fields and the derivation of the large-eddy simulation (LES) equations that would govern the larger scales of a turbulent flow field. The mixing layer consisted of two counterflowing gas streams, one of which was initially laden with evaporating liquid drops. The gas phase was composed of two perfect gas species, the carrier gas and the vapor emanating from the drops, and was computed in an Eulerian reference frame, whereas each drop was tracked individually in a Lagrangian manner. The flow perturbations that were initially imposed on the layer caused mixing and eventual transition to turbulence. The DNS database obtained included transitional states for layers with various liquid mass loadings. For the DNS, the gas-phase equations were the compressible Navier-Stokes equations for conservation of momentum and additional conservation equations for total energy and species mass. These equations included source terms representing the effect of the drops on the mass, momentum, and energy of the gas phase. From the DNS equations, the expression for the irreversible entropy production (dissipation) was derived and used to determine the dissipation due to the source terms. The LES equations were derived by spatially filtering the DNS set and the magnitudes of the terms were computed at transitional states, leading to a hierarchy of terms to guide simplification of the LES equations. It was concluded that effort should be devoted to the accurate modeling of both the subgridscale fluxes and the filtered source terms, which were the dominant unclosed terms appearing in the LES equations.

  4. Direct simulations of chemically reacting turbulent mixing layers

    NASA Technical Reports Server (NTRS)

    Riley, J. J.; Metcalfe, R. W.

    1984-01-01

    The report presents the results of direct numerical simulations of chemically reacting turbulent mixing layers. The work consists of two parts: (1) the development and testing of a spectral numerical computer code that treats the diffusion reaction equations; and (2) the simulation of a series of cases of chemical reactions occurring on mixing layers. The reaction considered is a binary, irreversible reaction with no heat release. The reacting species are nonpremixed. The results of the numerical tests indicate that the high accuracy of the spectral methods observed for rigid body rotation are also obtained when diffusion, reaction, and more complex flows are considered. In the simulations, the effects of vortex rollup and smaller scale turbulence on the overall reaction rates are investigated. The simulation results are found to be in approximate agreement with similarity theory. Comparisons of simulation results with certain modeling hypotheses indicate limitations in these hypotheses. The nondimensional product thickness computed from the simulations is compared with laboratory values and is found to be in reasonable agreement, especially since there are no adjustable constants in the method.

  5. Statistics of High Atwood Number Turbulent Mixing Layers

    NASA Astrophysics Data System (ADS)

    Baltzer, Jon; Livescu, Daniel

    2015-11-01

    The statistical properties of incompressible shear-driven planar mixing layers between two miscible streams of fluids with different densities are investigated by means of Direct Numerical Simulations. The simulations begin from a thin interface perturbed by a thin broadband random disturbance, and the mixing layers are allowed to develop to self-similar states. The temporal simulations are performed in unprecedented domain sizes, with grid sizes up to 6144 x 2048 x 1536, which allows turbulent structures to grow and merge naturally. This allows the flow to reach states far-removed from the initial disturbances, thereby enabling high-quality statistics to be obtained for higher moments, pdfs, and other quantities critical to developing closure models. A wide range of Atwood numbers are explored, ranging from nearly constant density to At=0.87. The consequences of increasing the density contrast are investigated for global quantities, such as growth rates, and asymmetries that form in statistical profiles. Additional simulations in smaller domains are performed to study the effects of domain size.

  6. Comparison of several methods for predicting separation in a compressible turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Gerhart, P. M.; Bober, L. J.

    1974-01-01

    Several methods for predicting the separation point for a compressible turbulent boundary layer were applied to the flow over a bump on a wind-tunnel wall. Measured pressure distributions were used as input. Two integral boundary-layer methods, three finite-difference boundary-layer methods, and three simple methods were applied at five free-stream Mach numbers ranging from 0.354 to 0.7325. Each of the boundary-layer methods failed to explicitly predict separation. However, by relaxing the theoretical separation criteria, several boundary-layer methods were made to yield reasonable separation predictions, but none of the methods accurately predicted the important boundary-layer parameters at separation. Only one of the simple methods consistently predicted separation with reasonable accuracy in a manner consistent with the theory. The other methods either indicated several possible separation locations or only sometimes predicted separation.

  7. Three dimensional compressible boundary-layer computations for a finite swept wing

    NASA Technical Reports Server (NTRS)

    Nash, J. F.; Scruggs, R. M.

    1972-01-01

    Three-dimensional, compressible turbulent boundary-layer calculations have been performed for the finite supercritical wing of the NASA modified F8 transonic research airplane. Data on the boundary-layer thickness, displacement thickness, skin friction components, and integrated streamwise skin friction are presented for points along the streamwise stations of which the pressure measurements were previously made. Representative velocity profiles are shown, and boundary-layer-thickness contour plots and skin-friction vector plots are presented. Results are given for a Reynolds number of 1.5 million per foot, and for Mach numbers of 0.50 and 0.99.

  8. The stability of the laminar boundary layer in a compressible fluid

    NASA Technical Reports Server (NTRS)

    Lees, Lester

    1947-01-01

    Report is a continuation of a theoretical investigation of the stability of the laminar boundary layer in a compressible fluid. An approximate estimate for the minimum critical Reynolds number, or stability limit, is obtained in terms of the distribution of the kinematic viscosity and the product of the mean density and mean vorticity across the boundary layer. The extension of the results of the stability analysis to laminar boundary-layer gas flows with a pressure gradient in the direction of the free stream is discussed. (author)

  9. CVS Filtering of 3D Turbulent Mixing Layers Using Orthogonal Wavelets

    NASA Technical Reports Server (NTRS)

    Schneider, Kai; Farge, Marie; Pellegrino, Giulio; Rogers, Michael

    2000-01-01

    Coherent Vortex Simulation (CVS) filtering has been applied to Direct Numerical Simulation (DNS) data of forced and unforced time-developing turbulent mixing layers. CVS filtering splits the turbulent flow into two orthogonal parts, one corresponding to coherent vortices and the other to incoherent background flow. We have shown that the coherent vortices can be represented by few wavelet modes and that these modes are sufficient to reproduce the vorticity probability distribution function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of CVS filtering, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.

  10. Bending elasticity of charged surfactant layers: the effect of mixing.

    PubMed

    Bergström, L Magnus

    2006-08-01

    Expressions have been derived from which the spontaneous curvature (H(0)), bending rigidity (k(c)), and saddle-splay constant (k(c)) of mixed monolayers and bilayers may be calculated from molecular and solution properties as well as experimentally available quantities such as the macroscopic hydrophobic-hydrophilic interfacial tension. Three different cases of binary surfactant mixtures have been treated in detail: (i) mixtures of an ionic and a nonionic surfactant, (ii) mixtures of two oppositely charged surfactants, and (iii) mixtures of two ionic surfactants with identical headgroups but different tail volumes. It is demonstrated that k(c)H(0), k(c), and k(c) for mixtures of surfactants with flexible tails may be subdivided into one contribution that is due to bending properties of an infinitely thin surface as calculated from the Poisson-Boltzmann mean field theory and one contribution appearing as a result of the surfactant film having a finite thickness with the surface of charge located somewhat outside the hydrophobic-hydrophilic interface. As a matter of fact, the picture becomes completely different as finite layer thickness effects are taken into account, and as a result, the spontaneous curvature is extensively lowered whereas the bending rigidity is raised. Furthermore, an additional contribution to k(c) is present for surfactant mixtures but is absent for k(c)H(0) and k(c). This contribution appears as a consequence of the minimization of the free energy with respect to the composition of a surfactant layer that is open in the thermodynamic sense and must always be negative (i.e., k(c) is generally found to be brought down by the process of mixing two or more surfactants). The magnitude of the reduction of k(c) increases with increasing asymmetry between two surfactants with respect to headgroup charge number and tail volume. As a consequence, the bending rigidity assumes the lowest values for layers formed in mixtures of two oppositely charged

  11. Continuous manufacturing of extended release tablets via powder mixing and direct compression.

    PubMed

    Ervasti, Tuomas; Simonaho, Simo-Pekka; Ketolainen, Jarkko; Forsberg, Peter; Fransson, Magnus; Wikström, Håkan; Folestad, Staffan; Lakio, Satu; Tajarobi, Pirjo; Abrahmsén-Alami, Susanna

    2015-11-10

    The aim of the current work was to explore continuous dry powder mixing and direct compression for manufacturing of extended release (ER) matrix tablets. The study was span out with a challenging formulation design comprising ibuprofen compositions with varying particle size and a relatively low amount of the matrix former hydroxypropyl methylcellulose (HPMC). Standard grade HPMC (CR) was compared to a recently developed direct compressible grade (DC2). The work demonstrate that ER tablets with desired quality attributes could be manufactured via integrated continuous mixing and direct compression. The most robust tablet quality (weight, assay, tensile strength) was obtained using high mixer speed and large particle size ibuprofen and HPMC DC2 due to good powder flow. At low mixer speed it was more difficult to achieve high quality low dose tablets. Notably, with HPMC DC2 the processing conditions had a significant effect on drug release. Longer processing time and/or faster mixer speed was needed to achieve robust release with compositions containing DC2 compared with those containing CR. This work confirms the importance of balancing process parameters and material properties to find consistent product quality. Also, adaptive control is proven a pivotal means for control of continuous manufacturing systems.

  12. Continuous manufacturing of extended release tablets via powder mixing and direct compression.

    PubMed

    Ervasti, Tuomas; Simonaho, Simo-Pekka; Ketolainen, Jarkko; Forsberg, Peter; Fransson, Magnus; Wikström, Håkan; Folestad, Staffan; Lakio, Satu; Tajarobi, Pirjo; Abrahmsén-Alami, Susanna

    2015-11-10

    The aim of the current work was to explore continuous dry powder mixing and direct compression for manufacturing of extended release (ER) matrix tablets. The study was span out with a challenging formulation design comprising ibuprofen compositions with varying particle size and a relatively low amount of the matrix former hydroxypropyl methylcellulose (HPMC). Standard grade HPMC (CR) was compared to a recently developed direct compressible grade (DC2). The work demonstrate that ER tablets with desired quality attributes could be manufactured via integrated continuous mixing and direct compression. The most robust tablet quality (weight, assay, tensile strength) was obtained using high mixer speed and large particle size ibuprofen and HPMC DC2 due to good powder flow. At low mixer speed it was more difficult to achieve high quality low dose tablets. Notably, with HPMC DC2 the processing conditions had a significant effect on drug release. Longer processing time and/or faster mixer speed was needed to achieve robust release with compositions containing DC2 compared with those containing CR. This work confirms the importance of balancing process parameters and material properties to find consistent product quality. Also, adaptive control is proven a pivotal means for control of continuous manufacturing systems. PMID:26320548

  13. Compression response of thick layer composite laminates with through-the-thickness reinforcement

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.; Smith, Barry T.; Maiden, Janice

    1992-01-01

    Compression and compression-after-impact (CAI) tests were conducted on seven different AS4-3501-6 (0/90) 0.64-cm thick composite laminates. Four of the seven laminates had through-the-thickness (TTT) reinforcement fibers. Two TTT reinforcement methods, stitching and integral weaving, and two reinforcement fibers, Kevlar and carbon, were used. The remaining three laminates were made without TTT reinforcements and were tested to establish a baseline for comparison with the laminates having TTT reinforcement. Six of the seven laminates consisted of nine thick layers whereas the seventh material was composed of 46 thin plies. The use of thick-layer material has the potential for reducing structural part cost because of the reduced part count (layers of material). The compression strengths of the TTT reinforced laminates were approximately one half those of the materials without TTT reinforcements. However, the CAI strengths of the TTT reinforced materials were approximately twice those of materials without TTT reinforcements. The improvement in CAI strength is due to an increase in interlaminar strength produced by the TTT reinforcement. Stitched laminates had slightly higher compression and CAI strengths than the integrally woven laminates.

  14. Analysis of compressive sensing with optical mixing using a spatial light modulator.

    PubMed

    Zhu, Zhijing; Chi, Hao; Zheng, Shilie; Jin, Tao; Jin, Xiaofeng; Zhang, Xianmin

    2015-03-10

    Compressive sensing (CS) in a photonic link has a high potential for acquisition of wideband sparse signals. In CS it is necessary to mix the input sparse signal with a pseudorandom sequence prior to subsampling. A pulse shaper with a spatial light modulator (SLM) can be used in photonic CS as an optical mixer to improve the speed of mixing. In this approach, the sparse signal is modulated on a chirped optical pulse and the pseudorandom sequence is recorded on the SLM within the pulse shaper. The optical mixing in the frequency domain is realized based on the principle of frequency-to-time mapping. In this paper, we investigate the performance and limitations of photonic CS with an SLM in detail. A theoretical model to describe optical mixing based on frequency-to-time mapping is presented. We point out that there is an upper limit on the length of the pseudorandom sequence recorded on the SLM that can be mixed with the sparse signal due to the condition of the far-field approximation of the frequency-to-time mapping. Since the length of the pseudorandom sequence is one of the major factors that affect the signal recovery performance in CS, this limitation should be fully considered in the system design of the CS with optical mixing in the frequency domain. We present numerical and experimental results to verify the theoretical findings. Discussion on the performance improvement is also presented.

  15. Indentation and overall compression behavior of multilayered thin-film composites. Effect of undulating layer geometry

    DOE PAGESBeta

    Jamison, Ryan D.; Shen, Y. -L.

    2015-03-19

    Two finite element models are used to investigate the behavior of aluminum/silicon carbide thin-film layered composites with imperfect internal geometry when subjected to various loadings. In both models, undulating layers are represented by regular waveforms with various amplitudes, wavelengths, and phase offsets. First, uniaxial compressive loading of the composite is considered. The modulus and stress/strain response of the composite is sensitive to both loading direction and frequency of the undulation. Second, the nanoindentation response of the composite is investigated. The derived hardness and modulus are shown to be sensitive to the presence of undulating layers and the relative size ofmore » the indenter to the undulation. Undulating layers create bands of tensile and compressive stress in the indentation direction that are significantly different from the flat layers. The amount of equivalent plastic strain in the Al layers is increased by the presence of undulating layers. The correlations between the two forms of loading, and the implications to composite property measurement are carefully examined in this study.« less

  16. Indentation and overall compression behavior of multilayered thin-film composites. Effect of undulating layer geometry

    SciTech Connect

    Jamison, Ryan D.; Shen, Y. -L.

    2015-03-19

    Two finite element models are used to investigate the behavior of aluminum/silicon carbide thin-film layered composites with imperfect internal geometry when subjected to various loadings. In both models, undulating layers are represented by regular waveforms with various amplitudes, wavelengths, and phase offsets. First, uniaxial compressive loading of the composite is considered. The modulus and stress/strain response of the composite is sensitive to both loading direction and frequency of the undulation. Second, the nanoindentation response of the composite is investigated. The derived hardness and modulus are shown to be sensitive to the presence of undulating layers and the relative size of the indenter to the undulation. Undulating layers create bands of tensile and compressive stress in the indentation direction that are significantly different from the flat layers. The amount of equivalent plastic strain in the Al layers is increased by the presence of undulating layers. The correlations between the two forms of loading, and the implications to composite property measurement are carefully examined in this study.

  17. Development of a Hybrid RANS/LES Method for Turbulent Mixing Layers

    NASA Technical Reports Server (NTRS)

    Georgiadis, Nicholas J.; Alexander, J. Iwan D.; Reshotko, Eli

    2001-01-01

    and LES equations to be solved with a single solution scheme and computational grid. The hybrid RANS-LES method has been applied to a benchmark compressible mixing layer experiment in which two isolated supersonic streams, separated by a splitter plate, provide the flows to a constant-area mixing section. Although the configuration is largely two dimensional in nature, three-dimensional calculations were found to be necessary to enable disturbances to develop in three spatial directions and to transition to turbulence. The flow in the initial part of the mixing section consists of a periodic vortex shedding downstream of the splitter plate trailing edge. This organized vortex shedding then rapidly transitions to a turbulent structure, which is very similar to the flow development observed in the experiments. Although the qualitative nature of the large-scale turbulent development in the entire mixing section is captured well by the LES part of the current hybrid method, further efforts are planned to directly calculate a greater portion of the turbulence spectrum and to limit the subgrid scale modeling to only the very small scales. This will be accomplished by the use of higher accuracy solution schemes and more powerful computers, measured both in speed and memory capabilities.

  18. Compressed air energy storage in depleted natural gas reservoirs: effects of porous media and gas mixing

    NASA Astrophysics Data System (ADS)

    Oldenburg, C. M.; Pan, L.

    2015-12-01

    Although large opportunities exist for compressed air energy storage (CAES) in aquifers and depleted natural gas reservoirs, only two grid-scale CAES facilities exist worldwide, both in salt caverns. As such, experience with CAES in porous media, what we call PM-CAES, is lacking and we have relied on modeling to elucidate PM-CAES processes. PM-CAES operates similarly to cavern CAES. Specifically, working gas (air) is injected through well(s) into the reservoir compressing the cushion gas (existing air in the reservoir). During energy recovery, high-pressure air from the reservoir flows first into a recuperator, then into an expander, and subsequently is mixed with fuel in a combustion turbine to produce electricity, thereby reducing compression costs. Energy storage in porous media is complicated by the solid matrix grains which provide resistance to flow (via permeability in Darcy's law); in the cap rock, low-permeability matrix provides the seal to the reservoir. The solid grains also provide storage capacity for heat that might arise from compression, viscous flow effects, or chemical reactions. The storage of energy in PM-CAES occurs variably across pressure gradients in the formation, while the solid grains of the matrix can release/store heat. Residual liquid (i.e., formation fluids) affects flow and can cause watering out at the production well(s). PG&E is researching a potential 300 MW (for ten hours) PM-CAES facility in a depleted gas reservoir near Lodi, California. Special considerations exist for depleted natural gas reservoirs because of mixing effects which can lead to undesirable residual methane (CH4) entrainment and reactions of oxygen and CH4. One strategy for avoiding extensive mixing of working gas (air) with reservoir CH4 is to inject an initial cushion gas with reduced oxygen concentration providing a buffer between the working gas (air) and the residual CH4 gas. This reduces the potential mixing of the working air with the residual CH4

  19. Model of Mixing Layer With Multicomponent Evaporating Drops

    NASA Technical Reports Server (NTRS)

    Bellan, Josette; Le Clercq, Patrick

    2004-01-01

    A mathematical model of a three-dimensional mixing layer laden with evaporating fuel drops composed of many chemical species has been derived. The study is motivated by the fact that typical real petroleum fuels contain hundreds of chemical species. Previously, for the sake of computational efficiency, spray studies were performed using either models based on a single representative species or models based on surrogate fuels of at most 15 species. The present multicomponent model makes it possible to perform more realistic simulations by accounting for hundreds of chemical species in a computationally efficient manner. The model is used to perform Direct Numerical Simulations in continuing studies directed toward understanding the behavior of liquid petroleum fuel sprays. The model includes governing equations formulated in an Eulerian and a Lagrangian reference frame for the gas and the drops, respectively. This representation is consistent with the expected volumetrically small loading of the drops in gas (of the order of 10 3), although the mass loading can be substantial because of the high ratio (of the order of 103) between the densities of liquid and gas. The drops are treated as point sources of mass, momentum, and energy; this representation is consistent with the drop size being smaller than the Kolmogorov scale. Unsteady drag, added-mass effects, Basset history forces, and collisions between the drops are neglected, and the gas is assumed calorically perfect. The model incorporates the concept of continuous thermodynamics, according to which the chemical composition of a fuel is described probabilistically, by use of a distribution function. Distribution functions generally depend on many parameters. However, for mixtures of homologous species, the distribution can be approximated with acceptable accuracy as a sole function of the molecular weight. The mixing layer is initially laden with drops in its lower stream, and the drops are colder than the gas

  20. Explicit mixed strain-displacement finite elements for compressible and quasi-incompressible elasticity and plasticity

    NASA Astrophysics Data System (ADS)

    Cervera, M.; Lafontaine, N.; Rossi, R.; Chiumenti, M.

    2016-09-01

    This paper presents an explicit mixed finite element formulation to address compressible and quasi-incompressible problems in elasticity and plasticity. This implies that the numerical solution only involves diagonal systems of equations. The formulation uses independent and equal interpolation of displacements and strains, stabilized by variational subscales. A displacement sub-scale is introduced in order to stabilize the mean-stress field. Compared to the standard irreducible formulation, the proposed mixed formulation yields improved strain and stress fields. The paper investigates the effect of this enhancement on the accuracy in problems involving strain softening and localization leading to failure, using low order finite elements with linear continuous strain and displacement fields ( P1 P1 triangles in 2D and tetrahedra in 3D) in conjunction with associative frictional Mohr-Coulomb and Drucker-Prager plastic models. The performance of the strain/displacement formulation under compressible and nearly incompressible deformation patterns is assessed and compared to analytical solutions for plane stress and plane strain situations. Benchmark numerical examples show the capacity of the mixed formulation to predict correctly failure mechanisms with localized patterns of strain, virtually free from any dependence of the mesh directional bias. No auxiliary crack tracking technique is necessary.

  1. Direct numerical simulations of a reacting turbulent mixing layer by a pseudospectral-spectral element method

    NASA Technical Reports Server (NTRS)

    Mcmurtry, Patrick A.; Givi, Peyman

    1992-01-01

    An account is given of the implementation of the spectral-element technique for simulating a chemically reacting, spatially developing turbulent mixing layer. Attention is given to experimental and numerical studies that have investigated the development, evolution, and mixing characteristics of shear flows. A mathematical formulation is presented of the physical configuration of the spatially developing reacting mixing layer, in conjunction with a detailed representation of the spectral-element method's application to the numerical simulation of mixing layers. Results from 2D and 3D calculations of chemically reacting mixing layers are given.

  2. Wall Effect on the Convective-Absolute Boundary for the Compressible Shear Layer

    NASA Astrophysics Data System (ADS)

    Robinet, Jean-Christophe; Dussauge, Jean-Paul; Casalis, Grégoire

    The linear stability of inviscid compressible shear layers is studied. When the layer develops at the vicinity of a wall, the two parallel flows can have a velocity of the same sign or of opposite signs. This situation is examined in order to obtain first hints on the stability of separated flows in the compressible regime. The shear layer is described by a hyperbolic tangent profile for the velocity component and the Crocco relation for the temperature profile. Gravity effects and the superficial tension are neglected. By examining the temporal growth rate at the saddle point in the wave-number space, the flow is characterized as being either absolutely unstable or convectively unstable. This study principally shows the effect of the wall on the convective-absolute transition in compressible shear flow. Results are presented, showing the amount of the backflow necessary to have this type of transition for a range of primary flow Mach numbers M1 up to 3.0. The boundary of the convective-absolute transition is defined as a function of the velocity ratio, the temperature ratio and the Mach number. Unstable solutions are calculated for both streamwise and oblique disturbances in the shear layer.

  3. Computation of three-dimensional mixed convective boundary layer flow

    NASA Technical Reports Server (NTRS)

    Gadepalli, Prashandt; Rahman, Muhammad M.

    1995-01-01

    The paper presents the numerical solution of heat and mass transfer during cross-flow (orthogonal) mixed convection. In this class of flow, a buoyancy-driven transport in the vertical direction and a forced convective flow in the horizontal direction results in a three-dimensional boundary layer structure adjacent to the plate. The rates of heat and mass transfer are determined by a combined influence of the two transport processes. The equations for the conservation of mass, momentum, energy, and species concentration were solved along with appropriate boundary conditions to determine the distributions of velocity components, temperature, and concentration across the thickness of the boundary layer at different locations on the plate. Results were expressed in dimensionless form using Reynolds number, Richardson number for heat transfer, Richardson number for mass transfer, Prandtl number, and Schmidt number as parameters. It was found that the transport is dominated by buoyancy at smaller vertical locations and at larger distances away from the forced convection leading edge. Effects of forced convection appeared to be very strong at smaller horizontal distances from the leading edge. The cross stream forced convection enhanced the rate of heat and mass transfer by a very significant amount.

  4. Online Detection of Mixed Layer Depth for Autonomous Underwater Vehicles

    NASA Astrophysics Data System (ADS)

    Chu, S.; Estlin, T.; Castano, R.; Woodward, G.; Gierach, M. M.; Thompson, A. F.; Schaffer, S.

    2015-12-01

    The accurate determination of the mixed layer depth (MLD) plays a crucial role in studying ocean dynamics and climate change. Various methods to estimate MLD have been proposed [1, 2]. However there is no current consensus on the best model, which leads to large uncertainty in the estimation. The variability, coupled with the complexity of physical, chemical and biological processes involved and the uncertainty and instabilities of the upper ocean surface, makes estimating MLD a challenging task. MLD varies significantly, even across a small spatial area (< 10km), and this depth is fluctuating, even over a short period of time (< 24 hrs), depending on the season. This abstract describes our proposed online algorithm for detecting mixed layer depth that would operate onboard an autonomous underwater vehicle (AUV). Using an online method permits a more adaptive approach to estimating MLD. Our proposed algorithm is based on an ensemble approach, which includes data mining techniques for real-time peak and change detection, learned seasonal variability profile, combined with MLD estimation criteria in [1]. In this study, we analyze measurements using glider data collected from the OSMOSIS (Ocean Surface Mixing, Ocean Submesoscale Interaction Study) project, concatenated into a year-long time series [3]. The glider data consists of nine full-depth moorings, which were deployed in a 15 km by 15 km box at the Porcupine Abyssal Plain in the northeast Atlantic, centered at 16.2°W, 48.7°N. Our algorithm utilizes direct measurements of salinity, temperature, depth and time and the design is based on the spatial and temporal variability of MLD learned. We will present our initial work on tracking the MLD based on real-time simulations using the OSMOSIS glider data and discussed for the case of deploying on a single AUV. Using an online algorithm for estimating MLD in-situ enables the system to rapidly adapt to the variability in a real-world environment and also allows for

  5. Tolerance of Mach 2.50 axisymmetric mixed-compression inlets to upstream flow variations

    NASA Technical Reports Server (NTRS)

    Choby, D. A.

    1972-01-01

    An investigation of the tolerances of two Mach 2.50 axisymmetric mixed-compression inlets to upstream flow variations was conducted. Tolerances of each inlet to angle of attack as a function of decreasing free-stream Mach number were obtained. A local region of overcompression was formed on the leeward side of the inlet at maximum angle of attack before unstart. This region of overcompression corresponded to local subsonic flow conditions ahead of the geometric throat. A uniform Mach number gradient of 0.10 at the cowl lip plane did not affect the inlet's pressure recovery, mass flow ratio, or diffuser exit total-pressure distortion.

  6. Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow

    NASA Technical Reports Server (NTRS)

    Mack, L. M.

    1967-01-01

    The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.

  7. Comparative Study of Three High Order Schemes for LES of Temporally Evolving Mixing Layers

    NASA Technical Reports Server (NTRS)

    Yee, Helen M. C.; Sjogreen, Biorn Axel; Hadjadj, C.

    2012-01-01

    Three high order shock-capturing schemes are compared for large eddy simulations (LES) of temporally evolving mixing layers (TML) for different convective Mach numbers (Mc) ranging from the quasi-incompressible regime to highly compressible supersonic regime. The considered high order schemes are fifth-order WENO (WENO5), seventh-order WENO (WENO7) and the associated eighth-order central spatial base scheme with the dissipative portion of WENO7 as a nonlinear post-processing filter step (WENO7fi). This high order nonlinear filter method (H.C. Yee and B. Sjogreen, Proceedings of ICOSAHOM09, June 22-26, 2009, Trondheim, Norway) is designed for accurate and efficient simulations of shock-free compressible turbulence, turbulence with shocklets and turbulence with strong shocks with minimum tuning of scheme parameters. The LES results by WENO7fi using the same scheme parameter agree well with experimental results of Barone et al. (2006), and published direct numerical simulations (DNS) work of Rogers & Moser (1994) and Pantano & Sarkar (2002), whereas results by WENO5 and WENO7 compare poorly with experimental data and DNS computations.

  8. Compressible Laminar Boundary Layer over a Yawed Infinite Cylinder with Heat Transfer and Arbitrary Prandtl Number

    NASA Technical Reports Server (NTRS)

    Reshotko, Eli; Beckwith, Ivan E

    1958-01-01

    The equations are presented for the development of the compressible laminar boundary layer over a yawed infinite cylinder. For compressible flow with a pressure gradient the chordwise and spanwise flows are not independent. Using the Stewartson transformation and a linear viscosity-temperature relation yields a set of three simultaneous ordinary differential equations in a form yielding similar solutions. These equations are solved for stagnation-line flow for surface temperatures from zero to twice the free-stream stagnation temperature and for a wide range of yaw angle and free-stream Mach number. The results indicate that the effect of yaw on the heat-transfer coefficient at the stagnation line depends markedly on the free-stream Mach number. An unusual result of the solutions is that for large yaw angles and stream Mach numbers the chordwise velocity within the boundary layer exceeds the local external chordwise velocity, even for a highly cooled wall.

  9. Efficient computation of the stability of three-dimensional compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Malik, M. R.; Orszag, S. A.

    1981-01-01

    Methods for the computer analysis of the stability of three-dimensional compressible boundary layers are discussed and the user-oriented Compressible Stability Analysis (COSAL) computer code is described. The COSAL code uses a matrix finite-difference method for local eigenvalue solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used initial-value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed which may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black-box stability code. Sample stability calculations are presented for the boundary layer profiles of an LFC swept wing.

  10. Influence of hydrophobic treatment on the structure of compressed gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Tötzke, C.; Gaiselmann, G.; Osenberg, M.; Arlt, T.; Markötter, H.; Hilger, A.; Kupsch, A.; Müller, B. R.; Schmidt, V.; Lehnert, W.; Manke, I.

    2016-08-01

    Carbon fiber based felt materials are widely used as gas diffusion layer (GDL) in fuel cells. Their transport properties can be adjusted by adding hydrophobic agents such as polytetrafluoroethylene (PTFE). We present a synchrotron X-ray tomographic study on the felt material Freudenberg H2315 with different PTFE finishing. In this study, we analyze changes in microstructure and shape of GDLs at increasing degree of compression which are related to their specific PTFE load. A dedicated compression device mimicking the channel-land pattern of the flowfield is used to reproduce the inhomogeneous compression found in a fuel cell. Transport relevant geometrical parameters such as porosity, pore size distribution and geometric tortuosity are calculated and consequences for media transport discussed. PTFE finishing results in a marked change of shape of compressed GDLs: surface is smoothed and the invasion of GDL fibers into the flow field channel strongly mitigated. Furthermore, the PTFE impacts the microstructure of the compressed GDL. The number of available wide transport paths is significantly increased as compared to the untreated material. These changes improve the transport capacity liquid water through the GDL and promote the discharge of liquid water droplets from the cell.

  11. Method of analysis for compressible flow through mixed-flow centrifugal impellers of arbitrary design

    NASA Technical Reports Server (NTRS)

    Hamrick, Joseph T; Ginsburg, Ambrose; Osborn, Walter M

    1952-01-01

    A method is presented for analysis of the compressible flow between the hub and the shroud of mixed-flow impellers of arbitrary design. Axial symmetry was assumed, but the forces in the meridional (hub to shroud) plane, which are derived from tangential pressure gradients, were taken into account. The method was applied to an experimental mixed-flow impeller. The analysis of the flow in the meridional plane of the impeller showed that the rotational forces, the blade curvature, and the hub-shroud profile can introduce severe velocity gradients along the hub and the shroud surfaces. Choked flow at the impeller inlet as determined by the analysis was verified by experimental results.

  12. The behaviour of a compressible turbulent boundary layer under incipient separation conditions

    NASA Technical Reports Server (NTRS)

    Muck, K. C.; Smits, A. J.

    1984-01-01

    This paper presents an experimental study of a turbulent boundary-layer/shock-wave interaction. The interaction was generated by a two-dimensional compression corner, and the flow was on the point of separating. Measurements were made using both normal and inclined hot wires, and the data include measurements of the longitudinal mass-flow fluctuation intensity and the mass-weighted Reynolds shear stress.

  13. An extension of the transpired skin-friction equation to compressible turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Silva-Freire, Atila P.

    1988-11-01

    A skin-friction equation for transpired incompressible turbulent boundary layer, proposed in a previous paper (Silva-Freire, 1988), is extended to compressible flow. The expression derived here is simple and gives more consistent results than the momentum-integral equation. The difficulty with the present formulation, however, is that the wake profile parameter due to injection has to be carefully determined in order to obtain good results.

  14. Harmonics of Tollmien — Schlichting waves in a compressible boundary layer

    NASA Astrophysics Data System (ADS)

    Petrov, G. V.

    2008-12-01

    The harmonics of Tollmien—Schlichting waves in a compressible boundary layer of a plate are computed with the aid of nonlinear parabolized stability equations. At the (downstream) growth of the second harmonic amplitude up to the values of the order of the basic harmonic amplitude, the amplification rate of the latter is shown to increase abruptly. A similar rapid deviation from the results of the linear theory characterizes the onset of the boundary-layer transition to turbulent state. Computations are carried out for the Mach numbers M = 0.01 and 2.

  15. Three-dimensional compressible boundary layer calculations to fourth order accuracy on wings and fuselages

    NASA Technical Reports Server (NTRS)

    Iyer, Venkit; Harris, Julius E.

    1989-01-01

    Laminar flow control and drag reduction research requires accurate boundary layer solutions as input to the three-dimensional stability analysis procedures currently under development. In support of these major programs, a fourth-order accurate finite difference scheme for solving the three-dimensional, compressible boundary layer equations has been developed and is presented in this paper. The method employs a two-point scheme in the wall normal direction and second order zigzag scheme in the cross flow direction. Accurate procedures to interface with the inviscid results are also presented. The results of applying the procedure to laminar flow on wings and fuselages are presented.

  16. Compressible Boundary Layer Predictions at High Reynolds Number using Hybrid LES/RANS Methods

    NASA Technical Reports Server (NTRS)

    Choi, Jung-Il; Edwards, Jack R.; Baurle, Robert A.

    2008-01-01

    Simulations of compressible boundary layer flow at three different Reynolds numbers (Re(sub delta) = 5.59x10(exp 4), 1.78x10(exp 5), and 1.58x10(exp 6) are performed using a hybrid large-eddy/Reynolds-averaged Navier-Stokes method. Variations in the recycling/rescaling method, the higher-order extension, the choice of primitive variables, the RANS/LES transition parameters, and the mesh resolution are considered in order to assess the model. The results indicate that the present model can provide good predictions of the mean flow properties and second-moment statistics of the boundary layers considered. Normalized Reynolds stresses in the outer layer are found to be independent of Reynolds number, similar to incompressible turbulent boundary layers.

  17. Improving powder flow properties of a direct compression formulation using a two-step glidant mixing process.

    PubMed

    Abe, Hidaka; Yasui, Shinichiro; Kuwata, Aya; Takeuchi, Hirofumi

    2009-07-01

    To improve powder flow of a high-dose direct compression formulation (drug content 30%), we compared a two-step operation for mixing glidants with a conventional one-step glidant mixing process. This two-step mixing operation was studied with two kinds of mixtures; an active pharmaceutical ingredient (API)-glidant combination and a direct compression excipient-glidant combination. The two-step operation permitted the selection of the optimum glidant type and concentration in each glidant-mixing procedure even though the formulation had different powder properties such as micronized API and enlarged direct compression vehicles, whereas the conventional approaches forced the selection of a certain glidant type and concentration at one-step mixing. The addition of 0.5% nonporous silica markedly improved API flow. In contrast, 1.0% porous silica was the appropriate glidant to enhance excipient flow at direct compression excipient-glidant mixing. The two-step operation dominantly enhanced powder flow when the appropriate API-glidant mixture and the suitable direct compression excipients-glidant mixture were blended compared to the one-step operation with its optimum glidant concentration. The results showed that the angle of repose was 43 degrees and the critical orifice diameter was 10 mm in the two-step operation, whereas it was 47 degrees and 16 mm in the one-step operation. The two-step operation of glidant mixing enhanced powder flow of the high-dose direct compression formulation compared with the one-step operation. The two-step operation eliminates the bottleneck of powder flow and allows direct compression to be more worth applying for formulation and process development trials.

  18. Wind induced mixing processes in the coastal surface layer

    NASA Astrophysics Data System (ADS)

    Fraunie, Philippe; Schaeffer, Amandine; Molcard, Anne; Forget, Philippe; Garreau, Pierre; Poitevin, Joel

    2010-05-01

    Mesoscale and submescale patterns participate in mixing processes in the coastal surface layer. A process oriented numerical investigation using MARS 3D code and high resolution atmospheric forcing using AROME is presented by comparison with HF radar measurements in the Gulf of Lions, Western Mediterranean Sea. As a result, wind reversal conditions have been observed to be responsible for inertial motion and anticyclonic eddy formation when vertical mixing due to internal waves is expected to erode the halocline. Acknowledgements : MeteoFrance and Ifremer support Amandine Schaeffer's PhD. This work is part of the GIRAC project in the framework of the Pole Mer http://polemerpaca.tvt.fr/ References : André G., Garreau P., Garnier V., Fraunie P., 2005. Modelled variability of the sea surface circulation in the North-western Mediterranean Sea and in the Gulf of Lions. Ocean Dynamics, 55: 294-308 André G., Garreau P., Fraunié P., (2009) Mesoscale slope current variability in the Gulf of Lions. Interpretation of in-situ measurements using a three-dimensional model, Cont. Shelf Res.29, 407-423 Bouttier F., 2007, "AROME, avenir de la prévision régionale", La Météorologie, 58, 12-20 Langlais C., Barnier B., Fraunié P. and Schiller A. 2009b: Resolving the diurnal variability of atmospheric forcing in a coastal ocean circulation model of the Gulf of Lions (NW Mediterranean): impact on the thermodynamical state of the upper ocean. Submitted. Schaeffer A. Molcard A. Forget P. Fraunié P. Gareau P. Generation mechanism of sub-mesoscale eddy in the Gulf of Lions : radar observation and modelling. Submitted Xing J., A.M. Davies, P. Fraunié, Model studies of near-inertial motion on the continental shelf off northeast Spain : a 3D/2D model comparison study, 24p, J. Geophys. Res., 109, C01017, doi:10.1029/2003JC001822, 2004.

  19. Parameterization of large-scale turbulent diffusion in the presence of both well-mixed and weakly mixed patchy layers

    NASA Astrophysics Data System (ADS)

    Osman, M. K.; Hocking, W. K.; Tarasick, D. W.

    2016-06-01

    Vertical diffusion and mixing of tracers in the upper troposphere and lower stratosphere (UTLS) are not uniform, but primarily occur due to patches of turbulence that are intermittent in time and space. The effective diffusivity of regions of patchy turbulence is related to statistical parameters describing the morphology of turbulent events, such as lifetime, number, width, depth and local diffusivity (i.e., diffusivity within the turbulent patch) of the patches. While this has been recognized in the literature, the primary focus has been on well-mixed layers, with few exceptions. In such cases the local diffusivity is irrelevant, but this is not true for weakly and partially mixed layers. Here, we use both theory and numerical simulations to consider the impact of intermediate and weakly mixed layers, in addition to well-mixed layers. Previous approaches have considered only one dimension (vertical), and only a small number of layers (often one at each time step), and have examined mixing of constituents. We consider a two-dimensional case, with multiple layers (10 and more, up to hundreds and even thousands), having well-defined, non-infinite, lengths and depths. We then provide new formulas to describe cases involving well-mixed layers which supersede earlier expressions. In addition, we look in detail at layers that are not well mixed, and, as an interesting variation on previous models, our procedure is based on tracking the dispersion of individual particles, which is quite different to the earlier approaches which looked at mixing of constituents. We develop an expression which allows determination of the degree of mixing, and show that layers used in some previous models were in fact not well mixed and so produced erroneous results. We then develop a generalized model based on two dimensional random-walk theory employing Rayleigh distributions which allows us to develop a universal formula for diffusion rates for multiple two-dimensional layers with

  20. The 3D Navier-Stokes analysis of a Mach 2.68 bifurcated rectangular mixed-compression inlet

    NASA Technical Reports Server (NTRS)

    Mizukami, M.; Saunders, J. D.

    1995-01-01

    The supersonic diffuser of a Mach 2.68 bifurcated, rectangular, mixed-compression inlet was analyzed using a three-dimensional (3D) Navier-Stokes flow solver. A two-equation turbulence model, and a porous bleed model based on unchoked bleed hole discharge coefficients were used. Comparisons were made with experimental data, inviscid theory, and two-dimensional Navier-Stokes analyses. The main objective was to gain insight into the inlet fluid dynamics. Examination of the computational results along with the experimental data suggest that the cowl shock-sidewall boundary layer interaction near the leading edge caused a substantial separation in the wind tunnel inlet model. As a result, the inlet performance may have been compromised by increased spillage and higher bleed mass flow requirements. The internal flow contained substantial waves that were not in the original inviscid design. 3D effects were fairly minor for this inlet at on-design conditions. Navier-Stokes analysis appears to be an useful tool for gaining insight into the inlet fluid dynamics. It provides a higher fidelity simulation of the flowfield than the original inviscid design, by taking into account boundary layers, porous bleed, and their interactions with shock waves.

  1. Chaos in a spatially-developing plane mixing layer

    NASA Technical Reports Server (NTRS)

    Broze, J. G.; Hussain, Fazle; Buell, J. C.

    1988-01-01

    A spatially-developing plane mixing layer was analyzed for chaotic behavior. A direct numerical simulation of the Navier-Stokes equations in a 2-D domain infinite in y and having inflow-outflow boundary conditions in x was used for data. Spectra, correlation dimension and the largest Lyapunov exponent were computed as functions of downstream distance x. When forced at a single (fundamental) frequency with maximum amplitude, the flow is periodic at the inflow but becomes aperiodic with increasing x. The aperiodic behavior is caused by the presence of a noisy subharmonic caused by the feedback between the necessarily nonphysical inflow and outflow boundary conditions. In order to overshadow this noise the flow was also studied with the same fundamental forcing and added random forcing of amplitude upsilon prime sub R/delta U = 0.01 at the inlet. Results were qualitatively the same in both cases: for small x, spectral peaks were sharp and dimension was nearly 1, but as x increased a narrowband spectral peak grew, spectra decayed exponentially at high frequencies and dimension increased to greater than 3. Based on these results, the flow appears to exhibit deterministic chaos. However, at no location was the largest Lyapunov exponent found to be significantly greater than zero.

  2. On the viscosity stratification in temporal mixing layer

    NASA Astrophysics Data System (ADS)

    Danaila, Luminita; Taguelmimt, Noureddine; Hadjadj, Abdellah; Turbulence Team

    2015-11-01

    We assess the effects of viscosity variations in low-speed temporally-evolving turbulent mixing layer. The two streams are density-matched, but the slow fluid is Rv times more viscous than the rapid stream. Direct Numerical Simulations (DNS) are performed for several viscosity ratios, Rv varying between 1 and 9. The space-time evolution of Variable-Viscosity Flow (VVF) is compared with that of the Constant-Viscosity Flow (CVF). The velocity fluctuations occur earlier and are more enhanced for VVF. In particular, the kinetic energy peaks earlier and is up to three times larger for VVF than for CVF at the earliest stages of the flow. Over the first stages of the flow, the temporal growth rate of the fluctuations kinetic energy is exponential, in full agreement with linear stability theory. The transport equation for the fluctuations kinetic energy is favourably compared with simulations data. The enhanced kinetic energy for VVF is mainly due to an increased production at the interface between the two fluids, in tight correlation with enlarged values of mean velocity gradient at the inflection point of the mean velocity profile. The transport equations of the one-and two-point kinetic energy show that self-preservation cannot be complete in variable-viscosity flows. ANR is acknowledged for financial support.

  3. In situ laser sensing of mixed layer turbulence

    NASA Astrophysics Data System (ADS)

    Dalgleish, Fraser; Hou, Weilin; Vuorenkoski, Anni; Nootz, Gero; Ouyang, Bing

    2013-06-01

    This paper will discuss and compare some recent oceanic test results from the Bahamas Optical Turbulence Exercise (BOTEX) cruise, where vertical profiling was conducted with both time-resolved laser backscatter measurements being acquired via a subsurface light detection and ranging (lidar) profiling instrument, and laser beam forward deflection measurements were acquired from a matrix of continuous wave (cw) laser beams (i.e. structured lighting) being imaged in the forward direction with a high speed camera over a one-way path, with both transmitter and camera firmly fixed on a rigid frame. From the latter, it was observed that when within a natural turbulent layer, the laser beams were being deflected from their still water location at the image plane, which was 8.8 meters distance from the laser dot matrix transmitter. As well as suggesting that the turbulent structures being encountered were predominately larger than the beam diameter, the magnitude of the deflection has been confirmed to correlate with the temperature dissipation rate. The profiling lidar measurements which were conducted in similar conditions, also used a narrow collimated laser beam in order to resolve small-scale spatial structure, but with the added attribute that sub-nanosecond short pulse temporal profile could potentially resolve small-scale vertical structure. In the clear waters of the Tongue of the Ocean in the Bahamas, it was hypothesized that the backscatter anomalies due to the effect of refractive index discontinuities (i.e. mixed layer turbulence) would be observable. The processed lidar data presented herein indicates that higher backscatter levels were observed in the regions of the water column which corresponded to higher turbulent mixing which occurs at the first and second themoclines. At the same test stations that the laser beam matrix and lidar measurements were conducted, turbulence measurements were made with two non-optical instruments, the Vertical Microstructure

  4. Inhomogeneous relaxation of a molecular layer on an insulator due to compressive stress.

    PubMed

    Bocquet, F; Nony, L; Mannsfeld, S C B; Oison, V; Pawlak, R; Porte, L; Loppacher, Ch

    2012-05-18

    We discuss the inhomogeneous stress relaxation of a monolayer of hexahydroxytriphenylene (HHTP) which adopts the rare line-on-line (LOL) coincidence on KCl(001) and forms moiré patterns. The fact that the hexagonal HHTP layer is uniaxially compressed along the LOL makes this system an ideal candidate to discuss the influence of inhomogeneous stress relaxation. Our work is a combination of noncontact atomic force microscopy experiments, density functional theory and potential energy calculations, and a thorough interpretation by means of the Frenkel-Kontorova model. We show that the assumption of a homogeneous molecular layer is not valid for this organic-inorganic heteroepitaxial system since the best calculated energy configuration correlates with the experimental data only if inhomogeneous relaxations of the layer are taken into account. PMID:23003159

  5. Inhomogeneous Relaxation of a Molecular Layer on an Insulator due to Compressive Stress

    NASA Astrophysics Data System (ADS)

    Bocquet, F.; Nony, L.; Mannsfeld, S. C. B.; Oison, V.; Pawlak, R.; Porte, L.; Loppacher, Ch.

    2012-05-01

    We discuss the inhomogeneous stress relaxation of a monolayer of hexahydroxytriphenylene (HHTP) which adopts the rare line-on-line (LOL) coincidence on KCl(001) and forms moiré patterns. The fact that the hexagonal HHTP layer is uniaxially compressed along the LOL makes this system an ideal candidate to discuss the influence of inhomogeneous stress relaxation. Our work is a combination of noncontact atomic force microscopy experiments, density functional theory and potential energy calculations, and a thorough interpretation by means of the Frenkel-Kontorova model. We show that the assumption of a homogeneous molecular layer is not valid for this organic-inorganic heteroepitaxial system since the best calculated energy configuration correlates with the experimental data only if inhomogeneous relaxations of the layer are taken into account.

  6. Development of a Three-Dimensional PSE Code for Compressible Flows: Stability of Three-Dimensional Compressible Boundary Layers

    NASA Technical Reports Server (NTRS)

    Balakumar, P.; Jeyasingham, Samarasingham

    1999-01-01

    A program is developed to investigate the linear stability of three-dimensional compressible boundary layer flows over bodies of revolutions. The problem is formulated as a two dimensional (2D) eigenvalue problem incorporating the meanflow variations in the normal and azimuthal directions. Normal mode solutions are sought in the whole plane rather than in a line normal to the wall as is done in the classical one dimensional (1D) stability theory. The stability characteristics of a supersonic boundary layer over a sharp cone with 50 half-angle at 2 degrees angle of attack is investigated. The 1D eigenvalue computations showed that the most amplified disturbances occur around x(sub 2) = 90 degrees and the azimuthal mode number for the most amplified disturbances range between m = -30 to -40. The frequencies of the most amplified waves are smaller in the middle region where the crossflow dominates the instability than the most amplified frequencies near the windward and leeward planes. The 2D eigenvalue computations showed that due to the variations in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the most amplified disturbances are shifted to 120 degrees compared to 90 degrees for the parallel theory. It is also observed that the nonparallel amplification rates are smaller than that is obtained from the parallel theory.

  7. Calculation of the flow field in supersonic mixed-compression inlets at angle of attack using the three-dimensional method of characteristics with discrete shock wave fitting

    NASA Technical Reports Server (NTRS)

    Vadyak, J.; Hoffman, J. D.

    1978-01-01

    The influence of molecular transport is included in the computation by treating viscous and thermal diffusion terms in the governing partial differential equations as correction terms in the method of characteristics scheme. The development of a production type computer program is reported which is capable of calculating the flow field in a variety of axisymmetric mixed-compression aircraft inlets. The results agreed well with those produced by the two-dimensional method characteristics when axisymmetric flow fields are computed. For three-dimensional flow fields, the results agree well with experimental data except in regions of high viscous interaction and boundary layer removal.

  8. Development and validation of a turbulent-mix model for variable-density and compressible flows

    NASA Astrophysics Data System (ADS)

    Banerjee, Arindam; Gore, Robert A.; Andrews, Malcolm J.

    2010-10-01

    The modeling of buoyancy driven turbulent flows is considered in conjunction with an advanced statistical turbulence model referred to as the BHR (Besnard-Harlow-Rauenzahn) k-S-a model. The BHR k-S-a model is focused on variable-density and compressible flows such as Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) driven mixing. The BHR k-S-a turbulence mix model has been implemented in the RAGE hydro-code, and model constants are evaluated based on analytical self-similar solutions of the model equations. The results are then compared with a large test database available from experiments and direct numerical simulations (DNS) of RT, RM, and KH driven mixing. Furthermore, we describe research to understand how the BHR k-S-a turbulence model operates over a range of moderate to high Reynolds number buoyancy driven flows, with a goal of placing the modeling of buoyancy driven turbulent flows at the same level of development as that of single phase shear flows.

  9. The inviscid compressible Görtler problem in three-dimensional boundary layers

    NASA Astrophysics Data System (ADS)

    Dando, Andrew

    1992-09-01

    In this paper we investigate numerical solutions for the growth rates of Görtler vortices in a compressible three-dimensional flow in the inviscid limit of a large Görtler number. We look at a range of Mach numbers and find that there are three different types of behaviour for the mode growth-rate, corresponding to whether the flow is incompressible, has a Mach number small enough so that temperature-adjustment-layer modes do not appear in the two-dimensional case, or has a Mach number large enough so that they do. We find that it takes a considerably greater crossflow to destroy the Görtler vortices for moderate Mach numbers than it did in the incompressible case looked at by Bassom and Hall (1991). From this we believe that Görtler vortices may well still be a cause of transition for many practical compressible inviscid three-dimensional flows.

  10. Compressibility effects on the non-linear receptivity of boundary layers to dielectric barrier discharges

    NASA Astrophysics Data System (ADS)

    Denison, Marie F. C.

    The reduction of drag and aerodynamic heating caused by boundary layer transition is of central interest for the development of hypersonic vehicles. Receptivity to flow perturbation in the form of Tollmien-Schlichting (TS) wave growth often determines the first stage of the transition process, which can be delayed by depositing specific excitations into the boundary layer. Weakly ionized Dielectric Barrier Discharge (DBD) actuators are being investigated as possible sources of such excitations, but little is known today about their interaction with high-speed flows. In this framework, the first part of the thesis is dedicated to a receptivity study of laminar compressible boundary layers over a flat plate by linear stability analysis following an adjoint operator formulation, under DBD representative excitations assumed independent of flow conditions. The second part of the work concentrates on the development of a coupled plasma-Navier and Stokes solver targeted at the study of supersonic flow and compressibility effects on DBD forcing and non-parallel receptivity. The linear receptivity study of quasi-parallel compressible flows reveals several interesting features such as a significant shift of the region of maximum receptivity deeper into the flow at high Mach number and strong wave amplitude reduction compared to incompressible flows. The response to DBD relevant excitation distributions and to variations of the base flow conditions and system length scales follows these trends. Observed absolute amplitude changes and relative sensitivity modifications between source types are related to the evolution of the offset between forcing peak profile and relevant adjoint mode maximum. The analysis highlights the crucial importance of designing and placing the actuator in a way that matches its force field to the position of maximum boundary layer receptivity for the specific flow conditions of interest. In order to address the broad time and length scale spectrum

  11. A defect stream function, law of the wall/wake method for compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Barnwell, Richard W.; Dejarnette, Fred R.; Wahls, Richard A.

    1989-01-01

    The application of the defect stream function to the solution of the two-dimensional, compressible boundary layer is examined. A law of the wall/law of the wake formulation for the inner part of the boundary layer is presented which greatly simplifies the computational task near the wall and eliminates the need for an eddy viscosity model in this region. The eddy viscosity model in the outer region is arbitrary. The modified Crocco temperature-velocity relationship is used as a simplification of the differential energy equation. Formulations for both equilibrium and nonequilibrium boundary layers are presented including a constrained zero-order form which significantly reduces the computational workload while retaining the significant physics of the flow. A formulation for primitive variables is also presented. Results are given for the constrained zero-order and second-order equilibrium formulations and are compared with experimental data. A compressible wake function valid near the wall has been developed from the present results.

  12. The effects of the laminar/turbulent boundary layer states on the development of a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Foss, J. F.

    1977-01-01

    The effect of the laminar/turbulent boundary layer state on the mean and rms velocities of a developing plane mixing layer was investigated. The use of commonly accepted nondimensional representations of the data confirm (at least) an approximately self-preserving condition. It is suggested that the effects of the laminar/turbulent initial condition persist in the self-preserving region.

  13. Mixed-layer simulation of buoy observations taken during Hurricane Eloise

    SciTech Connect

    Martin, P.J.

    1982-01-20

    A one-dimensional mixed-layer model is used to simulate observations made by a NOAA buoy in the Gulf of Mexico during Hurricane Eloise. The model-predicted SST, mixed-layer depth, and inertial current agree favorably with the observations. In addition, model experiments demonstrate the importance of the veering of the wind vector during the passage of the eye to the amplitude of the inertial current generated by the wind and the extent of vertical mixing.

  14. Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction

    NASA Technical Reports Server (NTRS)

    Omori, S.; Gross, K. W.

    1973-01-01

    The turbulent kinetic energy equation is coupled with boundary layer equations to solve the characteristics of compressible turbulent boundary layers with mass injection and combustion. The Reynolds stress is related to the turbulent kinetic energy using the Prandtl-Wieghardt formulation. When a lean mixture of hydrogen and nitrogen is injected through a porous plate into the subsonic turbulent boundary layer of air flow and ignited by external means, the turbulent kinetic energy increases twice as much as that of noncombusting flow with the same mass injection rate of nitrogen. The magnitudes of eddy viscosity between combusting and noncombusting flows with injection, however, are almost the same due to temperature effects, while the distributions are different. The velocity profiles are significantly affected by combustion. If pure hydrogen as a transpiration coolant is injected into a rocket nozzle boundary layer flow of combustion products, the temperature drops significantly across the boundary layer due to the high heat capacity of hydrogen. At a certain distance from the wall hydrogen reacts with the combustion products, liberating an extensive amount of heat.

  15. Study of dopant activation in biaxially compressively strained SiGe layers using excimer laser annealing

    NASA Astrophysics Data System (ADS)

    Luong, G. V.; Wirths, S.; Stefanov, S.; Holländer, B.; Schubert, J.; Conde, J. C.; Stoica, T.; Breuer, U.; Chiussi, S.; Goryll, M.; Buca, D.; Mantl, S.

    2013-05-01

    Excimer Laser Annealing (ELA) with a wavelength of 248 nm is used to study doping of biaxialy compressively strained Si1-xGex/Si heterostructures. The challenge is to achieve a high activation of As in SiGe, while conserving the elastic strain and suppressing dopant diffusion. Doping of 20 nm Si0.64Ge0.36 layers by ion implantation of 1 × 1015 As+/cm2 and subsequent laser annealing using single 20 ns pulse with an energy density of 0.6 J/cm2 leads to an As activation of about 20% and a sheet resistance of 650 Ω/sq. At this laser energy density, the entire SiGe layer melts and the subsequent fast recrystallization on a nanosecond time scale allows high As incorporation into the lattice. Moreover, using these annealing parameters, the SiGe layer exhibits epitaxial regrowth with negligible strain relaxation. ELA at energy densities greater than 0.6 J/cm2 resembles Pulsed Lased Induced Epitaxy, leading to an intermixing of the SiGe layer with the Si substrate, thus to thicker single-crystalline strained SiGe layers with sheet resistance down to 62 Ω/sq. Effects of energy densities on composition, crystal quality, activation of As and co-doping with B are discussed and related to the spatial and temporal evolution of the temperature in the irradiated zone, as simulated by Finite Element Methods.

  16. Gas-diffusion-layer structural properties under compression via X-ray tomography

    NASA Astrophysics Data System (ADS)

    Zenyuk, Iryna V.; Parkinson, Dilworth Y.; Connolly, Liam G.; Weber, Adam Z.

    2016-10-01

    There is a need to understand the structure properties of gas-diffusion layers (GDLs) in order to optimize their performance in various electrochemical devices. This information is important for mathematical modelers, experimentalists, and designers. In this article, a comprehensive study of a large set of commercially available GDLs' porosity, tortuosity, and pore-size distribution (PSD) under varying compression is presented in a single study using X-ray computed tomography (CT), which allows for a noninvasive measurement. Porosities and PSDs are directly obtained from reconstructed stacks of images, whereas tortuosity is computed with a finite-element simulation. Bimodal PSDs due to the presence of binder are observed for most of the GDLs, approaching unimodal distributions at high compressions. Sample to sample variability is conducted to show that morphological properties hold across various locations. Tortuosity values are the lowest for MRC and Freudenberg, highest for TGP, and in-between for SGL papers. The exponents for the MRC and Freudenberg tortuosity demonstrate a very small dependence on compression because the shapes of the pores are spherical indicating minimal heterogeneity. From the representative-elementary-volume studies it is shown that domains of 1 × 1 mm in-plane and full thickness in through-plane directions accurately represent GDL properties.

  17. Deformation of PEM fuel cell gas diffusion layers under compressive loading: An analytical approach

    NASA Astrophysics Data System (ADS)

    Norouzifard, Vahid; Bahrami, Majid

    2014-10-01

    In the PEM fuel cell stack, the fibrous porous gas diffusion layer (GDL) provides mechanical support for the membrane assembly against the compressive loads imposed by bipolar plates. In this study, a new mechanistic model is developed using fundamental beam theory that can accurately predict the mechanical deflection of GDL under compressive loads. The present analytical model is built on a unit cell approach, which assumes a simplified geometry for the complex and random GDL microstructure. The model includes salient microstructural parameters and properties of the fibrous porous medium including: carbon fiber diameter, fiber elastic modulus, pore size distribution, and porosity. Carbon fiber bending is proved to be the main deformation mechanism at the unit cell level. A comprehensive optical measurement study with statistical analysis is performed to determine the geometrical parameters of the model for a number of commercially available GDL samples. A comparison between the present model and our experimental stress-strain data shows a good agreement for the linear deformation region, where the compressive pressure is higher than 1 MPa.

  18. Synthesis of a predicted layered LiB via cold compression

    NASA Astrophysics Data System (ADS)

    Kolmogorov, A. N.; Hajinazar, S.; Angyal, C.; Kuznetsov, V. L.; Jephcoat, A. P.

    2015-10-01

    We have discovered stoichiometric LiB with hexagonal boron layers by compressing known LiB0.9 with linear boron chains. The s p to s p2 rebonding occurred at room temperature and pressures above 21 GPa. The study was motivated by a long-standing prediction that LiB in the stable layered configuration could be a close analog to the MgB2 superconductor. Apparent stacking disorder in LiB and a stoichiometry shift in LiBy (down to y ≈0.75 ) made material characterization a challenge. Ab initio modeling allowed us to establish the pressure-dependent composition of LiBy and predict related stable structures overlooked in previous studies. Synchrotron powder diffraction data on quenched samples in the diamond anvil cell indicate that LiB remains metastable at ambient pressure.

  19. The Compressible Laminar Boundary Layer with Heat Transfer and Arbitrary Pressure Gradient

    NASA Technical Reports Server (NTRS)

    Cohen, Clarence B; Reshotko, Eli

    1956-01-01

    An approximate method for the calculation of the compressible laminar boundary layer with heat transfer and arbitrary pressure gradient, based on Thwaites' correlation concept, is presented. With the definition of dimensionless shear and heat-transfer parameters and an assumed correlation of these parameters in terms of a momentum parameter, a complete system of relations for calculating skin friction and heat transfer results. Knowledge of velocity or temperature profiles is not necessary in using this calculation method. When the method is applied to a convergent-divergent, axially symmetric rocket nozzle, it shows that high rates of heat transfer are obtained at the initial stagnation point and at the throat of the nozzle. Also indicated are negative displacement thicknesses in the convergent portion of the nozzle; these occur because of the high density within the lower portions of the cooled boundary layer. (author)

  20. Wind, mixed-layer depth and Chl-a variability in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Gille, S. T.; Carranza, M. M.; Franks, P. J. S.; Girton, J. B.; Johnson, K. S.

    2014-12-01

    The Southern Ocean, contains some of the ocean's deepest mixed layers and is under the constant influence of strong winds and buoyancy forcing. Phytoplankton growth is hypothesized to be co-limited by iron and light. Because deep mixed layers can transport phytoplankton below the depth of the euphotic zone, light levels depend on mixed-layer depth. We use satellite winds from multiple wind sensors, combined with Argo data, to show that deep mixed layers are generally correlated with strong winds over the Southern Ocean. These deep mixed layers correspond to cold sea surface temperatures. This might also be expected to lead to nutrient upwelling and high chlorophyll-a (Chl-a), as measured by satellite ocean color sensors. However, Chl-a is less strongly correlated with wind speed than SST is, particularly at the mesoscale, and in summer Chl-a is not well correlated with mixed-layer depth. Using new in situ observations of subsurface Chl-a from sensors on southern elephant seals, EM-APEX floats, and bio-optical Argo floats, we find that Chl-a typically has a subsurface maximum in spring, summer, and fall. As a result satellite-sensed Chl-a is an inadequate measure of total biomass within the mixed layer. Satellite Chl-a and integrated Chl-a over the euphotic zone are negatively correlated with MLD from fall through spring, and uncorrelated during the summer. However, integrated Chl-a within the mixed layer shows significant positive correlations with MLD in all seasons. The fact that the deep Chl-a maximum sits at the base of the MLD, closer to the nutrient (or iron) maximum than the light maximum, suggests nutrient limitation plays a greater role than light limitation in governing productivity, and that wind and buoyancy forcing likely govern the mixing processes at the base of the mixed layer that control phytoplankton growth.

  1. Comparison of Several Numerical Methods for Simulation of Compressible Shear Layers

    NASA Technical Reports Server (NTRS)

    Kennedy, Christopher A.; Carpenter, Mark H.

    1997-01-01

    An investigation is conducted on several numerical schemes for use in the computation of two-dimensional, spatially evolving, laminar variable-density compressible shear layers. Schemes with various temporal accuracies and arbitrary spatial accuracy for both inviscid and viscous terms are presented and analyzed. All integration schemes use explicit or compact finite-difference derivative operators. Three classes of schemes are considered: an extension of MacCormack's original second-order temporally accurate method, a new third-order variant of the schemes proposed by Rusanov and by Kutier, Lomax, and Warming (RKLW), and third- and fourth-order Runge-Kutta schemes. In each scheme, stability and formal accuracy are considered for the interior operators on the convection-diffusion equation U(sub t) + aU(sub x) = alpha U(sub xx). Accuracy is also verified on the nonlinear problem, U(sub t) + F(sub x) = 0. Numerical treatments of various orders of accuracy are chosen and evaluated for asymptotic stability. Formally accurate boundary conditions are derived for several sixth- and eighth-order central-difference schemes. Damping of high wave-number data is accomplished with explicit filters of arbitrary order. Several schemes are used to compute variable-density compressible shear layers, where regions of large gradients exist.

  2. The Closure of the Ocean Mixed Layer Temperature Budget using Level-Coordinate Model Fields

    NASA Technical Reports Server (NTRS)

    Kim, Seung-Bum; Fukumori, Ichiro; Lee, Tong

    2005-01-01

    Entrainment is an important element of the mixed layer mass, heat, and temperature budgets. Conventional procedures to estimate entrainment heat advection often do not permit the closure of heat and temperature budgets because of inaccuracies in its formulation. In this study a rigorous approach to evaluate the effect of entrainment using the output of a general circulation model (GCM) that does not have an explicit prognostic mixed layer model is described. The integral elements of the evaluation are 1) the rigorous estimates of the temperature difference between mixed layer water and entrained water at each horizontal grid point, 2) the formulation of the temperature difference such that the budget closes over a volume greater than one horizontal grid point, and 3) the apparent warming of the mixed layer during the mixed layer shoaling to account for the weak vertical temperature gradient within the mixed layer. This evaluation of entrainment heat advection is compared with the estimates by other commonly used ad hoc formulations by applying them in three regions: the north-central Pacific, the Kuroshio Extension, and the Nino-3 areas in the tropical Pacific. In all three areas the imbalance in the mixed layer temperature budget by the ad hoc estimates is significant, reaching a maximum of about 4 K yr(exp -1).

  3. Comparison of High-Order and Low-Order Methods for Large-Eddy Simulation of a Compressible Shear Layer

    NASA Technical Reports Server (NTRS)

    Mankbadi, Mina R.; Georgiadis, Nicholas J.; DeBonis, James R.

    2015-01-01

    The objective of this work is to compare a high-order solver with a low-order solver for performing Large-Eddy Simulations (LES) of a compressible mixing layer. The high-order method is the Wave-Resolving LES (WRLES) solver employing a Dispersion Relation Preserving (DRP) scheme. The low-order solver is the Wind-US code, which employs the second-order Roe Physical scheme. Both solvers are used to perform LES of the turbulent mixing between two supersonic streams at a convective Mach number of 0.46. The high-order and low-order methods are evaluated at two different levels of grid resolution. For a fine grid resolution, the low-order method produces a very similar solution to the highorder method. At this fine resolution the effects of numerical scheme, subgrid scale modeling, and filtering were found to be negligible. Both methods predict turbulent stresses that are in reasonable agreement with experimental data. However, when the grid resolution is coarsened, the difference between the two solvers becomes apparent. The low-order method deviates from experimental results when the resolution is no longer adequate. The high-order DRP solution shows minimal grid dependence. The effects of subgrid scale modeling and spatial filtering were found to be negligible at both resolutions. For the high-order solver on the fine mesh, a parametric study of the spanwise width was conducted to determine its effect on solution accuracy. An insufficient spanwise width was found to impose an artificial spanwise mode and limit the resolved spanwise modes. We estimate that the spanwise depth needs to be 2.5 times larger than the largest coherent structures to capture the largest spanwise mode and accurately predict turbulent mixing.

  4. Comparison of High-Order and Low-Order Methods for Large-Eddy Simulation of a Compressible Shear Layer

    NASA Technical Reports Server (NTRS)

    Mankbadi, M. R.; Georgiadis, N. J.; DeBonis, J. R.

    2015-01-01

    The objective of this work is to compare a high-order solver with a low-order solver for performing large-eddy simulations (LES) of a compressible mixing layer. The high-order method is the Wave-Resolving LES (WRLES) solver employing a Dispersion Relation Preserving (DRP) scheme. The low-order solver is the Wind-US code, which employs the second-order Roe Physical scheme. Both solvers are used to perform LES of the turbulent mixing between two supersonic streams at a convective Mach number of 0.46. The high-order and low-order methods are evaluated at two different levels of grid resolution. For a fine grid resolution, the low-order method produces a very similar solution to the high-order method. At this fine resolution the effects of numerical scheme, subgrid scale modeling, and filtering were found to be negligible. Both methods predict turbulent stresses that are in reasonable agreement with experimental data. However, when the grid resolution is coarsened, the difference between the two solvers becomes apparent. The low-order method deviates from experimental results when the resolution is no longer adequate. The high-order DRP solution shows minimal grid dependence. The effects of subgrid scale modeling and spatial filtering were found to be negligible at both resolutions. For the high-order solver on the fine mesh, a parametric study of the spanwise width was conducted to determine its effect on solution accuracy. An insufficient spanwise width was found to impose an artificial spanwise mode and limit the resolved spanwise modes. We estimate that the spanwise depth needs to be 2.5 times larger than the largest coherent structures to capture the largest spanwise mode and accurately predict turbulent mixing.

  5. The radiation of sound by the instability waves of a compressible plane turbulent shear layer

    NASA Technical Reports Server (NTRS)

    Tam, C. K. W.; Morris, P. J.

    1980-01-01

    The problem of acoustic radiation generated by instability waves of a compressible plane turbulent shear layer is solved. The solution provided is valid up to the acoustic far-field region. It represents a significant improvement over the solution obtained by classical hydrodynamic-stability theory which is essentially a local solution with the acoustic radiation suppressed. The basic instability-wave solution which is valid in the shear layer and the near-field region is constructed in terms of an asymptotic expansion using the method of multiple scales. This solution accounts for the effects of the slightly divergent mean flow. It is shown that the multiple-scales asymptotic expansion is not uniformly valid far from the shear layer. Continuation of this solution into the entire upper half-plane is described. The extended solution enables the near- and far-field pressure fluctuations associated with the instability wave to be determined. Numerical results show that the directivity pattern of acoustic radiation into the stationary medium peaks at 20 degrees to the axis of the shear layer in the downstream direction for supersonic flows. This agrees qualitatively with the observed noise-directivity patterns of supersonic jets.

  6. Problem of the thermodynamic status of the mixed-layer minerals

    USGS Publications Warehouse

    Zen, E.-A.

    1962-01-01

    Minerals that show mixed layering, particularly with the component layers in random sequence, pose problems because they may behave thermodynamically as single phases or as polyphase aggregates. Two operational criteria are proposed for their distinction. The first scheme requires two samples of mixed-layer material which differ only in the proportions of the layers. If each of these two samples are allowed to equilibrate with the same suitably chosen monitoring solution, then the intensive parameters of the solution will be invariant if the mixed-layer sample is a polyphase aggregate, but not otherwise. The second scheme makes use of the fact that portions of many titration curves of clay minerals show constancy of the chemical activities of the components in the equilibrating solutions, suggesting phase separation. If such phase separation occurs for a mixed-layer material, then, knowing the number of independent components in the system, it should be possible to decide on the number of phases the mixed-layer material represents. Knowledge of the phase status of mixed-layer material is essential to the study of the equilibrium relations of mineral assemblages involving such material, because a given mixed-layer mineral will be plotted and treated differently on a phase diagram, depending on whether it is a single phase or a polyphase aggregate. Extension of the titration technique to minerals other than the mixed-layer type is possible. In particular, this method may be used to determine if cryptoperthites and peristerites are polyphase aggregates. In general, for any high-order phase separation, the method may be used to decide just at what point in this continuous process the system must be regarded operationally as a polyphase aggregate. ?? 1962.

  7. Determination of the Mixing Layer Height Over two Sites, Using Pilot Balloons During the MILAGRO Campaign

    NASA Astrophysics Data System (ADS)

    Wohrnschimmel, H.; Alonso, A. L.; Ángeles, F.; Sosa, G.; Varela, J.; Cárdenas, B.

    2007-12-01

    Among the mechanisms that affect air quality there is a variety of meteorological processes. An important process in this context are the changes in the mixing layer height during a day and over the year. The mixing layer height is the portion of the atmosphere close to the surface layer where air pollutants get diluted, without leaving this layer. Therefore, it is important to describe the variations in the height of the mixing layer, i.e. the vertical dilution of air pollution, since this is a process mitigating naturally the impact of emissions. There exist different methods to obtain information on the mixing layer height, among them radio soundings, the application of vertical wind profilers, and launching pilot balloons. In this study, pilot balloons have been used simultaneously over two sites of the Mexico City Metropolitan Area during the MILAGRO campaign in March 2006. The objective was to determine the vertical wind profiles and derive information on the mixing layer height. Daily, four pilot balloons were launched, at 9:00, 12:00, 15:00, and 18:00 hours, over Tenango del Aire (a rural area in the Southeast of Mexico City), and over Ciudad Universitaria, in the Southern metropolitan area. At some occasions, night time measurements have been carried out at 21:00 and 24:00. A variability of the diurnal evolution of the mixing layer was observed along March, which could be related to surface temperature. The diurnal evolution showed a sudden growth of the mixing layer between 9:00 and 12:00 hours. Data intercomparisons were carried out for pilot balloons versus radio soundings during a few days at a third site, Tula, in the North of Mexico City. Both intercomparisons showed that pilot balloons are an effective method to obtain information about the development of the mixing layer.

  8. Computer program for solving laminar, transitional, or turbulent compressible boundary-layer equations for two-dimensional and axisymmetric flow

    NASA Technical Reports Server (NTRS)

    Harris, J. E.; Blanchard, D. K.

    1982-01-01

    A numerical algorithm and computer program are presented for solving the laminar, transitional, or turbulent two dimensional or axisymmetric compressible boundary-layer equations for perfect-gas flows. The governing equations are solved by an iterative three-point implicit finite-difference procedure. The software, program VGBLP, is a modification of the approach presented in NASA TR R-368 and NASA TM X-2458, respectively. The major modifications are: (1) replacement of the fourth-order Runge-Kutta integration technique with a finite-difference procedure for numerically solving the equations required to initiate the parabolic marching procedure; (2) introduction of the Blottner variable-grid scheme; (3) implementation of an iteration scheme allowing the coupled system of equations to be converged to a specified accuracy level; and (4) inclusion of an iteration scheme for variable-entropy calculations. These modifications to the approach presented in NASA TR R-368 and NASA TM X-2458 yield a software package with high computational efficiency and flexibility. Turbulence-closure options include either two-layer eddy-viscosity or mixing-length models. Eddy conductivity is modeled as a function of eddy viscosity through a static turbulent Prandtl number formulation. Several options are provided for specifying the static turbulent Prandtl number. The transitional boundary layer is treated through a streamwise intermittency function which modifies the turbulence-closure model. This model is based on the probability distribution of turbulent spots and ranges from zero to unity for laminar and turbulent flow, respectively. Several test cases are presented as guides for potential users of the software.

  9. Internal waves in a compressible two-layer model atmosphere: Hamiltonian description

    NASA Astrophysics Data System (ADS)

    Ruban, V. P.

    2010-11-01

    We consider slow, compared to the speed of sound, motions of an ideal compressible fluid (gas) in a gravitational field in the presence of two isentropic layers with a small specific-entropy difference between them. Assuming the flow to be potential in each of the layers ( v 1, 2 = ▿ϕ1, 2) and neglecting the acoustic degrees of freedom (div( bar ρ ( z)▿ϕ1, 2) ≈ 0, where bar ρ ( z) is the average equilibrium density), we derive the equations of motion for the boundary in terms of the shape of the surface z = η( x, y, t) itself and the difference between the boundary values of the two velocity field potentials: ψ( x, y, t) = ψ1 - ψ2. We prove the Hamilto nian structure of the derived equations specified by a Lagrangian of the form ℒ = ∫ bar ρ (η)η t ψ dxdy - ℋ{η, ψ}. The system under consideration is the simplest theoretical model for studying internal waves in a sharply stratified atmosphere in which the decrease in equilibrium gas density due to gas compressibility with increasing height is essentially taken into account. For plane flows, we make a generalization to the case where each of the layers has its own constant potential vorticity. We investigate a system with a model dependence bar ρ ( z) ∝ e -2α z with which the Hamiltonian ℋ{η, ψ} can be represented explicitly. We consider a long-wavelength dynamic regime with dispersion corrections and derive an approximate nonlinear equation of the form u t + auu x - b[- hat partial _x^2 + α2]1/2 u x = 0 (Smith's equation) for the slow evolution of a traveling wave.

  10. [Particle dispersion by order motion in mixing layers

    SciTech Connect

    Troutt, T.R.

    1993-09-01

    Multiphase mixing in turbulent flows is a key element in many energy conversion and chemical processes. There is considerable need for improving the design and control of these processes. Free turbulent shear flows are the primary agents for particle mixing in these systems. Previous studies by this research group have shown that, if particle coupling effects are neglected, the organized vortex structures generated by these shear flows control the character of the particle mixing process. A coordinated experimental and numerical study is proposed to investigate the coupled effects of droplet mass and energy transfer on the turbulent multiphase mixing process in free shear flows. This study has important implications concerning the design of reacting flow systems. Experimental visualizations of the multiphase flow will be carried out using laser-sheet lighting and high speed photography. Local measurements of droplet size, velocity and concentration diagnostics, will be made with laser anemometry and phase Doppler diagnostics. Complementary analytical and numerical analyses will be carried out to assess the effect of coupling on vortex structure, stability and growth. The results of the proposed research will provide basic understanding concerning the coupled effects of particle concentration on the rate of multiphase mixing in turbulent flows. Information of this nature is essential to the improved designs of engineering systems with particulate or droplet flows.

  11. Low Velocity Difference Thermal Shear Layer Mixing Rate Measurements

    NASA Technical Reports Server (NTRS)

    Bush, Robert H.; Culver, Harry C. M.; Weissbein, Dave; Georgiadis, Nicholas J.

    2013-01-01

    Current CFD modeling techniques are known to do a poor job of predicting the mixing rate and persistence of slot film flow in co-annular flowing ducts with relatively small velocity differences but large thermal gradients. A co-annular test was devised to empirically determine the mixing rate of slot film flow in a constant area circular duct (D approx. 1ft, L approx. 10ft). The axial rate of wall heat-up is a sensitive measure of the mixing rate of the two flows. The inflow conditions were varied to simulate a variety of conditions characteristic of moderate by-pass ratio engines. A series of air temperature measurements near the duct wall provided a straightforward means to measure the axial temperature distribution and thus infer the mixing rate. This data provides a characterization of the slot film mixing rates encountered in typical jet engine environments. The experimental geometry and entrance conditions, along with the sensitivity of the results as the entrance conditions vary, make this a good test for turbulence models in a regime important to modern air-breathing propulsion research and development.

  12. Large mixed Ekman Hartmann boundary layers in magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Rousset, F.

    2004-03-01

    In this paper, we study the nonlinear stability of Ekman-Hartmann type boundary layers in a rotating magnetohydrodynamics flow under a sharp spectral assumption. This generalizes the result of Desjardins et al (1999 Nonlinearity 12 181-99) obtained under a smallness assumption on a Reynolds number and the result of Rousset (2003 Arch. Rat. Mech. Anal. in press) about the stability of Ekman layers.

  13. ICF Implosions, Space-Charge Electric Fields, and Their Impact on Mix and Compression

    NASA Astrophysics Data System (ADS)

    Knoll, Dana; Chacon, Luis; Simakov, Andrei

    2013-10-01

    The single-fluid, quasi-neutral, radiation hydrodynamics codes, used to design the NIF targets, predict thermonuclear ignition for the conditions that have been achieved experimentally. A logical conclusion is that the physics model used in these codes is missing one, or more, key phenomena. Two key model-experiment inconsistencies on NIF are: 1) a lower implosion velocity than predicted by the design codes, and 2) transport of pusher material deep into the hot spot. We hypothesize that both of these model-experiment inconsistencies may be a result of a large, space-charge, electric field residing on the distinct interfaces in a NIF target. Large space-charge fields have been experimentally observed in Omega experiments. Given our hypothesis, this presentation will: 1) Develop a more complete physics picture of initiation, sustainment, and dissipation of a current-driven plasma sheath / double-layer at the Fuel-Pusher interface of an ablating plastic shell implosion on Omega, 2) Characterize the mix that can result from a double-layer field at the Fuel-Pusher interface, prior to the onset of fluid instabilities, and 3) Quantify the impact of the double-layer induced surface tension at the Fuel-Pusher interface on the peak observed implosion velocity in Omega.

  14. Impact of compression on gas transport in non-woven gas diffusion layers of high temperature polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Froning, Dieter; Yu, Junliang; Gaiselmann, Gerd; Reimer, Uwe; Manke, Ingo; Schmidt, Volker; Lehnert, Werner

    2016-06-01

    Gas transport in non-woven gas diffusion layers of a high-temperature polymer electrolyte fuel cell was calculated with the Lattice Boltzmann method. The underlying micro structure was taken from two sources. A real micro structure was analyzed in the synchrotron under the impact of a compression mask mimicking the channel/rib structure of a flow field. Furthermore a stochastic geometry model based on synchrotron X-ray tomography studies was applied. The effect of compression is included in the stochastic model. Gas transport in these micro structures was simulated and the impact of compression was analyzed. Fiber bundles overlaying the micro structure were identified which affect the homogeneity of the gas flow. There are significant deviations between the impact of compression on effective material properties for this type of gas diffusion layers and the Kozeny-Carman equation.

  15. An experimental study of aero-optical aberration and dithering of supersonic mixing layer via BOS

    NASA Astrophysics Data System (ADS)

    Zhao, Yuxin; Yi, Shihe; Tian, Lifeng; He, Lin; Cheng, Zhongyu

    2010-01-01

    The optical performance of supersonic mixing layer is heavily deteriorated by the aero-optical aberration and dithering of coherent structures, but current measuring methods limit the spatiotemporal resolution in relevant studies. A high resolution whole-field aero-optical aberration and dithering measuring method based on the Background Orient Schlieren (BOS) technique was studied. The systematic structure, sensitivity and resolution of BOS are analyzed in this paper. The aero-optical aberration and dithering of streamwise structures in supersonic mixing layers were quantificationally studied with BOS. The aberration field of spanwise structures revealed the ribbon-like aberration structures, which heavily restrict the optical performance of a mixing layer. The quantifications of aero-optical aberration and dithering are very important in studying aero-optical performance of supersonic mixing layer.

  16. Detailed characteristics of drop-laden mixing layers: LES predictions compared to DNS

    NASA Technical Reports Server (NTRS)

    Okong'o, N.; Leboissetier, A.; Bellan, J.

    2004-01-01

    Results have been compared from Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) of a temporal mixing layer laden with evaporating drops, to assess the ability of LES to reproduce detailed characteristics of DNS.

  17. Coherent structures in a turbulent mixing layer - A comparison between direct numerical simulations and experiments

    NASA Technical Reports Server (NTRS)

    Metcalfe, R. W.; Menon, S.; Hussain, A. K. M. F.

    1985-01-01

    An eduction scheme has been developed in an attempt to determine the characteristics of large-scale vortical structures in a turbulent mixing layer. This analysis scheme has been applied to a set of experimental data taken in a new, larger mixing layer facility designed to minimize boundary and resonance effects. A similar scheme has been developed to apply to the results of a direct numerical simulation of a temporally growing mixing layer. A comparison of the two approaches shows important similarities in the coherent structures. The numerical simulations indicate that low levels of coherent forcing can dramatically change the evolution of the mixing layer. In the absence of such forcing, the numerical simulations and experiments show a lack of regularity in the transverse position, spacing, amplitude, shape and spanwise coherence of the large-scale vortical structures.

  18. Numerical investigation of sensitivity of the Black Sea mixed layer to vertical turbulent diffusion processes

    NASA Astrophysics Data System (ADS)

    Kvaratskhelia, Diana; Demetrashvili, Demuri

    2015-04-01

    The upper mixed-layer of seas and oceans is one of the important water areas, the thermodynamic state of which defines many important physical, chemical or biological processes in the sea- atmosphere environment. The same can be note concerning the Black Sea turbulent mixed layer, which represents the object of our investigation. It is well known that the depth of the mixed layer is generaly determined by measurements of water properties: temperature and sigma-t (density) but here the depth of the mixed layer and its variability are investigated by using of the basin-scale numerical model of the Black Sea dynamics of M. Nodia Institute of Geophysics (BSM-IG, Tbilisi, Georgia). The main object of this study is to investigate the Black Sea upper mixed-layer generation and its evolution in connection with the nonstationarity atmospheric circulation and thermohaline action in the inner-annual time scale. Besides, how the temperature and salinity fields of the Black Sea upper layer are substantially reacted by the vertical diffusion coefficient are the centre of our attention. Therefore, the coefficient of vertical turbulent diffusion for heat and salt are tested as constant equal to 10 cm2s-1 and it was parameterized by modified Oboukhov's formula. The results of the numerical investigations show that: in wintertime for any choosing of this vertical diffusion coefficient the intense wind-driven turbulence promotes mixing aproximetly till 16-26 m in deep layers of the Black Sea. Except for that, cold fluxes through the surface and precipitation-evapuration system play aditionally role on the mixed layer forming as well. During the transitive spring season (in difference from the cold season), when the depth of the mixed layer is aproxometly 2-4 m., the role of vertical turbulent viscosity insignificantly grows. In the warm season (summer), when the mixed layer does not observe in the upper layer of the Black Sea, the role of the vertical diffusion coefficient is more

  19. Lidar Characterization of Boundary Layer Transport and Mixing for Estimating Urban-Scale Greenhouse Gas Emissions

    NASA Astrophysics Data System (ADS)

    Hardesty, R. Michael; Brewer, W. Alan; Sandberg, Scott P.; Weickmann, Ann M.; Shepson, Paul B.; Cambaliza, Maria; Heimburger, Alexie; Davis, Kenneth J.; Lauvaux, Thomas; Miles, Natasha L.; Sarmiento, Daniel P.; Deng, A. J.; Gaudet, Brian; Karion, Anna; Sweeney, Colm; Whetstone, James

    2016-06-01

    A compact commercial Doppler lidar has been deployed in Indianapolis for two years to measure wind profiles and mixing layer properties as part of project to improve greenhouse measurements from large area sources. The lidar uses vertical velocity variance and aerosol structure to measure mixing layer depth. Comparisons with aircraft and the NOAA HRDL lidar generally indicate good performance, although sensitivity might be an issue under low aerosol conditions.

  20. Motion of particles with inertia in a compressible free shear layer

    NASA Technical Reports Server (NTRS)

    Samimy, M.; Lele, S. K.

    1991-01-01

    The effects of the inertia of a particle on its flow-tracking accuracy and particle dispersion are studied using direct numerical simulations of 2D compressible free shear layers in convective Mach number (Mc) range of 0.2 to 0.6. The results show that particle response is well characterized by tau, the ratio of particle response time to the flow time scales (Stokes' number). The slip between particle and fluid imposes a fundamental limit on the accuracy of optical measurements such as LDV and PIV. The error is found to grow like tau up to tau = 1 and taper off at higher tau. For tau = 0.2 the error is about 2 percent. In the flow visualizations based on Mie scattering, particles with tau more than 0.05 are found to grossly misrepresent the flow features. These errors are quantified by calculating the dispersion of particles relative to the fluid. Overall, the effect of compressibility does not seem to be significant on the motion of particles in the range of Mc considered here.

  1. Oceanic upper mixed layer depth determination by the use of satellite data

    NASA Technical Reports Server (NTRS)

    Yan, Xiao-Hai; Schubel, J. R.; Pritchard, D. W.

    1990-01-01

    A method has been developed to determine the oceanic daily mean mixed layer depth from satellite observations and a mixed layer thermal inertia (MLTI) model. The algorithms were developed to use remotely-sensed values of sea surface temperature, albedo, and surface wind speeds to calculate the thermal inertia and to predict changes in subsurface diurnal mixed layer depth. The MLTI model, based on a mixed layer model of the upper ocean, has been used to simulate the diurnal mixing process and thermal inertia distribution in the Sargasso Sea around 34 deg N, 70 deg W. Sea surface temperature and albedo have been obtained from the NOAA7-AVHRR images. Surface wind speeds have been derived from the Scanning Multichannel Microwave Radiometer (SMMR) aboard Nimbus 7. Image processing was performed for images gathered between June and July 1982. The daily mean mixed layer depths predicted by the MLTI model agree well with data gathered at the LOTUS mooring located in the Sargasso Sea. This suggests that vertical mixing is the dominant physical process that controls the thermal inertia distribution in the midocean, far from major current systems, and that remote sensing is a promising tool to study such upper ocean processes.

  2. Modeled mixed-layer salinity balance in the Gulf of Guinea: seasonal and interannual variability

    NASA Astrophysics Data System (ADS)

    Da-Allada, Casimir Y.; du Penhoat, Yves; Jouanno, Julien; Alory, Gael; Hounkonnou, Norbert Mahouton

    2014-12-01

    A regional numerical simulation and observations were used to investigate the various processes controlling mixed-layer salinity balance on seasonal and interannual time scales in the Gulf of Guinea. Processes were quantified using a mixed-layer salt budget. Model results correctly reproduced the mean, phase, and amplitude of observed seasonal near-surface salinity. The results indicated that on seasonal time scales, the mixed-layer salinity balance differed from one region to another. The surface salinity seasonal cycle was characterized by strong salinization during May for coastal areas north and south of the equator. Model results suggested that vertical mixing controls the mixed-layer salinity increase at the equator during May, while both vertical mixing and vertical advection contribute to the salinity increase in coastal regions. We also determined that freshening from horizontal advection and freshwater flux tended to balance the salinization effects of vertical diffusion and vertical advection during the seasonal cycle. On interannual time scales, based on the mixed-layer salinity balance and sensitivity experiments, we determined that for the northern and equatorial Gulf of Guinea, changes in near-surface salinity were largely due to changes in precipitation and winds. For the southern Gulf of Guinea, only wind changes were determined to be important for explaining near-surface salinity changes.

  3. Implicit large eddy simulation of a scalar mixing layer in fractal grid turbulence

    NASA Astrophysics Data System (ADS)

    Watanabe, Tomoaki; Sakai, Yasuhiko; Nagata, Kouji; Ito, Yasumasa; Hayase, Toshiyuki

    2016-07-01

    A scalar mixing layer in fractal grid turbulence is simulated by the implicit large eddy simulation (ILES) using low-pass filtering as an implicit subgrid-scale model. The square-type fractal grid with three fractal iterations is used for generating turbulence. The streamwise evolutions of the streamwise velocity statistics obtained in the ILES are in good agreement with the experimental results. The ILES results are used for investigating the development of the scalar mixing layer behind the fractal grid. The results show that the vertical development of the scalar mixing layer strongly depends on the spanwise location. Near the fractal grid, the scalar mixing layer rapidly develops just behind the largest grid bars owing to the vertical turbulent transport. The scalar mixing layer near the fractal grid also develops outside the largest grid bars because the scalar is transported between the outside and back of the largest grid bars by the spanwise turbulent transport. In the downstream region, the scalar mixing layer develops more rapidly near the grid centerline by the vertical turbulent transport and by the spanwise one which transports the scalar between the back of the largest grid bars and both the centerline and outer edge of the fractal grid. Then, the mean scalar profile becomes close to be homogeneous in the spanwise direction.

  4. Mixing-Height Time Series from Operational Ceilometer Aerosol-Layer Heights

    NASA Astrophysics Data System (ADS)

    Lotteraner, Christoph; Piringer, Martin

    2016-07-01

    A new method is described to derive mixing-height time series directly from aerosol-layer height data available from a Vaisala CL51 ceilometer. As complete as possible mixing-height time series are calculated by avoiding outliers, filling data gaps by linear interpolation, and smoothing. In addition, large aerosol-layer heights at night that can be interpreted as residual layers are not assigned as mixing heights. The resulting mixing-height time series, converted to an appropriate data format, can be used as input for dispersion calculations. Two case examples demonstrate in detail how the method works. The mixing heights calculated using ceilometer data are compared with values determined from radiosounding data at Vienna by applying the parcel, Heffter, and Richardson methods. The results of the parcel method, obtained from radiosonde profiles at noon, show the best fit to the ceilometer-derived mixing heights. For midnight radiosoundings, larger deviations between mixing heights from the ceilometer and those deduced from the potential temperature profiles of the soundings are found. We use data from two Vaisala CL51 ceilometers, operating in the Vienna area at an urban and rural site, respectively, during an overlapping period of about 1 year. In addition to the case studies, the calculated mixing-height time series are also statistically evaluated and compared, demonstrating that the ceilometer-based mixing height follows an expected daily and seasonal course.

  5. Mixing-Height Time Series from Operational Ceilometer Aerosol-Layer Heights

    NASA Astrophysics Data System (ADS)

    Lotteraner, Christoph; Piringer, Martin

    2016-11-01

    A new method is described to derive mixing-height time series directly from aerosol-layer height data available from a Vaisala CL51 ceilometer. As complete as possible mixing-height time series are calculated by avoiding outliers, filling data gaps by linear interpolation, and smoothing. In addition, large aerosol-layer heights at night that can be interpreted as residual layers are not assigned as mixing heights. The resulting mixing-height time series, converted to an appropriate data format, can be used as input for dispersion calculations. Two case examples demonstrate in detail how the method works. The mixing heights calculated using ceilometer data are compared with values determined from radiosounding data at Vienna by applying the parcel, Heffter, and Richardson methods. The results of the parcel method, obtained from radiosonde profiles at noon, show the best fit to the ceilometer-derived mixing heights. For midnight radiosoundings, larger deviations between mixing heights from the ceilometer and those deduced from the potential temperature profiles of the soundings are found. We use data from two Vaisala CL51 ceilometers, operating in the Vienna area at an urban and rural site, respectively, during an overlapping period of about 1 year. In addition to the case studies, the calculated mixing-height time series are also statistically evaluated and compared, demonstrating that the ceilometer-based mixing height follows an expected daily and seasonal course.

  6. Discrete element simulation of charging and mixed layer formation in the ironmaking blast furnace

    NASA Astrophysics Data System (ADS)

    Mitra, Tamoghna; Saxén, Henrik

    2015-11-01

    The burden distribution in the ironmaking blast furnace plays an important role for the operation as it affects the gas flow distribution, heat and mass transfer, and chemical reactions in the shaft. This work studies certain aspects of burden distribution by small-scale experiments and numerical simulation by the discrete element method (DEM). Particular attention is focused on the complex layer-formation process and the problems associated with estimating the burden layer distribution by burden profile measurements. The formation of mixed layers is studied, and a computational method for estimating the extent of the mixed layer, as well as its voidage, is proposed and applied on the results of the DEM simulations. In studying a charging program and its resulting burden distribution, the mixed layers of coke and pellets were found to show lower voidage than the individual burden layers. The dynamic evolution of the mixed layer during the charging process is also analyzed. The results of the study can be used to gain deeper insight into the complex charging process of the blast furnace, which is useful in the design of new charging programs and for mathematical models that do not consider the full behavior of the particles in the burden layers.

  7. Turbulent mixing and transport in a thermally stratified interfacial layer in decaying grid turbulence

    NASA Astrophysics Data System (ADS)

    Jayesh, Yoon, Kyunghwan; Warhaft, Z.

    1991-05-01

    A stably stratified mixing layer, sandwiched in between regions of neutral turbulence, was studied in decaying grid turbulence. The layer, which was shearless, was formed by heating the upper half of the flow by means of elements placed at the entrance to the plenum of a large, open circuit low speed wind tunnel 0.91×0.91 m2 in cross section and 9.14 m in length. The hot air above mixed with the cold below forming the stratified layer in between. As the flow evolved and the turbulence decayed, the buoyancy forces increased relative to the inertial forces (i.e., the Richardson number increased) causing the heat flux to collapse. This resulted in a thinning of the mixing layer with downstream distance (rather than growth which occurs for the passive case). Inside the layer the vertical velocity variance diminished and the vertical heat flux correlation coefficient was reduced to zero. Smoke wire photographs showed a wavylike damped region inside the layer, surrounded by the normal, more energetic turbulence outside. Second-order turbulence quantities scaled in the same way with the local Richardson number both along the layer and across it. The two stably stratified cases studied had centerline Froude numbers of 95 and 65 at 40 mesh lengths from the grid. The results are compared to a passive thermal mixing layer and are contrasted with recent experiments concerning a constant temperature gradient in grid turbulence.

  8. Turbulent mixing and transport in a thermally stratified interfacial layer in decaying grid turbulence

    SciTech Connect

    Jayesh; Yoon, K.; Warhaft, Z. )

    1991-05-01

    A stably stratified mixing layer, sandwiched in between regions of neutral turbulence, was studied in decaying grid turbulence. The layer, which was shearless, was formed by heating the upper half of the flow by means of elements placed at the entrance to the plenum of a large, open circuit low speed wind tunnel 0.91{times}0.91 m{sup 2} in cross section and 9.14 m in length. The hot air above mixed with the cold below forming the stratified layer in between. As the flow evolved and the turbulence decayed, the buoyancy forces increased relative to the inertial forces (i.e., the Richardson number increased) causing the heat flux to collapse. This resulted in a thinning of the mixing layer with downstream distance (rather than growth which occurs for the passive case). Inside the layer the vertical velocity variance diminished and the vertical heat flux correlation coefficient was reduced to zero. Smoke wire photographs showed a wavylike damped region inside the layer, surrounded by the normal, more energetic turbulence outside. Second-order turbulence quantities scaled in the same way with the local Richardson number both along the layer and across it. The two stably stratified cases studied had centerline Froude numbers of 95 and 65 at 40 mesh lengths from the grid. The results are compared to a passive thermal mixing layer and are contrasted with recent experiments concerning a constant temperature gradient in grid turbulence.

  9. Discrete element simulation of charging and mixed layer formation in the ironmaking blast furnace

    NASA Astrophysics Data System (ADS)

    Mitra, Tamoghna; Saxén, Henrik

    2016-11-01

    The burden distribution in the ironmaking blast furnace plays an important role for the operation as it affects the gas flow distribution, heat and mass transfer, and chemical reactions in the shaft. This work studies certain aspects of burden distribution by small-scale experiments and numerical simulation by the discrete element method (DEM). Particular attention is focused on the complex layer-formation process and the problems associated with estimating the burden layer distribution by burden profile measurements. The formation of mixed layers is studied, and a computational method for estimating the extent of the mixed layer, as well as its voidage, is proposed and applied on the results of the DEM simulations. In studying a charging program and its resulting burden distribution, the mixed layers of coke and pellets were found to show lower voidage than the individual burden layers. The dynamic evolution of the mixed layer during the charging process is also analyzed. The results of the study can be used to gain deeper insight into the complex charging process of the blast furnace, which is useful in the design of new charging programs and for mathematical models that do not consider the full behavior of the particles in the burden layers.

  10. An asymptotic analysis of supersonic reacting mixing layers

    NASA Technical Reports Server (NTRS)

    Jackson, T. L.; Hussaini, M. Y.

    1987-01-01

    The purpose of this paper is to present an asymptotic analysis of the laminar mixing of the simultaneous chemical reaction between parallel supersonic streams of two reacting species. The study is based on a one-step irreversible Arrhenius reaction and on large activation energy asymptotics. Essentially it extends the work of Linan and Crespo to include the effect of free shear and Mach number on the ignition regime, the deflagration regime and the diffusion flame regime. It is found that the effective parameter is the product of the characteristic Mach number and a shear parameter.

  11. Two-Layer Tight Frame Sparsifying Model for Compressed Sensing Magnetic Resonance Imaging

    PubMed Central

    Peng, Xi; Dong, Pei

    2016-01-01

    Compressed sensing magnetic resonance imaging (CSMRI) employs image sparsity to reconstruct MR images from incoherently undersampled K-space data. Existing CSMRI approaches have exploited analysis transform, synthesis dictionary, and their variants to trigger image sparsity. Nevertheless, the accuracy, efficiency, or acceleration rate of existing CSMRI methods can still be improved due to either lack of adaptability, high complexity of the training, or insufficient sparsity promotion. To properly balance the three factors, this paper proposes a two-layer tight frame sparsifying (TRIMS) model for CSMRI by sparsifying the image with a product of a fixed tight frame and an adaptively learned tight frame. The two-layer sparsifying and adaptive learning nature of TRIMS has enabled accurate MR reconstruction from highly undersampled data with efficiency. To solve the reconstruction problem, a three-level Bregman numerical algorithm is developed. The proposed approach has been compared to three state-of-the-art methods over scanned physical phantom and in vivo MR datasets and encouraging performances have been achieved. PMID:27747226

  12. Acoustic receptivity of compressible boundary layers: Receptivity by way of surface-temperature variations

    NASA Technical Reports Server (NTRS)

    Choudhari, Meelan

    1994-01-01

    The Goldstein-Ruban theory has been extended within the framework of Zavol'skii et al. to study the acoustic receptivity of compressible boundary layers. We consider the receptivity produced in a region of localized, small-amplitude variation in the surface temperature and compare it with the receptivity that is induced through a similar mechanism by a variation in the suction velocity at the surface. It is found that the orientation of the acoustic wave can have a significant impact on the receptivity process, with the maximum receptivity at a given sound-pressure level being produced by upstream oriented acoustic waves. At sufficiently low Mach numbers, the variation of receptivity with the acoustic-wave orientation can be predicted analytically and is the same for both surface suction and surface heating. However, as a result of the acoustic refraction across the mean boundary layer, the above dependence can become rather complex and, also, dependent on the type of surface nonuniformity. The results also suggest that the receptivity caused by temperature nonuniformities may turn out to be more significant than that produced by the mean-flow perturbations associated with strip suction.

  13. Protected Sulfur Cathode with Mixed Conductive Coating Layer for Lithium Sulfur Battery

    NASA Astrophysics Data System (ADS)

    Jin, Jun; Wen, Zhaoyin; Wang, Qingsong; Gu, Sui; Huang, Xiao; Chen, Chunhua

    2016-08-01

    A mixed conductive coating layer composed of lithium ion conductive ceramic powder, carbon and binder was introduced on the surface of a sulfur electrode. This coating layer is designed to suppress the migration of lithium polysulfides from the sulfur electrode, and improve the cycling capacity of a lithium sulfur battery. The protected sulfur cathode with a mixed conductive coating layer delivered an initial specific capacity of 1236 mAh g-1 at 0.5C and maintained a capacity of 842 mAh g-1 after 100 cycles. In particular, a soft package battery with protected cathode exhibits improved cycling capacity and excellent rate performance.

  14. The effect of boundary-layer turbulence on mixing in heated jets

    NASA Astrophysics Data System (ADS)

    Strykowski, P. J.; Russ, S.

    1992-05-01

    The mixing properties of a heated axisymmetric jet at a density ratio of 0.55 were examined for initially laminar and turbulent separated boundary layers. Initially laminar jets displayed large intermittent spread rates with half-angles up to 45° and a corresponding rapid decay of the streamwise velocity and temperature on the jet axis. When the boundary layer was disturbed upstream of the nozzle exit, creating an initially turbulent separated layer, the jet mixing was significantly reduced. Flow visualization revealed that the turbulent conditions eliminated the intermittent nature of the jet spreading, producing constant spreading rates at half-angles near 10°.

  15. The effect of boundary-layer turbulence on mixing in heated jets

    NASA Astrophysics Data System (ADS)

    Strykowski, P. J.; Russ, S.

    1992-05-01

    The mixing properties of a heated axisymmetric jet at a density ratio of 0.55 were examined for initially laminar and turbulent separated boundary layers. Initially laminar jets displayed large intermittent spread rates with half-angles up to 45 deg and a corresponding rapid decay af the streamwise velocity and temperature on the jet axis. When the boundary layer was disturbed upstream of the nozzle exit, creating an initially turbulent separated layer, the jet mixing was significantly reduced. Flow visualization revealed that the turbulent conditions eliminated the intermittent nature of the jet spreading, producing constant spreading rates at half-angles near 10 deg.

  16. Protected Sulfur Cathode with Mixed Conductive Coating Layer for Lithium Sulfur Battery

    NASA Astrophysics Data System (ADS)

    Jin, Jun; Wen, Zhaoyin; Wang, Qingsong; Gu, Sui; Huang, Xiao; Chen, Chunhua

    2016-10-01

    A mixed conductive coating layer composed of lithium ion conductive ceramic powder, carbon and binder was introduced on the surface of a sulfur electrode. This coating layer is designed to suppress the migration of lithium polysulfides from the sulfur electrode, and improve the cycling capacity of a lithium sulfur battery. The protected sulfur cathode with a mixed conductive coating layer delivered an initial specific capacity of 1236 mAh g-1 at 0.5C and maintained a capacity of 842 mAh g-1 after 100 cycles. In particular, a soft package battery with protected cathode exhibits improved cycling capacity and excellent rate performance.

  17. Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

    NASA Astrophysics Data System (ADS)

    Cronin, M. F.; Pelland, N.; Emerson, S. R.; Crawford, W. R.

    2015-12-01

    Data from two National Oceanographic and Atmospheric Administration (NOAA) surface moorings in the North Pacific, in combination with data from satellite, Argo floats and glider (when available), are used to evaluate the residual diffusive flux of heat across the base of the mixed layer from the surface mixed layer heat budget. The diffusion coefficient (i.e., diffusivity) is then computed by dividing the diffusive flux by the temperature gradient in the 20-m transition layer just below the base of the mixed layer. At Station Papa in the NE Pacific subpolar gyre, this diffusivity is 1×10-4 m2/s during summer, increasing to ~3×10-4 m2/s during fall. During late winter and early spring, diffusivity has large errors. At other times, diffusivity computed from the mixed layer salt budget at Papa correlate with those from the heat budget, giving confidence that the results are robust for all seasons except late winter-early spring and can be used for other tracers. In comparison, at the Kuroshio Extension Observatory (KEO) in the NW Pacific subtropical recirculation gyre, somewhat larger diffusivity are found based upon the mixed layer heat budget: ~ 3×10-4 m2/s during the warm season and more than an order of magnitude larger during the winter, although again, wintertime errors are large. These larger values at KEO appear to be due to the increased turbulence associated with the summertime typhoons, and weaker wintertime stratification.

  18. Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

    NASA Astrophysics Data System (ADS)

    Cronin, Meghan F.; Pelland, Noel A.; Emerson, Steven R.; Crawford, William R.

    2015-11-01

    Data from two National Oceanographic and Atmospheric Administration (NOAA) surface moorings in the North Pacific, in combination with data from satellite, Argo floats and glider (when available), are used to evaluate the residual diffusive flux of heat across the base of the mixed layer from the surface mixed layer heat budget. The diffusion coefficient (i.e., diffusivity) is then computed by dividing the diffusive flux by the temperature gradient in the 20 m transition layer just below the base of the mixed layer. At Station Papa in the NE Pacific subpolar gyre, this diffusivity is 1 × 10-4 m2/s during summer, increasing to ˜3 × 10-4 m2/s during fall. During late winter and early spring, diffusivity has large errors. At other times, diffusivity computed from the mixed layer salt budget at Papa correlate with those from the heat budget, giving confidence that the results are robust for all seasons except late winter-early spring and can be used for other tracers. In comparison, at the Kuroshio Extension Observatory (KEO) in the NW Pacific subtropical recirculation gyre, somewhat larger diffusivities are found based upon the mixed layer heat budget: ˜ 3 × 10-4 m2/s during the warm season and more than an order of magnitude larger during the winter, although again, wintertime errors are large. These larger values at KEO appear to be due to the increased turbulence associated with the summertime typhoons, and weaker wintertime stratification.

  19. Measurement of effective bulk and contact resistance of gas diffusion layer under inhomogeneous compression - Part II: Thermal conductivity

    NASA Astrophysics Data System (ADS)

    Roy Chowdhury, Prabudhya; Vikram, Ajit; Phillips, Ryan K.; Hoorfar, Mina

    2016-07-01

    The gas diffusion layer (GDL) is a thin porous layer sandwiched between a bipolar plate (BPP) and a catalyst coated membrane in a fuel cell. Besides providing passage for water and gas transport from and to the catalyst layer, it is responsible for electron and heat transfer from and to the BPP. In this paper, a method has been developed to measure the GDL bulk thermal conductivity and the contact resistance at the GDL/BPP interface under inhomogeneous compression occurring in an actual fuel cell assembly. Toray carbon paper GDL TGP-H-060 was tested under a range of compression pressure of 0.34 to 1.71 MPa. The results showed that the thermal contact resistance decreases non-linearly (from 3.8 × 10-4 to 1.17 × 10-4 Km2 W-1) with increasing pressure due to increase in microscopic contact area between the GDL and BPP; while the effective bulk thermal conductivity increases (from 0.56 to 1.42 Wm-1 K-1) with increasing the compression pressure. The thermal contact resistance was found to be greater (by a factor of 1.6-2.8) than the effective bulk thermal resistance for all compression pressure ranges applied here. This measurement technique can be used to identify optimum GDL based on minimum bulk and contact resistances measured under inhomogeneous compression.

  20. MAPLE preparation and characterization of mixed arylenevinylene based oligomers:C60 layers

    NASA Astrophysics Data System (ADS)

    Stanculescu, A.; Socol, G.; Vacareanu, L.; Socol, M.; Rasoga, O.; Breazu, C.; Girtan, M.; Stanculescu, F.

    2016-06-01

    This paper presents some studies about the preparation by matrix-assisted pulsed laser evaporation (MAPLE) of mixed layers based on two arylenevinylene oligomers, 1,4-bis [4-(N,N‧-diphenylamino)phenylvinyl] benzene (L78) and 3,3‧-bis(N-hexylcarbazole)vinylbenzene (L13) as donor and buckminsterfullerene (C60) as acceptor, blended in three different weight ratios: 1:1, 1:2 and 1:3. The optical, morphological, structural and electrical properties of these mixed layers have been investigated emphasizing the effect of the layer composition and of the significant degree of disorder. I-V characteristics have revealed typically solar cell behaviour for the heterostructures prepared with mixed layers containing L78 (L13) and fullerene blended in a weight ratio of 1:2. The solar cell structure glass/ITO/L13:C60/Al has shown the best parameters.

  1. Measurements of the streamwise vortical structures in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Bell, James H.; Mehta, Rabindra D.

    1992-01-01

    The 3D structure of a plane two-stream mixing layer of velocity ratio 0.6 and originating from laminar initial boundary layers was investigated through direct measurements made in a specially constructed mixing-layer wind tunnel. The main objective of the study was to establish quantitatively the presence and the role of the secondary streamwise vortex structure (of the kind that has been shown in past flow visualization investigations to ride among the primary spanwise vortices) in the development of a plane turbulent mixing layer at relatively high Reynolds numbers. Results indicate that the instability leading to the formation of streamwise vortices is initially amplified just downstream of the first spanwise roll-up. The streamwise vortices, which first appear in clusters containing vorticity of both signs, realign further downstream to form counterrotating pairs. Due to the amalgamation of like-sign vortices, the streamwise vortex spacing increases in a stepwise fashion.

  2. Sea ice and the ocean mixed layer over the Antarctic shelf seas

    NASA Astrophysics Data System (ADS)

    Petty, A.; Holland, P.; Feltham, D. L.

    2013-12-01

    An ocean mixed layer model has been incorporated into the Los Alamos sea ice model CICE, to investigate regional variations in the surface-driven formation of Antarctic shelf sea waters. The model captures well the expected sea ice thickness distribution and produces deep (>500 m) mixed layers in the Weddell and Ross shelf seas each winter. By deconstructing the surface power input to the mixed layer, we have shown that the salt/fresh water flux from sea ice growth/melt dominates the evolution of the mixed layer in all shelf sea regions, with a smaller contribution from the mixed layer-surface heat flux. The Weddell and Ross shelf seas have the highest annual ice growth, with a large fraction exported northwards each year, whereas the Bellingshausen shelf sea experiences the highest annual ice melt, driven by the advection of ice from the northeast. Forcing the model with ERA-Interim (1980-2011) and hadGEM2-ES (1980-2099) atmospheric data allows us to look at the impact of atmospheric trends on the sea ice and ocean mixed layer. Both simulations show a shallowing of the wintertime mixed layer in the Amundsen & Bellingshausen seas, potentially increasing the access of warm CDW to ice shelves in both regions. The ERA-I hindcast simulation shows a significant freshening in the Ross and salinification in the Weddell due to surface driven trends (primarily through changes in the sea ice). The Ross freshening is smaller than observed however, highlighting the important role of ice shelf melt in the Amundsen Sea.

  3. The roll-up and merging of coherent structures in shallow mixing layers

    NASA Astrophysics Data System (ADS)

    Lam, M. Y.; Ghidaoui, M. S.; Kolyshkin, A. A.

    2016-09-01

    The current study seeks a fundamental explanation to the development of two-dimensional coherent structures (2DCSs) in shallow mixing layers. A nonlinear numerical model based on the depth-averaged shallow water equations is used to investigate the temporal evolution of shallow mixing layers, where the mapping from temporal to spatial results is made using the velocity at the center of the mixing layers. The flow is periodic in the streamwise direction. Transmissive boundary conditions are used in the cross-stream boundaries to prevent reflections. Numerical results are compared to linear stability analysis, mean-field theory, and secondary stability analysis. Results suggest that the onset and development of 2DCS in shallow mixing layers are the result of a sequence of instabilities governed by linear theory, mean-field theory, and secondary stability theory. The linear instability of the shearing velocity gradient gives the onset of 2DCS. When the perturbations reach a certain amplitude, the flow field of the perturbations changes from a wavy shape to a vortical (2DCS) structure because of nonlinearity. The development of the vertical 2DCS does not appear to follow weakly nonlinear theory; instead, it follows mean-field theory. After the formation of 2DCS, separate 2DCSs merge to form larger 2DCS. In this way, 2DCSs grow and shallow mixing layers develop and grow in scale. The merging of 2DCS in shallow mixing layers is shown to be caused by the secondary instability of the 2DCS. Eventually 2DCSs are dissipated by bed friction. The sequence of instabilities can cause the upscaling of the turbulent kinetic energy in shallow mixing layers.

  4. Analysis of mixed-layer clay mineral structures

    USGS Publications Warehouse

    Bradley, W.F.

    1953-01-01

    Among the enormously abundant natural occurrences of clay minerals, many examples are encountered in which no single specific crystallization scheme extends through a single ultimate grain. The characterization of such assemblages becomes an analysis of the distribution of matter within such grains, rather than the simple identification of mineral species. It having become established that the particular coordination complex typified by mica is a common component of many natural subcrystalline assemblages, the opportunity is afforded to analyze scattering from random associations of these complexes with other structural units. Successful analyses have been made of mixed hydration states of montmorillonite, of montmorillonite with mica, of vermiculite with mica, and of montmorillonite with chlorite, all of which are variants of the mica complex, and of halloysite with hydrated halloysite.

  5. A model study of seasonal mixed-layer primary production in the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Brock, John; Sathyendranath, Shubha; Platt, Trevor

    1994-06-01

    We combined a surface irradiance model with a non-spectral photosynthesisirradiance model to estimate the daily, average rate of mixed-layer primary production in the Arabian Sea for the 15th day of months at the end of the northeast monsoon, the southwest monsoon, and the fall and spring inter-monsoons. Our model experiment uses climatologies of cloud cover, mixed-layer thickness, and satellite ocean-color observations of phytoplankton biomass. Modelled surface radiation is at an annual maximum in May beneath nearly cloud-free skies just prior to the summer solstice. The model estimate of surface radiation diminishes through the southwest monsoon over most of the northern Arabian Sea to an annual minimum in August due to intense cloudiness. In agreement with previous ship-based measurements, the photosynthesis-irradiance model predicts that the mixed-layer primary production in the Arabian Sea is extremely seasonal, and peaks annually during the southwest monsoon to the north-west of the atmospheric Findlater Jet and along the coast of Somalia. Northern Arabian Sea maxima predicted for both the summer and winter monsoons are separated by periods of low mixed-layer primary production, the fall and spring inter-monsoons. The annual cycles of modelled mixed-layer primary production differ by region in the Arabian Sea due to varying monsoon influence and circulation dynamics.

  6. Coherent structures and turbulent molecular mixing in gaseous planar shear layers

    NASA Astrophysics Data System (ADS)

    Meyer, T. R.; Dutton, J. C.; Lucht, R. P.

    2006-07-01

    Quantitative planar visualization of molecular mixing dynamics in large- and intermediate-scale coherent structures is reported for the first time in the developing and far-field regions of gaseous planar shear layers. A dual-tracer (nitric oxide and acetone) planar laser-induced fluorescence (PLIF) technique is implemented as the gaseous analogue to acid/base chemical reactions that have previously been used to study molecular mixing in liquid shear layers. Data on low-speed, high-speed, and total molecularly mixed fluid fractions are collected for low- to high-speed velocity ratios from 0.25 to 0.44 and Reynolds numbers, Re_{delta}, from 18 600 to 103 000. Within this range of conditions, mixed-fluid probability density functions and ensemble-averaged statistics are highly influenced by the homogenizing effect of large-scale Kelvin Helmholtz rollers and the competing action of intermediate-scale secondary instabilities. Small-scale turbulence leads to near-unity mixing efficiencies and mixed-fluid probabilities within the shear layer, with subresolution stirring being detected primarily along the interface with free-stream fluid. Current molecular-mixing data compare favourably with previous time-averaged probe-based measurements while providing new insight on the effects of coherent structures, velocity ratio, downstream distance, and differences between low- and high-speed fluid entrainment.

  7. Evaluation of the parameterization for cloud top-down mixing in the boundary layer

    NASA Astrophysics Data System (ADS)

    Lee, Eun-Hee; Hong, Song-You; Dudhia, Jimy

    2015-04-01

    An enhanced turbulent mixing due to radiative cooling at cloud or fog top located in the planetary boundary layer (PBL) is parameterized by adopting the top-down diffusivity profile and the cloud top entrainment. The algorithm is first implemented to YSU PBL scheme to be evaluated for idealized cases and then applied for the regional and global real case simulations. Since the modified algorithm consider the mixing height as near surface cloud top, its enhanced mixing effect appears more distinctly especially for the stabilized nocturnal boundary layer. As a result, in the idealized radiation fog case study, it is found that near-surface air temperature decreases due to both radiative cooling at fog top and boundary layer mixing of the new algorithm. Also, the moisture is diffused more effectively to the above the boundary layer, which leads to the rapid dispersion of the fog in the modified algorithm. As a result, the new algorithm simulates the warm and dried near-surface and the cool and moistened boundary layer top in the following daytime. It is also found that the modified algorithm affects the cloud structure frequently occurring at the ocean boundary layer top in the regional and global simulation results.

  8. Parameterization of mixed layer eddies. III: Implementation and impact in global ocean climate simulations

    NASA Astrophysics Data System (ADS)

    Fox-Kemper, B.; Danabasoglu, G.; Ferrari, R.; Griffies, S. M.; Hallberg, R. W.; Holland, M. M.; Maltrud, M. E.; Peacock, S.; Samuels, B. L.

    A parameterization for the restratification by finite-amplitude, submesoscale, mixed layer eddies, formulated as an overturning streamfunction, has been recently proposed to approximate eddy fluxes of density and other tracers. Here, the technicalities of implementing the parameterization in the coarse-resolution ocean component of global climate models are made explicit, and the primary impacts on model solutions of implementing the parameterization are discussed. Three global ocean general circulation models including this parameterization are contrasted with control simulations lacking the parameterization. The MLE parameterization behaves as expected and fairly consistently in models differing in discretization, boundary layer mixing, resolution, and other parameterizations. The primary impact of the parameterization is a shoaling of the mixed layer, with the largest effect in polar winter regions. Secondary impacts include strengthening the Atlantic meridional overturning while reducing its variability, reducing CFC and tracer ventilation, modest changes to sea surface temperature and air-sea fluxes, and an apparent reduction of sea ice basal melting.

  9. Measurement of effective bulk and contact resistance of gas diffusion layer under inhomogeneous compression - Part I: Electrical conductivity

    NASA Astrophysics Data System (ADS)

    Vikram, Ajit; Chowdhury, Prabudhya Roy; Phillips, Ryan K.; Hoorfar, Mina

    2016-07-01

    This paper describes a measurement technique developed for the determination of the effective electrical bulk resistance of the gas diffusion layer (GDL) and the contact resistance distribution at the interface of the GDL and the bipolar plate (BPP). The novelty of this study is the measurement and separation of the bulk and contact resistance under inhomogeneous compression, occurring in an actual fuel cell assembly due to the presence of the channels and ribs on the bipolar plates. The measurement of the electrical contact resistance, contributing to nearly two-third of the ohmic losses in the fuel cell assembly, shows a non-linear distribution along the GDL/BPP interface. The effective bulk resistance of the GDL under inhomogeneous compression showed a decrease of nearly 40% compared to that estimated for homogeneous compression at different compression pressures. Such a decrease in the effective bulk resistance under inhomogeneous compression could be due to the non-uniform distribution of pressure under the ribs and the channels. This measurement technique can be used to identify optimum GDL, BPP and channel-rib structures based on minimum bulk and contact resistances measured under inhomogeneous compression.

  10. Seasonal evolution of the mixed layer in the Subantarctic Zone south of Australia

    NASA Astrophysics Data System (ADS)

    Rintoul, Stephen R.; Trull, Thomas W.

    2001-12-01

    The circumpolar Subantarctic Zone (SAZ) is a globally significant region of water mass formation and carbon dioxide uptake from the atmosphere. Here we synthesize the results of nine voyages over 8 years to describe the seasonal variation in mixed layer properties in the SAZ south of Australia for comparison with biogeochemical process studies carried out in late summer (March 1998) as part of the SAZ Project. Winter mixing extends to depths >400 m, resulting in the formation of Subantarctic Mode Water. In summer the mixed layer shoals to 75-100 m, depths which are still sufficiently deep that phytoplankton growth may be light limited. Nitrate and phosphate concentrations are reduced in summer (e.g., nitrate decreases from >15 to <5 μmol kg-1) but remain well above limiting levels. Silicate, in contrast, is low throughout the year (4 μmol kg-1 in winter and <2 μmol kg-1 in summer). Water mass properties along a north-south hydrographic section in March 1998 suggest that near-surface waters spread from south to north across the Subantarctic Front (SAF), supplying cool, fresh, nutrient-rich water to the SAZ. As a consequence, the properties of the southern SAZ differ from those farther north: the mixed layer in the south is cooler, fresher, deeper, higher in nutrients, and bounded below by a halocline (rather than by a seasonal thermocline, as in the northern SAZ). The contrast between the northern and southern SAZ persists throughout the year, suggesting the cross-front exchange occurs year-round and likely contributes to the differences in seasonal thermal amplitude and algal biomass accumulation seen in satellite images. Density-compensated horizontal gradients of temperature and salinity are common in the mixed layer of the SAZ and the northern SAF, consistent with the hypothesis that the vigor of lateral mixing in the mixed layer is a strong function of the magnitude of the lateral density gradient.

  11. Application of continuous remote sensing of mixing layer height for assessment of airport air quality

    NASA Astrophysics Data System (ADS)

    Schäfer, Klaus; Helmis, Costas; Emeis, Stefan; Sgouros, George; Kurtenbach, Ralf; Wiesen, Peter; Münkel, Christoph; Jahn, Carsten; Hoffmann, Maria; Anamaterou, Evi; O'Connor, Michael

    2010-10-01

    The assessment of airport air quality requires not only the knowledge of the emissions and the temporal and spatial distribution of meteorological parameters like wind direction and wind speed but also of the mixing layer height, because this variable controls the vertical space for rapid mixing of near-surface pollutants. It was demonstrated that the lowest stable layer or temperature inversion limits the vertical exchange of primary pollutants emitted at or near the surface and thus controls the near-surface pollutant concentrations. Remote sensing is a suitable tool to determine mixing layer height continuously as was demonstrated in urban and sub-urban areas (Hannover, Munich, Budapest, Augsburg) as well as at airports (Zurich, Paris CDG, Mexico City International Airport, Athens International Airport). The Vaisala ceilometer LD40 was used which is an eye-safe commercial lidar and designed originally to detect cloud base heights and vertical visibility for aviation safety purposes. These measurements of the vertical aerosol distribution are routinely retrieved for mixing layer height estimation by using software which was improved continuously and compared with radiosonde data. Further, mixing layer height was determined by remote sensing with a combination of a Doppler- SODAR (Sound Detection and Ranging), a RASS (Radio Acustic Sounding System) and in-situ measurements. Vertical wind, temperature and turbulence parameter profiles up to 1500 m maximum were measured by this method too. Some results of interpretation of measured data at Athens International Airport will be discussed as the influence of mixing layer height upon airport air quality and estimation of the airport emission source strengths.

  12. COSAL: A black-box compressible stability analysis code for transition prediction in three-dimensional boundary layers

    NASA Technical Reports Server (NTRS)

    Malik, M. R.

    1982-01-01

    A fast computer code COSAL for transition prediction in three dimensional boundary layers using compressible stability analysis is described. The compressible stability eigenvalue problem is solved using a finite difference method, and the code is a black box in the sense that no guess of the eigenvalue is required from the user. Several optimization procedures were incorporated into COSAL to calculate integrated growth rates (N factor) for transition correlation for swept and tapered laminar flow control wings using the well known e to the Nth power method. A user's guide to the program is provided.

  13. The "limiting line" in mixed subsonic and supersonic flow of compressible fluids

    NASA Technical Reports Server (NTRS)

    Tsien, Hsue-Shen

    1944-01-01

    It is well known that the vorticity for any fluid element is constant if the fluid is non-viscous and the change of state of the fluid is isentropic. When a solid body is placed in a uniform stream, the flow far ahead of the body is irrotational. Then if the flow is further assumed to be isentropic, the vorticity will be zero over the whole filed of flow. In other words, the flow is irrotational. For such flow over a solid body, it is shown by Theodorsen that the solid body experiences no resistance. If the fluid has a small viscosity, its effect will be limited in the boundary layer over the solid body and the body will have a drag due to the skin friction. This type of essentially isentropic irrotational flow is generally observed for a streamlined body placed in a uniform stream, if the velocity of the stream is kept below the so-called "critical speed." At the critical speed or rather at a certain value of the ratio of the velocity of the undisturbed flow and the corresponding velocity of sound, shock waves appear. This phenomenon is called the "compressibility bubble." Along a shock wave, the change of state of the fluid is no longer isentropic, although still adiabatic. This results in an increase in entropy of the fluid and generally introduces vorticity in an originally irrotational flow. The increase in entropy of the fluid is, of course, the consequence of changing part of the mechanical energy into heat energy. In other words, the part of fluid affected by the shock wave has a reduced mechanical energy. Therefore, with the appearance of shock waves, the wake of the streamline body is very much widened, and the drag increases drastically. Furthermore, the accompanying change in the pressure distribution over the body changes the aerodynamic moment acting on it and in the case of an airfoil decreases the lift force. All these consequences of the breakdown of isentropic irrotational flow are generally undesirable in applied aerodynamics. Its occurrence

  14. One-dimensional mixing layer model for a shear Hele-Shaw flow

    NASA Astrophysics Data System (ADS)

    Kovtunenko, P. V.

    2016-06-01

    A shear flow of a viscosity-stratified fluid in a Hele-Shaw cell is considered. The long-wave approximation is applied to the governing equations. To describe the evolution of the mixing layer, a special flow with a three-layered structure is considered. A one-dimensional model is derived by averaging the motion equations over the cell width, taking into account the flow structure. For a stationary flow, solutions of motion equations are constructed. The influence of viscosity on the mixing layer evolution is investigated by performing a numerical experiment for a flow with different viscosities in the layers and for a flow with always zero viscosity. It is shown that viscosity has a significant influence on the flow evolution.

  15. Mixing layer growth and background air-quality measurements over the Colorado oil-shale area

    SciTech Connect

    Laulainen, N.S.; Whiteman, C.D.; Davis, W.E.; Thorp, J.M.

    1981-06-01

    The daily growth of convective boundary layers over the complex terrain of the oil shale areas of Colorado is a prominent feature of the meteorology of the region. The development of these layers was investigated using airsondes, rawinsondes, and aircraft. The deep growth of the layers in August, to heights in excess of 5500-m MSL on clear or partly cloudy days, is expected to have important implications for the dispersal of pollutants released in the region as the oil shale resource undergoes future development. Aircraft observations show that the present background air quality is good over the region and that pollutants, when present, become well mixed throughout the depth of the convective boundary layer. The layer therefore represents an important natural means of dilution for pollutants introduced into the atmosphere. Work is proceeding to incorporate the time-dependent convective boundary layer growth into air pollution models for the region.

  16. Turbulent mixing and transport in a thermally stratified interfacial layer in decaying grid turbulence

    NASA Astrophysics Data System (ADS)

    Yoon, Kyunghwan; Warhaft, Z.; Jayesh

    1991-05-01

    A stably stratified mixing layer, sandwiched in between regions of neutral turbulence, was studied in decaying grid turbulence. The layer, which was shearless, was formed by heating the upper half of the flow by means of elements placed at the entrance to the plenum of a large, open circuit low speed wind tunnel 0.91 x 0.91 sq m in cross section and 9.14 m in length. The hot air above mixed with the cold below forming the stratified layer in between. Smoke wire photographs showed a wavelike damped region inside the layer, surrounded by the normal, more energetic turbulence outside. Second-order turbulence quantities scaled in the same way with the local Richardson number both along the layer and across it. The two stably stratified cases studied had centerline Froude numbers of 95 and 65 at 40 mesh lengths from the grid. The results are compared to a passive thermal mixing layer and are contrasted with recent experiments concerning a constant temperature gradient in grid turbulence.

  17. Non-local closure model for vertical mixing in the convective boundary layer

    SciTech Connect

    Pleim, J.E.; Chang, J.S.

    1993-01-01

    A simple non-local closure model for vertical mixing in Convective Boundary Layers (CBL) has been developed specifically for application in regional or meso-scale atmospheric chemistry models. The model, named the Asymmetrical Convective Model (ACM), is based on the concept that vertical transport within the CBL is inherently asymmetrical. Upward transport by buoyant plumes originating in the surface layer is simulated by mixing from the lowest model layer directly to all other layers in the CBL. Downward transport, however, proceeds only to the next lower layer in order to emulate gradual compensatory subsidence. The realism of the ACM is tested through comparisons to large-eddy simulations of several idealized test cases. The ACM is also tested in the context of the Regional Acid Deposition Model (RADM) both to determine sensitivity to different CBL mixing schemes and to compare to vertically resolved aircraft measurements. These tests demonstrate quicker upward transport of ground level emissions by the ACM as compared to the eddy diffusion scheme currently used in RADM. The ACM also affects ozone photochemistry in the boundary layer resulting in lower ozone concentrations in areas of high NOx emissions.

  18. HST STIS Observations of the Mixing Layer in the Cat’s Eye Nebula

    NASA Astrophysics Data System (ADS)

    Fang, Xuan; Guerrero, Martín A.; Toalá, Jesús A.; Chu, You-Hua; Gruendl, Robert A.

    2016-05-01

    Planetary nebulae (PNe) are expected to have a ˜105 K interface layer between the ≥slant 106 K inner hot bubble and the ˜104 K optical nebular shell. The PN structure and evolution, and the X-ray emission, depend critically on the efficiency of the mixing of material at this interface layer. However, neither its location nor its spatial extent have ever been determined. Using high-spatial resolution HST STIS spectroscopic observations of the N v λ λ 1239,1243 lines in the Cat’s Eye Nebula (NGC 6543), we have detected this interface layer and determined its location, extent, and physical properties for the first time in a PN. We confirm that this interface layer, as revealed by the spatial distribution of the N v λ1239 line emission, is located between the hot bubble and the optical nebular shell. We estimate a thickness of 1.5× {10}16 cm and an electron density of ˜200 cm-3 for the mixing layer. With a thermal pressure of ˜2 × 10-8 dyn cm-2, the mixing layer is in pressure equilibrium with the hot bubble and ionized nebular rim of NGC 6543. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The observations are associated with program #12509.

  19. Ion-beam mixing of Fe/B layers for tribological applications

    SciTech Connect

    Fenske, G.R.; Hu, R.; Baldo, P.M.; Erck, R.A.; Erdemir, A.; Lee, R.H.; Busch, D.E.; Nichols, F.A.; Rehn, L.E.

    1990-01-01

    Ion-beam mixing of iron and boron deposited layers was investigated as a technique to produce improved tribological coatings on steel substrates. Analysis of the kinetics of the ion-mixing process indicated that processing temperatures between 300 and 450{degree}C were required to achieve mixing of iron and boron multilayered coatings. During film deposition, it is critical to avoid deposition processes such as rf sputtering that trap large quantities of inert gases in the growing films and form blisters during subsequent ion mixing at elevated temperatures. Tribological evaluation of annealed and ion-mixed coatings indicated that the major effect of the ion mixing is formation of hard, wear-resistant, polycrystalline Fe{sub 2}B and Fe{sub 3}B phases at 450{degree}C and amorphous layers at 300{degree}C. Under partially lubricated conditions, the hard phases increase the duration of a low-friction (coefficient of friction <0.2) regime by reducing wear, thereby maintaining a low surface roughness. Under boundary-lubrication conditions, reduced wear was observed in tests on ion-mixed samples and was found to be dependent on the humidity in the test environment. 16 refs., 9 figs., 3 tabs.

  20. The thermodynamics of polymer mixing and compression in the semidilute regime.

    PubMed

    Chan, Nikko Y; Dunstan, Dave E

    2010-08-19

    Polymers present a fascinating range of mechanical properties in the extension, compression, and flow of soft condensed matter. Entropy determines the physics of the elastic material behavior of polymeric systems in deformation. Classical models of polymer dynamics have assumed chain entanglement and resulting reptation in concentrated polymer solutions. Here, we present a thermodynamic treatment of interacting chains in solution with increasing concentration from the dilute to concentrated regimes. As the polymer chain concentration increases above the critical overlap, the chains must either compress or overlap and entangle, resulting in a decrease in chain configurational entropy. The free energy of chain entanglement is shown to be less favored than compression at concentrations above the critical overlap. Elastic forces act on the chains to reduce the dimensions to the ideal random walk size with increasing concentration. At significantly higher concentrations, the free energies reach an asymptote where chain compression and entanglement are simultaneously possible. Entanglement and reptation are shown to be statistically improbable in the semidilute regime, and it is concluded that the compression of polymer chains is favored at semidilute concentrations.

  1. Mixed layer warming-deepening in the Mediterranean Sea and its effect on the marine environment

    NASA Astrophysics Data System (ADS)

    Rivetti, Irene; Boero, Ferdinando; Fraschetti, Simonetta; Zambianchi, Enrico; Lionello, Piero

    2015-04-01

    This work aims at investigating the evolution of the ocean mixed layer in the Mediterranean Sea and linking it to the occurrence of mass mortalities of benthic invertebrates. The temporal evolution of selected parameters describing the mixed layer and the seasonal thermocline is provided for the whole Mediterranean Sea for spring, summer and autumn and for the period 1945-2011. For this analysis all temperature profiles collected in the basin with bottles, Mechanical Bathy-Thermographs (MBT), eXpendable Bathy-Thermographs (XBT), and Conductivity-Temperature-Depth (CTD) have been used (166,990). These data have been extracted from three public sources: the MEDAR-MEDATLAS, the World Ocean Database 2013 and the MFS-VOS program. Five different methods for estimating the mixed layer depth are compared using temperature profiles collected at the DYFAMED station in the Ligurian Sea and one method, the so-called three-segment method, has been selected for a systematic analysis of the evolution of the uppermost part of the whole Mediterranean Sea. This method approximates the upper water column with three segments representing mixed layer, thermocline and deep layer and has shown to be the most suitable method for capturing the mixed layer depth for most shapes of temperature profiles. Mass mortalities events of benthic invertebrates have been identified by an extensive search of all data bases in ISI Web of Knowledge considering studies published from 1945 to 2011. Studies reporting the geographical coordinates, the timing of the events, the species involved and the depth at which signs of stress occurred have been considered. Results show a general increase of thickness and temperature of the mixed layer, deepening and cooling of the thermocline base in summer and autumn. Possible impacts of these changes are mass mortalities events of benthic invertebrates that have been documented since 1983 mainly in summer and autumn. It is also shown that most mass mortalities

  2. Multiscale Variability of the Atmospheric Mixed Layer over the Western Pacific Warm Pool.

    NASA Astrophysics Data System (ADS)

    Johnson, Richard H.; Ciesielski, Paul E.; Cotturone, Jennifer A.

    2001-09-01

    Sounding data from Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) have provided a first opportunity to document the variability of the atmospheric mixed layer over the western Pacific warm pool on timescales ranging from diurnal to intraseasonal. Six-hourly sounding data from four sites-the atoll Kapingamarangi and R/Vs Moana Wave, Shiyan 3, and Xiangyanghong 5-are used to determine the mixed layer depth and its thermodynamic properties. Almost three-quarters of the soundings at these four sites exhibited well-mixed structures: nearly constant profiles of potential temperature and specific humidity capped by a 150-m-deep entrainment zone. The majority of the remaining soundings were modified by precipitation and their associated downdrafts. It is estimated that approximately 40%-50% of the total soundings in COARE were influenced by precipitation downdrafts.The mean mixed layer depth at the four sites was 512 m with large variations on multiple timescales. Mean depths decreased across the warm pool from west to east, consistent with the west-to-east increase in precipitation averaged over the 4-month Intensive Observing Period. Significant modulation of the mixed layer occurred on the timescale of the Madden-Julian oscillation (MJO): the mean depth was 562 m during the undisturbed, light-wind period prior to the strong westerly wind burst (WWB) associated with the December MJO; it decreased to 466 m during the heavy-rain period of the WWB, reflecting numerous, recovering precipitation downdraft wakes; and then increased to 629 m during the late stages of the WWB when precipitation had ended. Dry intrusions over the warm pool caused the mixed layer to deepen at times to 800 m and more. Since the surface buoyancy flux typically did not increase at these times, the deepening is linked to a suppression of shallow cumulus clouds by the dry air (reduced between-cloud subsidence) as well as a general reduction in the overall

  3. Nonlinear amplification and decay of phase-mixed waves in compressing plasma.

    PubMed

    Schmit, P F; Dodin, I Y; Rocks, J; Fisch, N J

    2013-02-01

    Through particle-in-cell simulations, we show that plasma waves carrying trapped electrons can be amplified manyfold via compressing plasma perpendicularly to the wave vector. These simulations are the first ab initio demonstration of the conservation of nonlinear action for such waves, which contains a term independent of the field amplitude. In agreement with the theory, the maximum of amplification gain is determined by the total initial energy of the trapped-particle average motion but otherwise is insensitive to the particle distribution. Further compression destroys the wave; electrons are then untrapped at suprathermal energies and form a residual beam. As compression continues, the bump-on-tail instability is triggered each time one of the discrete modes comes in resonance with this beam. Hence, periodic bursts of the electrostatic energy are produced until a wide quasilinear plateau is formed. PMID:23414024

  4. Nonlinear Amplification and Decay of Phase-mixed Waves in Compressing Plasma

    SciTech Connect

    Schmit, Paul F.; Dodin, I. Y.; Rocks, J.; Fisch, N. J.

    2012-09-25

    Through particle-in-cell simulations, we show that plasma waves carrying trapped electrons can be amplified manyfold via compressing plasma perpendicularly to the wave vector. These simulations are the first ab initio demonstration of the conservation of nonlinear action for such waves, which contains a term independent of the field amplitude. In agreement with the theory, the maximum of amplification gain is determined by the total initial energy of the trapped-particle average motion but otherwise is insensitive to the particle distribution. Further compression destroys the wave; electrons are then untrapped at suprathermal energies and form a residual beam. As compression continues, the bump-on-tail instability is triggered each time one of the discrete modes comes in resonance with this beam. Hence, periodic bursts of the electrostatic energy are produced until a wide quasilinear plateau is formed.

  5. Uncertainty Assessments of 2D and Axisymmetric Hypersonic Shock Wave - Turbulent Boundary Layer Interaction Simulations at Compression Corners

    NASA Technical Reports Server (NTRS)

    Gnoffo, Peter A.; Berry, Scott A.; VanNorman, John W.

    2011-01-01

    This paper is one of a series of five papers in a special session organized by the NASA Fundamental Aeronautics Program that addresses uncertainty assessments for CFD simulations in hypersonic flow. Simulations of a shock emanating from a compression corner and interacting with a fully developed turbulent boundary layer are evaluated herein. Mission relevant conditions at Mach 7 and Mach 14 are defined for a pre-compression ramp of a scramjet powered vehicle. Three compression angles are defined, the smallest to avoid separation losses and the largest to force a separated flow engaging more complicated flow physics. The Baldwin-Lomax and the Cebeci-Smith algebraic models, the one-equation Spalart-Allmaras model with the Catrix-Aupoix compressibility modification and two-equation models including Menter SST, Wilcox k-omega 98, and Wilcox k-omega 06 turbulence models are evaluated. Each model is fully defined herein to preclude any ambiguity regarding model implementation. Comparisons are made to existing experimental data and Van Driest theory to provide preliminary assessment of model form uncertainty. A set of coarse grained uncertainty metrics are defined to capture essential differences among turbulence models. Except for the inability of algebraic models to converge for some separated flows there is no clearly superior model as judged by these metrics. A preliminary metric for the numerical component of uncertainty in shock-turbulent-boundary-layer interactions at compression corners sufficiently steep to cause separation is defined as 55%. This value is a median of differences with experimental data averaged for peak pressure and heating and for extent of separation captured in new, grid-converged solutions presented here. This value is consistent with existing results in a literature review of hypersonic shock-turbulent-boundary-layer interactions by Roy and Blottner and with more recent computations of MacLean.

  6. Method of and apparatus for dynamically stabilizing the wind-mixed layer of a solar-water pond

    SciTech Connect

    Assaf, G.

    1986-03-25

    A method is described for dynamically stabilizing the convective wind-mixed layer of a salt-water solar pond, which covers a nonconvective halocline, the method comprising providing a source of brine whose salinity differs from the salinity of the water in the wind-mixed layer, and exchanging brine between the source and the wind-mixed layer for creating a two-layer flow regime in the wind-mixed layer due to differences in salinity whereby lighter less dense water flows adjacent the surface of the pond into the source, and heavier, more dense water, flows beneath the lighter water out of the source. A solar pond is described which consists of: (a) a convective wind-mixed layer of water on the surface of the pond; (b) a nonconvective halocline covered by the wind-mixed layer having a density that increases with depth; (c) a heat storage layer under the halocline for storing heat created in the pond by the absorption of solar radiation; and (d) a reservoir associated with the wind-mixed layer and containing water whose salinity is different from the average salinity of water in the wind-mixed layer, and means to exchange water between the reservoir and the wind-mixed layer for establishing a two-layer flow regime in the wind-mixed layer due to a difference in salinity between the layers whereby lighter less dense water flows adjacent the surface of the pond into the reservoir, and heavier, more dense water, flows beneath the lighter water out of the reservoir.

  7. Estimation of the mixing layer height over a high altitude site in Central Himalayan region by using Doppler lidar

    SciTech Connect

    Shukla, K. K.; Phanikumar, D. V.; Newsom, Rob K.; Kumar, Niranjan; Ratnam, Venkat; Naja, M.; Singh, Narendra

    2014-03-01

    A Doppler lidar was installed at Manora Peak, Nainital (29.4 N; 79.2 E, 1958 amsl) to estimate mixing layer height for the first time by using vertical velocity variance as basic measurement parameter for the period September-November 2011. Mixing layer height is found to be located ~0.57 +/- 0.1and 0.45 +/- 0.05km AGL during day and nighttime, respectively. The estimation of mixing layer height shows good correlation (R>0.8) between different instruments and with different methods. Our results show that wavelet co-variance transform is a robust method for mixing layer height estimation.

  8. Formation of amorphous Ti alloy layers by excimer laser mixing of Ti on AISI 304 stainless-steel surfaces

    NASA Astrophysics Data System (ADS)

    Jervis, T. R.; Nastasi, M.; Zocco, T. G.; Martin, J. A.

    1988-07-01

    We used excimer laser radiation at 308 nm to mix thin layers of Ti into AISI 304 stainless steel. Different numbers of shots at a fluence about twice the threshold for melting varied the amount of mixing. When mixing is sufficiently complete, an amorphous surface layer is formed with Ti substituting for Fe on a one-to-one basis in the alloy. The laser mixing process, unlike Ti ion implantation, does not result in high incorporation of C in the processed layer, although some C from surface and interface contamination is incorporated into the surface layer.

  9. Lidar Descriptions of Mixing-Layer Thickness Characteristics in a Complex Terrain/Coastal Environment.

    NASA Astrophysics Data System (ADS)

    McElroy, James L.; Smith, Ted B.

    1991-05-01

    Airborne lidar and supplementary measurements made during a major study of air chemistry in southern California (SCCCAMP 1985) provided a rare opportunity to examine atmospheric boundary-layer structure in a coastal area with complex terrain. This structure results from a combination of daytime heating or convection in the boundary layer (CBL), the intrusion of a marine layer into the inland areas, the thermal internal boundary layer (TIBL) formed within the marine onshore flow, inland growth of the TIBL, interactions of the CBL and the TIBL, and airflow interactions with terrain features.Measurements showed offshore mixing-layer thicknesses during SCCCAMP to be quite uniform spatially and day to day at 100-200 m. Movement of this layer onshore occurred readily with terrain that sloped gradually upward (e.g., to 300 m MSL at 50 km inland), but was effectively blocked by a 400-500 m high coastal ridge. In the higher terrain beyond the coastal ridge, aerosol layers aloft were often created as a result of deep convection and of a combination of onshore flow and heated, upslope airflow activity. Such aerosol layers can extend far offshore when embedded in reverse circulations aloft.The forward boundary of the marine layer was quite sharp, resembling a miniature cold front. Within the marine layer the onshore flow initiates a TIBL at the coastline, which increases in depth with distance inland due to roughness and convective influences. A coherent marine layer with imbedded TIBL was maintained for inland distances of 20-50 km, depending on terrain. Intense heating occurred inland prior to the arrival and undercutting by the marine front. The resulting, effective mixing layer increased in thickness from a few hundred meters to nearly two kilometers in a very short distance.Comparisons of a representative, physically based TIBL and convective mixing-layer models with observed data indicate that they generally do a credible job of estimating the depth of the marine layer

  10. Significant mixed layer nitrification in a natural iron-fertilized bloom of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Fripiat, F.; Elskens, M.; Trull, T. W.; Blain, S.; Cavagna, A.-J.; Fernandez, C.; Fonseca-Batista, D.; Planchon, F.; Raimbault, P.; Roukaerts, A.; Dehairs, F.

    2015-11-01

    Nitrification, the microbially mediated oxidation of ammonium into nitrate, is generally expected to be low in the Southern Ocean mixed layer. This paradigm assumes that nitrate is mainly provided through vertical mixing and assimilated during the vegetative season, supporting the concept that nitrate uptake is equivalent to the new primary production (i.e., primary production which is potentially available for export). Here we show that nitrification is significant (~40-80% of the seasonal nitrate uptake) in the naturally iron-fertilized bloom over the southeast Kerguelen Plateau. Hence, a large fraction of the nitrate-based primary production is regenerated, instead of being exported. It appears that nitrate assimilation (light dependent) and nitrification (partly light inhibited) are spatially separated between the upper and lower parts, respectively, of the deep surface mixed layers. These deep mixed layers, extending well below the euphotic layer, allow nitrifiers to compete with phytoplankton for the assimilation of ammonium. The high contributions of nitrification to nitrate uptake are in agreement with both low export efficiency (i.e., the percentage of primary production that is exported) and low seasonal nitrate drawdown despite high nitrate assimilation.

  11. [Mineralogy and genesis of mixed-layer clay minerals in the Jiujiang net-like red soil].

    PubMed

    Yin, Ke; Hong, Han-Lie; Li, Rong-Biao; Han, Wen; Wu, Yu; Gao, Wen-Peng; Jia, Jin-Sheng

    2012-10-01

    Mineralogy and genesis were investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) to understand the mineralogy and its genesis significance of mixed-layer clay minerals in Jiujiang red soil section. XRD and FTIR results show that the net-like red soil sediments are composed of illite, kaolinite, minor smectite and mixed-layer illite-smectite and minor mixed-layer kaolinite-smectite. HRTEM observation indicates that some smectite layers have transformed into kaolinite layers in net-like red soil. Mixed-layer illite-smectite is a transition phase of illite transforming into smectite, and mixed-layer kaolinite-smectite is a transitional product relative to kaolinite and smectite. The occurrence of two mixed-layer clay species suggests that the weathering sequence of clay minerals in net-like red soil traversed from illite to mixed-layer illite-smectite to smectite to mixed-layer kaolinite-smectite to kaolinite, which indicates that net-like red soil formed under a warm and humid climate with strengthening of weathering.

  12. Effects of vane-induced rotation on diffuser flow distortion in an axisymmetric mixed-compression inlet

    NASA Technical Reports Server (NTRS)

    Meleason, E. T.

    1972-01-01

    An investigation of vane-induced flow rotation to modify distorted steady-state total-pressure patterns in the subsonic diffuser of a supersonic mixed-compression inlet was conducted. Radial static-pressure gradients generated by the rotation was the mechanism used to modify the total-pressure distributions. Significant redistribution of circumferential distortion patterns into more compatible radial patterns was realized, but flow problems near the duct walls reduced the general effectiveness of the technique. Total-pressure losses associated with the swirl vanes were slight. Limited turbulence data indicated that vane istallation resulted in reduced turbulence levels.

  13. Digital-computer normal shock position and restart control of a Mach 2.5 axisymmetric mixed-compression inlet

    NASA Technical Reports Server (NTRS)

    Neiner, G. H.; Cole, G. L.; Arpasi, D. J.

    1972-01-01

    Digital computer control of a mixed-compression inlet is discussed. The inlet was terminated with a choked orifice at the compressor face station to dynamically simulate a turbojet engine. Inlet diffuser exit airflow disturbances were used. A digital version of a previously tested analog control system was used for both normal shock and restart control. Digital computer algorithms were derived using z-transform and finite difference methods. Using a sample rate of 1000 samples per second, the digital normal shock and restart controls essentially duplicated the inlet analog computer control results. At a sample rate of 100 samples per second, the control system performed adequately but was less stable.

  14. Computer analysis of a high-speed film of the plane turbulent mixing layer

    NASA Astrophysics Data System (ADS)

    Hernan, M. A.; Jimenez, J.

    1982-06-01

    To evaluate the usefulness of digital image analysis in extracting quantitative information from flow pictures we have studied a 16 mm cine film of a turbulent mixing layer. A sequence of 373 frames is digitized and analyzed to isolate and measure the concentration eddies that constitute the large structure and to follow their individual evolution in time. As a result, statistics are given on the life history of the eddies, the structure of the amalgamation process and the amount of entrainment, as measured by area change, due to amalgamation as compared to the total. It is found that most of the entrainment occurs during the normal life of eddies and not during pairing. Mixing intermittency is computed from the observed shape of the eddies and seen to compare well with previous measurements. The significance of these results in modelling the mixing layer is discussed briefly and some comments are given on the general usefulness of the techniques presented.

  15. Parametric investigation on mixing in a micromixer with two-layer crossing channels.

    PubMed

    Hossain, Shakhawat; Kim, Kwang-Yong

    2016-01-01

    This work presents a parametric investigation on flow and mixing in a chaotic micromixer consisting of two-layer crossing channels proposed by Xia et al. (Lab Chip 5: 748-755, 2005). The flow and mixing performance were numerically analyzed using commercially available software ANSYS CFX-15.0, which solves the Navier-Stokes and mass conservation equations with a diffusion-convection model in a Reynolds number range from 0.2 to 40. A mixing index based on the variance of the mass fraction of the mixture was employed to evaluate the mixing performance of the micromixer. The flow structure in the channel was also investigated to identify the relationship with mixing performance. The mixing performance and pressure-drop were evaluated with two dimensionless geometric parameters, i.e., ratios of the sub-channel width to the main channel width and the channels depth to the main channel width. The results revealed that the mixing index at the exit of the micromixer increases with increase in the channel depth-to-width ratio, but decreases with increase in the sub-channel width to main channel width ratio. And, it was found that the mixing index could be increased up to 0.90 with variations of the geometric parameters at Re = 0.2, and the pressure drop was very sensitive to the geometric parameters. PMID:27390635

  16. A three-dimensional, compressible, laminar boundary-layer method for general fuselages. Volume 1: Numerical method

    NASA Technical Reports Server (NTRS)

    Wie, Yong-Sun

    1990-01-01

    A procedure for calculating 3-D, compressible laminar boundary layer flow on general fuselage shapes is described. The boundary layer solutions can be obtained in either nonorthogonal 'body oriented' coordinates or orthogonal streamline coordinates. The numerical procedure is 'second order' accurate, efficient and independent of the cross flow velocity direction. Numerical results are presented for several test cases, including a sharp cone, an ellipsoid of revolution, and a general aircraft fuselage at angle of attack. Comparisons are made between numerical results obtained using nonorthogonal curvilinear 'body oriented' coordinates and streamline coordinates.

  17. Summertime mixed layer development in the marginal sea ice zone off the Mawson coast, East Antarctica

    NASA Astrophysics Data System (ADS)

    Williams, G. D.; Nicol, S.; Raymond, B.; Meiners, K.

    2008-02-01

    Two small-scale Antarctic marine ecosystem surveys were conducted offshore from the Mawson coast (61-66∘E), in the austral summers of January 2001 and 2003. Striking differences were observed in the state of the marine ecosystem between the surveys; in particular krill abundance and penguin breeding success were significantly lower in 2003. In this paper we examine the variability in the physical oceanography between the two surveys, and identify the development of the summer mixed layer (SML) as the key physical process influencing the differences in ecological conditions. The mixed layer in 2003 was warmer, fresher and reduced in both dissolved oxygen content and fluorescence relative to 2001. In 2001 the mean mixed-layer depth was 68.5±12.4m. In 2003, the mean mixed-layer depth was 33.8±11.2m, and increased through the remaining 14 days of the survey. The SML in 2003 was underdeveloped by over a month relative to the 2001 hydrography and we relate this to the seasonal variability in the pattern and timing of sea-ice melt. AVHRR satellite images show a region of fast ice against the Mawson coast that had greater spatial and temporal extent in 2003. We conclude that delayed mixed layer development due to persistent sea ice is likely to have a negative impact on the marine ecosystem of the Antarctic shelf. This may have important implications for predicting the impact of future variability in the sea-ice growth/melt transition due to climate change.

  18. Buoyant production and consumption of turbulence kinetic energy in cloud-topped mixed layers

    NASA Technical Reports Server (NTRS)

    Randall, D. A.

    1984-01-01

    It is pointed out that studies of the entraining planetary boundary layer (PBL) have generally emphasized the role of buoyancy fluxes in driving entrainment. The buoyancy flux is proportional to the rate of conversion of the potential energy of the mean flow into the kinetic energy of the turbulence. It is not unusual for conversion to proceed in both directions simultaneously. This occurs, for instance, in both clear and cloudy convective mixed layers which are capped by inversions. A partitioning of the net conversion into positive parts, generating turbulence kinetic energy (TKE), and negative parts (TKE-consuming), would make it possible to include the positive part in the gross production rate, and closure would be achieved. Three different approaches to partitioning have been proposed. The present investigation is concerned with a comparison of the three partitioning theories. Particular attention is given to the cloud-topped mixed layer because in this case the differences between two partitioning approaches are most apparent.

  19. Trace-Gas Mixing in Isolated Urban Boundary Layers: Results from the 2001 Phoenix Sunrise Experiment

    SciTech Connect

    Berkowitz, Carl M.; Doran, J C.; Shaw, William J.; Springston, Stephen R.; Spicer, Chet W.

    2006-01-01

    Measurements made from surface sites, from the 50-m and 140-m levels (the 16th and 39th floors) of a skyscraper and from an instrumented aircraft are used to characterize early morning profiles of CO, NOy and O3 within the mid-morning summertime convective atmospheric boundary layer (CABL) over Phoenix, Arizona. Although mixing was anticipated to produce uniform values of these species throughout the CABL, this was found not to be the case. Background air advected into the upper levels of the boundary layer and entrained air from above appears to be the most likely cause for the lack of well-mixed trace gases. The results show that surface measurements may provide only limited information on concentrations of trace gas species higher in the boundary layer.

  20. Semi-discrete Galerkin solution of the compressible boundary-layer equations with viscous-inviscid interaction

    NASA Technical Reports Server (NTRS)

    Day, Brad A.; Meade, Andrew J., Jr.

    1993-01-01

    A semi-discrete Galerkin (SDG) method is under development to model attached, turbulent, and compressible boundary layers for transonic airfoil analysis problems. For the boundary-layer formulation the method models the spatial variable normal to the surface with linear finite elements and the time-like variable with finite differences. A Dorodnitsyn transformed system of equations is used to bound the infinite spatial domain thereby providing high resolution near the wall and permitting the use of a uniform finite element grid which automatically follows boundary-layer growth. The second-order accurate Crank-Nicholson scheme is applied along with a linearization method to take advantage of the parabolic nature of the boundary-layer equations and generate a non-iterative marching routine. The SDG code can be applied to any smoothly-connected airfoil shape without modification and can be coupled to any inviscid flow solver. In this analysis, a direct viscous-inviscid interaction is accomplished between the Euler and boundary-layer codes through the application of a transpiration velocity boundary condition. Results are presented for compressible turbulent flow past RAE 2822 and NACA 0012 airfoils at various freestream Mach numbers, Reynolds numbers, and angles of attack.

  1. Investigation of gas diffusion layer compression by electrochemical impedance spectroscopy on running polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Dotelli, Giovanni; Omati, Luca; Gallo Stampino, Paola; Grassini, Paolo; Brivio, Davide

    Two gas diffusion layers based on the same carbon cloth substrate, produced by an Italian Company (SAATI), and coated with microporous layers of different hydrophobicities, were assembled in a polymer electrolyte membrane fuel cell and its performances assessed. For comparison the cell mounting the carbon cloth without microporous layer was also tested. The membrane electrode assembly was made of Nafion ® 212 with Pt load 0.3/0.6 mg cm -2 (anode/cathode). The cell testing was run at 60 °C and 80 °C with fully humidified air (100%RH) and 80%RH hydrogen feedings. The assembly of gas diffusion layers and membrane with electrodes was compressed to 30% and 50% of its initial thickness. For each configuration polarization and power curves were recorded; in order to evaluate the role of different GDLs, AC impedance spectroscopy of the running cell was also performed. The higher compression ratio caused the worsening of cell performances, partially mitigated when the operating temperature was raised to 80 °C. The presence of the microporous layer onto the carbon cloth resulted extremely beneficial for the operations especially at high current density; moreover, it sensibly reduces the high frequency resistance of the overall assembly.

  2. Band gap and refractive index tunability in thallium based layered mixed crystals

    NASA Astrophysics Data System (ADS)

    Gasanly, N. M.

    2015-07-01

    Compositional variation of the band gap energy and refractive index of TlMeX2-type (Me = Ga or In and X = S or Se) layered mixed crystals have been studied by the transmission and reflection measurements in the wavelength range of 400-1100 nm. The analysis of absorption data of TlGa1-xInxSe2, TlGa(S1-xSex)2, TlGa1-xInxS2, and TlIn(Se1-xSx)2 mixed crystals revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps of mixed crystals decrease at the replacing of gallium atoms by indium and of sulfur atoms by selenium ones. Through the similar replacing of atoms (smaller atoms by larger ones) in the studied mixed crystals, the refractive index shows the quite opposite behavior.

  3. Growth rate of a shocked mixing layer with known initial perturbations [Mixing at shocked interfaces with known perturbations

    SciTech Connect

    Weber, Christopher R.; Cook, Andrew W.; Bonazza, Riccardo

    2013-05-14

    Here we derive a growth-rate model for the Richtmyer–Meshkov mixing layer, given arbitrary but known initial conditions. The initial growth rate is determined by the net mass flux through the centre plane of the perturbed interface immediately after shock passage. The net mass flux is determined by the correlation between the post-shock density and streamwise velocity. The post-shock density field is computed from the known initial perturbations and the shock jump conditions. The streamwise velocity is computed via Biot–Savart integration of the vorticity field. The vorticity deposited by the shock is obtained from the baroclinic torque with an impulsive acceleration. Using the initial growth rate and characteristic perturbation wavelength as scaling factors, the model collapses the growth-rate curves and, in most cases, predicts the peak growth rate over a range of Mach numbers (1.1 ≤Mi≤1.9), Atwood numbers (₋0.73 ≤ A ≤ ₋0.35 and 0.22 ≤ A ≤ 0.73), adiabatic indices (1.40/1.67≤γ12≤1.67/1.09) and narrow-band perturbation spectra. Lastly, the mixing layer at late times exhibits a power-law growth with an average exponent of θ=0.24.

  4. Achieving a robust drug release from extended release tablets using an integrated continuous mixing and direct compression line.

    PubMed

    Lakio, Satu; Tajarobi, Pirjo; Wikström, Håkan; Fransson, Magnus; Arnehed, Johan; Ervasti, Tuomas; Simonaho, Simo-Pekka; Ketolainen, Jarkko; Folestad, Staffan; Abrahmsén-Alami, Susanna

    2016-09-10

    In the present work the viability of integrated continuous mixing and compression processes for manufacturing of extended release (ER) matrix tablets was investigated in terms of dissolution behavior. The purpose was also to evaluate the combined effect of processing variables and compositional variables on the release robustness. The continuous process was provoked by a challenging formulation design, including variable powder characteristics and compositions of high and low amount of poorly soluble and poorly flowing drug substance (ibuprofen). Additionally a relatively low amount of two different ER matrix former grades (standard granulation grade CR and direct compression grade DC2 of hydroxypropyl methylcellulose, HPMC) was used to challenge the system. Robust ibuprofen release was obtained faster when HPMC CR was used. However, robust release was also achieved when using HPMC DC2 at high ibuprofen content, even though it took slightly longer time to reach the steady state of the process. Due to its poor flow properties, HPMC CR would be very challenging to use in traditional direct compression. The results showed that by using continuous processing it is possible to manufacture and achieve robust performance of compositions that would not be possible with traditional batch processing due to for instance poorly flowability. PMID:27469074

  5. The influence of the mixed host emitting layer based on the TCTA and TPBi in blue phosphorescent OLED

    NASA Astrophysics Data System (ADS)

    Jiang, Zhong-Lin; Tian, Wei; Kou, Zhi-Qi; Cheng, Shuang; Li, Yi-Hang

    2016-08-01

    The performance of the blue phosphorescent organic light-emitting diodes (PHOLEDs) can be improved by changing the proportion and structure of the host materials in the emitting layer. A series of devices with the mixed host (TCTAx: TPBi1-x) single emitting layer is fabricated and the best performance appears when x is 1/2. Then, the highest luminance and power efficiency reach 7189 (cd/m2) at 10.5 V and 41.7 lm/W at 2.75 V respectively after changing the position of the single host (TCTA or TPBi) emitting layer and the mixed host (TCTA1/2: TPBi1/2) emitting layer in the multiple emitting layers device. The power efficiency is almost 37% improved in device with the optimized mixed host multiple emitting layers than that of device with the mixed host single emitting layer, the former device shows great potential to realize the high efficiency blue PHOLEDs.

  6. Shear, Stability and Mixing within the Ice-Shelf-Ocean Boundary Layer

    NASA Astrophysics Data System (ADS)

    Jenkins, Adrian

    2016-04-01

    Ocean-forced basal melting has been implicated in the widespread thinning of Antarctic ice shelves that has been causally linked with acceleration in the outflow of grounded ice. What determines the distribution and rates of basal melting and freezing beneath an ice shelf and how these respond to changes in the ocean temperature or circulation are therefore key questions. Recent years have seen major progress in our ability to observe basal melting and the ocean conditions that drive it, but data on the latter remain sparse, limiting our understanding of the key processes of ice-ocean heat transfer. In particular, we have no observations of current profiles through the buoyancy- and frictionally-controlled flows along the ice shelf base that drive mixing through the ice-ocean boundary layer. This presentation represents an attempt to address this gap in our knowledge through application of a very simple model of such boundary flows that considers only the spatial dimension perpendicular to the boundary. Initial results obtained with an unrealistic assumuption of constant eddy viscosity/diffusivity are nevertheless informative. For the buoyancy-driven flow two possible regimes exist: a weakly-stratified, geostrophic cross-slope current with an embedded Ekman layer, somewhat analogous to a conventional density current on a slope; or a strongly-stratified upslope jet with weak cross-slope flow, more analogous to an inverted katabatic wind. The latter is most appropriate when the ice-ocean interface is very steep, while for the gentle slopes typical of ice shelves the buoyant Ekman regime prevails. Introduction of a variable eddy viscosity/diffusivity derived from a local turbulence closure scheme modifies the current structure and stratification. There is a sharp step in properties across the surface layer, where the viscosity/diffusivity is low, weak gradients across the outer part of the boundary layer, where shear-driven mixing is strong, and a relatively strong

  7. Stratus: An interactive steady state mixed layer model for personal computers

    NASA Technical Reports Server (NTRS)

    Guinn, Thomas A.; Schubert, Wayne H.

    1990-01-01

    A steady-state, horizontally homogeneous, cloud-topped marine boundary layer model based primarily on the work of Lilly (1968) and Schubert et al., (1979) is presented. The conservative thermodynamic variables are equivalent potential temperature, theta(sub e), and total water mixing ratio, q + l. Some of the differences between this and Lilly's (1968) model are: radiation is allowed to penetrate into the boundary layer; cloud top values of longwave radiation, equivalent potential temperature, and water vapor mixing ratio are linear functions of height derived from climatological data at California coastal stations; and the closure assumption assumes a weighted average of Lilly's (1968) maximum and minimum entrainment theories. This model was programmed in FORTRAN and will run interactively on an IBM-compatible personal computer. The program allows the user to specify the geographical location, the wind speed, the sea-surface temperature, the large scale horizontal divergence, and the initial guess for cloud top height. Output includes the steady state values of cloud top and cloud base height, mixed layer equivalent potential temperature and total water mixing ratio, and the associated convective and radiative fluxes.

  8. Methylmercury production below the mixed layer in the North Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Blum, Joel D.; Popp, Brian N.; Drazen, Jeffrey C.; Anela Choy, C.; Johnson, Marcus W.

    2013-10-01

    Mercury enters marine food webs in the form of microbially generated monomethylmercury. Microbial methylation of inorganic mercury, generating monomethylmercury, is widespread in low-oxygen coastal sediments. The degree to which microbes also methylate mercury in the open ocean has remained uncertain, however. Here, we present measurements of the stable isotopic composition of mercury in nine species of marine fish that feed at different depths in the central North Pacific Subtropical Gyre. We document a systematic decline in δ202Hg, Δ199Hg and Δ201Hg values with the depth at which fish feed. We show that these mercury isotope trends can be explained only if monomethylmercury is produced below the surface mixed layer, including in the underlying oxygen minimum zone, that is, between 50 and more than 400m depth. Specifically, we estimate that about 20-40% of the monomethylmercury detected below the surface mixed layer originates from the surface and enters deeper waters either attached to sinking particles, or in zooplankton and micronekton that migrate to depth. We suggest that the remaining monomethylmercury found at depth is produced below the surface mixed layer by methylating microbes that live on sinking particles. We suggest that microbial production of monomethylmercury below the surface mixed later contributes significantly to anthropogenic mercury uptake into marine food webs.

  9. Mixing and Reaction in the Subsonic Two-Dimensional Turbulent Free Shear Layer.

    NASA Astrophysics Data System (ADS)

    Frieler, Clifford Eugene

    1992-09-01

    The amount of mixed fluid is estimated by performing "flip" experiments and sensing the heat released due to reactions between H_2, F _2 and NO carried in inert diluent gases. The effects of density ratio, chemical kinetics and Reynolds number were investigated using this approach which avoids the usual resolution limitations. Experiments covering a factor of 30 range in density ratio are presented. Several aspects of the mixing process, such as the distribution of mixed fluid, appear insensitive to density ratio. The integral amount of mixed fluid varies less than 6%. This insensitivity contrasts with that of the profiles of mixed fluid composition. While having similar shapes, the composition profile offset depends strongly upon the density ratio. Power spectral densities of the temperature fluctuations are presented and are found to collapse upon normalization with the adiabatic flame temperature and large-structure passage frequency. Probability density functions of composition are presented and indicate that for all density ratios, a predominant composition of the mixed fluid exists within the turbulence. The initial work of Mungal and Frieler on the effects of chemical kinetics on the formation of product in the 2-D mixing layer has been greatly expanded. Measurements have been extended to include a wider range of NO concentrations and have been performed for two other stoichiometries. Results indicate that the simple model used to explain the effects of reaction kinetics in Mungal and Frieler may only be suited for cases with extreme stoichiometry (very high or very low). It has also been found that more product is formed when F_2 is the rich reactant than when H_2 is the rich reactant. This dependence upon molecular character questions both the experimental technique and theory and modeling of this reacting flow, and stems from a coupling of the effects of differing diffusivity and chemical kinetics. Numerical calculations based on simplified flow models

  10. Processing of mixed-waste compressed-gas cylinders on the Oak Ridge Reservation

    SciTech Connect

    Morris, M.I.; Conley, T.B.; Osborne-Lee, I.W.

    1998-01-01

    To comply with restrictions on the storage of old compressed gas cylinders, the environmental management organization of Lockheed Martin Energy Systems must dispose of several thousand kilograms of compressed gases stored on the Oak Ridge Reservation (ORR) because the cylinders cannot be taken off-site for disposal in their current configuration. In the ORR Site Treatment Plan, a milestone is cited that requires repackaging and shipment off-site of 21 cylinders by September 30, 1997. A project was undertaken to first evaluate and then either recontainerize or neutralize these cylinders using a transportable compressed gas recontainerization skid (TCGRS), which was developed by Integrated Environmental Services of Atlanta. The transportable system can: (1) sample, analyze, and identify at the site the chemical and radiological content of each cylinder, even those with inoperable valves; (2) breach cylinders, when necessary, to release their contents into a containment chamber; and (3) either neutralize the gas or liquid contents within the containment chamber or transfer the gas or liquids to a new cylinder. The old cylinders and cylinder fragments were disposed of and the gases neutralized or transferred to new cylinders for transportation off-site for disposal. The entire operation to process the 21 cylinders took place in only 5 days once the system was approved for operation. The system performed as expected and can now be used to process the potentially thousands of more cylinders located across the US Department of Energy (DOE) complex that have not yet been declared surplus.

  11. Instabilities of the tidally induced bottom boundary layer in the rotating frame and their mixing effect

    NASA Astrophysics Data System (ADS)

    Sakamoto, K.; Akitomo, K.

    2006-08-01

    To investigate the stability of the bottom boundary layer induced by tidal flow (oscillating flow) in a rotating frame, numerical experiments have been carried out with a two-dimensional non-hydrostatic model. Under homogeneous conditions three types of instability are found depending on the temporal Rossby number Rot, the ratio of the inertial and tidal periods. When Rot < 0.9 (subinertial range), the Ekman type I instability occurs because the effect of rotation is dominant though the flow becomes more stable than the steady Ekman flow with increasing Rot. When Rot > 1.1 (superinertial range), the Stokes layer instability is excited as in the absence of rotation. When 0.9 < Rot < 1.1 (near-inertial range), the Ekman type I or type II instability appears as in the steady Ekman layer. Being much thickened (˜100 m), the boundary layer becomes unstable even if tidal flow is weak (˜5 cm/s). The large vertical scale enhances the contribution of the Coriolis effect to destabilization, so that the type II instability tends to appear when Rot > 1.0. However, when Rot < 1.0, the type I instability rather than the type II instability appears because the downward phase change of tidal flow acts to suppress the latter. To evaluate the mixing effect of these instabilities, some experiments have been executed under a weak stratification peculiar to polar oceans (the buoyancy frequency N2 ˜ 10 -6 s -2). Strong mixing occurs in the subinertial and near-inertial ranges such that tracer is well mixed in the boundary layer and an apparent diffusivity there is evaluated at 150-300 cm 2/s. This suggests that effective mixing due to these instabilities may play an important role in determining the properties of dense shelf water in the polar regions.

  12. Charts and Tables for Estimating the Stability of the Compressible Laminar Boundary Layer with Heat Transfer and Arbitrary Pressure Gradient

    NASA Technical Reports Server (NTRS)

    Tetervin, Neal

    1959-01-01

    The minimum critical Reynolds numbers for the similar solutions of the compressible laminar boundary layer computed by Cohen and Reshotko and also for the Falkner and Skan solutions as recomputed by Smith have been calculated by Lin's rapid approximate method for two-dimensional disturbances. These results enable the stability of the compressible laminar boundary layer with heat transfer and pressure gradient to be easily estimated after the behavior of the boundary layer has been computed by the approximate method of Cohen and Reshotko. The previously reported unusual result (NACA Technical Note 4037) that a highly cooled stagnation point flow is more unstable than a highly cooled flat-plate flow is again encountered. Moreover, this result is found to be part of the more general result that a favorable pressure gradient is destabilizing for very cool walls when the Mach number is less than that for complete stability. The minimum critical Reynolds numbers for these wall temperature ratios are, however, all larger than any value of the laminar-boundary-layer Reynolds number likely to be encountered. For Mach numbers greater than those for which complete stability occurs a favorable pressure gradient is stabilizing, even for very cool walls.

  13. Fixed-point observation of mixed layer evolution in seasonally ice-free Chukchi Sea: Turbulent mixing due to gale winds and internal gravity waves

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Y.; Inoue, J.; Nishino, S.

    2015-12-01

    A fixed-point observation using the R/V Mirai was conducted in the ice-free northern Chukchi Sea of the Arctic Ocean during September of 2013. During the program the authors performed repeated microstructure measurements to reveal the temporal evolution of the surface mixed layer and mixing processes in the upper water column. The shelf region was initially characterized by a distinct two-layer system comprising a warmer/ fresher top layer and a colder/saltier bottom layer. During the two-week observation period, the top-layer water showed two types of mixing processes: near-surface turbulence due to strong wind forcing and subsurface mixing due to internal gravity waves. In the first week, when the top layer was stratified with fresh sea ice meltwater, turbulent energy related to internal waves propagated through the subsurface stratification, resulting in a mechanical overturning near the pycnocline, followed by enhanced mixing there. In the second week, gale winds directly stirred up the upper water and then established a deeper homogenous layer. The combination of internal wave mixing and wind-driven turbulence may contribute to releasing the oceanic heat into the atmosphere, consequently promoting the preconditioning of surface water freezing.

  14. Precipitation Properties of Arctic Single-Layer Mixed-Phase Clouds

    NASA Astrophysics Data System (ADS)

    Ohigashi, T.; Kollias, P.; Szyrmer, W.

    2015-12-01

    In the Arctic, single-layer mixed-phase clouds rooted in the boundary layer with cloud top heights between several hundred meters and 2 km are frequently observed. Ice particles grow fast in these mixed-phase clouds and thus produce solid precipitation. Understanding the water cycle in the Arctic region requires an extensive study of the precipitation properties of the Arctic single-layer mixed-phase clouds. The US Department of Energy Atmospheric Radiation Measurement (ARM) facility at Barrow, North Slope of Alaska conducts long-term measurements of mixed-phase clouds using a combination of active and passive sensors. Using the data of 35-GHz (Ka-band) zenith pointing radar (KAZR), ceilometer, and microwave radiometer, 1-hour averaged estimates of mixed-phase clouds are produced. A total of 553 hours of single-layer mixed-phase clouds were visually identified between October 2011 and December 2014. Using the KAZR radar reflectivity measured just one radar range gate (30 m) below the liquid base of the mixed-phase, ice water content (IWC) estimates are derived. The correlation between the hourly-mean liquid water path (LWP) and IWC below the base is not high. On the other hand, the KAZR mean Doppler velocity (Vd) at the same level exhibits high correlation with the LWP. In the LWP regime above 220 g m-2, Vd is larger than 1.0 m s-1. Vd approached to 1.8 m s-1 at even higher LWP values. We assumed that the 1-hour averaged Vd values are representative of the reflectivity-weighted mean terminal velocity of the ice particles. The large terminal velocities cannot be explained if the ice particles grow only via the deposition process. It is suggested that the riming process contributed to the growth of the particles when large terminal velocities are observed. The correlation between LWP and the KAZR Vd near the surface is similarly high. From high correlations between LWP and Vd near the cloud base and near the surface, it is clear that the LWP exhibits some control

  15. Turbulent Friction in the Boundary Layer of a Flat Plate in a Two-Dimensional Compressible Flow at High Speeds

    NASA Technical Reports Server (NTRS)

    Frankl, F.; Voishel, V.

    1943-01-01

    In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.

  16. Sensitivity of the structure of untripped mixing layers to small changes in initial conditions

    NASA Technical Reports Server (NTRS)

    Plesniak, M. W.; Bell, J. H.; Mehta, R. D.

    1992-01-01

    An experimental study was conducted concerning the influence of small changes in initial conditions on the near- and far-field evolution of the three-dimensional structure of a plan mixing layer. A two-stream mixing layer with a velocity ratio of 0.6 was generated with the initial boundary layers on the splitter plate laminar and was nominally two-dimensional. The initial conditions were changed slightly by interchanging the high- and low-speed sides of the wind tunnel, while maintaining the same velocities, and hence velocity ratio. This resulted in small changes in the initial boundary layer properties, and the perturbations present in the boundary layers were interchanged between the high- and low-speed sides for the two cases. The results indicate that, even with this relatively minor change in initial conditions, the near-field regions of the two cases differ significantly. The peak Reynolds stress levels in the near-field differ by up to 100 percent, and this is attributed to a difference in the location of the initial spanwise vortex roll-up. In addition, the positions and shapes of the individual streamwise vortical structures differ for the two cases, although the overall structures differ for the two cases, although the overall qualitative description of these structures is comparable. The subsequent reorganization and decay of the streamwise vortical structures is very similar for the two cases. As a result, in the far field, both mixing layers achieve similar structure, yielding comparable growth rates, Reynolds stress, distribution, and spectral content.

  17. Digital integrated control of a Mach 2.5 mixed-compression supersonic inlet and an augmented mixed-flow turbofan engine

    NASA Technical Reports Server (NTRS)

    Batterton, P. G.; Arpasi, D. J.; Baumbick, R. J.

    1974-01-01

    A digitally implemented integrated inlet-engine control system was designed and tested on a mixed-compression, axisymmetric, Mach 2.5, supersonic inlet with 45 percent internal supersonic area contraction and a TF30-P-3 augmented turbofan engine. The control matched engine airflow to available inlet airflow. By monitoring inlet terminal shock position and over-board bypass door command, the control adjusted engine speed so that in steady state, the shock would be at the desired location and the overboard bypass doors would be closed. During engine-induced transients, such as augmentor light-off and cutoff, the inlet operating point was momentarily changed to a more supercritical point to minimize unstarts. The digital control also provided automatic inlet restart. A variable inlet throat bleed control, based on throat Mach number, provided additional inlet stability margin.

  18. Mixing Acid Salts and Layered Double Hydroxides in Nanoscale under Solid Condition.

    PubMed

    Nakayama, Hirokazu; Hayashi, Aki

    2014-01-01

    The immobilization of potassium sorbate, potassium aspartate and sorbic acid in layered double hydroxide under solid condition was examined. By simply mixing two solids, immobilization of sorbate and aspartate in the interlayer space of nitrate-type layered double hydroxide, so called intercalation reaction, was achieved, and the uptakes, that is, the amount of immobilized salts and the interlayer distances of intercalation compounds were almost the same as those obtained in aqueous solution. However, no intercalation was achieved for sorbic acid. Although intercalation of sorbate and aspartate into chloride-type layered double hydroxide was possible, the uptakes for these intercalation compounds were lower than those obtained using nitrate-type layered double hydroxide. The intercalation under solid condition could be achieved to the same extent as for ion-exchange reaction in aqueous solution, and the reactivity was similar to that observed in aqueous solution. This method will enable the encapsulation of acidic drug in layered double hydroxide as nano level simply by mixing both solids. PMID:25080007

  19. Engineering of an MBR supernatant fouling layer by fine particles addition: a possible way to control cake compressibility.

    PubMed

    Teychene, Benoît; Guigui, Christelle; Cabassud, Corinne

    2011-02-01

    For membrane bioreactors (MBR) applied to wastewater treatment membrane fouling is still the prevalent issue. The main limiting phenomena related to fouling is a sudden jump of the transmembrane pressure (TMP) often attributed to the collapse of the fouling layer. Among existing techniques to avoid or to delay this collapse, the addition of active particles membrane fouling reducers (polymer, resins, powdered activated carbon (PAC), zeolithe...) showed promising results. Thus the main objective of this work is to determine if fouling can be reduced by inclusion of inert particles (500 nm and inert compared to other fouling reducers) and which is the impact on filtration performances of the structuring of the fouling. Those particles were chosen for their different surface properties and their capability to form well structured layer. Results, obtained at constant pressure in dead end mode, show that the presence of particles changes foulant deposition and induces non-compressible fouling (in the range of 0.5-1 bar) and higher rejection values compared to filtration done on supernatant alone. Indeed dead end filtration tests show that whatever interactions between biofluid and particles, the addition of particles leads to better filtration performances (in terms of rejection, and fouling layer compressibility). Moreover results confirm the important role played by macromolecular compounds, during supernatant filtration, creating highly compressible and reversible fouling. In conclusion, this study done at lab-scale suggests the potential benefit to engineer fouling structure to control or to delay the collapse of the fouling layer. Finally this study offers the opportunities to enlarge the choice of membrane fouling reducers by taking into consideration their ability to form more consistent fouling (i.e. rigid, structured fouling). PMID:21232780

  20. A general method for calculating three-dimensional compressible laminar and turbulent boundary layers on arbitrary wings

    NASA Technical Reports Server (NTRS)

    Cebeci, T.; Kaups, K.; Ramsey, J. A.

    1977-01-01

    The method described utilizes a nonorthogonal coordinate system for boundary-layer calculations. It includes a geometry program that represents the wing analytically, and a velocity program that computes the external velocity components from a given experimental pressure distribution when the external velocity distribution is not computed theoretically. The boundary layer method is general, however, and can also be used for an external velocity distribution computed theoretically. Several test cases were computed by this method and the results were checked with other numerical calculations and with experiments when available. A typical computation time (CPU) on an IBM 370/165 computer for one surface of a wing which roughly consist of 30 spanwise stations and 25 streamwise stations, with 30 points across the boundary layer is less than 30 seconds for an incompressible flow and a little more for a compressible flow.

  1. Mixed-layer kerolite/stevensite from the Amargosa Desert, Nevada.

    USGS Publications Warehouse

    Eberl, D.D.; Jones, B.F.; Khoury, H.N.

    1982-01-01

    Mixed-layer clays of randomly interstratified kerolite/stevensite occur as an abundant mineral in lake and/or spring deposits of probable Pliocene and Pleistocene age in the Amargosa Desert of S Nevada, USA. Kerolite is a trioctahedral mineral similar to talc, but with a basal spacing of approx 9.65 A (cf. talc at 9.38 A). The data suggest that talc, kerolite and stevensite may form a continuous structural series based on layer charge. (Following abstract) -D.F.B.

  2. Effects of Top Layer, Nozzle Arrangement, and Gas Flow Rate on Mixing Time in Agitated Ladles by Bottom Gas Injection

    NASA Astrophysics Data System (ADS)

    Conejo, A. N.; Kitamura, S.; Maruoka, N.; Kim, S.-J.

    2013-08-01

    This research investigates mixing phenomena in bottom gas-stirred ladles using water modeling, which incorporates hexane as the top layer. The effects of slag thickness, nozzle position, number of nozzles, and gas flow rate on mixing time have been investigated. Conditions to improve mixing time have been identified. A single nozzle located at two-thirds of the ladle radius was found to produce the shortest mixing time. Under extremely low gas flow rates, an unusual behavior was observed, where the top layer promoted a decrease in mixing time.

  3. A theoretical study of mixing downstream of transverse injection into a supersonic boundary layer

    NASA Technical Reports Server (NTRS)

    Baker, A. J.; Zelazny, S. W.

    1972-01-01

    A theoretical and analytical study was made of mixing downstream of transverse hydrogen injection, from single and multiple orifices, into a Mach 4 air boundary layer over a flat plate. Numerical solutions to the governing three-dimensional, elliptic boundary layer equations were obtained using a general purpose computer program. Founded upon a finite element solution algorithm. A prototype three-dimensional turbulent transport model was developed using mixing length theory in the wall region and the mass defect concept in the outer region. Excellent agreement between the computed flow field and experimental data for a jet/freestream dynamic pressure ratio of unity was obtained in the centerplane region of the single-jet configuration. Poorer agreement off centerplane suggests an inadequacy of the extrapolated two-dimensional turbulence model. Considerable improvement in off-centerplane computational agreement occured for a multi-jet configuration, using the same turbulent transport model.

  4. On the Interaction of Buoyant Plumes With Ocean Mixed-Layer Fronts

    NASA Astrophysics Data System (ADS)

    Özgökmen, Tamay

    2010-11-01

    The ocean's surface mixed layer is notoriously complex due to high spatial and temporal gradients of density and velocity fields. The understanding and modeling of such flows have a wide range of applications. For instance, anomalous currents and density perturbations in the acoustic and optical environment can affect a variety of naval operations. These flows can also influence strongly the dispersion of surface and sub-surface pollutants. Large eddy simulations of an idealized mixed-layer problem are conducted using the spectral element model Nek5000. Sampling strategies of these fields are investigated using passive tracers and Lagrangian particles. These idealized fields are then used in order to explore the behavior of a buoyant plume through the water column, namely its surface and sub-surface dispersion, which is motivated by the Deepwater Horizon oil spill.

  5. On the Interaction of Buoyant Plumes With Ocean Mixed-Layer Fronts (Invited)

    NASA Astrophysics Data System (ADS)

    Ozgokmen, T. M.; Fischer, P. F.

    2010-12-01

    The ocean's surface mixed layer is notoriously complex due to high spatial and temporal gradients of density and velocity fields. The understanding and modeling of such flows have a wide range of applications. For instance, anomalous currents and density perturbations in the acoustic and optical environment can affect a variety of naval operations. These flows can also influence strongly the dispersion of surface and sub-surface pollutants. Large eddy simulations of an idealized mixed-layer problem are conducted using a non-hydrostatic spectral element model. Sampling strategies of these fields are investigated using passive tracers and Lagrangian particles. These idealized fields are then used in order to explore the behavior of a buoyant plume through the water column, namely its surface and sub-surface dispersion, which is motivated by the Deepwater Horizon oil spill.

  6. Asymptotic solution of the turbulent mixing layer for velocity ratio close to unity

    NASA Technical Reports Server (NTRS)

    Higuera, F. J.; Jimenez, J.; Linan, A.

    1996-01-01

    The equations describing the first two terms of an asymptotic expansion of the solution of the planar turbulent mixing layer for values of the velocity ratio close to one are obtained. The first term of this expansion is the solution of the well-known time-evolving problem and the second, which includes the effects of the increase of the turbulence scales in the stream-wise direction, obeys a linear system of equations. Numerical solutions of these equations for a two-dimensional reacting mixing layer show that the correction to the time-evolving solution may explain the asymmetry of the entrainment and the differences in product generation observed in flip experiments.

  7. Efficiency of eddy mixing in a stable stratified atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kurbatskiy, A. F.; Kurbatskaya, L. I.

    2011-12-01

    Based on a mesoscale RANS model of turbulence, the behavior of turbulent eddy mixing parameters is found to agree with the latest data of laboratory and atmospheric measurements. Some problems of the description of turbulent eddy mixing in the atmospheric boundary layer are studied. When the flow transforms to an extremely stable state, in particular, it is found the flux Richardson number Ri f can change nonmonotonically: it increases with increasing gradient Richardson number Rig until the state of saturation is reached at Ri g ≃ 1 and then decreases. The behavior of the coefficients of eddy diffusion of momentum and heat agrees with the concept of momentum (but not heat) transfer by internal waves propagating in an extremely stable atmospheric boundary layer.

  8. Mixed-layered bismuth-oxygen-iodine materials for capture and waste disposal of radioactive iodine

    SciTech Connect

    Krumhansl, James L; Nenoff, Tina M

    2013-02-26

    Materials and methods of synthesizing mixed-layered bismuth oxy-iodine materials, which can be synthesized in the presence of aqueous radioactive iodine species found in caustic solutions (e.g. NaOH or KOH). This technology provides a one-step process for both iodine sequestration and storage from nuclear fuel cycles. It results in materials that will be durable for repository conditions much like those found in Waste Isolation Pilot Plant (WIPP) and estimated for Yucca Mountain (YMP). By controlled reactant concentrations, optimized compositions of these mixed-layered bismuth oxy-iodine inorganic materials are produced that have both a high iodine weight percentage and a low solubility in groundwater environments.

  9. Mixed-layered bismuth--oxygen--iodine materials for capture and waste disposal of radioactive iodine

    DOEpatents

    Krumhansl, James L; Nenoff, Tina M

    2015-01-06

    Materials and methods of synthesizing mixed-layered bismuth oxy-iodine materials, which can be synthesized in the presence of aqueous radioactive iodine species found in caustic solutions (e.g. NaOH or KOH). This technology provides a one-step process for both iodine sequestration and storage from nuclear fuel cycles. It results in materials that will be durable for repository conditions much like those found in Waste Isolation Pilot Plant (WIPP) and estimated for Yucca Mountain (YMP). By controlled reactant concentrations, optimized compositions of these mixed-layered bismuth oxy-iodine inorganic materials are produced that have both a high iodine weight percentage and a low solubility in groundwater environments.

  10. Correcting the aero-optical aberration of the supersonic mixing layer with adaptive optics: concept validation.

    PubMed

    Gao, Qiong; Jiang, Zongfu; Yi, Shihe; Xie, Wenke; Liao, Tianhe

    2012-06-10

    We describe an adaptive optics (AO) system for correcting the aero-optical aberration of the supersonic mixing layer and test its performance with numerical simulations. The AO system is based on the measurement of distributed Strehl ratios and the stochastic parallel gradient descent (SPGD) algorithm. The aero-optical aberration is computed by the direct numerical simulation of a two-dimensional supersonic mixing layer. When the SPGD algorithm is applied directly, the AO cannot give effective corrections. This paper suggests two strategies to improve the performance of the SPGD algorithm for use in aero-optics. The first one is using an iteration process keeping finite memory, and the second is based on the frozen hypothesis. With these modifications, the performance of AO is improved and the aero-optical aberration can be corrected to some noticeable extent. The possibility of experimental implementation is also discussed. PMID:22695671

  11. DNS of spark ignition and edge flame propagation in turbulent droplet-laden mixing layers

    SciTech Connect

    Neophytou, A.; Mastorakos, E.; Cant, R.S.

    2010-06-15

    A parametric study of forced ignition at the mixing layer between air and air carrying fine monosized fuel droplets is done through one-step chemistry direct numerical simulations to determine the influence of the size and volatility of the droplets, the spark location, the droplet-air mixing layer initial thickness and the turbulence intensity on the ignition success and the subsequent flame propagation. The propagation is analyzed in terms of edge flame displacement speed, which has not been studied before for turbulent edge spray flames. Spark ignition successfully resulted in a tribrachial flame if enough fuel vapour was available at the spark location, which occurred when the local droplet number density was high. Ignition was achieved even when the spark was offset from the spray, on the air side, due to the diffusion of heat from the spark, provided droplets evaporated rapidly. Large kernels were obtained by sparking close to the spray, since fuel was more readily available. At long times after the spark, for all flames studied, the probability density function of the displacement speed was wide, with a mean value in the range 0.55-0.75S{sub L}, with S{sub L} the laminar burning velocity of a stoichiometric gaseous premixed flame. This value is close to the mean displacement speed in turbulent edge flames with gaseous fuel. The displacement speed was negatively correlated with curvature. The detrimental effect of curvature was attenuated with a large initial kernel and by increasing the thickness of the mixing layer. The mixing layer was thicker when evaporation was slow and the turbulence intensity higher. However, high turbulence intensity also distorted the kernel which could lead to high values of curvature. The edge flame reaction component increased when the maximum temperature coincided with the stoichiometric contour. The results are consistent with the limited available experimental evidence and provide insights into the processes associated with

  12. Surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea

    NASA Astrophysics Data System (ADS)

    Lincoln, B. J.; Rippeth, T. P.; Simpson, J. H.

    2016-08-01

    Inertial oscillations are a ubiquitous feature of the surface ocean. Here we combine new observations with a numerical model to investigate the role of inertial oscillations in driving deepening of the surface mixed layer in a seasonally stratified sea. Observations of temperature and current structure, from a mooring in the Western Irish Sea, reveal episodes of strong currents (>0.3 m s-1) lasting several days, resulting in enhanced shear across the thermocline. While the episodes of strong currents are coincident with windy periods, the variance in the shear is not directly related to the wind stress. The shear varies on a subinertial time scale with the formation of shear maxima lasting several hours occurring at the local inertial period of 14.85 h. These shear maxima coincide with the orientation of the surface current being at an angle of approximately 90° to the right of the wind direction. Observations of the water column structure during windy periods reveal deepening of the surface mixed layer in a series of steps which coincide with a period of enhanced shear. During the periods of enhanced shear gradient, Richardson number estimates indicate Ri-1 ≥ 4 at the base of the surface mixed layer, implying the deepening as a result of shear instability. A one-dimensional vertical exchange model successfully reproduces the magnitude and phase of the shear spikes as well as the step-like deepening. The observations and model results therefore identify the role of wind shear alignment as a key entrainment mechanism driving surface mixed layer deepening in a shallow, seasonally stratified sea.

  13. Trapped Heat and Cooling Processes in the Arctic Ocean Surface Mixed Layer

    NASA Astrophysics Data System (ADS)

    Bradley, A. C.; Palo, S. E.; Steele, M.

    2015-12-01

    With the changing Arctic climate, sea ice is disintegrating earlier and there is an increasing length of time during which the ocean is exposed to solar radiation. The surface mixed layer of the Arctic Ocean is reaching unprecedentedly warm temperatures. This study examines the cooling processes in the summer mixed layer of the upper ocean between the warm late-summer and the onset of ice growth. In situ measurements of upper ocean temperatures from UpTempO buoys and a number of CTD profiles in the Beaufort and Chukchi regions indicate that as expected, most of the heat in the upper ocean is lost to the atmosphere at the surface. Cooling to the atmosphere occurs predominantly through sudden cooling events associated with passing weather systems, with cooling rates greater than 0.2 °C/hour. However, a not-insubstantial amount of heat gets trapped in the summer halocline forming temperature features like the Near Surface Temperature Maximum isolated from the cooling associated with passing storms. These are clearly visible in the included figure. They come and go over the course of the cooling season, but typically persist through freeze-up. Heat stored in this layer will, on erosion of the summer halocline with wintertime ice growth, be mixed into the surface mixed layer and slow the growth of sea ice. This presentation quantifies the relative balance between heat loss to the atmosphere, temporary and seasonal heat storage in the summer halocline, and the relationship to fall season storminess in the region.

  14. Shear rheology of mixed protein adsorption layers vs their structure studied by surface force measurements.

    PubMed

    Danov, Krassimir D; Kralchevsky, Peter A; Radulova, Gergana M; Basheva, Elka S; Stoyanov, Simeon D; Pelan, Eddie G

    2015-08-01

    The hydrophobins are proteins that form the most rigid adsorption layers at liquid interfaces in comparison with all other investigated proteins. The mixing of hydrophobin HFBII with other conventional proteins is expected to reduce the surface shear elasticity and viscosity, E(sh) and η(sh), proportional to the fraction of the conventional protein. However, the experiments show that the effect of mixing can be rather different depending on the nature of the additive. If the additive is a globular protein, like β-lactoglobulin and ovalbumin, the surface rigidity is preserved, and even enhanced. The experiments with separate foam films indicate that this is due to the formation of a bilayer structure at the air/water interface. The more hydrophobic HFBII forms the upper layer adjacent to the air phase, whereas the conventional globular protein forms the lower layer that faces the water phase. Thus, the elastic network formed by the adsorbed hydrophobin remains intact, and even reinforced by the adjacent layer of globular protein. In contrast, the addition of the disordered protein β-casein leads to softening of the HFBII adsorption layer. Similar (an even stronger) effect is produced by the nonionic surfactant Tween 20. This can be explained with the penetration of the hydrophobic tails of β-casein and Tween 20 between the HFBII molecules at the interface, which breaks the integrity of the hydrophobin interfacial elastic network. The analyzed experimental data for the surface shear rheology of various protein adsorption layers comply with a viscoelastic thixotropic model, which allows one to determine E(sh) and η(sh) from the measured storage and loss moduli, G' and G″. The results could contribute for quantitative characterization and deeper understanding of the factors that control the surface rigidity of protein adsorption layers with potential application for the creation of stable foams and emulsions with fine bubbles or droplets.

  15. Mixed convection boundary layer flow over a horizontal elliptic cylinder with constant heat flux

    NASA Astrophysics Data System (ADS)

    Javed, Tariq; Ahmad, Hussain; Ghaffari, Abuzar

    2015-12-01

    Mixed convection boundary layer flow of a viscous fluid over a horizontal elliptic cylinder with a constant heat flux is investigated numerically. The governing partial differential equations are transformed to non-dimensional form and then are solved by an efficient implicit finite different scheme known as Keller-box method. The solutions are expressed in the form of skin friction and Nusselt number, which are plotted against the eccentric angle. The effect of pertinent parameters such as mixed convection parameter, aspect ratio (ratio of lengths of minor axis to major axis), and Prandtl number on skin friction and Nusselt number are illustrated through graphs for both blunt and slender orientations. The increase in the value of mixed convection parameter results in increase in skin friction coefficient and Nusselt number for blunt as well as slender orientations.

  16. An assumed pdf approach for the calculation of supersonic mixing layers

    NASA Technical Reports Server (NTRS)

    Baurle, R. A.; Drummond, J. P.; Hassan, H. A.

    1992-01-01

    In an effort to predict the effect that turbulent mixing has on the extent of combustion, a one-equation turbulence model is added to an existing Navier-Stokes solver with finite-rate chemistry. To average the chemical-source terms appearing in the species-continuity equations, an assumed pdf approach is also used. This code was used to analyze the mixing and combustion caused by the mixing layer formed by supersonic coaxial H2-air streams. The chemistry model employed allows for the formation of H2O2 and HO2. Comparisons are made with recent measurements using laser Raman diagnostics. Comparisons include temperature and its rms, and concentrations of H2, O2, N2, H2O, and OH. In general, good agreement with experiment was noted.

  17. Estimation of Mixed Layer Depth in the Gulf of Aden: A New Approach

    PubMed Central

    Alsaafani, M. A.; Alraddadi, T. M.; Albarakati, A. M.

    2016-01-01

    The mixed layer depth (MLD) in Gulf of Aden is analyzed using vertical high resolution (1m) profiles of both temperature and density. Firstly, we examined threshold and gradient methods for estimating the MLD. Close evaluation with individual profiles reveals the failure of both methods for most of the profiles. Furthermore, the curvature method, a relatively recent approach to define ocean MLDs, is established for open water profiles but for marginal seas, like the Gulf of Aden, it detects shallower depths than the actual MLD. These considerable differences motivated us to introduce a new approach of MLD identification, which is developed based on curvature method and is called segment method. Our segment method produces adequate MLD estimates for more than 95% of the profiles and overcomes major limitations of conventional methods. It is less biased and least scattered compared to other methods with a correlation coefficient > 0.95. The mixed layer in Gulf of Aden displays significant seasonal variability and is deeper in winter. Throughout the year, the western part of gulf experiences deeper mixed layer than the eastern part. Regional eddies dominate Gulf of Aden’s MLD pattern during all seasons. PMID:27788181

  18. Debye-Hückel theory of mixed charged-zwitterionic lipid layers

    NASA Astrophysics Data System (ADS)

    Mengistu, D. H.; May, S.

    2008-07-01

    Modeling electrostatic properties of macroions such as charged lipid membranes is especially simple within linear Debye-Hückel theory where analytical solutions are often available. Charged lipid layers typically also contain zwitterionic lipids that possess a large headgroup dipole. We incorporate the presence of zwitterionic lipids into the Debye-Hückel description and derive analytical expressions for the free energies of isolated and interacting lipid layers. Our approach accounts for two major characteristic features of zwitterionic lipids, the firm linkage of the dipole's negatively charged phosphate end to the lipid chain and the comparatively large conformational freedom of the opposite, positively charged, dipole end. This leads to differences in structural properties of mixed anionic and cationic lipid layers that are known from experiment and that the Debye-Hückel description qualitatively recovers. Most notably, this includes the different dependencies of the average cross-sectional area per lipid on the composition of mixed anionic and cationic membranes. In addition, we study the predictions of Debye-Hückel theory regarding the electrostatic influence of zwitterionic lipids on the stability of non-ideally mixed membranes as well as on the adsorption energy of oppositely charged macroions.

  19. Variations of surface mixed layer heat and salinity budget during DYNAMO

    NASA Astrophysics Data System (ADS)

    Chi, N.; Lien, R.; D'Asaro, E. A.

    2012-12-01

    The response of the oceanic surface mixed layer heat and salinity budget to different phases of the Madden-Julian oscillation (MJO) in the central Indian Ocean is evaluated. Data from shipboard and mooring observations (September 2011 - January 2012) from the DYNAMO field campaign is analyzed. During the DYNAMO campaign, 2 to 3 MJO events (depending on definition) were recorded. Of particular interest is the 2011 Thanksgiving arrival of a strong cyclone-assisted MJO event. Variations in surface heat flux, time rate of change of heat content, turbulent flux, and the definition of the mixed layer depth seem to dominate the overall results for the mixed layer throughout the observation period. During the Thanksgiving event, preliminary results suggest a complicated combination of factors modulating the near surface salinity. Interestingly, each of the following factors: wind, precipitation and horizontal advection, appears to dominate over the others for a period of time. We anticipate that these results can provide accurate tests of air-sea coupled models and help interpret the role of air-sea coupling and ocean heat storage on the evolution of the MJO.

  20. Computational and experimental analysis of particle clustering in a shearless turbulent mixing layer

    NASA Astrophysics Data System (ADS)

    Ireland, Peter; Good, Garrett; Warhaft, Zellman; Collins, Lance

    2011-11-01

    Entrainment, the drawing in of external fluid by a turbulent flow, is ubiquitous to both industrial and natural turbulent processes. This mechanism is particularly important in atmospheric clouds, where the entrainment of dry air by turbulence can affect precipitation mechanisms. We use parametrically matched wind-tunnel experiments and direct numerical simulations with inhomogeneous particle seeding to explore particle clustering in a shearless turbulent mixing layer. We find high degrees of clustering, both visually and statistically, even for particles with negligible inertia. These particle clusters have characteristic sizes on the order of the integral lengthscale of the turbulence and are thus much larger than those resulting from particle inertia. The degree of clustering at a particular location generally decreases as the mixing layer evolves and depends on both the turbulent kinetic energy ratio in the mixing layer and the magnitude and orientation of gravity. We observe the same qualitative trends in both the experiments and the simulations. We anticipate that a better understanding of particle clustering in entraining flows will lead to, among other things, improved cloud evolution predictions and more accurate climate models.

  1. The effects of temporal variability of mixed layer depth on primary productivity around Bermuda

    NASA Technical Reports Server (NTRS)

    Bissett, W. Paul; Meyers, Mark B.; Walsh, John J.; Mueller-Karger, Frank E.

    1994-01-01

    Temporal variations in primary production and surface chlorophyll concentrations, as measured by ship and satellite around Bermuda, were simulated with a numerical model. In the upper 450 m of the water column, population dynamics of a size-fractionated phytoplankton community were forced by daily changes of wind, light, grazing stress, and nutrient availability. The temporal variations of production and chlorophyll were driven by changes in nutrient introduction to the euphotic zone due to both high- and low-frequency changes of the mixed layer depth within 32 deg-34 deg N, 62 deg-64 deg W between 1979 and 1984. Results from the model derived from high-frequency (case 1) changes in the mixed layer depth showed variations in primary production and peak chlorophyll concentrations when compared with results from the model derived from low-frequency (case 2) mixed layer depth changes. Incorporation of size-fractionated plankton state variables in the model led to greater seasonal resolution of measured primary production and vertical chlorophyll profiles. The findings of this study highlight the possible inadequacy of estimating primary production in the sea from data of low-frequency temporal resolution and oversimplified biological simulations.

  2. Experiments on the Southern Oscillation with CAM3 coupled to a Mixed Layer Ocean

    NASA Astrophysics Data System (ADS)

    Monier, E.; Sokolov, A. P.

    2010-12-01

    Recent modeling studies suggest that the atmospheric component plays a dominant role in the El Nino/Southern Oscillation (ENSO) phenomenon. In particular, simulations in which an Atmospheric General Circulation Model (AGCM) is coupled to a mixed-layer ocean model can produce ‘ENSO-like’ variability with associated patterns in SST, precipitation, or atmospheric circulation similar to that of ENSO, and referred to as 'Atmospheric Walker Mode' (AWM). In the absence of Bjerknes feedback (no ocean dynamics), the AWM relies on ocean-to-atmosphere latent heat flux and cloud forcing feedback. To study the AWM, we perform a number of experiments using the Community Atmosphere Model (CAM) version 3 coupled to a mixed-layer ocean, including varying the model resolution and the depth of the mixed layer. We investigate the possible climate change impacts on the AWM by carrying out a number of equilibrium climate change simulations for a doubled CO2 with different values of the model's climate sensitivity. Results show that both the magnitude and the periodicity of the simulated AWM are rather different. This study provides further insight into the ENSO response to increasing greenhouse gas—induced radiative forcing.

  3. Boundary Layer CO2 mixing ratio measurements by an airborne pulsed IPDA lidar

    NASA Astrophysics Data System (ADS)

    Ramanathan, A. K.; Mao, J.; Abshire, J. B.; Allan, G. R.

    2014-12-01

    Since the primary signature of CO2 fluxes at the surface occurs in the planetary boundary layer (PBL), remote sensing measurements of CO2 that can resolve the CO2 absorption in the PBL separate from the total column are more sensitive to fluxes than those that can only measure a total column. The NASA Goddard CO2 sounder is a pulsed, range-resolved lidar that samples multiple (presently 30) wavelengths across the 1572.335 nm CO2 absorption line. The range resolution and line shape measurement enable CO2 mixing ratio measurements to be made in two or more altitude layers including the PBL via lidar cloud-slicing and multi-layer retrievals techniques. The pulsed lidar approach allows range-resolved backscatter of scattering from ground and cloud tops. Post flight data analysis can be used split the vertical CO2 column into layers (lidar cloud-slicing) and solve for the CO2 mixing ratio in each layer. We have demonstrated lidar cloud slicing with lidar measurements from a flight over Iowa, USA in August 2011 during the corn-growing season, remotely measuring a ≈15 ppm drawdown in the PBL CO2. We will present results using an improved lidar cloud slicing retrieval algorithm as well as preliminary measurements from the upcoming ASCENDS 2014 flight campaign. The CO2 absorption line is also more pressure broadened at lower altitudes. Analyzing the line shape also allows solving for some vertical resolution in the CO2 distribution. By allowing the retrieval process to independently vary the column concentrations in two or more altitude layers, one can perform a best-fit retrieval to obtain the CO2 mixing ratios in each of the layers. Analysis of airborne lidar measurements (in 2011) over Iowa, USA and Four Corners, New Mexico, USA show that for altitudes above 8 km, the CO2 sounder can detect and measure enhanced or diminished CO2 mixing ratios in the PBL even in the absence of clouds. We will present these results as well as preliminary measurements from the upcoming

  4. Vertical distribution and composition of phytoplankton under the influence of an upper mixed layer.

    PubMed

    Ryabov, Alexei B; Rudolf, Lars; Blasius, Bernd

    2010-03-01

    The vertical distribution of phytoplankton is of fundamental importance for the dynamics and structure of aquatic communities. Here, using an advection-reaction-diffusion model, we investigate the distribution and competition of phytoplankton species in a water column, in which inverse resource gradients of light and a nutrient can limit growth of the biomass. This problem poses a challenge for ecologists, as the location of a production layer is not fixed, but rather depends on many internal parameters and environmental factors. In particular, we study the influence of an upper mixed layer (UML) in this system and show that it leads to a variety of dynamic effects: (i) Our model predicts alternative density profiles with a maximum of biomass either within or below the UML, thereby the system may be bistable or the relaxation from an unstable state may require a long-lasting transition. (ii) Reduced mixing in the deep layer can induce oscillations of the biomass; we show that a UML can sustain these oscillations even if the diffusivity is less than the critical mixing for a sinking phytoplankton population. (iii) A UML can strongly modify the outcome of competition between different phytoplankton species, yielding bistability both in the spatial distribution and in the species composition. (iv) A light limited species can obtain a competitive advantage if the diffusivity in the deep layers is reduced below a critical value. This yields a subtle competitive exclusion effect, where the oscillatory states in the deep layers are displaced by steady solutions in the UML. Finally, we present a novel graphical approach for deducing the competition outcome and for the analysis of the role of a UML in aquatic systems.

  5. Vertical velocity variance in the mixed layer from radar wind profilers

    USGS Publications Warehouse

    Eng, K.; Coulter, R.L.; Brutsaert, W.

    2003-01-01

    Vertical velocity variance data were derived from remotely sensed mixed layer turbulence measurements at the Atmospheric Boundary Layer Experiments (ABLE) facility in Butler County, Kansas. These measurements and associated data were provided by a collection of instruments that included two 915 MHz wind profilers, two radio acoustic sounding systems, and two eddy correlation devices. The data from these devices were available through the Atmospheric Boundary Layer Experiment (ABLE) database operated by Argonne National Laboratory. A signal processing procedure outlined by Angevine et al. was adapted and further built upon to derive vertical velocity variance, w_pm???2, from 915 MHz wind profiler measurements in the mixed layer. The proposed procedure consisted of the application of a height-dependent signal-to-noise ratio (SNR) filter, removal of outliers plus and minus two standard deviations about the mean on the spectral width squared, and removal of the effects of beam broadening and vertical shearing of horizontal winds. The scatter associated with w_pm???2 was mainly affected by the choice of SNR filter cutoff values. Several different sets of cutoff values were considered, and the optimal one was selected which reduced the overall scatter on w_pm???2 and yet retained a sufficient number of data points to average. A similarity relationship of w_pm???2 versus height was established for the mixed layer on the basis of the available data. A strong link between the SNR and growth/decay phases of turbulence was identified. Thus, the mid to late afternoon hours, when strong surface heating occurred, were observed to produce the highest quality signals.

  6. Vertical velocity variance in the mixed layer from radar wind profilers.

    SciTech Connect

    Eng, K.; Coulter, R. L.; Brutsaert, W.; Environmental Research; Cornell Univ.

    2003-11-01

    Vertical velocity variance data were derived from remotely sensed mixed layer turbulence measurements at the Atmospheric Boundary Layer Experiments (ABLE) facility in Butler County, Kansas. These measurements and associated data were provided by a collection of instruments that included two 915 MHz wind profilers, two radio acoustic sounding systems, and two eddy correlation devices. The data from these devices were available through the Atmospheric Boundary Layer Experiment (ABLE) database operated by Argonne National Laboratory. A signal processing procedure outlined by Angevine et al. was adapted and further built upon to derive vertical velocity variance, {omega}'{sup 2}, from 915 MHz wind profiler measurements in the mixed layer. The proposed procedure consisted of the application of a height-dependent signal-to-noise ratio (SNR) filter, removal of outliers plus and minus two standard deviations about the mean on the spectral width squared, and removal of the effects of beam broadening and vertical shearing of horizontal winds. The scatter associated with {omega}'{sup 2} was mainly affected by the choice of SNR filter cutoff values. Several different sets of cutoff values were considered, and the optimal one was selected which reduced the overall scatter on {omega}'{sup 2} and yet retained a sufficient number of data points to average. A similarity relationship of {omega}'{sup 2} versus height was established for the mixed layer on the basis of the available data. A strong link between the SNR and growth/decay phases of turbulence was identified. Thus, the mid to late afternoon hours, when strong surface heating occurred, were observed to produce the highest quality signals.

  7. Computing the reconnection rate in turbulent kinetic layers by using electron mixing to identify topology

    SciTech Connect

    Daughton, W.; Nakamura, T. K. M.; Karimabadi, H.; Roytershteyn, V.; Loring, B.

    2014-05-15

    Three-dimensional kinetic simulations of magnetic reconnection for parameter regimes relevant to the magnetopause current layer feature the development of turbulence, driven by the magnetic and velocity shear, and dominated by coherent structures including flux ropes, current sheets, and flow vortices. Here, we propose a new approach for computing the global reconnection rate in the presence of this complexity. The mixing of electrons originating from separate sides of the magnetopause layer is used as a proxy to rapidly identify the magnetic topology and track the evolution of magnetic flux. The details of this method are illustrated for an asymmetric current layer relevant to the subsolar magnetopause and for a flow shear dominated layer relevant to the lower latitude magnetopause. While the three-dimensional reconnection rates show a number of interesting differences relative to the corresponding two-dimensional simulations, the time scale for the energy conversion remains very similar. These results suggest that the mixing of field lines between topologies is more easily influenced by kinetic turbulence than the physics responsible for the energy conversion.

  8. Analysis of the linear stability of compressible boundary layers using the PSE. [parabolic stability equations

    NASA Technical Reports Server (NTRS)

    Bertolotti, F. P.; Herbert, TH.

    1991-01-01

    The application of linearized parabolic stability equations (PSE) to compressible flow is considered. The effect of mean-flow nonparallelism is found to be weak on 2D waves and strong on 3D waves. Results for a single choice of free-stream parameters that corresponds to the atmospheric conditions at 15,000 m above sea level are presented.

  9. Shear effects in the evaporatively driven cloud-top mixing layer

    NASA Astrophysics Data System (ADS)

    Mellado, Juan Pedro

    2013-11-01

    A stably stratified shear layer destabilized locally by moist convection is studied using direct numerical simulations as a model to investigate the role of evaporative cooling at the top of stratocumulus clouds in the presence of vertical mean shear. Velocity and time scales are obtained from the study of the vertical structure. It is found that, overlapping with the background shear layer that has been often documented in the cloud-free cases, with a thickness (1 / 3) (Δu) 2 / Δb , where Δu and Δb are the velocity and buoyancy increments across the cloud top, the system develops a turbulence layer that is dominated by free convection inside the cloud and by shear production inside the relatively thin overlap region. As turbulence intensifies, the turbulence layer encroaches upwards into the background shear layer and defines thereby the entrainment velocity. This encroachment is well characterized by the penetration length formed with the in-cloud convective velocity and the buoyancy frequency inside the background shear layer. Consistently, the turbulence intensity inside the overlap region follows a mixed scaling combining the background mean shear and the in-cloud convective velocity.

  10. Mixed Layer Dynamics and the Diurnal Cycle in the Equatorial Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Wenegrat, J. O.; McPhaden, M. J.

    2014-12-01

    A unique 8-month data set of moored near-surface velocity observations is used to examine the diurnal cycle of near-surface shear and stratification at 0°N, 23°W in the central equatorial Atlantic Ocean. The ocean diurnal cycle is strongly modulated by seasonal variability in wind forcing, and during trade wind conditions descending diurnal shear layers are observed regularly in the late afternoon and evening. These descending shear layers are associated with reduced Richardson number, and marginal instability of the equatorial undercurrent below the mixed layer. The significance of these findings for deep-cycle turbulence in the central equatorial Atlantic will be discussed in relation to recent work from the Pacific.

  11. Interactions between a tropical mixed boundary layer and cumulus convection in a radiative-convective model

    SciTech Connect

    Dean, C.L.

    1993-05-01

    This report details a radiative-convective model, combining previously developed cumulus, stable cloud and radiation parameterizations with a boundary layer scheme, which was developed in the current study. The cloud model was modified to incorporate the effects of both small and large clouds. The boundary layer model was adapted from a mixed layer model was only slightly modified to couple it with the more sophisticated cloud model. The model was tested for a variety of imposed divergence profiles, which simulate the regions of the tropical ocean from approximately the intertropical Convergence Zone (ITCZ) to the subtropical high region. The sounding used to initialize the model for most of the runs is from the trade wind region of ATEX. For each experiment, the model was run with a timestep of 300 seconds for a period of 7 days.

  12. Mixing and reaction in the subsonic 2-D turbulent free shear layer

    NASA Astrophysics Data System (ADS)

    Frieler, Clifford Eugene

    Several aspects of mixing and reaction in a turbulent two-dimensional shear layer have been studied. Experiments have been performed with reacting H2, F2, and NO in inert diluent gases. Sensing the heat release by these reactions, several aspects of the mixing process can be examined without the usual resolution limitations. For example, in contrast with direct measurements of composition, the amount of mixed fluid can be conservatively estimated with the results of the "flip" experiments. These have been performed over a range of density ratios, Reynolds numbers and heat release.The effects of initial conditions are of primary importance when comparisons to other studies are undertaken. Aspects as fundamental as growth rate of the turbulent region, or as obscure as the mixed fluid flux ratio depend strongly on the boundary conditions of this flow. These effects are examined in conjunction with those of Reynolds number and density ratio. For most cases studied here, tripping of the high speed boundary layer led to growth rate decreases. An exception was found for the case of high density ratio where the opposite effect was observed. This anomalous result occurred at conditions under which a new mode of instability has been shown to exist. Parallels exist between this unusual result and those of Batt in the uniform density case.An extensive study of the effects of density ratio on the mixing and reaction in the 2-D shear layer has been performed. Results indicate that several aspects of the mixing process are remarkably similar. Profiles of mixed fluid change little as the density ratio varies by a factor of 30. The integral amount of mixed fluid varies less than 6% for all density ratios examined. This insensitivity contrasts with that of the profiles of mixed fluid composition. While having very similar shapes the profiles are offset by an amount which depends very strongly upon the density ratio. The entrainment into the mixing layer has also been examined. Power

  13. Simulation-Based Stochastic Sensitivity Analysis of a Mach 4.5 Mixed-Compression Intake Performance

    NASA Astrophysics Data System (ADS)

    Kato, H.; Ito, K.

    2009-01-01

    A sensitivity analysis of a supersonic mixed-compression intake of a variable-cycle turbine-based combined cycle (TBCC) engine is presented. The TBCC engine is de- signed to power a long-range Mach 4.5 transport capable of antipodal missions studied in the framework of an EU FP6 project, LAPCAT. The nominal intake geometry was designed using DLR abpi cycle analysis pro- gram by taking into account various operating require- ments of a typical mission profile. The intake consists of two movable external compression ramps followed by an isolator section with bleed channel. The compressed air is then diffused through a rectangular-to-circular subsonic diffuser. A multi-block Reynolds-averaged Navier- Stokes (RANS) solver with Srinivasan-Tannehill equilibrium air model was used to compute the total pressure recovery and mass capture fraction. While RANS simulation of the nominal intake configuration provides more realistic performance characteristics of the intake than the cycle analysis program, the intake design must also take into account in-flight uncertainties for robust intake performance. In this study, we focus on the effects of the geometric uncertainties on pressure recovery and mass capture fraction, and propose a practical approach to simulation-based sensitivity analysis. The method begins by constructing a light-weight analytical model, a radial-basis function (RBF) network, trained via adaptively sampled RANS simulation results. Using the RBF network as the response surface approximation, stochastic sensitivity analysis is performed using analysis of variance (ANOVA) technique by Sobol. This approach makes it possible to perform a generalized multi-input- multi-output sensitivity analysis based on high-fidelity RANS simulation. The resulting Sobol's influence indices allow the engineer to identify dominant parameters as well as the degree of interaction among multiple parameters, which can then be fed back into the design cycle.

  14. Counterintuitive effect of fall mixed layer deepening on eukaryotic new production in the Sargasso Sea

    NASA Astrophysics Data System (ADS)

    Fawcett, S. E.; Lomas, M. W.; Ward, B. B.; Sigman, D. M.

    2012-12-01

    The Sargasso Sea is characterized by a short period of deep vertical mixing in the late winter and early spring, followed by strong thermal stratification during the summer. Stratification persists into the fall, impeding the upward flux of nitrate from depth so that recycled forms of nitrogen (N) such as ammonium are thought to support most primary production. We collected particles from surface waters during March, July, October, and December, used flow cytometry to separate the prokaryotic and eukaryotic phytoplankton, and analyzed their respective 15N/14N. In all months, the 15N/14N of the prokaryotic genera, Prochlorococcus and Synechococcus, was low, indicative of reliance on recycled N throughout the year. In July, the 15N/14N of eukaryotic phytoplankton was variable but consistently higher than that of the prokaryotes, reflecting eukaryotic consumption of subsurface nitrate. Two eukaryotic profiles from October and December were similar to those from July. In three other fall profiles, the eukaryotes had a 15N/14N similar to that of the prokaryotes, suggesting a switch toward greater reliance on recycled N. This change in the dominant N source supporting eukaryotic production appears to be driven by the density structure of the upper water column. The very shallow low-density surface "mixed layer" (≤20 m) that develops in early-to-mid summer does not contribute to stratification at the base of the euphotic zone, and subsurface nitrate can mix up into the lower euphotic zone, facilitating continued production. The deepening of the mixed layer into the fall, typically taken as an indication of weaker overall stratification, actually strengthens the isolation of the euphotic zone as a whole, reducing the upward supply of nitrate to the photosynthetically active layer. The same counterintuitive dynamic explains the latitudinal patterns in a set of three October depth profiles. Two northern stations (32°N and 27°N) were characterized by a thick, low

  15. Artificial Fluid Properties for Large-Eddy Simulation of Compressible Turbulent Mixing

    SciTech Connect

    Cook, A W

    2007-01-08

    An alternative methodology is described for Large-Eddy Simulation of flows involving shocks, turbulence and mixing. In lieu of filtering the governing equations, it is postulated that the large-scale behavior of an ''LES'' fluid, i.e., a fluid with artificial properties, will be similar to that of a real fluid, provided the artificial properties obey certain constraints. The artificial properties consist of modifications to the shear viscosity, bulk viscosity, thermal conductivity and species diffusivity of a fluid. The modified transport coefficients are designed to damp out high wavenumber modes, close to the resolution limit, without corrupting lower modes. Requisite behavior of the artificial properties is discussed and results are shown for a variety of test problems, each designed to exercise different aspects of the models. When combined with a 10th-order compact scheme, the overall method exhibits excellent resolution characteristics for turbulent mixing, while capturing shocks and material interfaces in crisp fashion.

  16. Artificial fluid properties for large-eddy simulation of compressible turbulent mixing

    NASA Astrophysics Data System (ADS)

    Cook, Andrew W.

    2007-05-01

    An alternative methodology is described for large-eddy simulation (LES) of flows involving shocks, turbulence, and mixing. In lieu of filtering the governing equations, it is postulated that the large-scale behavior of a LES fluid, i.e., a fluid with artificial properties, will be similar to that of a real fluid, provided the artificial properties obey certain constraints. The artificial properties consist of modifications to the shear viscosity, bulk viscosity, thermal conductivity, and species diffusivity of a fluid. The modified transport coefficients are designed to damp out high wavenumber modes, close to the resolution limit, without corrupting lower modes. Requisite behavior of the artificial properties is discussed and results are shown for a variety of test problems, each designed to exercise different aspects of the models. When combined with a tenth-order compact scheme, the overall method exhibits excellent resolution characteristics for turbulent mixing, while capturing shocks and material interfaces in a crisp fashion.

  17. Diffusivity in turbulent fluid containing two dominant scales, and compressible shear layer according to a kinetic theory

    NASA Technical Reports Server (NTRS)

    Chung, P. M.

    1976-01-01

    The solution of the two nonequilibrium-degree kinetic equation was first determined for the effective length scale and turbulence energy for a spatially homogeneous turbulence field with two characteristic length scales, where the source for one family of eddies exists. This solution was applied to the evaluation of the eddy diffusivity in the combustion chamber of an internal combustion engine. The result was compared with another existing solution. This was carried out to demonstrate the feasibility of obtaining an effective length-scale equation within the context of the kinetic theory. A formulation and partial solution of the compressible plane shear layer are also presented.

  18. Simultaneous and instantaneous measurement of velocity and density in Rayleigh-Taylor mixing layers

    NASA Astrophysics Data System (ADS)

    Kraft, Wayne Neal

    There are two coupled primary objectives for this study of buoyancy-driven turbulence. The first objective is to create a new diagnostic for collection of measurements to capture the physics of Rayleigh-Taylor (RT) mixing. The second objective is to use the new diagnostic to specifically elucidate the physics of large Atwood number, At = (rho1 - rho 2)/(rho1+ rho2), RT mixing. Both of these objectives have been satisfied through the development of a new hot-wire diagnostic to study buoyancy-driven turbulence in a statistically steady gas channel of helium and air (0.03 ≤ At ≤ 0.6). The capability of the diagnostic to simultaneously and instantaneously measure turbulent velocity and density fluctuations allows for a unique investigation into the dynamics of Rayleigh-Taylor mixing layers at large A t, through measurements of turbulence and mixing statistics. The new hot-wire diagnostic uses temperature as a fluid marker for helium and air, which is possible due to the Lewis number ˜ 1 (Le = ratio of thermal diffusivity to mass diffusivity) for helium and air, and the new diagnostic has been validated in an At = 0.03 mixing layer. The energy density spectrum of rho'v', measured experimentally for the first time in RT mixing, is found to closely follow the energy distribution of v', up to the Reynolds numbers investigated (Reh = (2h)3/2 gAt/6 /vmix ˜ 1450). Large A t experiments, with At = 0.6, have also been achieved for the first time in a miscible RT mixing layer. An asymmetric penetration of the bubbles (rising fluid) and spikes (falling fluid) has been observed, resulting in measured self similar growth parameters alpha b = 0.060 and alphas = 0.088 for the bubbles and spikes, respectively. The first experimental measurements of turbulent velocity and density fluctuations for the large At case, show a strong similarity to lower At behaviors when normalized. However conditional statistics, which separate the bubble (light fluid) and spike (heavy fluid

  19. Observation and modeling of mixing-layer development in HED blast-wave-driven shear flow

    NASA Astrophysics Data System (ADS)

    di Stefano, Carlos

    2013-10-01

    This talk describes work exploring the sensitivity to initial conditions of hydrodynamic mixing-layer growth due to shear flow in the high-energy-density regime. This work features an approach in two parts, experimental and theoretical. First, an experiment, conducted at the OMEGA-60 laser facility, seeks to measure the development of such a mixing layer. This is accomplished by placing a layer of low-density (initially of either 0.05 or 0.1 g/cm3, to vary the system's Atwood number) carbon foam against a layer of higher-density (initially 1.4 g/cm3) polyamide-imide that has been machined to a nominally-flat surface at its interface with the foam. Inherent roughness of this surface's finish is precisely measured and varied from piece to piece. Ten simultaneous OMEGA beams, comprising a 4.5 kJ, 1-ns pulse focused to a roughly 1-mm-diameter spot, irradiate a thin polycarbonate ablator, driving a blast wave into the foam, parallel to its interface with the polyamide-imide. The ablator is framed by a gold washer, such that the blast wave is driven only into the foam, and not into the polyamide-imide. The subsequent forward motion of the shocked foam creates the desired shear effect, and the system is imaged by X-ray radiography 35 ns after the beginning of the driving laser pulse. Second, a simulation is performed, intending to replicate the flow observed in the experiment as closely as possible. Using the resulting simulated flow parameters, an analytical model can be used to predict the evolution of the mixing layer, as well as track the motion of the fluid in the experiment prior to the snapshot seen in the radiograph. The ability of the model to predict growth of the mixing layer under the various conditions observed in the experiment is then examined. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52- 08NA28616, by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE

  20. Characteristics and Evolution of Passive Tracers in the Oceanic Mixed Layer

    NASA Astrophysics Data System (ADS)

    Smith, Katherine; Hamlington, Peter; Fox-Kemper, Baylor

    2015-11-01

    Ocean tracers such as CO2 and plankton reside primarily in the mixed layer where air-sea gas exchange occurs and light is plentiful for photosynthesis. There can be substantial heterogeneity in the distributions of these tracers due to turbulent mixing, particularly in the submesoscale range where partly geostrophic eddies and small-scale 3D turbulence are both active. In this talk, LES spanning scales from 20km down to 5m are used to examine the role of turbulent mixing on nonreactive passive ocean tracers. The simulations include the effects of both wave-driven Langmuir turbulence and submesoscale eddies, and tracers with different initial and boundary conditions are examined. Tracer properties are characterized using spatial fields, statistics, multiscale fluxes, and spectra, and results show that passive tracer mixing depends on air-sea flux rate, release depth, and flow regime. The results indicate that while submesoscale eddies transport buoyancy upward to extract potential energy, the same is not true of passive tracers, whose entrainment is instead suppressed. Early in the evolution of some tracers, counter-gradient transport occurs co-located with regions of negative potential vorticity, suggesting that symmetric instabilities may act to oppose turbulent mixing.

  1. 2D dynamical arrest transition in a mixed nanoparticle-phospholipid layer studied in real and momentum spaces.

    PubMed

    Orsi, Davide; Guzmán, Eduardo; Liggieri, Libero; Ravera, Francesca; Ruta, Beatrice; Chushkin, Yuriy; Rimoldi, Tiziano; Cristofolini, Luigi

    2015-01-01

    We investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For this, we combine micro-tracking in real-space with measurement in momentum-space via x-ray photon-correlation spectroscopy and Digital Fourier Microscopy. Using these complementary techniques, we extend the spatial range of investigation beyond the limits of each one. We find a dynamical transition from Brownian diffusion to an arrested state driven by compression, characterized by intermittent rearrangements, compatible with a repulsive glass phase. The rearrangement and relaxation of the monolayer structure results dramatically hindered by the presence of NPs, which is relevant to explain some the mechanical features observed for the dynamic surface pressure response of these systems and which can be relevant for the respiratory physiology and for future drug-delivery composite systems. PMID:26658474

  2. 2D dynamical arrest transition in a mixed nanoparticle-phospholipid layer studied in real and momentum spaces

    PubMed Central

    Orsi, Davide; Guzmán, Eduardo; Liggieri, Libero; Ravera, Francesca; Ruta, Beatrice; Chushkin, Yuriy; Rimoldi, Tiziano; Cristofolini, Luigi

    2015-01-01

    We investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For this, we combine micro-tracking in real-space with measurement in momentum-space via x-ray photon-correlation spectroscopy and Digital Fourier Microscopy. Using these complementary techniques, we extend the spatial range of investigation beyond the limits of each one. We find a dynamical transition from Brownian diffusion to an arrested state driven by compression, characterized by intermittent rearrangements, compatible with a repulsive glass phase. The rearrangement and relaxation of the monolayer structure results dramatically hindered by the presence of NPs, which is relevant to explain some the mechanical features observed for the dynamic surface pressure response of these systems and which can be relevant for the respiratory physiology and for future drug-delivery composite systems. PMID:26658474

  3. 2D dynamical arrest transition in a mixed nanoparticle-phospholipid layer studied in real and momentum spaces

    NASA Astrophysics Data System (ADS)

    Orsi, Davide; Guzmán, Eduardo; Liggieri, Libero; Ravera, Francesca; Ruta, Beatrice; Chushkin, Yuriy; Rimoldi, Tiziano; Cristofolini, Luigi

    2015-12-01

    We investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For this, we combine micro-tracking in real-space with measurement in momentum-space via x-ray photon-correlation spectroscopy and Digital Fourier Microscopy. Using these complementary techniques, we extend the spatial range of investigation beyond the limits of each one. We find a dynamical transition from Brownian diffusion to an arrested state driven by compression, characterized by intermittent rearrangements, compatible with a repulsive glass phase. The rearrangement and relaxation of the monolayer structure results dramatically hindered by the presence of NPs, which is relevant to explain some the mechanical features observed for the dynamic surface pressure response of these systems and which can be relevant for the respiratory physiology and for future drug-delivery composite systems.

  4. Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction, volume 1. [theoretical analysis

    NASA Technical Reports Server (NTRS)

    Omori, S.

    1973-01-01

    The turbulent kinetic energy equation is coupled with boundary layer equations to solve the characteristics of compressible turbulent boundary layers with mass injection and combustion. The Reynolds stress is related to the turbulent kinetic energy using the Prandtl-Wieghardt formulation. When a lean mixture of hydrogen and nitrogen is injected through a porous plate into the subsonic turbulent boundary layer of air flow and ignited by external means, the turbulent kinetic energy increases twice as much as that of noncombusting flow with the same mass injection rate of nitrogen. The magnitudes of eddy viscosity between combusting and noncombusting flows with injection, however, are almost the same due to temperature effects, while the distributions are different. The velocity profiles are significantly affected by combustion; that is, combustion alters the velocity profile as if the mass injection rate is increased, reducing the skin-friction as a result of a smaller velocity gradient at the wall. If pure hydrogen as a transpiration coolant is injected into a rocket nozzle boundary layer flow of combustion products, the temperature drops significantly across the boundary layer due to the high heat capacity of hydrogen. At a certain distance from the wall, hydrogen reacts with the combustion products, liberating an extensive amount of heat. The resulting large increase in temperature reduces the eddy viscosity in this region.

  5. Comparison of Four Mixed Layer Mesoscale Parameterizations and the Equation for an Arbitrary Tracer

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Dubovikov, M. S.

    2011-01-01

    In this paper we discuss two issues, the inter-comparison of four mixed layer mesoscale parameterizations and the search for the eddy induced velocity for an arbitrary tracer. It must be stressed that our analysis is limited to mixed layer mesoscales since we do not treat sub-mesoscales and small turbulent mixing. As for the first item, since three of the four parameterizations are expressed in terms of a stream function and a residual flux of the RMT formalism (residual mean theory), while the fourth is expressed in terms of vertical and horizontal fluxes, we needed a formalism to connect the two formulations. The standard RMT representation developed for the deep ocean cannot be extended to the mixed layer since its stream function does not vanish at the ocean's surface. We develop a new RMT representation that satisfies the surface boundary condition. As for the general form of the eddy induced velocity for an arbitrary tracer, thus far, it has been assumed that there is only the one that originates from the curl of the stream function. This is because it was assumed that the tracer residual flux is purely diffusive. On the other hand, we show that in the case of an arbitrary tracer, the residual flux has also a skew component that gives rise to an additional bolus velocity. Therefore, instead of only one bolus velocity, there are now two, one coming from the curl of the stream function and other from the skew part of the residual flux. In the buoyancy case, only one bolus velocity contributes to the mean buoyancy equation since the residual flux is indeed only diffusive.

  6. Computation of three-dimensional compressible boundary layers to fourth-order accuracy on wings and fuselages

    NASA Technical Reports Server (NTRS)

    Iyer, Venkit

    1990-01-01

    A solution method, fourth-order accurate in the body-normal direction and second-order accurate in the stream surface directions, to solve the compressible 3-D boundary layer equations is presented. The transformation used, the discretization details, and the solution procedure are described. Ten validation cases of varying complexity are presented and results of calculation given. The results range from subsonic flow to supersonic flow and involve 2-D or 3-D geometries. Applications to laminar flow past wing and fuselage-type bodies are discussed. An interface procedure is used to solve the surface Euler equations with the inviscid flow pressure field as the input to assure accurate boundary conditions at the boundary layer edge. Complete details of the computer program used and information necessary to run each of the test cases are given in the Appendix.

  7. A possible analog to MgB2: Discovery of a predicted layered LiB via cold compression

    NASA Astrophysics Data System (ADS)

    Kolmogorov, Aleksey; Hajinazar, Samad; Angyal, Chris; Kuznetzov, Vladimir; Jephcoat, Andrew

    Stoichiometric LiB has been previously predicted to be a new synthesizable layered material with electronic and vibrational properties desired for MgB2-type superconductivity. However, previous experiments showed no signs of the proposed compound forming under high pressures. We report on the synthesis of the LiB via cold compression in the diamond anvil cell. Remarkably, the signature powder XRD peak from the new layered compound appeared above 21 GPa and remained visible down to ambient pressure upon sample quenching. Apparent stacking disorder in LiB and a stoichiometry shift in the starting LiBy (from y ~ 0.90 down to y ~ 0.75) made material characterization a challenge. Ab initio modeling allowed us to establish the pressure-dependent composition of LiBy and predict related stable structures overlooked in previous studies. Supported by NSF Grant DMR-1410514.

  8. Transfer of highly porous nanoparticle layers to various substrates through mechanical compression.

    PubMed

    Schopf, Sven O; Salameh, Samir; Mädler, Lutz

    2013-05-01

    A new two-step layer transfer process is introduced that is capable of fabricating mechanically stabilized highly porous nanoparticle layers on various substrates. In a first step titanium dioxide nanoparticles were synthesized with Flame-Spray-Pyrolysis and accumulated on a filter paper in the gas phase. In a second step this highly porous filter cake is subsequently transferred to a final substrate via low pressure lamination at room temperature. This leads to mechanical restructuring and stabilization of the porous layer. Pore size analysis indicates homogenization of the layers through rearrangement of the aggregates inside the layers that increases with applied pressure. Additionally, the Young's moduli of the layers were quantified through Colloidal-Probe-Technique indentation measurements with an Atomic-Force-Microscope. The highest lamination pressure of 2.5 MPa resulted in triplication of the Young's modulus. The results show that our novel two-step layer transfer process leads to mechanically stabilized layers that preserve their high porosity. Through the decoupling of the high temperature nanoparticle synthesis and the final substrate the process also enables the possibility to apply temperature sensitive substrates such as polypropylene foil. PMID:23532446

  9. Stability and Process of Destruction of Compressed Plate of Layered Composite Materials With Defects

    NASA Astrophysics Data System (ADS)

    Bokhoeva, L. A.; Rogov, V. E.; Chermoshentseva, A. S.; Lobanov, D. V.

    2016-08-01

    Interlayer defects in composite materials are a pressing problem, which affecting their performance characteristics. In this research, we considered the problem of the stability and of the fracture process of the compressed thin plate made of laminated composite materials with the interlayer defects. In this research we had got a critical equation for a plate with interlayer defect. The experiment showed the effect and the quantity of nano-dispersed additives on the mechanical properties of composite materials with interlayer defects.

  10. Boundary-layer turbulence modeling and vorticity dynamics: I. A kangaroo-process mixing model of boundary-layer turbulence

    NASA Astrophysics Data System (ADS)

    Dekker, H.; de Leeuw, G.; van den Brink, A. Maassen

    A nonlocal turbulence transport theory is presented by means of a novel analysis of the Reynolds stress, inter alia involving the construct of a sample path space and a stochastic hypothesis. An analytical sampling rate model (satisfying exchange) and a nonlinear scaling relation (mapping the path space onto the boundary layer) lead to an integro-differential equation for the mixing of scalar densities, which represents fully-developed boundary-layer turbulence as a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process. The underlying near-wall behavior (i.e. for y +→0) of fluctuating velocities fully agrees with recent direct numerical simulations. The model involves a scaling exponent ɛ, with ɛ→∞ in the diffusion limit. For the (partly analytical) solution for the mean velocity profile, excellent agreement with the experimental data yields ɛ≈0.58. The significance of ɛ as a turbulence Cantor set dimension (in the logarithmic profile region, i.e. for y +→∞) is discussed.

  11. Numerical simulation of small-scale mixing processes in the upper ocean and atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Druzhinin, O.; Troitskaya, Yu; Zilitinkevich, S.

    2016-02-01

    The processes of turbulent mixing and momentum and heat exchange occur in the upper ocean at depths up to several dozens of meters and in the atmospheric boundary layer within interval of millimeters to dozens of meters and can not be resolved by known large- scale climate models. Thus small-scale processes need to be parameterized with respect to large scale fields. This parameterization involves the so-called bulk coefficients which relate turbulent fluxes with large-scale fields gradients. The bulk coefficients are dependent on the properties of the small-scale mixing processes which are affected by the upper-ocean stratification and characteristics of surface and internal waves. These dependencies are not well understood at present and need to be clarified. We employ Direct Numerical Simulation (DNS) as a research tool which resolves all relevant flow scales and does not require closure assumptions typical of Large-Eddy and Reynolds Averaged Navier-Stokes simulations (LES and RANS). Thus DNS provides a solid ground for correct parameterization of small-scale mixing processes and also can be used for improving LES and RANS closure models. In particular, we discuss the problems of the interaction between small-scale turbulence and internal gravity waves propagating in the pycnocline in the upper ocean as well as the impact of surface waves on the properties of atmospheric boundary layer over wavy water surface.

  12. Mixed Layers of Nonionic Dendritic Amphiphiles and DPPC at the Water Surface.

    PubMed

    Degen, Patrick; Wieland, D C Florian; Strötges, Christian

    2015-11-01

    Nonionic dendritic amphiphiles that self-assemble into defined supramolecular aggregates are useful for the efficient solubilization of active agents, for example, in drug delivery. We investigated a new class of dendritic amphiphiles based on a hydrophilic polyol dendron head connected to a two-chain hydrophobic block. In analogy to phospholipids, these molecules form well-organized layers in bulk (vesicles) or at the water surface (Langmuir monolayer). The actual study focuses on the phase behavior and microscopic structure of mixed Langmuir layers of theses dendritic amphiphiles with the well-known phospholipid DPPC. The combination of surface pressure area isotherms with X-ray grazing incident diffraction and Brewster angle microscopy gives us information on the phase behavior of the mixed monolayers and the orientation of the amphiphiles inside the condensed domains with molecular resolution. We could prove that the dendritic generation and, by this, the headgroup size of the amphiphilic molecules have a significant influence on their interaction with DPPC at the air-water interface. Thus, our findings are important for the understanding of mixed lipid membranes in general as well as for the preparation of artificial membranes and vesicles with adjustable properties, e.g., their drug delivery potential. PMID:26447650

  13. Vortex-scalar element calculations of a diffusion flame stabilized on a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Ghoniem, Ahmed F.; Givi, Peyman

    1987-01-01

    The vortex-scalar element method, a scheme which utilizes vortex elements to discretize the region of high vorticity and scalar elements to represent species or temperature fields, is utilized in the numerical simulations of a two-dimensional reacting mixing layer. Computations are performed for a diffusion flame at high Reynolds and Peclet numbers without resorting to turbulence models. In the nonreacting flow, the mean and fluctuation profiles of a conserved scalar show good agreement with experimental measurements. Results for the reacting flow indicate that for temperature independent kinetics, the chemical reaction begins immediately downstream of the splitter plate where mixing starts. Results for the reacting flow with Arrhenius kinetics show an ignition delay, which depends on reactant temperature, before significant chemical reaction occurs. Harmonic forcing changes the structure of the layer, and concomitantly the rates of mixing and reaction, in accordance with experimental results. Strong stretch within the braids in the nonequilibrium kinetics case causes local flame quenching due to the temperature drop associated with the large convective fluxes.

  14. Data/model integration for vertical mixing in the stable Arctic boundary layer

    SciTech Connect

    Barr, S.; ReVelle, D.O.; Kao, C.Y.J.; Bigg, E.K.

    1998-12-31

    This is the final report of a short Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Data on atmospheric trace constituents and the vertical structure of stratus clouds from a 1996 expedition to the central Arctic reveal mechanisms of vertical mixing that have not been observed in mid-latitudes. Time series of the altitude and thickness of summer arctic stratus have been observed using an elastic backscatter lidar aboard an icebreaker. With the ship moored to the pack ice during 14 data collection stations and the lidar staring vertically, the time series represent advected cloud fields. The lidar data reveal a significant amount of vertical undulation in the clouds, strongly suggestive of traveling waves in the buoyantly damped atmosphere that predominates in the high Arctic. Concurrent observations of trace gases associated with the natural sulfur cycle (dimethyl sulfide, SO{sub 2}, NH{sub 3}, H{sub 2}O{sub 2}) and aerosols show evidence of vertical mixing events that coincide with a characteristic signature in the cloud field that may be called dropout or lift out. A segment of a cloud deck appears to be relocated from the otherwise quasicontinuous layer to another altitude a few hundred meters lower or higher. Atmospheric models have been applied to identify the mechanism that cause the dropout phenomenon and connect it dynamically to the surface layer mixing.

  15. Effects of High-frequency Wind Sampling on Simulated Mixed Layer Depth and Upper Ocean Temperature

    NASA Technical Reports Server (NTRS)

    Lee, Tong; Liu, W. Timothy

    2005-01-01

    Effects of high-frequency wind sampling on a near-global ocean model are studied by forcing the model with a 12 hourly averaged wind product and its 24 hourly subsamples in separate experiments. The differences in mixed layer depth and sea surface temperature resulting from these experiments are examined, and the underlying physical processes are investigated. The 24 hourly subsampling not only reduces the high-frequency variability of the wind but also affects the annual mean wind because of aliasing. While the former effect largely impacts mid- to high-latitude oceans, the latter primarily affects tropical and coastal oceans. At mid- to high-latitude regions the subsampled wind results in a shallower mixed layer and higher sea surface temperature because of reduced vertical mixing associated with weaker high-frequency wind. In tropical and coastal regions, however, the change in upper ocean structure due to the wind subsampling is primarily caused by the difference in advection resulting from aliased annual mean wind, which varies with the subsampling time. The results of the study indicate a need for more frequent sampling of satellite wind measurement and have implications for data assimilation in terms of identifying the nature of model errors.

  16. Effect of Strong Acid Functional Groups on Electrode Rise Potential in Capacitive Mixing by Double Layer Expansion

    SciTech Connect

    Hatzell, Marta C.; Raju, Muralikrishna; Watson, Valerie J.; Stack, Andrew G.; van Duin, Adri C. T.; Logan, Bruce E.

    2014-11-03

    We report that the amount of salinity-gradient energy that can be obtained through capacitive mixing based on double layer expansion depends on the extent the electric double layer (EDL) is altered in a low salt concentration (LC) electrolyte (e.g., river water). We show that the electrode-rise potential, which is a measure of the EDL perturbation process, was significantly (P = 10–5) correlated to the concentration of strong acid surface functional groups using five types of activated carbon. Electrodes with the lowest concentration of strong acids (0.05 mmol g–1) had a positive rise potential of 59 ± 4 mV in the LC solution, whereas the carbon with the highest concentration (0.36 mmol g–1) had a negative rise potential (₋31 ± 5 mV). Chemical oxidation of a carbon (YP50) using nitric acid decreased the electrode rise potential from 46 ± 2 mV (unaltered) to ₋6 ± 0.5 mV (oxidized), producing a whole cell potential (53 ± 1.7 mV) that was 4.4 times larger than that obtained with identical electrode materials (from 12 ± 1 mV). Changes in the EDL were linked to the behavior of specific ions in a LC solution using molecular dynamics and metadynamics simulations. The EDL expanded in the LC solution when a carbon surface (pristine graphene) lacked strong acid functional groups, producing a positive-rise potential at the electrode. In contrast, the EDL was compressed for an oxidized surface (graphene oxide), producing a negative-rise electrode potential. In conclusion, these results established the linkage between rise potentials and specific surface functional groups (strong acids) and demonstrated on a molecular scale changes in the EDL using oxidized or pristine carbons.

  17. Effect of Strong Acid Functional Groups on Electrode Rise Potential in Capacitive Mixing by Double Layer Expansion

    DOE PAGESBeta

    Hatzell, Marta C.; Raju, Muralikrishna; Watson, Valerie J.; Stack, Andrew G.; van Duin, Adri C. T.; Logan, Bruce E.

    2014-11-03

    We report that the amount of salinity-gradient energy that can be obtained through capacitive mixing based on double layer expansion depends on the extent the electric double layer (EDL) is altered in a low salt concentration (LC) electrolyte (e.g., river water). We show that the electrode-rise potential, which is a measure of the EDL perturbation process, was significantly (P = 10–5) correlated to the concentration of strong acid surface functional groups using five types of activated carbon. Electrodes with the lowest concentration of strong acids (0.05 mmol g–1) had a positive rise potential of 59 ± 4 mV in themore » LC solution, whereas the carbon with the highest concentration (0.36 mmol g–1) had a negative rise potential (₋31 ± 5 mV). Chemical oxidation of a carbon (YP50) using nitric acid decreased the electrode rise potential from 46 ± 2 mV (unaltered) to ₋6 ± 0.5 mV (oxidized), producing a whole cell potential (53 ± 1.7 mV) that was 4.4 times larger than that obtained with identical electrode materials (from 12 ± 1 mV). Changes in the EDL were linked to the behavior of specific ions in a LC solution using molecular dynamics and metadynamics simulations. The EDL expanded in the LC solution when a carbon surface (pristine graphene) lacked strong acid functional groups, producing a positive-rise potential at the electrode. In contrast, the EDL was compressed for an oxidized surface (graphene oxide), producing a negative-rise electrode potential. In conclusion, these results established the linkage between rise potentials and specific surface functional groups (strong acids) and demonstrated on a molecular scale changes in the EDL using oxidized or pristine carbons.« less

  18. Effect of strong acid functional groups on electrode rise potential in capacitive mixing by double layer expansion.

    PubMed

    Hatzell, Marta C; Raju, Muralikrishna; Watson, Valerie J; Stack, Andrew G; van Duin, Adri C T; Logan, Bruce E

    2014-12-01

    The amount of salinity-gradient energy that can be obtained through capacitive mixing based on double layer expansion depends on the extent the electric double layer (EDL) is altered in a low salt concentration (LC) electrolyte (e.g., river water). We show that the electrode-rise potential, which is a measure of the EDL perturbation process, was significantly (P = 10(–5)) correlated to the concentration of strong acid surface functional groups using five types of activated carbon. Electrodes with the lowest concentration of strong acids (0.05 mmol g(–1)) had a positive rise potential of 59 ± 4 mV in the LC solution, whereas the carbon with the highest concentration (0.36 mmol g(–1)) had a negative rise potential (−31 ± 5 mV). Chemical oxidation of a carbon (YP50) using nitric acid decreased the electrode rise potential from 46 ± 2 mV (unaltered) to −6 ± 0.5 mV (oxidized), producing a whole cell potential (53 ± 1.7 mV) that was 4.4 times larger than that obtained with identical electrode materials (from 12 ± 1 mV). Changes in the EDL were linked to the behavior of specific ions in a LC solution using molecular dynamics and metadynamics simulations. The EDL expanded in the LC solution when a carbon surface (pristine graphene) lacked strong acid functional groups, producing a positive-rise potential at the electrode. In contrast, the EDL was compressed for an oxidized surface (graphene oxide), producing a negative-rise electrode potential. These results established the linkage between rise potentials and specific surface functional groups (strong acids) and demonstrated on a molecular scale changes in the EDL using oxidized or pristine carbons. PMID:25365360

  19. Imaging of Compressed Pure-CH Shells and CH Shells with Titanium-Doped Layers on OMEGA

    NASA Astrophysics Data System (ADS)

    Smalyuk, V. A.; Yaakobi, B.; Goncharov, V. N.; Delettrez, J. A.; Marshall, F. J.; Meyerhofer, D. D.

    1999-11-01

    The compressed shell integrity of spherical targets has been studied using the 60-beam, 30-kJ UV, OMEGA laser system. The emission from the hot core has been imaged through the cold shell at two narrow, x-ray energy bands, absorbing and nonabsorbing by the shell, allowing nonuniformities in the core emission and the cold shell areal density to be measured. Images of the target have been obtained using a pinhole-array with K-edge filters. The x-ray energies used are around 2.8 and 4.5 keV for pure-CH shells, and around 4.5 and 6 keV for titanium-doped layers. Additional images of the shell are obtained with a framed monochromatic x-ray microscope and a time-integrated crystal-spectrometer/pinhole-array combination. We will present measurements of the compressed shell integrity at the stagnation stage of spherical implosions by varying the position of the titanium-doped layer within the shell, by varying the thickness of the CH shell, and by using two different laser pulse shapes. The experimental results will be compared with 2-D (ORCHID) hydrodynamic simulations. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460, the University of Rochester, and the New York State Energy Research and Development Authority.

  20. Evaluation of layered and mixed passive treatment systems for acid mine drainage.

    PubMed

    Jeen, Sung-Wook; Mattson, Bruce

    2016-11-01

    Laboratory column tests for passive treatment systems for mine drainage from a waste rock storage area were conducted to evaluate suitable reactive mixture, system configuration, effects of influent water chemistry, and required residence time. Five columns containing straw, chicken manure, mushroom compost, and limestone (LS), in either layered or mixed configurations, were set up to simulate the treatment system. The results showed that all of the five columns removed metals of concern (i.e. Al, Cd, Co, Cu, Fe, Ni, and Zn) with a residence time of 15 h and greater. Reaction mechanisms responsible for the removal of metals may include sulfate reduction and subsequent sulfide precipitation, precipitation of secondary carbonates and hydroxides, co-precipitation, and sorption on organic substrates and secondary precipitates. The results suggest that the mixed systems containing organic materials and LS perform better than the layered systems, sequentially treated by organic and LS layers, due to the enhanced pH adjustment, which is beneficial to bacterial activity and precipitation of secondary minerals. The column tests provide a basis for the design of a field-scale passive treatment system, such as a reducing and alkalinity producing system or a permeable reactive barrier. PMID:26998668

  1. Evaluation of the retinal nerve fibre layer and ganglion cell complex thickness in pituitary macroadenomas without optic chiasmal compression

    PubMed Central

    Cennamo, G; Auriemma, R S; Cardone, D; Grasso, L F S; Velotti, N; Simeoli, C; Di Somma, C; Pivonello, R; Colao, A; de Crecchio, G

    2015-01-01

    Purpose The aim of this prospective study was to measure the thickness of the circumpapillary retinal nerve fibre layer (cpRNFL) and the ganglion cell complex (GCC) using spectral domain optical coherence tomography (SD-OCT) in a cohort of consecutive de novo patients with pituitary macroadenomas without chiasmal compression. Patients and methods Twenty-two consecutive patients with pituitary macroadenoma without chiasmal compression (16 men, 6 women, aged 45.2±14.6 years, 43 eyes) entered the study between September 2011 and June 2013. Among them, 31.8% harboured a growth hormone-secreting pituitary adenoma, 27.3% a prolactin-secreting pituitary adenoma, 27.3% a corticotrophin-secreting pituitary adenoma, and 13.6% a non-secreting pituitary tumour. Eighteen subjects (nine females, nine males, mean age 36.47±6.37 years; 33 eyes) without pituitary adenoma, with normal ophthalmic examination, served as controls. In both patients and controls, cpRNFL and GCC thicknesses were measured by SD-OCT. Results Patients were significantly older (P=0.02) than controls. Best corrected visual acuity, intraocular pressure, colour fundus photography, and automatic perimetry test were within the normal range in patients and controls. Conversely, cpRNFL (P=0.009) and GCC (P<0.0001) were significantly thinner in patients than in controls. The average GCC (r=0.306, P=0.046) significantly correlated with the presence of arterial hypertension. OCT parameters did not differ significantly between patients with a tumour volume above the median and those with a tumour volume below the median. Conclusion Pituitary macroadenomas, even in the absence of chiasmal compression, may induce GCC and retinal nerve fibre layer thinning. SD-OCT may have a role in the early diagnosis and management of patients with pituitary tumours. PMID:25853400

  2. What percentage of the oceanic mixed layer is accessible to marine Lidar? Global and the Gulf of Mexico prospective.

    PubMed

    Bogucki, D J; Spiers, G

    2013-10-01

    The oceanic mixed layer is a nearly homogenous region of the upper ocean which, in principle, has a little or no variation in turbulence strength, temperature or density with depth. This layer mediates oceanic fluxes of gas, momentum and heat. Here, based on the chosen marine Lidar system, we have carried out estimates of the depth penetration of the Lidar when compared to the local mixed layer depth. On average, we have found that at least 50% of the global oceanic mixed layer depth is accessible to the Lidar observations. When operating in a single scattering mode, which is more attenuating but more amenable to analysis, the modeled Lidar was found to access 0.4 of global mixed layer depth in half of the cases. The single scattering Lidar was found to access a large fraction of the equatorial mixed layer - a region very important when addressing global climatic issues. In a coastal environment such as the Gulf of Mexico the single scattering Lidar was found to penetrate upper half of the mixed layer, underscoring the potential for Lidar to address environmental issues there.

  3. Band gap and refractive index tunability in thallium based layered mixed crystals

    SciTech Connect

    Gasanly, N. M.

    2015-07-21

    Compositional variation of the band gap energy and refractive index of TlMeX{sub 2}-type (Me = Ga or In and X = S or Se) layered mixed crystals have been studied by the transmission and reflection measurements in the wavelength range of 400–1100 nm. The analysis of absorption data of TlGa{sub 1-x}In{sub x}Se{sub 2}, TlGa(S{sub 1−x}Se{sub x}){sub 2}, TlGa{sub 1−x}In{sub x}S{sub 2}, and TlIn(Se{sub 1−x}S{sub x}){sub 2} mixed crystals revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps of mixed crystals decrease at the replacing of gallium atoms by indium and of sulfur atoms by selenium ones. Through the similar replacing of atoms (smaller atoms by larger ones) in the studied mixed crystals, the refractive index shows the quite opposite behavior.

  4. Effect of wave-induced Stokes drift on the dynamics of ocean mixed layer

    NASA Astrophysics Data System (ADS)

    Wang, Zhifeng; Wu, Kejian; Dong, Sheng; Deng, Zeng'an; Zhang, Xiaoshuang

    2015-01-01

    The wave-forcing `Coriolis-Stokes forcing' and `Stokes-vortex force' induced by Stokes drift affect the upper ocean jointly. To study the effect of the wave-induced Stokes drift on the dynamics of the ocean mixed layer, a new three-dimensional (3D) numerical model is derived using the primitive basic equations and Eulerian wave averaging. The Princeton Ocean Model (POM), a 3D primitive equation ocean model is used with the upper wave-averaged basic equations. The global ocean circulation is simulated using the POM model, and the Stokes drift is evaluated based on the wave data generated by WAVEWATCH III. We compared simulations with and without the Stokes drift. The results show that the magnitude of the Stokes drift is comparable with the Eulerian mean current. Including the Stokes drift in the ocean model affects both the Eulerian current and the Lagranian drift and causes the vertical mixing coefficients to increase.

  5. Fractal interfaces and product generation in the two dimensional mixing layer

    NASA Technical Reports Server (NTRS)

    Jimenez, Javier; Martel, Carlos

    1991-01-01

    The dependence of product generation on Peclet and Reynolds numbers in a numerically simulated, reacting, two dimensional, temporally growing mixing layer is related theoretically to the fractal dimension of the passive scalar interfaces. This relation is verified using product generation measurements and dimensions derived from a standard box counting technique. A transition from a low initial dimension to a higher one of approximately 5/3 is identified and shown to be associated to the kinematic distortion on the flow field during the first pairing interaction. It is suggested that the structures responsible for this transition are non-deterministic, non-random, inhomogeneous fractals. Only the large scales are involved. No further transitions, either in the spectra of the vorticity field or in the mixing behavior, are found for Reynolds numbers up to 90,000.

  6. Fractal interfaces and product generation in the two-dimensional mixing layer

    NASA Technical Reports Server (NTRS)

    Jimenez, Javier; Martel, Carlos

    1991-01-01

    The dependence of product generation on Peclet and Reynolds numbers in a numerically simulated, reacting, two-dimensional, temporally growing mixing layer is related theoretically to the fractal dimension of the passive scalar interfaces. This reaction is verified using product generation measurements and fractal dimensions derived from the box counting technique. A transition from a low initial dimension to a higher one of approximately 5/3 is identified and shown to be associated to the kinematic distortion of the flow field during the first pairing interaction. It is suggested that the structures reponsible for this transition are nondeterministic, nonrandom, inhomogeneous fractals. In the range of Schmidt numbers investigated (0.25-4), only the large scales are involved. No further transitions, either in the spectra of the vorticity field or in the mixing behavior, are found for Reynolds numbers up to 90,000.

  7. Material transport in a convective surface mixed layer under weak wind forcing

    NASA Astrophysics Data System (ADS)

    Mensa, Jean A.; Özgökmen, Tamay M.; Poje, Andrew C.; Imberger, Jörg

    2015-12-01

    Flows in the upper ocean mixed layer are responsible for the transport and dispersion of biogeochemical tracers, phytoplankton and buoyant pollutants, such as hydrocarbons from an oil spill. Material dispersion in mixed layer flows subject to diurnal buoyancy forcing and weak winds (| u10 | = 5m s-1) are investigated using a non-hydrostatic model. Both purely buoyancy-forced and combined wind- and buoyancy-forced flows are sampled using passive tracers, as well as 2D and 3D particles to explore characteristics of horizontal and vertical dispersion. It is found that the surface tracer patterns are determined by the convergence zones created by convection cells within a time scale of just a few hours. For pure convection, the results displayed the classic signature of Rayleigh-Benard cells. When combined with a wind stress, the convective cells become anisotropic in that the along-wind length scale gets much larger than the cross-wind scale. Horizontal relative dispersion computed by sampling the flow fields using both 2D and 3D passive particles is found to be consistent with the Richardson regime. Relative dispersion is an order of magnitude higher and 2D surface releases transition to Richardson regime faster in the wind-forced case. We also show that the buoyancy-forced case results in significantly lower amplitudes of scale-dependent horizontal relative diffusivity, kD(ℓ), than those reported by Okubo (1970), while the wind- and buoyancy-forced case shows a good agreement with Okubo's diffusivity amplitude, and the scaling is consistent with Richardson's 4/3rd law, kD ∼ ℓ4/3. These modeling results provide a framework for measuring material dispersion by mixed layer flows in future observational programs.

  8. Mixing layer height and its implications for air pollution over Beijing, China

    NASA Astrophysics Data System (ADS)

    Tang, Guiqian; Zhang, Jinqiang; Zhu, Xiaowan; Song, Tao; Münkel, Christoph; Hu, Bo; Schäfer, Klaus; Liu, Zirui; Zhang, Junke; Wang, Lili; Xin, Jinyuan; Suppan, Peter; Wang, Yuesi

    2016-03-01

    The mixing layer is an important meteorological factor that affects air pollution. In this study, the atmospheric mixing layer height (MLH) was observed in Beijing from July 2009 to December 2012 using a ceilometer. By comparison with radiosonde data, we found that the ceilometer underestimates the MLH under conditions of neutral stratification caused by strong winds, whereas it overestimates the MLH when sand-dust is crossing. Using meteorological, PM2.5, and PM10 observational data, we screened the observed MLH automatically; the ceilometer observations were fairly consistent with the radiosondes, with a correlation coefficient greater than 0.9. Further analysis indicated that the MLH is low in autumn and winter and high in spring and summer in Beijing. There is a significant correlation between the sensible heat flux and MLH, and the diurnal cycle of the MLH in summer is also affected by the circulation of mountainous plain winds. Using visibility as an index to classify the degree of air pollution, we found that the variation in the sensible heat and buoyancy term in turbulent kinetic energy (TKE) is insignificant when visibility decreases from 10 to 5 km, but the reduction of shear term in TKE is near 70 %. When visibility decreases from 5 to 1 km, the variation of the shear term in TKE is insignificant, but the decrease in the sensible heat and buoyancy term in TKE is approximately 60 %. Although the correlation between the daily variation of the MLH and visibility is very poor, the correlation between them is significantly enhanced when the relative humidity increases beyond 80 %. This indicates that humidity-related physicochemical processes is the primary source of atmospheric particles under heavy pollution and that the dissipation of atmospheric particles mainly depends on the MLH. The presented results of the atmospheric mixing layer provide useful empirical information for improving meteorological and atmospheric chemistry models and the forecasting

  9. A three-dimensional simulation of transition and early turbulence in a time-developing mixing layer

    NASA Technical Reports Server (NTRS)

    Cain, A. B.; Reynolds, W. C.; Ferziger, J. H.

    1981-01-01

    The physics of the transition and early turbulence regimes in the time developing mixing layer was investigated. The sensitivity of the mixing layer to the disturbance field of the initial condition is considered. The growth of the momentum thickness, the mean velocity profile, the turbulence kinetic energy, the Reynolds stresses, the anisotropy tensor, and particle track pictures of computations are all examined in an effort to better understand the physics of these regimes. The amplitude, spectrum shape, and random phases of the initial disturbance field were varied. A scheme of generating discrete orthogonal function expansions on some nonuniform grids was developed. All cases address the early or near field of the mixing layer. The most significant result shows that the secondary instability of the mixing layer is produced by spanwise variations in the straining field of the primary vortex structures.

  10. FLOW FIELD IN SUPERSONIC MIXED-COMPRESSION INLETS AT ANGLE OF ATTACK USING THE THREE DIMENSIONAL METHOD OF CHARACTERISTICS WITH DISCRETE SHOCK WAVE FITTING

    NASA Technical Reports Server (NTRS)

    Bishop, A. R.

    1994-01-01

    This computer program calculates the flow field in the supersonic portion of a mixed-compression aircraft inlet at non-zero angle of attack. This approach is based on the method of characteristics for steady three-dimensional flow. The results of this program agree with those produced by the two-dimensional method of characteristics when axisymmetric flow fields are calculated. Except in regions of high viscous interaction and boundary layer removal, the results agree well with experimental data obtained for threedimensional flow fields. The flow field in a variety of axisymmetric mixed compression inlets can be calculated using this program. The bow shock wave and the internal shock wave system are calculated using a discrete shock wave fitting procedure. The internal flow field can be calculated either with or without the discrete fitting of the internal shock wave system. The influence of molecular transport can be included in the calculation of the external flow about the forebody and in the calculation of the internal flow when internal shock waves are not discretely fitted. The viscous and thermal diffussion effects are included by treating them as correction terms in the method of characteristics procedure. Dynamic viscosity is represented by Sutherland's law and thermal conductivity is represented as a quadratic function of temperature. The thermodynamic model used is that of a thermally and calorically perfect gas. The program assumes that the cowl lip is contained in a constant plane and that the centerbody contour and cowl contour are smooth and have continuous first partial derivatives. This program cannot calculate subsonic flow, the external flow field if the bow shock wave does not exist entirely around the forebody, or the internal flow field if the bow flow field is injected into the annulus. Input to the program consists of parameters to control execution, to define the geometry, and the vehicle orientation. Output consists of a list of parameters

  11. Implementation of a 3D mixing layer code on parallel computers

    NASA Technical Reports Server (NTRS)

    Roe, K.; Thakur, R.; Dang, T.; Bogucz, E.

    1995-01-01

    This paper summarizes our progress and experience in the development of a Computational-Fluid-Dynamics code on parallel computers to simulate three-dimensional spatially-developing mixing layers. In this initial study, the three-dimensional time-dependent Euler equations are solved using a finite-volume explicit time-marching algorithm. The code was first programmed in Fortran 77 for sequential computers. The code was then converted for use on parallel computers using the conventional message-passing technique, while we have not been able to compile the code with the present version of HPF compilers.

  12. Seasonal cycle of the mixed-layer heat and freshwater budget in the eastern tropical Atlantic

    NASA Astrophysics Data System (ADS)

    Rath, Willi; Dengler, Marcus; Lüdke, Jan; Schmidtko, Sunke; Schlundt, Michael; Brandt, Peter; Partners, Preface

    2016-04-01

    A new seasonal mixed-layer heat flux climatology is used to explore the mechanisms driving seasonal variability of sea surface temperature and salinity in the eastern tropical Atlantic (ETA) with a focus on the eastern boundary upwelling regions. Until recently, large areas at the continental margins of the ETA were not well covered by publically available hydrographic data hampering a detailed understanding of the involved processes. In a collaborative effort between African and European partners within the EU-funded PREFACE program, a new seasonal climatology for different components of the heat and freshwater budget was compiled for the ETA using all publically available hydrographic data sets and a large trove of previously not-publically available hydrographic measurements from the territorial waters of western African countries, either from national programs or from the FAO supported EAF-Nansen program. The publically available data includes hydrographic data from global data repositories including most recent ARGO floats and glider measurements. This data set was complemented by velocity data from surface drifter and ARGO floats to allow determining horizontal heat and freshwater advection. Monthly means of air-sea heat fluxes were derived from the TropFlux climatology while precipitation rates were derived from monthly mean fields of the Global Precipitation Climatology Project. Finally, microstructure data from individual measurement campaigns allow estimating diapycnal heat and salt fluxes for certain regions during specific months. A detailed analysis of the seasonal cycle of mixed-layer heat and freshwater balance in previously poorly covered regions in the eastern tropical Atlantic upwelling is presented. In both eastern boundary upwelling region, off Senegal/Mauritania and off Angola/Namibia, average net surface heat fluxes warm the mixed layer at a rate between 50 and 80 W/m2 with maxima in the respective summer seasons. Horizontal advection

  13. Low-frequency variability in a climate model with a mixed-layer ocean

    SciTech Connect

    Gould-Stewart, S.

    1984-11-01

    A mixed-layer ocean model coupled to a global spectral atmospheric circulation model produces a warming in the model equatorial Pacific Ocean similar to the El Nino or Southern Oscillation (SO) response. The mechanism for producing the SO-like response in an ocean with heat storage and without ocean dynamics is investigated. The model is capable of simulating SO-like time scales, but the details of the structure of the warming differ significantly from the observed El Nino/Southern Oscillation (ENSO) response. 22 refs.

  14. Influence of convective conditions on three dimensional mixed convective hydromagnetic boundary layer flow of Casson nanofluid

    NASA Astrophysics Data System (ADS)

    Rauf, A.; Siddiq, M. K.; Abbasi, F. M.; Meraj, M. A.; Ashraf, M.; Shehzad, S. A.

    2016-10-01

    The present work deals with the steady laminar three-dimensional mixed convective magnetohydrodynamic (MHD) boundary layer flow of Casson nanofluid over a bidirectional stretching surface. A uniform magnetic field is applied normal to the flow direction. Similarity variables are implemented to convert the non-linear partial differential equations into ordinary ones. Convective boundary conditions are utilized at surface of the sheet. A numerical technique of Runge-Kutta-Fehlberg (RFK45) is used to obtain the results of velocity, temperature and concentration fields. The physical dimensionless parameters are discussed through tables and graphs.

  15. Nonstationary Axisymmetric Temperature Field in a Two-Layer Slab Under Mixed Heating Conditions

    NASA Astrophysics Data System (ADS)

    Turchin, I. N.; Timar, I.; Kolodii, Yu. A.

    2015-09-01

    With the use of the Laguerre and Hankel integral transforms, the solution of a two-dimensional initial-boundary-value heat conduction problem for a two-layer slab under mixed boundary conditions is constructed: one of the surfaces is heated by a heat flux distributed axisymmetrically in a circle of radius R and is cooled by the Newton law outside this circle. The solution of the problem is reduced to a sequence of infinite quasi-regular systems of algebraic equations. The results of numerical analysis of the temperature field in the two-layer slab made from an aluminum alloy and ceramicsare presented depending on the relative geometric properties of the components and cooling intensity.

  16. Preliminary mixed-layer model results for FIRE marine stratocumulus IFO conditions

    NASA Technical Reports Server (NTRS)

    Barlow, R.; Nicholls, S.

    1990-01-01

    Some preliminary results from the Turton and Nicholls mixed layer model using typical FIRE boundary conditions are presented. The model includes entrainment and drizzle parametrizations as well as interactive long and shortwave radiation schemes. A constraint on the integrated turbulent kinetic energy balance ensures that the model remains energetically consistent at all times. The preliminary runs were used to identify the potentially important terms in the heat and moisture budgets of the cloud layer, and to assess the anticipated diurnal variability. These are compared with typical observations from the C130. Sensitivity studies also revealed the remarkable stability of these cloud sheets: a number of negative feedback mechanisms appear to operate to maintain the cloud over an extended time period. These are also discussed. The degree to which such a modelling approach can be used to explain observed features, the specification of boundary conditions and problems of interpretation in non-horizontally uniform conditions is also raised.

  17. The development of a mixing layer under the action of weak streamwise vortices

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Mathew, Joseph

    1993-01-01

    The action of weak, streamwise vortices on a plane, incompressible, steady mixing layer is examined in the large Reynolds number limit. The outer, inviscid region is bounded by a vortex sheet to which the viscous region is confined. It is shown that the local linear analysis becomes invalid at streamwise distances O(epsilon sup -1), where (epsilon much less than 1) is the crossflow amplitude, and a new nonlinear analysis is constructed for this region. Numerical solutions of the nonlinear problem show that the vortex sheet undergoes an O(1) change in position and that the solution is ultimately terminated by a breakdown in the numerical procedure. The corresponding viscous layer shows downstream thickening, but appears to remain well behaved up to the terminal location.

  18. The development of a mixing layer under the action of weak streamwise vortices

    NASA Technical Reports Server (NTRS)

    Goldstein, Marvin E.; Mathew, Joseph

    1993-01-01

    The action of weak, streamwise vortices on a plane, incompressible, steady mixing layer is examined in the large Reynolds-number limit. The outer, inviscid region is bounded by a vortex sheet to which the viscous region is confined. It is shown that the local linear analysis becomes invalid at streamwise distances O(epsilon(sup -1)), where epsilon is much less than 1 is the cross flow amplitude, and a new nonlinear analysis is constructed for this region. Numerical solutions of the nonlinear problem show that the vortex sheet undergoes an O(1) change in position and that the solution is ultimately terminated by the appearance of a singularity. The corresponding viscous layer shows downstream thickening, but appears to remain well behaved up to the singular location.

  19. Turbulence in Compressible Flows

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.

  20. Stability and phase separation in mixed monopolar lipid/bolalipid layers.

    PubMed

    Longo, Gabriel S; Thompson, David H; Szleifer, I

    2007-10-15

    The phase stability of a fluid lipid layer that is a mixture of conventional monopolar lipids and C20 bipolar bolalipids was studied using a mean field theory that explicitly includes molecular details and configurational properties of the lipid molecules. The effect of changing the fraction of bolalipids, as well as the length of the hydrocarbon chain of the monopolar lipids, was probed. A phase separation between two liquid lipid phases was found when a mismatch exists in the optimal hydrophobic thicknesses of the pure bolalipid and monopolar lipid layers. The lipid mixture phase separates into a thin bolalipid-rich layer and a thicker monopolar-rich layer. The thin membrane phase is mainly composed of transmembrane bolalipid molecules whose polar heads are positioned at opposite membrane-water interfaces. In the monopolar lipid-rich phase, bolalipids are the minor component and most of them assume a looping configuration where both headgroups are present at the same membrane-water interface. For mixed layers that form a single lipid phase across all bolalipid concentrations, the hairpin-transmembrane ratio strongly depends on the hydrocarbon chain length of the monopolar lipid and the bolalipid concentration. The C-D bond order parameters of the different species have been calculated. Our findings suggest that the concentration-dependent phase transition should be experimentally observable by measuring of the order parameters through quadrupolar splitting experiments. The driving force for the phase separation in the monopolar lipid/bolalipid mixture is the packing mismatch between hydrophobic regions of the monopolar lipid hydrocarbon chains and the membrane-spanning bolalipid chains. The results from the molecular theory may be useful in the design of stable lipid layers for integral membrane protein sensing.

  1. Mixed Layer Depth Seasonality within the Coral Sea Based on Argo Data

    PubMed Central

    Jaffrés, Jasmine B. D.

    2013-01-01

    The worldwide deployment of Argo floats has enabled much more detailed studies of global and regional seas over the last decade. Here, the seasonal variability of the mixed layer depth (MLD) within the Coral Sea was examined with CTD profiles from Argo floats. Multiple threshold values for both temperature and density have been employed to determine the most suitable threshold values for the Coral Sea. A threshold value of 0.04 kg/m3 for density and 0.2°C for temperature appear the most fitting for this region. Although MLD and isothermal layer depth (ILD) coincide quite well in most cases, the relatively common presence of temporary, non-seasonal barrier layers induces an ILD that is significantly deeper than the MLD. Consequently, an MLD estimation based on density is more appropriate. A distinct seasonality in the MLD is evident throughout the Coral Sea, but is generally more pronounced in higher southern latitudes (20–30°S). Salinity inversions are rare and mainly occur in the south-eastern Coral Sea, while barrier layers are more commonly associated with the north-eastern Coral Sea, a region characterised by high rainfall. The significance of regional currents is evident in the north-western Coral Sea, where temperature and ocean heat content is relatively low due to a northward moving boundary current. Shallow bathymetry, in turn, is linked to the absence of Argo data on the continental shelf and in the central Coral Sea. PMID:23593368

  2. Measured and calculated optical property profiles in the mixed layer and free troposphere

    NASA Technical Reports Server (NTRS)

    Rosen, James M.; Bodhaine, Barry A.; Boatman, Joe F.; Deluisi, John J.; Post, M. J.; Kim, Young; Schnell, Russell C.; Sheridan, Patrick J.; Garvey, Dennis M.

    1992-01-01

    Nearly simultaneous measurements of the physical and optical properties of mixed layer and free tropospheric aerosols near Boulder, Colorado, were made on several occasions using aircraft, balloon, and ground-based sensors. This effort (Front Range Lidar, Aircraft, and Balloon experiment (FRLAB)) was conducted with the purpose of obtaining a diverse, self-consistent data set that could be used for testing optical model calculations based on measured physical characteristics such as apparent size distribution, composition, and shape. It was found that even with the uncertainties involved, the model predictions are in good agreement with the measurements in the visible and near infrared wavelength regions. At CO2 lidar wavelengths there is considerably more uncertainty in both the calculated and measured values; however, within the estimated errors there appears to be satisfactory agreement except for the highest free tropospheric layer studied. The results also indicate that during FRLAB the aerosol in the boundary layer and free troposphere behaved as spherical particles for optical modeling purposes. The utility of the observations for determining the extinction-to-backscatter ratio relevant to aerosols in the boundary layer and free troposphere is described with typical measured values being in the 20 to 30 sr range.

  3. Chlorophyll-a Variability in the Southern Ocean Mixed Layer and Euphotic Zone From Elephant Seals and Profiling Floats

    NASA Astrophysics Data System (ADS)

    Carranza, M. M.; Gille, S. T.; Franks, P. J. S.; Johnson, K. S.; Girton, J. B.

    2015-12-01

    The Southern Ocean contains some of the ocean's deepest mixed layers. Because deep mixed layers can transport phytoplankton below the euphotic zone, light levels depend on mixed-layer depth (MLD), and phytoplankton growth is hypothesized to be co-limited by iron and light. Estimates of Chl-a fluorescence, particle backscattering and hydrographic profiles collected by southern elephant seals, EM-APEX, and biogeochemical Argo floats are used to evaluate the extent to which MLD influences phytoplankton bloom development and the vertical structure of chlorophyll-a (Chl-a) in the Southern Ocean. We find that surface Chl-a (i.e., mean Chl-a for the upper light penetration depth) is a relatively good proxy of phytoplankton biomass (i.e., depth-integrated Chl-a) within the euphotic zone but gives an inadequate representation of biomass within the mixed layer, particularly in the summer. Although nearly vertically homogeneous Chl-a within the mixed layer prevails in seasonal mean profiles, subsurface Chl-a maxima are not uncommon from spring through fall. Deep Chl-a maxima that correlate with particle backscattering in summer and fall are found near the base of the mixed layer, closer to the nutrient maximum than the light maximum, suggesting that nutrient limitation (i.e., essentially iron) can play a greater role than light limitation in governing productivity.

  4. Transition to Turbulence and Effect of Initial Conditions on 3D Compressible Mixing in Planar Blast-wave-driven Systems

    SciTech Connect

    Miles, A R; Edwards, M J; Greenough, J A

    2004-11-08

    Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, results from three-dimensional numerical simulations of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams, 9(2), 209 (1991)] are presented. Using the multi-physics, adaptive mesh refinement, higher order Godunov Eulerian hydrocode, Raptor [L. H. Howell and J.A. Greenough, J. Comp. Phys. 184, 53 (2003)], the late nonlinear instability evolution, including transition to turbulence, is considered for various multimode perturbation spectra. The 3D post-transition state differs from the 2D result, but the process of transition proceeds similarly in both 2D and 3D. The turbulent mixing transition results in a reduction in the growth rate of the mixing layer relative to its pre-transition value and, in the case of the bubble front, relative to the 2D result. The post-transition spike front velocity is approximately the same in 2D and 3D. Implications for hydrodynamic mixing in core-collapse supernova are discussed.

  5. The role of molecular layer mixing on the thermal conductance of organic-inorganic heterojunctions

    NASA Astrophysics Data System (ADS)

    Majumdar, Shubhaditya; McGaughey, Alan J. H.; Malen, Jonathan A.

    The role of interfacial properties in affecting energy transport characteristics is an extensive area of research. Hybrid materials composed of organic-inorganic heterojunctions are gaining popularity as alternatives to conventional semiconductors for various energy-generation devices, thus requiring detailed study of their interfacial properties - especially thermal transport. Previous works have isolated the organic-inorganic interface thermal properties using self-assembled monolayer (SAM) junctions between two inorganic substrates and characterized them based on interfacial bonding strength, vibrational mismatch and molecule length. Here, we investigate the effect of having a mixed SAM layer on the thermal conductance of the SAM junction. The mixed SAM layers either have molecules of the same length but different end groups (thiols and methyl) or different lengths. This creates a modifiable bonding environment at one interface either through a varying ratio of strong and weakly bonded end groups or a decreasing surface coverage of the molecule. Both these scenarios are investigated to study the cooperative nature of the molecules/interface bonds and their effect on the heat transport across the junction. We follow a combined experimental and computational approach in our investigation - we fabricate the SAM junctions (alkanethiols between two gold substrates) and measure their thermal conductance using Frequency Domain Thermoreflectance, and use molecular dynamics simulations to get a deeper understanding of the role of intermolecular cross talk.

  6. Variable but persistent coexistence of Prochlorococcus ecotypes along temperature gradients in the ocean's surface mixed layer.

    PubMed

    Chandler, Jeremy W; Lin, Yajuan; Gainer, P Jackson; Post, Anton F; Johnson, Zackary I; Zinser, Erik R

    2016-04-01

    The vast majority of the phytoplankton communities in surface mixed layer of the oligotrophic ocean are numerically dominated by one of two ecotypes of Prochlorococcus, eMIT9312 or eMED4. In this study, we surveyed large latitudinal transects in the Atlantic and Pacific Ocean to determine if these ecotypes discretely partition the surface mixed layer niche, or if populations exist as a continuum along key environmental gradients, particularly temperature. Transitions of dominance occurred at approximately 19-21°C, with the eMED4 ecotype dominating the colder, and eMIT9312 ecotype dominating the warmer regions. Within these zones of regional dominance, however, the minority ecotype was not competed to extinction. Rather, a robust log-linear relationship between ecotype ratio and temperature characterized this stabilized coexistence: for every 2.5°C increase in temperature, the eMIT9312:eMED4 ratio increased by an order of magnitude. This relationship was observed in both quantitative polymerase chain reaction and in pyrosequencing assays. Water column stratification also contributed to the ecotype ratio along the basin-scale transects, but to a lesser extent. Finally, instances where the ratio of the eMED4 and eMIT9312 abundances did not correlate well with temperature were identified. Such occurrences are likely due to changes in water temperatures outpacing changes in community structure.

  7. Diffusion-flame ignition by shock-wave impingement on a supersonic mixing layer

    NASA Astrophysics Data System (ADS)

    Sanchez, Antonio L.; Huete, Cesar; Williams, Forman A.; Urzay, Javier

    2015-11-01

    Ignition in a supersonic mixing layer interacting with an oblique shock wave is investigated analytically and numerically under conditions such that the post-shock flow remains supersonic. The study requires consideration of the structure of the post-shock ignition kernel that is found to exist around the point of maximum temperature, which may be located either near the edge of the mixing layer or in its interior. The ignition kernel displays a balance between the rates of chemical reaction and of post-shock flow expansion, including the acoustic interactions of the chemical heat release with the shock wave, leading to increased front curvature. The analysis, which adopts a one-step chemistry model with large activation energy, indicates that ignition develops as a fold bifurcation, the turning point in the diagram of the peak perturbation induced by the chemical reaction as a function of the Damköhler number providing the critical conditions for ignition. Subsequent to ignition the lead shock will rapidly be transformed into a thin detonation on the fuel side of the ignition kernel, and, under suitable conditions, a deflagration may extend far downstream, along with the diffusion flame that must separate the rich and lean reaction products.

  8. Profiling float-based observations of net respiration beneath the mixed layer

    NASA Astrophysics Data System (ADS)

    Hennon, Tyler D.; Riser, Stephen C.; Mecking, Sabine

    2016-06-01

    We employ profiling floats with dissolved oxygen sensors to observe in situ temporal oxygen evolution below the mixed layer, allowing us to characterize net respiration of organic carbon in eight distinct regions over the globe. Export and export efficiency are generally high in locations with strong seasonal variability and low in locations of weak seasonality. Vertically integrated respiration is weakly, yet significantly, correlated with remote observations of chlorophyll, net primary production, and planktonic community size structure. These correlations suggest that regimes of high net primary production and large phytoplankton fuel elevated respiration at depth. Several regions of float-based observations intersect with sites of other detailed observations (e.g., Hawaii and Sargasso Sea), which allows us to compare our results to independent studies. We find that there is good agreement among export production estimates at highly seasonal locations, and that float-based observations may be biased low at weakly seasonal locations. We posit that the reason for the low-latitude discrepancy is the relative steady state of oxygen concentration caused by weak seasonality and shallow wintertime mixed layer depths.

  9. Simulation of mixed-host emitting layer based organic light emitting diodes

    SciTech Connect

    Riku, C.; Kee, Y. Y.; Ong, T. S.; Tou, T. Y.; Yap, S. S.

    2015-04-24

    ‘SimOLED’ simulator is used in this work to investigate the efficiency of the mixed-host organic light emitting devices (MH-OLEDs). Tris-(8-hydroxyquinoline) aluminum(3) (Alq{sub 3}) and N,N-diphenyl-N,N-Bis(3-methylphenyl)-1,1-diphenyl-4,4-diamine (TPD) are used as the electron transport layer (ETL) material and hole transport layer (HTL) material respectively, and the indium-doped tin oxide (ITO) and aluminum (Al) as anode and cathode. Three MH-OLEDs, A, B and C with the same structure of ITO / HTM (15 nm) / Mixed host (70 nm) / ETM (10 nm) /Al, are stimulated with ratios TPD:Alq{sub 3} of 3:5, 5:5, and 5:3 respectively. The Poole-Frenkel model for electron and hole mobilities is employed to compute the current density-applied voltage-luminance characteristics, distribution of the electric field, carrier concentrations and recombination rate.

  10. Quantifying subtropical North Pacific gyre mixed layer primary productivity from Seaglider observations of diel oxygen cycles

    NASA Astrophysics Data System (ADS)

    Nicholson, David P.; Wilson, Samuel T.; Doney, Scott C.; Karl, David M.

    2015-05-01

    Using autonomous underwater gliders, we quantified diurnal periodicity in dissolved oxygen, chlorophyll, and temperature in the subtropical North Pacific near the Hawaii Ocean Time-series (HOT) Station ALOHA during summer 2012. Oxygen optodes provided sufficient stability and precision to quantify diel cycles of average amplitude of 0.6 µmol kg-1. A theoretical diel curve was fit to daily observations to infer an average mixed layer gross primary productivity (GPP) of 1.8 mmol O2 m-3 d-1. Cumulative net community production (NCP) over 110 days was 500 mmol O2 m-2 for the mixed layer, which averaged 57 m in depth. Both GPP and NCP estimates indicated a significant period of below-average productivity at Station ALOHA in 2012, an observation confirmed by 14C productivity incubations and O2/Ar ratios. Given our success in an oligotrophic gyre where biological signals are small, our diel GPP approach holds promise for remote characterization of productivity across the spectrum of marine environments.

  11. Nonlocal stochastic mixing-length theory and the velocity profile in the turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Dekker, H.; de Leeuw, G.; Maassen van den Brink, A.

    1995-02-01

    Turbulence mixing by finite size eddies will be treated by means of a novel formulation of nonlocal K-theory, involving sample paths and a stochastic closure hypothesis, which implies a well defined recipe for the calculation of sampling and transition rates. The connection with the general theory of stochastic processes will be established. The relation with other nonlocal turbulence models (e.g. transilience and spectral diffusivity theory) is also discussed. Using an analytical sampling rate model (satisfying exchange) the theory is applied to the boundary layer (using a scaling hypothesis), which maps boundary layer turbulence mixing of scalar densities onto a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process. The resulting transpport equation for longitudinal momentum P x ≡ ϱ U is solved for a unified description of both the inertial and the viscous sublayer including the crossover. With a scaling exponent ε ≈ 0.58 (while local turbulence would amount to ε → ∞) the velocity profile U+ = ƒ(y +) is found to be in excellent agreement with the experimental data. Inter alia (i) the significance of ε as a turbulence Cantor set dimension, (ii) the value of the integration constant in the logarithmic region (i.e. if y+ → ∞), (iii) linear timescaling, and (iv) finite Reynolds number effects will be investigated. The (analytical) predictions of the theory for near-wall behaviour (i.e. if y+ → 0) of fluctuating quantities also perfectly agree with recent direct numerical simulations.

  12. Global and Koopman modes analysis of sound generation in mixing layers

    SciTech Connect

    Song, G.; Robinet, J.-C.; Gloerfelt, X.; Alizard, F.

    2013-12-15

    It is now well established that linear and nonlinear instability waves play a significant role in the noise generation process for a wide variety of shear flows such as jets or mixing layers. In that context, the problem of acoustic radiation generated by spatially growing instability waves of two-dimensional subsonic and supersonic mixing layers are revisited in a global point of view, i.e., without any assumption about the base flow, in both a linear and a nonlinear framework by using global and Koopman mode decompositions. In that respect, a timestepping technique based on disturbance equations is employed to extract the most dynamically relevant coherent structures for both linear and nonlinear regimes. The present analysis proposes thus a general strategy for analysing the near-field coherent structures which are responsible for the acoustic noise in these configurations. In particular, we illustrate the failure of linear global modes to describe the noise generation mechanism associated with the vortex pairing for the subsonic regime whereas they appropriately explain the Mach wave radiation of instability waves in the supersonic regime. By contrast, the Dynamic Mode Decomposition (DMD) analysis captures both the near-field dynamics and the far-field acoustics with a few number of modes for both configurations. In addition, the combination of DMD and linear global modes analyses provides new insight about the influence on the radiated noise of nonlinear interactions and saturation of instability waves as well as their interaction with the mean flow.

  13. Opposed-flow flame spread and extinction in mixed-convection boundary layers

    NASA Technical Reports Server (NTRS)

    Altenkirch, R. A.; Wedha-Nayagam, M.

    1989-01-01

    Experimental data for flame spread down thin fuel samples in an opposing, mixed-convection, boundary-layer flow are analyzed to determine the gas-phase velocity that characterizes how the flame reacts as it spreads toward the leading edge of the fuel sample into a thinning boundary layer. In the forced-flow limit where the cube of the Reynolds number divided by the Grashof number, Re exp 3/Gr, is large, L(q)/L(e), where L(q) is a theoretical flame standoff distance at extinction and L(e) is the measured distance from the leading edge of the sample where extinction occurs, is found to be proportional to Re exp n with n = -0.874 and Re based on L(e). The value of n is established by the character of the flow field near the leading edge of the flame. The Re dependence is used, along with a correction for the mixed-convection situation where Re exp 3/Gr is not large, to construct a Damkohler number with which the measured spread rates correlate for all values of Re exp 3/Gr.

  14. Observed and modeled mixed-layer variability on the continental shelf of Sardinia (Western Mediterranean)

    NASA Astrophysics Data System (ADS)

    Onken, Reiner

    2016-04-01

    An important task of Military Oceanography is the prediction of mixed-layer properties and their spatial and temporal variability. In the mainframe of the REP14-MED sea trial which was conducted under the lead of CMRE in June 2014 in the waters west of Sardinia, an oceanographic mooring was deployed on the continental shelf which recorded the seawater temperature between the surface and 40-m depth with high resolution for about twelve days; meteorological parameters were collected at the same time on top of the mooring by a meteorological buoy. A series of ROMS model runs was conducted and validated against the observations. Those runs applied different setups for the forcing at the lateral open boundaries and at the surface, different arrangements of the vertical coordinates, and different strategies for the assimilation of data from CTD casts and gliders. The goal was to test the sensitivity of the forecast skill to the different setups and to find a "cheap" setup which predicts the observed temperature and the mixed-layer depth and their temporal variabilities to a satisfactory degree. That setup is supposed to provide also reliable forecasts for the other areas of the model domain.

  15. Mach waves produced in the supersonic jet mixing layer by shock/vortex interaction

    NASA Astrophysics Data System (ADS)

    Oertel Sen, H.; Seiler, F.; Srulijes, J.; Hruschka, R.

    2016-05-01

    The noise emission of free jets has been extensively investigated for many decades. At subsonic jet velocities, coherent structures of the mixing layer move at subsonic speed and emit sound waves. Free jets blowing at supersonic speeds, however, can emit weak shock waves, called Mach waves. At supersonic speeds, two cases must be distinguished: the structures move either subsonically or supersonically relative to the inside and/or outside speed of sound. In the case of supersonic movement, the Mach waves exist inside as well as outside the jet. At subsonic speeds, no Mach waves appear. Although numerous theories have been established to find the origin of the Mach waves, to the authors' best knowledge, the mechanism of the Mach wave formation has not yet been clearly explained. Recently another theory of Mach waves in supersonic jets was developed, as described herein, which outlines the causes for the Mach wave production and stability as well as their dynamics. The theory's principle is that the Mach waves are initiated by vortices which move downstream at three speeds w, {w}' and {w}'' inside of the mixing layer. These three types of vortices and Mach waves are described in a comprehensive manner by the theory and are called the " w-, {w}'- and {w}''-vortices" and " w-, {w}'- and {w}''-Mach waves," respectively.

  16. Mixed mode transition in zero and adverse pressure gradient boundary layers

    NASA Astrophysics Data System (ADS)

    Bose, Rikhi; Durbin, Paul

    2015-11-01

    Flow regimes exist where interaction of Klebanoff streaks and the Tollmien-Sclichting waves trigger transition but either mode is individually insufficient. Such interaction between orderly and bypass routes of transition is called Mixed mode transition. In zero pressure gradient boundary layers, mixed mode transition follows three routes depending upon strength of these perturbation modes. At high free-stream turbulence intensity (Tu), bypass transition is dominant and the flow is very weakly sensitive to the TS mode strength. In the presence of a strong TS mode, low Tu triggers secondary instability of the TS wave forming Λ vortices. The Λ vortices are forced response due to the weak streaks rather than resonance mechanism seen in monochromatic excitations. When both of these modes are weak, secondary instability of streaks trigger consequent breakdown to turbulent spots. Three-dimensional visualization of the perturbation fields shows toroidal n = 0 and helical n = 1 modes observed in instability of axisymmetric jets and wakes. In adverese pressure gradient boundary layers, the presence of an inflection point significantly increases the growth rate of TS mode thereby strengthening the secondary instability route and the interaction is more interesting. This work was supported by NSF grant CBET-1228195. Computer time was provided by the Extreme Science and Engineering Discovery Environment (XSEDE).

  17. Perturbation Effects on a Supercritical C7H16/N2 Mixing Layer

    NASA Technical Reports Server (NTRS)

    Okongo'o, Nora; Bellan, Josette

    2008-01-01

    A computational-simulation study has been presented of effects of perturbation wavelengths and initial Reynolds numbers on the transition to turbulence of a heptane/nitrogen mixing layer at supercritical pressure. The governing equations for the simulations were the same as those of related prior studies reported in NASA Tech Briefs. Two-dimensional (2D) simulations were performed with initially im posed span wise perturbations whereas three-dimensional (3D) simulations had both streamwise and spanwise initial perturbations. The 2D simulations were undertaken to ascertain whether perturbations having the shortest unstable wavelength obtained from a linear stability analysis for inviscid flow are unstable in viscous nonlinear flows. The goal of the 3D simulations was to ascertain whether perturbing the mixing layer at different wavelengths affects the transition to turbulence. It was found that transitions to turbulence can be obtained at different perturbation wavelengths, provided that they are longer than the shortest unstable wavelength as determined by 2D linear stability analysis for the inviscid case and that the initial Reynolds number is proportionally increased as the wavelength is decreased. The transitional states thus obtained display different dynamic and mixture characteristics, departing strongly from the behaviors of perfect gases and ideal mixtures.

  18. Average properties of compressible laminar boundary layer on flat plate with unsteady flight velocity

    NASA Technical Reports Server (NTRS)

    Moore, Franklin K; Ostrach, Simon

    1957-01-01

    The time-average characteristics of boundary layers over a flat plate in nearly quasi-steady flow are determined. The plate may be either insulated or isothermal. The time averages are found without specifying the plate velocity explicitly except that it is positive and has an average value.

  19. Transient Growth Analysis of Compressible Boundary Layers with Parabolized Stability Equations

    NASA Technical Reports Server (NTRS)

    Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan

    2016-01-01

    The linear form of parabolized linear stability equations (PSE) is used in a variational approach to extend the previous body of results for the optimal, non-modal disturbance growth in boundary layer flows. This methodology includes the non-parallel effects associated with the spatial development of boundary layer flows. As noted in literature, the optimal initial disturbances correspond to steady counter-rotating stream-wise vortices, which subsequently lead to the formation of stream-wise-elongated structures, i.e., streaks, via a lift-up effect. The parameter space for optimal growth is extended to the hypersonic Mach number regime without any high enthalpy effects, and the effect of wall cooling is studied with particular emphasis on the role of the initial disturbance location and the value of the span-wise wavenumber that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary layer equations, mean flow solutions based on the full Navier-Stokes (NS) equations are used in select cases to help account for the viscous-inviscid interaction near the leading edge of the plate and also for the weak shock wave emanating from that region. These differences in the base flow lead to an increasing reduction with Mach number in the magnitude of optimal growth relative to the predictions based on self-similar mean-flow approximation. Finally, the maximum optimal energy gain for the favorable pressure gradient boundary layer near a planar stagnation point is found to be substantially weaker than that in a zero pressure gradient Blasius boundary layer.

  20. X-ray continuum as a measure of pressure and fuel-shell mix in compressed isobaric hydrogen implosion cores

    NASA Astrophysics Data System (ADS)

    Epstein, R.; Goncharov, V. N.; Marshall, F. J.; Betti, R.; Nora, R.; Christopherson, A. R.; Golovkin, I. E.; MacFarlane, J. J.

    2015-02-01

    Pressure, by definition, characterizes the conditions within an isobaric implosion core at peak compression [Gus'kov et al., Nucl. Fusion 16, 957 (1976); Betti et al., Phys. Plasmas 8, 5257 (2001)] and is a key parameter in quantifying its near-ignition performance [Lawson, Proc. Phys. Soc. London, B 70, 6 (1957); Betti et al., Phys. Plasmas 17, 058102 (2010); Goncharov et al., Phys. Plasmas 21, 056315 (2014); and Glenzer et al., Phys. Plasmas 19, 056318 (2012)]. At high spectral energy, where the x-ray emission from an imploded hydrogen core is optically thin, the emissivity profile can be inferred from the spatially resolved core emission. This emissivity, which can be modeled accurately under hot-core conditions, is dependent almost entirely on the pressure when measured within a restricted spectral range matched to the temperature range anticipated for the emitting volume. In this way, the hot core pressure at the time of peak emission can be inferred from the measured free-free emissivity profile. The pressure and temperature dependences of the x-ray emissivity and the neutron-production rate explain a simple scaling of the total filtered x-ray emission as a constant power of the total neutron yield for implosions of targets of similar design over a broad range of shell implosion isentropes. This scaling behavior has been seen in implosion simulations and is confirmed by measurements of high-isentrope implosions [Sangster et al., Phys. Plasmas 20, 056317 (2013)] on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)]. Attributing the excess emission from less-stable, low-isentrope implosions, above the level expected from this neutron-yield scaling, to the higher emissivity of shell carbon mixed into the implosion's central hot spot, the hot-spot "fuel-shell" mix mass can be inferred.

  1. X-ray continuum as a measure of pressure and fuel–shell mix in compressed isobaric hydrogen implosion cores

    SciTech Connect

    Epstein, R.; Goncharov, V. N.; Marshall, F. J.; Betti, R.; Nora, R.; Christopherson, A. R.; Golovkin, I. E.; MacFarlane, J. J.

    2015-02-01

    Pressure, by definition, characterizes the conditions within an isobaric implosion core at peak compression [Gus’kov et al., Nucl. Fusion 16, 957 (1976); Betti et al., Phys. Plasmas 8, 5257 (2001)] and is a key parameter in quantifying its near-ignition performance [Lawson, Proc. Phys. Soc. London, B 70, 6 (1957); Betti et al., Phys. Plasmas 17, 058102 (2010); Goncharov et al., Phys. Plasmas 21, 056315 (2014); and Glenzer et al., Phys. Plasmas 19, 056318 (2012)]. At high spectral energy, where the x-ray emission from an imploded hydrogen core is optically thin, the emissivity profile can be inferred from the spatially resolved core emission. This emissivity, which can be modeled accurately under hot-core conditions, is dependent almost entirely on the pressure when measured within a restricted spectral range matched to the temperature range anticipated for the emitting volume. In this way, the hot core pressure at the time of peak emission can be inferred from the measured free-free emissivity profile. The pressure and temperature dependences of the x-ray emissivity and the neutron-production rate explain a simple scaling of the total filtered x-ray emission as a constant power of the total neutron yield for implosions of targets of similar design over a broad range of shell implosion isentropes. This scaling behavior has been seen in implosion simulations and is confirmed by measurements of high-isentrope implosions [Sangster et al., Phys. Plasmas 20, 056317 (2013)] on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)]. Attributing the excess emission from less-stable, low-isentrope implosions, above the level expected from this neutron-yield scaling, to the higher emissivity of shell carbon mixed into the implosion’s central hot spot, the hot-spot “fuel–shell” mix mass can be inferred.

  2. X-ray continuum as a measure of pressure and fuel–shell mix in compressed isobaric hydrogen implosion cores

    SciTech Connect

    Epstein, R.; Goncharov, V. N.; Marshall, F. J.; Betti, R.; Nora, R.; Christopherson, A. R.; Golovkin, I. E.; MacFarlane, J. J.

    2015-02-15

    Pressure, by definition, characterizes the conditions within an isobaric implosion core at peak compression [Gus'kov et al., Nucl. Fusion 16, 957 (1976); Betti et al., Phys. Plasmas 8, 5257 (2001)] and is a key parameter in quantifying its near-ignition performance [Lawson, Proc. Phys. Soc. London, B 70, 6 (1957); Betti et al., Phys. Plasmas 17, 058102 (2010); Goncharov et al., Phys. Plasmas 21, 056315 (2014); and Glenzer et al., Phys. Plasmas 19, 056318 (2012)]. At high spectral energy, where the x-ray emission from an imploded hydrogen core is optically thin, the emissivity profile can be inferred from the spatially resolved core emission. This emissivity, which can be modeled accurately under hot-core conditions, is dependent almost entirely on the pressure when measured within a restricted spectral range matched to the temperature range anticipated for the emitting volume. In this way, the hot core pressure at the time of peak emission can be inferred from the measured free-free emissivity profile. The pressure and temperature dependences of the x-ray emissivity and the neutron-production rate explain a simple scaling of the total filtered x-ray emission as a constant power of the total neutron yield for implosions of targets of similar design over a broad range of shell implosion isentropes. This scaling behavior has been seen in implosion simulations and is confirmed by measurements of high-isentrope implosions [Sangster et al., Phys. Plasmas 20, 056317 (2013)] on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)]. Attributing the excess emission from less-stable, low-isentrope implosions, above the level expected from this neutron-yield scaling, to the higher emissivity of shell carbon mixed into the implosion's central hot spot, the hot-spot “fuel–shell” mix mass can be inferred.

  3. Modulation on coherent vortex structures by dispersed solid particles in a three-dimensional mixing layer.

    PubMed

    Fan, Jianren; Luo, Kun; Zheng, Youqu; Jin, Hanhui; Cen, Kefa

    2003-09-01

    Large-scale vortex structures and their effects on the dispersion of particles in turbulent free shear flows are very important in many industrial applications, such as combustion, pollution control, and materials processing. In order to understand large-scale vortex structures and particle dispersion in depth, as well as their interaction effects, a two-way-coupled three-dimensional mixing layer laden with particles at a Stokes number of 5 initially located in the upper half region is studied numerically. A pseudospectral method was used to directly simulate the flow fluid, and the Lagrangian approach was used to trace particles. The concept of computational particles is introduced to vary the mass loading of particles. The momentum coupling effect introduced by a particle approximates to a point force. The simulation results show that coherent structures are still dominant in the mixing layer, but the flow dynamics and particle dispersion are modulated. The length of large-scale vortex structures is shortened and the pairing is delayed. Higher mass loading results in lower energy of the fluid in the phase of Kelvin-Helmholtz rolling up, while in the pairing process of large-scale vortex structures, the energy of the fluid increases as the mass loading increases. Higher mass loading also leads to larger mixed fluid thickness and Reynolds stresses of the flow. In addition, the particle dispersion along the transverse direction differs from that along the spanwise direction, which indicates that the effects of the addition of a particle on the spanwise large-scale vortex structures are different from those on the streamwise large-scale vortex structures.

  4. Efficient white phosphorescent organic light-emitting diodes consisting of orange ultrathin and blue mixed host emission layers

    NASA Astrophysics Data System (ADS)

    Sheng, Ren; Zuo, Liangmei; Xue, Kaiwen; Duan, Yu; Chen, Ping; Cheng, Gang; Zhao, Yi

    2016-08-01

    We have successfully demonstrated highly efficient white phosphorescent organic light-emitting diodes (OLEDs) by inserting an ultrathin non-doped orange layer within blue mixed host emission layer. The key feature of the novel device is the employment of blue mixed host and orange ultrathin layers, resulting in an extended recombination region and more balanced charge carrier. The maximum efficiencies of 33.8 lm W‑1 and 32.2 cd A‑1 are obtained. Moreover, the resulting white device achieves a slight efficiency roll-off and a high luminance at low operating voltage. Our versatile concept suggests a promising simple method to achieve high performance white OLEDs.

  5. Efficient white phosphorescent organic light-emitting diodes consisting of orange ultrathin and blue mixed host emission layers

    NASA Astrophysics Data System (ADS)

    Sheng, Ren; Zuo, Liangmei; Xue, Kaiwen; Duan, Yu; Chen, Ping; Cheng, Gang; Zhao, Yi

    2016-08-01

    We have successfully demonstrated highly efficient white phosphorescent organic light-emitting diodes (OLEDs) by inserting an ultrathin non-doped orange layer within blue mixed host emission layer. The key feature of the novel device is the employment of blue mixed host and orange ultrathin layers, resulting in an extended recombination region and more balanced charge carrier. The maximum efficiencies of 33.8 lm W-1 and 32.2 cd A-1 are obtained. Moreover, the resulting white device achieves a slight efficiency roll-off and a high luminance at low operating voltage. Our versatile concept suggests a promising simple method to achieve high performance white OLEDs.

  6. A quiet flow Ludwieg tube for study of transition in compressible boundary layers: Design and feasibility

    NASA Technical Reports Server (NTRS)

    Schneider, Steven P.

    1991-01-01

    Laminar-turbulent transition in high speed boundary layers is a complicated problem which is still poorly understood, partly because of experimental ambiguities caused by operating in noisy wind tunnels. The NASA Langley experience with quiet tunnel design has been used to design a quiet flow tunnel which can be constructed less expensively. Fabrication techniques have been investigated, and inviscid, boundary layer, and stability computer codes have been adapted for use in the nozzle design. Construction of such a facility seems feasible, at a reasonable cost. Two facilities have been proposed: a large one, with a quiet flow region large enough to study the end of transition, and a smaller and less expensive one, capable of studying low Reynolds number issues such as receptivity. Funding for either facility remains to be obtained, although key facility elements have been obtained and are being integrated into the existing Purdue supersonic facilities.

  7. Effect of chemical heat release in a temporally evolving mixing layer

    NASA Technical Reports Server (NTRS)

    Higuera, F. J.; Moser, R. D.

    1994-01-01

    Two-dimensional numerical simulations of a temporally evolving mixing layer with an exothermic infinitely fast diffusion flame between two unmixed reactants have been carried out in the limit of zero Mach number to study the effect of the heat release on the early stages of the evolution of the flow. Attention has been directed to relatively large values of the oxidizer-to-fuel mass stoichiometric ratio typical of hydrocarbon flames, and initial vorticity distributions thicker than the temperature and species distributions have been chosen to mimic the situation at the outlet of a jet. The results show that, during the stages of the evolution covered by the present simulations, enhancement of combustion occurs by local stretching of the flame without much augmentation of its area. The rate of product generation depends strongly on the initial conditions, which suggests the possibility of controlling the combustion by acting on the flow. Rollup and vortex amalgamation still occur in these reacting flows but are very much affected by the production of new vorticity by baroclinic torques. These torques lead to counter rotating vortex pairs around the flame and, more importantly, in thin layers of light fluid that leave the vicinity of the flame when the Kelvin-Helmholtz instability begins to develop. Propelled by the vortex pairs, these layers wind around, split on reaching high pressure regions, and originate new vortex pairs in a process that ends up building large-scale vortices with a vorticity distribution more complex than for a constant density fluid.

  8. Mixed Layer Depth Trends in the Bay of Biscay over the Period 1975–2010

    PubMed Central

    Costoya, Xurxo; deCastro, Maite; Gómez-Gesteira, Moncho; Santos, Fran

    2014-01-01

    Wintertime trends in mixed layer depth (MLD) were calculated in the Bay of Biscay over the period 1975–2010 using the Simple Ocean Data Assimilation (SODA) package. The reliability of the SODA database was confirmed correlating its results with those obtained from the experimental Argo database over the period 2003–2010. An iso-thermal layer depth (TLD) and an iso-pycnal layer depth (PLD) were defined using the threshold difference method with ΔT = 0.5°C and Δσθ = 0.125 kg/m3. Wintertime trends of the MLD were calculated using winter extended (December-March) anomalies and annual maxima. Trends calculated for the whole Bay of Biscay using both parameters (TLD and PLD) showed to be dependent on the area. Thus, MLD became deeper in the southeastern corner and shallower in the rest of the area. Air temperature was shown to play a key role in regulating the different spatial behavior of the MLD. Negative air temperature trends localized in the southeastern corner coincide with MLD deepening in this area, while, positive air temperature trends are associated to MLD shoaling in the rest of the bay. Additionally, the temperature trend calculated along the first 700 m of the water column is in good agreement with the different spatial behavior revealed for the MLD trend. PMID:24922066

  9. Charge regulation and energy dissipation while compressing and sliding a cross-linked chitosan hydrogel layer.

    PubMed

    Liu, Chao; Thormann, Esben; Tyrode, Eric; Claesson, Per M

    2015-04-01

    Interactions between a silica surface and a surface coated with a grafted cross-linked hydrogel made from chitosan/PAA multilayers are investigated, utilizing colloidal probe atomic force microscopy. Attractive double-layer forces are found to dominate the long-range interaction over a broad range of pH and ionic strength conditions. The deduced potential at the hydrogel/aqueous interface is found to be very low. This situation is maintained in the whole pH-range investigated, even though the degree of protonation of chitosan changes significantly. This demonstrates that pH-variations change the concentration of counterions within the hydrogel to keep the interior close to uncharged, which is similar to what has been observed for polyelectrolyte brushes. Changes in pH and ionic strength affect the adhesion force and the friction force between the silica surface and the hydrogel layer, but not the friction coefficient. This suggests that the main energy dissipation mechanism arises from processes occurring within the hydrogel layer, rather than at the silica/hydrogel interface, and we suggest that it is related to stretching of polymer chains between the cross-linking points. We also find that an increased cross-linking density, from 40% to 100%, in the hydrogel reduces the friction coefficient.

  10. Selectivity of layered double hydroxides and their derivative mixed metal oxides as sorbents of hydrogen sulfide.

    PubMed

    Othman, Mohamed A; Zahid, Waleed M; Abasaeed, Ahmed E

    2013-06-15

    In the context of finding high efficient sorbent materials for removing hydrogen sulfide (H2S) from air stream, a screening study was performed to find the best combination of metals for the synthesis of layered double hydroxides (LDHs) and their derivative mixed metal oxides. Based on selectivity of 998 natural mineral species of sulfur-containing compounds, Cu(2+), Ni(2+) and Zn(2+) were selected as divalent metals, and Fe(3+), Al(3+) and Cr(3+) as trivalent metals to synthesis the LDHs sorbents. 10 LDHs materials and their calcined mixed metal oxides, Ni(0.66)Al(0.34), Cu(0.35)Ni(0.32)Al(0.33), Zn(0.66)Al(0.34), Cu(0.36)Zn(0.32)Al(0.32), Ni(0.64)Fe(0.36), Cu(0.35)Ni(0.31)Fe(0.34), Ni(0.66)Cr(0.34), Cu(0.35)Ni(0.31)Cr(0.34), Zn(0.66)Cr(0.34), Cu(0.33)Zn(0.32)Cr(0.35) were synthesized, characterized chemically and physically, and then tested using breakthrough test to determine their sulfur uptake. Ni(0.64)Fe(0.36) mixed metal oxides was found to have the best uptake of hydrogen sulfide (136 mg H₂S/g). Regeneration of spent Ni(0.64)Fe(0.36) mixed metal oxides was studied using two different mixture solutions, NaCl/NaOH and acetate-buffer/NaCl/NaOH. The latter mixture successfully desorbed the sulfur from the Ni0.64Fe0.36 sorbent for 2 cycles of regeneration/sorption.

  11. [Characteristics of Winter Atmospheric Mixing Layer Height in Beijing-Tianjin-Hebei Region and Their Relationship with the Atmospheric Pollution].

    PubMed

    Li, Meng; Tang, Gui-qian; Huang, Jun; Liu, Zi-rui; An, Jun-lin; Wang, Yue-si

    2015-06-01

    Atmospheric mixing layer height (MLH) is one of the main factors affecting the atmospheric diffusion and plays an important role in air quality assessment and distribution of the pollutants. Based on the ceilometers data, this paper has made synchronous observation on MLH in Beijing-Tianjin-Hebei region (Beijing, Tianjin, Shijiazhuang and Qinhuangdao) in heavy polluted February 2014 and analyzed the respective overall change and its regional features. Results show that in February 2014,the average of mixing layer height in Qinhuangdao is the highest, up to 865 +/- 268 m, and in Shijiazhuang is the lowest (568 +/- 207 m), Beijing's and Tianjin's are in between, 818 +/- 319 m and 834 +/- 334 m respectively; Combined with the meteorological data, we find that radiation and wind speed are main factors of the mixing layer height; The relationship between the particle concentration and mixing layer height in four sites suggests that mixing layer is less than 800 m, concentration of fine particulate matter in four sites will exceed the national standard (GB 3095-2012, 75 microg x m(-3)). During the period of observation, the proportion of days that mixing layer is less than 800 m in Beijing, Tianjin, Shijiazhuang and Qinhuangdao are 50%, 43%, 80% and 50% respectively. Shijiazhuang though nearly formation contaminant concentration is high, within the atmospheric mixed layer pollutant load is not high. Unfavorable atmospheric diffusion conditions are the main causes of heavy pollution in Shijiazhuang for a long time. The results of the study are of great significance for cognitive Beijing-Tianjin-Hebei area pollution distribution, and can provide a scientific reference for reasonable distribution of regional pollution sources.

  12. Mechanisms Controlling the Interannual Variation of Mixed Layer Temperature Averaged over the Nino-3 Region

    NASA Technical Reports Server (NTRS)

    Kim, Seung-Bum; Lee, Tong; Fukumori, Ichiro

    2007-01-01

    The present study examines processes governing the interannual variation of MLT in the eastern equatorial Pacific.Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the Nino-3 domain (5 deg N-5 deg S, 150 deg-90 deg W) are studied using an ocean data assimilation product that covers the period of 1993-2003. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. This allows the authors to characterize external advective processes that warm or cool the water within the domain as a whole. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed to mostly by Ekman current advecting large-scale temperature anomalies through the southern boundary of the domain. Unlike many previous studies, the subsurface processes that consist of vertical mixing and entrainment are explicitly evaluated. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to the temporal change in ML depth is negligible compared to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in upwelling and the temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Nina cooling events. However, such a warming tendency is overwhelmed by the cooling tendency associated with the large-scale upwelling by a factor of

  13. Control of Evaporation Behavior of an Inkjet-Printed Dielectric Layer Using a Mixed-Solvent System

    NASA Astrophysics Data System (ADS)

    Yang, Hak Soon; Kang, Byung Ju; Oh, Je Hoon

    2016-01-01

    In this study, the evaporation behavior and the resulting morphology of inkjet-printed dielectric layers were controlled using a mixed-solvent system to fabricate uniform poly-4-vinylphenol (PVP) dielectric layers without any pinholes. The mixed-solvent system consisted of two different organic solvents: 1-hexanol and ethanol. The effects of inkjet-printing variables such as overlap condition, substrate temperature, and different printing sequences (continuous and interlacing printing methods) on the inkjet-printed dielectric layer were also investigated. Increasing volume fraction of ethanol (VFE) is likely to reduce the evaporation rate gradient and the drying time of the inkjet-printed dielectric layer; this diminishes the coffee stain effect and thereby improves the uniformity of the inkjet-printed dielectric layer. However, the coffee stain effect becomes more severe with an increase in the substrate temperature due to the enhanced outward convective flow. The overlap condition has little effect on the evaporation behavior of the printed dielectric layer. In addition, the interlacing printing method results in either a stronger coffee stain effect or wavy structures of the dielectric layers depending on the VFE of the PVP solution. All-inkjet-printed capacitors without electrical short circuiting can be successfully fabricated using the optimized PVP solution (VFE = 0.6); this indicates that the mixed-solvent system is expected to play an important role in the fabrication of high-quality inkjet-printed dielectric layers in various printed electronics applications.

  14. Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. Part II: Multi-layered cloud

    SciTech Connect

    Morrison, H; McCoy, R B; Klein, S A; Xie, S; Luo, Y; Avramov, A; Chen, M; Cole, J; Falk, M; Foster, M; Genio, A D; Harrington, J; Hoose, C; Khairoutdinov, M; Larson, V; Liu, X; McFarquhar, G; Poellot, M; Shipway, B; Shupe, M; Sud, Y; Turner, D; Veron, D; Walker, G; Wang, Z; Wolf, A; Xu, K; Yang, F; Zhang, G

    2008-02-27

    Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a deep, multi-layered, mixed-phase cloud system observed during the ARM Mixed-Phase Arctic Cloud Experiment. This cloud system was associated with strong surface turbulent sensible and latent heat fluxes as cold air flowed over the open Arctic Ocean, combined with a low pressure system that supplied moisture at mid-level. The simulations, performed by 13 single-column and 4 cloud-resolving models, generally overestimate the liquid water path and strongly underestimate the ice water path, although there is a large spread among the models. This finding is in contrast with results for the single-layer, low-level mixed-phase stratocumulus case in Part I of this study, as well as previous studies of shallow mixed-phase Arctic clouds, that showed an underprediction of liquid water path. The overestimate of liquid water path and underestimate of ice water path occur primarily when deeper mixed-phase clouds extending into the mid-troposphere were observed. These results suggest important differences in the ability of models to simulate Arctic mixed-phase clouds that are deep and multi-layered versus shallow and single-layered. In general, models with a more sophisticated, two-moment treatment of the cloud microphysics produce a somewhat smaller liquid water path that is closer to observations. The cloud-resolving models tend to produce a larger cloud fraction than the single-column models. The liquid water path and especially the cloud fraction have a large impact on the cloud radiative forcing at the surface, which is dominated by the longwave flux for this case.

  15. Three-dimensional compressible laminar boundary layers on sharp and blunt circular cones at angle of attack

    NASA Technical Reports Server (NTRS)

    Popinski, Z.; Davis, R. T.

    1973-01-01

    A method for solving the three-dimensional compressible laminar boundary layer equations for the case of a circular cone and a sphere-cone body at an angle of attack is presented. The governing equations are modified by a similarity type transformation and then transformed into a Crocco-type form. The resulting set of equations is solved simultaneously by an iterative method using an implicit finite difference scheme by means of an efficient algorithm for equations of tridiagonal form. The effects of streamline swallowing on a sharp cone are included by introducing the true inviscid edge conditions at the distance from the wall equal to the boundary layer thickness. The validity of the approach was established by comparison of the computational results with similar results by other methods and with experimental data. It was concluded that at sufficiently high Mach number and moderate to large angles of attack, the streamline swallowing effects on a sharp cone result in higher values of skin friction and heat transfer as compared with the classical results for constant entropy.

  16. A numerical study of polydisperse spray flame ignition and extinction fronts in a mixing layer

    NASA Astrophysics Data System (ADS)

    Greenberg, J. B.; Kagan, L. S.; Sivashinsky, G. I.

    2013-12-01

    A new numerical study of laminar polydisperse flame ignition and extinction fronts in a mixing layer resulting from opposed streams of fuel and oxidant is presented. Two quite different initial droplet size distributions having the same Sauter mean diameter (SMD) are considered. The phenomenon of hysteresis is found to occur for a high initial droplet load but disappears as the latter decreases. The range of strain rate values for which hysteresis is prevalent depends on the initial size distribution. For example, whilst under certain operating conditions, an extinction front may result from using one initial droplet size distribution, use of another size distribution, even having the same SMD, can exhibit hysteresis. Other features of the influence of the initial spray polydispersity are discussed in depth.

  17. In situ atomic force microscopy imaging of electrodeposition of mixed layers of copper/cuprous oxide

    SciTech Connect

    Bonnefont, A.; Kostecki, R.; McLarnon, F.; Arrayet, J.C.; Servant, L.; Argoul, F.

    1999-11-01

    In situ atomic force microscopy (AFM) was applied to the dynamic characterization of the growth of mixed Cu/Cu{sub 2}O layers obtained by galvanostatic electrodeposition from alkaline Cu(II) lactate solutions. The correlation of the cathode potential profile with the average topographic profiles computed from the AFM images provided evidence for two transitions in the deposit growth during which the average growth velocity underwent rapid accelerations, the first one corresponding to zero interfacial concentration (Sand's time) and the second one to the emergence of the oscillations by a smooth transition. Despite its temporal resolution, the AFM technique could not capture the details of a single oscillation, but it proved to be quite adequate for tracking the general evolution of the electrode surface.

  18. The three-dimensional evolution of a plane mixing layer - Pairing and transition to turbulence

    NASA Technical Reports Server (NTRS)

    Moser, Robert D.; Rogers, Michael M.

    1993-01-01

    The evolution of three-dimensional temporally evolving plane mixing layers through as many as three pairings has been simulated numerically. All simulations were begun from a few low-wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity. Three-dimensional perturbations were used with amplitudes ranging from infinitesimal to large enough to trigger a rapid transition to turbulence. Pairing is found to inhibit the growth of infinitesimal three-dimensional disturbances, and to trigger the transition to turbulence in highly three-dimensional flows. The mechanisms responsible for the growth of three-dimensionality and onset of transition to turbulence are described. The transition to turbulence is accompanied by the formation of thin sheets of spanwise vorticity, which undergo secondary rollups. The post-transitional simulated flow fields exhibit many properties characteristic of turbulent flows.

  19. Behavior of streamwise rib vortices in a three-dimensional mixing layer

    NASA Technical Reports Server (NTRS)

    Lopez, J. M.; Bulbeck, C. J.

    1992-01-01

    The structure and behavior of a streamwise rib vortex in a direct numerical simulation of a time-developing three-dimensional incompressible plane mixing layer is examined. Where the rib vortex is being stretched, the vorticity vector is primarily directed in the vortex axial direction and the radial and azimuthal velocity distribution is similar to that of a Burger's vortex. In the region where the vortex stretching is negative, there is a change in the local topology of the vortex. The axial flow is decelerated and a negative azimuthal component of vorticity is induced. These features are characteristic of vortex breakdown. The temporal evolution of the rib vortex is similar to the evolution of an axisymmetric vortex in the early stages of vortex breakdown. The effect of vortex breakdown on other parts of the flow is, however, not as significant as the interaction between the rib vortex and other vortices.

  20. Effects of swell on transport and dispersion of oil plumes within the ocean mixed layer

    NASA Astrophysics Data System (ADS)

    Chen, Bicheng; Yang, Di; Meneveau, Charles; Chamecki, Marcelo

    2016-05-01

    The transport in the ocean mixed layer (OML) of oil plumes originated from deepwater blowouts is studied using large eddy simulations. In particular, we focus on the effects of swell on the modulation of turbulence in the OML and its impact on oil transport. Results show that when the misalignment between the wind and the swell propagation is small, Langmuir cells develop and significantly enhance the vertical dilution of the oil plume. Conversely, when the misalignment is large, vertical dilution is suppressed when compared to the no-swell case. Due to the strong directional shear of the mean flow within the OML, plume depth significantly impacts mean transport direction. The size of oil droplets in the plume also plays an important role in vertical dilution and mean transport direction.

  1. Tidally driven mixing and dissipation in the stratified boundary layer above steep submarine topography

    NASA Astrophysics Data System (ADS)

    Winters, K. B.

    2015-09-01

    A tidally driven, stratified boundary layer over supercritical topography is simulated numerically. The near-boundary flow is characterized by quasiperiodic, bore-like motions and episodic expulsion events where fluid is ejected into the stratified interior. The character of the bores is compared to the high-resolution ocean mooring data of van Haren (2006). The diffusivity of the flow near the boundary is estimated by means of a synthetic dye tracer experiment. The average dissipation rate within the dye cloud is computed and combined with the diffusivity estimate to yield an overall mixing efficiency of 0.15. Both the estimated diffusivity and dissipation rates are in reasonable agreement with the microstructure observations of Kunze et al. (2012) when scaled to the environmental conditions at the Monterey and Soquel Canyons and to the values estimated by van Haren and Gostiaux (2012) above the sloping bottom of the Great Meteor Seamount in the Canary Basin.

  2. High Spectral Resolution Lidar (HSRL)-2 Observations of Aerosol Variability and Mixing during Boundary Layer Evolution in Houston

    NASA Astrophysics Data System (ADS)

    Burton, S. P.; Scarino, A. J.; Rogers, R. R.; Hostetler, C. A.; Ferrare, R. A.; Sawamura, P.; Berkoff, T.; Harper, D. B.; Cook, A. L.; Saide, P. E.

    2014-12-01

    The NASA Langley airborne multi-wavelength High Spectral Resolution Lidar (HSRL-2) provides the vertical distribution of aerosol optical properties as "curtains" of aerosol extinction, backscatter and depolarization along the flight track, plus intensive properties that are used to infer aerosol type and external mixing of types. Deployed aboard the NASA Langley King Air on the DISCOVER-AQ field mission in Houston in September 2013, HSRL-2 flew a pattern that included 18 ground sites, repeated four times a day, coordinated with a suite of airborne in situ measurements. The horizontally and vertically resolved curtains of HSRL-2 measurements give an unparalleled view of the spatial and temporal variability of aerosol, which provide broad context for interpreting other measurements and models. In Houston, HSRL-2 generally observed significant variability with distinct layering: boundary layer, residual layer, and frequent upper layers of smoke transported from the Mississippi Valley. The period from Sep. 11-14 is notable for a large aerosol build-up and persistent layers in the free troposphere. We investigate the aerosol properties and evolution using the vertically resolved HSRL-2 measurements, typing and mixture analysis techniques, and boundary layer detection. Between morning and afternoon overpasses, as the boundary layer grows, many distinctions between the layers are lost as the aerosols become mixed. As the boundary layer collapses overnight, the aerosols are cut off and are observed in a distinct residual layer the following morning. HSRL-2 measurements of the upper smoke layers suggest slightly different properties each day as new smoke enters the region, while the morning boundary layer indicates more similarity in local emissions day-to-day. HSRL-2 intensive variables (indicators of aerosol type) reflect complex yet predictable mixing. We will present the analysis of aerosol mixtures, and explore the WRF-Chem chemical transport model along the HSRL-2

  3. Part 2 of a Computational Study of a Drop-Laden Mixing Layer

    NASA Technical Reports Server (NTRS)

    Okongo, Nora; Bellan, Josette

    2004-01-01

    This second of three reports on a computational study of a mixing layer laden with evaporating liquid drops presents the evaluation of Large Eddy Simulation (LES) models. The LES models were evaluated on an existing database that had been generated using Direct Numerical Simulation (DNS). The DNS method and the database are described in the first report of this series, Part 1 of a Computational Study of a Drop-Laden Mixing Layer (NPO-30719), NASA Tech Briefs, Vol. 28, No.7 (July 2004), page 59. The LES equations, which are derived by applying a spatial filter to the DNS set, govern the evolution of the larger scales of the flow and can therefore be solved on a coarser grid. Consistent with the reduction in grid points, the DNS drops would be represented by fewer drops, called computational drops in the LES context. The LES equations contain terms that cannot be directly computed on the coarser grid and that must instead be modeled. Two types of models are necessary: (1) those for the filtered source terms representing the effects of drops on the filtered flow field and (2) those for the sub-grid scale (SGS) fluxes arising from filtering the convective terms in the DNS equations. All of the filtered-sourceterm models that were developed were found to overestimate the filtered source terms. For modeling the SGS fluxes, constant-coefficient Smagorinsky, gradient, and scale-similarity models were assessed and calibrated on the DNS database. The Smagorinsky model correlated poorly with the SGS fluxes, whereas the gradient and scale-similarity models were well correlated with the SGS quantities that they represented.

  4. Formation of mixed-layer structures in smectites intercalated with tryptone

    NASA Astrophysics Data System (ADS)

    Block, K. A.; Trusiak, A.; Steiner, J. C.; Katz, A.; Gottlieb, P.; Alimova, A.

    2012-12-01

    Stable clay-protein complexes are fundamental to studies of the critical zone, terrestrial ecosystems, pharmacology, and industrial applications such as bioremediation. Two sets of montmorillonite clays were purified and made homoionic for Na and Mg. Mg-montmorillonite and Na-montmorillonite were mixed with tryptone (casein digest) in a 9:1 and 18:1 clay:tryptone ratio, resulting in the formation of reversible intercalated structures. X-ray diffraction analysis of the protein-clay complexes produced profiles consisting of two peaks associated with the smectite 001 reflection and a related tryptone-packet peak similar to that produced by a mixed layer clay structure. Shifts in the 002, 003, and 004 diffraction maxima are attributed to disorder caused by the interaction with the protein. Line broadening in the smectite-tryptone XRD spectra is interpreted to be the result of interlayer absorption. Adsorption produces coherent crystalline packets of regularly interbedded tryptone and smectite platelets. SEM images reveal clay platelets with upwardly rolled edges that tend toward cylindrical structures with the production of occasional tubes in the smaller platelet size range as noted for organic compound-kaolinite intercalation reported by Fenoll Hach-Ali and Weiss (1969). Reference: Fenoll Hach-Ali, P.F., Weiss, A., 1969. Estudio de la reaccion de caolinita y N-metilform- amida. Quimica LXV, 769-790. Scanning electron micrograph of tryptone-intercalated clay platelets exhibiting rolled edge structure.

  5. Sputtering and Reflection Data for Mixed Tungsten/Beryllium Layers Under Typical FIRE Divertor Fluxes

    NASA Astrophysics Data System (ADS)

    Ruzic, D. N.; Nieto, M.; Alman, D. A.; Brooks, J. N.

    2001-10-01

    Computer modeling has been done as part of the Fusion Ignition Research Experiment (FIRE) design study. The current focus is on beryllium/tungsten mixed-material erosion. The FIRE design calls for a beryllium first wall and tungsten divertors. Beryllium can be sputtered from the first wall and transported to the divertor, forming a Be/W mixture on the divertor. The beryllium sputtering from the first wall is obtained from fluxes calculated by the DEGAS2 neutral transport code. Subsequent transport to the divertor is calculated by the REDEP code. VFTRIM-3D, a variant of the TRIM-SP binary-collision code, is used to investigate the sputtering properties of the Be/W divertor. Finally, WBC can compute beryllium and tungsten erosion and core plasma contamination using the sputtering and reflection coefficients obtained with VFTRIM-3D. In the present work, the VFTRIM-3D code was run on a W/Be surface with the Be content varied from 0 to 100 atomic percent. Deuterium and tritium (ions and neutrals), oxygen, beryllium from the first wall, and tungsten being redeposited are all incident on this mixed W/Be layer. Data on reflection and sputtering coefficients as a function of beryllium content in the bombarded surface will be presented.

  6. Mixed layers of sodium caseinate + dextran sulfate: influence of order of addition to oil-water interface.

    PubMed

    Jourdain, Laureline S; Schmitt, Christophe; Leser, Martin E; Murray, Brent S; Dickinson, Eric

    2009-09-01

    We report on the interfacial properties of electrostatic complexes of protein (sodium caseinate) with a highly sulfated polysaccharide (dextran sulfate). Two routes were investigated for preparation of adsorbed layers at the n-tetradecane-water interface at pH = 6. Bilayers were made by the layer-by-layer deposition technique whereby polysaccharide was added to a previously established protein-stabilized interface. Mixed layers were made by the conventional one-step method in which soluble protein-polysaccharide complexes were adsorbed directly at the interface. Protein + polysaccharide systems gave a slower decay of interfacial tension and stronger dilatational viscoelastic properties than the protein alone, but there was no significant difference in dilatational properties between mixed layers and bilayers. Conversely, shear rheology experiments exhibited significant differences between the two kinds of interfacial layers, with the mixed system giving much stronger interfacial films than the bilayer system, i.e., shear viscosities and moduli at least an order of magnitude higher. The film shear viscoelasticity was further enhanced by acidification of the biopolymer mixture to pH = 2 prior to interface formation. Taken together, these measurements provide insight into the origin of previously reported differences in stability properties of oil-in-water emulsions made by the bilayer and mixed layer approaches. Addition of a proteolytic enzyme (trypsin) to both types of interfaces led to a significant increase in the elastic modulus of the film, suggesting that the enzyme was adsorbed at the interface via complexation with dextran sulfate. Overall, this study has confirmed the potential of shear rheology as a highly sensitive probe of associative electrostatic interactions and interfacial structure in mixed biopolymer layers. PMID:19459686

  7. Spreading Layers in Accreting Objects: Role of Acoustic Waves for Angular Momentum Transport, Mixing, and Thermodynamics

    NASA Astrophysics Data System (ADS)

    Philippov, Alexander A.; Rafikov, Roman R.; Stone, James M.

    2016-01-01

    Disk accretion at a high rate onto a white dwarf (WD) or a neutron star has been suggested to result in the formation of a spreading layer (SL)—a belt-like structure on the object's surface, in which the accreted matter steadily spreads in the poleward (meridional) direction while spinning down. To assess its basic characteristics, we perform two-dimensional hydrodynamic simulations of supersonic SLs in the relevant morphology with a simple prescription for cooling. We demonstrate that supersonic shear naturally present at the base of the SL inevitably drives sonic instability that gives rise to large-scale acoustic modes governing the evolution of the SL. These modes dominate the transport of momentum and energy, which is intrinsically global and cannot be characterized via some form of local effective viscosity (e.g., α-viscosity). The global nature of the wave-driven transport should have important implications for triggering Type I X-ray bursts in low-mass X-ray binaries. The nonlinear evolution of waves into a system of shocks drives effective rearrangement (sensitively depending on thermodynamical properties of the flow) and deceleration of the SL, which ultimately becomes transonic and susceptible to regular Kelvin–Helmholtz instability. We interpret this evolution in terms of the global structure of the SL and suggest that mixing of the SL material with the underlying stellar fluid should become effective only at intermediate latitudes on the accreting object's surface, where the flow has decelerated appreciably. In the near-equatorial regions the transport is dominated by acoustic waves and mixing is less efficient. We speculate that this latitudinal nonuniformity of mixing in accreting WDs may be linked to the observed bipolar morphology of classical nova ejecta.

  8. Reduced kinetic mechanism of ignition for nonpremixed hydrogen/air in a supersonic mixing layer

    SciTech Connect

    Ju, Y.; Niioka, T. . Inst. of Fluid Science)

    1994-11-01

    Transient ignition processes in a two-dimensional spatially evolving supersonic mixing layer consisting of a parallel nonpremixed airstream and a hydrogen stream both with temperatures higher than 1,000 K were investigated numerically by using the full chemistry and its reduced chemistry. A phenomenon different from that examined in previous studies, in which ignition of hydrogen/oxygen mixtures was considered, was found in the nonpremixed case examined here. It was shown that the concentration of O was greater than that of OH before ignition, but became smaller with the development of ignition process. Fourteen important reactions for ignition were obtained and verified using sensitivity analyses of ignition delay time and radical concentrations. Several different four-step and three-step reduced kinetic mechanisms were then deduced by introducing the steady-state approximation to different species. Comparison of these reduced kinetic mechanisms with the full chemistry showed that the steady-state approximation of O used in previous studies caused serious errors in the prediction of ignition delay time in supersonic flow, in which nonpremixed character is predominant and the transport phenomenon is important. Ignition locations predicted with the proper four-step and three-step reduced kinetic mechanisms were within 5% and 20% of those predicted with the full chemistry. Finally, these two reduced mechanisms were used to evaluate the effect of viscous dissipation on ignition in the supersonic shear layer. Good agreements between the results of the present reduced kinetic mechanisms and those of the full chemistry were obtained.

  9. Mixed Layer Heights Derived from the NASA Langley Research Center Airborne High Spectral Resolution Lidar

    NASA Technical Reports Server (NTRS)

    Scarino, Amy J.; Burton, Sharon P.; Ferrare, Rich A.; Hostetler, Chris A.; Hair, Johnathan W.; Obland, Michael D.; Rogers, Raymond R.; Cook, Anthony L.; Harper, David B.; Fast, Jerome; Dasilva, Arlindo; Benedetti, Angela

    2012-01-01

    The NASA airborne High Spectral Resolution Lidar (HSRL) has been deployed on board the NASA Langley Research Center's B200 aircraft to several locations in North America from 2006 to 2012 to aid in characterizing aerosol properties for over fourteen field missions. Measurements of aerosol extinction (532 nm), backscatter (532 and 1064 nm), and depolarization (532 and 1064 nm) during 349 science flights, many in coordination with other participating research aircraft, satellites, and ground sites, constitute a diverse data set for use in characterizing the spatial and temporal distribution of aerosols, as well as properties and variability of the Mixing Layer (ML) height. We describe the use of the HSRL data collected during these missions for computing ML heights and show how the HSRL data can be used to determine the fraction of aerosol optical thickness within and above the ML, which is important for air quality assessments. We describe the spatial and temporal variations in ML heights found in the diverse locations associated with these experiments. We also describe how the ML heights derived from HSRL have been used to help assess simulations of Planetary Boundary Layer (PBL) derived using various models, including the Weather Research and Forecasting Chemistry (WRF-Chem), NASA GEOS-5 model, and the ECMWF/MACC models.

  10. Mapping the Interactions between Shocks and Mixing Layers in a 3-Stream Supersonic Jet

    NASA Astrophysics Data System (ADS)

    Lewalle, Jacques; Ruscher, Christopher; Kan, Pinqing; Tenney, Andrew; Gogineni, Sivaram; Kiel, Barry

    2015-11-01

    Pressure is obtained from an LES calculation of the supersonic jet (Ma1 = 1 . 6) issuing from a rectangular nozzle in a low-subsonic co-flow; a tertiary flow, also rectangular with Ma3 = 1 insulates the primary jet from an aft-deck plate. The developing jet exhibits complex three-dimensional interactions between oblique shocks, multiple mixing layers and corner vortices, which collectively act as a skeleton for the flow. Our study is based on several plane sections through the pressure field, with short signals (0.1 s duration at 80 kHz sampling rate). Using wavelet-based band-pass filtering and cross-correlations, we map the directions of propagation of information among the various ``bones'' in the skeleton. In particular, we identify upstream propagation in some frequency bands, 3-dimensional interactions between the various shear layers, and several key bones from which the pressure signals, when taken as reference, provide dramatic phase-locking for parts of the skeleton. We acknowledge the support of AFRL through an SBIR grant.

  11. Ozone Transport and Mixing Processes in the Boundary Layer Observed with Lidar during Discover-AQ

    NASA Astrophysics Data System (ADS)

    Senff, C. J.; Langford, A. O.; Alvarez, R. J. _II, II; Choukulkar, A.; Brewer, A.; Weickmann, A. M.; Kirgis, G.; Sandberg, S.; Hardesty, M.; Delgado, R.; Long, R.; Brown, S. S.

    2014-12-01

    The final two Discover-AQ air quality studies were conducted in Houston, TX in September 2013 and the Colorado Front Range in July/August 2014. These two regions are characterized by different ozone precursor sources and exhibit unique regional wind flow patterns. During these studies, NOAA deployed its truck-based, scanning TOPAZ ozone lidar to document the vertical structure and temporal evolution of ozone concentrations from near the surface up to about 2.5 km above ground level. In Houston, TOPAZ was located next to a radar wind profiler while during the Colorado campaign, Doppler wind lidars collocated with TOPAZ measured wind profiles and vertical velocity statistics throughout the boundary layer (BL). For both studies, nearby in situ sensors provided continuous observations of surface ozone and NOx. These combinations of remote and in situ sensors lend themselves to study the influence of BL transport and mixing processes on surface-level ozone. In this presentation, we focus on characterizing and quantifying changes in surface ozone due to several BL processes, including the Houston land-sea breeze circulation, the terrain-driven BL flow in the Colorado Front Range area, thunderstorm outflows, BL growth rate and depth, and entrainment of air from the residual layer or lower free troposphere into the BL.

  12. Climatology of the mixed layer depth in the East/Japan Sea

    NASA Astrophysics Data System (ADS)

    Lim, SeHan; Jang, Chan Joo; Oh, Im Sang; Park, JongJin

    2012-08-01

    A climatology for the mixed layer depth (MLD) in the East/Japan Sea was produced using temperature profile data collected from 1931 to 2005. MLD is defined as the depth at which the temperature differs from that at 10 m depth by 0.2 °C. It varies seasonally with a range of about 20 m, a minimum, near the subpolar front (SPF, 38°-41°N), 60-100 m in south of 38°N and north of 41°N, and about 200 m near the winter convection region (132°-135°E & 41°-43°N). The weaker seasonality near the SPF seems to result from year-round strong stratification sustained largely by advected warm water of the East Korean Warm Current and a result of complex dynamic process of frontogenesis including lateral dynamics or wind-induced friction. The temperature-based MLD does not show any significant difference (mostly less than 20 m) from the density-based values over most of the East/Japan Sea except a few localized regions near the Russian and Japanese coasts where barrier layers form from late fall through early spring. This study confirms that atmospheric forcing largely dominates the overall magnitude of MLD seasonal variability in most of the East/Japan Sea.

  13. On the instabilities of supersonic mixing layers - A high-Mach-number asymptotic theory

    NASA Technical Reports Server (NTRS)

    Balsa, Thomas F.; Goldstein, M. E.

    1990-01-01

    The stability of a family of tanh mixing layers is studied at large Mach numbers using perturbation methods. It is found that the eigenfunction develops a multilayered structure, and the eigenvalue is obtained by solving a simplified version of the Rayleigh equation (with homogeneous boundary conditions) in one of these layers which lies in either of the external streams. This analysis leads to a simple hypersonic similarity law which explains how spatial and temporal phase speeds and growth rates scale with Mach number and temperature ratio. Comparisons are made with numerical results, and it is found that this similarity law provides a good qualitative guide for the behavior of the instability at high Mach numbers. In addition to this asymptotic theory, some fully numerical results are also presented (with no limitation on the Mach number) in order to explain the origin of the hypersonic modes (through mode splitting) and to discuss the role of oblique modes over a very wide range of Mach number and temperature ratio.

  14. Heterogeneous distribution of plankton within the mixed layer and its implications for bloom formation in tropical seas.

    PubMed

    Calbet, Albert; Agersted, Mette Dalgaard; Kaartvedt, Stein; Møhl, Malene; Møller, Eva Friis; Enghoff-Poulsen, Søren; Paulsen, Maria Lund; Solberg, Ingrid; Tang, Kam W; Tönnesson, Kajsa; Raitsos, Dionysios E; Nielsen, Torkel Gissel

    2015-01-01

    Intensive sampling at the coastal waters of the central Red Sea during a period of thermal stratification, prior to the main seasonal bloom during winter, showed that vertical patches of prokaryotes and microplankton developed and persisted for several days within the apparently density uniform upper layer. These vertical structures were most likely the result of in situ growth and mortality (e.g., grazing) rather than physical or behavioural aggregation. Simulating a mixing event by adding nutrient-rich deep water abruptly triggered dense phytoplankton blooms in the nutrient-poor environment of the upper layer. These findings suggest that vertical structures within the mixed layer provide critical seeding stocks that can rapidly exploit nutrient influx during mixing, leading to winter bloom formation. PMID:26062783

  15. Heterogeneous distribution of plankton within the mixed layer and its implications for bloom formation in tropical seas

    NASA Astrophysics Data System (ADS)

    Calbet, Albert; Agersted, Mette Dalgaard; Kaartvedt, Stein; Møhl, Malene; Møller, Eva Friis; Enghoff-Poulsen, Søren; Paulsen, Maria Lund; Solberg, Ingrid; Tang, Kam W.; Tönnesson, Kajsa; Raitsos, Dionysios E.; Nielsen, Torkel Gissel

    2015-06-01

    Intensive sampling at the coastal waters of the central Red Sea during a period of thermal stratification, prior to the main seasonal bloom during winter, showed that vertical patches of prokaryotes and microplankton developed and persisted for several days within the apparently density uniform upper layer. These vertical structures were most likely the result of in situ growth and mortality (e.g., grazing) rather than physical or behavioural aggregation. Simulating a mixing event by adding nutrient-rich deep water abruptly triggered dense phytoplankton blooms in the nutrient-poor environment of the upper layer. These findings suggest that vertical structures within the mixed layer provide critical seeding stocks that can rapidly exploit nutrient influx during mixing, leading to winter bloom formation.

  16. Heterogeneous distribution of plankton within the mixed layer and its implications for bloom formation in tropical seas

    PubMed Central

    Calbet, Albert; Agersted, Mette Dalgaard; Kaartvedt, Stein; Møhl, Malene; Møller, Eva Friis; Enghoff-Poulsen, Søren; Paulsen, Maria Lund; Solberg, Ingrid; Tang, Kam W.; Tönnesson, Kajsa; Raitsos, Dionysios E.; Nielsen, Torkel Gissel

    2015-01-01

    Intensive sampling at the coastal waters of the central Red Sea during a period of thermal stratification, prior to the main seasonal bloom during winter, showed that vertical patches of prokaryotes and microplankton developed and persisted for several days within the apparently density uniform upper layer. These vertical structures were most likely the result of in situ growth and mortality (e.g., grazing) rather than physical or behavioural aggregation. Simulating a mixing event by adding nutrient-rich deep water abruptly triggered dense phytoplankton blooms in the nutrient-poor environment of the upper layer. These findings suggest that vertical structures within the mixed layer provide critical seeding stocks that can rapidly exploit nutrient influx during mixing, leading to winter bloom formation. PMID:26062783

  17. Mixing layer height measurements determines influence of meteorology on air pollutant concentrations in urban area

    NASA Astrophysics Data System (ADS)

    Schäfer, Klaus; Blumenstock, Thomas; Bonn, Boris; Gerwig, Holger; Hase, Frank; Münkel, Christoph; Nothard, Rainer; von Schneidemesser, Erika

    2015-10-01

    Mixing layer height (MLH) is a key parameter to determine the influence of meteorological parameters upon air pollutants such as trace gas species and particulate concentrations near the surface. Meteorology, and MLH as a key parameter, affect the budget of emission source strengths, deposition, and accumulation. However, greater possibilities for the application of MLH data have been identified in recent years. Here, the results of measurements in Berlin in 2014 are shown and discussed. The concentrations of NO, NO2, O3, CO, PM1, PM2.5, PM10 and about 70 volatile organic compounds (anthropogenic and biogenic of origin) as well as particle size distributions and contributions of SOA and soot species to PM were measured at the urban background station of the Berlin air quality network (BLUME) in Nansenstr./Framstr., Berlin-Neukölln. A Vaisala ceilometer CL51, which is a commercial mini-lidar system, was applied at that site to detect the layers of the lower atmosphere in real time. Special software for these ceilometers with MATLAB provided routine retrievals of MLH from vertical profiles of laser backscatter data. Five portable Bruker EM27/SUN FTIR spectrometers were set up around Berlin to detect column averaged abundances of CO2 and CH4 by solar absorption spectrometry. Correlation analyses were used to show the coupling of temporal variations of trace gas compounds and PM with MLH. Significant influences of MLH upon NO, NO2, PM10, PM2.5, PM1 and toluene (marker for traffic emissions) concentrations as well as particle number concentrations in the size modes 70 - 100 nm, 100 - 200 nm and 200 - 500 nm on the basis of averaged diurnal courses were found. Further, MLH was taken as important auxiliary information about the development of the boundary layer during each day of observations, which was required for the proper estimation of CO2 and CH4 source strengths from Berlin on the basis of atmospheric column density measurements.

  18. Effects of stable stratification on turbulent/nonturbulent interfaces in turbulent mixing layers

    NASA Astrophysics Data System (ADS)

    Watanabe, T.; Riley, J. J.; Nagata, K.

    2016-08-01

    Direct numerical simulations are used for investigating the effects of stable stratification on the turbulent/nonturbulent (T/NT) interface in stably stratified mixing layers whose buoyancy Reynolds number Reb on the centerline is large enough for small-scale three-dimensional turbulence to exist. The stratification changes the interface geometry, and a large part of the interface is oriented with normal in the vertical direction in the stratified flows. The structures of the T/NT interface layer are similar between the nonstratified and stratified flows, and the T/NT interface consists of the viscous superlayer and the turbulent sublayer. The stratification is locally strengthened near the T/NT interface as evidenced by the large vertical density gradient, resulting in the decrease in Reb in the T/NT interface layer. Thus, even the small-scale dissipation range is directly affected by the buoyancy near the T/NT interface, although the small scales are somewhat free from the direct effects of the buoyancy in the turbulent core region. The production rates of enstrophy and scalar dissipation, which arise from the strain/vorticity and strain/density-gradient interactions, are decreased near the T/NT interface because the stratification modifies the alignments among the vorticity, density gradient, and strain-rate eigenvectors near the T/NT interface. This influence on the small-scale turbulence dynamics is not observed in the turbulent core region because of the large Reb. A possible explanation is given for the influence of buoyancy on the alignment statistics based on the suppression of the vertical turbulent motions by buoyancy.

  19. On the Behavior of Three-dimensional Wave Packets in Viscously Spreading Mixing Layers

    NASA Technical Reports Server (NTRS)

    Balsa, Thomas F.

    1994-01-01

    We consider analytically the evolution of a three-dimensional wave packet generated by an impulsive source in a mixing layer. The base flow is assumed to be spreading due to viscous diffusion. The analysis is restricted to small disturbances (linearized theory). A suitable high-frequency ansatz is used to describe the packet; the key elements of this description are a complex phase and a wave action density. It is found that the product of this density and an infinitesimal material volume convecting at the local group velocity is not conserved: there is a continuous interaction between the base flow and the wave action. This interaction is determined by suitable mode-weighted averages of the second and fourth derivatives of the base-flow velocity profile. Although there is some tendency for the dominant wave number in the packet to shift from the most unstable value toward the neutral value, this shift is quite moderate. In practice, wave packets do not become locally neutral in a diverging base flow (as do instability modes), therefore, they are expected to grow more suddenly than pure instability modes and do not develop critical layers. The group velocity is complex; the full significance of this is realized by analytically continuing the equations for the phase and wave action into a complex domain. The implications of this analytic continuation are discussed vis-a-vis the secondary instabilities of the packet: very small scale perturbations on the phase can grow very rapidly initially, but saturate later because most of the energy in these perturbations is convected away by the group velocity. This remark, as well as the one regarding critical layers, has consequences for the nonlinear theories.

  20. Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

    NASA Astrophysics Data System (ADS)

    Jähn, Michael; Muñoz-Esparza, Domingo; Chouza, Fernando; Reitebuch, Oliver; Knoth, Oswald; Haarig, Moritz; Ansmann, Albert; Tegen, Ina

    2016-04-01

    Large eddy simulations (LESs) with ASAM (All Scale Atmospheric Model) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. This method is now also validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE (Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment) field campaign is used for both model initialization and comparisons. Several sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" or when the turbulent marine boundary layer flow is replaced by laminar winds. Additional simulation cases deal with modified surface characteristics and their impacts on the simulation results. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with lidar data show similarities in the downwind vertical wind structure and accurately reproduces the development of the daytime convective boundary layer measured by the Raman lidar.

  1. Radon-222, a proxy for vertical mixing of emissions in the urban nocturnal boundary layer

    NASA Astrophysics Data System (ADS)

    Chambers, S.; Williams, A. G.; Griffiths, A.; Crawford, J.; Zahorowski, W.

    2012-04-01

    There has been growing concern in recent decades regarding the health implications of fine particles (≤ 2.5μm), which are readily deposited deep within the lungs. In the interests of public health, and improving the predictive ability of Chemical Transport Models, it is imperative to improve our understanding of the diurnal variability of primary pollutant and precursor concentrations by, among others, improving our understanding of the underlying physics of transport and mixing processes. From the time of their release until they are removed from the atmosphere, the level of public exposure to emissions is closely related to rates of near-surface horizontal and vertical dispersion, the depth of the atmospheric boundary layer, and the venting from the boundary layer. These parameters, in turn, are dependent upon the amount and nature of mixing, which is closely related to atmospheric stability. With the exception of bushfires and dust storms, the greatest risk of public exposure to emissions occurs under "inversion" conditions, when the atmosphere is stably stratified. These very conditions are notoriously the most problematic for contemporary weather and chemical transport models. At such times the structure of the lowest 10-100m of the atmosphere can be quite complex, potentially containing multiple disconnected layers, and even stability measures based on surface similarity theory can fail (or yield inconclusive results) without sufficient vertical and temporal measurement resolution. Near-surface radon measurements provide a direct measure of the degree of dilution of surface-emitted scalar quantities by vertical mixing at night that is completely independent of local meteorological measurements and does not fail under conditions of near calm, which occur on the most stable nights. As such, they are a valuable proxy for potential pollution accumulation. In this study we analyse and discuss 22 months of continuous hourly observations within an urban airshed

  2. Simulation of the tropical oceans with an ocean GCM coupled to an atmospheric mixed-layer model

    SciTech Connect

    Murtugudde, R.; Seager, R.; Busalacchi, A.

    1996-08-01

    A reduced gravity, primitive equation, ocean general circulation model (GCM) is coupled to an advective atmospheric mixed-layer (AML) model to demonstrate the importance of a nonlocal atmospheric mixed-layer parameterization for a proper simulation of surface heat fluxes and sea surface temperatures (SST). Seasonal variability of the model SSTs and the circulation are generally in good agreement with the observations in each of the tropical oceans. These results are compared to other simulations that use a local equilibrium mixed-layer model. Inclusion of the advective AML model is demonstrated to lead to a significant improvement in the SST simulation in all three oceans. Advection and diffusion of the air humidity play significant roles in determining SSTs even in the tropical Pacific where the local equilibrium assumption was previously deemed quite accurate. The main, and serious, model flaw is an inadequate representation of the seasonal cycle in the upwelling regions of the eastern Atlantic and Pacific Oceans. The results indicate that the feedback between mixed-layer depths and SSTs can amplify SST errors, implying that increased realism in the modeling of the ocean mixed layer increases the demand for realism in the representation of the surface heat fluxes. The performance of the GCM with a local-equilibrium mixed-layer model in the Atlantic is as poor as previous simple ocean model simulations of the Atlantic. The conclusion of earlier studies that the simple ocean model was at fault may, in fact, not be correct. Instead the local-equilibrium heat flux parameterization appears to have been the major source of error. Accurate SST predictions may, hence, be feasible by coupling the AML model to computationally efficient simple ocean models. 69 refs., 18 figs., 1 tab.

  3. Weakly Penetrative Mixing in the Surface Layer of the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Lozovatsky, I.; Jinadasa, S. U. P.; Lucas, A.; MacKinnon, J. A.; Fernando, H. J.; Wijesekera, H. W.

    2014-12-01

    The first microstructure measurements under the ASIRI program were conducted in Bay of Bengal (BoB) during November 2014 in a region bounded by 16.95-16.25 N and 86.7- 87.0 E. Measurements were taken during the research cruise of r/v Roger Revelle using the VMP profiler down to ~ 140 m to infer the kinetic energy dissipation rate eps, temperature T, salinity S, and potential density anomaly sigT. Very strong stratification was observed just below a thin (less than 15-20 m deep) vertically homogeneous turbulent surface layer (SL), which effectively decoupled the former from the underlying thermohalocline. The upper boundary of the near-surface pycnocline was at z ~ 10 - 11 m and its lower boundary at z ~ 15 m. Under moderate (11 - 12 m/s) winds, the dissipation in the SL gradually decreased from the sea surface down to 10^-6 - 10^-8 W/kg at depths z ~ 10 - 15 m. Below z ~ 15 m, the dissipation rate sharply dropped to ~10^-9 W/kg, remaining approximately constant downward. The horizontal/temporal differences of T, S and sigT in the middle of SL were as high as dT ~ 0.25 C, dS ~ 0.4 psu, and dsigT ~ 0.22, respectively, over a distance of ~ 2 km. On the next day, under higher winds (~ 16 - 18 m/s), the SL deepened only slightly, being nominally decoupled from the pycnocline. The intensification of wind stress from ~ 0.16 to ~ 0.51 N/m2, led to an increase of eps to 10^-6 - 10^-7 W/kg across the entire mixing layer. The enhanced turbulence not only produced vertical mixing, but also initiated horizontal stirring, thus dramatically reducing thermohaline differences in the mixed SL down to dT ~ 0.017C, dS ~ 0.02 psu, and dsigT ~ 0.008, respectively. However, very strong stratification in the pycnocline suppressed the wind-induced vertical mixing, which did not penetrate below z ~ 22 - 25 m. No internal sources of turbulence were evident in the water interior, suggesting that under mild or even relatively strong but short-sustained winds small-scale dynamics of the SL and

  4. The seasonal cycle of the mixing layer height and its impact on black carbon concentrations in the Kathmandu Valley (Nepal)

    NASA Astrophysics Data System (ADS)

    Mues, Andrea; Rupakheti, Maheswar; Hoor, Peter; Bozem, Heiko; Münkel, Christoph; Lauer, Axel; Butler, Tim

    2016-04-01

    The properties and the vertical structure of the mixing layer as part of the planetary boundary layer are of key importance for local air quality. They have a substantial impact on the vertical dispersion of pollutants in the lower atmosphere and thus on their concentrations near the surface. In this study, ceilometer measurements taken within the framework of the SusKat project (Sustainable Atmosphere for the Kathmandu Valley) are used to investigate the mixing layer height in the Kathmandu Valley, Nepal. The applied method is based on the assumption that the aerosol concentration is nearly constant in the vertical and distinctly higher within the mixing layer than in the air above. Thus, the height with the steepest gradient within the ceilometer backscatter profile marks the top of the mixing layer. Ceilometer and black carbon (BC) measurements conducted from March 2013 through February 2014 provide a unique and important dataset for the analysis of the meteorological and air quality conditions in the Kathmandu Valley. In this study the mean diurnal cycle of the mixing layer height in the Kathmandu Valley for each season (pre-monsoon, monsoon, post-monsoon and winter season) and its dependency on the meteorological situation is investigated. In addition, the impact of the mixing layer height on the BC concentration is analyzed and compared to the relevance of other important processes such as emissions, horizontal advection and deposition. In all seasons the diurnal cycle is typically characterized by low mixing heights during the night, gradually increasing after sun rise reaching to maximum values in the afternoon before decreasing again. Seasonal differences can be seen particularly in the height of the mixing layer, e.g. from on average 153/1200 m (pre-monsoon) to 241/755 m (monsoon season) during the night/day, and the duration of enhanced mixing layer heights during daytime (around 12 hours (pre-monsoon season) to 8 hours (winter)). During the monsoon

  5. Mixed layer impact of Hurricane Katia passing over the Amazon/Orinoco plume as viewed in remotely sensed salinity observations

    NASA Astrophysics Data System (ADS)

    Carton, J.; Grodsky, S. A.; Nicolas, R.; Lagerloef, G. S.; Reverdin, G. P.; Chapron, B.; Yves, Q.; Kudryavtsev, V. N.; Kao, H.

    2012-12-01

    Hurricane strength increases dramatically with increasing sea surface temperature (SST) and decreases in response to entrainment of cooler sub-mixed layer water into the ocean mixed layer. At its seasonal peak the Amazon/Orinoco plume covers a region of one million square kilometers in the western tropical Atlantic with more than 1m of extra freshwater, creating a near-surface barrier layer that inhibits this mixing and warms to temperatures >29C. Here new remotely sensed sea surface salinity (SSS) observations help elucidate the ocean response to hurricane Katia, which crossed the plume in early fall, 2011. Its passage left a 1.5psu high salinity wake (in its impact on density, the equivalent of a 3.5C cooling) due to mixing of the shallow barrier layer, reminiscent of features previously observed at fixed locations in the Indian Ocean and Gulf of Mexico. Destruction of this barrier layer decreased SST cooling in the plume that would otherwise have occurred, thus preserving elevated SST and evaporation.

  6. The Effect of Different Mixing Methods on the Flow Rate and Compressive Strength of Mineral Trioxide Aggregate and Calcium-Enriched Mixture

    PubMed Central

    Shahi, Shahriar; Ghasemi, Negin; Rahimi, Saeed; Yavari, Hamid Reza; Samiei, Mohammad; Janani, Maryam; Bahari, Mahmood; Moheb, Sanaz

    2015-01-01

    Introduction: Flow rate (FR) and compressive strength (CS) are important properties of endodontic biomaterials that may be affected by various mixing methods. The aim of this experimental study was to evaluate the effect of different mixing methods on these properties of mineral trioxide aggregate (MTA) and calcium-enriched mixture (CEM) cement. Materials and methods: Hand, amalgamator and ultrasonic techniques were used to mix both biomaterials. Then 0.5 mL of each mixture was placed on a glass slab to measure FR. The second glass slab (100 g) was placed on the samples and 180 sec after the initiation of mixing a 100-g force was applied on it for 10 min. After 10 min, the load was removed, and the minimum and maximum diameters of the sample disks were measured. To measure the CS, 6 sample of each group were placed in steel molds and were then stored in distilled water for 21 h and 21 days. Afterwards, the CS test was performed. Data were analyzed with multi-variant ANOVA and post hoc Tukey tests. The level of significance was set at 0.05. Results: There were significant differences in FR of MTA and CEM cement with different mixing techniques (P<0.05). In the MTA group, none of the mixing techniques exhibited a significant effect on CS (P>0.05); however, in CEM group the CS at 21-h and 21-day intervals was higher with the hand technique (P<0.05). Conclusion: Mixing methods affected the flowability of both biomaterials and compressive strength of CEM cement. PMID:25598811

  7. Remote Sensing of Urban Mixed Layer Structure in Los Angeles, with Applications to Greenhouse Gas Emissions Quantification

    NASA Astrophysics Data System (ADS)

    Ware, J.; Kort, E. A.; Duren, R. M.; Decola, P.

    2015-12-01

    Urban areas are responsible for a large and increasing part of global greenhouse gas emissions. Effective policy for controlling urban emissions depends on an accurate understanding of those emissions, including their trends in time, distribution across source types, and the effects of regulatory, economic, or technological changes on the rate of emissions. The level of detail required will demand input both from bottom-up inventories and from top-down atmospheric concentration measurements, which must then be translated into emissions fluxes. Among the meteorological information needed for that translation, the mixing dynamics of the lower atmosphere are crucial; an error in the depth of the mixed layer produces a proportional error in the flux estimate. Ground-based remote sensing can provide continuous information about the mixed layer. We present results highlighting the importance of such continuous information. A Sigma Space mini-Micro Pulse Lidar (miniMPL) and a Vaisala ceilometer were deployed in the Los Angeles megacity, California over a period of several years. A locally appropriate, wavelet-based algorithm was devised to estimate the depth of the mixed layer on the basis of this remote sensing data. A voting scheme, novel for this application, was used to establish confidence. While a seasonal trend in mixed layer depth does exist, that trend is masked by very high day-to-day variability. Daily maximum mixed layer depths often differ by a factor of two from monthly or seasonal averages. We use a simplified model to demonstrate the impact of this variability on top-down approaches to greenhouse gas emissions quantification, demonstrating the value of continuous observations.

  8. Effects of Precipitation on Ocean Mixed-Layer Temperature and Salinity as Simulated in a 2-D Coupled Ocean-Cloud Resolving Atmosphere Model

    NASA Technical Reports Server (NTRS)

    Li, Xiaofan; Sui, C.-H.; Lau, K-M.; Adamec, D.

    1999-01-01

    A two-dimensional coupled ocean-cloud resolving atmosphere model is used to investigate possible roles of convective scale ocean disturbances induced by atmospheric precipitation on ocean mixed-layer heat and salt budgets. The model couples a cloud resolving model with an embedded mixed layer-ocean circulation model. Five experiment are performed under imposed large-scale atmospheric forcing in terms of vertical velocity derived from the TOGA COARE observations during a selected seven-day period. The dominant variability of mixed-layer temperature and salinity are simulated by the coupled model with imposed large-scale forcing. The mixed-layer temperatures in the coupled experiments with 1-D and 2-D ocean models show similar variations when salinity effects are not included. When salinity effects are included, however, differences in the domain-mean mixed-layer salinity and temperature between coupled experiments with 1-D and 2-D ocean models could be as large as 0.3 PSU and 0.4 C respectively. Without fresh water effects, the nocturnal heat loss over ocean surface causes deep mixed layers and weak cooling rates so that the nocturnal mixed-layer temperatures tend to be horizontally-uniform. The fresh water flux, however, causes shallow mixed layers over convective areas while the nocturnal heat loss causes deep mixed layer over convection-free areas so that the mixed-layer temperatures have large horizontal fluctuations. Furthermore, fresh water flux exhibits larger spatial fluctuations than surface heat flux because heavy rainfall occurs over convective areas embedded in broad non-convective or clear areas, whereas diurnal signals over whole model areas yield high spatial correlation of surface heat flux. As a result, mixed-layer salinities contribute more to the density differences than do mixed-layer temperatures.

  9. Low-Temperature Solution Synthesis of Few-Layer 1T '-MoTe2 Nanostructures Exhibiting Lattice Compression.

    PubMed

    Sun, Yifan; Wang, Yuanxi; Sun, Du; Carvalho, Bruno R; Read, Carlos G; Lee, Chia-Hui; Lin, Zhong; Fujisawa, Kazunori; Robinson, Joshua A; Crespi, Vincent H; Terrones, Mauricio; Schaak, Raymond E

    2016-02-18

    Molybdenum ditelluride, MoTe2 , is emerging as an important transition-metal dichalcogenide (TMD) material because of its favorable properties relative to other TMDs. The 1T ' polymorph of MoTe2 is particularly interesting because it is semimetallic with bands that overlap near the Fermi level, but semiconducting 2H-MoTe2 is more stable and therefore more accessible synthetically. Metastable 1T '-MoTe2 forms directly in solution at 300 °C as uniform colloidal nanostructures that consist of few-layer nanosheets, which appear to exhibit an approx. 1 % lateral lattice compression relative to the bulk analogue. Density functional theory calculations suggest that small grain sizes and polycrystallinity stabilize the 1T ' phase in the MoTe2 nanostructures and suppress its transformation back to the more stable 2H polymorph through grain boundary pinning. Raman spectra of the 1T '-MoTe2 nanostructures exhibit a laser energy dependence, which could be caused by electronic transitions. PMID:26804980

  10. Some Finite Difference Solutions of the Laminar Compressible Boundary Layer Showing the Effects of Upstream Transpiration Cooling

    NASA Technical Reports Server (NTRS)

    Howe, John T.

    1959-01-01

    Three numerical solutions of the partial differential equations describing the compressible laminar boundary layer are obtained by the finite difference method described in reports by I. Flugge-Lotz, D.C. Baxter, and this author. The solutions apply to steady-state supersonic flow without pressure gradient, over a cold wall and over an adiabatic wall, both having transpiration cooling upstream, and over an adiabatic wall with upstream cooling but without upstream transpiration. It is shown that for a given upstream wall temperature, upstream transpiration cooling affords much better protection to the adiabatic solid wall than does upstream cooling without transpiration. The results of the numerical solutions are compared with those of approximate solutions. The thermal results of the finite difference solution lie between the results of Rubesin and Inouye, and those of Libby and Pallone. When the skin-friction results of one finite difference solution are used in the thermal analysis of Rubesin and Inouye, improved agreement between the thermal results of the two methods of solution is obtained.

  11. The effects of cell assembly compression on the performance of carbon electrochemical double-layer capacitor electrodes

    NASA Astrophysics Data System (ADS)

    Gourdin, Gerald; Jiang, Thomas; Smith, Patricia; Qu, Deyang

    2012-10-01

    Our previous work concluded that the application of force altered the physical structure of the activated carbon electrodes, which resulted in a decrease in the accessible surface area and a displacement of the electrolyte. In this work, the response that different carbon material electrodes exhibit to an applied force was evaluated. Activated carbon powders possess different porous structures, which would exhibit different behaviors when subjected to an applied force and after the release of that force. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to characterize the response behaviors of the different carbons. Furthermore, a porosimetry analysis was conducted on the carbon material of the electrode before and after the application of force. It was concluded that the application of force shifted the pore distribution toward overall smaller pores through a compression of the porous structure of the carbon. This resulted in a decrease in the more easily accessible surface area, which was exhibited as a decrease in the capacitance values as calculated from the cyclic voltammetry data. There was no longer sufficient time to access the now smaller powers at the given time scale of the cyclic voltammetry analysis, which negatively impacted the formation of the double layer.

  12. Low-Temperature Solution Synthesis of Few-Layer 1T '-MoTe2 Nanostructures Exhibiting Lattice Compression.

    PubMed

    Sun, Yifan; Wang, Yuanxi; Sun, Du; Carvalho, Bruno R; Read, Carlos G; Lee, Chia-Hui; Lin, Zhong; Fujisawa, Kazunori; Robinson, Joshua A; Crespi, Vincent H; Terrones, Mauricio; Schaak, Raymond E

    2016-02-18

    Molybdenum ditelluride, MoTe2 , is emerging as an important transition-metal dichalcogenide (TMD) material because of its favorable properties relative to other TMDs. The 1T ' polymorph of MoTe2 is particularly interesting because it is semimetallic with bands that overlap near the Fermi level, but semiconducting 2H-MoTe2 is more stable and therefore more accessible synthetically. Metastable 1T '-MoTe2 forms directly in solution at 300 °C as uniform colloidal nanostructures that consist of few-layer nanosheets, which appear to exhibit an approx. 1 % lateral lattice compression relative to the bulk analogue. Density functional theory calculations suggest that small grain sizes and polycrystallinity stabilize the 1T ' phase in the MoTe2 nanostructures and suppress its transformation back to the more stable 2H polymorph through grain boundary pinning. Raman spectra of the 1T '-MoTe2 nanostructures exhibit a laser energy dependence, which could be caused by electronic transitions.

  13. In Situ Study of the Formation of Silicide Phases in Amorphous Co–Si Mixed Layers

    SciTech Connect

    Van Bockstael, C.; De Keyser, K; Demeulemeester, J; Vantomme, A; Van Meirhaeghe, R; Detavernier, C; Jordan-Sweet, J; Lavoie, C

    2010-01-01

    We investigate Co silicide phase formation when extra Si is added within an as deposited 50 nm Co film. The addition of Si is investigated for both the Co/SiO{sub 2} and Co/Si(1 0 0) system. A series of 10 Co-Si mixed films with a Si content varying from 21 to 59 at.% was prepared and investigated during annealing with in situ X-ray diffraction. The oxide system is used as reference system to identify phases that initially crystallize in an amorphous mixture of a given composition. Multiple phases can nucleate, and the temperature of crystallization depends on the Co-Si atomic ratio. Upon heating of the Co(Si)/Si system, the first reaction is a similar crystallization reaction of the Co(Si) mixture. Once the first phase is formed, one has the normal system of a silicide phase in contact with an unlimited amount of Si from the substrate, and the sequential phase formation towards CoSi{sub 2} is established. For deposited layers of composition ranging from 48%Si to 52%Si, the CoSi is the first phase to form and increasing the amount of Si leads to a remarkable improvement of the thermal stability of CoSi on Si(1 0 0). CoSi{sub 2} nucleation was extensively delayed by 150 C compared to the reaction observed from a pure Co film on Si(1 0 0). Electron backscatter diffraction measurements reveal that in this range, the gradual Si increase systematically leads to bigger CoSi grains (up to 20 {micro}m). This shows that the grain size of the CoSi precursor strongly affects the nucleation of the following CoSi{sub 2} phase. Laser-light scattering measurements suggest that adding more than 42%Si reduces the roughness of the CoSi{sub 2} layer.

  14. Hydrodynamic and Nonhydrodynamic Behavior of Layer-Compression Modulus B at the Nematic-Smectic- A Phase Transition in 8 OCB

    NASA Astrophysics Data System (ADS)

    Martinoty, P.; Gallani, J. L.; Collin, D.

    1998-07-01

    We present dynamic compression experiments which show that layer-compression modulus B does not exhibit dispersion in the 100 Hz-1 kHz domain and varies with temperature according to a simple power law over four decades. These results indicate that the saturation effect predicted by Nelson and Toner does not exist for this compound, and that the thermal variation of B determined at higher frequencies by a second-sound technique is not hydrodynamic, contrary to what is claimed. We show that it is affected by two relaxation mechanisms.

  15. A MULTI-STREAM MODEL FOR VERTICAL MIXING OF A PASSIVE TRACER IN THE CONVECTIVE BOUNDARY LAYER

    EPA Science Inventory

    We study a multi-stream model (MSM) for vertical mixing of a passive tracer in the convective boundary layer, in which the tracer is advected by many vertical streams with different probabilities and diffused by small scale turbulence. We test the MSM algorithm for investigatin...

  16. FerryBox-assisted monitoring of mixed layer pH in the Norwegian Coastal Current

    NASA Astrophysics Data System (ADS)

    Reggiani, Emanuele R.; King, Andrew L.; Norli, Marit; Jaccard, Pierre; Sørensen, Kai; Bellerby, Richard G. J.

    2016-10-01

    The evaluation of marine carbonate system variability and the impacts of ocean acidification (OA) on coastal marine ecosystems increasingly rely on monitoring platforms capable of delivering near real-time in situ carbonate system observations. These observations are also used for developing models and scenarios of OA, including potential impacts on marine ecosystem structure and function. An embedded flow-through spectrophotometric pH detection system has been developed alongside an underway seawater sampling system - termed a FerryBox - operating on ships of opportunity (SOOP), and can deliver a continuous data stream of mixed layer seawater pH with an in situ uncertainty of < 0.003. We report metrological approaches behind the pH detection procedure and the evaluation of dye addition perturbation with analytical precision as low as 0.0005. In addition, we present field-based observations from a deployment of the pH detection system along the Norwegian Coastal Current in winter, spring, and summer periods of 2015. Spring and summertime pH was generally 0.1 higher, and up to 0.255 higher, in comparison to winter pH observations. Here we show the necessity for a regular, high density monitoring approach, and the suitability of this pH detection technique for unmanned observational platforms.

  17. Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

    DOE PAGESBeta

    Sulmonetti, Taylor P.; Pang, Simon H.; Claure, Micaela Taborga; Lee, Sungsik; Cullen, David A.; Agrawal, Pradeep K.; Jones, Christopher W.

    2016-03-09

    The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the othermore » catalysts, with promising activity compared to related catalysts in the literature. In conclusion, the use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.« less

  18. Evolution of streamwise vortices and generation of small-scale motion in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Nygaard, K. J.; Glezer, A.

    1991-01-01

    The present study investigates the evolution of streamwise vortices in a plane mixing layer and their role in the generation of small-scale 3D motion in a closed-return water facility. Spanwise-periodic streamwise vortices are excited by a time-harmonic wavetrain with spanwise-periodic amplitude variations synthesized by a mosaic of 32 surface film heaters flush-mounted on the low partition. The onset of streamwise vortices is accompanied by significant distortion in the transverse distribution of the streamwise velocity component. The presence of inflexion points, absent in corresponding velocity distributions of the unforced flow, suggests the formation of locally unstable regions of large shear in which broadband perturbations already present in the base flow undergo rapid amplification, followed by breakdown to small-scale motion. The cores of the primary vortices are significantly altered as a result of spanwise nonuniform excitation. The 3D features of the streamwise vortices and their interaction with the base flow are inferred from surfaces or rms velocity fluctuations and an approximation to cross-stream vorticity using 3D single component velocity data.

  19. Phytoplankton behavior affects ocean mixed layer dynamics through biological-physical feedback mechanisms

    NASA Astrophysics Data System (ADS)

    Sonntag, S.; Hense, I.

    2011-08-01

    Biologically induced changes in physical oceanic properties through phytoplankton provide potential positive and negative feedback loops. In particular, surface floating cyanobacteria, which are expected to be favored from future environmental conditions and can form large surface mats, can increase light absorption and the surface albedo and decrease momentum input from the atmosphere by wind. In this work we study the effect of a changing phytoplankton community composition to one dominated by buoyant cyanobacteria on the physical oceanic properties. We use the water column model General Ocean Turbulence Model and set up an idealized biological model taking into account the phytoplankton species' characteristics as well as the effects of biology on physics. The model results show that an increase of buoyant cyanobacteria leads to substantial changes in the seasonal cycle of the mixed layer. The results furthermore indicate that the effects due to altered absorption and biologically induced reduction of the wind drag are larger than contrary effects due to changes in the surface albedo. Overall, our model results suggest that the development of cyanobacterial surface blooms and their feedbacks on light absorption and wind drag need to be taken into account in ocean models used for climate scenarios in order to capture changes in the dynamics of the upper ocean.

  20. Defect physics vis-à-vis electrochemical performance in layered mixed-metal oxide cathode materials

    NASA Astrophysics Data System (ADS)

    Hoang, Khang; Johannes, Michelle

    Layered mixed-metal oxides with different compositions of (Ni,Co,Mn) [NCM] or (Ni,Co,Al) [NCA] have been used in commercial lithium-ion batteries. Yet their defect physics and chemistry is still not well understood, despite having important implications for the electrochemical performance. In this presentation, we report a hybrid density functional study of intrinsic point defects in the compositions LiNi1/3Co1/3Mn1/3O2 (NCM1/3) and LiNi1/3Co1/3Al1/3O2 (NCA1/3) which can also be regarded as model compounds for NCM and NCA. We will discuss defect landscapes in NCM1/3 and NCA1/3 under relevant synthesis conditions with a focus on the formation of metal antisite defects and its implications on the electrochemical properties and ultimately the design of NCM and NCA cathode materials.

  1. Improved layered mixed transition metal oxides for Li-ion batteries

    SciTech Connect

    Doeff, Marca M.; Conry, Thomas; Wilcox, James

    2010-03-05

    Recent work in our laboratory has been directed towards development of mixed layered transition metal oxides with general composition Li[Ni, Co, M, Mn]O2 (M=Al, Ti) for Li ion battery cathodes. Compounds such as Li[Ni1/3Co1/3Mn1/3]O2 (often called NMCs) are currently being commercialized for use in consumer electronic batteries, but the high cobalt content makes them too expensive for vehicular applications such as electric vehicles (EV), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs). To reduce materials costs, we have explored partial or full substitution of Co with Al, Ti, and Fe. Fe substitution generally decreases capacity and results in poorer rate and cycling behavior. Interestingly, low levels of substitution with Al or Ti improve aspects of performance with minimal impact on energy densities, for some formulations. High levels of Al substitution compromise specific capacity, however, so further improvements require that the Ni and Mn content be increased and Co correspondingly decreased. Low levels of Al or Ti substitution can then be used offset negative effects induced by the higher Ni content. The structural and electrochemical characterization of substituted NMCs is presented in this paper.

  2. Numerical simulation of two-dimensional spatially-developing mixing layers

    NASA Technical Reports Server (NTRS)

    Wilson, R. V.; Demuren, A. O.

    1994-01-01

    Two-dimensional, incompressible, spatially developing mixing layer simulations are performed at Re = 10(exp 2) and 10(exp 4) with two classes of perturbations applied at the inlet boundary; combinations of discrete modes from linear stability theory, and a broad spectrum of modes derived from experimentally measured velocity spectra. The effect of the type and strength of inlet perturbations on vortex dynamics and time-averaged properties are explored. Two-point spatial velocity and autocorrelations are used to estimate the size and lifetime of the resulting coherent structures and to explore possible feedback effects. The computed time-averaged properties such as mean velocity profiles, turbulent statistics, and spread rates show good agreement with experimentally measured values. It is shown that by forcing with a broad spectrum of modes derived from an experimental energy spectrum many experimentally observed phenomena can be reproduced by a 2-D simulation. The strength of the forcing merely affected the length required for the dominant coherent structures to become fully-developed. Thus intensities comparable to those of the background turbulence in many wind tunnel experiments produced the same results, given sufficient simulation length.

  3. Effects of radiative heat transfer on the turbulence structure in inert and reacting mixing layers

    NASA Astrophysics Data System (ADS)

    Ghosh, Somnath; Friedrich, Rainer

    2015-05-01

    We use large-eddy simulation to study the interaction between turbulence and radiative heat transfer in low-speed inert and reacting plane temporal mixing layers. An explicit filtering scheme based on approximate deconvolution is applied to treat the closure problem arising from quadratic nonlinearities of the filtered transport equations. In the reacting case, the working fluid is a mixture of ideal gases where the low-speed stream consists of hydrogen and nitrogen and the high-speed stream consists of oxygen and nitrogen. Both streams are premixed in a way that the free-stream densities are the same and the stoichiometric mixture fraction is 0.3. The filtered heat release term is modelled using equilibrium chemistry. In the inert case, the low-speed stream consists of nitrogen at a temperature of 1000 K and the highspeed stream is pure water vapour of 2000 K, when radiation is turned off. Simulations assuming the gas mixtures as gray gases with artificially increased Planck mean absorption coefficients are performed in which the large-eddy simulation code and the radiation code PRISSMA are fully coupled. In both cases, radiative heat transfer is found to clearly affect fluctuations of thermodynamic variables, Reynolds stresses, and Reynolds stress budget terms like pressure-strain correlations. Source terms in the transport equation for the variance of temperature are used to explain the decrease of this variance in the reacting case and its increase in the inert case.

  4. Effects of radiative heat transfer on the turbulence structure in inert and reacting mixing layers

    SciTech Connect

    Ghosh, Somnath; Friedrich, Rainer

    2015-05-15

    We use large-eddy simulation to study the interaction between turbulence and radiative heat transfer in low-speed inert and reacting plane temporal mixing layers. An explicit filtering scheme based on approximate deconvolution is applied to treat the closure problem arising from quadratic nonlinearities of the filtered transport equations. In the reacting case, the working fluid is a mixture of ideal gases where the low-speed stream consists of hydrogen and nitrogen and the high-speed stream consists of oxygen and nitrogen. Both streams are premixed in a way that the free-stream densities are the same and the stoichiometric mixture fraction is 0.3. The filtered heat release term is modelled using equilibrium chemistry. In the inert case, the low-speed stream consists of nitrogen at a temperature of 1000 K and the highspeed stream is pure water vapour of 2000 K, when radiation is turned off. Simulations assuming the gas mixtures as gray gases with artificially increased Planck mean absorption coefficients are performed in which the large-eddy simulation code and the radiation code PRISSMA are fully coupled. In both cases, radiative heat transfer is found to clearly affect fluctuations of thermodynamic variables, Reynolds stresses, and Reynolds stress budget terms like pressure-strain correlations. Source terms in the transport equation for the variance of temperature are used to explain the decrease of this variance in the reacting case and its increase in the inert case.

  5. Effects of swell on dispersion of oil plumes within the ocean mixed layer

    NASA Astrophysics Data System (ADS)

    Chen, Bicheng; Yang, Di; Chamecki, Marcelo; Meneveau, Charles

    2014-11-01

    Oil plumes from deep-water blowouts rise through the ocean and reach the ocean mixed layer (OML), where dispersion is strongly affected by Langmuir turbulence generated by interactions between the wind forcing and the wave regime. The wind-driven wave field is approximately aligned with wind direction. However, the swell wave can have an arbitrary orientation relative to the local wind. We used large-eddy simulation (LES) to study the influences of the misalignment between wind and wave field on the transport and dispersion of oil plumes in the OML. Results show that the plume response to these forcing is strongly dependent on the size of the oil droplets. For the large oil droplets, the center line of the time-averaged surface plume tends to follow the mean surface current direction; for small droplets, the change of orientation of center line with wave direction is smaller than that of large droplets. Vertical eddy diffusivity calculated from LES data is compared to closures currently used in ocean models (such as the KPP model employed in HYCOM). The magnitude of the eddy diffusivity changes by a factor of two as the misalignment between swell and wind changes, and it is typically much larger than predicted by KPP. This study is supported by a Gulf of Mexico Research Initiative research grant.

  6. Generation of isentropic compression by use of multi-layer composite flyer and its influence on system thermodynamics: A simulation study

    NASA Astrophysics Data System (ADS)

    Ray, Aditi

    2014-05-01

    Recently the possibility of achieving quasi-isentropic compression using functionally graded materials, in both gas gun and explosive driven systems was explored by hydro-dynamic simulations. In the current paper, we show that multi-layered composite flyer with progressively increasing shock impedances, referred to as graded density impactor (GDI), has the potential to enable increased flexibility in suitably tailoring the applied-pressure profiles, further relaxing constraints on the thermodynamic path of compressed material. Present simulation study pertaining to constant velocity impact of GDI reveals that linear ramp pulses of different pressure rise times, with comparable peak values can be realized only by changing the layer thicknesses of a particular GDI. We report generation of three different slope ramp pulses by five layer GDI made of PMMA, Al, Ti, Cu and Ta with different set of thicknesses obtained by genetic algorithm based optimization technique. Generation of long duration (μs) isentropic pressures using discrete GDI is a significant step, since it is devoid of fabrication difficulties of ultra-thin lamellae of FGM. Signatures of isentropic compression of a thin Cu target under different slope ramp loadings are identified from basic thermodynamic aspects in terms of temperature rise and entropy production. It is shown that that extent of entropy increase is closely related to the slope of ramping pulse. Further, a physical model has been constructed to determine approximate time profile of pressure pulse generated by equal layer-width GDI.

  7. Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

    NASA Astrophysics Data System (ADS)

    Jähn, M.; Muñoz-Esparza, D.; Chouza, F.; Reitebuch, O.; Knoth, O.; Haarig, M.; Ansmann, A.

    2016-01-01

    Large eddy simulations (LESs) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind and Raman lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the downwind vertical wind structure. Additionally, the model results accurately reproduce the

  8. Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. I: Single layer cloud

    SciTech Connect

    Klein, Stephen A.; McCoy, Renata; Morrison, H.; Ackerman, Andrew; Avramov, Alexander; DeBoer, GIJS; Chen, Mingxuan; Cole, Jason N.; DelGenio, Anthony D.; Falk, Michael; Foster, Mike; Fridlind, Ann; Golaz, Jean-Christophe; Hashino, Tempei; Harrington, Jerry Y.; Hoose, Corinna; Khairoutdinov, Marat; Larson, Vince; Liu, Xiaohong; Luo, Yali; McFarquhar, Greg; Menon, Surabi; Neggers, Roel; Park, Sungsu; Poellot, M. R.; Schmidt, Jerome M.; Sednev, Igor; Shipway, Ben; Shupe, Matthew D.; Spangenberg, D.; Sud, Yogesh; Turner, David D.; Veron, Dana; Von Salzen, Knut; Walker, Gregory K.; Wang, Zhien; Wolf, Audrey; Xie, Shaocheng; Xu, Kuan-Man; Yang, Fanglin; Zhang, G.

    2009-05-21

    Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a cold-air outbreak mixed-phase stratocumulus cloud observed during the ARM Mixed-Phase Arctic Cloud Experiment. The observed cloud occurred in a well-mixed boundary layer with a cloud top temperature of –15°C. While the cloud was water dominated, ice precipitation appears to have lowered the liquid water path to about 2/3 of the adiabatic value. The simulations, which were performed by seventeen single column and nine cloud-resolving models, generally underestimate the liquid water path with the median single-column and cloud-resolving model liquid water path a factor of 3 smaller than observed. While the simulated ice water path is in general agreement with the observed values, results from a sensitivity study in which models removed ice microphysics indicate that in many models the interaction between liquid and ice phase microphysics is responsible for the strong model underestimate of liquid water path. Although no single factor is found to lead to a good simulation, these results emphasize the need for care in the model treatment of mixed-phase microphysics. This case study, which has been well observed from both aircraft and ground-based remote sensors, could be benchmark for model simulations of mixed-phase clouds.

  9. Lidar observations of the diurnal variations in the depth of urban mixing layer: a case study on the air quality deterioration in Taipei, Taiwan.

    PubMed

    Chou, Charles C-K; Lee, C-T; Chen, W-N; Chang, S-Y; Chen, T-K; Lin, C-Y; Chen, J-P

    2007-03-01

    An aerosol light detection and ranging (LIDAR) system was used to measure the depth of the atmospheric mixing layer over Taipei, Taiwan in the spring of 2005. This paper presents the variations of the mixing height and the mixing ratios of air pollutants during an episode of air quality deterioration (March 7-10, 2005), when Taipei was under an anti-cyclonic outflow of a traveling high-pressure system. It was found that, during those days, the urban mixing height reached its daily maximum of 1.0-1.5 km around noon and declined to 0.3-0.5 km around 18:00 (LST). In terms of hourly averages, the mixing height increased with the ambient temperature linearly by a slope of 166 m/degrees C in daytime. The consistency between the changes in the mixing height and in the ambient temperature implied that the mixing layer dynamics were dominated by solar thermal forcing. As the cap of the mixing layer descended substantially in the afternoon, reduced dispersion in the shallow mixing layer caused the concentrations of primary air pollutants to increase sharply. Consequently, the pollutant concentration exhibited an anti-correlation with the mixing height. While attentions are usually focused on the pollution problems occurring in a morning inversion layer, the results of this study indicate that the air pollution and its health impacts could be even more severe as the mixing layer is getting shallow in the afternoon.

  10. Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

    NASA Astrophysics Data System (ADS)

    Jähn, M.; Muñoz-Esparza, D.; Chouza, F.; Reitebuch, O.

    2015-08-01

    Large eddy simulations (LES) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ~ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the formation of the daytime convective plume and the mean vertical wind structure.

  11. Control of shock unsteadiness in shock boundary-layer interaction on a compression corner using mechanical vortex generators

    NASA Astrophysics Data System (ADS)

    Verma, S. B.; Manisankar, C.; Raju, C.

    2012-07-01

    An experimental study was conducted to control the unsteadiness of separation shock in a Mach 2 24° compression ramp-induced interaction using mechanical vortex generators (VG). Control devices in the form of an array of single-row delta-ramps were placed upstream of the interaction region and tested for two streamwise locations with respect to the boundary layer thickness ( δ) at the interaction location and height ` h' of the delta-ramps, i.e., at 27.5 δ or h/ δ = 0.65 and at 12.5 δ or h/ δ = 0.26, respectively. Surface oil study revealed traces of streamwise counter-rotating vortex pairs generated downstream of these devices. Measurements using pressure-sensitive paint also showed a spanwise sinusoidal pattern of wall pressure variation indicating generation of streamwise vortices from these control devices. These vortices, on interaction with the reverse flow in the separation bubble, replaced a well-defined separation line (for no control) by a highly corrugated separation line. In the region of separation, the mean pressure distribution gets modified while the peak rms value in the intermittent region of separation showed significant changes. Additionally, the spanwise spacing ` s' of the vertex of the delta ramps seemed to be an important parameter in controlling the peak rms value. A decrease in this spacing, i.e., VG1 with s = 0, significantly reduced the peak rms value (by 50 and 35 %) while an increase in the spacing, i.e., VG2 with s = 1 mm, consistently showed an increase (by 12 and 30 %) in the separation shock unsteadiness relative to no control, irrespective of their placement location (of h/ δ = 0.65 and 0.26, respectively).

  12. Mixed Layer Sub-Mesoscale Parameterization - Part 1: Derivation and Assessment

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Dubovikov, M. S.

    2010-01-01

    Several studies have shown that sub-mesoscales (SM 1km horizontal scale) play an important role in mixed layer dynamics. In particular, high resolution simulations have shown that in the case of strong down-front wind, the re-stratification induced by the SM is of the same order of the de-stratification induced by small scale turbulence, as well as of that induced by the Ekman velocity. These studies have further concluded that it has become necessary to include SM in ocean global circulation models (OGCMs), especially those used in climate studies. The goal of our work is to derive and assess an analytic parameterization of the vertical tracer flux under baroclinic instabilities and wind of arbitrary directions and strength. To achieve this goal, we have divided the problem into two parts: first, in this work we derive and assess a parameterization of the SM vertical flux of an arbitrary tracer for ocean codes that resolve mesoscales, M, but not sub-mesoscales, SM. In Part 2, presented elsewhere, we have used the results of this work to derive a parameterization of SM fluxes for ocean codes that do not resolve either M or SM. To carry out the first part of our work, we solve the SM dynamic equations including the non-linear terms for which we employ a closure developed and assessed in previous work. We present a detailed analysis for down-front and up-front winds with the following results: (a) down-front wind (blowing in the direction of the surface geostrophic velocity) is the most favorable condition for generating vigorous SM eddies; the de-stratifying effect of the mean flow and re-stratifying effect of SM almost cancel each other out,

  13. A numerical study of ignition in the supersonic hydrogen/air laminar mixing layer

    SciTech Connect

    Nishioka, M.; Law, C.K.

    1997-01-01

    The ignition evolution in the supersonic nonpremixed hydrogen/air laminar mixing layer, consisting of a relatively hot, fast air stream next to a cold, slower hydrogen stream, was computationally simulated using detailed transport and chemical reaction mechanisms and compared with results from asymptotic analysis with reduced mechanisms. The study emphasizes identifying the controlling chemical mechanisms in effecting ignition, on the relative importance of external versus viscous heating as the dominant ignition source, on the roles of thermal versus kinetic-induced ignition in which heat release and hence nonlinear thermal feedback are not needed in initiating system runaway, and on the consequences of imposing the conventional constant property assumptions in analytical studies. Results show that the state of the hydrogen/oxygen second explosion limit has the dominant influence in the system response in that, for all practical purposes, ignition is not possible when the air-stream temperature is lower than the crossover temperature, even allowing for viscous heating. On the other hand, when the air-stream temperature is higher than the crossover temperature, the predicted ignition distance indicates that ignition is feasible within practical supersonic combustion engines. Furthermore, for the latter situations, the ignition event is initiated by radical proliferation and hence runaway instead of thermal runaway. Finally, it is shown that, while the present computed results qualitatively agree well with those from the asymptotic analysis with reduced mechanisms, the analytically predicted ignition distances are much shorter than the computed values because the analysis has overemphasized the viscous effect through the constant Chapman-Rubesin parameter {rho}{mu} and unity Prandtl number assumptions.

  14. Image analysis applied to the study of mixing in a stably stratified shear layer

    NASA Astrophysics Data System (ADS)

    Querzoli, Giorgio; Monti, Paolo; Cenedese, Antonio

    2008-10-01

    The development and breaking of Kelvin Helmholtz waves is one of the primary causes of mixing in many geophysical and engineering flows with layers of fluids having different densities and horizontal velocities. Although this phenomenon was extensively studied in the field, a complete description can be experimentally obtained only by the use of image analysis techniques that are applicable only in laboratory experiments. The particular nature of the flow, especially before the development of the waves when the flow is parallel but in opposite direction, makes the application of the classical image velocimetry techniques non-trivial. With this in mind, a stably stratified shear flow was reproduced in the laboratory by means of a tilting tank. The velocity and density fields were measured simultaneously with multipoint time-resolved techniques during the formation and development of the Kelvin Helmholtz waves. A novel particle tracking procedure is proposed that includes the stretching of the acquired images in the direction orthogonal to the main motion. Tests on synthetic images show a meaningful improvement in the effectiveness of particle tracking when using the proposed technique. Laser-Induced Fluorescence (LIF) data have been acquired by a second camera, equipped with a band-pass filter in order to measure only the fluoresced light. Particle Tracking Velocimetry (PTV) and LIF data have been referenced to the same frame by a registration procedure based on an affine transformation. In the range of the parameters investigated during the experiments, the evolution of the interface thickness and sharpness scales with the advective time scale. The analysis of the space time evolution of the longitudinal statistics gives a comprehensive picture of the development and breaking of the waves.

  15. Data Assimilation In A Marine Ecosystem Coupled To A Mixed Layer Model of The Upper Ocean.

    NASA Astrophysics Data System (ADS)

    Magri, S.; Brasseur, P.; Lacroix, G.

    Data assimilation have been conducted in a one-dimensional, coupled physical ecosys- tem model of the upper ocean to characterize the observability properties of in situ and satellite observing systems. The assimilation method is based on the Singular Evolu- tive Extended Kalman (SEEK) filter, in which the error sub-space is decomposed into multivariate orthogonal functions of the system's variability. The coupled model simulates the primary production in a coastal zone of the Ligurian Sea, where oligotrophic conditions prevail. The ecosystem dynamics is represented by 12 interacting compartments expressed in nitrogen units. The coupling with a hydrodynamic model determines the physical constraints asso- ciated to the development of a seasonal mixed layer. The stratification of the water column, according to the computation of the vertical turbulent diffusivities, is a key parameter of the evolution of the marine ecosystem. The coupled system has been developed and validated on the basis of field data col- lected during the FRONTAL campains, between 1984 and 1988. As a first approach, twin experiments are performed to check the algorithmic imple- mentation of the SEEK filter, and to verify the statistical consistence of the assimila- tion scheme in non-linear regimes. Vertical temperature and salinity profiles have been assimilated to evaluate the impact of a better representation of the water column strat- ification on the primary production. Then, nitrate and chlorophyll-a profiles have been assimilated to try to control the ecosystem in spite of an imperfect physical model. Finally, physical and biological profiles of in situ data collected during the FRONTAL campains, will be used to reconstruct the seasonal evolution of the ecosystem.

  16. Enhancing the comprehension of mixed layer depth control on the Mediterranean phytoplankton phenology

    NASA Astrophysics Data System (ADS)

    Lavigne, HéLoïSe; D'Ortenzio, Fabrizio; Migon, Christophe; Claustre, Hervé; Testor, Pierre; D'Alcalã, Maurizio Ribera; Lavezza, Rosario; Houpert, LoïC.; Prieur, Louis

    2013-07-01

    Phytoplankton phenology is primarily affected by physical forcing. However, its quantification is far from being completely understood. Among the physical forcing factors, the mixed layer depth (MLD) is considered to have the strongest impact on phytoplankton dynamics, and consequently, on their phenology. The role of MLD variations in shaping the phytoplankton phenology was explored in the Mediterranean Sea, a basin displaying contrasting phenological regimes. A database of MLD estimations was merged with ocean color chlorophyll concentrations ([Chl]SAT) to generate concomitant annual MLD and [Chl]SAT cycles. Several indices were calculated to quantitatively analyze these cycles. The relevance of indices summarizing the temporal difference between main characteristics of MLD and [Chl]SAT cycles was emphasized. As previously observed, two dominant phenological regimes coexist in the Mediterranean Sea. The first is marked by a typical spring bloom, as in temperate regions. The second displays a low seasonality and an absence of an intense [Chl]SAT peak as in subtropical areas. The MLD is shown to play a key role in determining the dominant phenological regime in a given area. Results also show that regions having low seasonality display concomitant MLD and [Chl]SAT maxima, whereas [Chl]SAT peaks are generally observed 30 days after MLD peaks in regions with strongest seasonality. Over the whole basin, [Chl]SAT increase starts 1 month after the initiation of MLD deepening. Finally, after examining the impact of MLD on light and nutrient availability for phytoplankton, mechanisms were proposed to explain the time lags between MLD and [Chl]SAT increase and MLD and [Chl]SAT maxima.

  17. Mixed-layer ocean responses to anthropogenic aerosol dimming from 1870 to 2000

    NASA Astrophysics Data System (ADS)

    Dallafior, T. N.; Folini, D.; Knutti, R.; Wild, M.

    2016-01-01

    It is debated to what extent surface solar radiation (SSR) changes through varying anthropogenic aerosol emissions since industrialization affected surface temperatures (tsurf). We use mixed-layer ocean experiments with the general circulation model ECHAM6.1 and explicit aerosols (HAM2.2) to identify regions where this effect is discernible. For each decade from 1870 to 2000 we derive three equilibria: anthropogenic aerosol emissions and greenhouse gas concentrations at the respective decade's levels (ALL), either aerosols or greenhouse gases fixed at year 1850 levels (GHG and AERO). We duplicated parts of the experiments with different prescribed divergence of ocean heat transport (Q_ALL, Q_AERO, and Q_GHG). Comparing year 2000 with year 1870 equilibria, we find global average cooling of -1.4 K for AERO and warming of 1.4 K for GHG. ALL and Q_ALL warm by 0.6 K and 0.4 K, respectively. The way divergence of ocean heat transport is prescribed thus matters. Pattern correlations of year 2000 tsurf responses in ALL with the sum of AERO and GHG are higher (0.88) than with Q_ALL (0.71) confirming additivity of global patterns, but not of global means. The imprint of anthropogenic aerosols on tsurf response patterns in ALL is distinct, thus potentially detectable. Over the decades, ocean fractions affected by either changing aerosol optical depth or all-sky SSR vary in concert, supporting linkage between anthropogenic aerosols and all-sky SSR. SSR changes and tsurf responses are marginally collocated. Oceanic regions with strongest tsurf response to aerosol-induced SSR changes are the northern midlatitudes and North Pacific with tsurf sensitivities up to -0.7 K W m-2 SSR change.

  18. Dimming over the oceans: mixed layer ocean experiments from 1870 to 2000

    NASA Astrophysics Data System (ADS)

    Dallafior, Tanja; Folini, Doris; Knutti, Reto; Wild, Martin

    2015-04-01

    Sea surface temperature (SSTs) changes are known to affect precipitation patterns. However, it is still subject to debate, whether anthropogenic aerosols are capable of affecting SSTs, which could feed back on precipitation patterns. To influence SSTs, anthropogenic aerosols need to reduce incoming surface solar radiation (SSR) through direct or indirect effects for a sufficiently long time span over a sufficiently large area. To quantify the maximum potential SST response to anthropogenic aerosol dimming over the past decades, we performed equilibrium experiments with the general circulation model, ECHAM and explicit aerosol representation (ECHAM6-HAM2.2) and a mixed-layer ocean (MLO). Every ten years, we let the system equilibrate to the conditions (aerosol and greenhouse gas burdens, GHG) of that specific year. Each experiment is conducted over 50 years, of which the first 10 years are discarded. We generated three sets of decadal equilibria covering the entire 20th century and part of the 19th century (from 1870) : One, where both GHG and anthropogenic aerosols are set to the respective decade, one where GHG levels are held constant at 1850s levels, and one where anthropogenic aerosols are held constant at 1850s levels. Deep ocean heat fluxes are prescribed based on the surface energy flux climatology derived from an atmosphere-only integration with pre-industrial (year 1850) conditions for aerosols and GHG and climatological SSTs (average of Hadley Center SSTs, observation based, over the years 1871-1900). Results of these findings will be discussed, especially the SST and precipitation responses seen in the different equilibria. Moreover, results will be put in context with transient experiments with prescribed SSTs. The presented results are part of a project aiming at quantifying the effect of anthropogenic aerosols on SSTs. The results will serve as a basis for future experiments using a dynamic ocean model to quantify the transient response of the ocean

  19. Mixed-layer ocean responses to anthropogenic aerosol dimming from 1870 to 2000

    NASA Astrophysics Data System (ADS)

    Dallafior, Tanja; Folini, Doris; Knutti, Reto; Wild, Martin

    2016-04-01

    It is still debated, to what extent anthropogenic aerosol-induced changes in surface solar radiation (SSR) since industrialization affected surface temperatures (tsurf). We use mixed-layer ocean (MLO) experiments with the general circulation model ECHAM6.1 and explicit aerosols (HAM2.2) to identify regions where this effect is discernible. For each decade from 1870 to 2000 we derive three equilibria: anthropogenic aerosol emissions and greenhouse gas concentrations at the respective decade's levels (ALL), either aerosols or greenhouse gases fixed at year 1850 levels (GHG and AERO). We duplicated parts of the experiments with different prescribed divergence of ocean heat transport (Q_ALL, Q_AERO, Q_GHG). Comparing year 2000 with year 1870 equilibria, we find global average cooling of -1.4K for AERO, and warming of 1.4K for GHG. ALL and Q_ALL warm by 0.6K and 0.4K, respectively. The way divergence of ocean heat transport is prescribed thus matters. Pattern correlations of year 2000 tsurf responses in ALL with the sum of AERO and GHG are higher (0.88) than with Q_ALL (0.71) confirming additivity of global patterns, but not of global means. The imprint of anthropogenic aerosols on tsurf response patterns in ALL is distinct, thus potentially detectable. Over the decades, ocean fractions affected by either changing aerosol optical depth or all-sky SSR vary in concert, supporting linkage between anthropogenic aerosols and all-sky SSR. SSR changes and tsurf responses are marginally collocated. Oceanic regions with strongest tsurf response to aerosol-induced SSR changes are the northern mid-latitudes and North Pacific with tsurf sensitivities up to -0.7K per Wm-2 SSR change. Results presented have been published under the same title in the Journal of Geophysical Research, Volume 121, DOI 10.1002/2015JD024070.

  20. Investigating CloudSat Retrievals Sensitivity to Forward Iterative Algorithm Parameters in the Mixed Cloud Layers

    NASA Astrophysics Data System (ADS)

    Qiu, Yujun; Lu, Chunsong

    2016-08-01

    When millimeter-wave cloud radar data are used for the forward iterative retrieval of the liquid water content (LWC) and effective radius of cloud droplets (R e) in a cloud layer, the prior values and tolerance ranges of the cloud droplet number density (N t), scale parameter (R g) and spectral width parameter (W g) in the iterative algorithm are the main factors that affect the retrieval accuracy. In this study, we used data from stratus and convective clouds that were simultaneously observed by CloudSat and aircraft to conduct a sensitivity analysis of N t, R g, and W g for the retrieval accuracies of LWC and R e in both stratus and convective clouds. N t is the least sensitive parameter for accurately retrieving stratus LWC and R e in both stratus and convective clouds, except for retrieving the convective cloud LWC. Opposite to N t, R g is the most sensitive parameter for both LWC and R e retrievals. As to the effects of parameter tolerance ranges on the retrievals of LWC and R e, the least important parameter is the N t tolerance range; the most important one is the W g tolerance range for retrieving convective cloud LWC and R e, the R g is the important parameter for retrieving stratus LWC and R e. To obtain accurate retrieved values for clouds in a specific region, it is important to use typical values of the sensitive parameters, which could be calculated from in situ observations of cloud droplet size distributions. In addition, the sensitivities of the LWC and R e to the three parameters are stronger in convective clouds than in stratus clouds. This may be related to the melting and merging of solid cloud droplets during the convective mixing process in the convective clouds.

  1. Investigating CloudSat Retrievals Sensitivity to Forward Iterative Algorithm Parameters in the Mixed Cloud Layers

    NASA Astrophysics Data System (ADS)

    Qiu, Yujun; Lu, Chunsong

    2016-09-01

    When millimeter-wave cloud radar data are used for the forward iterative retrieval of the liquid water content (LWC) and effective radius of cloud droplets ( R e) in a cloud layer, the prior values and tolerance ranges of the cloud droplet number density ( N t), scale parameter ( R g) and spectral width parameter ( W g) in the iterative algorithm are the main factors that affect the retrieval accuracy. In this study, we used data from stratus and convective clouds that were simultaneously observed by CloudSat and aircraft to conduct a sensitivity analysis of N t, R g, and W g for the retrieval accuracies of LWC and R e in both stratus and convective clouds. N t is the least sensitive parameter for accurately retrieving stratus LWC and R e in both stratus and convective clouds, except for retrieving the convective cloud LWC. Opposite to N t, R g is the most sensitive parameter for both LWC and R e retrievals. As to the effects of parameter tolerance ranges on the retrievals of LWC and R e, the least important parameter is the N t tolerance range; the most important one is the W g tolerance range for retrieving convective cloud LWC and R e, the R g is the important parameter for retrieving stratus LWC and R e. To obtain accurate retrieved values for clouds in a specific region, it is important to use typical values of the sensitive parameters, which could be calculated from in situ observations of cloud droplet size distributions. In addition, the sensitivities of the LWC and R e to the three parameters are stronger in convective clouds than in stratus clouds. This may be related to the melting and merging of solid cloud droplets during the convective mixing process in the convective clouds.

  2. Seasonal and interannual variations of mixed layer salinity in the southeast tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Zhang, Ningning; Feng, Ming; Du, Yan; Lan, Jian; Wijffels, Susan E.

    2016-07-01

    In this study, seasonal and interannual variations of the mixed layer salinity (MLS) in the southeast tropical Indian Ocean (SETIO) are analyzed using satellite observations, historical data sets, and data-assimilating ocean model outputs. On the seasonal cycle, the MLS in the SETIO becomes fresher in austral winter and saltier in austral summer: between the Java-Lesser Sunda coast and the South Equatorial Current (SEC, 12°S), where positive entrainment and fresh advections counterbalance each other, the annual cycle of the MLS closely follows the variation of the air-sea freshwater forcing; off the northwest and west Australian coasts, the MLS variations are influenced by the annual cycles of the Indonesian Throughflow (ITF) and Leeuwin Current (LC) transports as well as the air-sea freshwater forcing, with eddy fluxes acting to freshen the MLS along the SEC, the Eastern Gyral Current, and the LC. On the interannual-scale, El Niño (La Niña) events are typically associated with saltier (fresher) MLS in the SETIO. Composite and budget analyses reveal that interannual variations in precipitations drive the MLS anomalies off the Java-Lesser Sunda coast; between 12°S and the northwest Australian coast, the MLS variations are influenced by both advection anomalies and local precipitation anomalies; whereas anomalous meridional currents contribute to the MLS variations off the west Australian coast. Both enhanced local precipitations and the ITF transport anomalies have substantial contributions to the drastic freshening of the Indonesian-Australian Basin between the Java-Lesser Sunda coast and the northwest Australian coast during the extended La Niña events in 1999-2001 and 2010-2012.

  3. Synthesis, characterization, and application of novel microporous mixed metal oxides, and nanostructured layered material-polymer films

    NASA Astrophysics Data System (ADS)

    Jeong, Hae-Kwon

    Zeolites are microporous crystalline aluminosilicates with pores and cavities of molecular dimension. They consist of interconnected aluminum and silicon tetrahedra to build a variety of 3D open framework structures. Due to their structure, stability, and activity, zeolites have been widely used in a broad variety of applications in industry. It is, therefore, of great interest to make new structures with potentially novel properties. In this regard, there has recently been a growing interest in the synthesis of novel mixed metal oxides with octahedral and tetrahedral units owing to the possibility to find unique electronic and optical properties. Hence, these materials can find advanced applications as well as conventional applications, just like zeolites. Research efforts have led to the discovery of several mixed octahedral and tetrahedral metal oxides with novel crystal structures including titanium silicates and cerium silicate. Layered materials with transport paths along the thickness of the layers are of particular interest due to potential usage as selective layers of nanometer scale in nanocomposite membranes. A new layered silicate (we call AMH-3) has been synthesized under hydrothermal conditions. The crystal structure solution via powder X-ray diffraction has revealed its unique layer structure of three dimensional microporosity within layers. Layered materials with porous layers will open up new areas of applications, such as selective nanocomposite separation membranes. Polymer/selective-flake nanocomposite membranes have been fabricated for the first time, which can, in principle, be scaled down to submicrometer structures. A layered aluminophosphate with a porous net layer is used as a selective phase and a polyimide as a continuous phase. The microstructures of the nanocomposite membranes were investigated using various characterization techniques. Nanocomposite membranes with 10 wt% layered aluminophosphate show substantial enhancement in

  4. Analysis of wind-tunnel boundary-layer transition experiments on axisymmetric bodies at transonic speeds using compressible boundary-layer stability theory

    NASA Technical Reports Server (NTRS)

    Vijgen, P. M. H. W.; Dodbele, S. S.; Pfenninger, W.; Holmes, B. J.

    1988-01-01

    The design of laminar flow fuselages and advanced swept wings at high-subsonic compressible speeds can benefit from a correlation of compressible transition experiments with the e exp n transition-prediction method. A computational analysis has been conducted to investigate the detailed transition measurements obtained by Boltz et al. (1956, 1960) for two bodies-of-revolution. Nonadiabatic wall conditions were included in the analysis when wall-temperature measurements were available.

  5. Upper mixed layer temperature anomalies at the North Atlantic storm-track zone

    NASA Astrophysics Data System (ADS)

    Moshonkin, S. N.; Diansky, N. A.

    1995-10-01

    Synoptic sea surface temperature anomalies (SSTAs) were determined as a result of separation of time scales smaller than 183 days. The SSTAs were investigated using daily data of ocean weather station C (52.75°N; 35.5°W) from 1 January 1976 to 31 December 1980 (1827 days). There were 47 positive and 50 negative significant SSTAs (lifetime longer than 3 days, absolute value greater than 0.10 °C) with four main intervals of the lifetime repetitions: 1. 4-7 days (45% of all cases), 2. 9-13 days (20-25%), 3. 14-18 days (10-15%), and 4. 21-30 days (10-15%) and with a magnitude 1.5-2.0 °C. An upper layer balance model based on equations for temperature, salinity, mechanical energy (with advanced parametrization), state (density), and drift currents was used to simulate SSTA. The original method of modelling taking into account the mean observed temperature profiles proved to be very stable. The model SSTAs are in a good agreement with the observed amplitudes and phases of synoptic SSTAs during all 5 years. Surface heat flux anomalies are the main source of SSTAs. The influence of anomalous drift heat advection is about 30-50% of the SSTA, and the influence of salinity anomalies is about 10-25% and less. The influence of a large-scale ocean front was isolated only once in February-April 1978 during all 5 years. Synoptic SSTAs develop just in the upper half of the homogeneous layer at each winter. We suggest that there are two main causes of such active sublayer formation: 1. surface heat flux in the warm sectors of cyclones and 2. predominant heat transport by ocean currents from the south. All frequency functions of the ocean temperature synoptic response to heat and momentum surface fluxes are of integral character (red noise), though there is strong resonance with 20-days period of wind-driven horizontal heat advection with mixed layer temperature; there are some other peculiarities on the time scales from 5.5 to 13 days. Observed and modelled frequency functions

  6. Experimental study of an active grid-generated shearless mixing layer and comparisons with large-eddy simulation

    NASA Astrophysics Data System (ADS)

    Kang, Hyung Suk; Meneveau, Charles

    2008-12-01

    A shearless mixing layer characterized by interactions between two regions with different turbulence intensities but without mean shear is investigated experimentally in a wind tunnel. Reynolds numbers higher than those of prior studies [B. Gilbert, "Diffusion mixing in grid turbulence without mean shear," J. Fluid Mech. 100, 349 (1980); S. Veeravalli and Z. Warhaft, "The shearless turbulent mixing layer," J. Fluid Mech. 207, 191 (1989); B. Knaepen, O. Debliquy, and D. Carati, "Direct numerical simulation and large-eddy simulation of a shear-free mixing layer," J. Fluid Mech. 514, 153 (2004); D. Tordella and M. Iovieno, "Numerical experiments on the intermediate asymptotics of shear-free turbulent transport and diffusion," J. Fluid Mech. 549, 429 (2006); D. A. Briggs, J. H. Ferziger, J. R. Koseff, and S. G. Monismith, "Entrainment in a shear-free turbulent mixing layer," J. Fluid Mech. 310, 215 (1996)] are achieved by using an active grid with rotating winglets on one-half of its cross section. Stationary flow-conditioning fine meshes are used to avoid mean velocity gradients. Measurements are performed at five different downstream wind-tunnel locations using an X-type hot-wire probe and a stereoscopic particle image velocimetry system. The Reynolds numbers based on the Taylor microscale in the high- and low-kinetic energy regions are 170 and 88, respectively. The energy and integral length-scale ratios between the two regions are 4.27 and 1.73, respectively. The inlet turbulence in the upper and lower portions of the shearless mixing layer is not fully isotropic, with the streamwise velocity fluctuations being between 6% and 13% higher than the cross-stream ones. Fundamental statistical properties of the flow are documented and analyzed at various scales using band-pass box-filtered velocities. Downstream evolution of variance and half-width of the mixing layer, skewness and flatness factors, as well as the statistics of two-point velocity increments at various

  7. Influence of surface forcing on near-surface and mixing layer turbulence in the tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Callaghan, Adrian H.; Ward, Brian; Vialard, Jérôme

    2014-12-01

    An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rate of dissipation of turbulent kinetic energy (ε) in the tropical Indian Ocean during a single diurnal cycle, from about 50 m depth to the sea surface. This dataset is one of only a few to resolve upper ocean ε over a diurnal cycle from below the active mixing layer up to the air-sea interface. Wind speed was weak with an average value of ~5 m s-1 and the wave field was swell-dominated. Within the wind and wave affected surface layer (WWSL), ε values were on the order of 10-7-10-6 W kg-1 at a depth of 0.75 m and when averaged, were almost a factor of two above classical law of the wall theory, possibly indicative of an additional source of energy from the wave field. Below this depth, ε values were closer to wall layer scaling, suggesting that the work of the Reynolds stress on the wind-induced vertical shear was the major source of turbulence within this layer. No evidence of persistent elevated near-surface ε characteristic of wave-breaking conditions was found. Profiles collected during night-time displayed relatively constant ε values at depths between the WWSL and the base of the mixing layer, characteristic of mixing by convective overturning. Within the remnant layer, depth-averaged values of ε started decaying exponentially with an e-folding time of 47 min, about 30 min after the reversal of the total surface net heat flux from oceanic loss to gain.

  8. Results from long-term detection of mixing layer height: ceilometer and comparison with Radio-Acoustic Sounding System

    NASA Astrophysics Data System (ADS)

    Schäfer, Klaus; Emeis, Stefan; Jahn, Carsten; Tuma, Michael; Münkel, Christoph; Suppan, Peter

    2012-11-01

    The mixing layer height (MLH) is an important factor which influences exchange processes of ground level emissions. The continuous knowledge of MLH is supporting the understanding of processes directing air quality. If the MLH is located near to the ground, which occurs mainly during winter and night-time, air pollution can be high due to a strongly limited air mass dilution. Since 2006 different methods for long-term continuous remote sensing of mixing layer height (MLH) are operated in Augsburg. The Vaisala ceilometers LD40 and CL31 are used which are eye-safe commercial mini-lidar systems. The ceilometer measurements provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the borders of mixed layers. Special software for these ceilometers provides routine retrievals of lower atmosphere layering from vertical profiles of laser backscatter data. The radiosonde data from the station Oberschleissheim near Munich (about 50 km away from Augsburg city) are also used for MLH determination. The profile behavior of relative humidity (strong decrease) and virtual potential temperature (inversion) of the radiosonde agree mostly well with the MLH indication from ceilometer laser backscatter density gradients. A RASS (Radio-Acoustic Sounding System) from Metek is applied which detects the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component as well as the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions which mark atmospheric layers. These data of RASS measurements are the input for a software-based determination of MLH. A comparison of the results of the remote sensing methods during simultaneous measurements was performed. The information content of the different remote sensing instruments for MLH in dependence from different weather classes was

  9. A Priori Analysis of Subgrid-Scale Models for Large Eddy Simulations of Supercritical Binary-Species Mixing Layers

    NASA Technical Reports Server (NTRS)

    Okong'o, Nora; Bellan, Josette

    2005-01-01

    Models for large eddy simulation (LES) are assessed on a database obtained from direct numerical simulations (DNS) of supercritical binary-species temporal mixing layers. The analysis is performed at the DNS transitional states for heptane/nitrogen, oxygen/hydrogen and oxygen/helium mixing layers. The incorporation of simplifying assumptions that are validated on the DNS database leads to a set of LES equations that requires only models for the subgrid scale (SGS) fluxes, which arise from filtering the convective terms in the DNS equations. Constant-coefficient versions of three different models for the SGS fluxes are assessed and calibrated. The Smagorinsky SGS-flux model shows poor correlations with the SGS fluxes, while the Gradient and Similarity models have high correlations, as well as good quantitative agreement with the SGS fluxes when the calibrated coefficients are used.

  10. Measuring ice- and liquid-water properties in mixed-phase cloud layers at the Leipzig Cloudnet station

    NASA Astrophysics Data System (ADS)

    Bühl, Johannes; Seifert, Patric; Myagkov, Alexander; Ansmann, Albert

    2016-08-01

    An analysis of the Cloudnet data set collected at Leipzig, Germany, with special focus on mixed-phase layered clouds is presented. We derive liquid- and ice-water content together with vertical motions of ice particles falling through cloud base. The ice mass flux is calculated by combining measurements of ice-water content and particle Doppler velocity. The efficiency of heterogeneous ice formation and its impact on cloud lifetime is estimated for different cloud-top temperatures by relating the ice mass flux and the liquid-water content at cloud top. Cloud radar measurements of polarization and Doppler velocity indicate that ice crystals formed in mixed-phase cloud layers with a geometrical thickness of less than 350 m are mostly pristine when they fall out of the cloud.

  11. The prediction of sea-surface temperature variations by means of an advective mixed-layer ocean model

    NASA Technical Reports Server (NTRS)

    Atlas, R. M.

    1976-01-01

    An advective mixed layer ocean model was developed by eliminating the assumption of horizontal homogeneity in an already existing mixed layer model, and then superimposing a mean and anomalous wind driven current field. This model is based on the principle of conservation of heat and mechanical energy and utilizes a box grid for the advective part of the calculation. Three phases of experiments were conducted: evaluation of the model's ability to account for climatological sea surface temperature (SST) variations in the cooling and heating seasons, sensitivity tests in which the effect of hypothetical anomalous winds was evaluated, and a thirty-day synoptic calculation using the model. For the case studied, the accuracy of the predictions was improved by the inclusion of advection, although nonadvective effects appear to have dominated.

  12. Thermal conductivity of a graphite bipolar plate (BPP) and its thermal contact resistance with fuel cell gas diffusion layers: Effect of compression, PTFE, micro porous layer (MPL), BPP out-of-flatness and cyclic load

    NASA Astrophysics Data System (ADS)

    Sadeghifar, Hamidreza; Djilali, Ned; Bahrami, Majid

    2015-01-01

    This paper reports on measurements of thermal conductivity of a graphite bipolar plate (BPP) as a function of temperature and its thermal contact resistance (TCR) with treated and untreated gas diffusion layers (GDLs). The thermal conductivity of the BPP decreases with temperature and its thermal contact resistance with GDLs, which has been overlooked in the literature, is found to be dominant over a relatively wide range of compression. The effects of PTFE loading, micro porous layer (MPL), compression, and BPP out-of-flatness are also investigated experimentally. It is found that high PTFE loadings, MPL and even small BPP out-of-flatness increase the BPP-GDL thermal contact resistance dramatically. The paper also presents the effect of cyclic load on the total resistance of a GDL-BPP assembly, which sheds light on the behavior of these materials under operating conditions in polymer electrolyte membrane fuel cells.

  13. The effects of stabilizing and destabilizing longitudinal curvature on the structure of turbulent, two-stream mixing layers

    NASA Technical Reports Server (NTRS)

    Plesniak, Michael W.; Johnston, J. P.

    1989-01-01

    The construction and development of the multi-component traversing system and associated control hardware and software are presented. A hydrogen bubble/laser sheet flow visualization technique was developed to visually study the characteristics of the mixing layers. With this technique large-scale rollers arising from the Taylor-Gortler instability and its interaction with the primary Kelvin-Helmholtz structures can be studied.

  14. Comment on "Mixed-layer deepening during Heinrich events: a multi-planktonic foraminiferal delta18O approach".

    PubMed

    Hillaire-Marcel, Claude; de Vernal, Anne

    2008-05-30

    Rashid and Boyle (Reports, 19 October 2007, p. 439) analyzed oxygen isotopes in planktonic foraminera from marine sediments and concluded that Heinrich events (massive iceberg discharges into the North Atlantic Ocean) caused upper water masses to deepen. We question the robustness of this interpretation and argue that a strongly stratified mixed layer characterized by dense sea-ice cover and production of oxygen-18-depleted brines likely prevailed during such events. PMID:18511673

  15. The fluxes of CN neutrinos from the Sun in case of mixing in a spherical layer in the solar core

    SciTech Connect

    Kopylov, Anatoly; Petukhov, Valery E-mail: beril@inr.ru

    2012-03-01

    The results of the calculation are presented for the fluxes of CN neutrinos from the Sun in case of mixing in a spherical layer in the solar core, consistent with the seismic data and with the measured solar neutrino fluxes. It is shown that a substantial increase of the flux of {sup 13}N neutrinos can be gained in this case. The possible implications for experiment are discussed.

  16. Lidar measurements of the atmospheric entrainment zone and the potential temperature jump across the top of the mixed layer

    NASA Technical Reports Server (NTRS)

    Boers, R.; Eloranta, E. W.

    1986-01-01

    Lidar data of the atmospheric entrainment zone from six days of clear air convection obtained in central Illinois during July 1979 are presented. A new method to measure the potential temperature jump across the entrainment zone based on only one temperature sounding and continuous lidar measurements of the mixed layer height is developed. An almost linear dependence is found between the normalized entrainment rate and the normalized thickness of the entrainment zone.

  17. The analysis and modeling of dilatational terms in compressible turbulence

    NASA Technical Reports Server (NTRS)

    Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.; Kreiss, H. O.

    1989-01-01

    It is shown that the dilatational terms that need to be modeled in compressible turbulence include not only the pressure-dilatation term but also another term - the compressible dissipation. The nature of these dilatational terms in homogeneous turbulence is explored by asymptotic analysis of the compressible Navier-Stokes equations. A non-dimensional parameter which characterizes some compressible effects in moderate Mach number, homogeneous turbulence is identified. Direct numerical simulations (DNS) of isotropic, compressible turbulence are performed, and their results are found to be in agreement with the theoretical analysis. A model for the compressible dissipation is proposed; the model is based on the asymptotic analysis and the direct numerical simulations. This model is calibrated with reference to the DNS results regarding the influence of compressibility on the decay rate of isotropic turbulence. An application of the proposed model to the compressible mixing layer has shown that the model is able to predict the dramatically reduced growth rate of the compressible mixing layer.

  18. Effects of Mesoscale Eddies in the Active Mixed Layer: Test of the Parametrisation in Eddy Resolving Simulations

    NASA Technical Reports Server (NTRS)

    Luneva, M. V.; Clayson, C. A.; Dubovikov, Mikhail

    2015-01-01

    In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200-207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1-2 degrees and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher (0.5-0.74) correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes