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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. 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.

  3. Stability of compressible reacting mixing layer

    NASA Technical Reports Server (NTRS)

    Shin, D. S.; Ferziger, J. H.

    1991-01-01

    Linear instability of compressible reacting mixing layers is analyzed with emphasis on the effects of heat release and compressibility. Laminar solutions of the compressible boundary-layer equations are used as the base flows. The parameters of this study are the adiabatic flame temperature, the Mach number of the upper stream, frequency, wavenumber, and the direction of propagation of the disturbance wave. Stability characteristics of the flow are presented. Three groups of unstable modes are found when the Mach number and/or heat release are large. Finally, it is shown that the unstable modes are two-dimensional for large heat release even in highly compressible flow.

  4. Wavy structures in compressible mixing layers

    NASA Astrophysics Data System (ADS)

    Chen, Jun; Shi, Xiao-Tian; Wang, Tie-Jin; She, Zhen-Su

    2013-10-01

    Semi-periodic structures namely inclined wavy structures (IWS) are experimentally observed in compressible mixing layers at two convective Mach numbers ( M c = 0.11 and 0.47). Flow structures are visualized by the laserinduced planar laser Mie scattering (PLMS) technique. Two methods are developed to investigate the spatial distribution and geometry of IWS: (1) the dominant mode extraction (DME) method, to extract the dominant modes of IWS from the streamwise gray-level fluctuation, and (2) the phase tracking (PT) method, to identify the shape of IWS. The results suggest that pressure perturbations account for the formation of IWS in the initialmixing region and the joint effect of dilatation and coherent vortices enhances IWS in the welldeveloped region. The large transverse (cross-flow) scale of the IWS and their relation to coherent vortices (CV) indicate that the disturbance originated from CV in the mixing center propagates far into the free streams. The DME and the PT method are shown to be the effective tools to study the geometrical features of wavy structures in compressible shear flows.

  5. Linear Stability Regime Analysis of the Compressible Reacting Mixing Layer

    NASA Technical Reports Server (NTRS)

    Day, M. J.; Reynolds, William C.; Mansour, N. N.; Rai, Man Mohan (Technical Monitor)

    1995-01-01

    Previous investigations have shown that a compressible reacting mixing layer can develop two peaks in the mean density weighted vorticity profile. Linear stability analyses show that at these peaks two distinct 'outer' instability modes appear in addition to the more common central mode, which exists unaccompanied in incompressible nonreacting flows. The present study parametrically analyzes the effects of compressibility, heat release, stoichiometry, and density ratio on the amplification rate and obliquity of each stability mode. The mean profiles used in the spatial stability calculation are generated by self-similar solutions of the compressible boundary layer equations combined with the assumption of infinitely fast chemistry. It is shown that the influence of stoichiometry and density ratio on the peaks of the density weighted vorticity profile determines which modes will dominate. Of particular interest are the conditions where two modes are equally amplified, causing the mixing layer to develop into a 'colayer' structure.

  6. Linear stability of the confined compressible reacting mixing layer

    NASA Technical Reports Server (NTRS)

    Shin, D. S.; Ferziger, J. H.

    1993-01-01

    This paper investigates the linear stability of confined mixing layers with special emphasis on the effects of heat release and compressibility. The results show that reflection of supersonic disturbances by the walls makes the confined supersonic mixing layer more unstable than the unconfined free shear layer. Decreasing the distance between the walls makes the flow more unstable. However, subsonic disturbances are relatively unaffected by the walls. Heat release and Mach number hardly change the growth rates of supersonic disturbances. The most unstable supersonic disturbances are two-dimensional in rectangular channel flows, but three-dimensional in partially confined flows. Finally, the reactants are not strongly mixed by supersonic instabilities, which mainly disturb one side of the layer.

  7. High-speed cinematography of compressible mixing layers

    NASA Astrophysics Data System (ADS)

    Mahadevan, R.; Loth, Eric

    1994-07-01

    Experiments are performed using high-speed film cinematography to temporally resolve compressible planar mixing layer structures using shadowgraphs and planar light sheet visualization. The technique is relatively inexpensive and allows multiple images. The time-dependent shadowgraph and Mie scattering images are documented with a rotating mirror camera operating at approximately 350 kHz. The results show the presence of large scale structures in the mixing layer which flatten as they convect downstream. Both spatial and temporal covariances have been obtained through digital image processing which yield, on average, elliptical structures with convective speeds above the isentropic prediction, and non-isotropic streamwise and transverse scalar transport fluctuations.

  8. Compressibility effects in a turbulent annular mixing layer

    NASA Astrophysics Data System (ADS)

    Freund, Jonathan Ben

    1998-12-01

    Mixing between supersonic streams is critical to many technological applications, especially scramjets. This work uses direct numerical simulations of time evolving annular mixing layers, which correspond to the early development of round jets, to study compressibility effects on turbulence dynamics and mixing in free shear flow. Nine cases were considered with convective Mach numbers ranging from Mc = 0.1 to 1.8 and turbulent Mach numbers reaching as high as Mt = 0.8. Growth rates of the simulated mixing layers are suppressed with increasing Mach number as observed experimentally. The Reynolds stresses, with exception of the axial normal stress, /overline[ux/sp/prime x/sp'], are also suppressed. Flow visualizations show a distinct change in turbulence structure with increasing Mach number. At low Mach numbers, the flow is dominated by large azimuthally correlated rollers whereas at high Mach numbers the flow is dominated by small streamwise oriented structures. Dilatational terms are found to have negligible net effect upon the turbulence energetics despite the fact that shocklets are found at high Mach numbers. The growth rate suppression is analyzed with the Reynolds stress transport equations and a simple relation between mixing layer growth rate and the pressure-strain-rate correlation is found. This correlation is suppressed at higher Mach numbers due to suppressed pressure fluctuations. A change in structure caused by a 'communication' breakdown across supersonically deforming eddies is found to be responsible for the suppression of pressure fluctuations and this effect is parameterized with a gradient Mach number, Mg=[/ell/over a][/partial/bar u/over/partial y]. Mixing is studied with a passive scalar transport equation. Increasing the Mach number changes the mixture fraction probability density function from non-marching to marching and the mixing efficiency from 0.5 at Mc = 0.1 to 0.67 at Mc = 1.5. The scalar concentration and the axial velocity

  9. Filtered Rayleigh scattering based measurements in compressible mixing layers

    NASA Technical Reports Server (NTRS)

    Elliott, G. S.; Samimy, M.; Arnette, S. A.

    1992-01-01

    Results are presented of experiments in which a Rayleigh-scattering-based technique was used to make quantitative planar measurements in the compressible free shear layers. To this end, the absorption characteristics of the iodine molecular filter were investigated, and initial planar density measurements in M(c) = 0.51 shear layer were performed. The preliminary results presented here demonstrate the validity of the measurement technique.

  10. Study of compressible mixing layers using filtered Rayleigh scattering based visualizations

    NASA Technical Reports Server (NTRS)

    Elliott, Gregory S.; Samimy, MO; Arnette, Stephen A.

    1992-01-01

    Filtered Rayleigh scattering-based flow visualizations of compressible mixing layers are reported. The lower compressibility case (Mc = 0.51) displays well-defined roller-type spanwise structures and streamwise streaks. The structures of the high compressibility case (Mc = 0.86) are more 3D and oblique.

  11. A study of compressible mixing layers using filtered Rayleigh scattering

    NASA Technical Reports Server (NTRS)

    Elliott, Gregory S.; Samimy, MO; Arnette, Stephen A.

    1992-01-01

    High Reynolds number compressible planar free shear layers were studied using a planar laser visualization technique. Two convective Mach numbers, M(c) = 0.51 and 0.86, were studied in the developing and fully developed regions. The structures in the M(c) = 0.51 case were characterized by 2D core and roller regions, similar to subsonic shear layers. Also for the M(c) = 0.51 case, plan views in the developing region showed the existence of streamwise streaks, possibly indicating the presence of organized streamwise vorticity. The M(c) = 0.86 flow was much less organized than the lower convective Mach number case and highly three dimensional.

  12. Absolute/convective instabilities and the convective Mach number in a compressible mixing layer

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    Two aspects of the stability of a compressible mixing layer: Absolute/Convective instability and the convective Mach number were considered. It was shown that, for Mach numbers less than one, the compressible mixing layer is convectively unstable unless there is an appreciable amount of backflow. Also presented was a rigorous derivation of a convective Mach number based on linear stability theory for the flow of a multi-species gas in a mixing layer. The result is compared with the heuristic definitions of others and to selected experimental results.

  13. Absolute/convective instabilities and the convective Mach number in a compressible mixing layer

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    Two aspects of the stability of a compressible mixing layer: Absolute/Convective instability and the convective Mach number were considered. It was shown that, for Mach numbers less than one, the compressible mixing layer is convectively unstable unless there is an appreciable amount of backflow. Also presented was a rigorous derivation of a convective Mach number based on linear stability theory for the flow of a multi-species gas in a mixing layer. The result is compared with the heuristic definitions of others and to selected experimental results.

  14. 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.

  15. Effect of heat release on the stability of compressible reacting mixing layer

    NASA Technical Reports Server (NTRS)

    Shin, Dong-Shin; Ferziger, J. H.

    1991-01-01

    Reacting free shear layers are of fundamental importance in many industrial systems including gas turbine combustors and rockets. Efficient propulsion systems are essential for air breathing supersonic ramjets in the high Mach number range. A limiting factor in these engines is the time for fuel and oxidizer to mix in the combustion chamber; for fast mixing, the flow must be vigorously turbulent which requires the laminar flow to be unstable. Understanding the stability characteristics of compressible reacting free shear layers is, therefore, very important and may allow one to control the flow. Low speed shear layers are highly unstable but, as chemical reaction and compressibility effects tend to stabilize them, it is important to investigate the stability of high speed reacting mixing layers. The latter consists of two fluid streams containing fuel and oxidizer respectively, and the conclusions are expected to apply, with quantitative modifications, to other shear flows, e.g., jets. Since low speed reacting cases have been studied earlier, we concentrate on the effects of Mach number and heat release. We are primarily interested in solving the stability problem over a large range of Mach number and heat release. In order to understand the effect of the heat release on the stability of this flow, one must first study the characteristics of the non-reacting flow. Inviscid theory is a reliable guide for understanding stability of compressible shear flows at moderate and large Reynolds numbers and is the basis for this work.

  16. Three-dimensional numerical simulation of a compressible, spatially evolving mixing layer

    NASA Astrophysics Data System (ADS)

    Grinstein, Fernando F.; Oran, Elaine S.; Hussain, Fazle

    1988-01-01

    The results from three-dimensional finite-difference simulations of a subsonic, spatially evolving mixing layer are presented. The numerical model solves the compressible time-dependent conservation equations for mass, momentum and energy density using the Flux-Corrected Transport algorithm and direction and timestep splitting. The mixing layer was found to be very sensitive to spanwise perturbations of the cross-stream velocity. Streamwise vortices, appearing in counter-rotating pairs, occurred in the region of the braids in response to sinusoidal coherent spanwise perturbations. These vortices are observed as identifiable coherent structures superimposed on the primary spanwise rolls and affecting considerably the vorticity distribution within their cores. Mass-density drops associated with the maxima of spanwise vorticity, were due to the formation and interaction of coherent structures. The growth rate of the mixing layer was observed to be much faster when streamwise vortical structures are present.

  17. 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.

  18. Control of shock-wave boundary-layer interactions by bleed in supersonic mixed compression inlets

    NASA Technical Reports Server (NTRS)

    Fukuda, M. K.; Reshotko, E.; Hingst, W. R.

    1975-01-01

    An experimental investigation has been conducted to determine the effect of bleed region geometry and bleed rate on shock wave-boundary layer interactions in an axisymmetric, mixed-compression inlet at a Mach number of 2.5. The full realizable reduction in transformed form factor is obtained by bleeding off about half the incident boundary layer mass flow. Bleeding upstream or downstream of the shock-induced pressure rise is preferable to bleeding across the shock-induced pressure rise. Slanted holes are more effective than normal holes. Two different bleed hole sizes were tested without detectable difference in performance.

  19. Control of shock wave-boundary layer interactions by bleed in supersonic mixed compression inlets

    NASA Technical Reports Server (NTRS)

    Fukuda, M. K.; Hingst, W. G.; Reshotko, E.

    1975-01-01

    An experimental investigation was conducted to determine the effect of bleed on a shock wave-boundary layer interaction in an axisymmetric mixed-compression supersonic inlet. The inlet was designed for a free-stream Mach number of 2.50 with 60-percent supersonic internal area contraction. The experiment was conducted in the NASA Lewis Research Center 10-Foot Supersonic Wind Tunnel. The effects of bleed amount and bleed geometry on the boundary layer after a shock wave-boundary layer interaction were studied. The effect of bleed on the transformed form factor is such that the full realizable reduction is obtained by bleeding of a mass flow equal to about one-half of the incident boundary layer mass flow. More bleeding does not yield further reduction. Bleeding upstream or downstream of the shock-induced pressure rise is preferable to bleeding across the shock-induced pressure rise.

  20. Large-Eddy Simulation (LES) of a Compressible Mixing Layer and the Significance of Inflow Turbulence

    NASA Technical Reports Server (NTRS)

    Mankbadi, Mina Reda; Georgiadis, Nicholas J.; Debonis, James R.

    2017-01-01

    In the context of Large Eddy Simulations (LES), the effects of inflow turbulence are investigated through the Synthetic Eddy Method (SEM). The growth rate of a turbulent compressible mixing layer corresponding to operating conditions of GeobelDutton Case 2 is investigated herein. The effects of spanwise width on the growth rate of the mixing layer is investigated such that spanwise width independence is reached. The error in neglecting inflow turbulence effects is quantified by comparing two methodologies: (1) Hybrid-RANS-LES methodology and (2) SEM-LES methodology. Best practices learned from Case 2 are developed herein and then applied to a higher convective mach number corresponding to Case 4 experiments of GeobelDutton.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Compressibility effects on turbulent mixing

    NASA Astrophysics Data System (ADS)

    Panickacheril John, John; Donzis, Diego

    2016-11-01

    We investigate the effect of compressibility on passive scalar mixing in isotropic turbulence with a focus on the fundamental mechanisms that are responsible for such effects using a large Direct Numerical Simulation (DNS) database. The database includes simulations with Taylor Reynolds number (Rλ) up to 100, turbulent Mach number (Mt) between 0.1 and 0.6 and Schmidt number (Sc) from 0.5 to 1.0. We present several measures of mixing efficiency on different canonical flows to robustly identify compressibility effects. We found that, like shear layers, mixing is reduced as Mach number increases. However, data also reveal a non-monotonic trend with Mt. To assess directly the effect of dilatational motions we also present results with both dilatational and soleniodal forcing. Analysis suggests that a small fraction of dilatational forcing decreases mixing time at higher Mt. Scalar spectra collapse when normalized by Batchelor variables which suggests that a compressive mechanism similar to Batchelor mixing in incompressible flows might be responsible for better mixing at high Mt and with dilatational forcing compared to pure solenoidal mixing. We also present results on scalar budgets, in particular on production and dissipation. Support from NSF is gratefully acknowledged.

  12. 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.

  13. Infrared spectroscopy analysis of mixed DPPC/fibrinogen layer behavior at the air/liquid interface under a continuous compression-expansion condition.

    PubMed

    Yin, Chia-Lin; Chang, Chien-Hsiang

    2006-07-18

    The mixed layer behavior of dipalmitoyl phosphatidylcholine (DPPC) with fibrinogen at continuously compressed-expanded air/liquid interfaces was analyzed in situ by infrared reflection-absorption spectroscopy (IRRAS). The reflectance-absorbance (RA) intensities and/or wavenumbers of nu(a)-CH2 and amide I bands for a mixed DPPC/fibrinogen layer at the interface were obtained directly by an infrared spectrometer with a monolayer/grazing angle accessory and a removable Langmuir trough. The nu(a)-CH2 RA intensity-area hysteresis curves of a DPPC monolayer indicate a significant loss of free DPPC molecules at the interface during the first compression stage, which is also supported by the corresponding nu(a)-CH2 wavenumber-area hysteresis curves. For a mixed DPPC/fibrinogen layer at the interface, the amide I RA intensity-area hysteresis curves suggest that the fibrinogen molecules were expelled from the interface upon compression, apparently because of the presence of insoluble DPPC molecules. The squeeze-out of fibrinogen evidently removed a pronounced amount of DPPC from the interface, as judged from the corresponding nu(a)-CH2 intensity and wavenumber data. Moreover, significant adsorption of fibrinogen was found during the subsequent interface expansion stage. With the in situ IRRAS analysis of the mixed layer behavior at the interface, the induced loss of DPPC by fibrinogen expulsion from the compressed interface and the dominant adsorption of fibrinogen to the expanded interface were clearly demonstrated.

  14. Compressible turbulent mixing: Effects of compressibility.

    PubMed

    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.

  15. 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.

  16. Boundary layer bleed system study for a full-scale, mixed-compression inlet with 45 percent internal contraction

    NASA Technical Reports Server (NTRS)

    Shaw, R. J.; Wasserbauer, J. F.; Neumann, H. E.

    1976-01-01

    The results of an experimental bleed development study for a full-scale, Mach 2.5, axisymmetric, mixed-compression inlet were presented. The inlet was designed to satisfy the airflow requirements of the TF30-P-3 turbofan engine. Capabilities for porous bleed on the cowl surface and ram-scoop/flush-slot bleed on the centerbody were provided. A configuration with no bleed on the cowl achieved a minimum stable, diffuser exit, total pressure recovery of 0.894 with a centerbody-bleed mass flow ratio of 0.02. Configurations with cowl bleed had minimum stable recoveries as high as 0.900 but suffered range decrement penalties from the increased bleed mass flow removal. Limited inlet stability and unstart angle-of-attack data are presented.

  17. MHD turbulent mixing layers

    SciTech Connect

    Esquivel, A.; Lazarian, A.; Benjamin, R.A.; Cho, J.; Leitner, S.N.

    2005-09-28

    Turbulent mixing layers have been proposed to explain observations of line ratios of highly ionized elements in the interstellar medium. We present preliminary results of numerical simulations of turbulent mixing layers in a magnetized medium. We developed a MHD code with radiative cooling. The magnetic field is expected to be a controlling factor by suppressing instabilities that lead to the turbulent mixing. Our results suggest that the difference in turbulent mixing in the unmagnetized case as compared to the case of a weak magnetic field, {beta} = Pgas/Pmag {approx} 10, is insignificant. With a more thorough exploration of parameter space, this work will provide more reliable diagnostics of turbulent mixing layers than those available today.

  18. 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.

  19. Stability of compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Nayfeh, Ali H.

    1989-01-01

    The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of disturbances in supersonic laminar boundary layers and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.

  20. Phase decorrelation, streamwise vortices and acoustic radiation in mixing layers

    NASA Technical Reports Server (NTRS)

    Ho, C. M.; Zohar, Y.; Moser, R. D.; Rogers, M. M.; Lele, S. K.; Buell, J. C.

    1988-01-01

    Several direct numerical simulations were performed and analyzed to study various aspects of the early development of mixing layers. Included are the phase jitter of the large-scale eddies, which was studied using a 2-D spatially-evolving mixing layer simulation; the response of a time developing mixing layer to various spanwise disturbances; and the sound radiation from a 2-D compressible time developing mixing layer.

  1. Towards Natural Transition in Compressible Boundary Layers

    DTIC Science & Technology

    2016-06-29

    AFRL-AFOSR-CL-TR-2016-0011 Towards natural transition in compressible boundary layers Marcello Faraco de Medeiros FUNDACAO PARA O INCREMENTO DA...to 29-03-2016 Towards natural transition in compressible boundary layers FA9550-11-1-0354 Marcello A. Faraco de Medeiros Germán Andrés Gaviria...unlimited. 109 Final report Towards natural transition in compressible boundary layers Principal Investigator: Marcello Augusto Faraco de Medeiros

  2. 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.

  3. Effect of three-dimensionality on compressible mixing

    NASA Astrophysics Data System (ADS)

    Papamoschou, Dimitri

    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.

  4. 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.

  5. 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

  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. Compressibility effects in free shear layers

    NASA Technical Reports Server (NTRS)

    Samimy, M.; Elliott, G. S.

    1990-01-01

    High-Reynolds-number compressible free shear layers were studied experimentally to explore the effects of compressibility on the turbulence field. A reduction in both the level and the lateral extent of turbulence fluctuations with increasing convective Mach number (Mc) (reported earlier for Mc of 0.51 and 0.64) is much higher at Mc of 0.86. The higher-order moments of turbulence fluctuations such as skewness and flatness show that the intermittency due to the excursion of large-scale structures into the free streams at the edge of shear layers was significantly reduced (both in the level and the extent) due to increased Mc.

  8. Numerical simulation of excited jet mixing layers

    NASA Astrophysics Data System (ADS)

    Scott, J. N.; Hankey, W. L.

    1987-01-01

    A numerical simulation of unsteady flow in jet mixing layers, both with and without external excitation, has been performed by solving the time-dependent compressible Navier-Stokes equations. Computations were performed on a CRAY X-MP computer using MacCormick's explicit finite difference algorithm. Different excitation methods were investigated and were shown to be very effective in controlling the well organized periodic production, shedding and pairing of large scale vortex structures. It is found that pressure excitation was generally more effective than temperature excitation, and that grid refinement results in substantial improvement in the resolution of unsteady features. The location and orientation, in addition to the frequency, of the excitation source are shown to have a significant influence on the production and interaction of large scale vortex structures in the jet mixing layer.

  9. Influence of orientation on the evolution of small perturbations in compressible shear layers with inflection points

    NASA Astrophysics Data System (ADS)

    Karimi, Mona; Girimaji, Sharath S.

    2017-03-01

    We investigate the influence of orientation on the evolution of small perturbations in compressible shear layers with inflection points. By using linear analysis, we demonstrate that perturbations along the shear plane are most affected by compressibility. The influence of compressibility gradually diminishes with increasing obliqueness of the perturbations with respect to the shear plane. It is demonstrated that the effective gradient Mach number is an appropriate compressibility parameter. We establish that spanwise perturbations, orthogonal to the shear plane, are impervious to compressibility effects. Direct numerical simulations of compressible mixing layers subject to the perturbations at various obliqueness angles verify the analytical findings.

  10. Mixing in straight shear layers

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Planar laser-induced fluorescence measurements were performed in a liquid plane mixing layer to extract the probability density function (pdf) of the mixture fraction of a passive scalar across the layer. Three Reynolds number (Re) cases were studied, 10,000, 33,000 and 90,000, with Re based on velocity difference and visual thickness. The results show that a non-marching pdf (central hump invariant from edge to edge of the layer) exists for Re = 10,000 but that a marching type pdf characterizes the Re = 33,000 and Re = 90,000 cases. For all cases, a broad range of mixture fraction values is found at each location across the layer. Streamwise and spanwise ramps across the layer, and structure-to-structure variation were observed and are believed to be responsible for the above behavior of the composition field. Tripping the boundary layer on the high-speed side of the splitter plate for each of the above three cases resulted in increased three-dimensionality and a change in the composition field. Average and average mixed fluid compositions are reported for all cases.

  11. 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.

  12. Effects of compressibility on the characteristics of free shear layers

    NASA Technical Reports Server (NTRS)

    Samimy, M.; Elliott, G. S.

    1990-01-01

    A high Reynolds number two-dimensional constant pressure compressible shear layer was formed at the trailing edge of an 0.5 mm-thick splitter plate. Convective Mach numbers of 0.51 and 0.64 were investigated using a two-component coincident LDV for the measurements. For the lower convective Mach number case, the nondimensionalized shear-layer and vorticity thickness growth rates were over 20 percent higher and the momentum thickness growth rate was over 30 percent higher than those of the higher convective Mach number case. The results seen to indicate that both small scale and large scale mixing are reduced with increasing convective Mach number.

  13. Hypersonic mixed-compression inlet shock-induced combustion ramjets

    NASA Astrophysics Data System (ADS)

    Alexander, Derrick

    This study investigates the performance and flow field features of a mixed-compression inlet shock-induced combustion ramjet (shcramjet). In a shcramjet, oncoming air is compressed with shocks in the inlet and then further compressed and mixed with hydrogen fuel in a duct prior to shock-induced combustion and expansion of the combustion products through a divergent nozzle to provide thrust. Numerical studies are undertaken using the WARP code that solves the Favre-averaged Navier-Stokes equations closed by the Wilcox k-o turbulence model. Hydrogen/air combustion is solved via the twenty reaction, nine species combustion model of Jachimowski. Mixing augmentation through the use of cantilevered ramp injector arrays on opposite shcramjet inlet walls is studied and the influence of relative array locations is quantified. Increased spanwise distance between adjacent injectors on opposite walls allows for increased jet penetration and fuel distributions in the center of the engine duct. Chemically reacting studies verify an air buffer is created between the fuel and walls that suppresses premature ignition while still allowing for an air based mixing efficiency of up to 0.46-0.54. Combustion is produced over aerodynamic wedges with the spatial flow variation dictating both detonation and shock-induced combustion can be present over constant angle wedges. The initial inlet angle must be as high as possible, while avoiding premature ignition, to generate the pressure in the combustor needed for significant positive thrust. Thrust production from combustion is found to be insensitive to wedge angle if combustion is initiated across the cross-sectional area. Strong recirculation regions are formed via shock/boundary layer interactions in the confined engine duct. Mitigation of the recirculation is demonstrated with correct placement of the nozzle expansion in conjunction with air blowing in the boundary layer at a mass flow rate on the order of that of the fuel injection

  14. Towards Natural Transition in Compressible Boundary Layers

    DTIC Science & Technology

    2016-06-29

    St., Ste 325 Arlington, VA 22203 James M. Fillerup AFOSR/NA and AFOSR/SOARD DISTRIBUTION STATEMENT A. Approved for public release; distribution is...30-09-2011 to 29-03-2016, with Dr. James M. Fillerup serving as program manager. In this project, a DNS code was developed to investigate problems on...modes in compressible boundary layers. Journal of Fluid Mechanics, 586:295–322, 9 2007. [87] Adam P. Tunney, James P. Denier, Trent W. Mattner, and John

  15. Turbulent shear stresses in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Laderman, A. J.; Demetriades, A.

    1979-01-01

    Hot-wire anemometer measurements of turbulent shear stresses in a Mach 3 compressible boundary layer were performed in order to investigate the effects of heat transfer on turbulence. Measurements were obtained by an x-probe in a flat plate, zero pressure gradient, two dimensional boundary layer in a wind tunnel with wall to freestream temperature ratios of 0.94 and 0.71. The measured shear stress distributions are found to be in good agreement with previous results, supporting the contention that the shear stress distribution is essentially independent of Mach number and heat transfer for Mach numbers from incompressible to hypersonic and wall to freestream temperature ratios of 0.4 to 1.0. It is also found that corrections for frequency response limitations of the electronic equipment are necessary to determine the correct shear stress distribution, particularly at the walls.

  16. 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.

  17. 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.

  18. 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.

  19. Compressibility and shock wave interaction effects on free shear layers

    NASA Technical Reports Server (NTRS)

    Samimy, M.; Erwin, D. E.; Elliott, G. S.

    1989-01-01

    Two compressible free shear layers with convective Mach numbers of .51 and .86 were studied as baseline configurations to investigate the effects of compressibility on the turbulence characteristics. These shear layers were then disturbed by the placement of an obstruction in the shear layer in an attempt to enhance the shear layer growth rate. These models produced a curved shock in the supersonic side of the shear layer. The results indicate a significant reduction in turbulence levels with increased compressibility. However, there are not any significant changes due to the bow shock interaction with the shear layer.

  20. Bypass transition in compressible boundary layers

    NASA Astrophysics Data System (ADS)

    Vandervegt, J. J.

    1992-09-01

    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.

  1. Aspects of turbulent-shear-layer dynamics and mixing

    NASA Astrophysics Data System (ADS)

    Slessor, Michael David

    Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility to investigate some aspects of high-Reynolds-number, turbulent, shearlayer flows in both incompressible- and compressible-flow regimes. Experiments designed to address several issues were performed; effects of inflow boundary conditions, freestream conditions (supersonic/subsonic flow), and compressibility, on both large-scale dynamics and small-scale mixing, are described. Chemically-reacting and non-reacting flows were investigated, the former relying on the (H2 + NO/F2) chemical system, in the fast-kinetic regime, to infer the structure and amount of molecular-scale mixing through use of "flip" experiments. A variety of experimental techniques, including a color-schlieren visualization system developed as part of this work, were used to study the flows. Both inflow conditions and compressibility are found to have significant effects on the flow. In particular, inflow conditions are "remembered" for long distances downstream, a sensitivity similar to that observed in low-dimensionality, non-linear (chaotic) systems. The global flowfields (freestreams coupled by the shear layer) of transonic flows exhibit a sensitivity to imposed boundary conditions, i. e., local area ratios. A previously-proposed mode-selection rule for turbulent-structure convection speeds, based on the presence of a lab-frame subsonic freestream, was experimentally demonstrated to be incorrect. Compressibility, when decoupled from all other parameters, e.g., Reynolds number, velocity and density ratios, etc., reduces laxge-scale entrainment and turbulent growth, but slightly enhances smallscale mixing, with an associated change in the structure of the molecularly-mixed fluid. This reduction in shear-layer growth rate is examined and a new parameter that interprets compressibility as an energy-exchange mechanism is proposed. The parameter reconciles and collapses experimentally-observed growth rates.

  2. 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.

  3. Analysis of unsteady compressible viscous layers

    NASA Technical Reports Server (NTRS)

    Power, G. D.; Verdon, J. M.; Kousen, K. A.

    1990-01-01

    The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy-Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.

  4. High-speed cinematography of supersonic mixing layers

    NASA Astrophysics Data System (ADS)

    Mahadevan, R.; Guglielmo, James J.; Frank, Robert S.; Loth, Eric

    1992-07-01

    An experimental investigation of the fundamental physical mechanisms which control three-dimensional supersonic mixing has been conducted. Experiments are performed in a newly constructed supersonic wind tunnel using high-speed cinematography to capture the supersonic mixing layer structures on film. Results are presented that describe how large-scale structures evolve at a relative Mach number of 1.67, and the importance of their role in mixing. Nonintrusive optical diagnostic techniques include shadowgraph methods and a planar light sheet visualization technique based on the scalar transport of ethyl alcohol. Product formation studies have also been completed but have been limited to single shot results. The time-dependent shadowgraph and Mie scattering data are documented with a Beckman-Whitley Model 192 rotating mirror camera run at between 195,000 and 500,000 frames per second. The results thus far have demonstrated both the technique's feasibility and the compressibility and mixing dynamics of the supersonic shear layer.

  5. 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

  6. 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.

  7. Helicity in supercritical temporal mixing layers

    NASA Technical Reports Server (NTRS)

    Bellan, J.; Okong'o, N.

    2003-01-01

    Databases of transitional states obtained from Direct Numerical Simulations (DNS) of temporal, supercritical mixing layers for two species systems, 02/H2 and C7Hle/N2, are analyzed to elucidate species-specific turbulence aspects.

  8. Effects of Oxide Layer Composition and Radial Compression on Nickel Release in Nitinol Stents

    NASA Astrophysics Data System (ADS)

    Sullivan, Stacey J. L.; Dreher, Maureen L.; Zheng, Jiwen; Chen, Lynn; Madamba, Daniel; Miyashiro, Katie; Trépanier, Christine; Nagaraja, Srinidhi

    2015-09-01

    There is a public health need to understand the effects of surface layer thickness and composition on corrosion in nickel-containing medical devices. To address this knowledge gap, five groups of Nitinol stents were manufactured by various processing methods that altered the titanium oxide layer. The following surfaces were created: >3500 nm thick mixed thermal oxide (OT), ~420 nm thick mixed thermal oxide (SP), ~130 nm thick mixed thermal oxide (AF), ~4 nm thick native oxide (MP), and an ~4 nm thick passivated oxide (EP). Radially compressed and not compressed devices were evaluated for nickel (Ni) ion release in a 60-day immersion test. The results indicated that OT stents released the most Ni, followed by stents in the SP and AF groups. For OT and SP stents, which exhibited the thickest oxide layers, radial compression significantly increased Ni release when compared to non-compressed stents. This result was not observed in AF, MP, SP stents indicating that the increased Ni release may be explained by cracking of the thicker oxide layers during crimping. Strong correlations were observed between oxide layer thickness and cumulative Ni release. These findings elucidate the importance of oxide layer thickness and composition on uniform corrosion of laser-cut Nitinol stents.

  9. 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.

  10. Cylindrical Mixing Layer Model in Stellar Jet

    NASA Astrophysics Data System (ADS)

    Choe, Seung-Urn; Yu, Kyoung Hee

    1994-12-01

    We have developed a cylindrical mixing layer model of a stellar jet including cooling effect in order to understand an optical emission mechanism along collimated high velocity stellar jets associated with young stellar objects. The cylindrical results have been calculated to be the same as the 2D ones presented by Canto & Raga(1991) because the entrainment efficiency in our cylindrical model has been obtained to be the same value as the 2D model has given. We have discussed the morphological and physical characteristics of the mixing layers by the cooling effect. As the jet Mach number increases, the initial temperature of the mixing layer goes high because the kinetic energy of the jet partly converts to the thermal energy of the mixing layer. The initial cooling of the mixing layer is very severe, changing its outer boundary radius. A subsequent change becomes adiabatic. The number of the Mach disks in the stellar jet and the total radiative luminosity of the mixing layer, based on our cylindrical calculation, have quite agreed with the observation.

  11. An Argo mixed layer climatology and database

    NASA Astrophysics Data System (ADS)

    Holte, James; Talley, Lynne D.; Gilson, John; Roemmich, Dean

    2017-06-01

    A global climatology and database of mixed layer properties are computed from nearly 1,250,000 Argo profiles. The climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth (MLD) and a standard threshold method. The climatology provides accurate information about the depth, properties, extent, and seasonal patterns of global mixed layers. The individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest. The climatology and database are available online at http://mixedlayer.ucsd.edu. The MLDs calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method, particularly in regions of deep winter mixed layers; the new climatology differs the most from existing mixed layer climatologies in these regions. Examples are presented from the Labrador and Irminger Seas, the Southern Ocean, and the North Atlantic Ocean near the Gulf Stream. In these regions the threshold method tends to overestimate winter MLDs by approximately 10% compared to the algorithm.

  12. Wave phenomena in a high Reynolds number compressible boundary layer

    NASA Technical Reports Server (NTRS)

    Bayliss, A.; Maestrello, L.; Parikh, P.; Turkel, E.

    1985-01-01

    Growth of unstable disturbances in a high Reynolds number compressible boundary layer is numerically simulated. Localized periodic surface heating and cooling as a means of active control of these disturbances is studied. It is shown that compressibility in itself stabilizes the flow but at a lower Mach number, significant nonlinear distortions are produced. Phase cancellation is shown to be an effective mechanism for active boundary layer control.

  13. Linear stability of the reacting mixing layer

    NASA Technical Reports Server (NTRS)

    Shin, D. S.; Ferziger, J. H.

    1990-01-01

    This work is aimed at understanding the stability of reacting mixing layers. Linear instability is analyzed for a wide variety of mixing layers to study the effects of the heat release. Analytic functions as well as laminar solutions of thin shear layer equations are used as the base flows. Both temporal and spatial developing layers are investigated. The laminar solutions are more consistent than the analytic functions. The stability properties are sensitive to the mean profiles. Including variable transport properties changes the mean profiles considerably. Chemical reaction during the instability is not very important; its primary effect is to change the laminar profiles. New modes are found in the outer part of the layer when the heat release is significant, and become dominant for large heat release. In general, heat release stabilizes the center mode but the outer mode is less affected.

  14. 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.

  15. Linear models for sound from supersonic reacting mixing layers

    NASA Astrophysics Data System (ADS)

    Chary, P. Shivakanth; Samanta, Arnab

    2016-12-01

    We perform a linearized reduced-order modeling of the aeroacoustic sound sources in supersonic reacting mixing layers to explore their sensitivities to some of the flow parameters in radiating sound. Specifically, we investigate the role of outer modes as the effective flow compressibility is raised, when some of these are expected to dominate over the traditional Kelvin-Helmholtz (K-H) -type central mode. Although the outer modes are known to be of lesser importance in the near-field mixing, how these radiate to the far-field is uncertain, on which we focus. On keeping the flow compressibility fixed, the outer modes are realized via biasing the respective mean densities of the fast (oxidizer) or slow (fuel) side. Here the mean flows are laminar solutions of two-dimensional compressible boundary layers with an imposed composite (turbulent) spreading rate, which we show to significantly alter the growth of instability waves by saturating them earlier, similar to in nonlinear calculations, achieved here via solving the linear parabolized stability equations. As the flow parameters are varied, instability of the slow modes is shown to be more sensitive to heat release, potentially exceeding equivalent central modes, as these modes yield relatively compact sound sources with lesser spreading of the mixing layer, when compared to the corresponding fast modes. In contrast, the radiated sound seems to be relatively unaffected when the mixture equivalence ratio is varied, except for a lean mixture which is shown to yield a pronounced effect on the slow mode radiation by reducing its modal growth.

  16. Vortex simulation of forced mixing layers

    NASA Technical Reports Server (NTRS)

    Inoue, O.; Leonard, A.

    1986-01-01

    Two-dimensional, spatially growing, turbulent mixing layers are simulated numerically by a vortex method and the results are compared with those determined experimentally. The effects of artificial forcing on flow development are also studied. Many of the flow features which have been observed experimentally are reproduced, and good quantitative agreements between experiments and computations are obtained.

  17. Transition in compressible free shear layers.

    NASA Technical Reports Server (NTRS)

    Birch, S. F.; Keyes, J. W.

    1972-01-01

    The transition Reynolds number for shear layers produced by interactions between weak and strong shock waves is determined on the basis of experiments performed in a 20-in. (Mach 6) and an 11-in. (Mach 6.9) hypersonic tunnel. A variable angle wedge was used to generate a planar shock wave which interacted with the bow wave of a blunt body. An average value of the transition length (defined as the length along the shear layer from the shock interaction to the point where turbulence became visible on schlieren photographs) was used to determine the transition Reynolds number.

  18. Transition in compressible free shear layers.

    NASA Technical Reports Server (NTRS)

    Birch, S. F.; Keyes, J. W.

    1972-01-01

    The transition Reynolds number for shear layers produced by interactions between weak and strong shock waves is determined on the basis of experiments performed in a 20-in. (Mach 6) and an 11-in. (Mach 6.9) hypersonic tunnel. A variable angle wedge was used to generate a planar shock wave which interacted with the bow wave of a blunt body. An average value of the transition length (defined as the length along the shear layer from the shock interaction to the point where turbulence became visible on schlieren photographs) was used to determine the transition Reynolds number.

  19. Effects of compressibility on boundary-layer turbulence

    NASA Technical Reports Server (NTRS)

    Acharya, M.

    1976-01-01

    A series of turbulence measurements in a subsonic compressible turbulent boundary-layer flow in the Mach number range of 0.1 to 0.7 is described. Measurements include detailed surveys of the turbulence intensities and Reynolds shear stresses, and other quantities such as the turbulent kinetic energy. These data are examined to bring out the effects of compressibility and show that the stream-wise and transverse fluctuations and the turbulent shear stress follow a universal scaling law. A preliminary attempt is made to examine some of the assumptions made in turbulence models commonly used in numerical codes for the calculation of compressible flows.

  20. Wave phenomena in a high Reynolds number compressible boundary layer

    NASA Technical Reports Server (NTRS)

    Bayliss, A.; Maestrello, L.; Parikh, P.; Turkel, E.

    1987-01-01

    The behavior of spatially unstable waves in a high Reynolds number compressible laminar boundary layer is investigated by solution of the laminar two-dimensional compressible Navier-Stokes equations (solved to fourth-order accuracy) over a flat plate with a fluctuating disturbance generated at the inflow. A significant nonlinear distortion is produced, in qualitative agreement with experimental data. It is shown that increasing compressibility can significantly stabilize the flow over a flat plate, and that the mechanism of phase cancellation is a viable mechanism for the control of growing disturbances.

  1. 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.

  2. New applications of a simple mixed-layer model

    NASA Astrophysics Data System (ADS)

    Fitzjarrald, David R.

    1982-04-01

    Model formulation of the balance between surface heat and moisture fluxes and subsidence that determines the state of the mixed layer is used to estimate cooling and drying rates in the mixed layer above the tropical ocean based on GATE observations. Estimated cooling rates are comparable to observed radiative cooling rates for thick mixed layers characteristic of undisturbed conditions but are up to five times larger for shallow mixed layers observed during disturbed periods. The additional cooling and drying in the mixed layer needed to maintain shallow, cool mixed layers is hypothesized to be the net result of an assemblage of downdrafts. A new scaling scheme for non-dimensionalizing the mixed-layer thermodynamic budget equations is introduced. The ratio of subsidence at the top of the mixed layer to the product of the entrainment coefficient, a bulk aerodynamic transfer coefficient, and the surface-layer wind speed is shown theoretically to be a fundamental descriptor of the mixed-layer environment.

  3. 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.

  4. 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.

  5. Scalar transport in plane mixing layers

    NASA Astrophysics Data System (ADS)

    Vanormelingen, J.; Van den Bulck, E.

    This paper describes the application of the Eulerian, single-point, single-time joint-scalar probability density function (PDF) equation for predicting the scalar transport in mixing layer with a high-speed and a low-speed stream. A finite-volume procedure is applied to obtain the velocity field with the k-ɛ closure being used to describe turbulent transport. The scalar field is represented through the modelled evolution equation for the scalar PDF and is solved using a Monte Carlo simulation. The PDF equation employs gradient transport modelling to represent the turbulent diffusion, and the molecular mixing term is modelled by the LMSE closure. There is no source term for chemical reaction as only an inert mixing layer is considered here. The experimental shear layer data published by Batt is used to validate the computational results despite the fact that comparisons between experiments and computational results are difficult because of the high sensitivity of the shear layer to initial conditions and free stream turbulence phenomena. However, the bimodal shape of the RMS scalar fluctuation as was measured by Batt can be reproduced with this model, whereas standard gradient diffusion calculations do not predict the dip in this profile. In this work for the first time an explanation is given for this phenomenon and the importance of a micromixing model is stressed. Also it is shown that the prediction of the PDF shape by the LMSE model is very satisfactory.

  6. Locating the mixing layer: algorithms to identify the mixing layer height using lidar signals

    NASA Astrophysics Data System (ADS)

    Mehnert, Jan; Pesch, Markus

    2007-10-01

    The mixing layer (ML) provides a vertical atmospheric barrier and its height has become an important parameter in meteorology and air quality control. In locating the mixing layer using Lidar it has always to be considered that the signals may be biased by noise and the mixing layer itself can contain more than a single layer. In previous studies use was made of the fact that the main part of aerosols are located within the mixing layer and outside this layer, in the so called free atmosphere, the concentration of aerosols decreased significantly. This leads to a sharp change of the backscattering signal at the boundary layers. In this paper an algorithm is presented that determines the height of the mixing layer (MLH) by an intensive analysis of the global and local maxima of the Lidar signal and its first derivative. The algorithm searches for a maximum of the backscatter signal followed by a minimum in the first derivative. The results are compared with the MLH calculated by a model.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Compressibility effects in the shear layer over a rectangular cavity

    DOE PAGES

    Beresh, Steven J.; Wagner, Justin L.; Casper, Katya M.

    2016-10-26

    we studied the influence of compressibility on the shear layer over a rectangular cavity of variable width in a free stream Mach number range of 0.6–2.5 using particle image velocimetry data in the streamwise centre plane. As the Mach number increases, the vertical component of the turbulence intensity diminishes modestly in the widest cavity, but the two narrower cavities show a more substantial drop in all three components as well as the turbulent shear stress. Furthermore, this contrasts with canonical free shear layers, which show significant reductions in only the vertical component and the turbulent shear stress due to compressibility.more » The vorticity thickness of the cavity shear layer grows rapidly as it initially develops, then transitions to a slower growth rate once its instability saturates. When normalized by their estimated incompressible values, the growth rates prior to saturation display the classic compressibility effect of suppression as the convective Mach number rises, in excellent agreement with comparable free shear layer data. The specific trend of the reduction in growth rate due to compressibility is modified by the cavity width.« less

  12. Compressibility effects in the shear layer over a rectangular cavity

    SciTech Connect

    Beresh, Steven J.; Wagner, Justin L.; Casper, Katya M.

    2016-10-26

    we studied the influence of compressibility on the shear layer over a rectangular cavity of variable width in a free stream Mach number range of 0.6–2.5 using particle image velocimetry data in the streamwise centre plane. As the Mach number increases, the vertical component of the turbulence intensity diminishes modestly in the widest cavity, but the two narrower cavities show a more substantial drop in all three components as well as the turbulent shear stress. Furthermore, this contrasts with canonical free shear layers, which show significant reductions in only the vertical component and the turbulent shear stress due to compressibility. The vorticity thickness of the cavity shear layer grows rapidly as it initially develops, then transitions to a slower growth rate once its instability saturates. When normalized by their estimated incompressible values, the growth rates prior to saturation display the classic compressibility effect of suppression as the convective Mach number rises, in excellent agreement with comparable free shear layer data. The specific trend of the reduction in growth rate due to compressibility is modified by the cavity width.

  13. Negative Linear Compressibility Due to Layer Sliding in a Layered Metal-Organic Framework.

    PubMed

    Zeng, Qingxin; Wang, Kai; Qiao, Yuancun; Li, Xiaodong; Zou, Bo

    2017-04-06

    Negative linear compressibility (NLC) is a rare and counterintuitive phenomenon because materials with this property would expand along one specific direction when uniformly compressed. NLC materials have a broad range of potential applications in designing pressure sensors, artificial muscles, and so on. Designing and searching for systems with NLC is desired and crucial for material and compression science. Herein, with the help of high-pressure X-ray diffraction measurements and density functional theory calculations, we find that the 2D layered Co(SCN)2(pyrazine)2 exhibits NLC with a new mechanism: layer sliding. When compressed, the ab planes slide along the a axis, leading to the decrease of lattice parameter β, which results in the NLC effect along principal axis X3 (≈ -0.84a - 0.55c). The layer sliding mechanism opens exciting opportunities for seeking, designing, and synthesizing new classes of materials with anomalous mechanical properties in monoclinic layered or other related systems.

  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. Hot wire anemometry in compressible turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    1981-11-01

    Hot-wire anemometry in compressible flow was studied. New techniques for the measurement of turbulence in compressible flows with thermal sensors are described. The greatest amount of information about fluctuating flow variables as achieved using the newly developed sensors and techniques in conjunction with the classical hot-wire mode diagram method. It was found that the hot wire has no fundamental handicap for accurate high speed turbulence measurements in non-separated boundary layers outside the immediate wall region. It was also known that extreme overheating of a supported sensors leads to advantages in simplicity and accuracy of measurements of turbulent fluctuations over the full Mach number range.

  18. Multilayer scaling of mean velocity and thermal fields of compressible turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Bi, Weitao; Wu, Bin; Zhang, Yousheng; Hussain, Fazle; She, Zhen-Su

    2014-11-01

    Recently, a symmetry based structural ensemble dynamics (SED) theory was proposed by She et al. for canonical wall bounded turbulent flows, yielding prediction of the mean velocity profile at an unprecedented accuracy (99%). Here, we extend the theory to compressible turbulent boundary layers (TBL) at supersonic and hypersonic Mach numbers. The flows are acquired by spatially evolving direct numerical simulations (DNS). A momentum mixing length displays a four layer structure and quantitatively obeys the dilation group invariance as for the incompressible TBL. In addition, a temperature mixing length behaves very similarly to the momentum mixing length when the wall is adiabatic, with a small difference in the scaling exponents in the buffer layer - consistent with the strong Reynolds analogy. The Lie group based formulization of the two mixing lengths yields a multilayer model for the turbulent Prandtl number, along with predictions to the mean thermal and velocity profiles, both in good agreement with the DNS. Thus, we assert that the compressible TBLs are governed by the same symmetry principle as that in the canonical wall bounded turbulent flows, and its mean fields can be accurately described by the SED theory.

  19. Nonlinear evolution of oblique waves on compressible shear layers

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Leib, S. J.

    1989-01-01

    The effects of critical-layer nonlinearity on spatially growing oblique instability waves on compressible shear layers between two parallel streams are considered. The analysis shows that mean temperature nonuniformities cause nonlinearity to occur at much smaller amplitudes than it does when the flow is isothermal. The nonlinear instability wave growth rate effects are described by an integrodifferential equation which bears some resemblance to the Landau equation, in that it involves a cubic-type nonlinearity. The numerical solutions to this equation are worked out and discussed in some detail. Inviscid solutions always end in a singularity at a finite downstream distance, but viscosity can eliminate this singularity for certain parameter ranges.

  20. Linear and nonlinear PSE for compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Chang, Chau-Lyan; Malik, Mujeeb R.; Erlebacher, Gordon; Hussaini, M. Yousuff

    1993-01-01

    Compressible stability of growing boundary layers is studied by numerically solving the partial differential equations under a parabolizing approximation. The resulting parabolized stability equations (PSE) account for nonparallel as well as nonlinear effects. Evolution of disturbances in compressible flat-plate boundary layers are studied for freestream Mach numbers ranging from 0 to 4.5. Results indicate that the effect of boundary-layer growth is important for linear disturbances. Nonlinear calculations are performed for various Mach numbers. Two-dimensional nonlinear results using the PSE approach agree well with those from direct numerical simulations using the full Navier-Stokes equations while the required computational time is less by an order of magnitude. Spatial simulation using PSE were carried out for both the fundamental and subharmonic type breakdown for a Mach 1.6 boundary layer. The promising results obtained show that the PSE method is a powerful tool for studying boundary-layer instabilities and for predicting transition over a wide range of Mach numbers.

  1. A compressible boundary layer algorithm for use with SINDA '85

    NASA Technical Reports Server (NTRS)

    Sakowski, Barbara; Darling, Douglas; Vandewall, Allan

    1992-01-01

    It is useful to interface a high-speed-flow solution and SINDA to analyze the thermal behavior of systems that include both conduction and high speed flows. When interfacing a high-speed-flow solution to SINDA, it may be necessary to include the viscous effects in the energy equations. Boundary layer effects of interest include heat transfer coefficients (including convection and viscous dissipation) and friction coefficients. To meet this need, a fast, uncoupled, compressible, two-dimensional, boundary layer algorithm was developed that can model flows with and without separation. This algorithm was used as a subroutine with SINDA. Given the core flow properties and the wall heat flux from SINDA, the boundary layer algorithm returns a wall temperature to SINDA and boundary layer algorithm are iterated until they predict the same wall temperature.

  2. Observation of Compressible Plasma Mix in Cylindrically Convergent Implosions

    NASA Astrophysics Data System (ADS)

    Barnes, Cris W.; Batha, Steven H.; Lanier, Nicholas E.; Magelssen, Glenn R.; Tubbs, David L.; Dunne, A. M.; Rothman, Steven R.; Youngs, David L.

    2000-10-01

    An understanding of hydrodynamic mix in convergent geometry will be of key importance in the development of a robust ignition/burn capability on NIF, LMJ and future pulsed power machines. We have made use of the OMEGA laser facility at the University of Rochester to investigate directly the mix evolution in a convergent geometry, compressible plasma regime. The experiments comprise a plastic cylindrical shell imploded by direct laser irradiation. The cylindrical shell surrounds a lower density plastic foam which provides sufficient back pressure to allow the implosion to stagnate at a sufficiently high radius to permit quantitative radiographic diagnosis of the interface evolution near turnaround. The susceptibility to mix of the shell-foam interface is varied by choosing different density material for the inner shell surface (thus varying the Atwood number). This allows the study of shock-induced Richtmyer-Meshkov growth during the coasting phase, and Rayleigh-Taylor growth during the stagnation phase. The experimental results will be described along with calculational predictions using various radiation hydrodynamics codes and turbulent mix models.

  3. Layer-to-layer compression and enhanced optical properties of few-layer graphene nanosheet induced by ion irradiation

    NASA Astrophysics Data System (ADS)

    Shang, Zhen; Tan, Yang; Zhou, Shengqiang; Chen, Feng

    2016-08-01

    We report on the first experimental study of the layer-to-layer compression and enhanced optical properties of few-layer graphene nanosheet by applying ion irradiation. The deformation of graphene layers is investigated both theoretically and experimentally. It is observed that after the irradiation of energetic ion beams, the space between separate graphene layers is reduced due to layer-to-layer compression, resulting in tighter contact of the graphene sheet with the surface of the substrate. This processing enables enhanced interaction of the graphene with the evanescent-field wave near the surface, which induces reinforced polarization-dependent light absorption of the graphene. Utilizing the ion-bombarded graphene nanosheets as saturable absorbers, we have realized efficient Q-switched waveguide lasing with enhanced performance through the interaction of the graphene and evanescent field.

  4. Modeling spatial evolution of aero-optical wave front aberration caused by a supersonic mixing layer

    NASA Astrophysics Data System (ADS)

    Guo, Guangming; Liu, Hong

    2017-03-01

    A method used to build a prediction model for spatial evolution of the aero-optical wave front aberration caused by a supersonic mixing layer is presented. The large eddy simulation is used to visualize the instantaneous dynamical characteristics of vortices inside the flow field. The time-averaged boundary of the supersonic mixing layer is described by a piecewise function in which the two turning points are defined and expressed by a universal formula. The growth rate for supersonic mixing layers is first proposed as a function of the velocity ratio, density ratio, and compressibility of the flow field. A model for spatial evolution of aero-optical wave front aberration caused by a supersonic mixing layer is developed based on experimental data presented in the open literature and validated with numerically simulated data from two typical examples. Finally, the universality and potential application of the model built is also discussed.

  5. 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.

  6. 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.

  7. 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'.

  8. 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.

  9. Variable geometry for supersonic mixed-compression inlets

    NASA Technical Reports Server (NTRS)

    Sorensen, N. E.; Latham, E. A.; Smeltzer, D. B.

    1974-01-01

    Study of two-dimensional and axisymmetric supersonic mixed-compression inlet systems has shown that the geometry of both systems can be varied to provide adequate transonic airflow to satisfy the airflow demand of most jet engines. Collapsing geometry systems for both types of inlet systems provide a generous amount of transonic airflow for any design Mach number inlet system. However, the mechanical practicality of collapsing centerbodies for axisymmetric inlet systems is doubtful. Therefore, translating centerbody axisymmetric inlets with auxiliary airflow systems to augment the transonic airflow capability are an attractive alternative. Estimates show that the capture mass-flow ratio at Mach number 1.0 can be increased approximately 0.20 for a very short axisymmetric inlet system designed for Mach number 2.37. With this increase in mass-flow ratio, even variable-cycle engine transonic airflow demand can be matched without oversizing the inlet at the design Mach number.

  10. Instabilities in compressible attachment-line boundary layers

    NASA Astrophysics Data System (ADS)

    Le Duc, Anne; Sesterhenn, Jörn; Friedrich, Rainer

    2006-04-01

    The hydrodynamic stability of the weakly compressible attachment-line boundary layer, with a sweep Mach number ranging from 0.1 to 1.3, is studied using a temporal compressible direct numerical simulation. A flow impinging non-normally onto an infinitely extended flat plate was computed. This complements the study of Hall et al. [Proc. R. Soc. London, Ser. A 395, 229 (1984)] who investigated the linear stability of an incompressible attachment-line boundary layer under the assumption of Görtler-Hämmerlin perturbation modes. In the present work, the base flow is modeled starting from the incompressible swept Hiemenz flow. Using Rayleigh-Jansen Mach number expansions, we obtain a family of base flows parameterized with the sweep Mach number ranging from 0.1 to 1.3. The Reynolds number of the simulation is higher than the incompressible critical Reynolds number, and the plate is adiabatic. Small purely vortical stochastic perturbations are inserted in the boundary layer and followed in time. For Mach numbers up to 0.3, developed velocity and pressure modes are similar to the ones assumed by Görtler and Hämmerlin. The chordwise dependencies of the temperature mode are presented. When increasing the Mach number, the structure of the modes changes; for high Mach numbers, a significantly slower decay of the eigenfunction with wall-normal distance is observed. Above M =0.5, the perturbations are exponentially decaying. This demonstrates the strong stabilizing effect of compressibility in the moderate Mach regime. Furthermore, for the same base flow, a higher exponential growth rate of the perturbation is obtained, if an isothermal wall boundary condition is applied instead of an adiabatic one.

  11. 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.

  12. 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.

  13. Characteristics of a Mixed Refrigerant Vapor Compression Cycle

    NASA Astrophysics Data System (ADS)

    Hihara, Eiji; Muneta, Yoshihiro; Saito, Takamoto

    In comparison with conventional refrigerants, the use of non-azeotropic binary mixtures of refrigerants in vapor compression refrigerating systems can result in extension of the application limits, higher reliability, and savings in power consumption. This paper discusses the high temperature heat pump system performance operating with mixed refrigerants. In order to survey the system performances with various mixtures, six kinds of mixtures are examined : R22-R1l4, R22-R11, R12-R114, R12-R11, R 12-R113, and R22-R12. Thermodynamic properties of the first five mixtures are calculated from the Peng-Robinson equation of state with the mixing rules proposed by Ototake, and R22-R12 mixtures by the BWR type equation of state proposed by Kagawa et al. When counter-flow heat exchangers with large surface areas are used for the evaporator and the condenser, the temperature differences between the refrigerant and the heat sink / source fluids can be reduced, and so the energy waste resulting from irreversible heat trasfer can be reduced. Comparing the mixed refrigerants with the pure ones by fixing the refrigerant temperature at the evaporator inlet and the dewpoint temperature at the condenser, higher coefficients of performance (COP), lower condensing pressures, and lower pressure ratios in the refrigerant compressor can be realized. But the performances of the mixtures with R114 as a less volatile component are not so good. When the heat transfer surface area is not large, the mean temperature difference becomes large. If the dewpoint temperatures at the evaporator and the condenser fixed, the range of composition for the improvement of the COP is restricted.

  14. Transverse ageostrophic circulations associated with elevated mixed layers

    NASA Technical Reports Server (NTRS)

    Keyser, D.; Carlson, T. N.

    1984-01-01

    The nature of the frontogenetically forced transverse ageostrophic circulations connected with elevated mixed layer structure is investigated as a first step toward diagnosing the complex vertical circulation patterns occurring in the vicinity of elevated mixed layers within a severe storm environment. The Sawyer-Eliassen ageostrophic circulation equation is reviewed and applied to the elevated mixed layer detected in the SESAME IV data set at 2100 GMT of May 9, 1979. The results of the ageostrophic circulation diagnosis are confirmed and refined by considering an analytic specification for the elevated mixed layer structure.

  15. Analytical and experimental evaluation of a 3-D hypersonic fixed-geometry, swept, mixed compression inlet

    NASA Technical Reports Server (NTRS)

    Agnone, Anthony M.

    1987-01-01

    The performance of a fixed-geometry, swept, mixed compression hypersonic inlet is presented. The experimental evaluation was conducted for a Mach number of 6.0 and for several angles of attack. The measured surface pressures and pitot pressure surveys at the inlet throat are compared to computations using a three-dimensional Euler code and an integral boundary layer theory. Unique features of the intake design, including the boundary layer control, insure a high inlet performance. The experimental data show the inlet has a high mass averaged total pressure recovery, a high mass capture and nearly uniform flow diffusion. The swept inlet exhibits excellent starting characteristics, and high flow stability at angle of attack.

  16. Velocity-vorticity correlation structures in compressible turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Chen, Jun; Li, Shi-Yao; She, Zhen-Su

    2016-11-01

    A velocity-vorticity correlation structure (VVCS) analysis is applied to analyze data of 3-dimensional (3-D) direct numerical simulations (DNS), to investigate the quantitative properties of the most correlated vortex structures in compressible turbulent boundary layer (CTBL) at Mach numbers, Ma = 2 . 25 and 6 . 0 . It is found that the geometry variation of the VVCS closely reflects the streamwise development of CTBL. In laminar region, the VVCS captures the instability wave number of the boundary layer. The transition region displays a distinct scaling change of the dimensions of VVCS. The developed turbulence region is characterized by a constant spatial extension of the VVCS. For various Mach numbers, the maximum correlation coefficient of the VVCS presents a clear multi-layer structure with the same scaling laws as a recent symmetry analysis proposed to quantifying the sublayer, the log-layer, and the wake flow. A surprising discovery is that the wall friction coefficient, Cf, holds a "-1"-power law of the wall normal distance of the VVCS, ys. This validates the speculation that the wall friction is determined by the near-wall coherent structure, which clarifies the correlation between statistical structures and the near-wall dynamics. Project 11452002 and 11172006 supported by National Natural Science Foundation of China.

  17. Mixed DPPC/DPPG monolayers at very high film compression.

    PubMed

    Saad, Sameh M I; Policova, Zdenka; Acosta, Edgar J; Hair, Michael L; Neumann, A Wilhelm

    2009-09-15

    A drop shape technique using a constrained sessile drop constellation (ADSA-CSD) has been introduced as a superior technique for studying spread films specially at high collapse pressures [Saad et al. Langmuir 2008, 24, 10843-10850]. It has been shown that ADSA-CSD has certain advantages including the need only for small quantities of liquid and insoluble surfactants, the ability to measure very low surface tension values, easier deposition procedure, and leak-proof design. Here, this technique was applied to investigate mixed DPPC/DPPG monolayers to characterize the role of such molecules in maintaining stable film properties and surface activity of lung surfactant preparations. Results of compression isotherms were obtained for different DPPC/DPPG mixture ratios: 90/10, 80/20, 70/30, 60/40, and 50/50 in addition to pure DPPC and pure DPPG at room temperature of 24 degrees C. The ultimate collapse pressure of DPPC/DPPG mixtures was found to be 70.5 mJ/m2 (similar to pure DPPC) for the cases of low DPPG content (up to 20%). Increasing the DPPG content in the mixture (up to 40%) caused a slight decrease in the ultimate collapse pressure. However, further increase of DPPG in the mixture (50% or more) caused a sharp decrease in the ultimate collapse pressure to a value of 59.9 mJ/m2 (similar to pure DPPG). The change in film elasticity was also tracked for the range of mixture ratios studied. The physical reasons for such changes and the interaction between DPPC and DPPG molecules are discussed. The results also show a change in the film hysteresis upon successive compression and expansion cycles for different mixture ratios.

  18. Real-Gas Effects on Binary Mixing Layers

    NASA Technical Reports Server (NTRS)

    Okong'o, Nora; Bellan, Josette

    2003-01-01

    This paper presents a computational study of real-gas effects on the mean flow and temporal stability of heptane/nitrogen and oxygen/hydrogen mixing layers at supercritical pressures. These layers consist of two counterflowing free streams of different composition, temperature, and density. As in related prior studies reported in NASA Tech Briefs, the governing conservation equations were the Navier-Stokes equations of compressible flow plus equations for the conservation of total energy and of chemical- species masses. In these equations, the expressions for heat fluxes and chemical-species mass fluxes were derived from fluctuation-dissipation theory and incorporate Soret and Dufour effects. Similarity equations for the streamwise velocity, temperature, and mass fractions were derived as approximations to the governing equations. Similarity profiles showed important real-gas, non-ideal-mixture effects, particularly for temperature, in departing from the error-function profile, which is the similarity solution for incompressible flow. The temperature behavior was attributed to real-gas thermodynamics and variations in Schmidt and Prandtl numbers. Temporal linear inviscid stability analyses were performed using the similarity and error-function profiles as the mean flow. For the similarity profiles, the growth rates were found to be larger and the wavelengths of highest instability shorter, relative to those of the errorfunction profiles and to those obtained from incompressible-flow stability analysis. The range of unstable wavelengths was found to be larger for the similarity profiles than for the error-function profiles

  19. 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.

  20. Aero-optic characteristics of turbulent compressible boundary layers

    NASA Astrophysics Data System (ADS)

    Wyckham, Christopher Mark

    This dissertation presents a detailed study of the aberrating effect on a plane incident wavefront of light due to its passage through a turbulent, compressible boundary layer. This aberration has important implications for the design of airborne optical systems for imaging, communications, or projection. A Shack-Hartmann sensor and associated data analysis software suite were developed and validated for the high resolution measurement of two dimensional wavefront phase. Significant improvements in wavefront reconstruction were achieved by using the calculated centroid uncertainties to weight the least squares fitting of the phase surface. Using the Shack-Hartmann sensor in a high speed, one dimensional mode, individual structures are observed propagating past the sensor in a transonic flow. The uncertainties on the reconstructed phase in this mode are very high, however. In a two dimensional mode the uncertainties are greatly reduced and a large database of individual, uncorrelated wavefronts was collected, allowing statistics to be calculated such as the rms wavefront height and the Strehl ratio. Data were collected at transonic and hypersonic speeds and with no injection or with helium or nitrogen injection into the boundary layer. In all cases except the hypersonic helium injection case, the time averaged wavefronts reveal no features in the boundary layer which are steady in time. In the hypersonic helium injection case, however, steady, longitudinal features are observed, in agreement with previous observations. When helium is injected for window cooling at high speeds, the results show there may be an opportunity to reduce the resulting distortion by taking advantage of the stable structures that form in the boundary layer by using a low bandwidth adaptive optic system. A new scaling argument is also presented to allow the prediction and comparison of wavefront data for different compressible boundary layer flow conditions. The proposed formula gives

  1. Compressibility Considerations for kappa-omega Turbulence Models in Hypersonic Boundary Layer Applications

    NASA Technical Reports Server (NTRS)

    Rumsey, C. L.

    2009-01-01

    The ability of kappa-omega models to predict compressible turbulent skin friction in hypersonic boundary layers is investigated. Although uncorrected two-equation models can agree well with correlations for hot-wall cases, they tend to perform progressively worse - particularly for cold walls - as the Mach number is increased in the hypersonic regime. Simple algebraic models such as Baldwin-Lomax perform better compared to experiments and correlations in these circumstances. Many of the compressibility corrections described in the literature are summarized here. These include corrections that have only a small influence for kappa-omega models, or that apply only in specific circumstances. The most widely-used general corrections were designed for use with jet or mixing-layer free shear flows. A less well-known dilatation-dissipation correction intended for boundary layer flows is also tested, and is shown to agree reasonably well with the Baldwin-Lomax model at cold-wall conditions. It exhibits a less dramatic influence than the free shear type of correction. There is clearly a need for improved understanding and better overall physical modeling for turbulence models applied to hypersonic boundary layer flows.

  2. A novel representation and compression method in layered depth video

    NASA Astrophysics Data System (ADS)

    Li, Zefu; Ma, Ran; Kang, Mengmeng; Hu, Xiangyu; An, Ping

    2016-10-01

    Layered depth video (LDV) is a sparse representation of MVD, which is considered as a promising 3D video format for supporting 3D video services. This format consists of one full view and additional residual data that represents side views. However, the amount of residual data becomes larger when the distance between the central view and side views increases. To address this problem, a new inpainting-based residual data generation method is proposed in this paper. Then, the inpainting-induced artifacts is considered as new residual data and the residual data of two side views is merged into one buffer to further reduce the amount of data. On the other hand, the block wise alignment is used for higher coding efficiency. And in order to fit the shape or distribution of residual data, a new compression algorithm for coding residual data is proposed. The experiments show high compression efficiency of the proposed method. The proposed method allows reduction of required bitrate of at least 30% comparing to classical LDV method, while they have the similar quality of intermediate virtual view in the terminal's display.

  3. LAMINAR TRANSITIONAL AND TURBULENT BOUNDARY LAYERS FOR COMPRESSIBLE AXISYMMETRIC FLOW

    NASA Technical Reports Server (NTRS)

    Albers, J. A.

    1994-01-01

    This is a finite-difference program for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to a fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain factors of arbitrary Reynolds number, free-stream Mach number, free stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile. This program has been implemented on the IBM 7094/7044 Direct Couple System. This program is written in FORTRAN IV and was developed in 1974.

  4. LAMINAR TRANSITIONAL AND TURBULENT BOUNDARY LAYERS FOR COMPRESSIBLE AXISYMMETRIC FLOW

    NASA Technical Reports Server (NTRS)

    Albers, J. A.

    1994-01-01

    This is a finite-difference program for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to a fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain factors of arbitrary Reynolds number, free-stream Mach number, free stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile. This program has been implemented on the IBM 7094/7044 Direct Couple System. This program is written in FORTRAN IV and was developed in 1974.

  5. Tests of Parameterized Langmuir Circulation Mixing in the Oceans Surface Mixed Layer II

    DTIC Science & Technology

    2017-08-11

    Parameterized Langmuir-Circulation Mixing in the Ocean’s Surface Mixed Layer II Paul J. Martin Ocean Dynamics and Prediction Branch Oceanography...Division ivan B. Savelyev Coastal and Ocean Remote Sensing Branch Remote Sensing Division August 11, 2017 i REPORT DOCUMENTATION PAGE Form ApprovedOMB No...the ocean found that LC can significantly increase the rate of mixing within the SML and sometimes increase the mixed layer depth (MLD). This report

  6. A critique of some recent second-order turbulence closure models for compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Rubesin, M. W.; Crisalli, A. J.; Horstman, C. C.; Acharya, M.; Lanfranco, M. J.

    1977-01-01

    Computations based on two recently developed second-order turbulence closure models are compared with a series of boundary-layer experiments and with predictions of these experiments using an algebraic mixing length model. One of the models employs an eddy viscosity, whereas the other evaluates components of the Reynolds stress tensor. For flat plates, the computations are compared with the van Driest skin-friction transformation to assess the handling of compressibility. For boundary layers in pressure gradients, four experiments at Mach 4 and one at Mach 6.7 are used as the bases for comparison. In general, both models represent mean velocities and skin friction reasonably well, but represent the turbulence shear stress less accurately.

  7. Vortex-induced disturbance field in a compressible shear layer

    NASA Technical Reports Server (NTRS)

    Papamoschou, D.; Lele, S. K.

    1992-01-01

    The disturbance field induced by a small isolated vortex in a compressible shear layer is studied using direct simulation in a convected frame. The convective Mach number, M(sub c), is varied from 0.1 to 1.25. The vorticity perturbation is rapidly sheared by the mean velocity gradient. The resulting disturbance pressure field is observed to decrease both in magnitude and extent with increasing M(sub c), becoming a narrow transverse zone for M(sub c) greater than 0.8. A similar trend is seen for the perturbation velocity magnitude and for the Reynolds shear stress. By varying the vortex size, we verified that the decrease in perturbation levels is due to the mean-flow Mach number and not the Mach number across the vortex. At high M(sub c), the vortex still communicates with the edges of the shear layer, although communication in the mean-flow direction is strongly inhibited. The growth rate of perturbation kinetic energy declines with M(sub c) primarily due to the reduction in shear stress. For M(sub c) greater than or equal to 0.6, the pressure dilatation also contributes to the decrease of growth rates. Calculation of the perturbation field induced by a vortex doublet revealed the same trends as in the single-vortex case, illustrating the insensitivity of the Mach-number effect to the specific form of initial conditions.

  8. The salinity effect in a mixed layer ocean model

    NASA Technical Reports Server (NTRS)

    Miller, J. R.

    1976-01-01

    A model of the thermally mixed layer in the upper ocean as developed by Kraus and Turner and extended by Denman is further extended to investigate the effects of salinity. In the tropical and subtropical Atlantic Ocean rapid increases in salinity occur at the bottom of a uniformly mixed surface layer. The most significant effects produced by the inclusion of salinity are the reduction of the deepening rate and the corresponding change in the heating characteristics of the mixed layer. If the net surface heating is positive, but small, salinity effects must be included to determine whether the mixed layer temperature will increase or decrease. Precipitation over tropical oceans leads to the development of a shallow stable layer accompanied by a decrease in the temperature and salinity at the sea surface.

  9. 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

  10. Baroclinic mixed layer instability in the presence of convection

    NASA Astrophysics Data System (ADS)

    Callies, Joern; Ferrari, Raffaele

    2015-11-01

    It has recently been discovered that geostrophic turbulence in the upper ocean undergoes a seasonal cycle at submesoscales, the scales smaller than the most energetic mesoscale eddies. Observations and theory suggest that baroclinic mixed layer instabilities release potential energy stored in deep mixed layers, energizing the submesoscales in winter. In shallow summer mixed layers, there is no such energization. The oceanic mixed layer, besides being prone to baroclinic instabilities, is subject to atmospheric forcing, which drives convective overturns. We here study how this forced convection interacts with baroclinic instabilities in a set of idealized numerical simulations resolving both processes. A major question is whether baroclinic instabilities can be damped out by convection. Implications for the seasonal cycle in submesoscale turbulence will be discussed.

  11. 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.

  12. Modeling a Rain-Induced Mixed Layer

    DTIC Science & Technology

    1990-06-01

    te -)-A-- e e -2)- . (7) ’&Z AZ Az D Using the exponential relations with trigonometry , equation (7) becomes, Ok n) 3 (I- cos2ikAz)+ D (1- cos ikAz...completely unknown because there are no prior studies which predict what portion of total energy may go into subsurface mixing. The biggest obstacle

  13. [The influence of mixing and heating on the compressive strength of investment materials].

    PubMed

    Papadopoulos, T; Caracatsanis, M

    1989-08-01

    In the present study, the compressive strength of four representative dental investment materials was compared. The whole investigation was divided in three experiments. In the first one the effect of different ways of mixing on the compressive strength of the investments was examined. In the second the compressive strength of investments mixed mechanically under vacuum was compared: a) two hours after mixing, b) at the highest heating temperature and c) at room temperature after the heating procedure. In the third experiment, a comparison was made between the compressive strength of investments at the highest heating temperature. The investments were mixed mechanically under vacuum but half of the specimens were placed in a pressure device during setting. From the results obtained the following conclusions were made: a) Mixing mechanically under vacuum increases the compressive strength of the investments, b) the compressive strength of phosphate-bonded investments increases at the highest temperature of the heating procedure and c) the use of a pressure device during the setting of the investments results also in an increased compressive strength.

  14. 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.

  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. A perspective view of the plane mixing layer

    NASA Technical Reports Server (NTRS)

    Jimenez, J.; Cogollos, M.; Bernal, L. P.

    1984-01-01

    A three-dimensional model of the plane mixing layer is constructed by applying digital image processing and computer graphic techniques to laser fluorescent motion pictures of its transversal sections. A system of streamwise vortex pairs is shown to exist on top of the classical spanwise eddies. Its influence on mixing is examined.

  17. Laboratory simulations of the atmospheric mixed-layer in flow ...

    EPA Pesticide Factsheets

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundary layer can have a strong influence on the concentration of pollutants within this layer. Deflections of streamlines at the height of the interface are primarily a function of hill Froude number (Fr), the ratio of mixed-layer height (zi) to terrain height (h), and the crosswind dimension of the terrain. The magnitude of the deflections increases as Fr increases and zi / h decreases. For mixing-height streamlines that are initially below the terrain top, the response is linear with Fr; for those initially above the terrain feature the response to Fr is more complex. Once Fr exceeds about 2, the terrain related response of the mixed layer interface decreases somewhat with increasing Fr (toward more neutral flow). Deflections are also shown to increase as the crosswind dimensions of the terrain increases. Comparisons with numerical modeling, limited field data and other laboratory measurements reported in the literature are favorable. Additionally, visual observations of dye streamers suggests that the flow structure exhibited for our elevated inversions passing over three dimensional hills is similar to that reported in the literature for continuously stratified flow over two-dimensional h

  18. Laboratory simulations of the atmospheric mixed-layer in flow ...

    EPA Pesticide Factsheets

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundary layer can have a strong influence on the concentration of pollutants within this layer. Deflections of streamlines at the height of the interface are primarily a function of hill Froude number (Fr), the ratio of mixed-layer height (zi) to terrain height (h), and the crosswind dimension of the terrain. The magnitude of the deflections increases as Fr increases and zi / h decreases. For mixing-height streamlines that are initially below the terrain top, the response is linear with Fr; for those initially above the terrain feature the response to Fr is more complex. Once Fr exceeds about 2, the terrain related response of the mixed layer interface decreases somewhat with increasing Fr (toward more neutral flow). Deflections are also shown to increase as the crosswind dimensions of the terrain increases. Comparisons with numerical modeling, limited field data and other laboratory measurements reported in the literature are favorable. Additionally, visual observations of dye streamers suggests that the flow structure exhibited for our elevated inversions passing over three dimensional hills is similar to that reported in the literature for continuously stratified flow over two-dimensional h

  19. Numerical simulation of a wave-guide mixing layer on a Cray C-90

    NASA Astrophysics Data System (ADS)

    Greenough, Jeffrey A.; Crutchfield, William Y.; Rendleman, Charles A.

    1995-05-01

    The development of a three-dimensional spatially evolving compressible mixing layer is investigated numerically using a parallel implementation of Adaptive Mesh Refinement (AMR) on a Cray C-90. The parallel implementation allowed the flow to be highly resolved while significantly reducing the wall-clock runtime. A sustained computation rate of 5.3 Gigaflops including I/O was obtained for a typical production run on a 16 processor machine. A novel mixing layer configuration is investigated where a pressure mismatch is maintained between the two inlet streams. In addition, the sonic character of the two streams is sufficiently different so that the pressure relief wave is trapped in the high speed stream. The trapped wave forces the mixing layer to form a characteristic cellular pattern. The cellular structure introduces curvature into the mixing layer that excites centrifugal instabilities characterized by large-scale counter-rotating vortical pairs embedded within the mixing layer. These are the dominant feature of the flow. Visualizations of these structures in cross-section show the pumping action which lifts dense fluid up into light gas. This effect has a strong impact on mixing enhancement as monitored by a conserved scalar formulation. Once the large-scale structures axe well established in the flow and undergo intensification from favorable velocity gradients, the time-averaged integrated product shows almost a four-fold increase. A spectral analysis of the flow-field over the cellular structures, as part of a full space-time analysis, shows these structures to be zero-frequency modes that develop from low level essentially broad-banded noise. This characterization of the vortical structures and their appearance is consistent with a recent linear stability analysis, of a mixing layer over a curved wall that predicts the most unstable modes to be zero frequency streamwise vortices.

  20. Mixed layer development in a double-diffusive, thermohaline system

    SciTech Connect

    Poplawsky, C.J.; Incropera, F.P.; Viskanta, R.

    1981-11-01

    A double-diffusive, thermohaline system has been studied under laboratory conditions involving uniform heating from below. Shadowgraph visualization has been used with temperature and salt concentration measurements to investigate mixing layer development and the onset of diffusion layer instabilities. Such instabilities were observed to occur in two of the experiments and were approximately predicted by an existing stability criterion. 17 refs.

  1. 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.

  2. Boundary-layer losses. [friction trailing edges, and mixing losses

    NASA Technical Reports Server (NTRS)

    Prust, H. W., Jr.

    1973-01-01

    The primary cause of losses in a turbine is the boundary layer that builds up on the blade and end-wall surfaces. Analytical and experimental methods for determining the friction, trailing edge, and mixing losses associated with the boundary layer are reported. The theory presented herein refers primarily to two dimensional blade section boundary layers. Methods for obtaining three dimensional blade plus end wall losses from the two-dimensional results are also discussed.

  3. Temperature Versus Salinity Gradients Below the Ocean Mixed Layer

    DTIC Science & Technology

    2012-05-03

    where salinity controls the depth of the mixed layer are understood to have “barrier” layers [Lukas and Lindstrom , 1991], where the depth of vertically...the horizontal. For example, Rudnick and Martin [2002] have shown that the ocean mixed layer at sub-mesoscales is horizontally well density compensated...Res., 102, 23,063–23,078, doi:10.1029/97JC01443. Barron, C. N., A. B. Kara, P. J. Martin , R. C. Rhodes, and L. F. Smedstad (2006), Formulation

  4. Comparison of experimental and computational techniques for plane mixing layers

    NASA Technical Reports Server (NTRS)

    Mehta, R. D.; Bell, J. H.; Inoue, O.; King, L. S.

    1987-01-01

    In this paper, results from two experimental and two computational investigations of plane turbulent mixing layers are presented and compared. The experimental results include flow visualization data using the smoke laser technique and mean flow and turbulence measurements obtained with hot X-wires and a two-component LDV. Reasonably good agreement is found among these techniques, at least for turbulence quantities up to second order. Reynolds-averaged computations are successful at capturing the complete evolution of the mixing layer, including wake effects in the near field and approach to self-preservation in the far field. The two-dimensional vortex method shows excellent qualitative and quantitative agreement with measured data for the forced mixing layer. For the unforced layer, the results seem to indicate that a three-dimensional computation may be necessary.

  5. The total energy flux leaving the ocean's mixed layer

    NASA Astrophysics Data System (ADS)

    Rimac, Antonija; von Storch, Jin-Song; Eden, Carsten

    2017-04-01

    Interior density mixing contributes to drive the large-scale ocean circulation. The energy needed for this mixing is believed to be supplied predominantly by the tidal and wind forcing. In this study, we focus on the wind-power input to three different types of motions, that is, near-inertial waves, sub-inertial fluctuations, and time-mean flows. Surface winds can generate near-inertial waves which propagate freely into the ocean's interior and after escaping the mixed layer contribute to interior mixing. Winds also input power into the ocean to maintain the time-mean circulation and to generate sub-inertial fluctuations, either by the vertical or horizontal shear instability of the large-scale flows, or directly via wind induced fluctuations at the ocean surface. The energy of both the sub-inertial fluctuations and the time-mean flow will be eventually dissipated (or transferred to the internal gravity wave field or small scale turbulence). However, the exact portion of the power that escapes the turbulent mixed layer and that can potentially affect the interior mixing, is still unknown. The total energy flux leaving the ocean's spatially and seasonally varying mixed layer is estimated using a global 1/10° ocean general circulation model. From the total wind-power input of 3.33 TW into near-inertial waves (0.35 TW) sub-inertial fluctuations (0.87 TW), and the time-mean circulation (2.11 TW), 0.92 TW leave the mixed layer; with 0.04 TW (11.4%) due to near-inertial motions, 0.07 TW (8.3%) due to sub-inertial fluctuations, and 0.81 TW (38.4%) due to time-mean motions. Of the 0.81 TW from the time-mean motions, 0.5 TW result from the projection of the horizontal flux onto the sloped bottom of the mixed layer. This projection is negligible for the transient fluxes. The spatial structure of the vertical flux is determined principally by the wind stress curl. The mean and sub-inertial fluxes leaving the mixed layer are approximately 40-50% smaller than the respective

  6. Effect of shock interactions on mixing layer between co-flowing supersonic flows in a confined duct

    NASA Astrophysics Data System (ADS)

    Rao, S. M. V.; Asano, S.; Imani, I.; Saito, T.

    2017-04-01

    Experiments are conducted to observe the effect of shock interactions on a mixing layer generated between two supersonic streams of Mach number M _{1} = 1.76 and M _{2} = 1.36 in a confined duct. The development of this mixing layer within the duct is observed using high-speed schlieren and static pressure measurements. Two-dimensional, compressible Reynolds averaged Navier-Stokes equations are solved using the k-ω SST turbulence model in Fluent. Further, adverse pressure gradients are imposed by placing inserts of small (<7% of duct height) but finite (> boundary layer thickness) thickness on the walls of the test section. The unmatched pressures cause the mixing layer to bend and lead to the formation of shock structures that interact with the mixing layer. The mixing layer growth rate is found to increase after the shock interaction (nearly doubles). The strongest shock is observed when a wedge insert is placed in the M _{2} flow. This shock interacts with the mixing layer exciting flow modes that produce sinusoidal flapping structures which enhance the mixing layer growth rate to the maximum (by 1.75 times). Shock fluctuations are characterized, and it is observed that the maximum amplitude occurs when a wedge insert is placed in the M _{2} flow.

  7. 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.

  8. Transmission of thin light beams through turbulent mixing layers

    NASA Astrophysics Data System (ADS)

    Wissler, John B.

    1991-09-01

    Light transmission through incompressible gaseous turbulent mixing layers is investigated with the objective of understanding the effects of large-scale coherent structures and mixing transition on the optical quality of the mixing layer. Experiments are done in a vertically flowing mixing layer which is enclosed inside a pressure tank and fed by two banks of high-pressure gas bottles. The study considers both the unequal density (high-speed Helium and low-speed Nitrogen) and equal density (high-speed N2 and low-speed He-Ar) cases; the mixing of dissimilar gases is the source of the optical aberrations. Large-scale Reynolds numbers range between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics are first studied qualitatively using a network of thin sheets of short-exposure (about 1 microsec) white light which are aberrated by the mixing layer and then image directly onto photographic film. Light transmission characteristics are then studied quantitatively using a lateral effect detector to dynamically track a thin Helium-Neon laser beam as it wanders under the influence of the passing coherent structures. The study finds that the spanwise coherent structures generate systematic deflections of the light beam in the streamwise direction; the greatest deflections occur near the trailing edges of the structures at a formation called the cusp, where the high-speed fluid and low-speed fluid are entrained into the vortex core.

  9. 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.

  10. 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%.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. Transmission of light through a turbulent mixing layer

    NASA Astrophysics Data System (ADS)

    Roshko, Anatol; Wissler, John

    1992-08-01

    Light transmission through incompressible gaseous turbulent mixing layers was investigated with the objective of understanding the effects of large-scale coherent structures and mixing transition on the optical quality of the mixing layer. Experiments were done in a vertically flowing mixing layer which is enclosed inside a pressure tank and fed by two banks of high-pressure gas bottles. The study considered both the unequal density (high-speed He and low-speed N2) and equal density (high-speed N2 and low-speed He-Ar) cases; the mixing of dissimilar gases is the source of the optical aberrations. Large-scale Reynolds numbers ranged between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics were first studied qualitatively using a network of thin sheets of short-exposure (approximately 1 microsec) white light which were aberrated by the mixing layer and then imaged directly onto photographic film. Light transmission characteristics were then studied quantitatively using a lateral effect detector to dynamically track a thin He-Ne laser beam as it wandered under the influence of the passing coherent structures. The study found that the spanwise coherent structures generate systematic deflections of the light beam in the streamwise direction; the greatest deflections occur near the trailing edges of the structures at a formation called the cusp, where the high-speed fluid and low-speed fluid are entrained into the vortex core. The streamwise coherent structures, which form later in the mixing layer's development than the spanwise structures, generate substantial beam deflections in the spanwise direction which are closely associated with the streamwise streaks in plan-view shadowgraphs.

  17. Computer program for solving compressible nonsimilar-boundary-layer equations for laminar, transitional, or turbulent flows of a perfect gas

    NASA Technical Reports Server (NTRS)

    Price, J. M.; Harris, J. F.

    1972-01-01

    A computer program is described which solves the compressible laminar, transitional, or turbulent boundary-layer equations for planar or axisymmetric flows. Three-point implicit difference relations are used to reduce the momentum and energy equations to finite-difference form. These equations are solved simultaneously without iteration. Turbulent flow is treated by the inclusion of either a two-layer eddy-viscosity model or a mixing-length formulation. The eddy conductivity is related to the eddy viscosity through a static turbulent Prandtl number which may be an arbitrary function of the distance from the wall boundary. The transitional boundary layer is treated by the inclusion of an intermittency function which modifies the fully turbulent model. The laminar-boundary-layer equations are recovered when the intermittency is zero, and the fully turbulent equations are solved when the intermittency is unity.

  18. A procedure for the automatic estimation of mixed layer height.

    SciTech Connect

    Coulter, R. L.

    1998-04-15

    The daytime mixed layer results from mechanical and thermal turbulence processes driven by differences in air-surface temperature and moisture. As such, the height of the mixed layer (z{sub i}) is a measure of the effectiveness of energy transfer from the sun to the earth's surface and, in turn, to the lower atmosphere (Stun, 1989). Maximum daytime values for z{sub i} in the region of the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) vary from less than 100 m in cloudy, moist, calm, stable conditions to nearly 3 km in clear, dry, unstable conditions. The principal characteristic of the mixed layer is that scalar quantities such as moisture and temperature are mixed throughout. Thus, z{sub i} becomes one of the principal scaling parameters used to describe the structure of the lower planetary boundary layer. Normally, a stable layer (a potential temperature inversion) at the top of the mixed layer interfaces between processes in the lower atmosphere and in the free atmosphere above. The strength of this inversion limits the rate of growth of z{sub i} with time and the vertical transfer of energy and moisture. When and if z{sub i} reaches the condensation level, clouds can form; hence, cloud base height (particularly for fair-weather cumulus clouds) often coincides with z{sub i} later in the day. Although the concept of the mixed layer height is straightforward, its measurement can be relatively difficult, or at least awkward. The most reliable method is an analysis of potential temperature and mixing ratio profiles retrieved from balloon ascents. (The potential temperature changes from constant to increasing with height; the mixing ratio changes from constant to decreasing with height.) Often however, the profiles of temperature and moisture are ambiguous, with multiple inversions or none at all. In addition these profiles supply only a snapshot of the atmospheric structure that may well be unrepresentative of the average, either in time or space

  19. 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.

  20. 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).

  1. Calculation of external-internal flow fields for mixed-compression inlets

    NASA Technical Reports Server (NTRS)

    Chyu, W. J.; Kawamura, T.; Bencze, D. P.

    1986-01-01

    Supersonic inlet flows with mixed external-internal compressions were computed using a combined implicit-explicit (Beam-Warming-Steger/MacCormack) method for solving the three-dimensional unsteady, compressible Navier-Stokes equations in conservation form. Numerical calculations were made of various flows related to such inlet operations as the shock-wave intersections, subsonic spillage around the cowl lip, and inlet started versus unstarted conditions. Some of the computed results were compared with wind tunnel data.

  2. 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.

  3. 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.

  4. Transmission of thin light beams through turbulent mixing layers

    NASA Astrophysics Data System (ADS)

    Wissler, John B.

    Light transmission through incompressible gaseous turbulent mixing layers is investigated with the objective of understanding the effects of large-scale coherent structures and mixing transition on the optical quality of the mixing layer. Experiments are done in a vertically flowing mixing layer which is enclosed inside a pressure tank and fed by two banks of high-pressure gas bottles. The study considers both the unequal density (high-speed [...] and low-speed [...]) and equal density (high-speed [...] and low-speed [...]) cases; the mixing of dissimilar gases is the source of the optical aberrations. Large-scale Reynolds numbers range between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics are first studied qualitatively using a network of thin sheets of short-exposure ([...]) white light which are aberrated by the mixing layer and then image directly onto photographic film. Light transmission characteristics are then studied quantitatively using a lateral effect detector to dynamically track a thin He-Ne laser beam as it wanders under the influence of the passing coherent structures.The study finds that the spanwise coherent structures generate systematic deflections of the light beam in the streamwise direction; the greatest deflections occur near the trailing edges of the structures at a formation called the cusp, where the high-speed fluid and low-speed fluid are entrained into the vortex core. The streamwise coherent structures, which form later in the mixing layer's development than the spanwise structures, generate substantial beam deflections in the span-wise direction which are closely associated with the streamwise streaks in plan-view shadowgraphs. The rms fluctuations of the streamwise and spanwise deflection angles increase rapidly during mixing transition, peaking at 380 high-speed-side momentum thicknesses downstream from the splitter plate, then decrease far down-stream to asymptotic values of 0.6 to 0.8 as scaled

  5. Transmission of Thin Light Beams Through Turbulent Mixing Layers.

    NASA Astrophysics Data System (ADS)

    Wissler, John B.

    1992-01-01

    Light transmission through incompressible gaseous turbulent mixing layers is investigated with the objective of understanding the effects of large-scale coherent structures and mixing transition on the optical quality of the mixing layer. Experiments are done in a vertically flowing mixing layer which is enclosed inside a pressure tank and fed by two banks of high-pressure gas bottles. The study considers both the unequal density (high-speed He and low-speed N_2) and equal density (high-speed N_2 and low-speed He-Ar) cases; the mixing of dissimilar gases is the source of the optical aberrations. Large-scale Reynolds numbers range between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics are first studied qualitatively using a network of thin sheets of short-exposure (~ 1musec) white light which are aberrated by the mixing layer and then image directly onto photographic film. Light transmission characteristics are then studied quantitatively using a lateral effect detector to dynamically track a thin He-Ne laser beam as it wanders under the influence of the passing coherent structures. The study finds that the spanwise coherent structures generate systematic deflections of the light beam in the streamwise direction; the greatest deflections occur near the trailing edges of the structures at a formation called the cusp, where the high-speed fluid and low-speed fluid are entrained into the vortex core. The streamwise coherent structures, which form later in the mixing layer's development than the spanwise structures, generate substantial beam deflections in the spanwise direction which are closely associated with the streamwise streaks in plan-view shadowgraphs. The rms fluctuations of the streamwise and spanwise deflection angles increase rapidly during mixing transition, peaking at 380 high-speed-side momentum thicknesses downstream from the splitter plate, then decrease far downstream to asymptotic values of 0.6 to 0.8 as scaled by

  6. Three-Dimensional Structure of Plane Mixing Layers.

    NASA Astrophysics Data System (ADS)

    Bell, James Horatio

    Recent studies have shown the existence of an organized and persistent streamwise vortex structure in plane mixing layers, which is believed to take the form of a row of alternating-sign streamwise vortices. So far, this streamwise vortex structure has been studied mostly through flow-visualization at relatively low Reynolds numbers. The main objective of the present work was to obtain quantitative measurements of the streamwise vorticity at Reynolds numbers more comparable to those commonly found in practical applications. In the first experiment, the artificially induced streamwise vortex was observed to decay as approximately 1/X^2 within the mixing layer. The effect of the vortex was to locally distort the mean strain distribution in the mixing layer, thus altering the production of the Reynolds stresses. Peak values of the normal stresses were increased by about 20% over the undisturbed case in the region of the streamwise vortex. In particular a strong, pronounced peak was generated in the secondary shear stress, (overline{u^' w^ '}).. In the second experiment, "naturally-occurring" streamwise vorticity was clearly observed in a two-stream mixing layer. Concentrated streamwise vortices appeared just downstream of the first roll-up of the spanwise vorticity, with an initial circulation which was roughly half that of the spanwise vortex circulation. The streamwise vortices first appeared in "clusters", the positions of which seemed to be related to small disturbances in one of the upstream boundary layers. The clusters quickly reorganized into a single row of alternating-sign vortices under the influence of vortex dynamics and changes in the normal stress anisotropy. The streamwise vortex spacing increased in a stepwise fashion, at least partially through the amalgamation of like-sign vortices. The wavelength of the streamwise vortices increased approximately as the mixing layer vorticity thickness, while their strength decayed as roughly 1/X^ {1.5}. In the

  7. Isotopic evidence for nitrification in the Antarctic winter mixed layer

    NASA Astrophysics Data System (ADS)

    Smart, Sandi M.; Fawcett, Sarah E.; Thomalla, Sandy J.; Weigand, Mira A.; Reason, Chris J. C.; Sigman, Daniel M.

    2015-04-01

    We report wintertime nitrogen and oxygen isotope ratios (δ15N and δ18O) of seawater nitrate in the Southern Ocean south of Africa. Depth profile and underway surface samples collected in July 2012 extend from the subtropics to just beyond the Antarctic winter sea ice edge. We focus here on the Antarctic region (south of 50.3°S), where application of the Rayleigh model to depth profile δ15N data yields estimates for the isotope effect (the degree of isotope discrimination) of nitrate assimilation (1.6-3.3‰) that are significantly lower than commonly observed in the summertime Antarctic (5-8‰). The δ18O data from the same depth profiles and lateral δ15N variations within the mixed layer, however, imply O and N isotope effects that are more similar to those suggested by summertime data. These findings point to active nitrification (i.e., regeneration of organic matter to nitrate) within the Antarctic winter mixed layer. Nitrite removal from samples reveals a low δ15N for nitrite in the winter mixed layer (-40‰ to -20‰), consistent with nitrification, but does not remove the observation of an anomalously low δ15N for nitrate. The winter data, and the nitrification they reveal, explain the previous observation of an anomalously low δ15N for nitrate in the temperature minimum layer (remnant winter mixed layer) of summertime depth profiles. At the same time, the wintertime data require a low δ15N for the combined organic N and ammonium in the autumn mixed layer that is available for wintertime nitrification, pointing to intense N recycling as a pervasive condition of the Antarctic in late summer.

  8. What is the existing evidence supporting the efficacy of compression bandage systems containing both elastic and inelastic components (mixed-component systems)? A systematic review.

    PubMed

    Welsh, Lynn

    2017-05-01

    To analyse current evidence on the efficacy of bandage systems containing both elastic and inelastic components (mixed-component systems). International consensus on the efficacy of types of compression systems is difficult to achieve; however, mixed-component systems are being promoted as combining the best properties of both elastic and inelastic bandage systems and increasingly being used to treat venous leg ulcers in practice. A systematic literature review. Search terms such as venous leg ulcer, varicose ulcer, leg ulcer, compression, bandage, elastic, inelastic, short stretch, healing rate, interface pressure, mixed component, two-layer, four-layer and multi-layer were used in database and hand searches in several combinations. Limits were set for years 2005-March 2015 and English-language publications. A total of 475 studies were identified at initial search, and following elimination from abstract and title, this was reduced to 7. A further study was identified on Google Scholar, bringing the final number of studies fitting inclusion criteria to 8. The following subgroups relating to outcomes of efficacy were identified: ulcer healing, maintenance of interface pressure, slippage, ease of application and patient quality of life. Mixed-component systems were found to have comparable ulcer healing rates to alternative compression systems and be easy to apply; have similar abilities to maintain pressure as four-layer bandages and better abilities than short-stretch bandages; have less slippage than alternative systems; and to be significantly associated with several favourable quality of life outcomes. Clinician skill in bandage application was an uncontrolled variable in all eight papers included in the review, which may limit reliability of findings. This review synthesises existing evidence on the efficacy of mixed-component systems and encourages clinicians to regard them as an effective alternative to purely elastic or inelastic compression systems

  9. Mixing and recirculation in two-layer exchange flows

    NASA Astrophysics Data System (ADS)

    StenströM, Petter

    2003-08-01

    Mixing and recirculation due to interfacial friction in two-layer exchange flows through topographic constrictions are investigated using a nonhydrostatic, three-dimensional numerical model. The simulated exchange flows are always lower than what inviscid hydraulic theory predicts; the reduction is greater for a contraction than for a sill, with intermediate values for sill-contraction combinations. A large fraction of a tracer flux in one layer is lost to the other layer from an inflow section at the entrance of the contraction (foot of the sill) up to the throat of the contraction (sill crest). For a contraction this fraction is about equal for the two layers, whereas for a sill the loss from the upper to the lower layer is about 6 times as high as the loss from the lower to the upper layer. Sill-contraction combinations show similar behavior to a contraction toward the dense reservoir and to a sill toward the light reservoir. The variation in recirculation fractions over a tidal cycle is small for flow over a sill, but greater for flow through a contraction. The peak rate of loss from a layer occurs when the flow in the other layer has its maximum, i.e., at maximum negative barotropic flow for the lower layer and at maximum positive barotropic flow for the upper layer.

  10. 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.

  11. An improved enhancement layer for octree based point cloud compression with plane projection approximation

    NASA Astrophysics Data System (ADS)

    Ainala, Khartik; Mekuria, Rufael N.; Khathariya, Birendra; Li, Zhu; Wang, Ye-Kui; Joshi, Rajan

    2016-09-01

    Recent advances in point cloud capture and applications in VR/AR sparked new interests in the point cloud data compression. Point Clouds are often organized and compressed with octree based structures. The octree subdivision sequence is often serialized in a sequence of bytes that are subsequently entropy encoded using range coding, arithmetic coding or other methods. Such octree based algorithms are efficient only up to a certain level of detail as they have an exponential run-time in the number of subdivision levels. In addition, the compression efficiency diminishes when the number of subdivision levels increases. Therefore, in this work we present an alternative enhancement layer to the coarse octree coded point cloud. In this case, the base layer of the point cloud is coded in known octree based fashion, but the higher level of details are coded in a different way in an enhancement layer bit-stream. The enhancement layer coding method takes the distribution of the points into account and projects points to geometric primitives, i.e. planes. It then stores residuals and applies entropy encoding with a learning based technique. The plane projection method is used for both geometry compression and color attribute compression. For color coding the method is used to enable efficient raster scanning of the color attributes on the plane to map them to an image grid. Results show that both improved compression performance and faster run-times are achieved for geometry and color attribute compression in point clouds.

  12. Investigation of the Dynamics of the Jet Mixing Layer

    DTIC Science & Technology

    2001-09-17

    Proper Orthogonal Decomposition ( POD ) techniques. The experiments utilize 138 hot-wires in the mixing layer of an axisymmetric jet to simultaneously...resolve the instantaneous stream wise velocity field at all locations. The POD is then applied to a double Fourier transform in time and azimuthal direction

  13. 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.

  14. Vortex simulation of forced/unforced mixing layers

    NASA Technical Reports Server (NTRS)

    Inoue, Osamu; Leonard, Anthony

    1987-01-01

    Two-dimensional, spatially growing, turbulent mixing layers are simulated numerically by a vortex method and the results are compared with those determined experimentally. The effects of artificial forcing on flow development are also studied. Many of the flow features which have been observed experimentally are reproduced, and good quantitative agreements between experiments and computations are obtained.

  15. 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.

  16. 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.

  17. 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

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

    NASA Astrophysics Data System (ADS)

    Tritarelli, R. C.; Kleiser, L.

    2017-03-01

    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.

  19. Structural properties of ion beam mixed tungsten/steel layers

    NASA Astrophysics Data System (ADS)

    Piatkowska, A.; Jagielski, J.; Kopcewicz, M.; Matz, W.; Zalar, A.; Mozetic, M.

    2003-05-01

    Structural properties of Kr ion beam mixed layers of tungsten deposited on high-speed steel have been studied by using Grazing incidence X-ray diffraction, conversion electron Mössbauer spectroscopy and Auger electron spectroscopy techniques. The results show that ion beam mixing at room temperature leads to the formation of an amorphous layer composed of the mixture of amorphous tungsten and amorphous Fe-W phase. The amorphous structure is stable upon annealing up to at least 450 °C. The ion beam mixing at the temperatures above 350 °C results in the formation of crystalline W 2C phase in addition to the amorphous Fe-W one persisting up to at least 450 °C.

  20. Simultaneous measurements and flow visualization in a plane mixing layer

    NASA Astrophysics Data System (ADS)

    Sherikar, S. V.; Chevray, R.

    Wind tunnel experiments performed to determine the flow characteristics of a plane mixing layer are described. Two parallel streams of air moving at different velocities were separated by a splitter plate prior to their mixing in the test section. Gaseous NH3 and gaseous HCI were introduced near the splitter plate to produce an ammonium chloride aerosol which made flow visualization possible. Flow visualization records (movies) and velocity measurements, using laser-doppler-velocimeters tracking silicone oil particles in the flow, were made simultaneously and synchronized using a chopped beam of a He-Ne laser which left a signature on the move film and provided a signal for flow rate data acquisition. Analysis of these synchronized data verified the existence of large, essentially two-dimensional coherent structures in the plane mixing layer.

  1. Mixing layer control for tangential slot injection in turbulent flows

    NASA Technical Reports Server (NTRS)

    Mcinville, R. M.; Goodman, W. L.; Hassan, H. A.

    1985-01-01

    Tangential injection into turbulent flows is one of the most promising methods of minimizing skin friction and providing thermal protection. The technique also has application to laser hardening. The effectiveness of the injected material can be increased if the spreading rate of the resulting mixing region can be reduced. Various techniques which have been shown to be effective in manipulating the rate of growth of mixing layers under certain conditions have been applied to a slot configuration having a thick external turbulent boundary layer. These include geometry modifications to the slot lip trailing edge and acoustic excitation of the slot exit plane over a wide range of frequencies. Neither of these approaches produced any noticeable effect on the downstream evolution of the mixing layer. This lack of effectiveness is attributed to the dominating influence of the well-developed incoming turbulent boundary layer. The placement of large-eddy breakup devices in this boundary layer upstream of the injection point did produce significantly lower velocities in the near-wall region of the flow downstream of the slot exit.

  2. Membrane filtration device for studying compression of fouling layers in membrane bioreactors

    PubMed Central

    Bugge, Thomas Vistisen; Larsen, Poul; Nielsen, Per Halkjær; Christensen, Morten Lykkegaard

    2017-01-01

    A filtration devise was developed to assess compressibility of fouling layers in membrane bioreactors. The system consists of a flat sheet membrane with air scouring operated at constant transmembrane pressure to assess the influence of pressure on resistance of fouling layers. By fitting a mathematical model, three model parameters were obtained; a back transport parameter describing the kinetics of fouling layer formation, a specific fouling layer resistance, and a compressibility parameter. This stands out from other on-site filterability tests as model parameters to simulate filtration performance are obtained together with a characterization of compressibility. Tests on membrane bioreactor sludge showed high reproducibility. The methodology’s ability to assess compressibility was tested by filtrations of sludges from membrane bioreactors and conventional activated sludge wastewater treatment plants from three different sites. These proved that membrane bioreactor sludge showed higher compressibility than conventional activated sludge. In addition, detailed information on the underlying mechanisms of the difference in fouling propensity were obtained, as conventional activated sludge showed slower fouling formation, lower specific resistance and lower compressibility of fouling layers, which is explained by a higher degree of flocculation. PMID:28749990

  3. Membrane filtration device for studying compression of fouling layers in membrane bioreactors.

    PubMed

    Jørgensen, Mads Koustrup; Bugge, Thomas Vistisen; Larsen, Poul; Nielsen, Per Halkjær; Christensen, Morten Lykkegaard

    2017-01-01

    A filtration devise was developed to assess compressibility of fouling layers in membrane bioreactors. The system consists of a flat sheet membrane with air scouring operated at constant transmembrane pressure to assess the influence of pressure on resistance of fouling layers. By fitting a mathematical model, three model parameters were obtained; a back transport parameter describing the kinetics of fouling layer formation, a specific fouling layer resistance, and a compressibility parameter. This stands out from other on-site filterability tests as model parameters to simulate filtration performance are obtained together with a characterization of compressibility. Tests on membrane bioreactor sludge showed high reproducibility. The methodology's ability to assess compressibility was tested by filtrations of sludges from membrane bioreactors and conventional activated sludge wastewater treatment plants from three different sites. These proved that membrane bioreactor sludge showed higher compressibility than conventional activated sludge. In addition, detailed information on the underlying mechanisms of the difference in fouling propensity were obtained, as conventional activated sludge showed slower fouling formation, lower specific resistance and lower compressibility of fouling layers, which is explained by a higher degree of flocculation.

  4. Results from computational analysis of a mixed compression supersonic inlet

    NASA Technical Reports Server (NTRS)

    Saunders, J. D.; Keith, T. G.

    1991-01-01

    A numerical study was performed to simulate the critical flow through a supersonic inlet. This flow field has many phenomena such as shock waves, strong viscous effects, turbulent boundary layer development, boundary layer separations, and mass flow suction through the walls, (bleed). The computational tools used were two full Navier-Stokes (FNS) codes. The supersonic inlet that was analyzed is the Variable Diameter Centerbody, (VDC), inlet. This inlet is a candidate concept for the next generation supersonic involved effort in generating an efficient grid geometry and specifying boundary conditions, particularly in the bleed region and at the outflow boundary. Results for a critical inlet operation compare favorably to Method of Characteristics predictions and experimental data.

  5. 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.

  6. Direct simulation of shock-induced mixing layer

    SciTech Connect

    Greenough, J.A.; Bell, J.B.

    1993-03-01

    The interaction of a shock wave with a dense fluid layer in three dimensions is investigated using direct numerical simulations. The underlying numerical method is a second-order Godunov scheme. This is coupled to an implementation of Adaptive Mesh Refinement which is used to manage the hierarchical grid structure. An anomalous shock refraction is formed as the initiating shock wave impinges on a quiescent thin dense gas layer. One of the two resulting centered waves from the refraction, the contact surface, serves as the site for initial deposition of primarily spanwise vorticity and represents the primary mixing layer instability. The other wave, the transmitted shock wave, through repeated interactions with the free-surface, forms a cellular structure within the dense layer. The initial interaction introduces three dimensional perturbations onto the slip surface. These perturbations are selectively enhanced, due to favorable velocity gradients over part of the cellular structures, and form large-scale counter-rotating streamwise vertical structures. The structures characterize the secondary instability of this mixing layer. These vortices are quite unstable and transition to small-scales within a distance spanned by two of the cellular structures behind the initiating shock. The transition location has been verified in physical experiments. The fine-scale structure contains evidence of hairpin vortices. The evolution of a conserved scalar is used to monitor mixing progress. Increases in the rate of mixing are directly tied to intensification events associated with the streamwise vortices. Overall the large-scale streamwise structures provide an efficient mechanism for mixing the light and dense fluids. Analysis of time-series data from the calculation shows evidence of what are termed energetic smallscales. This is the characteristic signature of the hairpin vortices undergoing intensification.

  7. Mixed-layer carbon cycling at the Kuroshio Extension Observatory

    NASA Astrophysics Data System (ADS)

    Fassbender, Andrea J.; Sabine, Christopher L.; Cronin, Meghan F.; Sutton, Adrienne J.

    2017-02-01

    Seven years of data from the NOAA Kuroshio Extension Observatory (KEO) surface mooring, located in the North Pacific Ocean carbon sink region, were used to evaluate drivers of mixed-layer carbon cycling. A time-dependent mass balance approach relying on two carbon tracers was used to diagnostically evaluate how surface ocean processes influence mixed-layer carbon concentrations over the annual cycle. Results indicate that the annual physical carbon input is predominantly balanced by biological carbon uptake during the intense spring bloom. Net annual gas exchange that adds carbon to the mixed layer and the opposing influence of net precipitation that dilutes carbon concentrations make up smaller contributions to the annual mixed-layer carbon budget. Decomposing the biological term into annual net community production (aNCP) and calcium carbonate production (aCaCO3) yields 7 ± 3 mol C m-2 yr-1 aNCP and 0.5 ± 0.3 mol C m-2 yr-1 aCaCO3, giving an annually integrated particulate inorganic carbon to particulate organic carbon production ratio of 0.07 ± 0.05, as a lower limit. Although we find that vertical physical processes dominate carbon input to the mixed layer at KEO, it remains unclear how horizontal features, such as eddies, influence carbon production and export by altering nutrient supply as well as the depth of winter ventilation. Further research evaluating linkages between Kuroshio Extension jet instabilities, eddy activity, and nutrient supply mechanisms is needed to adequately characterize the drivers and sensitivities of carbon cycling near KEO.

  8. Mixed mosaic membranes prepared by layer-by-layer assembly for ionic separations.

    PubMed

    Rajesh, Sahadevan; Yan, Yu; Chang, Hsueh-Chia; Gao, Haifeng; Phillip, William A

    2014-12-23

    Charge mosaic membranes, which possess distinct cationic and anionic domains that traverse the membrane thickness, are capable of selectively separating dissolved salts from similarly sized neutral solutes. Here, the generation of charge mosaic membranes using facile layer-by-layer assembly methodologies is reported. Polymeric nanotubes with pore walls lined by positively charged polyethylenimine moieties or negatively charged poly(styrenesulfonate) moieties were prepared via layer-by-layer assembly using track-etched membranes as sacrificial templates. Subsequently, both types of nanotubes were deposited on a porous support in order to produce mixed mosaic membranes. Scanning electron microscopy demonstrates that the facile deposition techniques implemented result in nanotubes that are vertically aligned without overlap between adjacent elements. Furthermore, the nanotubes span the thickness of the mixed mosaic membranes. The effects of this unique nanostructure are reflected in the transport characteristics of the mixed mosaic membranes. The hydraulic permeability of the mixed mosaic membranes in piezodialysis operations was 8 L m(-2) h(-1) bar(-1). Importantly, solute rejection experiments demonstrate that the mixed mosaic membranes are more permeable to ionic solutes than similarly sized neutral molecules. In particular, negative rejection of sodium chloride is observed (i.e., the concentration of NaCl in the solution that permeates through a mixed mosaic membrane is higher than in the initial feed solution). These properties illustrate the ability of mixed mosaic membranes to permeate dissolved ions selectively without violating electroneutrality and suggest their utility in ionic separations.

  9. Determination of mixing layer heights from ceilometer data

    NASA Astrophysics Data System (ADS)

    Schafer, Klaus; Emeis, Stefan M.; Rauch, Andreas; Munkel, Christoph; Vogt, Siegfried

    2004-11-01

    The Vaisala ceilometer LD40 is an eye-safe commercial lidar. It is designed originally to detect cloud base heights and vertical visibility for aviation safety purposes. The instrument was operated continuously at different measurement campaigns to detect mixing layer height from aerosol backscatter profiles. First results with the CT25K ceilometer were presented last year in the paper SPIE 5235-64 from the environmental measuring campaign in the frame of the BMBF-funded project VALIUM in Hanover, Germany, investigating the air pollution in a street canyon and the surrounding with various sensors. A software for routine retrieval of mixing layer height (MLH) from ceilometer data was developed. A comparison with mixing layer height retrievals from a SODAR and a wind-temperature-radar (WTR) operated in the urban region of Munich will be shown. The three instruments give information that partly agree and partly complement each other. The ceilometer gives information on the aerosol content of the air and the WTR provides a direct measurement of the vertical temperature distribution in the boundary layer. The WTR and the ceilometer add information on the moisture structure of the boundary layer that is not detected by the SODAR which gives information on the thermal structure. On the other hand this comparison validates known techniques by which the MLH is derived from SODAR data. In the absence of low clouds and precipitation ceilometers can estimate the mixing-layer-height fairly well. The potential of the ceilometer, being the smallest instrument among the used ones as LIDAR, SODAR and WTR, will be discussed to be used in future MLH studies.

  10. 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

  11. On compression and rarefaction waves in a dispersed layer

    NASA Astrophysics Data System (ADS)

    Teplitskii, Yu. S.; Kovenskii, V. I.

    2008-11-01

    Mathematical modeling of nonstationary filtration regimes with instantaneous reduction (increase) in the pressure at entry into the granular bed has been carried out within the framework of the two-temperature approximation. The regularities of transmission of rarefaction and compression waves have been investigated. Equations for calculation of the minimum and maximum temperature of the heat-transfer agent in criterial form and of the time of reaching a new stationary state have been obtained.

  12. New algorithm for lossless hyper-spectral image compression with mixing transform to eliminate redundancy

    NASA Astrophysics Data System (ADS)

    Xie, ChengJun; Xu, Lin

    2008-03-01

    This paper presents a new algorithm based on mixing transform to eliminate redundancy, SHIRCT and subtraction mixing transform is used to eliminate spectral redundancy, 2D-CDF(2,2)DWT to eliminate spatial redundancy, This transform has priority in hardware realization convenience, since it can be fully implemented by add and shift operation. Its redundancy elimination effect is better than (1D+2D)CDF(2,2)DWT. Here improved SPIHT+CABAC mixing compression coding algorithm is used to implement compression coding. The experiment results show that in lossless image compression applications the effect of this method is a little better than the result acquired using (1D+2D)CDF(2,2)DWT+improved SPIHT+CABAC, still it is much better than the results acquired by JPEG-LS, WinZip, ARJ, DPCM, the research achievements of a research team of Chinese Academy of Sciences, NMST and MST. Using hyper-spectral image Canal of American JPL laboratory as the data set for lossless compression test, on the average the compression ratio of this algorithm exceeds the above algorithms by 42%,37%,35%,30%,16%,13%,11% respectively.

  13. 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

  14. Mixed Layer Depth in the Aegean, Marmara, Black and Azov Seas: Part II: Relation to the Sonic Layer Depth

    DTIC Science & Technology

    2009-03-03

    r.com/ locate / jmarsysMixed layer depth in the Aegean, Marmara, Black and Azov Seas : Part II: Relation to the sonic layer depth Robert W. Helber a...index terms: The Aegean Sea The Black Sea The Azov Sea Keywords: Sound transmission Mixed layer depth Climatologyt analysis of the seasonal evolution of...the sonic layer depth (SLD) relative to the mixed layer depth (MLD) for the Aegean, Marmara, Black, and Azov Seas . SLD identifies the acoustic ducting

  15. 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.

  16. 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.

  17. 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...

  18. 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...

  19. Hydrodynamic Mixing of Ablator Material into the Compressed Fuel and Hot Spot of Direct-Drive DT Cryogenic Implosions

    NASA Astrophysics Data System (ADS)

    Regan, S. P.; Goncharov, V. N.; Epstein, R.; Betti, R.; Bonino, M. J.; Cao, D.; Collins, T. J. B.; Campbell, E. M.; Forrest, C. J.; Glebov, V. Yu.; Harding, D. R.; Marozas, J. A.; Marshall, F. J.; McKenty, P. W.; Sangster, T. C.; Stoeckl, C.; Luo, R. W.; Schoff, M. E.; Farrell, M.

    2016-10-01

    Hydrodynamic mixing of ablator material into the compressed fuel and hot spot of direct-drive DT cryogenic implosions is diagnosed using time-integrated, spatially resolved xray spectroscopy. The laser drive ablates most of the 8- μm-thick CH ablator, which is doped with trace amounts of Ge ( 0.5 at.) and surrounds the cryogenic DT layer. A small fraction of the ablator material is mixed into the compressed shell and the hot spot by the ablation-front Rayleigh-Taylor hydrodynamic instability seeded by laser imprint, the target mounting stalk, and surface debris. The amount of mix mass inferred from spectroscopic analysis of the Ge K-shell emission will be presented. This material is based upon work supported by the Department Of Energy National Nuclear Security Administration under Award Number DE-NA0001944. Part of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Layered compression scheme for multicasting medical images across heterogeneous networks

    NASA Astrophysics Data System (ADS)

    Banerjea, Anindo; Tan, Wai-tian; Zakhor, Avideh

    1997-05-01

    In this paper we evaluate a layered coding technique based on subband coding for the purpose of encoding medical images for realtime transmission over heterogeneous networks. The objective of this research is to support a medical conference in a heterogeneous networking scenario. The scalable coding scheme under study in this paper generates a single bit-stream, from which a number of sub-streams of varying bit-rates can be extracted. This makes it possible to support a multicast transmission scenario, where the different receivers are capable of receiving different bit- rate streams from the same source, in an efficient and scalable way. The multirate property also allows us to provide graceful degradation to loss when used over networks which support multiple priorities. This paper evaluates the quality of the video images encoded with the layered encoding technique at different bit-rates in terms of the peak signal to noise ratio for cine-angiogram video. It also describes experiments with the transmission of the video across an asynchronous transfer mode (ATM) local area network, using two layer encoded video stream, and assigning different network service classes to the two layers. We study how the quality of the reconstructed signal changes with the ratio of the bit-rates of the high and low priority layers, for various levels of congestion in the ATM network.

  5. 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.

  6. The Effects of Curvature on Turbulent Mixing Layers,

    DTIC Science & Technology

    1984-01-01

    Elimination of the pressure leads to the stability equation of Rayleigh . (U - c)(*" -z ) - (’t =0. (1.2.5) p-- Rayleigh (1880) proved that a necessary...viscosity. Using a model equation in which viscosity is incorporated as a damp- ing term for a second-order system, Plesset and Whipple (1974) found that...the (" case of mixing layers with different densities, three-dlmensionality is greatly enhanced by Rayleigh -Taylor instability if the inner stream is

  7. 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.

  8. 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.

  9. 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.

  10. 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)

  11. Calculation of three-dimensional compressible laminar and turbulent boundary layers. Calculation of three-dimensional compressible boundary layers on arbitrary wings

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

    A very general method for calculating compressible three-dimensional laminar and turbulent boundary layers on arbitrary wings is described. The method utilizes a nonorthogonal coordinate system for the boundary-layer calculations and includes a geometry package that represents the wing analytically. In the calculations all the geometric parameters of the coordinate system are accounted for. The Reynolds shear-stress terms are modeled by an eddy-viscosity formulation developed by Cebeci. The governing equations are solved by a very efficient two-point finite-difference method used earlier by Keller and Cebeci for two-dimensional flows and later by Cebeci for three-dimensional flows.

  12. 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.

  13. 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.

  14. 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

  15. Effects of compressibility on the temperature jump at the interface of layered, spherical-shell convection

    NASA Technical Reports Server (NTRS)

    Yen, David A.; Zhang, Shuxia; Langenberger, Sherri E.

    1988-01-01

    Large temperature jumps at the interface of layered convection are important to the argument used against the likelihood of separate circulations in the upper and lower mantles. This problem was studied within the framework of a compressible, constant viscosity spherical-shell model. Both mechanical and thermal coupling configurations are considered. Although the temperature jumps are reduced by compressibility, their magnitudes remain quite large, in the case of mechanical coupling. For thermal coupling, the temperature jumps become smaller but still are substantial, between 500 to 1000 C. In layered spherical-shell convection, flows in the lower mantle are several times greater than the surface velocities.

  16. Stability of compressible boundary layers over a smooth backward-facing step

    NASA Technical Reports Server (NTRS)

    Ragab, S. A.; Nayfeh, A. H.; Krishna, R. C.

    1990-01-01

    An investigation is conducted into the determination of the credibility of interacting boundary layers in predicting compressible subsonic flows over smooth surface imperfections. The case of smooth backward-facing steps is considered. The predicted mean flows are compared with those obtained using a Navier-Stokes solver. Moreover, the linear 2-D compressible stability characteristics of both mean flows are compared. The results show that the interacting boundary-layer formulation produces accurate mean flows that yield accurate linear stability characteristics, such as growth rates and amplification factors.

  17. Stability of compressible boundary layers over a smooth backward-facing step

    NASA Technical Reports Server (NTRS)

    Ragab, S. A.; Nayfeh, A. H.; Krishna, R. C.

    1989-01-01

    An investigation is conducted into the determination of the credibility of interacting boundary layers in predicting compressible subsonic flows over smooth surface imperfections. The case of smooth backward-facing steps is considered. The predicted mean flows are compared with those obtained using a Navier-Stokes solver. Moreover, the linear 2-D compressible stability characteristics of both mean flows are compared. The results show that the interacting boundary-layer formulation produces accurate mean flows that yield accurate linear stability characteristics, such as growth rates and amplification factors.

  18. Assessment of Mixed Layer Mesoscale Parameterization in Eddy Resolving Simulations.

    NASA Astrophysics Data System (ADS)

    Clayson, C. A.; Luneva, M. V.; Dubovikov, M. S.

    2014-12-01

    In eddy resolving simulations we test a mixed layer mesoscale parameterization, developed recently by Canuto and Dubovikov (2011). The parameterization yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy. An expression for the later in terms of mean fields has been found too to get a closed parameterization in terms of the mean fields only. In 40 numerical experiments we simulated the two types of flows: idealized flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow in shallow and narrow straits. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1o - 2o and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are highly correlated with the parameterization. After averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations, are quite consistent with the parameterization for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parameterization unless vertical turbulent mixing in the upper layer becomes strong enough to compare with mesoscale advection. In the later case, numerical simulations demonstrate that the deviation of the fluxes from the parameterization is controlled by the dimensionless parameter γ, estimating the ratio of vertical diffusion term to a mesoscale advection. The empirical dependence of vertical flux on γ is found. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.

  19. 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.

  20. Mixing layer height and air pollution levels in urban area

    NASA Astrophysics Data System (ADS)

    Schäfer, Klaus; Wagner, Patrick; Emeis, Stefan; Jahn, Carsten; Muenkel, Christoph; Suppan, Peter

    2012-10-01

    Ceilometers are applied by KIT/IMK-IFU to detect layering of the lower atmosphere continuously. This is necessary because not only wind speed and direction but also atmospheric layering and especially the mixing layer height (MLH) influence exchange processes of ground level emissions. It will be discussed how the ceilometer monitoring information is used to interpret the air pollution near the ground. The information about atmospheric layering is continuously monitored by uninterrupted remote sensing measurements with the Vaisala ceilometer CL51 which is an eye-safe commercial mini-lidar system. Special software for this ceilometer provides routine retrievals of lower atmosphere layering from vertical profiles of laser backscatter data. An intensive measurement period during the winter 2011/2012 is studied. The meteorological influences upon air pollutant concentrations are investgated and the correlations of air pollutant concentrations with ceilometer MLH are determined. Benzene was detected by department of Applied Climatology and Landscape Ecology, University of Duisburg-Essen (UDE) with a gas chromatograph during the measurement period. The meteorological data are collected by UDE and the monitoring station Essen of the German national meteorological service DWD. The concentrations of the air pollutants NO, NO2 and PM10 are provided by the national air pollution network LANUV.

  1. Arctic Cloud-driven Mixed Layers and Surface Coupling State

    NASA Astrophysics Data System (ADS)

    Shupe, M.; Persson, O. P.; Solomon, A.; de Boer, G.

    2013-12-01

    Arctic low-level clouds interact with the atmosphere and underlying surface via many inter-related processes. The balance of cloud radiative warming and cooling effects imparts a strong control on the net surface energy budget. Cloud-driven atmospheric circulations can impact surface turbulent heat fluxes and influence the vertical mixing of atmospheric state parameters and aerosols. Large-scale advection of heat and moisture provides the background context within which these local interactions unfold. Importantly, these radiative, dynamical, and advective processes also contribute to a complex web of self-sustaining cloud processes that can promote cloud maintenance over long periods of time. We examine many of these processes, with a specific focus on the dynamical linkages between Arctic clouds and the surface that influence low-level atmospheric structure and mixing. Comprehensive, ground-based observations from meteorological towers, remote-sensors, and radiosondes are used to simultaneously characterize surface fluxes, atmospheric structure, cloud properties, in-cloud motions, and the depth of the cloud-driven mixed layer in multiple Arctic environments. Relationships among these parameters are explored to elucidate the properties of the system that determine the degree of vertical atmospheric mixing and the coupling state between cloud and surface. The influence of temperature and moisture inversions on this system is also explored. Transitions in the coupling state are utilized to illustrate the relative roles of different processes. Cases from a coastal Arctic site at Barrow, Alaska and a station embedded in the Arctic sea-ice pack are used to contrast conditional influences related to season and surface type. It is found that over sea-ice, where surface turbulent fluxes are weak, the coupling of cloud-level processes to the surface layer is largely due to proximity of the cloud-driven mixed layer to the surface, which appears to be primarily influenced by

  2. Transient evolution and high stratification scaling in horizontal mixing layers

    NASA Astrophysics Data System (ADS)

    Arratia, C.; Ortiz, S.; Chomaz, J. M.

    Mixing layers (sheared flows in homogeneous or stratified fluid) are present in many geophysical contexts and may lead to turbulence and mixing. In several cases, mixing layers are known to exhibit the Kelvin-Helmholtz instability leading to the roll-up of spanwise vortices, the Kelvin-Helmholtz (KH) billows. This is an essentially two-dimensional (2D) process. In fact, in the homogeneous cases the Squire's theorem implies that the most unstable mode is 2D. However, Squire's theorem applies only for the exponentially growing perturbations that control the large time dynamics and is not valid for the transient dynamics at short time. Indeed, Iams et al.[1] have shown that, in the non-stratified case, the most amplified optimal perturbations for short times are three-dimensional (3D) and result from a cooperation between the lift-up and Orr mechanisms[2]. This provides a finite time mechanism for spanwise scale selection, scale that may persist at later times if nonlinearities are strong enough.

  3. Direct numerical simulation of reacting scalar mixing layers

    NASA Astrophysics Data System (ADS)

    de Bruyn Kops, S. M.; Riley, J. J.; Kosály, G.

    2001-05-01

    Understanding the passive reaction of two chemical species in shear-free turbulence with order unity Schmidt number is important in atmospheric and turbulent combustion research. The canonical configuration considered here is the reacting scalar mixing layer; in this problem two initially separated species mix and react downstream of a turbulence generating grid in a wind tunnel. A conserved scalar in this flow is, with some restrictions, analogous to temperature in a thermal mixing layer, and considerable laboratory data are available on the latter. In this paper, results are reported from high resolution, direct numerical simulations in which the evolution of the conserved scalar field accurately matches that of the temperature field in existing laboratory experiments. Superimposed on the flow are passive, single-step reactions with a wide range of activation energies and stoichiometric ratios (r). The resulting data include species concentrations as a function of three spatial dimensions plus time, and statistical moments and spectra of all species. Several aspects of the flow are investigated here with the conclusions that (1) reactions in which r≠1 are more accurately modeled by frozen and equilibrium chemistry limits than are reactions in which r=1, (2) an existing definition of a reduced Damköhler number that includes temperature and stoichiometry effects is a useful measure of reaction rate, and (3) existing theoretical models for predicting the coherence and phase of fuel-oxidizer cross-spectra and the spectrum of the equilibrium fuel mass fraction when r=1 yield accurate predictions.

  4. Pressure-based real-time measurements in compressible free shear layers

    NASA Technical Reports Server (NTRS)

    Samimy, M.; Elliott, G. S.; Reeder, M. F.

    1990-01-01

    A preliminary experimental study has been conducted to gain insight into the temporal and spatial contents of largescale structures in a convective Mach number = 0.51 high Reynolds number planar two-dimensional compressible free shear layer. Power spectra, coherence, and space-time correlations were obtained using single- and two-point pressure measurements. Both developing and fully developed regions of the flow were investigated. The passage frequency of structures were found to be 10-15 kHz in the developing region and 4-8 kHz in the fully developed region. The convective velocity obtained from the space-time correlation in the middle of the shear layer was close to the theoretical value but varied toward the edge of the shear layer. The structures were shown to be surprisingly three-dimensional even in this low compressibility level shear layer. The structures size and spacing were also determined and discussed.

  5. Goertler instability in compressible boundary layers along curved surfaces with suction and cooling

    NASA Technical Reports Server (NTRS)

    El-Hady, N.; Verma, A. K.

    1982-01-01

    The Goertler instability of the laminar compressible boundary layer flows along concave surfaces is investigated. The linearized disturbance equations for the three-dimensional, counter-rotating streamwise vortices in two-dimensional boundary layers are presented in an orthogonal curvilinear coordinate. The basic approximation of the disturbance equations, that includes the effect of the growth of the boundary layer, is considered and solved numerically. The effect of compressibility on critical stability limits, growth rates, and amplitude ratios of the vortices is evaluated for a range of Mach numbers for 0 to 5. The effect of wall cooling and suction of the boundary layer on the development of Goertler vortices is investigated for different Mach numbers.

  6. 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.

  7. 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.

  8. Heat Transfer in the Turbulent Boundary Layer of a Compressible Gas at High Speeds

    NASA Technical Reports Server (NTRS)

    Frankl, F.

    1942-01-01

    The Reynolds law of heat transfer from a wall to a turbulent stream is extended to the case of flow of a compressible gas at high speeds. The analysis is based on the modern theory of the turbulent boundary layer with laminar sublayer. The investigation is carried out for the case of a plate situated in a parallel stream. The results are obtained independently of the velocity distribution in the turbulent boundar layer.

  9. A Critical Compilation of Compressible Turbulent Boundary Layer Data

    DTIC Science & Technology

    1977-06-01

    profile boundary conditions has been accepted, The source 11 data were reduced assuming an iso -energetic boundary layer and Sutherland’s viscosity law...SP#0I W.’#MN-0a ?.9000"ItO 1.0000 Ale0~f0 4 0.1 ISO 1.13 0 6 0 3 .S1I0+02 2.1337s0#0 70040o4QI 2.1530 1 .0000 4.k23Z".n3 I .oo-0 140 ! I.54.40 1.534.1...12 basis of iso -energetic flow. The editors have replaced this assumption with the van Driest / Crocco temperature-velocity correlation assuminq an

  10. An analysis of the stability of the compressible Ekman boundary layer

    NASA Astrophysics Data System (ADS)

    Spall, J. R.; Wood, H. G., III

    1984-12-01

    The linear stability problem for the compressible Ekman boundary layer common to rotating fluids is formulated and the stability properties determined numerically. Three classes of unstable waves are identified (called class A, B, and C), their properties are described. The class C waves have only recently been reported in the literature and are present only in compressible Ekman boundary layers. Most of the calculations presented here are for uranium hexafluoride gas; however, critical Reynolds numbers are also computed for air and ammonia gas. Compressibility is generally found to decrease the critical Reynolds number for each class of wave. A comparison of results for the three different gases shows the stability to be largely unaffected by changes in the gas properties. Maximum growth rate calculations for each wave show the class A and B waves to be the dominant instabilities.

  11. An analysis of the stability of the compressible Ekman boundary layer

    NASA Technical Reports Server (NTRS)

    Spall, J. R.; Wood, H. G., III

    1984-01-01

    The linear stability problem for the compressible Ekman boundary layer common to rotating fluids is formulated and the stability properties determined numerically. Three classes of unstable waves are identified (called class A, B, and C), their properties are described. The class C waves have only recently been reported in the literature and are present only in compressible Ekman boundary layers. Most of the calculations presented here are for uranium hexafluoride gas; however, critical Reynolds numbers are also computed for air and ammonia gas. Compressibility is generally found to decrease the critical Reynolds number for each class of wave. A comparison of results for the three different gases shows the stability to be largely unaffected by changes in the gas properties. Maximum growth rate calculations for each wave show the class A and B waves to be the dominant instabilities.

  12. Effect of Different Mixing and Placement Methods on the Compressive Strength of Calcium-Enriched Mixture

    PubMed Central

    Sahebi, Safoora; Sadatshojaee, Nooshin; Jafari, Zahra

    2015-01-01

    Introduction: The aim of this experimental laboratory study was to evaluate the effect of different mixing and placement techniques on compressive strength (CS) of calcium-enriched mixture (CEM) cement. Methods and Materials: CEM powder was mixed with its liquid either by hand mixing or amalgamator mixing. The mixture was loaded to cylindrical acrylic molds with 6.0±0.1 mm height and 4.0±1 mm diameter. Half of the specimens in each group were selected randomly and ultrasonic energy was applied to them for 30 sec. All samples were incubated for 7 days at 37°C. The CS test was performed by means of a universal testing machine. The data were analyzed by the two-way analysis of variance (ANOVA) and Tukey’s post hoc tests. The level of significance was set at 0.05. Results: The maximum CS was seen in the amalgamator-mixed samples that did not receive ultrasonic agitation. The CS value of amalgamator-mixed samples was significantly higher than manually-mixed ones (P=0.003). Ultrasonic vibration did not change the CS of specimens. Conclusion: According to the results, mixing with amalgamator increases the CS of CEM cement, while ultrasonic vibration had no positive effect. PMID:25834593

  13. Dynamic Negative Compressibility of Few-Layer Graphene, h-BN, and MoS2

    NASA Astrophysics Data System (ADS)

    Neves, Bernardo; Barboza, Ana Paula; Chacham, Helio; Oliveira, Camilla; Fernandes, Thales; Martins Ferreira, Erlon; Archanjo, Braulio; Batista, Ronaldo; Oliveira, Alan

    2013-03-01

    We report a novel mechanical response of few-layer graphene, h-BN, and MoS2 to the simultaneous compression and shear by an atomic force microscope (AFM) tip. The response is characterized by the vertical expansion of these two-dimensional (2D) layered materials upon compression. Such effect is proportional to the applied load, leading to vertical strain values (opposite to the applied force) of up to 150%. The effect is null in the absence of shear, increases with tip velocity, and is anisotropic. It also has similar magnitudes in these solid lubricant materials (few-layer graphene, h-BN, and MoS2), but it is absent in single-layer graphene and in few-layer mica and Bi2Se3. We propose a physical mechanism for the effect where the combined compressive and shear stresses from the tip induce dynamical wrinkling on the upper material layers, leading to the observed flake thickening. The new effect (and, therefore, the proposed wrinkling) is reversible in the three materials where it is observed.[2] Financial support from CNPq, Fapemig, Rede Nacional de Pesquisa em Nanotubos de Carbono and INCT-Nano-Carbono

  14. 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.

  15. 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.

  16. A lossless compression method based on mix coding and IWT for MODIS image

    NASA Astrophysics Data System (ADS)

    Ren, Ruizhi; Guo, Shuxu; Gu, Lingjia; Wang, Lang; Wang, Xu

    2009-08-01

    In order to effectively store and transmit MODIS multispectral data, a lossless compression method based on mix coding and integer wavelet transform (IWT) is proposed in this paper. Firstly, the algorithm computes the correlation coefficients between spectrums in MODIS data. Using proper coefficient threshold, the original bands will be divided two groups: one group use spectral prediction method and then compress residual error, while the other group data is directly compressed by some standard compressor. For the spectral prediction group, we can find the current band that has greatest correlation with the previous band by the judgments of correlation coefficient, thus the optimal spectral prediction sequence is obtained by band reordering. The prediction band data can be computed with the previous band data and optimal linear predictor, so the spectral redundancy can be eliminated by using spectral prediction. In order to reduce residual differences in further, the block optimal linear predictor is designed in this paper. Next, except for the first band of the spectral prediction sequence, the residual errors of other bands are encoded by IWT and SPIHT. The direct compression bands and the first band of spectral prediction sequence are compressed by JPEG2000. Finally, the coefficients of block optimal linear predictor and other side information are encoded by adaptive arithmetic coding. The experimental results show that the proposed method is efficient and practical for MODIS data.

  17. Computer program for calculating laminar, transitional, and turbulent boundary layers for a compressible axisymmetric flow

    NASA Technical Reports Server (NTRS)

    Albers, J. A.; Gregg, J. L.

    1974-01-01

    Finite-difference computer program calculates viscous compressible boundary layer flow over either planar or axisymmetric surfaces. Flow may be initially laminar and progress through transitional zone to fully turbulent flow, or it may remain laminar, depending on imposed boundary conditions, laws of viscosity, and numerical solution of momentum and energy equations.

  18. Optical Properties of Compressible Inhomogeneous Shear Layers Relevant to High Power Lasers.

    DTIC Science & Technology

    1987-04-30

    191 615 OPTICAL PROPERTIES OF COMPRESSIBLE INb4ONOGENEOUS SHEAR 1/1 LAYERS RELEVANT TO HIGH PONER LASERS(U) WASHINGTON UNIV SEATTLE II H...so that a near-diffraction- limited laser beam may be attained. With the general trend of laser development towards shorter wavelengths, the fluid

  19. Large-eddy simulation of a turbulent mixing layer

    NASA Technical Reports Server (NTRS)

    Mansour, N. N.; Ferziger, J. H.; Reynolds, W. C.

    1978-01-01

    The three dimensional, time dependent (incompressible) vorticity equations were used to simulate numerically the decay of isotropic box turbulence and time developing mixing layers. The vorticity equations were spatially filtered to define the large scale turbulence field, and the subgrid scale turbulence was modeled. A general method was developed to show numerical conservation of momentum, vorticity, and energy. The terms that arise from filtering the equations were treated (for both periodic boundary conditions and no stress boundary conditions) in a fast and accurate way by using fast Fourier transforms. Use of vorticity as the principal variable is shown to produce results equivalent to those obtained by use of the primitive variable equations.

  20. 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.

  1. Study of atmospheric aerosols and mixing layer by LIDAR.

    PubMed

    Angelini, Federico; Barnaba, Francesca; Landi, Tony Christian; Caporaso, Luca; Gobbi, Gian Paolo

    2009-12-01

    The LIDAR (laser radar) is an active remote sensing technique, which allows for the altitude-resolved observation of several atmospheric constituents. A typical application is the measurement of the vertically resolved aerosol optical properties. By using aerosol particles as a marker, continuous determination of the mixing layer height (MLH) can also be obtained by LIDAR. Some examples of aerosol extinction coefficient profiles and MLH extracted from a 1-year LIDAR data set collected in Milan (Italy) are discussed and validated against in situ data (from a balloon-borne optical particle counter). Finally a comparison of the observation-based MLH with relevant numerical simulations (mesoscale model MM5) is provided.

  2. 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.

  3. Weakly nonlinear models for turbulent mixing in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Liou, William W.; Morris, Philip J.

    1992-01-01

    New closure models for turbulent free shear flows are presented in this paper. They are based on a weakly nonlinear theory with a description of the dominant large-scale structures as instability waves. Two models are presented that describe the evolution of the free shear flows in terms of the time-averaged mean flow and the dominant large-scale turbulent structure. The local characteristics of the large-scale motions are described using linear theory. Their amplitude is determined from an energy integral analysis. The models have been applied to the study of an incompressible mixing layer. For both models, predictions of the mean flow developed are made. In the second model, predictions of the time-dependent motion of the large-scale structures in the mixing layer are made. The predictions show good agreement with experimental observations.

  4. Weakly nonlinear models for turbulent mixing in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Liou, William W.; Morris, Philip J.

    1992-01-01

    New closure models for turbulent free shear flows are presented in this paper. They are based on a weakly nonlinear theory with a description of the dominant large-scale structures as instability waves. Two models are presented that describe the evolution of the free shear flows in terms of the time-averaged mean flow and the dominant large-scale turbulent structure. The local characteristics of the large-scale motions are described using linear theory. Their amplitude is determined from an energy integral analysis. The models have been applied to the study of an incompressible mixing layer. For both models, predictions of the mean flow developed are made. In the second model, predictions of the time-dependent motion of the large-scale structures in the mixing layer are made. The predictions show good agreement with experimental observations.

  5. Three-dimensional wave packets in a compressible boundary layer

    NASA Astrophysics Data System (ADS)

    Forgoston, Eric; Tumin, Anatoli

    2006-10-01

    A three-dimensional wave packet generated by a local disturbance in a two-dimensional hypersonic boundary layer flow is studied with the aid of the previously solved initial-value problem. The solution to this problem can be expanded in a biorthogonal eigenfunction system as a sum of modes consisting of continuous and discrete spectra of temporal stability theory. A specific disturbance consisting of an initial temperature spot is considered, and the receptivity to this initial temperature spot is computed for both the two-dimensional and three-dimensional cases. Using previous analysis of the discrete and continuous spectrum, the inverse Fourier transform is computed numerically. The two-dimensional inverse Fourier transform is calculated for two discrete modes: Mode F and Mode S. The Mode S result is compared with an asymptotic approximation of the Fourier integral, which is obtained using the Gaussian model as well as the method of steepest descent. It is shown that the method of steepest descent provides an excellent approximation to the more computationally intensive numerical evaluation of the inverse Fourier transform. Additionally, the three-dimensional inverse Fourier transform is found using an asymptotic approximation of the Fourier integral. A main feature of the resulting three-dimensional wave packet is its two-dimensional nature, which arises from an association of Mode S with Mack's second mode.

  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. Self-assembled polyelectrolyte complexes films as efficient compression coating layers for controlled-releasing tablets.

    PubMed

    Li, Wenyan; Huo, Mengmeng; Sen Chaudhuri, Arka; Yang, Chen; Cao, Dazhong; Wu, Zhenghong; Qi, Xiaole

    2017-05-01

    Currently, polysaccharide-based hydrogels are widely studied macromolecular networks to modify drug dissolution from controlled-releasing matrix tablets. Among them, polyelectrolyte complexes (PEC) films consisted of chitosan (CS) and sodium alginate (SA) could be obtained via spontaneously assembling under physiological gastrointestinal environment. Here, we utilized these self-assembled PEC films as an efficient coating materials to develop controlled-released matrix tablets through compression coating process, with paracetamol (APAP) as model drug. The constitutive and morphology characteristic studies on these PEC films illustrated that the mixture of CS and SA with the weight ratio of 1:1 would be an promising outer layer for compression-coating tablets. In addition, the in vitro drug releasing behavior experiments demonstrated that the optimized compression coating tablets displayed satisfied zero-order drug releasing profits. Furthermore, the in vivo pharmacokinetic studies of these APAP loaded compression-coated tablets in New Zealand rabbits gave that the Tmax (12.32 ± 1.05 h) was significantly prolonged (p < 0.01), compared to that (0.89 ± 0.26 h) of common APAP tablets (Jinfuning(®)) after oral administration. These studies suggest that the compression-coated tablets with self-assembled PEC film as coating outer layer may be a promising strategy for peroral controlled release delivery system of water soluble drugs.

  8. The spatial evolution of the mixing layer in the Kelvin-Helmholtz instability at the Martian ionopause

    NASA Astrophysics Data System (ADS)

    Aizawa, Sae; Terada, Naoki; Kasaba, Yasumasa; Yagi, Manabu; Matsumoto, Yosuke; Delcourt, Dominique

    2017-04-01

    We investigate the growth of the mixing layer thickness in the Kelvin-Helmholtz instability (KHI) using an extended-local MHD model to estimate the ion loss rate from the Martian ionopause. The KHI is expected to play a major role in transporting mass, momentum and energy across the ionopause between the sheath flow and ionospheric plasmas. Since the mixing layer has a finite thickness between them, this layer has a potential for the removal of a huge amount of ions from Mars through its history. The recent MAVEN observation reported that the density ratio across the ionopause reaches as high as 100 5000. With such a large density ratio, compressible effects are expected to modify the structure of the KH vortices and the evolution of the mixing layer by generating high-amplitude nonlinear fast-mode plane waves from ridges of the KH waves. In order to reproduce Martian ionopause, we developed an extended-local MHD model with aperiodic boundary condition for the evaluation of traveling waves along the dayside Martian ionopause ( 6,000km). Spatial resolution is set with 3km to resolve the thin mixing layer. We find two factors that accelerate the growth of the mixing layer. Firstly, the KH wave with the fastest growing mode behaves like a wall to the leading vortex in the aperiodic condition. The sheath flow is stagnated by this wall-like structure and induces an enhanced vortex return flow, resulting in a deeper excavation of the ionospheric plasma. Secondly, fast-mode rarefaction waves generated by compressible effects make wall-like structures more effective by lowering pressure around antinodes of the KH waves. Such a pressure profile further accelerates the stagnation and the excavation. In addition, KH vortices are merging not one by one but also some vortices are merged together at time. Thus, the large wave like structure can be seen when the effect of compressibility is not so large. The mixing layer spread with the lapse of time and it depends on the density

  9. 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)

  10. 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.

  11. 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.

  12. Mixing layer height as an indicator for urban air quality?

    NASA Astrophysics Data System (ADS)

    Geiß, Alexander; Wiegner, Matthias; Bonn, Boris; Schäfer, Klaus; Forkel, Renate; von Schneidemesser, Erika; Münkel, Christoph; Chan, Ka Lok; Nothard, Rainer

    2017-08-01

    The mixing layer height (MLH) is a measure for the vertical turbulent exchange within the boundary layer, which is one of the controlling factors for the dilution of pollutants emitted near the ground. Based on continuous MLH measurements with a Vaisala CL51 ceilometer and measurements from an air quality network, the relationship between MLH and near-surface pollutant concentrations has been investigated. In this context the uncertainty of the MLH retrievals and the representativeness of ground-based in situ measurements are crucial. We have investigated this topic by using data from the BAERLIN2014 campaign in Berlin, Germany, conducted from June to August 2014. To derive the MLH, three versions of the proprietary software BL-VIEW and a novel approach COBOLT were compared. It was found that the overall agreement is reasonable if mean diurnal cycles are considered. The main advantage of COBOLT is the continuous detection of the MLH with a temporal resolution of 10 min and a lower number of cases when the residual layer is misinterpreted as mixing layer. We have calculated correlations between MLH as derived from the different retrievals and concentrations of pollutants (PM10, O3 and NOx) for different locations in the metropolitan area of Berlin. It was found that the correlations with PM10 are quite different for different sites without showing a clear pattern, whereas the correlation with NOx seems to depend on the vicinity of emission sources in main roads. In the case of ozone as a secondary pollutant, a clear correlation was found. We conclude that the effects of the heterogeneity of the emission sources, chemical processing and mixing during transport exceed the differences due to different MLH retrievals. Moreover, it seems to be unrealistic to find correlations between MLH and near-surface pollutant concentrations representative for a city like Berlin (flat terrain), in particular when traffic emissions are dominant. Nevertheless it is worthwhile to use

  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. 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.

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

    DOE PAGES

    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. A noniterative finite difference method for the compressible unsteady laminar boundary layer

    NASA Astrophysics Data System (ADS)

    Chang, K. S.; Kim, J. S.

    1985-11-01

    An investigation involving the determination of the friction drag and the rate of heat transfer at the surface of a body in dynamic motion must take into account details regarding the unsteady viscous flow. Difficulties concerning such an investigation are related to interaction effects due to aspects of increased dimensionality, nonlinearity, and compressibility. In the present study, the nonlinearity is eliminated by making use of approaches considered by Beam and Warming (1978) and Orlandi and Ferziger (1981). These approaches involve the employment of a technique of linearizing the general nonlinear implicit finite difference equations without sacrificing accuracy. A noniterative numerical formulation is developed to solve the unsteady compressible laminar boundary layer equations efficiently.

  17. Effect of a Shear Layer on the Stability of an Axisymmetric External Compression Air Intake,

    DTIC Science & Technology

    1985-10-21

    ID , E = OF A SHEAR LAY ON THE STABILITY OF AN AXISYI4~M=C EXTERNAL QYM2RESSION AIR INTAKE by Z. Kunyuan, Y. Shaozhi, P. Chenyi Approved for public...t 110E 4 EFFECT OF A SItEAR LAYER ON THE STABILITY OF AN AXISYMMETRICEXTERNAL COMPRESSION AIR INTAKE Zhang Kunyuan, Yu Shaozhi, Peng Chenyi (Nanjing...positions on the stability of a variable center cone external compression air intake under the condition of a M 1.72 incident stream. It was experimentally

  18. Turbulence and mixing in the stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Yagüe, C.; Morales, G.; Terradellas, E.; Cuxart, J.

    2003-04-01

    Transport and mixing in the Stable Atmospheric Boundary Layer is not well understood yet. However this is an important feature in atmospheric pollution as well as in other environmental studies. A Stable Atmospheric Boundary Layer Experiment in Spain (SABLES98) took place from the 10th to the 28th of September 1998. Two masts (100 m and 10 m) were instrumented with five sonic anemometers, 14 thermocouples, 8 cup anemometers, vanes,radiometers, etc. In addition, a sodar, a tethered balloon and a triangular array of cup anemometers were operating during the campaign. The experiment showed three different regimes, being specially interesting the one between 14th and 21st of September where stable and very stable conditions were present. In this work we present the behaviour of turbulent and stability parameters at several heights. The different evolutions of the Nocturnal Boundary Layer and the main parameters that controle its behaviour are discussed.The influence of internal gravity waves and their interaction with turbulence is also studied using wavelets.

  19. 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.

  20. 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

  1. Optimal Linear Fitting for Objective Determination of Ocean Mixed Layer Depth from Glider Profiles

    DTIC Science & Technology

    2010-09-06

    profile is around 1 m . All the profiles are deeper than 700 m and clearly show the existence of layered structure: mixed layer, thermocline, and deep...controlled profiles observed by the two Seagliders. With high vertical resolution (1 m ), we chose n 5 4. The value of Hmix was calculated for each...compared to the fluctuations in the mixed layer depth observed after this date. The mixed layer depth oscillates between 50 and 90 m before 25 November 2007

  2. Atomic layer deposition of metal oxide patterns on nonwoven fiber mats using localized physical compression.

    PubMed

    Sweet, William J; Oldham, Christopher J; Parsons, Gregory N

    2014-06-25

    Patterning is an essential part of many industrial processes from printing to semiconductor manufacturing. In this work, we demonstrate a new method to pattern and selectively coat nonwoven textiles by atomic layer deposition (ALD) using compressive mask patterning. A physical mask combined with mechanical compression allows lateral definition and fidelity of the ALD coating to be controlled. We produce features of several sizes on different nonwoven fiber materials and demonstrate the ability to limit diffusion effects to within <200 μm of the pattern edge. Lateral and vertical penetration of reactive growth species into nonwoven mats is investigated by plan-view and cross-sectional imaging. Vertical growth is also analyzed by imaging coating depth into fiber mat stacks. We develop a fully quantitative transport model that describes well the effect of fiber structure and mechanical compression on the extent of coating under the physical mask. This method could be implemented for high-volume patterning for applications including flexible electronics.

  3. Generalized wall function and its application to compressible turbulent boundary layer over a flat plate

    NASA Astrophysics Data System (ADS)

    Liu, J.; Wu, S. P.

    2017-04-01

    Wall function boundary conditions including the effects of compressibility and heat transfer are improved for compressible turbulent boundary flows. Generalized wall function formulation at zero-pressure gradient is proposed based on coupled velocity and temperature profiles in the entire near-wall region. The parameters in the generalized wall function are well revised. The proposed boundary conditions are integrated into Navier-Stokes computational fluid dynamics code that includes the shear stress transport turbulence model. Numerical results are presented for a compressible boundary layer over a flat plate at zero-pressure gradient. Compared with experimental data, the computational results show that the generalized wall function reduces the first grid spacing in the directed normal to the wall and proves the feasibility and effectivity of the generalized wall function method.

  4. 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.

  5. 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.

  6. A theoretical study of ignition in the laminar mixing layer

    SciTech Connect

    Law, C.K.; Law, H.K.

    1981-01-01

    The structure of the weakly-reactive states leading to ignition in the laminar mixing layer flow is studied both analytically and numerically. It is shown that the flow consists of a reactive region and a self-similar frozen region separated by a transitional, non-similar frozen region that the reactive region is intrinsically non-similar because of its excessively slow diffusion rate and that the ignition characteristics are primarily governed by the velocity of the hot stream and therefore minimally dependent on the velocity distribution. Fundamental functional groups are identified and an explicit prescription is presented, for large activation energy reactions, for the evaluation of the minimum streamwise distance to achieve ignition.

  7. Local structures around the substituted elements in mixed layered oxides

    PubMed Central

    Akama, Shota; Kobayashi, Wataru; Amaha, Kaoru; Niwa, Hideharu; Nitani, Hiroaki; Moritomo, Yutaka

    2017-01-01

    The chemical substitution of a transition metal (M) is an effective method to improve the functionality of a material, such as its electrochemical, magnetic, and dielectric properties. The substitution, however, causes local lattice distortion because the difference in the ionic radius (r) modifies the local interatomic distances. Here, we systematically investigated the local structures in the pure (x = 0.0) and mixed (x = 0.05 or 0.1) layered oxides, Na(M1−xM′x)O2 (M and M′ are the majority and minority transition metals, respectively), by means of extended X-ray absorption fine structure (EXAFS) analysis. We found that the local interatomic distance (dM-O) around the minority element approaches that around the majority element to reduces the local lattice distortion. We further found that the valence of the minority Mn changes so that its ionic radius approaches that of the majority M. PMID:28252008

  8. Vortex simulation of three-dimensional mixing layers

    NASA Technical Reports Server (NTRS)

    Inoue, Osamu

    1987-01-01

    Spanwise structures of 'nominally' two-dimensional (2D), spatially growing, turbulent mixing layers are simulated numerically by a three-dimensional (3D) vortex method. Small-amplitude 3D disturbances are introduced into an otherwise 2D flow field. Results show that a large-scale spanwise variation of the flow field is produced because of amplification of initial disturbances. Pairs of counterrotating streamwise vortices are formed as a result of stretching of primary spanwise vortices. The streamwise vortices are formed at a fixed spanwise location which depends on initial disturbances. The calculated magnitude of streamwise vorticity is close to that of the spanwise vorticity. The results also suggest that the presence of background disturbances may be essential for the formation of streamwise vortices. The results are in good qualitative agreement with experiments.

  9. Local structures around the substituted elements in mixed layered oxides

    NASA Astrophysics Data System (ADS)

    Akama, Shota; Kobayashi, Wataru; Amaha, Kaoru; Niwa, Hideharu; Nitani, Hiroaki; Moritomo, Yutaka

    2017-03-01

    The chemical substitution of a transition metal (M) is an effective method to improve the functionality of a material, such as its electrochemical, magnetic, and dielectric properties. The substitution, however, causes local lattice distortion because the difference in the ionic radius (r) modifies the local interatomic distances. Here, we systematically investigated the local structures in the pure (x = 0.0) and mixed (x = 0.05 or 0.1) layered oxides, Na(M1-xM‧x)O2 (M and M‧ are the majority and minority transition metals, respectively), by means of extended X-ray absorption fine structure (EXAFS) analysis. We found that the local interatomic distance (dM-O) around the minority element approaches that around the majority element to reduces the local lattice distortion. We further found that the valence of the minority Mn changes so that its ionic radius approaches that of the majority M.

  10. Direct numerical simulations of supercritical fluid mixing layers applied to heptane nitrogen

    NASA Astrophysics Data System (ADS)

    Miller, Richard S.; Harstad, Kenneth G.; Bellan, Josette

    2001-06-01

    Direct numerical simulations (DNS) are conducted of a model hydrocarbon nitrogen mixing layer under supercritical conditions. The temporally developing mixing layer configuration is studied using heptane and nitrogen supercritical fluid streams at a pressure of 60 atm as a model system related to practical hydrocarbon-fuel/air systems. An entirely self-consistent cubic Peng Robinson equation of state is used to describe all thermodynamic mixture variables, including the pressure, internal energy, enthalpy, heat capacity, and speed of sound along with additional terms associated with the generalized heat and mass transport vectors. The Peng Robinson formulation is based on pure-species reference states accurate to better than 1% relative error through comparisons with highly accurate state equations over the range of variables used in this study (600 [less-than-or-eq, slant] T [less-than-or-eq, slant] 1100 K, 40 [less-than-or-eq, slant] p [less-than-or-eq, slant] 80 atm) and is augmented by an accurate curve fit to the internal energy so as not to require iterative solutions. The DNS results of two-dimensional and three-dimensional layers elucidate the unique thermodynamic and mixing features associated with supercritical conditions. Departures from the perfect gas and ideal mixture conditions are quantified by the compression factor and by the mass diffusion factor, both of which show reductions from the unity value. It is found that the qualitative aspects of the mixing layer may be different according to the specification of the thermal diffusion factors whose value is generally unknown, and the reason for this difference is identified by examining the second-order statistics: the constant Bearman Kirkwood (BK) thermal diffusion factor excites fluctuations that the constant Irwing Kirkwood (IK) one does not, and thus enhances overall mixing. Combined with the effect of the mass diffusion factor, constant positive large BK thermal diffusion factors retard

  11. 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

  12. Dynamic study of compressed electron layer driven by linearly polarized laser

    NASA Astrophysics Data System (ADS)

    Feng-chao, Wang

    2016-05-01

    The dynamics of the compressed electron layer (CEL) are investigated when a linearly polarized (LP) laser pulse irradiates a plasma target. The turbulent motion of the CEL is investigated by a simple model, which is verified by particle-in-cell (PIC) simulations. It is found that the compressed layer disperses in a few cycles of the laser duration, because the CEL comes back with a large velocity in the opposite direction of the laser incident. A larger wavelength laser can be used to tailor the proton beam by reducing the turbulence of the CEL in the region of the LP laser acceleration. Project supported by the Shanghai Provincial Special Foundation for Outstanding Young Teachers in University, China (Grant No. yyy10043).

  13. Skin friction and velocity profile family for compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Huang, P. G.; Bradshaw, P.; Coakley, T. J.

    1993-01-01

    The paper presents a general approach to constructing mean velocity profiles for compressible turbulent boundary layers with isothermal or adiabatic walls. The theory is based on a density-weighted transformation that allows the extension of the incompressible similarity laws of the wall to the compressible regions. The velocity profile family is compared to a range of experimental data, and excellent agreement is obtained. A self-consistent skin friction law, which satisfies the proposed velocity profile family, is derived and compared with the well-known Van Driest II theory for boundary layers in zero pressure gradient. The results are found to be at least as good as those obtained by using the Van Driest II transformation.

  14. Skin friction and velocity profile family for compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Huang, P. G.; Bradshaw, P.; Coakley, T. J.

    1993-01-01

    The paper presents a general approach to constructing mean velocity profiles for compressible turbulent boundary layers with isothermal or adiabatic walls. The theory is based on a density-weighted transformation that allows the extension of the incompressible similarity laws of the wall to the compressible regions. The velocity profile family is compared to a range of experimental data, and excellent agreement is obtained. A self-consistent skin friction law, which satisfies the proposed velocity profile family, is derived and compared with the well-known Van Driest II theory for boundary layers in zero pressure gradient. The results are found to be at least as good as those obtained by using the Van Driest II transformation.

  15. 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.

  16. 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.

  17. 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.

  18. Inertial particles in a shearless mixing layer: direct numerical simulations

    NASA Astrophysics Data System (ADS)

    Ireland, Peter; Collins, Lance

    2010-11-01

    Entrainment, the drawing in of external fluid by a turbulent flow, is present in nearly all turbulent processes, from exhaust plumes to oceanic thermoclines to cumulus clouds. While the entrainment of fluid and of passive scalars in turbulent flows has been studied extensively, comparatively little research has been undertaken on inertial particle entrainment. We explore entrainment of inertial particles in a shearless mixing layer across a turbulent-non-turbulent interface (TNI) and a turbulent-turbulent interface (TTI) through direct numerical simulation (DNS). Particles are initially placed on one side of the interface and are advanced in time in decaying turbulence. Our results show that the TTI is more efficient in mixing droplets than the TNI. We also find that without the influence of gravity, over the range of Stokes numbers present in cumulus clouds, particle concentration statistics are essentially independent of the dissipation scale Stokes number. The DNS data agrees with results from experiments performed in a wind tunnel with close parametric overlap. We anticipate that a better understanding of the role of gravity and turbulence in inertial particle entrainment will lead to improved cloud evolution predictions and more accurate climate models. Sponsored by the U.S. NSF.

  19. Analysis of distortion data from TF30-P-3 mixed compression inlet test

    NASA Technical Reports Server (NTRS)

    King, R. W.; Schuerman, J. A.; Muller, R. G.

    1976-01-01

    A program was conducted to reduce and analyze inlet and engine data obtained during testing of a TF30-P-3 engine operating behind a mixed compression inlet. Previously developed distortion analysis techniques were applied to the data to assist in the development of a new distortion methodology. Instantaneous distortion techniques were refined as part of the distortion methodology development. A technique for estimating maximum levels of instantaneous distortion from steady state and average turbulence data was also developed as part of the program.

  20. Application of a Reynolds Stress Turbulence Model to the Compressible Shear Layer

    DTIC Science & Technology

    1990-02-01

    source vector containing the terms causing production, destruc- tion and redistribution of the Reynolds stresses . To numerically obtain the solution...OTIC FiLE Copy W. . NASA Contractor Report 182002 ICASE Report No. 90-18 0 ZICASE APPLICATION OF A REYNOLDS STRESS TURBULENCE MODEL TO THE...Virginia 23665-5225 k L APPLICATION OF A REYNOLDS STRESS TURBULENCE . MODEL TO THE COMPRESSIBLE SHEAR LAYER S. Sarkar1 .1’eSo For Institute for

  1. 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.

  2. Nonparallel stability of three-dimensional compressible boundary layers. Part 1: Stability analysis

    NASA Technical Reports Server (NTRS)

    El-Hady, N. M.

    1980-01-01

    A compressible linear stability theory is presented for nonparallel three-dimensional boundary-layer flows, taking into account the normal velocity component as well as the streamwise and spanwise variations of the basic flow. The method of multiple scales is used to account for the nonparallelism of the basic flow, and equations are derived for the spatial evolution of the disturbance amplitude and wavenumber. The numerical procedure for obtaining the solution of the nonparallel problem is outlined.

  3. Zinc-impregnated and odour-control two-layer compression.

    PubMed

    Stephen-Haynes, Jackie; Callaghan, Rosie

    This article presents the results of 40 patients using two versions of a new two-layer compression system in a large primary care organisation. The evaluation was undertaken to explore the following areas formulary inclusion consideration: ease of use, clinical acceptability, clinical outcome and additional patient benefits of an alternative new low-profile bandage system containing zinc (n=30) and odour-control properties (n=10).

  4. Higher-order accurate Osher schemes with application to compressible boundary layer stability

    NASA Technical Reports Server (NTRS)

    Vandervegt, J. J. W.

    1993-01-01

    Two fourth order accurate Osher schemes are presented which maintain higher order accuracy on nonuniform grids. They use either a conservative finite difference or finite volume discretization. Both methods are successfully used for direct numerical simulations of flat plate boundary layer instability at different Mach numbers. Results of growth rates of Tollmien-Schlichting waves compare well with direct simulations of incompressible flow and for compressible flow with results obtained by solving the parabolic stability equations.

  5. 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.

  6. Lidar determination of mixing layer height with high resolution

    NASA Astrophysics Data System (ADS)

    Martucci, Giovanni; Matthey, Renaud; Mitev, Valentin; Richner, Hans

    2005-10-01

    Ecological monitoring and analysis of the planetary boundary layer (PBL) dynamics require determination of the mixing layer height (MLH) on a continuous basis. In a number of cases it is necessary to determine the MLH with sufficiently high resolution - both altitude and temporal. The backscatter lidar provides a convenient tool for such determination, using the aerosol as tracer and determining its vertical profile and its time-evolution, with the capability for continuous measurements. Although methods already exist, based on the altitude derivative of the backscatter lidar signal (altitude Gradient method) and its time-variance (Variance method), the application of these methods with high resolution is limited by the background noise presence. We report here a further development of backscatter lidar gradient and variance methods for MLH determination, allowing higher resolutions. In it, the MLH determination from the gradient and the variance of the lidar signal is supported by a convenient filter technique. Time scale of increased temporal resolution allows the investigation of the fine atmospheric dynamic structures like convective motion. A number of examples in MLH retrieval are presented. The examples are based on backscatter lidar measurements performed in the PBL above Neuchatel, Switzerland (47.00°N, 6.95°S, 485m asl). The examples show the applicability and the usefulness of the reported technique in measurements of the daily cycle of the MLH dynamics.

  7. Turbulent Mixing Layer Control using Ns-DBD Plasma Actuators

    NASA Astrophysics Data System (ADS)

    Singh, Ashish; Little, Jesse

    2016-11-01

    A low speed turbulent mixing layer (Reθo =1282, U1 /U2 = 0 . 28 and U2 = 11 . 8 m / s) is subject to nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation. The forcing frequency corresponds to a Strouhal number (St) of 0.032 which is the most amplified frequency based on stability theory. Flow response is studied as a function of the pulse energy, the energy input time scale (carrier frequency) and the duration of actuation (duty cycle). It is found that successful actuation requires a combination of forcing parameters. An evaluation of the forcing efficacy is achieved by examining different flow quantities such as momentum thickness, vorticity and velocity fluctuations. In accordance with past work, a dependence is found between the initial shear layer thickness and the energy coupled to the flow. More complex relationships are also revealed such as a limitation on the maximum pulse energy which yields control. Also, the pulse energy and the carrier frequency (inverse of period between successive pulses) are interdependent whereby an optimum exists between them and extreme values of either parameter is inconsonant with the control desired. These observations establish a rich and complex process behind ns-DBD plasma actuation. Air Force Office of Scientific Research (FA9550-12-1-0044).

  8. 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

  9. A Survey of Measurements and Measuring Techniques in Rapidly Distorted Compressible Turbulent Boundary Layers

    NASA Technical Reports Server (NTRS)

    Fernholz, H. H.; Finley, P. J.; Dussauge, J. P.; Smits, A. J.; Reshotko, E. (Editor)

    1989-01-01

    A wide range of recent work on compressible turbulent boundary layers is described. Special attention was paid to flows with rapid changes in pressure including flows with shock waves, curved walls, and expansions. The application of rapid distortion theory to flows transversing expansion and shock waves is reviewed. This is followed by an account of experiments aimed at elucidating the large scale structures present in supersonic boundary layers. The current status of laser-Doppler and hot-wire anemometry in supersonic flow is discussed, and a new interferometric technique for the determination of wall-stress is described. The use of small pressure transducers to deduce information about the structure of zero pressure-gradient and severely perturbed boundary layers is investigated. Finally, there is an extension of the data presentation of AGARDographs 223, 253 and 263 to cover rapidly distorted boundary layers.

  10. Instability of compressible boundary layers along curved walls with suction or cooling

    NASA Technical Reports Server (NTRS)

    El-Hady, N. M.; Verma, A. K.

    1982-01-01

    This paper investigates the effect of suction of the boundary layer and wall cooling on the growth and development of three-dimensional longitudinal vortices over concave walls. The study is carried out for compressible flows for a range of Mach numbers from 0 to 5. Despite indications that small suction or small cooling rates locally reduce the critical Goertler number (destabilize the boundary layer), the overall effect of suction or cooling is to stabilize the boundary layer by reducing the amplitude ratio of the vortices. In case of suction, this becomes more difficult with increasing Mach number unless high suction rates are used. On the other hand, stabilizing the boundary layer with respect to Goertler vortices can hardly be achieved by cooling even when high cooling rates are used.

  11. A Survey of Measurements and Measuring Techniques in Rapidly Distorted Compressible Turbulent Boundary Layers

    NASA Technical Reports Server (NTRS)

    Fernholz, H. H.; Finley, P. J.; Dussauge, J. P.; Smits, A. J.; Reshotko, E. (Editor)

    1989-01-01

    A wide range of recent work on compressible turbulent boundary layers is described. Special attention was paid to flows with rapid changes in pressure including flows with shock waves, curved walls, and expansions. The application of rapid distortion theory to flows transversing expansion and shock waves is reviewed. This is followed by an account of experiments aimed at elucidating the large scale structures present in supersonic boundary layers. The current status of laser-Doppler and hot-wire anemometry in supersonic flow is discussed, and a new interferometric technique for the determination of wall-stress is described. The use of small pressure transducers to deduce information about the structure of zero pressure-gradient and severely perturbed boundary layers is investigated. Finally, there is an extension of the data presentation of AGARDographs 223, 253 and 263 to cover rapidly distorted boundary layers.

  12. 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.

  13. Estimation of Atmospheric Mixing Layer Height from radiosonde data

    NASA Astrophysics Data System (ADS)

    Wang, X.; Wang, K.

    2013-12-01

    Mixing layer is the lowest layer of the troposphere where surface turbulence can reach during the daytime. Mixing layer height (MLH) is an important parameter for understanding the transport process, air pollution, weather and climate change. MLH can be determined from the radiosonde profiles of relative humidity (RH), specific humidity (q), potential temperature (θ) and atmospheric refractivity (N) by searching for the strongest gradients of these parameters within a specific height above the surface. However, substantially different MLHs have been found from different parameters. The occurrence of cloud impacts on MLHs derived in two ways: (1) clouds impact the measurements of θ and RH, resulting in spurious MLHs derived by θ and RH, (2) clouds may amplify or depress turbulence, that is MLH can be at cloud top or cloud base when it occurs. However, MLHs determined by existing methods can generally be at cloud top. To solve these problems, we propose a method to estimate MLH by integrating the information of θ, RH, q, N and discriminating different cloud impacts on MLH. We apply this method to high vertical resolution (~30 m) radiosonde data collected at the 79 stations over North America during the period of 1998 to 2008 released by the Stratospheric Processes and their Role in Climate Data Center. The results show good agreement with those from N as the information of temperature and humidity contained in N, however the impact of clouds including in the new method has increased the reliability of MLH. The new results show good agreement with independent MLH determined from Lidar observations. MLH over the North America is 1647×323 meter with a strong east-west gradient, higher MLH (generally greater than 1800 m) over the Midwest America and lower MLH (less than 1300 m) over Alaska and west coast of America. The scatter plot of climatological MLHnew with MLHθ, MLHRH, MLHq, MLHN and MLHint for the period of 1998 to 2008. Pattern of climatological MLH of our

  14. Laboratory simulations of the atmospheric mixed-layer in flow over complex topography

    EPA Science Inventory

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundar...

  15. Laboratory simulations of the atmospheric mixed-layer in flow over complex topography

    EPA Science Inventory

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundar...

  16. 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.

  17. 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.

  18. The spatial evolution of the mixing layer in the Kelvin-Helmholtz instability at the Martian ionopause

    NASA Astrophysics Data System (ADS)

    Aizawa, S.; Terada, N.; Kasaba, Y.; Yagi, M.; Matsumoto, Y.

    2016-12-01

    We investigate the growth of the mixing layer thickness in the Kelvin-Helmholtz (KH) instability using an extended-local MHD model to estimate the ion loss rate from the Martian ionopause. This instability is expected to play a major role in transporting mass, momentum and energy across the ionopause between the sheath flow and ionospheric plasmas. Since the mixing layer has a finite thickness between them, this layer has a potential for the removal of a huge amount of ions from Mars through its history. The recent MAVEN observation reported that the density ratio across the ionopause reaches as high as 100 5000. With such a large density ratio, compressible effects are expected to modify the structure of the KH vortices and the evolution of the mixing layer by generating high-amplitude nonlinear fast-mode plane waves from ridges of the KH waves. In order to reproduce a realistic Martian ionopause, we developed an extended-local MHD model with aperiodic boundary condition for the evaluation of traveling waves along the dayside Martian ionopause ( 6,000km). Spatial resolution is set with 3km to resolve the thin mixing layer. We find two factors that accelerate the growth of the mixing layer. Firstly, the KH wave with the fastest growing mode behaves like a wall to the leading vortex in the aperiodic condition. The sheath flow is stagnated by this wall-like structure and induces an enhanced vortex return flow, resulting in a deeper excavation of the ionospheric plasma. Secondly, fast-mode rarefaction waves generated by compressible effects make wall-like structures more effective by lowering pressure around antinodes of the KH waves. Such a pressure profile further accelerates the stagnation and the excavation. Thus, the mixing layer becomes about 1.5 times wider than that obtained from a periodic local model when the density ratio is 100. It indicates that more ionospheric plasmas will escape than expected. The ion loss rate drastically increases after reaching the

  19. 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.

  20. Further considerations on modeling the sea breeze with a mixed-layer model

    NASA Technical Reports Server (NTRS)

    Anthes, R. A.; Keyser, D.; Deardorff, J. W.

    1982-01-01

    Mixed-layer models have been used to simulate low-level flows under a variety of situations, including flow over complex terrain and in the vicinity of coastal zones. The advantage of mixed-layer models compared to multilevel models is their simplicity and minimal computational requirements. A disadvantage is that the atmosphere above the mixed layer is not modeled explicitly and approximations pertaining to this layer become necessary. This paper examines five approximations for treating this upper layer for a simple sea-breeze circulation. Approximating the flow immediately above the mixed-layer height h by the mixed-layer velocity and using this velocity to advect potential temperature above h gives a better simulation of the sea breeze than the approximation used by Anthes et al. (1980), which neglected horizontal advection at this level.

  1. 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

  2. Ignition of hydrogen/air mixing layer in turbulent flows

    SciTech Connect

    Im, H.G.; Chen, J.H.; Law, C.K.

    1998-03-01

    Autoignition of a scalar hydrogen/air mixing layer in homogeneous turbulence is studied using direct numerical simulation. An initial counterflow of unmixed nitrogen-diluted hydrogen and heated air is perturbed by two-dimensional homogeneous turbulence. The temperature of the heated air stream is chosen to be 1,100 K which is substantially higher than the crossover temperature at which the rates of the chain branching and termination reactions become equal. Three different turbulence intensities are tested in order to assess the effect of the characteristic flow time on the ignition delay. For each condition, a simulation without heat release is also performed. The ignition delay determined with and without heat release is shown to be almost identical up to the point of ignition for all of the turbulence intensities tested, and the predicted ignition delays agree well within a consistent error band. It is also observed that the ignition kernel always occurs where hydrogen is focused, and the peak concentration of HO{sub 2} is aligned well with the scalar dissipation rate. The dependence of the ignition delay on turbulence intensity is found to be nonmonotonic. For weak to moderate turbulence the ignition is facilitated by turbulence via enhanced mixing, while for stronger turbulence, whose timescale is substantially smaller than the ignition delay, the ignition is retarded due to excessive scalar dissipation, and hence diffusive loss, at the ignition location. However, for the wide range of initial turbulence fields studied, the variation in ignition delay due to the corresponding variation in turbulence intensity appears to be quite small.

  3. Heat budget of the surface mixed layer south of Africa

    NASA Astrophysics Data System (ADS)

    Faure, Vincent; Arhan, Michel; Speich, Sabrina; Gladyshev, Sergey

    2011-10-01

    ARGO hydrographic profiles, two hydrographic transects and satellite measurements of air-sea exchange parameters were used to characterize the properties and seasonal heat budget variations of the Surface Mixed Layer (SML) south of Africa. The analysis distinguishes the Subtropical domain (STZ) and the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ) of the Antarctic Circumpolar Current. While no Subantarctic Mode Water forms in that region, occurrences of deep SML (up to ˜450 m) are observed in the SAZ in anticyclones detached from the Agulhas Current retroflection or Agulhas Return Current. These are present latitudinally throughout the SAZ, but preferentially at longitudes 10-20° E where, according to previous results, the Subtropical Front is interrupted. Likely owing to this exchange window and to transfers at the Subantarctic Front also enhanced by the anticyclones, the SAZ shows a wide range of properties largely encroaching upon those of the neighbouring domains. Heat budget computations in each zone reveal significant meridional changes of regime. While air-sea heat fluxes dictate the heat budget seasonal variability everywhere, heat is mostly brought through lateral geostrophic advection by the Agulhas Current in the STZ, through lateral diffusion in the SAZ and through air-sea fluxes in the PFZ and AZ. The cooling contributions are by Ekman advection everywhere, lateral diffusion in the STZ (also favoured by the ˜10° breach in the Subtropical Front) and geostrophic advection in the SAZ. The latter likely reflects an eastward draining of water warmed through mixing of the subtropical eddies.

  4. Study of compression settlement of a three-layer rigid-plastic strip between parallel plates

    NASA Astrophysics Data System (ADS)

    Aleksandrov, S. E.; Goldstein, R. V.

    2014-11-01

    The process of compression settlement of a three-layer strip between parallel plates is investigated under the plane strain conditions. The inner layer of the strip is assumed to be made of a rigid-plastic hardening material, and the two outer layers are assumed to be ideally rigid-plastic. The boundary value problem has two symmetry axes. It is assumed that the strip thickness is much less than its width. The boundary conditions at the strip edge and at the center are satisfied in integral form. Two friction regimes, i.e., sliding and adhesion, are possible on the surface of contact between the strip and the plates and on the interface between the layers. It is shown that the general structure of the solution depends on the regimes realized at the moment. In particular, one of the layers can remain rigid at a certain stage of the deformation process. The differential equations are stated which permit exactly determining the conditions of the friction regime change and the state of each layer (rigid or plastic); these equations must be solved numerically. For some values of parameters of the boundary value problem, the velocity field is singular near one or both surfaces of friction. In these cases, it is necessary to calculate the strain rate intensity coefficient whose value probably controls the process of formation of a narrow layer with strongly changed properties near the corresponding surface of friction.

  5. Mixing layers in stellar outflows-II. Interfaces between two moving fluids

    NASA Astrophysics Data System (ADS)

    Raga, A. C.; Cabrit, S.; Canto, J.

    1995-03-01

    We present a formalism for describing turbulent mixing layers between two moving inhomogeneous media. This represents an extension of the model of Canto & Raga, who considered the case of a mixing layer between a uniform stream and a motionless environment. We apply this formalism to two problems: (i) the mixing layer between a fast, uniform beam of gas in contact with a slower (also uniform) flow; and (ii) the mixing layer formed by the interaction of a stellar wind with an impinging supersonic stream. These problems have direct applicability in the field of stellar outflows, and provide an illustration of the capabilities of the formalism that we have developed.

  6. Random vibration analysis of axially compressed cylindrical shells under turbulent boundary layer in a symplectic system

    NASA Astrophysics Data System (ADS)

    Li, Yuyin; Zhang, Yahui; Kennedy, David

    2017-10-01

    A random vibration analysis of an axially compressed cylindrical shell under a turbulent boundary layer (TBL) is presented in the symplectic duality system. By expressing the cross power spectral density (PSD) of the TBL as a Fourier series in the axial and circumferential directions, the problem of structures excited by a random distributed pressure due to the TBL is reduced to solving the harmonic response function, which is the response of structures to a spatial and temporal harmonic pressure of unit magnitude. The governing differential equations of the axially compressed cylindrical shell are derived in the symplectic duality system, and then a symplectic eigenproblem is formed by using the method of separation of variables. Expanding the excitation vector and unknown state vector in symplectic space, decoupled governing equations are derived, and then the analytical solution can be obtained. In contrast to the modal decomposition method (MDM), the present method is formulated in the symplectic duality system and does not need modal truncation, and hence the computations are of high precision and efficiency. In numerical examples, harmonic response functions for the axially compressed cylindrical shell are studied, and a comparison is made with the MDM to verify the present method. Then, the random responses of the shell to the TBL are obtained by the present method, and the convergence problems induced by Fourier series expansion are discussed. Finally, influences of the axial compression on random responses are investigated.

  7. Log-law and compressibility effects in transcritical turbulent boundary layers at supercritical pressure

    NASA Astrophysics Data System (ADS)

    Kawai, Soshi

    2015-11-01

    In this talk, we discuss the log-law and effects of compressibility in transcritical heated turbulent boundary layers on a zero-pressure-gradient flat plate at supercritical pressure conditions by solving the compressible Navier-Stokes equations using direct numerical simulation. In the supercritical fluids (especially at transcritical conditions), due to the strong real fluid effects thermodynamic properties vary abruptly within a narrow temperature range through the pseudo-critical temperature and significantly deviate from the ideal fluid. Peculiar interactions between the strongly non-linear real fluid effects and wall turbulence, and its resultant log-law and turbulence statistics are discussed, which have never been seen in the ideal-fluid turbulent boundary layers. We also show non-negligible compressibility effects in the flow even in the low-Mach number regime considered in this study. This work was supported by Japan Society for the Promotion of Science KAKENHI Grant Number 26709066. Computer time was provided by the K computer at the RIKEN Advanced Institute for Computational Science through the HPCI System Research project hp150035.

  8. Evaluating the sonic layer depth relative to the mixed layer depth

    NASA Astrophysics Data System (ADS)

    Helber, Robert W.; Barron, Charlie N.; Carnes, Michael R.; Zingarelli, Robert A.

    2008-07-01

    Using a global set of in situ temperature and salinity profile observations, the sonic layer depth (SLD) and the mixed layer depth (MLD) are analyzed and compared over the annual cycle. The SLD characterizes the potential of the upper ocean to trap acoustic energy in a surface duct while MLD characterizes upper ocean mixing. The SLD is computed from temperature and salinity profile pairs using a new tunable method while MLD is computed using recently developed methods and either temperature only profiles or temperature and salinity profile pairs. Both SLD and MLD estimates provide information on different and important aspects of the upper ocean. The SLD and MLD often coincide because sound speed increases with depth down to the MLD, where (typically) a decrease in temperature occurs, resulting in a local maximum sound speed. The depth of this maximum sound speed is the SLD. The SLD and MLD are not always the same because sound speed is substantially more sensitive to temperature than to salinity compared to density. Since MLD is a commonly known and studied parameter, MLD is often used as a proxy for SLD in scientific and operational applications. In the boreal spring when fresh restratification events occur, the SLD is 10 m deeper (shallower) than the MLD in 39% (7%) of the observed profiles. A parabolic equation acoustic transmission model is used to evaluate the relative skill of the SLD and MLD estimates to predict surface acoustic trapping as measured by a simple metric.

  9. 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.

  10. Predicting the mean fields of compressible turbulent boundary layer via a symmetry approach

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    A symmetry approach for canonical wall turbulence is extended to develop mean-field predictions for compressible turbulent boundary layer (CTBL). A stress length and a weighted heat flux length are identified to obey the multilayer dilation symmetry of canonical flows, giving rise to predictions of the mean velocity and temperature profiles for a range of Reynolds number (Re), Mach number (Ma) and wall temperature (Tw). Also predicted are the streamwise developments of the shape factor, the boundary layer edge velocity and the boundary layer thicknesses, etc. Only three parameters are involved in the predictions, which have sound physics and organized behaviors with respect to the Re, Ma and Tw effects. The predictions are extensively validated by direct numerical simulation and experimental data, showing better accuracies than the previous theories. The results provide new quantifications that can be used to assess computations, measurements and turbulence models of CTBL, as well as to provide new insights for the CTBL physics.

  11. 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.

  12. 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.

  13. 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.

  14. Long-term measurement of daytime atmospheric mixing layer height over Hong Kong

    NASA Astrophysics Data System (ADS)

    Yang, Dongwei; Li, Chengcai; Lau, Alexis Kai-Hon; Li, Ying

    2013-03-01

    Lidar has unique advantages in temporal and spatial resolution to measure the atmospheric mixing layer height (MLH), which is important for analyzing atmospheric phenomena. However, long-term MLH information over several years, which has important significance in air quality and climate studies, is seldom obtained from lidar data due to the scarcity of long-running lidar observations. In this paper, we retrieve and analyze daytime MLH from a data set of a lidar that operated continuously over 6.5 years at Yuen Long, Hong Kong. A new algorithm has been developed for consistently retrieving MLH from this large data set, handling all possible weather conditions and aerosol layer structures. We analyze the diurnal, seasonal and inter-annual variation of MLH over Hong Kong and find a unique phenomenon that the afternoon MLH is higher in autumn than in summer, which is verified by radiosonde results and explained by thermal stability and humidity effect. Moreover, we find a slightly decreasing trend of the daily maximum of MLH, which implies a continually compressed air volume into which pollutants and their precursors are emitted, which is one of the possible factors leading to deteriorated air quality over Hong Kong region.

  15. 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.

  16. 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

  17. 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

  18. Mixed layer variability and chlorophyll a biomass in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Narvekar, J.; Prasanna Kumar, S.

    2014-07-01

    The mixed layer is the most variable and dynamically active part of the marine environment that couples the underlying ocean to the atmosphere and plays an important role in determining the oceanic primary productivity. We examined the basin-scale processes controlling the seasonal variability of mixed layer depth in the Bay of Bengal and its association with chlorophyll using a suite of in situ as well as remote sensing data. A coupling between mixed layer depth and chlorophyll was seen during spring intermonsoon and summer monsoon, but for different reasons. In spring intermonsoon the temperature-dominated stratification and associated shallow mixed layer makes the upper waters of the Bay of Bengal nutrient depleted and oligotrophic. In summer, although the salinity-dominated stratification in the northern Bay of Bengal shallows the mixed layer, the nutrient input from adjoining rivers enhance the surface chlorophyll. This enhancement is confined only to the surface layer and with increase in depth, the chlorophyll biomass decreases rapidly due to reduction in sunlight by suspended sediment. In the south, advection of high salinity waters from the Arabian Sea and westward propagating Rossby waves from the eastern Bay of Bengal led to the formation of deep mixed layer. In contrast, in the Indo-Sri Lanka region, the shallow mixed layer and nutrient enrichment driven by upwelling and Ekman pumping resulted in chlorophyll enhancement. The mismatch between the nitrate and chlorophyll indicated the inadequacy of present data to fully unravel its coupling to mixed layer processes.

  19. Mixed layer formation and restratification in presence of mesoscale and submesoscale turbulence

    NASA Astrophysics Data System (ADS)

    Couvelard, X.; Dumas, F.; Garnier, V.; Ponte, A. L.; Talandier, C.; Treguier, A. M.

    2015-12-01

    Recent realistic high resolution modeling studies show a net increase of submesoscale activity in fall and winter when the mixed layer depth is at its maximum. This submesoscale activity increase is associated with a reduced deepening of the mixed layer. Both phenomena can be related to the development of mixed layer instabilities, which convert available potential energy into submesoscale eddy kinetic energy and contribute to a fast restratification by slumping the horizontal density gradient in the mixed layer. In the present work, the mixed layer formation and restratification were studied by uniformly cooling a fully turbulent zonal jet in a periodic channel at different resolutions, from eddy resolving (10 km) to submesoscale permitting (2 km). The effect of the submesoscale activity, highlighted by these different horizontal resolutions, was quantified in terms of mixed layer depth, restratification rate and buoyancy fluxes. Contrary to many idealized studies focusing on the restratification phase only, this study addresses a continuous event of mixed layer formation followed by its complete restratification. The robustness of the present results was established by ensemble simulations. The results show that, at higher resolution, when submesoscale starts to be resolved, the mixed layer formed during the surface cooling is significantly shallower and the total restratification is almost three times faster. Such differences between coarse and fine resolution models are consistent with the submesoscale upward buoyancy flux, which balances the convection during the formation phase and accelerates the restratification once the surface cooling is stopped. This submesoscale buoyancy flux is active even below the mixed layer. Our simulations show that mesoscale dynamics also cause restratification, but on longer time scales. Finally, the spatial distribution of the mixed layer depth is highly heterogeneous in the presence of submesoscale activity, prompting the

  20. A minimal composite theory for stability of non-parallel compressible boundary-layer flow

    NASA Astrophysics Data System (ADS)

    Sanjeev Rao, K.; Seshadri, Rajeswari; Govindarajan, Rama

    2004-08-01

    A new "minimal composite" theory that extends the approach of Govindarajan and Narasimha [1] is proposed here for 2D non-parallel compressible boundary-layer stability subject to 3D disturbances. The mean profiles are obtained from Horton's analysis, which provides a good approximation for a large range of Prandtl numbers at non-zero pressure gradients. In the lowest order, all effects of order lower than O(R-2/3) anywhere in the boundary-layer are included, R being the local boundary-layer Reynolds number; the resulting non-parallel formulation yields a set of four ordinary differential equations, as compared to the five coupled equations of classical parallel flow theory of Mack [2]. The largest effect on stability of flow non-parallelism is found to be due to the wall-normal advection of velocity and temperature disturbance quantities by the mean flow. The present theory shows that the bulk viscosity, invariably included in compressible stability theories, is irrelevant at the lowest order. In comparison with the "full" [O(R-1)] non-parallel theory, the present theory is marginally better than the parallel flow theory.

  1. On the wall-normal velocity of the compressible boundary-layer equations

    NASA Technical Reports Server (NTRS)

    Pruett, C. David

    1991-01-01

    Numerical methods for the compressible boundary-layer equations are facilitated by transformation from the physical (x,y) plane to a computational (xi,eta) plane in which the evolution of the flow is 'slow' in the time-like xi direction. The commonly used Levy-Lees transformation results in a computationally well-behaved problem for a wide class of non-similar boundary-layer flows, but it complicates interpretation of the solution in physical space. Specifically, the transformation is inherently nonlinear, and the physical wall-normal velocity is transformed out of the problem and is not readily recovered. In light of recent research which shows mean-flow non-parallelism to significantly influence the stability of high-speed compressible flows, the contribution of the wall-normal velocity in the analysis of stability should not be routinely neglected. Conventional methods extract the wall-normal velocity in physical space from the continuity equation, using finite-difference techniques and interpolation procedures. The present spectrally-accurate method extracts the wall-normal velocity directly from the transformation itself, without interpolation, leaving the continuity equation free as a check on the quality of the solution. The present method for recovering wall-normal velocity, when used in conjunction with a highly-accurate spectral collocation method for solving the compressible boundary-layer equations, results in a discrete solution which is extraordinarily smooth and accurate, and which satisfies the continuity equation nearly to machine precision. These qualities make the method well suited to the computation of the non-parallel mean flows needed by spatial direct numerical simulations (DNS) and parabolized stability equation (PSE) approaches to the analysis of stability.

  2. Horizontal turbulent diffusivity in a convective mixed layer

    NASA Astrophysics Data System (ADS)

    Ito, J.; Niino, H.; Nakanishi, M.

    2013-12-01

    Numerical models of geophysical flows, which have extremely large Reynolds numbers, inevitably need to parameterize turbulent transports. Various kinds of parameterizations of the turbulent transports are proposed in the literature. Most of the parameterizations in atmospheric models, however, address vertical turbulent transports, and there have been surprisingly little studies on the horizontal ones. However, horizontal turbulent transports are essential when a reliable prediction of dispersion of pollutant is required, and also are increasing their importance as the horizontal resolution of the models becomes sub-kilometer. In this study, a Large Eddy Simulation (LES) is used to estimate a reliable horizontal turbulent diffusivity of a passive scalar in a convective mixed layer (CML). The LES resolves turbulent eddies associated with convection cells in the CML which is produced by heating a stably stratified atmosphere from below at a constant surface heat flux Q. At a certain instant after the CML is well developed, a fixed horizontal gradient of a passive scalar is introduced. The resulting ensemble average of horizontal turbulent fluxes is used to estimate the horizontal diffusivity. A budget analysis of the horizontal turbulent flux is also made to clarify the physical mechanism to cause the horizontal diffusion. The horizontal turbulent diffusivity of the passive scalar thus obtained is found to be on the order of 100 m2 s-1 for a CML in a typical terrestrial atmosphere in a quasi-steady state. Furthermore, its vertical profile is shown to become universal when its magnitude is scaled by a product of the convective velocity w* = (gαQ)1/3 and the depth of CML h, and the height by h, where g is the gravity acceleration and α volume expansion coefficient: the scaled horizontal turbulent diffusivity is large near the top and bottom of the CML, and its dimensional value at the middle height is given by 0.08×w*h. The diffusivity in the stably stratified layer

  3. Mixing layer height retrievals by multichannel microwave radiometer observations

    NASA Astrophysics Data System (ADS)

    Cimini, D.; De Angelis, F.; Dupont, J.-C.; Pal, S.; Haeffelin, M.

    2013-06-01

    The mixing layer height (MLH) is a key parameter for boundary layer studies, including meteorology, air quality, and climate. MLH estimates are inferred from in situ radiosonde measurements or remote sensing observations from instruments like lidar, wind profiling radar, or sodar. Methods used to estimate MLH from radiosonde profiles are also used with atmospheric temperature and humidity profiles retrieved by microwave radiometers (MWR). This paper proposes an alternative approach to estimate MLH from MWR data, based on direct observations (brightness temperatures, Tb) instead of retrieved profiles. To our knowledge, MLH estimates directly from Tb observations has never been attempted before. The method consists of a multivariate linear regression trained with an a priori set of collocated MWR Tb observations (multi-frequency and multi-angle) and MLH estimates from a state-of-the-art lidar system. Results show that the method is able to follow both the diurnal cycle and the day-to-day variability as suggested by the lidar measurements, and also it can detect low MLH values that are below the full overlap limit (~ 200 m) of the lidar system used. Statistics of the comparison between MWR- and reference lidar-based MLH retrievals show mean difference within 10 m, RMS within 340 m, and correlation coefficient higher than 0.77. Monthly mean analysis for day-time MLH from MWR, lidar, and radiosonde shows consistent seasonal variability, peaking at ~ 1200-1400 m in June and decreasing down to ~ 600 m in October. Conversely, night-time monthly mean MLH from all methods are within 300-500 m without any significant seasonal variability. The proposed method provides results that are more consistent with radiosonde estimates than MLH estimates from MWR retrieved profiles. MLH monthly mean values agree well within 1 std with bulk Richardson number method applied at radiosonde profiles at 11:00 and 23:00 UTC. The method described herewith operates continuously and it is

  4. Mixing layer height retrievals by multichannel microwave radiometer observations

    NASA Astrophysics Data System (ADS)

    Cimini, D.; De Angelis, F.; Dupont, J.-C.; Pal, S.; Haeffelin, M.

    2013-11-01

    The mixing layer height (MLH) is a key parameter for boundary layer studies, including meteorology, air quality, and climate. MLH estimates are inferred from in situ radiosonde measurements or remote sensing observations from instruments like lidar, wind profiling radar, or sodar. Methods used to estimate MLH from radiosonde profiles are also used with atmospheric temperature and humidity profiles retrieved by microwave radiometers (MWR). This paper proposes an alternative approach to estimate MLH from MWR data, based on direct observations (brightness temperatures, Tb) instead of retrieved profiles. To our knowledge, MLH estimates directly from Tb observations have never been attempted before. The method consists of a multivariate linear regression trained with an a priori set of collocated MWR Tb observations (multifrequency and multi-angle) and MLH estimates from a state-of-the-art lidar system. The proposed method was applied to a 7-month data set collected at a typical midlatitude site. Results show that the method is able to follow both the diurnal cycle and the day-to-day variability as suggested by the lidar measurements, and also it can detect low MLH values that are below the full overlap limit (~200 m) of the lidar system used. Statistics of the comparison between MWR- and reference lidar-based MLH retrievals show mean difference within 10 m, root mean square within 340 m, and correlation coefficient higher than 0.77. Monthly mean analysis for daytime MLH from MWR, lidar, and radiosonde shows consistent seasonal variability, peaking at ~1200-1400 m in June and decreasing down to ~600 m in October. Conversely, nighttime monthly mean MLH from all methods are within 300-500 m without any significant seasonal variability. The proposed method provides results that are more consistent with radiosonde estimates than MLH estimates from MWR-retrieved profiles. MLH monthly mean values agree well within 1 standard deviation with the bulk Richardson number method

  5. Compressive uniaxially strained silicon on insulator by prestrained wafer bonding and layer transfer

    NASA Astrophysics Data System (ADS)

    Himcinschi, C.; Reiche, M.; Scholz, R.; Christiansen, S. H.; Gösele, U.

    2007-06-01

    Wafer level compressive uniaxially strained silicon on insulator is obtained by direct wafer bonding of silicon wafers in cylindrically curved state, followed by thinning one of the wafers using the smart-cut process. The mapping of the wafer bow demonstrates the uniaxial character of the strain induced by the cylindrical bending. The interfacial properties are investigated by infrared transmission imaging, scanning acoustic microscopy, and transmission electron microscopy. UV-Raman spectroscopy is employed to determine the strain in the thin transferred layer as a function of radius of curvature of the initial bending.

  6. Modeling of viscoplastic rate-dependent hardening-softening behavior of hot mix asphalt in compression

    NASA Astrophysics Data System (ADS)

    Yun, Taeyoung; Kim, Y. Richard

    2011-02-01

    The objective of this paper is to model viscoplastic rate-dependent hardening-softening behavior that is experimentally observed from hot mix asphalt (HMA) under repetitive creep and recovery loading in compression. A differential equation is utilized to incorporate the effects of the stress history into yield stress, and an internal variable representing rate dependence in the equation is set as a function of the viscoplastic strain rate to address the change in rate dependence of the material due to gradual hardening. Also, a separate rate-dependent function concept is adopted to describe the difference in rate dependence of the yield stress during unloading and loading. The developed viscoplastic model is applied using the time-temperature superposition principle and shows good agreement with the measured viscoplastic responses of HMA under repetitive creep and recovery loading with various load levels and rest periods.

  7. 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.

  8. Numerical Investigations of Wave-Induced Mixing in Upper Ocean Layer

    NASA Astrophysics Data System (ADS)

    Guan, Changlong

    2017-04-01

    The upper ocean layer is playing an important role in ocean-atmosphere interaction. The typical characteristics depicting the upper ocean layer are the sea surface temperature (SST) and the mixed layer depth (MLD). So far, the existing ocean models tend to over-estimate SST and to under-estimate MLD, due to the inadequate mixing in the mixing layer, which is owing to that several processes related mixing in physics are ignored in these ocean models. The mixing induced by surface gravity wave is expected to be able to enhance the mixing in the upper ocean layer, and therefore the over-estimation of SST and the under-estimate of MLD could be improved by including wave-induced mixing. The wave-induced mixing could be accomplished by the physical mechanisms, such as wave breaking (WB), wave-induced Reynolds stress (WR), and wave-turbulence interaction (WT). The General Ocean Turbulence Model (GOTM) is employed to investigate the effects of the three mechanisms concerning wave-induced mixing. The numerical investigation is carried out for three turbulence closure schemes, say, k-epsilon, k-omega and Mellor-Yamada (1982), with the observational data from OSC Papa station and wave data from ECMWF. The mixing enhancement by various waved-induced mixing mechanisms is investigated and verified.

  9. Mixing layer produced by a screen and its dependence on initial conditions

    NASA Astrophysics Data System (ADS)

    Oguchi, H.; Inoue, O.

    1984-05-01

    Attention is given to dependence on initial disturbances in an attempt to elucidate the structure of turbulent mixing layers produced by setting a woven wire screen perpendicular to the freestream in a wind tunnel test section in order to obstruct part of the flow. Three kinds of model geometry screens yielded mixing layers that can be regarded as the equivalents of the plane mixing layer, and of two-dimensional and axisymmetric wakes, issuing into ambient streams of higher velocity. Flow features are visualized by the smoke-wire method, and statistical quantities are measured by a laser-Doppler velocimeter. Large scale transverse vortices persist in all cases. The mixing layers are in self-preserving state up to at least the third-order moments, but the self-preserving state is different in each case. Mixing layer growth rates strongly depend on the disturbance initially imposed.

  10. 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.

  11. The behavior of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient. Ph.D. Thesis - Washington Univ., Seattle, Aug. 1972

    NASA Technical Reports Server (NTRS)

    Rose, W. C.

    1973-01-01

    The results of an experimental investigation of the mean- and fluctuating-flow properties of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient are presented. The turbulent boundary layer developed on the wall of an axially symmetric nozzle and test section whose nominal free-stream Mach number and boundary-layer thickness Reynolds number were 4 and 100,000, respectively. The adverse pressure gradient was induced by an externally generated conical shock wave. Mean and time-averaged fluctuating-flow data, including the complete experimental Reynolds stress tensor and experimental turbulent mass- and heat-transfer rates are presented for the boundary layer and external flow, upstream, within and downstream of the pressure gradient. The mean-flow data include distributions of total temperature throughout the region of interest. The turbulent mixing properties of the flow were determined experimentally with a hot-wire anemometer. The calibration of the wires and the interpretation of the data are discussed. From the results of the investigation, it is concluded that the shock-wave - boundary-layer interaction significantly alters the turbulent mixing characteristics of the boundary layer.

  12. Evolution of a Western Arctic Ice Ocean Boundary Layer and Mixed Layer Across a Developing Thermodynamically Forced Marginal Ice Zone

    DTIC Science & Technology

    2016-09-01

    NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA DISSERTATION Approved for public release. Distribution is unlimited. EVOLUTION ...blank) 2. REPORT DATE September 2016 3. REPORT TYPE AND DATES COVERED Dissertation 4. TITLE AND SUBTITLE EVOLUTION OF A WESTERN ARCTIC ICE...measurements were collected across the Canada Basin to study the summer evolution of the ice-ocean boundary layer (IOBL) and ocean mixed layer (OML

  13. 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.

  14. 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.

  15. 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)

  16. Similar solutions for the compressible laminar boundary layer with heat transfer and pressure gradient

    NASA Technical Reports Server (NTRS)

    Cohen, Clarence B; Reshotko, Eli

    1956-01-01

    Stewartson's transformation is applied to the laminar compressible boundary-layer equations and the requirement of similarity is introduced, resulting in a set of ordinary nonlinear differential equations previously quoted by Stewartson, but unsolved. The requirements of the system are Prandtl number of 1.0, linear viscosity-temperature relation across the boundary layer, an isothermal surface, and the particular distributions of free-stream velocity consistent with similar solutions. This system admits axial pressure gradients of arbitrary magnitude, heat flux normal to the surface, and arbitrary Mach numbers. The system of differential equations is transformed to integral system, with the velocity ratio as the independent variable. For this system, solutions are found by digital computation for pressure gradients varying from that causing separation to the infinitely favorable gradient and for wall temperatures from absolute zero to twice the free-stream stagnation temperature. Some solutions for separated flows are also presented.

  17. Hyper-spectral image compression algorithm based on mixing transform of wave band grouping to eliminate redundancy

    NASA Astrophysics Data System (ADS)

    Xie, ChengJun; Xu, Lin

    2008-03-01

    This paper presents an algorithm based on mixing transform of wave band grouping to eliminate spectral redundancy, the algorithm adapts to the relativity difference between different frequency spectrum images, and still it works well when the band number is not the power of 2. Using non-boundary extension CDF(2,2)DWT and subtraction mixing transform to eliminate spectral redundancy, employing CDF(2,2)DWT to eliminate spatial redundancy and SPIHT+CABAC for compression coding, the experiment shows that a satisfied lossless compression result can be achieved. Using hyper-spectral image Canal of American JPL laboratory as the data set for lossless compression test, when the band number is not the power of 2, lossless compression result of this compression algorithm is much better than the results acquired by JPEG-LS, WinZip, ARJ, DPCM, the research achievements of a research team of Chinese Academy of Sciences, Minimum Spanning Tree and Near Minimum Spanning Tree, on the average the compression ratio of this algorithm exceeds the above algorithms by 41%,37%,35%,29%,16%,10%,8% respectively; when the band number is the power of 2, for 128 frames of the image Canal, taking 8, 16 and 32 respectively as the number of one group for groupings based on different numbers, considering factors like compression storage complexity, the type of wave band and the compression effect, we suggest using 8 as the number of bands included in one group to achieve a better compression effect. The algorithm of this paper has priority in operation speed and hardware realization convenience.

  18. Parametrics on 2D 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 two-dimensional (2D) Navier-Stokes flow solver. Parametric studies were performed on turbulence models, computational grids and bleed models. The computer flowfield was substantially different from the original inviscid design, due to interactions of shocks, boundary layers, and bleed. Good agreement with experimental data was obtained in many aspects. Many of the discrepancies were thought to originate primarily from 3D effects. Therefore, a balance should be struck between expending resources on a high fidelity 2D simulation, and the inherent limitations of 2D analysis. The solutions were fairly insensitive to turbulence models, grids and bleed models. Overall, the k-e turbulence model, and the bleed models based on unchoked bleed hole discharge coefficients or uniform velocity are recommended. The 2D Navier-Stokes methods appear to be a useful tool for the design and analysis of supersonic inlets, by providing a higher fidelity simulation of the inlet flowfield than inviscid methods, in a reasonable turnaround time.

  19. 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.

  20. A near-wall four-equation turbulence model for compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Sommer, T. P.; So, R. M. C.; Zhang, H. S.

    1992-01-01

    A near-wall four-equation turbulence model is developed for the calculation of high-speed compressible turbulent boundary layers. The four equations used are the k-epsilon equations and the theta(exp 2)-epsilon(sub theta) equations. These equations are used to define the turbulent diffusivities for momentum and heat fluxes, thus allowing the assumption of dynamic similarity between momentum and heat transport to be relaxed. The Favre-averaged equations of motion are solved in conjunction with the four transport equations. Calculations are compared with measurements and with another model's predictions where the assumption of the constant turbulent Prandtl number is invoked. Compressible flat plate turbulent boundary layers with both adiabatic and constant temperature wall boundary conditions are considered. Results for the range of low Mach numbers and temperature ratios investigated are essentially the same as those obtained using an identical near-wall k-epsilon model. In general, the numerical predictions are in very good agreement with measurements and there are significant improvements in the predictions of mean flow properties at high Mach numbers.

  1. Saint-Venant flow in a thin layer under plastic compression

    NASA Astrophysics Data System (ADS)

    Georgievskii, D. V.

    2011-08-01

    The flow of perfectly rigid-plastic material in a thin layer subjected to a load was considered in numerous studies, including the classical ones [1-12]. In the case of rigid plates coinciding with the layer face surfaces and approaching each other in a prescribed way, we deal with the Prandtl problem, which was considered in [1], or with its numerous generalizations (e.g., see [13, 14]). Traditionally, the process of obtaining the Prandtl solution is based on the hypothesis that the tangential stress is linear in thickness and hence the tangential stress attains its maximum absolute value on the surfaces of the rough plates. The asymptotic analysis carried out in [15] with a natural small geometric parameter without any original static or kinematic hypotheses led to a solution coinciding with the generalization of the Prandtl solution to the case of plates with an arbitrary roughness factor. This solution is exact in the sense that there are finitely many nonzero terms in the asymptotic series. The ill-posedness of the expansions chosen near the middle cross-section of the layer rigorously follows from the loss of the asymptotic property in the sense of the Poincaré of the series for the velocity longitudinal component in this region. Another internal expansion constructed in [15] also exactly and physically corresponds to compression of a thin vertical strip in the middle of the layer. The present paper is a generalization of [15] to the case of an arbitrary region occupied with a layer in horizontal projection. We present an algorithm for constructing the asymptotic solution of the problem and consider the possibility of perfectly rigid-plastic flow along one of a family of coordinate lines. To this end, it is necessary that the roughness of the pressing plates depend on the coordinates in a certain way. We also perform a detailed study of the axisymmetric analogue of the Prandtl problem (compression of a circular layer) and the kinematics of an elliptic layer

  2. 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.

  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. 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.

  5. 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.

  6. Numerical simulation of topographically forced mesoscale variability in a well-mixed marine layer

    NASA Technical Reports Server (NTRS)

    Eddington, Lee W.; O'Brien, J. J.; Stuart, D. W.

    1992-01-01

    A simple nonlinear numerical model of a well-mixed marine layer is employed to examine topographically forced mesoscale variability off coastal California. This model is utilized to simulate a persistent wind maximum observed near Point Conception during northwesterly winds. The model solves for the two horizontal components of the marine-layer height and the marine-layer wind.

  7. The ocean mixed layer under Southern Ocean sea-ice: Seasonal cycle and forcing

    NASA Astrophysics Data System (ADS)

    Pellichero, Violaine; Sallée, Jean-Baptiste; Schmidtko, Sunke; Roquet, Fabien; Charrassin, Jean-Benoît

    2017-02-01

    The oceanic mixed layer is the gateway for the exchanges between the atmosphere and the ocean; in this layer, all hydrographic ocean properties are set for months to millennia. A vast area of the Southern Ocean is seasonally capped by sea-ice, which alters the characteristics of the ocean mixed layer. The interaction between the ocean mixed layer and sea-ice plays a key role for water mass transformation, the carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the under-ice mixed layer are poorly understood due to the sparseness of in situ observations and measurements. In this study, we combine distinct sources of observations to overcome this lack in our understanding of the polar regions. Working with elephant seal-derived, ship-based, and Argo float observations, we describe the seasonal cycle of the ocean mixed-layer characteristics and stability of the ocean mixed layer over the Southern Ocean and specifically under sea-ice. Mixed-layer heat and freshwater budgets are used to investigate the main forcing mechanisms of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity, and vertical entrainment play only secondary roles. Our results suggest that changes in regional sea-ice distribution and annual duration, as currently observed, widely affect the buoyancy budget of the underlying mixed layer, and impact large-scale water mass formation and transformation with far reaching consequences for ocean ventilation.

  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. Statistics of Vortical Structures in Variable-Density Turbulent Mixing Layers

    NASA Astrophysics Data System (ADS)

    Baltzer, Jon; Livescu, Daniel

    2016-11-01

    Direct Numerical Simulations are performed of temporal incompressible shear-driven planar mixing layers between two miscible streams of fluids with different densities. The simulations begin from thin disturbed interfaces and develop into self-similar states. We use very large domain sizes, corresponding to grids of up to 6144 x 2048 x 1536 points, to produce high-quality statistics and allow natural growth of turbulent structures. A wide range of Atwood numbers are explored, ranging from nearly constant density to A=0.87 (or a density ratio of 14). At high Atwood numbers, a variety of statistics show that variable-density effects produce significant asymmetries. Here we focus on the differences in vortical structure of the light and heavy fluid streams and the importance of non-Boussinesq effects as Atwood number increases. Detailed budgets of vorticity moments are examined in conjunction with the alignments of vorticity relative to other flow quantities. The results display the variable density effects due to compositional variations, a distinctly different mechanism from the density variations associated with compressibility in high-speed flows.

  10. 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).

  11. 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).

  12. 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.

  13. [Particle dispersion by ordered motion in mixing layers]. [Annual report

    SciTech Connect

    Troutt, T.R.

    1989-12-31

    Multiphase mixing in turbulent flows is a key element in many practical energy conversion, chemical mixing and pollutant dispersal problems. Numerous important technological and environmental processes could be better addressed with improvements in understanding in this area. Progress in developing understanding of this field, however, has traditionally been difficult because of the complexities involved with the turbulent flows employed to provide the mixing mechanisms. To address this problem from a new perspective several years ago this research group initiated an ongoing investigation concerning the potential connections between organized turbulent vortex structures and the particle dispersion process. This report details activities during this reporting period.

  14. Ordered mixed-layer structures in the Mighei carbonaceous chondrite matrix

    NASA Technical Reports Server (NTRS)

    Mackinnon, I. D. R.

    1982-01-01

    High resolution transmission electron microscopy of the Mighei carbonaceous chondrite matrix has revealed the presence of a new mixed layer structure material. This mixed-layer material consists of an ordered arrangement of serpentine-type (S) and brucite-type (B) layers in the sequence SBBSBB. Electron diffraction and imaging techniques show that the basal periodicity is approximately 17 A. Discrete crystals of SBB-type material are typically curved, of small size (less than 1 micron) and show structural variations similar to the serpentine group minerals. Mixed-layer material also occurs in association with planar serpentine. Characteristics of SBB-type material are not consistent with known terrestrial mixed-layer clay minerals. Evidence for formation by a condensation event or by subsequent alteration of pre-existing material is not yet apparent.

  15. Enhancement of Exciton Emission in Lead Halide-Based Layered Perovskites by Cation Mixing.

    PubMed

    Era, Masanao; Komatsu, Yumeko; Sakamoto, Naotaka

    2016-04-01

    Spin-coated films of a lead halide, PbX: X = I and Br, layered perovskites having cyclohexenylethyl ammonium molecule as an organic layer, which were mixed with other metal halide-based layered perovskites consisting of various divalent metal halides (for example, Ca2, Cdl2, FeI2, SnBr2 and so on), were prepared. The results of X-ray diffraction measurements exhibited that solid solution formation between PbX-based layered perovskite and other divalent metal halide-based layered perovskites was observed up to very high molar concentration of 50 molar% in the mixed film samples when divalent cations having ionic radius close to that of Pb2+ were employed. In the solid solution films, the exciton emission was much enhanced at room temperature. Exciton emission intensity of Pbl-based layered perovskite mixed with Cal-based layered perovskite (20 molar%) is about 5 times large that of the pristine Pbl-based layered perovskite, and that of PbBr-based layered perovskite mixed with SnBr-based layered perovskite (20 molar%) was also about 5 times large that of the pristine PbBr-based layered perovskite at room temperature.

  16. VenUS IV (Venous leg Ulcer Study IV) - compression hosiery compared with compression bandaging in the treatment of venous leg ulcers: a randomised controlled trial, mixed-treatment comparison and decision-analytic model.

    PubMed Central

    Ashby, Rebecca L; Gabe, Rhian; Ali, Shehzad; Saramago, Pedro; Chuang, Ling-Hsiang; Adderley, Una; Bland, J Martin; Cullum, Nicky A; Dumville, Jo C; Iglesias, Cynthia P; Kang'ombe, Arthur R; Soares, Marta O; Stubbs, Nikki C; Torgerson, David J

    2014-01-01

    BACKGROUND Compression is an effective and recommended treatment for venous leg ulcers. Although the four-layer bandage (4LB) is regarded as the gold standard compression system, it is recognised that the amount of compression delivered might be compromised by poor application technique. Also the bulky nature of the bandages might reduce ankle or leg mobility and make the wearing of shoes difficult. Two-layer compression hosiery systems are now available for the treatment of venous leg ulcers. Two-layer hosiery (HH) may be advantageous, as it has reduced bulk, which might enhance ankle or leg mobility and patient adherence. Some patients can also remove and reapply two-layer hosiery, which may encourage self-management and could reduce costs. However, little robust evidence exists about the effectiveness of two-layer hosiery for ulcer healing and no previous trials have compared two-layer hosiery delivering 'high' compression with the 4LB. OBJECTIVES Part I To compare the clinical effectiveness and cost-effectiveness of HH and 4LB in terms of time to complete healing of venous leg ulcers. Part II To synthesise the relative effectiveness evidence (for ulcer healing) of high-compression treatments for venous leg ulcers using a mixed-treatment comparison (MTC). Part III To construct a decision-analytic model to assess the cost-effectiveness of high-compression treatments for venous leg ulcers. DESIGN Part I A multicentred, pragmatic, two-arm, parallel, open randomised controlled trial (RCT) with an economic evaluation. Part II MTC using all relevant RCT data - including Venous leg Ulcer Study IV (VenUS IV). Part III A decision-analytic Markov model. SETTINGS Part I Community nurse teams or services, general practitioner practices, leg ulcer clinics, tissue viability clinics or services and wound clinics within England and Northern Ireland. PARTICIPANTS Part I Patients aged ≥ 18 years with a venous leg ulcer, who were willing and able to tolerate high

  17. VenUS IV (Venous leg Ulcer Study IV) - compression hosiery compared with compression bandaging in the treatment of venous leg ulcers: a randomised controlled trial, mixed-treatment comparison and decision-analytic model.

    PubMed

    Ashby, Rebecca L; Gabe, Rhian; Ali, Shehzad; Saramago, Pedro; Chuang, Ling-Hsiang; Adderley, Una; Bland, J Martin; Cullum, Nicky A; Dumville, Jo C; Iglesias, Cynthia P; Kang'ombe, Arthur R; Soares, Marta O; Stubbs, Nikki C; Torgerson, David J

    2014-09-01

    Compression is an effective and recommended treatment for venous leg ulcers. Although the four-layer bandage (4LB) is regarded as the gold standard compression system, it is recognised that the amount of compression delivered might be compromised by poor application technique. Also the bulky nature of the bandages might reduce ankle or leg mobility and make the wearing of shoes difficult. Two-layer compression hosiery systems are now available for the treatment of venous leg ulcers. Two-layer hosiery (HH) may be advantageous, as it has reduced bulk, which might enhance ankle or leg mobility and patient adherence. Some patients can also remove and reapply two-layer hosiery, which may encourage self-management and could reduce costs. However, little robust evidence exists about the effectiveness of two-layer hosiery for ulcer healing and no previous trials have compared two-layer hosiery delivering 'high' compression with the 4LB. Part I To compare the clinical effectiveness and cost-effectiveness of HH and 4LB in terms of time to complete healing of venous leg ulcers. Part II To synthesise the relative effectiveness evidence (for ulcer healing) of high-compression treatments for venous leg ulcers using a mixed-treatment comparison (MTC). Part III To construct a decision-analytic model to assess the cost-effectiveness of high-compression treatments for venous leg ulcers. Part I A multicentred, pragmatic, two-arm, parallel, open randomised controlled trial (RCT) with an economic evaluation. Part II MTC using all relevant RCT data - including Venous leg Ulcer Study IV (VenUS IV). Part III A decision-analytic Markov model. Part I Community nurse teams or services, general practitioner practices, leg ulcer clinics, tissue viability clinics or services and wound clinics within England and Northern Ireland. Part I Patients aged ≥ 18 years with a venous leg ulcer, who were willing and able to tolerate high compression. Part I Participants in the

  18. The ocean mixed layer under Southern Ocean sea-ice: seasonal cycle and forcing.

    NASA Astrophysics Data System (ADS)

    Violaine, P.; Sallee, J. B.; Schmidtko, S.; Roquet, F.; Charrassin, J. B.

    2016-02-01

    The mixed-layer at the surface of the ocean is the gateway for all exchanges between air and sea. A vast area of the Southern Ocean is however seasonally capped by sea-ice, which alters this gateway and the characteristic the ocean mixed-layer. The interaction between the ocean mixed-layer and sea-ice plays a key role for water-mass formation and circulation, carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the mixed layer, as well as the processes responsible for its evolution, are poorly understood due to the lack of in-situ observations and measurements. We urgently need to better understand the forcing and the characteristics of the ocean mixed-layer under sea-ice if we are to understand and predict the world's climate. In this study, we combine a range of distinct sources of observation to overcome this lack in our understanding of the Polar Regions. Working on Elephant Seal-derived data as well as ship-based observations and Argo float data, we describe the seasonal cycle of the characteristics and stability of the ocean mixed layer over the entire Southern Ocean (South of 40°S), and specifically under sea-ice. Mixed-layer budgets of heat and freshwater are used to investigate the main forcings of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget, and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity and vertical entrainment play only secondary role.Our results suggest that changes in regional sea-ice distribution or sea-ice seasonal cycle duration, as currently observed, would widely affect the buoyancy budget of the underlying mixed-layer, and impacts large-scale water-mass formation and transformation.

  19. A comparative study of several compressibility corrections to turbulence models applied to high-speed shear layers

    NASA Technical Reports Server (NTRS)

    Viegas, John R.; Rubesin, Morris W.

    1991-01-01

    Several recently published compressibility corrections to the standard k-epsilon turbulence model are used with the Navier-Stokes equations to compute the mixing region of a large variety of high speed flows. These corrections, specifically developed to address the weakness of higher order turbulence models to accurately predict the spread rate of compressible free shear flows, are applied to two stream flows of the same gas mixing under a large variety of free stream conditions. Results are presented for two types of flows: unconfined streams with either (1) matched total temperatures and static pressures, or (2) matched static temperatures and pressures, and a confined stream.

  20. 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.

  1. 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.

  2. Linear stability analysis in compressible, flat-plate boundary-layers

    NASA Astrophysics Data System (ADS)

    Özgen, Serkan; Kırcalı, Senem Atalayer

    2008-01-01

    The stability problem of two-dimensional compressible flat-plate boundary layers is handled using the linear stability theory. The stability equations obtained from three-dimensional compressible Navier-Stokes equations are solved simultaneously with two-dimensional mean flow equations, using an efficient shoot-search technique for adiabatic wall condition. In the analysis, a wide range of Mach numbers extending well into the hypersonic range are considered for the mean flow, whereas both two- and three-dimensional disturbances are taken into account for the perturbation flow. All fluid properties, including the Prandtl number, are taken as temperature-dependent. The results of the analysis ascertain the presence of the second mode of instability (Mack mode), in addition to the first mode related to the Tollmien-Schlichting mode present in incompressible flows. The effect of reference temperature on stability characteristics is also studied. The results of the analysis reveal that the stability characteristics remain almost unchanged for the most unstable wave direction for Mach numbers above 4.0. The obtained results are compared with existing numerical and experimental data in the literature, yielding encouraging agreement both qualitatively and quantitatively.

  3. 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.

  4. [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.

  5. 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.

  6. Computer program for calculating laminar, transitional, and turbulent boundary layers for a compressible axisymmetric flow

    NASA Technical Reports Server (NTRS)

    Albers, J. A.; Gregg, J. L.

    1974-01-01

    A finite-difference program is described for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain the factors of arbitrary Reynolds number, free-stream Mach number, free-stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile.

  7. An experimental investigation of compressible three-dimensional boundary layer flow in annular diffusers

    NASA Technical Reports Server (NTRS)

    Om, Deepak; Childs, Morris E.

    1987-01-01

    An experimental study is described in which detailed wall pressure measurements have been obtained for compressible three-dimensional unseparated boundary layer flow in annular diffusers with and without normal shock waves. Detailed mean flow-field data were also obtained for the diffuser flow without a shock wave. Two diffuser flows with shock waves were investigated. In one case, the normal shock existed over the complete annulus whereas in the second case, the shock existed over a part of the annulus. The data obtained can be used to validate computational codes for predicting such flow fields. The details of the flow field without the shock wave show flow reversal in the circumferential direction on both inner and outer surfaces. However, there is a lag in the flow reversal between the inner nad the outer surfaces. This is an interesting feature of this flow and should be a good test for the computational codes.

  8. Effects of Initial Conditions on Compressible Mixing in Supernova-Relevant Laboratory Experiments

    SciTech Connect

    Miles, A R; Edwards, M; Greenough, J

    2004-04-30

    In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen-helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. In this paper, we summarize recent results from our computational study of unstable systems driven by high Mach number shock and blast waves. For planar multimode systems, compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions (IC's) by allowing for memory of the initial conditions to be retained in the mix-width at all times. With higher-dimensional blast waves, divergence restores the properties necessary for establishment of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for the incident blast wave. Initial conditions predicted by some recent stellar calculations are incompatible with self-similarity.

  9. A Computer Program 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

    A computer program for calculating three dimensional compressible laminar and turbulent boundary layers on arbitrary wings is described and presented. The computer program consists of three separate programs, namely, a geometry program to represent the wing analytically, a velocity program to compute the external velocity components from a given experimental pressure distribution and a finite difference boundary layer method to solve the governing equations for compressible flows. To illustrate the usage of the computer program, three different test cases are presented and the preparation of the input data as well as the computed output data is discussed in some detail.

  10. 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.

  11. Area production in supercritical, transitional mixing layers for reactive flow applications

    NASA Technical Reports Server (NTRS)

    Bellan, J.; Okong'o, N.

    2002-01-01

    An investigation of surface area production is conducted for supercritical mixing layers; the results are relevant to flame area evolution and fluid disintegration. In this study, the surface is chosen perpendicular to the mass fraction gradient.

  12. 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.

  13. Variability of the mixed layer height derived by ceilometer measurements in the Bavarian pre-Alps

    NASA Astrophysics Data System (ADS)

    Kohnert, Katrin; Mauder, Matthias; Foken, Thomas

    2013-04-01

    The mixed layer height is an important parameter in air pollution studies, for modeling atmospheric turbulences and might be related to the energy balance closure problem. It is known that the mixed layer height is varying above different surfaces and undergoes diurnal variations. About differences of the mixed layer height on small spatial scale, only little is known. This is, however, of particular importance for atmospheric modeling on regional and global scales. In our work, we studied the mixed layer height at three study sites in the Bavarian pre-Alps as part of the Terrestrial Environmental Observatories (TERENO) network. The sites are located along a north-south gradient within a distance of 30 km at an altitude between 600 m asl at the northernmost site and 865 m asl at the site located furthest in the south. The measurement systems were installed above flat meadows at each site. The surrounding topography at the sites, however, varies remarkably. The area around the northern site (Fendt) is rather flat apart from a plateau to the west that is elevated about 130 m compared to the measuring devices. At the central site (Rottenbuch) the surrounding can be considered as gentle hills. The site in the south (Graswang) is located in a valley bordered by mountains that reach altitudes of more than 1000 m above the valley bottom. In order to study the mixed layer height, ceilometers were installed at the three sites. Additionally, all sites are equipped with eddy-covariance energy balance measurement systems. In our analysis, we included data from July to October 2012. One focus was put on the variability of the mixed layer height from summer to autumn months and along with that the correlation of mixed layer height with global radiation. The effect of topographic differences on the mixed layer height was studied by a comparison between the study sites on a monthly scale, giving statistically different results at the three sites. Moreover, at one side we analyzed

  14. Performance properties of asphalt mixes for rich bottom layers (RBL)

    NASA Astrophysics Data System (ADS)

    Bureš, Petr; Fiedler, Jiří; Kašpar, Jiří; Sýkora, Michal; Hýzl, Petr

    2017-09-01

    The binder content of asphalt mixes has an important influence on the performance properties. Higher binder content improves fatigue resistance. That is why the concept of RBL was developed in USA and applied for “perpetual pavements”. However excessive binder content could lead to the decrease of the mix stiffness and to permanent deformations of asphalt pavement during hot summer. The advantages and limitations of RBL concept have been studied in research project CESTI. Fatigue tests of mixes with road bitumen and polymer modified bitumen and RBL were realised. Deformation behaviour of these mixes was also evaluated. The experience from the test section with RBL laid in 2015 will be presented. The results corresponded to expectations. However, low void content was obtained on one subsection. In spite of it, there were no permanent deformations during summer 2016. The analysis of methods for the prediction of the permanent deformation was also undertaken in research project CESTI. Some information about the results of these analysis related to the use of RBL will be also briefly mentioned.

  15. Plasma interfacial mixing layers: Comparisons of fluid and kinetic models

    NASA Astrophysics Data System (ADS)

    Vold, Erik; Yin, Lin; Taitano, William; Albright, B. J.; Chacon, Luis; Simakov, Andrei; Molvig, Kim

    2016-10-01

    We examine plasma transport across an initial discontinuity between two species by comparing fluid and kinetic models. The fluid model employs a kinetic theory approximation for plasma transport in the limit of small Knudsen number. The kinetic simulations include explicit particle-in-cell simulations (VPIC) and a new implicit Vlasov-Fokker-Planck code, iFP. The two kinetic methods are shown to be in close agreement for many aspects of the mixing dynamics at early times (to several hundred collision times). The fluid model captures some of the earliest time dynamic behavior seen in the kinetic results, and also generally agrees with iFP at late times when the total pressure gradient relaxes and the species transport is dominated by slow diffusive processes. The results show three distinct phases of the mixing: a pressure discontinuity forms across the initial interface (on times of a few collisions), the pressure perturbations propagate away from the interfacial mixing region (on time scales of an acoustic transit) and at late times the pressure relaxes in the mix region leaving a non-zero center of mass flow velocity. The center of mass velocity associated with the outward propagating pressure waves is required to conserve momentum in the rest frame. Work performed under the auspices of the U.S. DOE by the LANS, LLC, Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396. Funding provided by the Advanced Simulation and Computing (ASC) Program.

  16. 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

  17. 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.

  18. Tropical Cyclone Footprint in the Ocean Mixed Layer Observed by Argo in the Northwest Pacific

    DTIC Science & Technology

    2014-10-25

    RESEARCH ARTICLE 10.1002/2014JC010316 Tropical cyclone footprint in the ocean mixed layer observed by Argo in the Northwest Pacific HongLi Fu1...Postgraduate School, Monterey, California, USA Abstract This study systematically investigated the ocean mixed layer responses to tropical cyclone (TC...5 m, with IL cooling up to 0.4C. 1. Introduction Oceanic response to tropical cyclones (TCs) has been a hot topic due to its importance for climate

  19. Numerical Investigation of Statistical Turbulence Effects on Beam Propagation through 2-D Shear Mixing Layer

    DTIC Science & Technology

    2010-03-01

    NUMERICAL INVESTIGATION OF STATISTICAL TURBULENCE EFFECTS ON BEAM PROPAGATION THROUGH 2-D SHEAR MIXING LAYER THESIS James C. Bowers, Captain, USAF...STATISTICAL TURBULENCE EFFECTS ON BEAM PROPAGATION THROUGH 2-D SHEAR MIXING LAYER THESIS Presented to the Faculty Department of Engineering Physics...robust method for calculating atmospheric turbulence effects on optical beam propagation, which could simplify similar approaches to chaotic aero-optical

  20. Recombination Zone by Mixed-Source Evaporation in Organic Light Emitting Diodes with Graded Mixed-Layer Structures

    NASA Astrophysics Data System (ADS)

    Kee, Y. Y.; Siew, W. O.; Yap, S. S.; Tou, T. Y.

    Thermal evaporation of a mixed-source of electron and hole-transport materials at appropriate heating rates, namely, tris-(8-hydroxyquinoline)aluminum(3) (Alq3) and N,N-diphenyl-N, N-bis(3-methylphenyl)-1, 1-diphenyl-4,4-diamine (TPD) can produce a continuously graded mixed-layer structure (CGM). This enables CGM-OLEDs to be fabricated on ITO-coated glass. Although I-V characteristic of CGM-OLEDs may not be significantly modified by a single mixed layer, as compared to the conventional bi-layer heterojunction (HJ) OLED, the power efficiency from the CGM-OLEDs can be increased by a factor of 3.3. The improvement in CGM-OLEDs can be largely explained by the broadening of its recombination zone. The spatial distributions of Alq3 and TPD in CGM-layers are obtained by depth-profiling of X-ray Photoelectron Spectroscopy. The optimum layer structure for CGM-OLEDs is discussed qualitatively in term of charge balance and electrode quenching.

  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. Laboratory simulations of the atmospheric mixed-layer in flow over complex topography

    NASA Astrophysics Data System (ADS)

    Perry, Steven G.; Snyder, William H.

    2017-02-01

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundary layer can have a strong influence on the concentration of pollutants within this layer. Deflections of streamlines at the height of the interface are primarily a function of hill Froude number (Fr), the ratio of mixed-layer height (zi) to terrain height (h), and the crosswind dimension of the terrain. The magnitude of the deflections increases as Fr increases and zi/h decreases. For mixing-height streamlines that are initially below the terrain top, the response is linear with Fr; for those initially above the terrain feature the response to Fr is more complex. Once Fr exceeds about 2, the terrain-related response of the mixed layer interface decreases somewhat with increasing Fr (toward more neutral flow). Deflections are also shown to increase as the crosswind dimensions of the terrain increase. Comparisons with numerical modeling, limited field data, and other laboratory measurements reported in the literature are favorable. Additionally, visual observations of dye streamers suggest that the flow structure exhibited for our elevated inversions passing over three dimensional hills is similar to that reported in the literature for continuously stratified flow over two-dimensional hills.

  4. Negative thermal expansion due to negative area compressibility in TlGaSe2 semiconductor with layered crystalline structure

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Suleymanov, Rauf A.

    2010-09-01

    We conducted comparison of the original experimental data of the temperature dependences of thermal expansion in crystals with layered crystalline structure. It is shown that in most crystals with layered structure (graphite, boron nitride, GaSe, GaS, and InSe) the effect of negative thermal expansion can be explained by the specific character of the phonon spectra. It was shown, that in contrast to other crystals with layered structure, negative thermal expansion in the layers' plane of TlGaSe2 is the result of negative area compressibility. We demonstrate that the thermal expansion of TlGaSe2 crystals can be controlled by illumination, external electric field, and thermal annealing. The nature of observed effects and a special mechanism of the negative area compressibility in TlGaSe2 crystals are discussed.

  5. 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.

  6. Direct nanomechanical measurement of layer thickness and compressibility of smectic liquid crystals.

    PubMed

    Carbone, Giovanni; Zappone, Bruno; Barberi, Riccardo; Bartolino, Roberto; Musevic, Igor

    2011-05-01

    Using an atomic force microscope (AFM) we confined a smectic-A liquid crystal (LC) between a flat glass plate and a 10-μm glass sphere attached to the free end of the AFM cantilever. Both surfaces were treated with a surfactant that induces normal alignment of the LC molecules. We measured the force F acting on the cantilever while varying the plate-sphere distance D with subnanometer precision. For D < 50 nm, the force was periodically oscillating and decayed as D was increased. Analyzing the force in the framework of a simple model of elastic deformation of the smectic layers, we have evaluated the undeformed layer thickness a(0) and compressibility modulus B. Compared to other techniques used to determine a(0) and B, AFM measurements are faster and require a much smaller amount (microliters) of LC. Moreover, they are based on purely mechanical deformations of the LC structure and do not require any static or radiative electromagnetic field.

  7. 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

  8. Nonlinear evolution of subsonic and supersonic disturbances on a compressible free shear layer

    NASA Technical Reports Server (NTRS)

    Leib, S. J.

    1991-01-01

    The effects of a nonlinear-nonequilibrium-viscous critical layer on the spatial evolution of subsonic and supersonic instability modes on a compressible free shear layer is considered. It is shown that the instability wave amplitude is governed by an integrodifferential equation with cubic-type nonlinearity. Numerical and asymptotic solutions to this equation show that the amplitude either ends in a singularity at a finite downstream distance or reaches an equilibrium value, depending on the Prandtl number, viscosity law, viscous parameter and a real parameter which is determined by the linear inviscid stability theory. A necessary condition for the existence of the equilibrium solution is derived, and whether or not this condition is met is determined numerically for a wide range of physical parameters including both subsonic and supersonic disturbances. it is found that no equilibrium solution exists for the subsonic modes unless the temperature ratio of the low-to-high-speed streams exceeds a critical value, while equilibrium solutions for the most rapidly growing supersonic mode exist over most of the parameter range examined.

  9. Shear-Induced Isostructural Phase Transition and Metallization of Layered Tungsten Disulfide under Nonhydrostatic Compression

    SciTech Connect

    Duwal, Sakun; Yoo, Choong-Shik

    2016-02-16

    Pressure-induced structural and electronic transformations of tungsten disulfide (WS2) have been studied to 60 GPa, in both hydrostatic and non-hydrostatic conditions, using four-probe electrical resistance measurements, micro-Raman spectroscopy and synchrotron x-ray diffraction. Our results show the evidence for an isostructural phase transition from hexagonal 2Hc phase to hexagonal 2Ha phase, which accompanies the metallization at ~37 GPa. This isostructural transition occurs displacively over a large pressure range between 15 and 45 GPa and is driven by the presence of strong shear stress developed in the layer structure of WS2 under non-hydrostatic compression. Interestingly, this transition is absent in hydrostatic conditions using He pressure medium, underscoring its strong dependence on the state of stress. We also attribute the absence to the incorporation of He atoms between the layers, mitigating the development of shear stress. We also conjecture a possibility of magnetic ordering in WS2 that may occur at low temperature near the metallization.

  10. Shear-Induced Isostructural Phase Transition and Metallization of Layered Tungsten Disulfide under Nonhydrostatic Compression

    DOE PAGES

    Duwal, Sakun; Yoo, Choong-Shik

    2016-02-16

    Pressure-induced structural and electronic transformations of tungsten disulfide (WS2) have been studied to 60 GPa, in both hydrostatic and non-hydrostatic conditions, using four-probe electrical resistance measurements, micro-Raman spectroscopy and synchrotron x-ray diffraction. Our results show the evidence for an isostructural phase transition from hexagonal 2Hc phase to hexagonal 2Ha phase, which accompanies the metallization at ~37 GPa. This isostructural transition occurs displacively over a large pressure range between 15 and 45 GPa and is driven by the presence of strong shear stress developed in the layer structure of WS2 under non-hydrostatic compression. Interestingly, this transition is absent in hydrostatic conditionsmore » using He pressure medium, underscoring its strong dependence on the state of stress. We also attribute the absence to the incorporation of He atoms between the layers, mitigating the development of shear stress. We also conjecture a possibility of magnetic ordering in WS2 that may occur at low temperature near the metallization.« less

  11. 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.

  12. A three-dimensional, compressible, laminar boundary-layer method for general fuselages. Volume 2: User's manual

    NASA Technical Reports Server (NTRS)

    Wie, Yong-Sun

    1990-01-01

    This user's manual contains a complete description of the computer programs developed to calculate three-dimensional, compressible, laminar boundary layers for perfect gas flow on general fuselage shapes. These programs include the 3-D boundary layer program (3DBLC), the body-oriented coordinate program (BCC), and the streamline coordinate program (SCC). Subroutine description, input, output and sample case are discussed. The complete FORTRAN listings of the computer programs are given.

  13. 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.

  14. Effect of nonzero surface admittance on receptivity and stability of compressible boundary layer

    NASA Technical Reports Server (NTRS)

    Choudhari, Meelan

    1994-01-01

    The effect of small-amplitude short-scale variations in surface admittance on the acoustic receptivity and stability of two-dimensional compressible boundary layers is examined. In the linearized limit, the two problems are shown to be related both physically and mathematically. This connection between the two problems is used, in conjunction with some previously reported receptivity results, to infer the modification of stability properties due to surface permeability. Numerical calculations are carried out for a self-similar flat-plate boundary layer at subsonic and low supersonic speeds. Variations in mean suction velocity at the perforated admittance surface can also induce receptivity to an acoustic wave. For a subsonic boundary layer, the dependence of admittance-induced receptivity on the acoustic-wave orientation is significantly different from that of the receptivity produced via mean suction variation. The admittance-induced receptivity is generally independent of the angle of acoustic incidence, except in a relatively narrow range of upstream-traveling waves for which the receptivity becomes weaker. However, this range of angles is precisely that for which the suction-induced receptivity tends to be large. At supersonic Mach numbers, the admittance-induced receptivity to slow acoustic models is relatively weaker than that in the case of the fast acoustic modes. We also find that purely real values for the surface admittance tend to have a destabilizing effect on the evolution of an instability wave over a slightly permeable surface. The limits on the validity of the linearized approximation are also assessed in one specific case.

  15. 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.

  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. Mixed-layer deepening during Heinrich events: a multi-planktonic foraminiferal delta18O approach.

    PubMed

    Rashid, Harunur; Boyle, Edward A

    2007-10-19

    Proxies from Greenland ice cores and North Atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle, including periods of intense ice rafting called Heinrich events (HEs). We have found similar oxygen isotope variations recorded in mixed-layer-and thermocline-dwelling planktonic foraminifera during HEs 0, 1, and 4, suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column. This implies that the surface mixed layer was deeper during HEs. Similar deepening occurred on the northern margin of the ice-rafted-debris belt, implying that these deep mixed layers during HEs were widespread in the region. We suggest that an increase in storminess during HEs intensified the vertical mixing of meltwater from ice rafting in the upper ocean.

  18. Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump

    NASA Astrophysics Data System (ADS)

    Dall'Olmo, Giorgio; Dingle, James; Polimene, Luca; Brewin, Robert J. W.; Claustre, Hervé

    2016-11-01

    The ocean region known as the mesopelagic zone, which is at depths of about 100-1,000 m, harbours one of the largest ecosystems and fish stocks on the planet. Life in this region is believed to rely on particulate organic carbon supplied by the biological carbon pump. Yet this supply appears insufficient to meet mesopelagic metabolic demands. An additional organic carbon source to the mesopelagic zone could be provided by the seasonal entrainment of surface waters in deeper layers, a process known as the mixed-layer pump. Little is known about the magnitude and spatial distribution of this process globally or its potential to transport carbon to the mesopelagic zone. Here we combine mixed-layer depth data from Argo floats with satellite estimates of particulate organic carbon concentrations to show that the mixed-layer pump supplies an important seasonal flux of organic carbon to the mesopelagic zone. We estimate that this process is responsible for a global flux of 0.1-0.5 Pg C yr-1. In high-latitude regions where the mixed layer is usually deep, this flux amounts on average to 23% of the carbon supplied by fast sinking particles, but it can be greater than 100%. We conclude that the seasonal mixed-layer pump is an important source of organic carbon for the mesopelagic zone.

  19. 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.

  20. 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.

  1. Mixed-mode toughness of human cortical bone containing a longitudinal crack in far-field compression.

    PubMed

    Olvera, Diana; Zimmermann, Elizabeth A; Ritchie, Robert O

    2012-01-01

    Bone is generally loaded under multiaxial conditions in vivo; as it invariably contains microcracks, this leads to complex mixed-mode stress-states involving combinations of tension, compression and shear. In previous work on the mixed-mode loading of human cortical bone (using an asymmetric bend test geometry), we found that the bone toughness was lower when loaded in far-field shear than in tension (opposite to the trend in most brittle materials), although only for the transverse orientation. This is a consequence of the competition between preferred mechanical vs. microstructural crack-path directions, the former dictated by the direction of the maximum mechanical "driving force" (which changes with the mode-mixity), and the latter by the "weakest" microstructural path (which in human bone is along the osteonal interfaces or cement lines). As most microcracks are oriented longitudinally, we investigate here the corresponding mixed-mode toughness of human cortical bone in the longitudinal (proximal-distal) orientation using a "double cleavage drilled compression" test geometry, which provides a physiologically-relevant loading condition for bone in that it characterizes the toughness of a longitudinal crack loaded in far-field compression. In contrast to the transverse toughness, results show that the longitudinal toughness, measured using the strain-energy release rate, is significantly higher in shear (mode II) than in tension (mode I). This is consistent, however, with the individual criteria of preferred mechanical vs. microstructural crack paths being commensurate in this orientation.

  2. 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.

  3. 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.

  4. 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.

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

    SciTech Connect

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

    2016-09-15

    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.

  6. The Daytime Mixed Layer Observed by Radiosonde, Profiler, and Lidar during MILAGRO

    NASA Astrophysics Data System (ADS)

    Shaw, W. J.; Pekour, M. S.; Coulter, R. L.; Martin, T. J.; Walters, J.

    2007-12-01

    During the 2006 MILAGRO field campaign centered in the Mexico City area, scientists from Pacific Northwest National Laboratory (PNNL), Argonne National Laboratory (ANL), and the University of Alabama in Huntsville (UAH) operated a variety of atmospheric profiling systems. The systems were located at the Mexican Petroleum Institute (IMP) in central Mexico City, at Tecámac University on the northeastern edge of the Mexico City urban area, and at Rancho la Bisnaga, a privately owned ranch. These sites are referred to as T0, T1, and T2 to reflect the idea of sequential arrival times of air parcels at each site under common transport conditions. T2 was approximately 50 km north of T1. Similar 915 MHz wind profiling radars were operated at all three sites. ANL additionally operated a sodar, a 523-nm micropulse lidar, and a radiosonde system at T1. At T2, PNNL additionally operated a radiosonde system. On aircraft sampling days, five radiosondes were launched at T1 during the daytime, and three were launched at T2. The collocation of profiling systems afforded an opportunity to compare the three primary methods of measuring the depth of deep mixing layers in the Mexico City environment. In this paper we will describe the methods of extracting mixing layer depth from each system as well as the results of the comparison. The results highlight the general agreement among the various methods, but also the ambiguity that results from multiple inversions for radiosondes and from elevated layers with significant particulate matter for lidars. We conclude that the wind profiler is the system of choice for identifying mixing layer depth from the MILAGRO campaign. In addition to the instrument comparison, we also have completed a description of the temporal variability of the mixing layer during the campaign as well as spatial variations among the three sites. We have interpreted our results in the contexts of the widely reported Norte events, of the days with and without

  7. Saturn's Polar Cyclones: Idealized 2-layer Experiments of Vorticity Mixing

    NASA Astrophysics Data System (ADS)

    O'Neill, M. E.; Emanuel, K.; Flierl, G.

    2013-12-01

    The Cassini mission has provided unprecedented high-resolution observations of Saturn's atmosphere. Among many discoveries, a massive warm-core cyclonic vortex has been observed on each pole. The South Polar Vortex (SPV), specifically, has the highest measured temperatures on Saturn, a double eyewall, deep eye and a rapid cyclonic jet with the second highest windspeeds observed on the planet. However, in part because Saturn lacks the thermal disequilibrium mechanism understood to be the energy source for tropical cyclones, scientists have yet to explain the storms' dynamics and energy source. Interestingly, numerous small, vortical (in the case of at least the SPV), and potentially convective systems are embedded within the large-scale flow of both polar vortices. We explore one potential mechanism of vortex maintenance: up-scale, poleward vorticity flux due to vortical hot towers (VHTs). Large GCMs cannot yet resolve local deep convection in the weather layer. Using a two-layer shallow water model on a polar β-plane, we represent deep convection with heton-like vortex pairs and allow them to move freely. We present results from a forced-dissipative system where the forcing is only at the convective scale, and show the effect of this 'convection' on a polar cyclone.

  8. 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.

  9. Efficiency enhancement of blue phosphorescent organic light-emitting diodes using mixed electron transport layer

    NASA Astrophysics Data System (ADS)

    Yoo, Seung Il; Yoon, Ju-An; Kim, Nam Ho; Kim, Jin Wook; Lee, Ho Won; Kim, Young Kwan; He, Gufeng; Kim, Woo Young

    2015-01-01

    Blue phosphorescent organic light-emitting diodes (OLED) using mixed electron transport layer (ETL) were fabricated with the device structure of ITO/NPB/mCP:Firpic-8%/TPBi:BCP or TPBi:3TPYMB/Liq/Al to observe mixed ETL's influence on their electrical and optical characteristics. OLED device with mixed ETL of TPBi with BCP or 3TPYMB significantly improved its current efficiency to 30.4 and 34.2 cd/A comparing to 19.8 cd/A of single ETL with BCP only. We examined mixed ETL's capability of electron transport and triplet exciton confinement enhancing phosphorescent OLED's luminance and luminous efficiency.

  10. Microstructures of mixed group III-nitride epitaxial layers

    NASA Astrophysics Data System (ADS)

    Westmeyer, Andrew Nathan

    InGaN and AlGaN epitaxial layers were deposited by metalorganic chemical vapor deposition on sapphire substrates with GaN buffer layers. For the growth of InGaN at a given temperature, the trimethylgallium flow rate has the greatest influence on the In incorporation, whereas the trimethylindium flow rate has little influence. These effects are attributed to the suppression of In desorption by increasing the growth rate and the saturation of the surface with In adatoms, respectively. If the growth temperature is increased by 2.4°C, then the In content is lowered by 1% for the investigated temperature range of 785--845°C. For the growth of AlGaN, the solid fraction of Al has a sub-linear dependence on the gas composition. This was attributed to the composition pulling effect, in which incoming species are rejected in order to reduce the strain with the underlying buffer layer. A strain analysis was performed on all samples by X-ray diffraction in order to determine the composition and degree of relaxation. These values were compared to those obtained by Rutherford backscattering spectroscopy. By this method the varied reported values for elastic constants were evaluated to ascertain which set provided the best correlation. Transmission electron microscopy was performed. Plan-view images of InGaN contain domains differing in the direction of the modulations. Zone-axis diffraction patterns reveal sidebands adjacent to several Bragg reflections. These observations can be explained by diffraction effects resulting from periodic composition modulations, which are an intermediate stage in the process of phase separation. Since Young's modulus for the nitrides is isotropic in the (0001) plane, no particular direction is favored for the modulations based on strain energy considerations. In the case of AlGaN, periodic composition modulations are observed not in the growth plane (0001) but in the growth direction [0001]. Satellites in diffraction patterns are aligned in this

  11. Effects of ocean mixed layer with 3-D ocean data on WRF model for Typhoon simulation

    NASA Astrophysics Data System (ADS)

    Kwun, J.; You, S.; Ryoo, S.; Cho, C.

    2010-12-01

    The accurate typhoon prediction is an essential point for the mitigation of natural disaster and economic losses. Oceanic environment such as SST, ocean heat contents and ocean mixed layer depth has great influences on the intensity and thermodynamic features of Tropical Cyclone. The accurate establishment of air-sea interaction could lead to better performances of Typhoon prediction. In this study, we developed high resolution weather model considering ocean mixed layer(OML) with 3-D ocean data in order to take a close look at the characteristics of oceanic effects induced from applying air-sea interaction process during Typhoon Ewiniar(0603). We performed typhoon simulation using the Advanced Research Weather Research and Forecast(ARW-WRF) model version 3.2 with 10 km horizontal grid resolution and 40 sigma levels of vertical resolution. The initial and boundary condition of WRF model were obtained from the Global Data Assimilation and Prediction System(GDAPS) in Korea Meteorological Administration(KMA). NCEP Final(FNL) Global Analysis data was used for bottom condition such as soil moisture and soil temperature. For ocean feedback processing, we used WRF model coupled with the ocean mixed layer model. The OML model loaded in WRF model is a simplified 1-D ocean model rather than full layered model(Pollard et al.,1973) which included wind driven ocean mixing and mixed layer deepening process. In order to establish spatially varying upper-ocean thermodynamic structure to OML model, 3-D Hybrid Coordinate Ocean Model(HYCOM) temperature profile data(www.hycom.org) was used to calculate the initial ocean mixed layer depth, which is applied to OML model as the initial condition. The mixed layer depth was calculated by considering ocean heat content. The OML model is applied at every atmospheric model grid point and used the same time step. The updated SST is fed back to the atmospheric surface conditions. Moreover, Tropical Cyclone (TC) Bogussing scheme was used to

  12. Reynolds number and pressure gradient effects on compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Acharya, M.; Kussoy, M. I.; Horstman, C. C.

    1978-01-01

    A detailed investigation of attached supersonic turbulent boundary layers over an extensive range of Reynolds numbers (12 x 10 to the 6th to 314 x 10 to the 6th) is presented. Experimental measurements were obtained for adverse pressure gradients ranging in magnitude from those of previous investigations to those approaching separation. The measurements include mean values of surface pressure and skin-friction, mean-flow profiles, and profiles of the three turbulent velocity fluctuation components and turbulent shear stress. Numerical solutions, employing three turbulence models of various degrees of complexity have been compared with the details of the measured flow fields. Generally, it was found that the more sophisticated turbulence models are superior to a mixing length model for predicting the Reynolds number and pressure gradient effects. However, some details of the turbulent fluctuations as well as the exact Reynolds number trends indicated by the data were not accurately predicted with any of the turbulence models considered.

  13. Effect of velocity ratio on plane mixing layer development - Influence of the splitter plate wake

    NASA Technical Reports Server (NTRS)

    Mehta, R. D.

    1991-01-01

    The effect of the velocity ratio on the approach of a plane mixing layer to self-similarity was investigated experimentally. In the experiment, plane mixing layers with velocity ratios 0.5, 0.6, 0.7, 0.8, and 0.9 were generated in a mixing-layer wind tunnel consisting of two individually driven legs, in which the two streams were allowed to merge at the sharp edge of a tappered splitter plate. The leg driven by the bigger blower was operated at a free-stream velocity in the test section of 21 m/s, while the flow speed in the other leg was varied to change the velocity ratio. For each velocity ratio, the mean flow- and turbulence measurements were carried out at eight streamwise locations. Results showed that, for velocity ratios between 0.5 and 0.7, self-similarity of the mixing layer was achieved, with the asymptotic states comparable; mixing layers with higher velocity ratios failed to achieve a self-similar state within the measurement domain.

  14. Combustion in a turbulent mixing layer formed at a rearward-facing step

    NASA Technical Reports Server (NTRS)

    Pitz, R. W.; Daily, J. W.

    1983-01-01

    A premixed propane/air flame was stabilized in a turbulent mixing layer formed at a rearward-facing step. The mean and rms averages of the turbulent velocity flowfield were determined by laser velocimetry for both reacting (phi = 0.57) and nonreacting flows (Re = 15,000-37,000 based on step height). The reacting-flow was visualized by high-speed schlieren photography. Large-scale structures dominate the reacting mixing layer. The growth of the large-scale structures was tied to the propagation of the flame. The linear growth rate of the reacting mixing layer defined by the mean velocity profiles was unchanged by combustion but the virtual origin moves downstream. The reacting mixing layer boundaries based on the mean velocity profiles were shifted toward the recirculation zone and reattachment lengths were shortened by 30 percent. The edge of the flame controlled by the large-scale structure development propagated faster into the incoming reactants than the boundary of the mixing layer given by the mean velocity flowfield. Thus, the region of high velocity gradient did not coincide with the region of high reaction and heat transfer.

  15. Investigations of Subsonic Compressible Boundary Layer Flows using Hybrid Large Eddy Simulations

    NASA Astrophysics Data System (ADS)

    Taylor, Sara Jo

    The objective of this thesis is to investigate the spatially developing turbulent compressible boundary layer on a flat plate using the Spalart-Allmaras Detached Eddy Simulation (SA-DES) model [22] and the Nichols-Nelson hybrid Reynolds-Averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) model [13] which have been implemented into the Wind-US 3.0 computational fluid dynamics code [30]; both of the hybrid approaches involve RANS modeling in the near-wall region and LES treatment in the outer region. Generation of unsteady turbulent inflow data is achieved via the prescribed energy spectrum method. The studies illustrated dependence on Reynolds number based on momentum thickness, Reθ, ranging from 3018 to 19430, and dependence on Mach number, M = 0.5 and M = 0.9. The SA-DES model predicted mean flow profiles to a satisfactory degree, and the Nichols-Nelson hybrid RANS/LES model adequately predicted density field fluctuations; the aero-thermal effects captured by the Nichols-Nelson model can be useful for near-field aero optics applications.

  16. Effect of heat transfer on the subharmonic instability of compressible boundary layers

    NASA Astrophysics Data System (ADS)

    Masad, J. A.; Nayfeh, A. H.

    1991-09-01

    The effect of heat transfer on the subharmonic instability of a two-dimensional compressible boundary layer over a flat plate is analyzed using the Floquet model. The resulting problem is solved numerically by using both finite differences and the computer code suport. Results are presented for different Mach numbers. For supersonic flows, results for the first and second modes are presented. The results for an adiabatic flat plate are in good agreement with the results of the numerical simulations of Thumm et al. [in Laminar-Turbulent Transition, edited by D. Arnal and R. Michel (Springer-Verlag, Berlin, 1990), p. 271; (private communication)]. When the wall temperature is decreased and the primary wave is a second-mode wave, it is found that the subharmonic instability is shifted to higher frequencies and downstream locations. When the primary wave is a first-mode wave, the effect of cooling might be stabilizing or destabilizing depending on the frequency. When the primary wave is a first mode, cooling stabilizes the subharmonic wave at low spanwise wave numbers and destabilizes it at higher spanwise wave numbers. When the primary wave is either a first- or a second-mode wave, the most amplified subharmonic mode shifts toward a higher spanwise wave number as the cooling level increases.

  17. A compressible two-layer model for transient gas-liquid flows in pipes

    NASA Astrophysics Data System (ADS)

    Demay, Charles; Hérard, Jean-Marc

    2017-03-01

    This work is dedicated to the modeling of gas-liquid flows in pipes. As a first step, a new two-layer model is proposed to deal with the stratified regime. The starting point is the isentropic Euler set of equations for each phase where the classical hydrostatic assumption is made for the liquid. The main difference with the models issued from the classical literature is that the liquid as well as the gas is assumed compressible. In that framework, an averaging process results in a five-equation system where the hydrostatic constraint has been used to define the interfacial pressure. Closure laws for the interfacial velocity and source terms such as mass and momentum transfer are provided following an entropy inequality. The resulting model is hyperbolic with non-conservative terms. Therefore, regarding the homogeneous part of the system, the definition and uniqueness of jump conditions is studied carefully and acquired. The nature of characteristic fields and the corresponding Riemann invariants are also detailed. Thus, one may build analytical solutions for the Riemann problem. In addition, positivity is obtained for heights and densities. The overall derivation deals with gas-liquid flows through rectangular channels, circular pipes with variable cross section and includes vapor-liquid flows.

  18. 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.

  19. Calculation of turbulent boundary layers with heat transfer and pressure gradient utilizing a compressibility transformation. Part 3: Computer program manual

    NASA Technical Reports Server (NTRS)

    Schneider, J.; Boccio, J.

    1972-01-01

    A computer program is described capable of determining the properties of a compressible turbulent boundary layer with pressure gradient and heat transfer. The program treats the two-dimensional problem assuming perfect gas and Crocco integral energy solution. A compressibility transformation is applied to the equation for the conservation of mass and momentum, which relates this flow to a low speed constant property flow with simultaneous mass transfer and pressure gradient. The resulting system of describing equations consists of eight ordinary differential equations which are solved numerically. For Part 1, see N72-12226; for Part 2, see N72-15264.

  20. 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.

  1. A diagnostic relation to estimate the mixing layer height under convective conditions

    NASA Astrophysics Data System (ADS)

    Casasanta, Giampietro; Pietroni, Ilaria; Petenko, Igor; Argentini, Stefania

    2014-05-01

    In the framework of the "Atmospheric Boundary Layer Climate" (ABLCLIMAT) project, measurements of mixing-layer height were carried out with a high resolution surface-layer sodar at the French-Italian station of Concordia (Dome C, Antarctica). The behaviour of the mixing-layer height was monitored and estimated during several days in the austral summer 2011-2012. Despite the low temperatures, the mixing layer evolution at Dome C is similar to that observed at mid-latitudes, i.e. a nocturnal shallow stable layer followed by a typical diurnal growth. The mixing-layer heights were found to vary between 10 and 300 m. These observations were complemented by radiosounding profiles, and continuous near-surface turbulent fluxes measurements. Focusing on convective conditions only, a new diagnostic equation is proposed and evaluated. The diagnostic equation is based on a dimensional analysis that takes into account the time-averaged integral of the near-surface turbulent heat flux, the background static stability, and the buoyancy parameter. Despite its simplicity, the proposed model is in good agreement with the observations, and it is able to reproduce the entire diurnal evolution with satisfactory accuracy. To test the diagnostic relation on a larger and completely different data set, it was also applied to measurement from the suburb of Rome (Italy). Although diagnostic models are applicable under quasi-stationary conditions only, the obtained results support the use of a limited number of variables to characterize the general convective mixing layer behaviour. This equation can be a useful tool when direct measurements are not available, or more sophisticated model cannot be used.

  2. The "Limiting Line" in Mixed Subsonic and Supersonic Flow of Compressible Fluids

    DTIC Science & Technology

    1944-11-01

    burble ." Along a shock wave, the change of state of the fluid is no longer isentropic, although still adiabatic. This results in an increase in en...number,-" The actual critical Mach number for the appearance of shock waves and the compressibility burble must lie between these two limits. By...gradients along the \\ surface of the body, the compressibility burble can be delayed, / AXIALLY SYMMETEIC FLOW The solution of the exact

  3. 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

  4. Determination of mixing layer heights by ceilometer and influences upon air quality at Mexico City airport

    NASA Astrophysics Data System (ADS)

    Schäfer, Klaus; Flores-Jardines, Edgar; Emeis, Stefan; Grutter, Michel; Kurtenbach, Ralf; Wiesen, Peter; Münkel, Christoph

    2009-09-01

    Monitoring of mixing layer height (MLH) was performed during different measurement campaigns in urban and suburban area (Hannover, Munich, Budapest, Zürich, Augsburg) by the Vaisala ceilometer LD40. It is an eye-safe commercial lidar and designed originally to detect cloud base heights and vertical visibility for aviation safety purposes. Software for routine retrieval of mixing layer height from ceilometer data was developed and improved continuously. MLH was determined during a one-week-campaign at the airport Mexico City. Air pollutants like NO, NOx, CO and O3 as well as meteorological parameters like wind, temperature and irradiance are measured at the airport in addition to the air quality monitoring network RAMA in Mexico City. The influence of MLH together with wind, temperature and cloudiness upon air pollution is investigated. These continuous MLH and meteorological data are correlated with simultaneous measured air pollutants. The influence of mixing layer height upon air quality is shown.

  5. Does the vertical profile of ethane contain more insight into mixing layer height than carbon monoxide?

    NASA Astrophysics Data System (ADS)

    Herndon, Scott; Yacovitch, Tara; Pusede, Sally; Diskin, Glenn; DiGangi, Joshua; Sachse, Glenn; Crawford, James

    2015-04-01

    To improve the interpretation of satellite data measurements near the surface, the DISCOVER-AQ project embarked on a four year campaign to produce an integrated dataset of airborne and surface based measurements at various locations in North America. One of the key metrics when pursuing the the goal of measuring the surface air quality from space is the mixing layer height. The measurement phase in 2014 included the novel 1-Hz Aerodyne Research, Inc. fast Ethane Spectrometer to distinguish the methane emissions from thermogenic (oil&gas) and biogenic sources in the Denver-Julesberg basin. A second potential use of ethane as a determinant of mixing layer height is revealed in the analysis of 213 vertical profiles collected at 7 points during 21 flights. The findings are evaluated relative to other in-situ metrics, such as carbon monoxide and remote sensing attributions of mixing layer height.

  6. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Model of mixing of shells of a thermonuclear laser target upon spherical compression

    NASA Astrophysics Data System (ADS)

    Zmitrenko, N. V.; Proncheva, N. G.; Rozanov, Vladislav B.; Yakhin, R. A.

    2007-08-01

    Based on many direct numerical simulations of the development of hydrodynamic instabilities upon compression of laser thermonuclear targets, an efficient model is developed for describing the width of the mixing region taking into account the influence of the initial conditions on the mixing process dynamics. Approaches are proposed which are based on the evolution theory of the development of hydrodynamic instabilities [1], which was specially elaborated to describe the compression of targets for inertial thermonuclear fusion.

  7. Mixing layer development in compound channel flows with submerged and emergent rigid vegetation over the floodplains

    NASA Astrophysics Data System (ADS)

    Dupuis, Victor; Proust, Sébastien; Berni, Céline; Paquier, André

    2017-04-01

    This laboratory study aims at investigating the longitudinal development of a mixing layer in a compound open-channel (two-stage geometry with a main channel and adjacent floodplains). The floodplains are covered with two roughness types: either a bed roughness representing a submerged dense meadow or emergent roughness elements (cylinders) representing an alluvial forest. The theoretical background used for plane mixing layers is adapted to the highly three-dimensional mixing layer that develops at the main channel/floodplain interface. The mixing layer width is divided into two parts on either side of the interface. For the wooded floodplain, the mixing layer width on the floodplain side levels off downstream much more rapidly than for the grassed floodplain. The lateral profiles of normalised velocity and turbulence quantities are found to be self-similar in the longitudinal direction for a fixed elevation. However, shallowness effects prevented the normalised lateral profiles of velocity and turbulence quantities from coinciding at different elevations. The respective contributions of lateral Reynolds stresses and secondary currents to the lateral exchange of momentum are estimated. At the main channel/floodplain interface, the momentum exchange is driven by Reynolds stresses. In the main channel, both Reynolds stresses and secondary currents contribute to the lateral flux of momentum. Secondary currents are stronger with emergent macro-roughness elements than with bed-roughness only on the floodplains. Large-scale turbulent coherent structures are investigated based on two-point space-time correlations of velocity. These structures are found to span the entire floodplain flow depth, and their convection velocity is close to the depth-averaged longitudinal velocity at the interface. The coherent fluctuations of the longitudinal and lateral velocities have different Strouhal number values, similar to those found in plane mixing layers.

  8. Evaluations of Threshold and Curvature Mixed Layer Depths by Various Mixing Schemes in the Mediterranean Sea

    DTIC Science & Technology

    2010-01-01

    variables, is used to evaluate the treatment of turbulent processes in each model run. In addition to overall spatial and temporal variability...each model run. In addition to overall spatial and temporal variability, analyses of MLD are pre- sented using an extensive set (3976) of...10.1016/j.ocemod.2010.05.006 to compensate for sparse data coverage, and temporal variability of mixing processes along with MLD is examined at

  9. 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.

  10. The optical spectra of atomic/ionic mixing layers in outflows from young stars

    NASA Astrophysics Data System (ADS)

    Binette, L.; Cabrit, S.; Raga, A.; Cantó, J.

    1999-06-01

    It has been previously suggested on kinematical grounds that at least part of the emission from Herbig-Haro (HH) objects might be produced in turbulent mixing layers associated with high velocity outflows. In order to explore this possibility, we compute 1D models of the temperature and ionization cross sections of mixing layers between a high velocity flow and a stationary environment (both the jet beam and the environment being atomic). The mixing layer models are very simple from the dynamical point of view (being based on a ``turbulent viscosity'' approach), but include a detailed treatment of the relevant atomic/ionic processes and radiative cooling for the 8 most important elements (H, He, C, N, O, Ne, S, Fe). In this way, we produce a grid of 1D models with three free parameters: the velocity of the jet, the local width of the mixing layer h, and the environment pressure Penv. These models are to some extent comparable to a family of plane-parallel, steady shock models computed for different pre-shock velocities and densities. We find that the temperature cross-section changes from parabolic to flat-topped as the layer width increases, as predicted by earlier analytical results. The ionization fraction does not show this behavior and is always strongly out of coronal equilibrium, because of turbulent diffusion of neutral gas from the jet and external medium into the layer. Above a minimum jet velocity, we find that the predicted temperature and optical spectra of the mixing-layer depend mostly on the combination hPenv/(alpha v_j(2)equiv ) Sigma [where alpha ( =~ 0.007) is the adopted turbulent viscosity parameter and v_j the velocity of the jet]. This contrasts with shock models, where line ratios are strongly dependent upon the shock velocity. The [O I]6300/Hα ratio predicted by mixing-layer models appears too high by a factor of two compared with the line ratios of low-excitation HH objects. However, it may be compatible with line ratios in the

  11. On the stability of a plate under longitudinal compression on a two-layer half-space with lower layer prestressed by gravity forces

    NASA Astrophysics Data System (ADS)

    Alexandrov, V. M.; Zarubov, D. I.

    2008-06-01

    In the plane (plane strain) and axially symmetric statements, we study the problem of stability, under the action of longitudinal compressing forces, of an infinite elastic plate in two-sided contact with an elastic half-space. The upper layer of finite depth is described by the usual equations of linear theory of elasticity; the lower layer, which is geometrically nonlinear, incompressible, and infinite in depth, is prestressed by gravity forces. The total adhesion between the layer of finite depth and the lower half-space is realized. It is also assumed that the same adhesion takes place between the upper layer of the half-space and the plate with the contact tangential stresses taken into account. The results can be used to calculate the working capacity of coated bodies and layered composites and in problems of geophysics. The problem of stability of an infinite elastic plate under longitudinal compression under conditions of two-sided contact with an elastic base was studied earlier in the monograph [1] (Fuss-Winkler base) and in [2-4].

  12. 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.

  13. Submesoscale Flows and Mixing in the Ocean Surface Layer Using the Regional Oceanic Modeling System (ROMS)

    DTIC Science & Technology

    2013-09-30

    energy towards the dissipative scales of non- geostrophic turbulence. An advanced understanding of surface layer processes at these small scales is...modes are mixed layer instabilities that are essentially geostrophic in nature but have a smaller horizontal scale due to the reduced scale of the...targeted regions and by consulting on the data-assimilation system design and performance. Current quasi -operational, 3DVar applications are in

  14. An Optical Spectroscopic Study of HH 110: a Turbulent Mixing Layer?

    NASA Astrophysics Data System (ADS)

    Ayala, S.; Raga, A. C.; Curiel, S.

    2003-01-01

    The HH 110 jet extends 3 arcmin in length and consists of numerous knots forming the flow. Noriega-Crespo et al. (1996) found that the turbulent optical and near-infrared morphology of the HH 110 jet is consistent with that of a boundary layer. In this work, we have analyzed some line ratios along and across the jet in order to make a quantitative comparison with the line ratios predicted by the current mixing layer models.

  15. Comparison of different remote sensing methods for mixing layer height monitoring

    NASA Astrophysics Data System (ADS)

    Emeis, Stefan; Schäfer, Klaus; Münkel, Christoph; Friedl, Roman; Suppan, Peter

    2010-10-01

    Since 2006 different remote monitoring methods for mixing layer height have been operated in Augsburg. One method is based on eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter intensities recorded with these ceilometers provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the tops of mixed layers. A special software for these ceilometers provides routine retrievals of lower atmosphere layering. A second method, based on SODAR (Sound Detection and Ranging) observations, 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. This information is extended by measurements with a RASS (Radio-Acoustic Sounding System) which provide the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions which mark atmospheric layers. These SODAR and RASS data are the input to a software-based determination of mixing layer heights developed with MATLAB. A comparison of results of the three remote sensing methods during simultaneous measurements was performed. The information content of the ceilometer data is assessed by comparing it to the results from the other two instruments and near-by radiosonde data.

  16. 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.

  17. The daytime mixing layer observed by radiosonde, profiler, and lidar during MILAGRO

    NASA Astrophysics Data System (ADS)

    Shaw, W. J.; Pekour, M. S.; Coulter, R. L.; Martin, T. J.; Walters, J. T.

    2007-10-01

    During the MILAGRO campaign centered in the Mexico City area, Pacific Northwest National Laboratory (PNNL) and Argonne National Laboratory (ANL) operated atmospheric profiling systems at Veracruz and at two locations on the Central Mexican Plateau in the region around Mexico City. These systems included radiosondes, wind profilers, a sodar, and an aerosol backscatter lidar. An additional wind profiler was operated by the University of Alabama in Huntsville (UAH) at the Mexican Petroleum Institue (IMP) near the center of Mexico City. Because of the opportunity afforded by collocation of profilers, radiosondes, and a lidar, and because of the importance of boundary layer depth for aerosol properties, we have carried out a comparison of mixing layer depth as determined independently from these three types of measurement systems during the campaign. We have then used results of this comparison and additional measurements to develop a detailed description of the daily structure and evolution of the boundary layer on the Central Mexican Plateau during MILAGRO. Our analysis indicates that the profilers were more consistently successful in establishing the mixing layer depth during the daytime. The boundary layer growth was similar at the three locations, although the mixing layer tended to be slightly deeper in the afternoon in central Mexico City. The sodar showed that convection began about an hour after sunrise. Maximum daily mixing layer depths always reached 2000 m a.g.l. and frequently extended to 4000 m. The rate and variability of mixing layer growth was essentially the same as that observed during the IMADA-AVER campaign in the same season in 1997. This growth did not seem to be related to whether deep convection was reported on a given day. Wind speeds within the boundary layer exhibited a daily low-altitude maximum in the late afternoon with lighter winds aloft, consistent with previous reports of diurnal regional circulations. Norte events, which produced high

  18. 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

  19. 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.

  20. A similarity rule for compressibility and sidewall-boundary-layer effects in two-dimensional wind tunnels

    NASA Technical Reports Server (NTRS)

    Barnwell, R. W.

    1979-01-01

    The effect of the sidewall boundary layer on flow in two-dimensional wind tunnels is determined. The small-disturbance and isentropic approximations are made, and the sidewall-boundary-layer dynamics are modeled with the von Karman momentum-integral equation. The effects of the edge-velocity-gradient term in the sidewall momentum integral, which is usually dominant near the model, and the compressibility term are shown to be similar. It is shown that the effect of sidewall suction around the model is not similar to two-dimensional flow. Comparisons with experiment are made to verify the similarity rule.

  1. Effect of afterburner lights and inlet unstarts on a mixed compression inlet turbofan engine operating at Mach 2.5

    NASA Technical Reports Server (NTRS)

    Baumbick, R. J.; Batterton, P. G.; Daniele, C. J.

    1975-01-01

    Data are presented to show the response of an uncontrolled inlet to afterburner lightoff disturbances when a mixed-compression inlet is coupled to a turbofan engine. The results show a significant upstream shock excursion when the afterburner lights which is a result of the direct communication between the afterburner region and the inlet by means of the fan duct and fan stages. In addition results of a waveform analysis on the inlet pressure response to the afterburner light is presented. Inlet unstarts and their effect on operation of the propulsion system is also discussed.

  2. Quantitative investigation of compressible mixing: Staged transverse injection into Mach 2 flow

    NASA Technical Reports Server (NTRS)

    Hollo, Steven D.; Mcdaniel, James C.; Hartfield, Roy J., Jr.

    1994-01-01

    Planar measurements of the injectant mole fraction distribution and the velocity field within a supersonic mixing flowfield have been made using laser-induced iodine fluorescence. The flowfield investigated in this work is staged transverse injection of air into a Mach 2 freestream. A complete three-dimensional survey of the injectant mole fraction distribution has been generated, and a single planar velocity measurement has been completed. The measurements reveal the dramatic effect of streamwise vortices on the mixing in the near field of the injectors, as well as the rapid mixing generated by staging two fuel injectors. Analysis of the downstream decay of the maximum injectant mole fraction in this and other supersonic mixing flowfields indicates that the relative rate of injectant mixing well downstream of the injectors is independent of injection geometry, freestream Mach number, and injectant molecular weight. Mixing within this region of the flowfield is dominated by small-scale turbulence within the injectant plume. The transition of the dominant mixing mechanism, from vortex-driven mixing in the near field to small-scale turbulent mixing in the far field, was found to occur in the region about 10 diameters downstream of the injectors.

  3. 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.

  4. 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

  5. The Daytime Mixed Layer Observed by Radiosonde, Profiler, and LIDAR during MILAGRO

    SciTech Connect

    Shaw, William J.; Pekour, Mikhail S.; Coulter, Richard L.; Martin, Tim J.; Walters, Justin

    2007-10-19

    During the MILAGRO campaign centered in the Mexico City area, Pacific Northwest National Laboratory (PNNL) and Argonne National Laboratory (ANL) operated several atmospheric profiling systems at Veracruz and at two locations on the Central Mexican Plateau in the region around Mexico City. These systems included radiosondes, wind profilers, a sodar, and an aerosol backscatter lidar. An additional wind profiler was operated by the University of Alabama in Huntsville (UAH) at the Mexican Petroleum Institue (IMP) near the center of Mexico City. Because of the opportunity afforded by collocation of profilers, radiosondes, and a lidar, and because of the importance of boundary layer depth on aerosol properties, we have carried out a comparison of mixed layer depth as determined independently from these three types of measurement systems during the campaign. We have then used results of this comparison and additional measurements to develop a detailed description of the daily structure and evolution of the boundary layer on the Central Mexican Plateau during MILAGRO. Our analysis indicates that the profilers were more consistently successful in establishing the mixing layer depth during the daytime. The boundary layer growth was similar at the three locations, although the mixing layer tended to be slightly deeper in the afternoon in central Mexico City. The sodar showed that convection began about an hour after sunrise. Maximum daily mixed layer depths always reached 2000 m AGL and frequently extended to 4000 m. The rate and variability of mixing layer growth was essentially the same as that observed during the IMADA-AVER campaign in the same season in 1997. This growth did not seem to be related to whether deep convection was reported on a given day. Wind speeds within the boundary layer exhibited a daily low-altitude maximum in the late afternoon with lighter winds aloft, consistent with previous reports of diurnal regional circulations. Norte events, which produced

  6. [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.

  7. Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump.

    PubMed

    Dall'Olmo, Giorgio; Dingle, James; Polimene, Luca; Brewin, Robert J W; Claustre, Hervé

    2016-11-01

    The "mesopelagic" is the region of the ocean between about 100 and 1000 m that harbours one of the largest ecosystems and fish stocks on the planet1,2. This vastly unexplored ecosystem is believed to be mostly sustained by chemical energy, in the form of fast-sinking particulate organic carbon, supplied by the biological carbon pump3. Yet, this supply appears insufficient to match mesopelagic metabolic demands4-6. The mixed-layer pump is a physically-driven biogeochemical process7-11 that could further contribute to meet these energetic requirements. However, little is known about the magnitude and spatial distribution of this process at the global scale. Here we show that the mixed-layer pump supplies an important seasonal flux of organic carbon to the mesopelagic. By combining mixed-layer depths from Argo floats with satellite retrievals of particulate organic carbon, we estimate that this pump exports a global flux of about 0.3 Pg C yr(-1) (range 0.1 - 0.5 Pg C yr(-1)). In high-latitude regions where mixed-layers are deep, this flux is on average 23%, but can be greater than 100% of the carbon supplied by fast sinking particles. Our results imply that a relatively large flux of organic carbon is missing from current energy budgets of the mesopelagic.

  8. Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump

    PubMed Central

    Dall’Olmo, Giorgio; Dingle, James; Polimene, Luca; Brewin, Robert J.W.; Claustre, Hervé

    2016-01-01

    The “mesopelagic” is the region of the ocean between about 100 and 1000 m that harbours one of the largest ecosystems and fish stocks on the planet1,2. This vastly unexplored ecosystem is believed to be mostly sustained by chemical energy, in the form of fast-sinking particulate organic carbon, supplied by the biological carbon pump3. Yet, this supply appears insufficient to match mesopelagic metabolic demands4–6. The mixed-layer pump is a physically-driven biogeochemical process7–11 that could further contribute to meet these energetic requirements. However, little is known about the magnitude and spatial distribution of this process at the global scale. Here we show that the mixed-layer pump supplies an important seasonal flux of organic carbon to the mesopelagic. By combining mixed-layer depths from Argo floats with satellite retrievals of particulate organic carbon, we estimate that this pump exports a global flux of about 0.3 Pg C yr−1 (range 0.1 – 0.5 Pg C yr−1). In high-latitude regions where mixed-layers are deep, this flux is on average 23%, but can be greater than 100% of the carbon supplied by fast sinking particles. Our results imply that a relatively large flux of organic carbon is missing from current energy budgets of the mesopelagic. PMID:27857779

  9. 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.

  10. The use of Argo for validation and tuning of mixed layer models

    NASA Astrophysics Data System (ADS)

    Acreman, D. M.; Jeffery, C. D.

    We present results from validation and tuning of 1-D ocean mixed layer models using data from Argo floats and data from Ocean Weather Station Papa (145°W, 50°N). Model tests at Ocean Weather Station Papa showed that a bulk model could perform well provided it was tuned correctly. The Large et al. [Large, W.G., McWilliams, J.C., Doney, S.C., 1994. Oceanic vertical mixing: a review and a model with a nonlocal boundary layer parameterisation. Rev. Geophys. 32 (Novermber), 363-403] K-profile parameterisation (KPP) model also gave a good representation of mixed layer depth provided the vertical resolution was sufficiently high. Model tests using data from a single Argo float indicated a tendency for the KPP model to deepen insufficiently over an annual cycle, whereas the tuned bulk model and general ocean turbulence model (GOTM) gave a better representation of mixed layer depth. The bulk model was then tuned using data from a sample of Argo floats and a set of optimum parameters was found; these optimum parameters were consistent with the tuning at OWS Papa.

  11. Mixed layer depth variations in the Kuroshio Extension in relation to Japanese sardine

    NASA Astrophysics Data System (ADS)

    Yasuda, I.; Nishikawa, H.; Itoh, S.

    2008-12-01

    Mixed layer depths in and south of the Kuroshio Extension changed from deep to shallow states in the late- 1980s and early-1990s. This change corresponded to the collapse of Japanese sardine (Sardinops melanostictus). This mixed layer shoaling was accompanied by lower temperature in 200-400m depths and higher temperature near the surface. Wintertime field survey in 2006 (Hakuho-maru KH06-1 cruise) demonstrated that late winter maximum mixed layer depth reach deeper with the greater isothermal depth of 14-15degC and higher temperature in 300-400m depth. High-resolution ocean model hindcast data suggests that the accelerated near-surface Kuroshio/Kuroshio Extension associated with the elevated sea-surface height anomaly enhanced the heat transport near the surface. This greater heat advection near the surface overrides the cooler subtropical mode water that was created in the previous years possibly causes the shallower winter mixed layer and collapse of the Japanese sardine.

  12. Numerical simulation of a plane turbulent mixing layer, with applications to isothermal, rapid reactions

    NASA Technical Reports Server (NTRS)

    Lin, P.; Pratt, D. T.

    1987-01-01

    A hybrid method has been developed for the numerical prediction of turbulent mixing in a spatially-developing, free shear layer. Most significantly, the computation incorporates the effects of large-scale structures, Schmidt number and Reynolds number on mixing, which have been overlooked in the past. In flow field prediction, large-eddy simulation was conducted by a modified 2-D vortex method with subgrid-scale modeling. The predicted mean velocities, shear layer growth rates, Reynolds stresses, and the RMS of longitudinal velocity fluctuations were found to be in good agreement with experiments, although the lateral velocity fluctuations were overpredicted. In scalar transport, the Monte Carlo method was extended to the simulation of the time-dependent pdf transport equation. For the first time, the mixing frequency in Curl's coalescence/dispersion model was estimated by using Broadwell and Breidenthal's theory of micromixing, which involves Schmidt number, Reynolds number and the local vorticity. Numerical tests were performed for a gaseous case and an aqueous case. Evidence that pure freestream fluids are entrained into the layer by large-scale motions was found in the predicted pdf. Mean concentration profiles were found to be insensitive to Schmidt number, while the unmixedness was higher for higher Schmidt number. Applications were made to mixing layers with isothermal, fast reactions. The predicted difference in product thickness of the two cases was in reasonable quantitative agreement with experimental measurements.

  13. Revealing the Location of the Mixing Layer in a Hot Bubble

    NASA Astrophysics Data System (ADS)

    Guerrero, M. A.; Fang, X.; Chu, Y. H.; Toalá, J. A.; Gruendl, R. A.

    2017-03-01

    The fast stellar winds can blow bubbles in the circumstellar material ejected from previous phases of stellar evolution. These are found at different scales, from planetary nebulae (PNe) around stars evolving to the white dwarf stage, to Wolf-Rayet (WR) bubbles and up to large-scale bubbles around massive star clusters. In all cases, the fast stellar wind is shock-heated and a hot bubble is produced. At the mixing layer between the hot bubble and optical nebula, processes of mass evaporation and mixing of nebular material and heat conduction are key to determine the thermal structure of these bubbles and their evolution. In this contribution we review our current understanding of the X-ray observations of hot bubbles in PNe and present the first spatially-resolved study of a mixing layer in a PN.

  14. The three-dimensional evolution of a plane mixing layer - The Kelvin-Helmholtz rollup

    NASA Technical Reports Server (NTRS)

    Rogers, Michael M.; Moser, Robert D.

    1992-01-01

    The hydrodynamic evolution of an incompressible plane mixing layer is addressed to elucidate scalar mixing in free shear flows. A detailed description of the onset of three-dimensionality in a mixing layer before or in the absence of pairing is presented. Various simulations were performed to investigate the sensitivity of these results to variations in initial conditions. These variations included changes in amplitude, wavelength, functional form, and relative phasing of the initial low-wavenumber disturbances. Pierrehumber and Widnall's (1982) translative instability eigenfunctions are found to include rib vortices in the braid region and oppositely signed streamwise vorticity in the roller core. The translative instability is an instability of the late-time oversaturated flow. Three-dimensional perturbation growth similar to that of the translative instability can occur whenever spanwise vorticity is present in the braid region. The nonlinear effects that occur when the initial rib circulation is sufficiently high are discussed.

  15. An updated length-scale formulation for turbulent mixing in clear and cloudy boundary layers

    NASA Astrophysics Data System (ADS)

    Lenderink, G.; Holtslag, A. A. M.

    2004-10-01

    A new mixing-length scale is presented for turbulence-closure schemes, with special emphasis on neutral-to-convective conditions in clear and cloudy boundary layers. The length scale is intended for a prognostic turbulent-kinetic-energy closure. It is argued that present-day length-scale formulations may easily fail in one of two limiting situations. Schemes based on a local stability measure (e.g.the Richardson number) display unrealistic behaviour and instabilities in the convective limit. This strongly limits the representation of mixing in cloudy boundary layers. On the other hand, it is shown that non-local parcel methods may misrepresent mixing near the surface. The new length-scale formulation combines local and non-local stability in a new way; it uses vertical integrals over the stability (the Richardson number) in a simple 'parcel' framework. The length scale matches with surface-layer similarity for near-neutral conditions and displays a realistic convective limit. The use of the length-scale formulation can be extended easily to cloudy boundary layers. The scheme is numerically stable and computationally cheap. The behaviour of the length scale is evaluated in a single-column model (SCM) and in a high-resolution limited-area model (LAM). The SCM shows good behaviour in three cases with and without boundary-layer clouds. The prediction of the near-surface wind and temperature in the LAM compares favourably with tower measurements at Cabauw (the Netherlands).

  16. 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.

  17. 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.

  18. The potential flow bounded by a mixing layer and a solid surface

    NASA Astrophysics Data System (ADS)

    Wood, D. H.; Ferziger, J. H.

    1984-10-01

    The present investigation is a companion study to that of Wood and Bradshaw (1982), who measured the change in turbulence structure as the single-stream mixing layer approached that wind tunnnel floor. On the basis of spatial correlation measurements taken where the influence of the wall is small, Wood and Bradshaw concluded that the large turbulent eddies were essentially three-dimensional. In the present investigation it is shown that the extensions of Phillips's (1955) theory to include one-dimensional spectra and spatial correlations in the near-field potential flow provide an explanation for the large correlation scales, relative to the shear layer thickness, which have been measured outside turbulent mixing layers.

  19. Nutrient interleaving below the mixed layer of the Kuroshio Extension Front

    NASA Astrophysics Data System (ADS)

    Nagai, Takeyoshi; Clayton, Sophie

    2017-08-01

    Nitrate interleaving structures were observed below the mixed layer during a cruise to the Kuroshio Extension in October 2009. In this paper, we investigate the formation mechanisms for these vertical nitrate anomalies, which may be an important source of nitrate to the oligotrphoc surface waters south of the Kuroshio Extension Front. We found that nitrate concentrations below the main stream of the Kuroshio Extension were elevated compared to the ambient water of the same density ( σ 𝜃 = 23.5-25). This appears to be analogous to the "nutrient stream" below the mixed layer, associated with the Gulf Stream. Strong turbulence was observed above the vertical nitrate anomaly, and we found that this can drive a large vertical turbulent nitrate flux >O (1 mmol N m-2 day-1). A realistic, high-resolution (2 km) numerical simulation reproduces the observed Kuroshio nutrient stream and nitrate interleaving structures, with similar lateral and vertical scales. The model results suggest that the nitrate interleaving structures are first generated at the western side of the meander crest on the south side of the Kuroshio Extension, where the southern tip of the mixed layer front is under frontogenesis. Lagrangian analyses reveal that the vertical shear of geostrophic and subinertial ageostrophic flow below the mixed layer tilts the existing along-isopycnal nitrate gradient of the Kuroshio nutrient stream to form nitrate interleaving structures. This study suggests that the multi-scale combination of (i) the lateral stirring of the Kuroshio nutrient stream by developed mixed layer fronts during fall to winter, (ii) the associated tilting of along-isopycnal nitrate gradient of the nutrient stream by subinertial shear, which forms vertical interleaving structures, and (iii) the strong turbulent diffusion above them, may provide a route to supply nutrients to oligotrophic surface waters on the south side of the Kuroshio Extension.

  20. Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

    DOE PAGES

    Flippo, K. A.; Doss, F. W.; Kline, J. L.; ...

    2016-11-23

    While using a large volume high-energy-density fluid shear experiment ( 8.5 cm 3 ) at the National Ignition Facility, we have demonstrated for the first time the ability to significantly alter the evolution of a supersonic sheared mixing layer by controlling the initial conditions of that layer. Furthermore, by altering the initial surface roughness of the tracer foil, we demonstrate the ability to transition the shear mixing layer from a highly ordered system of coherent structures to a randomly ordered system with a faster growing mix layer, indicative of strong mixing in the layer at a temperature of several tensmore » of electron volts and at near solid density. Moreover, simulations using a turbulent-mix model show good agreement with the experimental results and poor agreement without turbulent mix.« less

  1. Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

    NASA Astrophysics Data System (ADS)

    Flippo, K. A.; Doss, F. W.; Kline, J. L.; Merritt, E. C.; Capelli, D.; Cardenas, T.; DeVolder, B.; Fierro, F.; Huntington, C. M.; Kot, L.; Loomis, E. N.; MacLaren, S. A.; Murphy, T. J.; Nagel, S. R.; Perry, T. S.; Randolph, R. B.; Rivera, G.; Schmidt, D. W.

    2016-11-01

    Using a large volume high-energy-density fluid shear experiment (8.5 cm3 ) at the National Ignition Facility, we have demonstrated for the first time the ability to significantly alter the evolution of a supersonic sheared mixing layer by controlling the initial conditions of that layer. By altering the initial surface roughness of the tracer foil, we demonstrate the ability to transition the shear mixing layer from a highly ordered system of coherent structures to a randomly ordered system with a faster growing mix layer, indicative of strong mixing in the layer at a temperature of several tens of electron volts and at near solid density. Simulations using a turbulent-mix model show good agreement with the experimental results and poor agreement without turbulent mix.

  2. Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

    SciTech Connect

    Flippo, K. A.; Doss, F. W.; Kline, J. L.; Merritt, E. C.; Capelli, D.; Cardenas, T.; DeVolder, B.; Fierro, F.; Huntington, C. M.; Kot, L.; Loomis, E. N.; MacLaren, S. A.; Murphy, T. J.; Nagel, S. R.; Perry, T. S.; Randolph, R. B.; Rivera, G.; Schmidt, D. W.

    2016-11-23

    Using a large volume high-energy-density fluid shear experiment (8.5 cm3) at the National Ignition Facility, we have demonstrated for the first time the ability to significantly alter the evolution of a supersonic sheared mixing layer by controlling the initial conditions of that layer. By altering the initial surface roughness of the tracer foil, we demonstrate the ability to transition the shear mixing layer from a highly ordered system of coherent structures to a randomly ordered system with a faster growing mix layer, indicative of strong mixing in the layer at a temperature of several tens of electron volts and at near solid density. Simulations using a turbulent-mix model show good agreement with the experimental results and poor agreement without turbulent mix.

  3. An Observational Study of Wind Profiles in the Baroclinic Convective Mixed Layer

    NASA Astrophysics Data System (ADS)

    Lemone, Margaret A.; Zhou, Mingyu; Moeng, Chin-Hoh; Lenschow, Donald H.; Miller, L. Jay; Grossman, Robert L.

    A comprehensive planetary boundary-layer (PBL) and synoptic data set is used to isolate the mechanisms that determine the vertical shear of the horizontal wind in the convective mixed layer. To do this, we compare a fair-weather convective PBL with no vertical shear through the mixed layer (10 March 1992), with a day with substantial vertical shear in the north-south wind component (27 February). The approach involves evaluating the terms of the budget equations for the two components of the vertical shear of the horizontal wind; namely: the time-rate-of-change or time-tendency term, differential advection, the Coriolis terms (a thermal wind term and a shear term), and the second derivative of the vertical transport of horizontal momentum with respect to height (turbulent-transport term). The data, gathered during the 1992 STorm-scale Operational and Research Meteorology (STORM) Fronts Experiments Systems Test (FEST) field experiment, are from gust-probe aircraft horizontal legs and soundings, 915-MHz wind profilers, a 5-cm Doppler radar, radiosondes, and surface Portable Automated Mesonet (PAM) stations in a roughly 50 × 50 km boundary-layer array in north-eastern Kansas, nested in a mesoscale-to-synoptic array of radiosondes and surface data.We present evidence that the shear on 27 February is related to the rapid growth of the convective boundary layer. Computing the shear budget over a fixed depth (the final depth of the mixed layer), we find that the time-tendency term dominates, reflecting entrainment of high-shear air from above the boundary layer. We suggest that shear within the mixed layer occurs when the time-tendency term is sufficiently large that the shear-reduction terms - namely the turbulent-transport term and differential advection terms - cannot compensate. In contrast, the tendency term is small for the slowly-growing PBL of 10 March, resulting in a balance between the Coriolis terms and the turbulent-transport term. Thus, the thermal wind

  4. 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.

  5. 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.

  6. Mixing and trapping of dissolved CO2 in deep geologic formations with shale layers

    NASA Astrophysics Data System (ADS)

    Agartan, Elif; Cihan, Abdullah; Illangasekare, Tissa H.; Zhou, Quanlin; Birkholzer, Jens T.

    2017-07-01

    For dissolution trapping, the spatial variability of the geologic properties of naturally complex storage formations can significantly impact flow patterns and storage mechanisms of dissolved CO2. The significance of diffusive mixing that occurs in low permeability layers embedded between relatively higher permeability materials was highlighted by Agartan et al. (2015) using a highly controlled laboratory experimental study on trapping of dissolved CO2 in multilayered systems. In this paper, we present a numerical modeling study on the impacts of low permeability layers on flow and storage of dissolved CO2 in realistic field-scale settings. The simulator of variable-density flow used in this study was first verified using the experimental data in Agartan et al. (2015) to capture the observed processes. The simulator was then applied to a synthetic, field-scale multilayered system, with 19 sensitivity cases having variable permeability and thickness of the shale layers as well as the source strength and geometry of the source zone of dissolved CO2. Simulation results showed that the presence of continuous shale layers in the storage system disrupts the convective mixing by enhancing lateral spreading of dissolved CO2 in sandstone layers and retarding the vertical mixing of dissolved CO2. The effectiveness of trapping of dissolved CO2 depends on the physical properties of the shale layers and configurations of the source zone. The comparison to homogeneous cases with effective vertical permeability shows that it is important to capture these continuous thin shale layers in a storage formation and include them in the models to enhance dissolution trapping.

  7. Compression-triggered instabilities of multi-layer systems: From thin elastic membranes to lipid bilayers on flexible substrates

    NASA Astrophysics Data System (ADS)

    Stone, Howard A.

    2013-03-01

    Instabilities are triggered when elastic materials are subjected to compression. We explore new features of two distinct systems of this type. First, we describe a two-layer polymeric system under biaxial compressive stress, which exhibits a repetitive wrinkle-to-fold transition that subsequently generates a hierarchical network of folds during reorganization of the stress field. The folds delineate individual domains, and each domain subdivides into smaller ones over multiple generations. By modifying the boundary conditions and geometry, we demonstrate control over the final network morphology. Some analogies to the venation pattern of leaves are indicated. Second, motivated by the confined configurations common to cells, which are wrapped in lipid bilayer membranes, we study a lipid bilayer, coupled to an elastic sheet, and demonstrate that, upon straining, the confined lipid membrane is able to passively regulate its area. In particular, by stretching the elastic support, the bilayer laterally expands without rupture by fusing adhered lipid vesicles; upon compression, lipid tubes grow out of the membrane plane, thus reducing its area. These transformations are reversible, as we show using cycles of expansion and compression, and closely reproduce membrane processes found in cells during area regulation. The two distinct systems illustrate the influence of the substrate on finite amplitude shape changes, for which we describe the time-dependent shape evolution as the stress relaxes. This talk describes joint research with Manouk Abkarian, Marino Arroyo, Pilnam Kim, Mohammad Rahimi and Margarita Staykova.

  8. 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.

  9. 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, has been investigated. The maximum Ux/nu allowed by the facility was 6.7 x 100.000; the maximum x station surveyed corresponds to approximately 2000 and 700 initial momentum thicknesses for the laminar and turbulent cases respectively. The use of commonly accepted non-dimensional representations of the data confirm (at least) an approximately self-preserving condition. They also suggest that the effects of the laminar/turbulent initial condition persist in the self-preserving region. A direct comparison of the data reveals that the persistence so observed is illusory. An interpretation of the reason for this misunderstanding is advanced.

  10. 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

  11. Direct quantification of the mechanical anisotropy and fracture of an individual exoskeleton layer via uniaxial compression of micropillars.

    PubMed

    Han, Lin; Wang, Lifeng; Song, Juha; Boyce, Mary C; Ortiz, Christine

    2011-09-14

    A common feature of the outer layer of protective biological exoskeletons is structural anisotropy. Here, we directly quantify the mechanical anisotropy and fracture of an individual material layer of a hydroxyapatite-based nanocomposite exoskeleton, the outmost ganoine of Polypterus senegalus scale. Uniaxial compression was conducted on cylindrical micropillars of ganoine fabricated via focused ion beam at different orientations relative to the hydroxyapatite rod long axis (θ = 0°, 45°, 90°). Engineering stress versus strain curves revealed significant elastic and plastic anisotropy, off-axial strain hardening, and noncatastrophic crack propagation within ganoine. Off-axial compression (θ = 45°) showed the lowest elastic modulus, E (36.2 ± 1.6 GPa, n ≥ 10, mean ± SEM), and yield stress, σ(Y) (0.81 ± 0.02 GPa), while compression at θ = 0° showed the highest E (51.8 ± 1.7 GPa) and σ(Y) (1.08 ± 0.05 GPa). A 3D elastic-plastic composite nanostructural finite element model revealed this anisotropy was correlated to the alignment of the HAP rods and could facilitate energy dissipation and damage localization, thus preventing catastrophic failure upon penetration attacks.

  12. 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). Copyright © 2010 Elsevier Ltd. All rights reserved.

  13. 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.

  14. 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.

  15. Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Jen, Shih-Hui; Bertrand, Jacob A.; George, Steven M.

    2011-04-01

    Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30-50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ˜1.0%. The critical compressive strain increased to ˜2.0% at a film thickness of ˜20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ˜1.0% for film thicknesses of 30-50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses

  16. Observed mesoscale eddy signatures in Southern Ocean surface mixed-layer depth

    NASA Astrophysics Data System (ADS)

    Hausmann, U.; McGillicuddy, Dennis J.; Marshall, John

    2017-01-01

    Combining satellite altimetry with Argo profile data a systematic observational estimate of mesoscale eddy signatures in surface mixed-layer depth (MLD) is provided across the Southern Ocean (SO). Eddy composite MLD anomalies are shallow in cyclones, deep in anticyclones, and increase in magnitude with eddy amplitude. Their magnitudes show a pronounced seasonal modulation roughly following the depth of the climatological mixed layer. Weak eddies of the relatively quiescent SO subtropics feature peak late-winter perturbations of ±10 m. Much larger MLD perturbations occur over the vigorous eddies originating along the Antarctic Circumpolar Current (ACC) and SO western boundary current systems, with late-winter peaks of -30 m and +60 m in the average over cyclonic and anticyclonic eddy cores (a difference of ≈ 100 m). The asymmetry between modest shallow cyclonic and pronounced deep anticyclonic anomalies is systematic and not accompanied by corresponding asymmetries in eddy amplitude. Nonetheless, the net deepening of the climatological SO mixed layer by this asymmetry in eddy MLD perturbations is estimated to be small (few meters). Eddies are shown to enhance SO MLD variability with peaks in late winter and eddy-intense regions. Anomalously deep late-winter mixed layers occur disproportionately within the cores of anticyclonic eddies, suggesting the mesoscale heightens the frequency of deep winter surface-mixing events along the eddy-intense regions of the SO. The eddy modulation in MLD reported here provides a pathway via which the oceanic mesoscale can impact air-sea fluxes of heat and carbon, the ventilation of water masses, and biological productivity across the SO.

  17. Direct compression of cushion-layered ethyl cellulose-coated extended release pellets into rapidly disintegrating tablets without changes in the release profile.

    PubMed

    Hosseini, Armin; Körber, Martin; Bodmeier, Roland

    2013-12-05

    The aim of this study was to develop and optimize a segregation-free ethyl cellulose-coated extended release multiparticulate formulation to be compressed into tablets without affecting the drug release. Standard tableting excipients (e.g., microcrystalline cellulose, lactose or sorbitol) were layered onto ethyl cellulose-coated propranolol hydrochloride pellets to form a cushion layer in order to eliminate segregation problems normally resulting from particle size difference between coated pellets and excipient powders and second to protect the integrity of the brittle ethyl cellulose coating during compression. The disintegration behavior of the tablets depended strongly on the composition of the cushion layer. Rapid tablet disintegration was obtained with microcrystalline cellulose and the disintegrant sodium croscarmellose. However, the drug release from these cushion-layered pellets still increased upon compression. Incorporation of a glidant into the cushion layer or between the cushion layer and the ethyl cellulose coating reduced the compression effect on drug release markedly. Glidant-containing formulations showed a delayed deformation and damage of the ethyl cellulose-coated pellet upon mechanical stress. In summary, cushion layer based on microcrystalline cellulose facilitated segregation-free compression of a highly compression-sensitive extended release ethyl cellulose-coated pellets into fast-disintegrating and hard tablets without compromising the release properties of the multiparticulates. Directly compressible cushion-layered pellets protected the pellet coating significantly better from damages during tabletting when compared to the conventional compression of blends of coated pellets and excipient powders. Copyright © 2013. Published by Elsevier B.V.

  18. The Role of Late Summer Melt Pond Water Layers in the Ocean Mixed Layer on Enhancing Ice/Ocean Albedo Feedbacks in the Arctic

    NASA Astrophysics Data System (ADS)

    Stanton, T. P.; Shaw, W. J.

    2016-02-01

    Drainage of surface melt pond water into the top of the ocean mixed layer is seen widely in the Arctic ice pack in later summer (for example Gallaher et al 2015). Under calm conditions, this fresh water forms a thin, stratified layer immediately below the ice which is dynamically decoupled from the thicker, underlying seasonal mixed layer by the density difference between the two layers. The ephemeral surface layer is significantly warmer than the underlying ocean water owing to the higher freezing temperature of the fresh melt water. How the presence of this warm ephemeral layer enhances basal melt rate and speeds the destruction of the floes is investigated. High resolution timeseries measurements of T/S profiles in the 2m of the ocean immediately below the ice, and eddy-correlation fluxes of heat, salt and momentum 2.5m below the ice were made from an Autonomous Ocean Flux Buoy over a 2 month interval in later summer of 2015 as a component of the ONR Marginal Ice Zone project. The stratification and turbulent forcing observations are used with a 1 D turbulence closure model to understand how momentum and incoming radiative energy are stored and redistributed within the ephemeral layer. Under low wind forcing conditions both turbulent mixing energy and the water with high departure from freezing are trapped in the ephemeral layer by the strong density gradient at the base of the layer, resulting in rapid basal melting. This case is contrasted with model runs where the ephemeral layer heat is allowed to mix across the seasonal mixed layer, which results in slower basal melt rates. Consequently, the salinity-trapped warm ephemeral layer results in the formation of more open water earlier in the summer season, in turn resulting in increased cumulative heating of the ocean mixed layer, enhancing ice/ocean albedo feedbacks.

  19. A compressible wall-adapting similarity mixed model for large-eddy simulation of the impinging round jet

    NASA Astrophysics Data System (ADS)

    Lodato, Guido; Vervisch, Luc; Domingo, Pascale

    2009-03-01

    Wall-jet interaction is studied with large-eddy simulation (LES) in which a mixed-similarity subgrid scale (SGS) closure is combined with the wall-adapting local eddy-viscosity (WALE) model for the eddy-viscosity term. The macrotemperature and macropressure are introduced to deduce a weakly compressible form of the mixed-similarity model, and the relevant formulation for the energy equation is deduced accordingly. LES prediction capabilities are assessed by comparing flow statistical properties against experiment of an unconfined impinging round jet at Reynolds numbers of 23 000 and 70 000. To quantify the benefit of the proposed WALE-similarity mixed model, the lower Reynolds number simulations are also performed using the standard WALE and Lagrangian dynamic Smagorinsky approaches. The unsteady compressible Navier-Stokes equations are integrated over 2.9 M, 3.5 M, and 5.5 M node Cartesian grids with an explicit fourth-order finite volume solver. Nonreflecting boundary conditions are enforced using a methodology accounting for the three-dimensional character of the turbulent flow at boundaries. A correct wall scaling is achieved from the combination of similarity and WALE approaches; for this wall-jet interaction, the SGS closure terms can be computed in the near-wall region without the necessity of resorting to additional specific treatments. The possible impact of turbulent energy backscatter in such flow configurations is also addressed. It is found that, for the present configuration, the correct reproduction of reverse energy transfer plays a key role in the estimation of near-wall statistics, especially when the viscous sublayer is not properly resolved.

  20. The convection of large and intermediate scale fluctuations in a turbulent mixing layer

    NASA Astrophysics Data System (ADS)

    Buxton, O. R. H.; de Kat, R.; Ganapathisubramani, B.

    2013-12-01

    The convection velocity of large and intermediate scale velocity fluctuations in a nominally two-dimensional planar mixing layer, and its dependence upon the length scale, is explored by carrying out particle image velocimetry (PIV) experiments. A "global" convection velocity, containing the convection of all the length scales present in the flow, is produced by examining the autocorrelation functions between velocity fluctuations in successive PIV records across the mixing layer. This "global" convection velocity is found to be similar to the mean flow, although fluctuations on the low speed side of the mixing layer on average convect at speeds greater than the mean and fluctuations on the high speed side of the mixing layer are observed to convect at speeds less than the mean. Scale specific convection velocity profiles are then produced by examining the phase difference between the spectral content specific to one wavenumber in streamwise velocity fluctuation traces in successive PIV records, offset by time τ. Probability density functions (pdfs) are produced of this phase difference, which is subsequently converted into a convection displacement, and these show that the convection of single length scale fluctuations exhibits a significant variance, particularly so for larger scale fluctuations and in the high speed side of the mixing layer. Convection velocity profiles are produced from these pdfs using both the mean convection distance and the modal convection distance. It is observed that the convection velocity is relatively insensitive to the length scale of the fluctuations considered, particularly when the mean convection distance is used. A slight sensitivity to length scale is, however, observed for convection velocities based on the modal convection distance. This dependence is primarily observed in the high speed side of the mixing layer, in which smaller length-scale fluctuations convect more quickly than larger length-scale fluctuations. It is also

  1. 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.

  2. On the non-resistive limit and the magnetic boundary-layer for one-dimensional compressible magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Jiang, Song; Zhang, Jianwen

    2017-09-01

    We consider an initial-boundary value problem for the one-dimensional equations of compressible isentropic magnetohydrodynamic (MHD) flows. The non-resistive limit of the global solutions with large data is justified. As a by-product, the global well-posedness of the compressible non-resistive MHD equations is established. Moreover, the thickness of the magnetic boundary-layer of the value O(ν^α) with 0<α<1/2 is proved, where ν>0 is the resistivity coefficient. The proofs of these results are based on a full use of the so-called ‘effective viscous flux’, the material derivative and the structure of the equations.

  3. Effects of compressibility and free-stream turbulence on boundary layer transition in high-subsonic and transonic flows

    NASA Technical Reports Server (NTRS)

    Murthy, S. V.; Steinle, F. W.

    1986-01-01

    Based on the existing boundary layer transition data, the effects of compressibility, pressure fluctuations, and free-stream turbulence have been reexamined for subsonic and transonic flow speeds. It is confirmed that the compressibility effects may be adequately expressed in terms of a simple correlation with free-stream Mach number. Pressure fluctuations, especially at low levels, do not seem to significantly affect the transition phenomenon. Effects of free-stream turbulence in high-subsonic and transonic flows are similar to the trends observed for low-speed flows and the transition process is hastened. The trends, as seen from slender cone flow data, seem to suggest power law correlations between transition Reynolds number and free-stream turbulence.

  4. Effects of compressibility and free-stream turbulence on boundary layer transition in high-subsonic and transonic flows

    NASA Technical Reports Server (NTRS)

    Murthy, S. V.; Steinle, F. W.

    1986-01-01

    Based on the existing boundary layer transition data, the effects of compressibility, pressure fluctuations, and free-stream turbulence have been reexamined for subsonic and transonic flow speeds. It is confirmed that the compressibility effects may be adequately expressed in terms of a simple correlation with free-stream Mach number. Pressure fluctuations, especially at low levels, do not seem to significantly affect the transition phenomenon. Effects of free-stream turbulence in high-subsonic and transonic flows are similar to the trends observed for low-speed flows and the transition process is hastened. The trends, as seen from slender cone flow data, seem to suggest power law correlations between transition Reynolds number and free-stream turbulence.

  5. a Novel pt and Npt Mixed Igbt Having a New n-BUFFER Layer

    NASA Astrophysics Data System (ADS)

    Zhang, Fei; Luo, Shuhua; Zhang, Liang; Wang, Wei; Yu, Wen; Li, Chengfang; Sun, Xiaowei

    For the first time, a novel mixed insulated gate bipolar transistor (MIGBT) is proposed and verified by two-dimensional (2D) mixed device-circuit simulations. The structure of the proposed device is almost identical with that of the conventional IGBT, except for the buffer layer which is formed by employing the n+/n- structure, so that the trade-off relation between the conduction and switching losses is greatly improved and efficiently decoupled. Furthermore, the proposed device exhibits larger forward blocking voltage and positive temperature coefficient of the forward voltage drop, facilitating parallel integration.

  6. Effects of a Periodic Disturbance on Structure and Mixing in Turbulent Shear Layers and Wakes

    DTIC Science & Technology

    1985-01-01

    34 , § B.7.3 770 77 attt 0 ,§B.2 .. . . . . . . . * -xvii - constant, see equation (B.85b) in § B.5 z coordinate of a point on the interface, § B.2 real part...This should be compared to the boundary layer on the real side-wall which had developed over the entire contraction length of approximately 80cm...useful in a real combustion situation. Not only does the amount of mixing increase as a result of forcing, but the mixing occurs in the center of the

  7. Mixed convection boundary layer flow over a horizontal circular cylinder in a Jeffrey fluid

    NASA Astrophysics Data System (ADS)

    Zokri, S. M.; Arifin, N. S.; Mohamed, M. K. A.; Salleh, M. Z.; Kasim, A. R. M.; Mohammad, N. F.

    2017-05-01

    In this paper, the mixed convection boundary layer flow and heat transfer of Jeffrey fluid past a horizontal circular cylinder with viscous dissipation effect and constant heat flux is discussed. The governing nonlinear partial differential equations are transformed into dimensionless forms using the appropriate non-similar transformation. Numerical solutions are obtained by using the Keller-box method, which is proven well-tested, flexible, implicit and unconditionally stable. The numerical results for the velocity, temperature, skin friction coefficient and local Nusselt number are attained for various values of mixed convection parameter.

  8. 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.

  9. Pathfinder: applying graph theory to consistent tracking of daytime mixed layer height with backscatter lidar

    NASA Astrophysics Data System (ADS)

    de Bruine, Marco; Apituley, Arnoud; Donovan, David Patrick; Klein Baltink, Hendrik; Jorrit de Haij, Marijn

    2017-05-01

    The height of the atmospheric boundary layer or mixing layer is an important parameter for understanding the dynamics of the atmosphere and the dispersion of trace gases and air pollution. The height of the mixing layer (MLH) can be retrieved, among other methods, from lidar or ceilometer backscatter data. These instruments use the vertical backscatter lidar signal to infer MLHL, which is feasible because the main sources of aerosols are situated at the surface and vertical gradients are expected to go from the aerosol loaded mixing layer close to the ground to the cleaner free atmosphere above. Various lidar/ceilometer algorithms are currently applied, but accounting for MLH temporal development is not always well taken care of. As a result, MLHL retrievals may jump between different atmospheric layers, rather than reliably track true MLH development over time. This hampers the usefulness of MLHL time series, e.g. for process studies, model validation/verification and climatology. Here, we introduce a new method pathfinder, which applies graph theory to simultaneously evaluate time frames that are consistent with scales of MLH dynamics, leading to coherent tracking of MLH. Starting from a grid of gradients in the backscatter profiles, MLH development is followed using Dijkstra's shortest path algorithm (Dijkstra, 1959). Locations of strong gradients are connected under the condition that subsequent points on the path are limited to a restricted vertical range. The search is further guided by rules based on the presence of clouds and residual layers. After being applied to backscatter lidar data from Cabauw, excellent agreement is found with wind profiler retrievals for a 12-day period in 2008 (R2 = 0.90) and visual judgment of lidar data during a full year in 2010 (R2 = 0.96). These values compare favourably to other MLHL methods applied to the same lidar data set and corroborate more consistent MLH tracking by pathfinder.

  10. Aerosol black carbon characteristics over Central India: Temporal variation and its dependence on mixed layer height

    NASA Astrophysics Data System (ADS)

    Kompalli, Sobhan Kumar; Babu, S. Suresh; Moorthy, K. Krishna; Manoj, M. R.; Kumar, N. V. P. Kiran; Shaeb, K. Hareef Baba; Joshi, Ashok Kumar

    2014-10-01

    In a first of its kind study over the Indian region, concurrent and extensive measurements of black carbon (BC) concentration and atmospheric boundary layer parameters are used to quantify the role of atmospheric boundary layer in producing temporal changes in BC. During this study, 18 months (2011-12) data of continuous measurements of BC aerosols, made over a semi-urban location, Nagpur, in Central India are used along with concurrent measurements of vertical profiles of atmospheric thermodynamics, made using weekly ascents of GPS aided Radiosonde for a period of 1 year. From the balloon data, mixed layer heights and ventilation coefficients are estimated, and the monthly and seasonal changes in BC mass concentration are examined in the light of the boundary layer changes. Seasonally, the BC mass concentration was highest (~ 4573 ± 1293 ng m- 3) in winter (December-February), and lowest (~ 1588 ± 897 ng m- 3) in monsoon (June-September), while remained moderate (~ 3137 ± 1446 ng m- 3) in pre-monsoon (March-May), and post-monsoon (~ 3634 ± 813 ng m- 3) (October-November) seasons. During the dry seasons, when the rainfall is scanty or insignificantly small, the seasonal variations in BC concentrations have a strong inverse relationship with mixed layer height and ventilation coefficient. However, the lowest BC concentrations do not occur during the season when the mixed layer height (MLH) is highest or the ventilation coefficient is the highest; rather it occurs when the rainfall is strong (during summer monsoon season) and airmass changes to primarily of marine origin.

  11. The Influence of Multiple Nested Layer Waviness on the Compression Strength of Double Nested Wave Formations in a Carbon Fiber Composite Laminate

    NASA Astrophysics Data System (ADS)

    Khan, Z. M.; Adams, D. O.; Anas, S.

    2016-01-01

    As advanced composite materials having superior physical and mechanical properties are being developed, the optimization of their processing techniques is eagerly sought. One of the most common defects arising during processing of structural composites is layer waviness. The layer waviness is more pronounced in thick-section flat and cylindrical laminates, which are extensively used in large wind turbine blades, submersibles, and space platforms. The layer waviness undulates the entire layer of a multidirectional laminate in the throughthe-thickness direction, leading to a gross deterioration of its compressive strength. This research investigates the influence of multiple layer waviness in a double nest formation on the compression strength of a composite laminate. Different wave fractions of wavy 0° layers were fabricated in an IM/8551-7 carbon-epoxy composite laminate on a steel mold by using a single-step fabrication procedure. The test laminates were cured on a heated press according to the specific curing cycle of epoxy. Their static compression testing was performed using a NASA short block compression fixture on an MTS servohydraulic machine. The purpose of these tests was to determine the effects of multiple layer wave regions on the compression strength of the composite laminate. The experimental and analytical results obtained revealed that the reduction in the compression strength of composite laminate was constant after the fraction of the wavy 0° layers exceeded 35%. This analysis indicated that the percentage of the 0° wavy layer may be used to estimate the reduction in the compression strength of a double nested wave formation in a composite laminate.

  12. Mixed-layer kaolinite-montmorillonite from the Yucatan Peninsula, Mexico

    USGS Publications Warehouse

    Schultz, L.G.; Shepard, A.O.; Blackmon, P.D.; Starkey, H.C.

    1971-01-01

    Clay beds 1-2 m thick and interbedded with marine limestones probably of early Eocene age are composed of nearly pure mixed-layer kaolinite-montmorillonite. Particle size studies, electron micrographs, X-ray diffraction studies, chemical analyses, cation exchange experiments, DTA, and TGA indicate that clays from three different localities contain roughly equal proportions of randomly interlayered kaolinite and montmorillonite layers. The montmorillonite structural formulas average K0??2Na0??2Ca0??2Mg0??2(Al2??5Fe1??03+Mg0??5)(Al0??75Si7??25)O20+(OH)4-, with a deficiency of structural (OH) in either the montmorillonite or kaolinite layers. Nonexchangeable K+ indicates that a few layers are mica-like. Crystals are mostly round plates 1 10 to 1 20 ?? across. The feature most diagnostic of the mixed-layer character is an X-ray reflection near 8 A?? after heating at 300 ??C. The clays are inferred to have developed by weathering of volcanic ash and subsequent erosion and deposition in protected nearshore basins. ?? 1971.

  13. Time accurate simulations of compressible shear flows

    NASA Technical Reports Server (NTRS)

    Givi, Peyman; Steinberger, Craig J.; Vidoni, Thomas J.; Madnia, Cyrus K.

    1993-01-01

    The objectives of this research are to employ direct numerical simulation (DNS) to study the phenomenon of mixing (or lack thereof) in compressible free shear flows and to suggest new means of enhancing mixing in such flows. The shear flow configurations under investigation are those of parallel mixing layers and planar jets under both non-reacting and reacting nonpremixed conditions. During the three-years of this research program, several important issues regarding mixing and chemical reactions in compressible shear flows were investigated.

  14. 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.

  15. Direct numerical simulations of a temporally evolving mixing layer subject to forcing

    NASA Technical Reports Server (NTRS)

    Claus, Russell W.

    1986-01-01

    The vortical evolution of mixing layers subject to various types of forcing is numerically simulated using pseudospectral methods. The effect of harmonic forcing and random noise in the initial conditions is examined with some results compared to experimental data. Spanwise forcing is found to enhance streamwise vorticity in a nonlinear process leading to a slow, secondary growth of the shear layer. The effect of forcing on a chemical reaction is favorably compared with experimental data at low Reynolds numbers. Combining harmonic and subharmonic forcing is shown to both augment and later destroy streamwise vorticity.

  16. Spherical electric double layers containing mixed electrolytes: A case study for multivalent counterions

    NASA Astrophysics Data System (ADS)

    Patra, Chandra N.

    2017-10-01

    Spherical electric double layers containing mixed electrolytes with multivalent counterions, is studied using density functional theory and Monte Carlo simulation. The macroion and small ions are represented as uniformly charged hard spheres within a continuum solvent. The theory involves an weighted density approximation for the hard-sphere contribution, whereas the electrical part is evaluated through a functional expansion around the uniform fluid. The system includes a number of parameters, viz. ionic concentrations, macroion charge density, and the valence of the counterion. This study points towards the distinctive evidence of size and charge correlations manifested through layering and charge reversal phenomena.

  17. Numerical implementation of the mixed potential integral equation for planar structures with ferrite layers arbitrarily magnetized

    NASA Astrophysics Data System (ADS)

    Mesa, F.; Medina, F.

    2006-12-01

    This work presents a new implementation of the mixed potential integral equation (MPIE) for planar structures that can include ferrite layers arbitrarily magnetized. The implementation of the MPIE here reported is carried out in the space domain. Thus it will combine the well-known numerical advantages of working with potentials as well as the flexibility for analyzing nonrectangular shape conductors with the additional ability of including anisotropic layers of arbitrarily magnetized ferrites. In this way, our approach widens the scope of the space domain MPIE and sets this method as a very efficient and versatile numerical tool to deal with a wide class of planar microwave circuits and antennas.

  18. Simulation of mixed-host emitting layer based organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Riku, C.; Kee, Y. Y.; Ong, T. S.; Yap, S. S.; Tou, T. Y.

    2015-04-01

    `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) (Alq3) 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:Alq3 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.

  19. 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.

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

    DOEpatents

    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.