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.
Planar velocity measurements in compressible mixing layers
NASA Astrophysics Data System (ADS)
Urban, William David
1999-10-01
The efficiency of high-Mach number airbreathing propulsion devices is critically dependent upon the mixing of gases in turbulent shear flows. However, compressibility is known to suppress the growth rates of these mixing layers, posing a problem of both practical and scientific interest. In the present study, particle image velocimetry (PIV) is used to obtain planar, two- component velocity fields for Planar gaseous shear layers at convective Mach numbers Mc of 0.25, 0.63, and 0.76. The experiments are performed in a large-scale blowdown wind tunnel, with high-speed freestream Mach numbers up to 2.25 and shear-layer Reynolds numbers up to 106 . The instantaneous data are analyzed to produce maps of derived quantities such as vorticity, and ensemble averaged to provide turbulence statistics. Specific issues relating to the application of PIV to supersonic flows are addressed. In addition to the fluid- velocity measurements, we present double-pulsed scalar visualizations, permitting inference of the convective velocity of the large-scale structures, and examine the interaction of a weak wave with the mixing layer. The principal change associated with compressibility is seen to be the development of multiple high-gradient regions in the instantaneous velocity field, disrupting the spanwise-coherent `roller' structure usually associated with incompressible layers. As a result, the vorticity peaks reside in multiple thin sheets, segregated in the transverse direction. This suggests a decrease in cross-stream communication and a disconnection of the entrainment processes at the two interfaces. In the compressible case, steep-gradient regions in the instantaneous velocity field often correspond closely with the local sonic line, suggesting a sensitivity to lab-frame disturbances; this could in turn explain the effectiveness of sub-boundary layer mixing enhancement strategies in this flow. Large- ensemble statistics bear out the observation from previous single
Spatial stability of a compressible mixing layer
NASA Technical Reports Server (NTRS)
Jackson, T. L.; Grosch, C. E.
1988-01-01
Presented are the results of a study of the inviscid spatial stability of a parallel compressible mixing layer. The parameters of this study are the Mach number of the moving stream, the ratio of the temperature of the stationary stream to that of the moving stream, the frequency and the direction of propagation of the disturbance wave. Stability characteristics of the flow as a function of these parameters are given. It is shown that if the Mach number exceeds a critical value there are always two groups of unstable waves. One of these groups is fast with phase speeds greater than 1/2, and the other is slow with speeds less than 1/2. Phase speeds for the neutral and unstable modes are given, as well as growth rates for the unstable modes. It is shown that three dimensional modes have the same general behavior as the two dimensional modes but with higher growth rates over some range of propagation direction. Finally, a group of very low frequency unstable modes was found for sufficiently large Mach numbers. These modes have very low phase speeds but large growth rates.
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.
Nonlinear Stability and Structure of Compressible Reacting Mixing Layers
NASA Technical Reports Server (NTRS)
Day, M. J.; Mansour, N. N.; Reynolds, W. C.
2000-01-01
The parabolized stability equations (PSE) are used to investigate issues of nonlinear flow development and mixing in compressible reacting shear layers. Particular interest is placed on investigating the change in flow structure that occurs when compressibility and heat release are added to the flow. These conditions allow the 'outer' instability modes- one associated with each of the fast and slow streams-to dominate over the 'central', Kelvin-Helmholtz mode that unaccompanied in incompressible nonreacting mixing layers. Analysis of scalar probability density functions in flows with dominant outer modes demonstrates the ineffective, one-sided nature of mixing that accompany these flow structures. Colayer conditions, where two modes have equal growth rate and the mixing layer is formed by two sets of vortices, offer some opportunity for mixing enhancement. Their extent, however, is found to be limited in the mixing layer's parameter space. Extensive validation of the PSE technique also provides a unique perspective on central- mode vortex pairing, further supporting the view that pairing is primarily governed perspective sheds insight on how linear stability theory is able to provide such an accurate prediction of experimentally-observed, fully nonlinear flow phenomenon.
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.
The stability of compressible mixing layers in binary gases
NASA Technical Reports Server (NTRS)
Kozusko, F.; Lasseigne, D. G.; Grosch, C. E.; Jackson, T. L.
1996-01-01
We present the results of a study of the inviscid two-dimensional spatial stability of a parallel compressible mixing layer in a binary gas. The parameters of this study are the Mach number of the fast stream, the ratio of the velocity of the slow stream to that of the fast stream, the ratio of the temperatures, the composition of the gas in the slow stream and in the fast stream, and the frequency of the disturbance wave. The ratio of the molecular weight of the slow stream to that of the fast stream is found to be an important quantity and is used as an independent variable in presenting the stability characteristics of the flow. It is shown that differing molecular weights have a significant effect on the neutral-mode phase speeds, the phase speeds of the unstable modes, the maximum growth rates and the unstable frequency range of the disturbances. The molecular weight ratio is a reasonable predictor of the stability trends. We have further demonstrated that the normalized growth rate as a function of the convective Mach number is relatively insensitive (Approx. 25%) to changes in the composition of the mixing layer. Thus, the normalized growth rate is a key element when considering the stability of compressible mixing layers, since once the basic stability characteristics for a particular combination of gases is known at zero Mach number, the decrease in growth rates due to compressibility effects at the larger convective Mach numbers is somewhat predictable.
Mixing length in low Reynolds number compressible turbulent boundary layers
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Holley, B. B.
1975-01-01
The paper studies the effect of low Reynolds number in high-speed turbulent boundary layers on variations of mixing length. Boundary layers downstream of natural transition on plates, cones and cylinders, and boundary layers on nozzle walls without laminarization-retransition are considered. The problem of whether low Reynolds number amplification of shear stress is a result of transitional flow structure is considered. It is concluded that a knowledge of low Reynolds number boundary layer transition may be relevant to the design of high-speed vehicles.
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Roussel, Olivier; Schneider, Kai
2010-03-01
An adaptive mulitresolution method based on a second-order finite volume discretization is presented for solving the three-dimensional compressible Navier-Stokes equations in Cartesian geometry. The explicit time discretization is of second-order and for flux evaluation a 2-4 Mac Cormack scheme is used. Coherent Vortex Simulations (CVS) are performed by decomposing the flow variables into coherent and incoherent contributions. The coherent part is computed deterministically on a locally refined grid using the adaptive multiresolution method while the influence of the incoherent part is neglected to model turbulent dissipation. The computational efficiency of this approach in terms of memory and CPU time compression is illustrated for turbulent mixing layers in the weakly compressible regime and for Reynolds numbers based on the mixing layer thickness between 50 and 200. Comparisons with direct numerical simulations allow to assess the precision and efficiency of CVS.
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Schneider, Kai; Roussel, Olivier; Farge, Marie
2007-11-01
Coherent Vortex Simulation is based on the wavelet decomposition of the flow into coherent and incoherent components. An adaptive multiresolution method using second order finite volumes with explicit time discretization, a 2-4 Mac Cormack scheme, allows an efficient computation of the coherent flow on a dynamically adapted grid. Neglecting the influence of the incoherent background models turbulent dissipation. We present CVS computation of three dimensional compressible time developing mixing layer. We show the speed up in CPU time with respect to DNS and the obtained memory reduction thanks to dynamical octree data structures. The impact of different filtering strategies is discussed and it is found that isotropic wavelet thresholding of the Favre averaged gradient of the momentum yields the most effective results.
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.
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
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.
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.
Compressible turbulent mixing: Effects of compressibility
NASA Astrophysics Data System (ADS)
Ni, Qionglin
2016-04-01
We studied by numerical simulations the effects of compressibility on passive scalar transport in stationary compressible turbulence. The turbulent Mach number varied from zero to unity. The difference in driven forcing was the magnitude ratio of compressive to solenoidal modes. In the inertial range, the scalar spectrum followed the k-5 /3 scaling and suffered negligible influence from the compressibility. The growth of the Mach number showed (1) a first reduction and second enhancement in the transfer of scalar flux; (2) an increase in the skewness and flatness of the scalar derivative and a decrease in the mixed skewness and flatness of the velocity-scalar derivatives; (3) a first stronger and second weaker intermittency of scalar relative to that of velocity; and (4) an increase in the intermittency parameter which measures the intermittency of scalar in the dissipative range. Furthermore, the growth of the compressive mode of forcing indicated (1) a decrease in the intermittency parameter and (2) less efficiency in enhancing scalar mixing. The visualization of scalar dissipation showed that, in the solenoidal-forced flow, the field was filled with the small-scale, highly convoluted structures, while in the compressive-forced flow, the field was exhibited as the regions dominated by the large-scale motions of rarefaction and compression.
Advances in compressible turbulent mixing
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.
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.
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.
NASA Technical Reports Server (NTRS)
Chen, J. H.; Chong, M. S.; Soria, J.; Sondergaard, R.; Perry, A. E.; Rogers, M.; Moser, R.; Cantwell, B. J.
1990-01-01
A preliminary investigation of the geometry of flow patterns in numerically simulated compressible and incompressible mixing layers was carried out using 3-D critical point methodology. Motions characterized by high rates of kinetic energy dissipation and/or high enstrophy were of particular interest. In the approach the partial derivatives of the velocity field are determined at every point in the flow. These are used to construct the invariants of the velocity gradient tensor and the rate-of-strain tensor (P, Q, R, and P(sub s), Q(sub s), R(sub s) respectively). For incompressible flow the first invariant is zero. For the conditions of the compressible simulation, the first invariant is found to be everywhere small, relative to the second and third invariants, and so in both cases the local topology at a point is mainly determined by the second and third invariants. The data at every grid point is used to construct scatter plots of Q versus R and Q(sub s) versus R(sub s). Most points map to a cluster near the origin in Q-R space. However, fine scale motions, that is motions which are characterized by velocity derivatives which scale with the square root of R(sub delta), tend to map to regions which lie far from the origin. Definite trends are observed for motions characterized by high enstrophy and/or high dissipation. The observed trends suggest that, for these motions, the second and third invariants of the velocity gradient and rate-of-strain tensors are strongly correlated. The second and third invariants of the rate-of-strain tensor are related by K(-Q(sub s))(exp 3/2), which is consistent with the above scaling of velocity derivatives. The quantity K appears to depend on Reynolds number with an upper limit K = 2(the square root of 3)/9 corresponding to locally axisymmetric flow. For both the compressible and incompressible mixing layer, regions corresponding to high rates of dissipation are found to be characterized by comparable magnitudes of R(sub ij
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.
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.
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.
Compressible turbulent mixing: Effects of compressibility and Schmidt number
NASA Astrophysics Data System (ADS)
Ni, Qionglin
2015-11-01
Effects of compressibility and Schmidt number on passive scalar in compressible turbulence were studied. On the effect of compressibility, the scalar spectrum followed the k- 5 / 3 inertial-range scaling and suffered negligible influence from compressibility. The transfer of scalar flux was reduced by the transition from incompressible to compressible flows, however, was enhanced by the growth of Mach number. The intermittency parameter was increased by the growth of Mach number, and was decreased by the growth of the compressive mode of driven forcing. The dependency of the mixing timescale on compressibility showed that for the driven forcing, the compressive mode was less efficient in enhancing scalar mixing. On the effect of Schmidt number (Sc), in the inertial-convective range the scalar spectrum obeyed the k- 5 / 3 scaling. For Sc >> 1, a k-1 power law appeared in the viscous-convective range, while for Sc << 1, a k- 17 / 3 power law was identified in the inertial-diffusive range. The transfer of scalar flux grew over Sc. In the Sc >> 1 flow the scalar field rolled up and mixed sufficiently, while in the Sc << 1 flow that only had the large-scale, cloudlike structures. In Sc >> 1 and Sc << 1 flows, the spectral densities of scalar advection and dissipation followed the k- 5 / 3 scaling, indicating that in compressible turbulence the processes of advection and dissipation might deferring to the Kolmogorov picture. Finally, the comparison with incompressible results showed that the scalar in compressible turbulence lacked a conspicuous bump structure in its spectrum, and was more intermittent in the dissipative range.
Compressibility of Quantum Mixed-State Signals
Koashi, Masato; Imoto, Nobuyuki
2001-07-02
We present a formula that determines the optimal number of qubits per message that allows asymptotically faithful compression of the quantum information carried by an ensemble of mixed states. The set of mixed states determines a decomposition of the Hilbert space into the redundant part and the irreducible part. After removing the redundancy, the optimal compression rate is shown to be given by the von Neumann entropy of the reduced ensemble.
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.
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
Some design considerations for supersonic cruise mixed compression inlets
NASA Technical Reports Server (NTRS)
Bowditch, D. N.
1973-01-01
A mixed compression inlet designed for supersonic cruise has very demanding requirements for high total pressure recovery and low bleed and cowl drag. However, since the optimum inlet for supersonic cruise performance may have other undesirable characteristics, it is necessary to establish trade-offs between inlet performance and other inlet characteristics. Some of these trade-offs between the amount of internal compression, aerodynamic performance and angle-of-attack tolerance are reviewed. Techniques for analysis of boundary layer control and subsonic diffuser flow are discussed.
Goertler instability of compressible boundary layers
NASA Technical Reports Server (NTRS)
El-Hady, N. M.; Verma, A. K.
1984-01-01
The instability of the laminar compressible boundary-layer flows along concave surfaces is investigated. The linearized disturbance equations for the three-dimensional, counter-rotating, longitudinal-type vortices in two-dimensional boundary layers are presented in an orthogonal curvilinear system of coordinates. The basic approximation of the disturbance equations, which includes the effect of the growth of the boundary layer, is considered and solved numerically.
Scalar mixing in the supersonic shear layer
NASA Technical Reports Server (NTRS)
Clemens, N. T.; Mungal, M. G.; Hanson, R. K.; Paul, P. H.
1991-01-01
Experiments were conducted in a two-stream planar mixing layer facility at convective Mach numbers of 0.28 and 0.62. Mie scattering from condensed alcohol droplets and planar laser-induced fluorescence (PLIF) of nitric oxide were used for flow visualization in both the side and plan views. The PLIF signals were approximately proportional to mixture fraction and were used to generate statistical quantities. Visualizations using both the Mie scattering and PLIF indicate the structure is essentially two-dimensional at Mc = 0.28 and three-dimensional at Mc = 0.62. Perspective renderings of side view images show the structures are streamwise ramped at Mc = 0.28 and cross-stream ramped at Mc = 0.62. This difference appears to be associated with decreasing streamwise structure spacings at the higher Mc condition. The statistical analysis suggests that with increasing compressibility, the scalar fluctuations are smaller, and the fraction of mixed fluid is higher.
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.
Compressible turbulent mixing: Effects of Schmidt number.
Ni, Qionglin
2015-05-01
We investigated by numerical simulations the effects of Schmidt number on passive scalar transport in forced compressible turbulence. The range of Schmidt number (Sc) was 1/25∼25. In the inertial-convective range the scalar spectrum seemed to obey the k(-5/3) power law. For Sc≫1, there appeared a k(-1) power law in the viscous-convective range, while for Sc≪1, a k(-17/3) power law was identified in the inertial-diffusive range. The scaling constant computed by the mixed third-order structure function of the velocity-scalar increment showed that it grew over Sc, and the effect of compressibility made it smaller than the 4/3 value from incompressible turbulence. At small amplitudes, the probability distribution function (PDF) of scalar fluctuations collapsed to the Gaussian distribution whereas, at large amplitudes, it decayed more quickly than Gaussian. At large scales, the PDF of scalar increment behaved similarly to that of scalar fluctuation. In contrast, at small scales it resembled the PDF of scalar gradient. Furthermore, the scalar dissipation occurring at large magnitudes was found to grow with Sc. Due to low molecular diffusivity, in the Sc≫1 flow the scalar field rolled up and got mixed sufficiently. However, in the Sc≪1 flow the scalar field lost the small-scale structures by high molecular diffusivity and retained only the large-scale, cloudlike structures. The spectral analysis found that the spectral densities of scalar advection and dissipation in both Sc≫1 and Sc≪1 flows probably followed the k(-5/3) scaling. This indicated that in compressible turbulence the processes of advection and dissipation except that of scalar-dilatation coupling might deferring to the Kolmogorov picture. It then showed that at high wave numbers, the magnitudes of spectral coherency in both Sc≫1 and Sc≪1 flows decayed faster than the theoretical prediction of k(-2/3) for incompressible flows. Finally, the comparison with incompressible results showed that
Compressible turbulent mixing: Effects of Schmidt number
NASA Astrophysics Data System (ADS)
Ni, Qionglin
2015-05-01
We investigated by numerical simulations the effects of Schmidt number on passive scalar transport in forced compressible turbulence. The range of Schmidt number (Sc) was 1/25 ˜25 . In the inertial-convective range the scalar spectrum seemed to obey the k-5 /3 power law. For Sc≫1 , there appeared a k-1 power law in the viscous-convective range, while for Sc≪1 , a k-17 /3 power law was identified in the inertial-diffusive range. The scaling constant computed by the mixed third-order structure function of the velocity-scalar increment showed that it grew over Sc, and the effect of compressibility made it smaller than the 4/3 value from incompressible turbulence. At small amplitudes, the probability distribution function (PDF) of scalar fluctuations collapsed to the Gaussian distribution whereas, at large amplitudes, it decayed more quickly than Gaussian. At large scales, the PDF of scalar increment behaved similarly to that of scalar fluctuation. In contrast, at small scales it resembled the PDF of scalar gradient. Furthermore, the scalar dissipation occurring at large magnitudes was found to grow with Sc. Due to low molecular diffusivity, in the Sc≫1 flow the scalar field rolled up and got mixed sufficiently. However, in the Sc≪1 flow the scalar field lost the small-scale structures by high molecular diffusivity and retained only the large-scale, cloudlike structures. The spectral analysis found that the spectral densities of scalar advection and dissipation in both Sc≫1 and Sc≪1 flows probably followed the k-5 /3 scaling. This indicated that in compressible turbulence the processes of advection and dissipation except that of scalar-dilatation coupling might deferring to the Kolmogorov picture. It then showed that at high wave numbers, the magnitudes of spectral coherency in both Sc≫1 and Sc≪1 flows decayed faster than the theoretical prediction of k-2 /3 for incompressible flows. Finally, the comparison with incompressible results showed that the
Scalar entrainment in the mixing layer
NASA Technical Reports Server (NTRS)
Sandham, N. D.; Mungal, M. G.; Broadwell, J. E.; Reynolds, W. C.
1988-01-01
New definitions of entrainment and mixing based on the passive scalar field in the plane mixing layer are proposed. The definitions distinguish clearly between three fluid states: (1) unmixed fluid, (2) fluid engulfed in the mixing layer, trapped between two scalar contours, and (3) mixed fluid. The difference betwen (2) and (3) is the amount of fluid which has been engulfed during the pairing process, but has not yet mixed. Trends are identified from direct numerical simulations and extensions to high Reynolds number mixing layers are made in terms of the Broadwell-Breidenthal mixing model. In the limit of high Peclet number (Pe = ReSc) it is speculated that engulfed fluid rises in steps associated with pairings, introducing unmixed fluid into the large scale structures, where it is eventually mixed at the Kolmogorov scale. From this viewpoint, pairing is a prerequisite for mixing in the turbulent plane mixing layer.
Geometric invariance of compressible turbulent boundary layers
NASA Astrophysics Data System (ADS)
Bi, Wei-Tao; Wu, Bin; She, Zhen-Su; Hussain, Fazle
2015-11-01
A symmetry based approach is applied to analyze the mean velocity and temperature fields of compressible, flat plate turbulent boundary layers (CTBL). A Reynolds stress length scale and a turbulent heat flux length scale are identified to possess the same defect scaling law in the CTBL bulk, which is solely owing to the constraint of the wall to the geometry of the wall-attached eddies, but invariant to compressibility and wall heat transfer. This invariance is called the geometric invariance of CTBL eddies and is likely the origin of the Mach number invariance of Morkovin's hypothesis, as well as the similarity of energy and momentum transports. A closure for the turbulent transport by using the invariant lengths is attainted to predict the mean velocity and temperature profiles in the CTBL bulk- superior to the van Driest transformation and the Reynolds analogy based relations for its sound physics and higher accuracy. Additionally, our approach offers a new understanding of turbulent Prandtl number.
Turbulence models for compressible boundary layers
NASA Technical Reports Server (NTRS)
Huang, P. G.; Bradshaw, P.; Coakley, T. J.
1994-01-01
It is shown that to satisfy the general accepted compressible law of the wall derived from the Van Driest transformation, turbulence modeling coefficients must actually be functions of density gradients. The transformed velocity profiles obtained by using standard turbulence model constants have too small a value of the effective von Karman constant kappa in the log-law region (inner layer). Thus, if the model is otherwise accurate, the wake component is overpredicted and the predicted skin friction is lower than the expected value.
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.
Coherent structures in compressible free-shear-layer flows
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.
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.
Experiments on shear layer mixing at hypervelocity conditions
Erdos, J.; Tamango, J.; Bakos, R.; Trucco, R. )
1992-01-01
Utilization of an expansion tube to acquire turbulent, compressible free shear layer data with gases of direct relevance to hypersonic combustion systems (nitrogen, hydrogen, and oxygen) is demonstrated. Visualizations of the free shear layer by laser holographic interferometry and schlieren imaging show a distinctly asymmetric growth rate that is highly preferential toward the lower speed (secondary stream) side. For the nitrogen/nitrogen case, for which the convective velocity was lowest and convective Mach number highest, the growth rate on the primary side was virtually zero until the mixing layer reached the opposite (secondary) wall. 11 refs.
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.
CUMULUS CLOUD VENTING OF MIXED LAYER OZONE
Observations are presented which substantiate the hypothesis that significant vertical exchange of ozone and aerosols (and possibly other compounds) occurs between the mixed layer and the free troposphere during cumulus cloud convective activity. The experiments conducted in July...
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.
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.
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.
NASA Technical Reports Server (NTRS)
Boers, R.; Eloranta, E. W.; Coulter, R. L.
1984-01-01
Ground based lidar measurements of the atmospheric mixed layer depth, the entrainment zone depth and the wind speed and wind direction were used to test various parameterized entrainment models of mixed layer growth rate. Six case studies under clear air convective conditions over flat terrain in central Illinois are presented. It is shown that surface heating alone accounts for a major portion of the rise of the mixed layer on all days. A new set of entrainment model constants was determined which optimized height predictions for the dataset. Under convective conditions, the shape of the mixed layer height prediction curves closely resembled the observed shapes. Under conditions when significant wind shear was present, the shape of the height prediction curve departed from the data suggesting deficiencies in the parameterization of shear production. Development of small cumulus clouds on top of the layer is shown to affect mixed layer depths in the afternoon growth phase.
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.
Compression behavior of single-layer graphenes.
Frank, Otakar; Tsoukleri, Georgia; Parthenios, John; Papagelis, Konstantinos; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S; Galiotis, Costas
2010-06-22
Central to most applications involving monolayer graphenes is its mechanical response under various stress states. To date most of the work reported is of theoretical nature and refers to tension and compression loading of model graphenes. Most of the experimental work is indeed limited to the bending of single flakes in air and the stretching of flakes up to typically approximately 1% using plastic substrates. Recently we have shown that by employing a cantilever beam we can subject single graphenes to various degrees of axial compression. Here we extend this work much further by measuring in detail both stress uptake and compression buckling strain in single flakes of different geometries. In all cases the mechanical response is monitored by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene. Despite the infinitely small thickness of the monolayers, the results show that graphenes embedded in plastic beams exhibit remarkable compression buckling strains. For large length (l)-to-width (w) ratios (> or =0.2) the buckling strain is of the order of -0.5% to -0.6%. However, for l/w < 0.2 no failure is observed for strains even higher than -1%. Calculations based on classical Euler analysis show that the buckling strain enhancement provided by the polymer lateral support is more than 6 orders of magnitude compared to that of suspended graphene in air. PMID:20496881
The upper-branch stability of compressible boundary layer flows
NASA Technical Reports Server (NTRS)
Gajjar, J. S. B.; Cole, J. W.
1989-01-01
The upper-branch linear and nonlinear stability of compressible boundary layer flows is studied using the approach of Smith and Bodonyi (1982) for a similar incompressible problem. Both pressure gradient boundary layers and Blasius flow are considered with and without heat transfer, and the neutral eigenrelations incorporating compressibility effects are obtained explicitly. The compressible nonlinear viscous critical layer equations are derived and solved numerically and the results indicate some solutions with positive phase shift across the critical layer. Various limiting cases are investigated including the case of much larger disturbance amplitudes and this indicates the structure for the strongly nonlinear critical layer of the Benney-Bergeon (1969) type. It is also shown how a match with the inviscid neutral inflexional modes arising from the generalized inflexion point criterion, is achieved.
Efficient Quantum Compression for Ensembles of Identically Prepared Mixed States
NASA Astrophysics Data System (ADS)
Yang, Yuxiang; Chiribella, Giulio; Ebler, Daniel
2016-02-01
We present one-shot compression protocols that optimally encode ensembles of N identically prepared mixed states into O (log N ) qubits. In contrast to the case of pure-state ensembles, we find that the number of encoding qubits drops down discontinuously as soon as a nonzero error is tolerated and the spectrum of the states is known with sufficient precision. For qubit ensembles, this feature leads to a 25% saving of memory space. Our compression protocols can be implemented efficiently on a quantum computer.
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.
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.
Lagrangian analysis of a convective mixed layer
NASA Astrophysics Data System (ADS)
D'Asaro, Eric A.; Winters, Kraig B.; Lien, Ren-Chieh
2002-05-01
We characterize and quantify the transport of heat (Boussinesq density) in a highly idealized entraining convective mixed layer based on simulations of Lagrangian measurements in a two-dimensional model. The primary objectives are to assess and explore the merits and difficulties in estimating the heat budget from perfect and imperfect Lagrangian floats. A significant advantage of Lagrangian measurements is that the time derivative of temperature along these trajectories gives a direct measure of the diffusive heat flux. Using simulated perfect Lagrangian floats, estimates of the surface buoyancy flux, the depth of the mixed layer, vertical profiles of advective and diffusive heat flux, and the overall rate of cooling are shown to agree accurately with the known results extracted from the Eulerian simulations. The Lagrangian nature of the data is exploited to reveal the structure of the flow within the convective layer and to quantify the heat fluxes associated with the different types of eddies. Phase plots of Lagrangian trajectories in density-depth space reveal three distinct classes of motions: (1) plumes, which develop in the cold, heavy near-surface thermal boundary layer and plunge into the mixed layer interior carrying heavy water downward; (2) interior turbulence, comprising random motions between the base of the thermal boundary layer and the base of the surface mixed layer; and (3) entrainment of interior water into plumes below the thermal boundary layer, i.e., a transition from class 2 to class 1. Plumes dominate the heat transport. Simulations were also made using slightly buoyant floats; these are not perfectly Lagrangian. Buoyancy concentrates the floats near the surface resulting in an oversampling of the stronger plumes. Making the same heat budget calculations as with the perfect floats results in a nonzero estimated Lagrangian heating rate in the interior and a curved profile of vertical heat flux that is up to 3 times too large. The local time
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.
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.
NASA Astrophysics Data System (ADS)
Tötzke, C.; Manke, I.; Gaiselmann, G.; Bohner, J.; Müller, B. R.; Kupsch, A.; Hentschel, M. P.; Schmidt, V.; Banhart, J.; Lehnert, W.
2015-04-01
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.
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.
Compressive failure of delamination-embedded layered structures
NASA Astrophysics Data System (ADS)
Wu, Li-Chun
1997-11-01
Various failure mechanisms involving both local and global deformation mechanisms of layered structures, consisting of differently oriented orthotropic laminae, are investigated with a large deformation finite element analysis. The aim of this study is to identify the dominant mode which leads to the structural failure under a given boundary condition and geometrical shape. It is assumed that these structures contain initial interlaminar flaws represented by embedded delaminations. Such flaws can play a significant role in defining overall structural integrity and deformation mechanisms. The energy release rate, mixed-mode stress intensity factors and phase angle are computed to quantify the crack driving force and used to measure likelihood of delamination growth in two-dimensional and three- dimensional composite structures. In the first part, two composite structures with distinguished shapes, consisting of four laminae are considered in two-dimensional analysis. One is a flat panel under compressive load and the other structure is a cylindrical shell subjected to external pressure. In the flat panel model, two buckling modes, a global and a local ligament, are observed under quasi-static loading conditions. The interaction of these two modes produces an unstable post-buckling behavior. It is found that the energy release rate exceeds experimentally estimated fracture toughness values only after buckling occurs. In the cylindrical shell study, lower critical buckling loads are observed for models with longer interlaminar delamination as in the flat panel model. However, unlike the flat panel case, the energy release rate surpasses the critical toughness well before the applied pressure reaches the buckling load of the flawed cylindrical shell. This behavior implies that a shell containing an embedded defect along an interface can fail by delamination growth and therefore has a failure load lower than its critical buckling load. Also for thicker cylindrical
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.
Lidar measurements of the atmospheric boundary layer height, the entrainment zone, wind speed and direction, ancillary temperature profiles and surface flux data were used to test current parameterized entrainment models of mixed layer growth rate. Six case studies under clear ai...
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.
Secondary three-dimensional instability in compressible boundary layers
NASA Technical Reports Server (NTRS)
El-Hady, Nabil M.
1989-01-01
Three dimensional linear secondary instability theory is extended for compressible boundary layers on a flat plate in the presence of finite amplitude Tollmien-Schlichting waves. The focus is on principal parametric resonance responsible for strong growth of subharmonics in low disturbance environment.
A mixed transform approach for efficient compression of medical images.
Ramaswamy, A; Mikhael, W B
1996-01-01
A novel technique is presented to compress medical data employing two or more mutually nonorthogonal transforms. Both lossy and lossless compression implementations are considered. The signal is first resolved into subsignals such that each subsignal is compactly represented in a particular transform domain. An efficient lossy representation of the signal is achieved by superimposing the dominant coefficients corresponding to each subsignal. The residual error, which is the difference between the original signal and the reconstructed signal is properly formulated. Adaptive algorithms in conjunction with an optimization strategy are developed to minimize this error. Both two-dimensional (2-D) and three-dimensional (3-D) approaches for the technique are developed. It is shown that for a given number of retained coefficients, the discrete cosine transform (DCT)-Walsh mixed transform representation yields a more compact representation than using DCT or Walsh alone. This lossy technique is further extended for the lossless case. The coefficients are quantized and the signal is reconstructed. The resulting reconstructed signal samples are rounded to the nearest integer and the modified residual error is computed. This error is transmitted employing a lossless technique such as the Huffman coding. It is shown that for a given number of retained coefficients, the mixed transforms again produces the smaller rms-modified residual error. The first-order entropy of the error is also smaller for the mixed-transforms technique than for the DCT, thus resulting in smaller length Huffman codes. PMID:18215915
Large-scale structure evolution in axisymmetric, compressible free-shear layers
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.
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.
Efficiency of shear induced entrainment in convectively mixed layers
NASA Technical Reports Server (NTRS)
Boers, Reinout
1988-01-01
Lidar data of mixed layer height are used to compare the model of process partitioning to that of Eulerian partitioning. It is found that the Eulerian partitioning model more closely follows the data and that the process partitioning model underpredicts the mixed layer depth. The results suggest that shear production and consumption of turbulent kinetic energy at the mixed layer top are local processes.
Surface-cooling effects on compressible boundary-layer instability
NASA Technical Reports Server (NTRS)
Seddougui, Sharon O.; Bowles, R. I.; Smith, F. T.
1990-01-01
The influence of surface cooling on compressible boundary layer instability is discussed theoretically for both viscous and inviscid modes, at high Reynolds numbers. The cooling enhances the surface heat transfer and shear stress, creating a high heat transfer sublayer. This has the effect of distorting and accentuating the viscous Tollmien-Schlichting modes to such an extent that their spatial growth rates become comparable with, and can even exceed, the growth rates of inviscid modes, including those found previously. This is for moderate cooling, and it applies at any Mach number. In addition, the moderate cooling destabilizes otherwise stable viscous or inviscid modes, in particular triggering outward-traveling waves at the edge of the boundary layer in the supersonic regime. Severe cooling is also discussed as it brings compressible dynamics directly into play within the viscous sublayer. All the new cooled modes found involve the heat transfer sublayer quite actively, and they are often multi-structured in form and may be distinct from those observed in previous computational and experimental investigations. The corresponding nonlinear processes are also pointed out with regard to transition in the cooled compressible boundary layer. Finally, comparisons with Lysenko and Maslov's (1984) experiments on surface cooling are presented.
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.
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.
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.
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.
A constrained two-layer compression technique for ECG waves.
Byun, Kyungguen; Song, Eunwoo; Shim, Hwan; Lim, Hyungjoon; Kang, Hong-Goo
2015-08-01
This paper proposes a constrained two-layer compression technique for electrocardiogram (ECG) waves, of which encoded parameters can be directly used for the diagnosis of arrhythmia. In the first layer, a single ECG beat is represented by one of the registered templates in the codebook. Since the required coding parameter in this layer is only the codebook index of the selected template, its compression ratio (CR) is very high. Note that the distribution of registered templates is also related to the characteristics of ECG waves, thus it can be used as a metric to detect various types of arrhythmias. The residual error between the input and the selected template is encoded by a wavelet-based transform coding in the second layer. The number of wavelet coefficients is constrained by pre-defined maximum distortion to be allowed. The MIT-BIH arrhythmia database is used to evaluate the performance of the proposed algorithm. The proposed algorithm shows around 7.18 CR when the reference value of percentage root mean square difference (PRD) is set to ten. PMID:26737691
Electronic compressibility of layer-polarized bilayer graphene
NASA Astrophysics Data System (ADS)
Young, A. F.; Dean, C. R.; Meric, I.; Sorgenfrei, S.; Ren, H.; Watanabe, K.; Taniguchi, T.; Hone, J.; Shepard, K. L.; Kim, P.
2012-06-01
We report on a capacitance study of dual gated bilayer graphene. The measured capacitance allows us to probe the electronic compressibility as a function of carrier density, temperature, and applied perpendicular electrical displacement D¯. As a band gap is induced with increasing D¯, the compressibility minimum at charge neutrality becomes deeper but remains finite, suggesting the presence of localized states within the energy gap. Temperature dependent capacitance measurements show that compressibility is sensitive to the intrinsic band gap. For large displacements, an additional peak appears in the compressibility as a function of density, corresponding to the presence of a one-dimensional van Hove singularity (vHs) at the band edge arising from the quartic bilayer graphene band structure. For D¯>0, the additional peak is observed only for electrons, while for D¯<0 the peak appears only for holes. This asymmetry can be understood in terms of the finite interlayer separation and may be useful as a direct probe of the layer polarization.
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.
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.
Compressive sensing of sparse radio frequency signals using optical mixing.
Valley, George C; Sefler, George A; Shaw, T Justin
2012-11-15
We demonstrate an optical mixing system for measuring properties of sparse radio frequency (RF) signals using compressive sensing (CS). Two types of sparse RF signals are investigated: (1) a signal that consists of a few 0.4 ns pulses in a 26.8 ns window and (2) a signal that consists of a few sinusoids at different frequencies. The RF is modulated onto the intensity of a repetitively pulsed, wavelength-chirped optical field, and time-wavelength-space mapping is used to map the optical field onto a 118-pixel, one-dimensional spatial light modulator (SLM). The SLM pixels are programmed with a pseudo-random bit sequence (PRBS) to form one row of the CS measurement matrix, and the optical throughput is integrated with a photodiode to obtain one value of the CS measurement vector. Then the PRBS is changed to form the second row of the mixing matrix and a second value of the measurement vector is obtained. This process is performed 118 times so that we can vary the dimensions of the CS measurement matrix from 1×118 to 118×118 (square). We use the penalized ℓ(1) norm method with stopping parameter λ (also called basis pursuit denoising) to recover pulsed or sinusoidal RF signals as a function of the small dimension of the measurement matrix and stopping parameter. For a square matrix, we also find that penalized ℓ(1) norm recovery performs better than conventional recovery using matrix inversion. PMID:23164876
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'.
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.
Linearized analysis for compressible laminar boundary layers by ECVL technique
NASA Astrophysics Data System (ADS)
Soong, Chyi-Yeou
1987-04-01
The effective convective velocity linearization (ECVL) technique of Soong (1984) is applied to simplify the equations for steady two-dimensional compressible laminar boundary-layer flow of a perfect gas with constant Prandtl number and specific heat. The derivation of the linearized momentum equation is explained, and numerical results for zero-pressure-gradient and pressure-gradient flows are presented graphically and compared with experimental measurements and analytical results obtained with other approaches. The accuracy and simplicity of the ECVL method are demonstrated, and its practical applicability is indicated.
The stability of a compressible stratified shear layer
NASA Technical Reports Server (NTRS)
Wang, Z.; Pritchett, P. L.
1989-01-01
The stability of a shear layer under the effect of gravity is investigated using the compressible magnetohydrodynamic (MHD) equations, including an effective gravity term to represent the curvature effects of the flow and magnetic field line geometry. A general eigenmode equation is derived for a two-dimensional MHD fluid, and an energy-principle analysis to explain the effect of compressibility on the critical Richardson number is presented. For the case of a hyperbolic tangent shear flow and exponential density profile, it was found that, in the Boussinesq approximation, the compressibility raises the critical Richardson number from 1/4 to as much as 1/2, with the exact value depending on the value of the magnetic field at infinity. Under approximation of a strong asymptotic magnetic field, without invoking the Boussinesq approximation, it is shown both analytically and numerically that the density gradient terms cause the shear instability to be dispersive. The long-wavelength stability boundary for the Richardson number J = 0 is characterized by a normalized phase velocity c =
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.
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... phosphates mixed with compressed gas. Hexaethyl tetraphosphate, parathion, tetraethyl dithio pyrophosphate, tetraethyl pyrophosphate, or other Division 6.1 organic phosphates (including a compound or mixture), may...
Calculation of compressible adverse pressure gradient turbulent boundary layers.
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Alston, D. W.
1972-01-01
Difficulties encountered in computing profile shapes in supersonic turbulent boundary layers with large pressure gradients, which result from a disagreement between data and theory, are investigated. Possible reasons given by various authors for this disagreement are discussed. Initial results seem to indicate that conventional reasons do not account for the observed difficulties. However, inclusion of the effect of curvature upon turbulent mixing has brought an improvement in calculations. Possible three-dimensional effects are also examined.
Raman Lidar Retrievals of Mixed Layer Heights
NASA Astrophysics Data System (ADS)
Ferrare, R. A.; Clayton, M.; Turner, D. D.; Newsom, R. K.; Goldsmith, J.
2012-12-01
Accurate determination of the atmospheric mixing layer (ML) height is important for modeling the transport of aerosols and aerosol precursors and forecasting air quality. Aerosol and water vapor profiles measured by the DOE ARM SGP and the new TWP (Darwin) ground based Raman lidars provide direct measurements of the vertical structure of ML. We have developed automated algorithms to identify sharp gradients in aerosols and water vapor at the top of the ML and have used these algorithms to derive ML heights for extended periods over the last few years. During the afternoon, these ML heights generally compare favorably with ML heights derived from potential temperature profiles derived from coincident radiosondes. However, retrieving ML heights via lidar measurements of water vapor and aerosol gradients is problematic in the presence of elevated aerosol and water vapor layers which are often observed, especially at night. Consequently, we take advantage of recent modifications to these lidars that permit continuous temperature profiling, and compute ML heights using potential temperature profiles derived from Raman lidar and Atmospheric Emitted Radiance Interferometer (AERI) measurements. The resulting ML heights agree well with ML heights derived from radiosondes and provide a more realistic representation of the diurnal ML behavior. We use the Raman lidar aerosol and water vapor profiles and ML heights to derive the fractions of total column precipitable water vapor and aerosol optical thickness within and above the ML and show how the ML heights and these fractions vary with time of day and season. The SGP Raman lidar measurements show that the fraction of the aerosol optical thickness and precipitable water vapor above the ML increases from 30-60% during the day to 60-80% at night. The Darwin Raman lidar measurements reveal a shallow, moist cloud-topped ML with little diurnal variability during the austral summer and deeper ML with more diurnal variability during
Nomogram for the Height of the Daytime Mixed Layer
NASA Astrophysics Data System (ADS)
Nyrén, Kenneth; Gryning, Sven-Erik
A method to construct a nomogram of the daytime mixed-layer-height evolution is presented. The nomogram will be specific for a given location and land surface type and is intended to be an easy tool to achieve a general understanding of mixed-layer behaviour. Also it is a pedagogical graphical one-pager that displays the bulk of data that controls the evolution of the mixed layer. Nomograms from northern, central and southern Europe are presented and discussed. Comparison with data from two sites shows good agreement although the nomograms overestimated the mixing height when it was low.
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
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.
Linear stability analysis of three-dimensional compressible boundary layers
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.; Orszag, Steven A.
1987-01-01
A compressible stability analysis computer code is developed. The code uses a matrix finite-difference method for local eigenvale solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used inital-value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed that may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black-box stability code. Sample stability calculations are presented for the boundary layer profiles of an LFC swept wing.
Effect of heat release on the spatial stability of a supersonic reacting mixing layer
NASA Technical Reports Server (NTRS)
Jackson, T. L.; Grosch, C. E.
1988-01-01
A numerical study of the stability of compressible mixing layers in which a diffusion flame is embedded is described. The mean velocity profile has been approximated by a hyperbolic tangent profile and the limit of infinite activation energy taken, which reduces the diffusion flame to a flame sheet. The addition of combustion in the form of a flame sheet was found to have important, and complex, effects on the flow stability.
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.
Evolution of density compensated fronts in simulated ocean mixed layers
NASA Astrophysics Data System (ADS)
Helber, R. W.; Hebert, D. A.; Koch, A.
2015-12-01
Observations within the ocean surface mixed layer indicate a tendency for temperature gradients to form that are compensated for their effect on density by salinity gradients. These density compensated fronts tend to occur in the absence of strong surface forcing and thus weak vertical mixing. Observations show that density compensated fronts are quickly erased by surface cooling events. The presence of density compensated gradients in the surface mixed layer, however, are not well represented in regional and global ocean circulation model predictions. In these models, subgrid-scale processes are parameterized with minimal ability to represent double diffusion. Recent advances in parameterizations have been developed to model the re-stratification of the mixed layer by sub-mesoscale eddies. These ageostrophic dynamics can lead to long filaments that are governed by process on length scales from 100 m to 10 km and time scales near a day. The impact of these processes in model physics on density compensated fronts is unclear. To improve our understanding of compensated front evolution in the ocean, three different mixing schemes are tested to evaluate the creation of horizontally density compensated gradients in model simulations. One scheme extracts potential energy of ocean fronts for mixing dependent on horizontal and vertical buoyancy gradients, mixed layer depth, and inertial period. The other two schemes mix temperature and salinity horizontally dependent on the buoyancy gradient. All schemes provide a three dimensional approach to mixing that differentiates the horizontal eddy diffusion of temperature and salinity.
NASA Astrophysics Data System (ADS)
Nakagawa, Masaki
2001-07-01
Understanding effects of compressibility on the entrainment and mixing properties of supersonic turbulent shear flows is a key to successful development of the next generation of high-speed airbreathing propulsion systems. Previous studies have focused largely on supersonic mixing layers, and have shown dramatic reductions in the entrainment and mixing rates with increasing compressibility which has been widely believed to be a generic effect of compressibility in supersonic turbulent shear flows. The present dissertation reports results from an experimental investigation of entrainment and mixing in supersonic, planar, turbulent, bluff-body wakes to clarify the generic effects of compressibility in turbulent shear flows. The experimental techniques, including conventional pressure measurements, shadowgraph and planar laser Mie scattering (PLMS) visualizations, and particle image velocimetry (PIV), were used to study instantaneous and mean velocity fields, scaling properties, turbulence statistics, and large-scale structure in instantaneous and phase-averaged vorticity fields over a range of relative Mach numbers. These were compared with corresponding results from incompressible wakes and from supersonic mixing layers. Results indicate that the classical vortex street-like large scale structure of incompressible planar turbulent wakes is recovered in supersonic wakes where the local relative Mach number Mr(x) has decreased to sufficiently small values, but no comparable large-scale organized structure is evident where the relative Mach number is large. Moreover, at downstream locations where Mr(x) is large, a reduction in the growth rate of the flow is observed due to compressibility, but this reduction is significantly smaller than that reported from studies of supersonic mixing layers. Results also show that the wake undergoes a self-induced forcing where it passes through reflected expansion waves produced by the wake generator. This local forcing alters the
EVIDENCE FOR CLOUD VENTING OF MIXED LAYER OZONE
Observations are presented which substantiate the hypothesis that significant vertical exchange of ozone and aerosol pollutants occurs between the mixed layer and the free troposphere during cumulus cloud convective activity. Flight experiments conducted in July 1981, utilized th...
NASA Technical Reports Server (NTRS)
Michell, G. A.
1971-01-01
Vortex generators were investigated as a means of controlling the throat boundary layer in a Mach 2.5 mixed-compression inlet. With or without throat bleed, the generators were unable to produce the inlet peak recoveries available with good performance bleed. Generators placed on the unbled inlet centerbody ahead of the cowl shock impingement point degraded inlet performance. Generators placed further aft on the unbled centerbody, but ahead of the throat, improved inlet performance at conditions where the terminal shock could cause boundary layer separation. Adding generators to the inlet with throat bleed reduced performance. Bleed aft of the generators degraded the vortex flow field.
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
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.
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.
Gradient layer entrainment in a thermohaline system with mixed layer circulation
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.
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.
Direct numerical simulations of a reacting mixing layer with chemical heat release
NASA Technical Reports Server (NTRS)
Mcmurtry, P. A.; Jou, W.-H.; Metcalfe, R. W.; Riley, J. J.
1985-01-01
In order to study the coupling between chemical heat release and fluid dynamics, direct numerical simulations of a chemically reacting mixing layer with heat release are performed. The fully compressible equations as well as an approximate set of equations that is asymptotically valid for low-Mach-number flows are treated. These latter equations have the computational advantage that high-frequency acoustic waves have been filtered out, allowing much larger time steps to be taken in the numerical solution procedure. A detailed derivation of these equations along with an outline of the numerical solution technique is given. Simulation results indicate that the rate of chemical product formed, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release.
Three-wave mixing mediated femtosecond pulse compression in β-barium borate.
Grün, A; Austin, Dane R; Cousin, Seth L; Biegert, J
2015-10-15
Nonlinear pulse compression mediated by three-wave mixing is demonstrated for ultrashort Ti:sapphire pulses in a type II phase-matched β-barium borate (BBO) crystal using noncollinear geometry. 170 μJ pulses at 800 nm with a pulse duration of 74 fs are compressed at their sum frequency to 32 fs with 55 μJ of pulse energy. Experiments and computer simulations demonstrate the potential of sum-frequency pulse compression to match the group velocities of the interacting waves to crystals that were initially not considered in the context of nonlinear pulse compression. PMID:26469593
Response of a supersonic boundary layer to a compression corner
NASA Technical Reports Server (NTRS)
Vandromme, D.; Zeman, O.
1992-01-01
On the basis of direct numerical simulations of rapidly compressed turbulence, Zeman and Coleman have developed a model to represent rapid directional compression contribution to the pressure dilatation term in the turbulent kinetic energy equation. The model has been implemented in the CFD code for simulation of supersonic compression corner flow with an extended separated region. The computational results have shown a significant improvement with respect to the baseline solution given by the standard k- epsilon turbulence model which does not contain any compressibility corrections.
Geometric Frustration in the Mixed Layer Pnictide Oxides
Enjalran, M.; Scalettar, R.T.; Kauzlarich, S.M.
2000-06-06
The authors present results from a Monte Carlo investigation of a simple bilayer model with geometrically frustrated interactions similar to those found in the mixed layer pnictide oxides (Sr{sub 2}Mn{sub 3}Pn{sub 2}O{sub 2}, Pn = As, Sb). The model is composed of two inequivalent square lattices with nearest-neighbor intra- and interlayer interactions. They find a ground state composed of two independent Neel ordered layers when the interlayer exchange is an order of magnitude weaker than the intralayer exchange, as suggested by experiment. Evidence for local orthogonal order between the layers is found, but it occurs in regions of parameter space which are not experimentally realized. Qualitatively similar results were observed in models with a larger number of layers. They conclude that frustration caused by nearest-neighbor interactions in the mixed layer pnictide oxides is not sufficient to explain the long-range orthogonal order that is observed experimentally.
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.
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.
Direct simulations of chemically reacting turbulent mixing layers, part 2
NASA Astrophysics Data System (ADS)
Metcalfe, Ralph W.; McMurtry, Patrick A.; Jou, Wen-Huei; Riley, James J.; Givi, Peyman
1988-06-01
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.
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%.
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
Simulations of free shear layers using a compressible kappa-epsilon model
NASA Technical Reports Server (NTRS)
Yu, S. T.; Chang, C. T.; Marek, C. J.
1991-01-01
A two-dimensional, compressible Navier-Stokes equation with a k-epsilon turbulence model is solved numerically to simulate the flow of a compressible free shear layer. The appropriate form of k and epsilon equations for compressible flow is discussed. Sarkar's modeling is adopted to simulate the compressibility effects in the k and epsilon equations. The numerical results show that the spreading rate of the shear layers decreases with increasing convective Mach number. In addition, favorable comparison was found between the calculated results and experimental data.
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.
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.
Double-diffusive layering and mixing in Patagonian fjords
NASA Astrophysics Data System (ADS)
Pérez-Santos, Iván; Garcés-Vargas, José; Schneider, Wolfgang; Ross, Lauren; Parra, Sabrina; Valle-Levinson, Arnoldo
2014-12-01
Double-diffusive layering was quantified for the first time in the Chilean Patagonian fjords region (41.5-56°S). Approximately 600 temperature and salinity profiles collected during 1995-2012 were used to study water masses, quantify diffusive layering and compute the vertical diffusivity of heat. Development of 'diffusive-layering' or simply 'layering' was favored by relatively fresh-cold waters overlying salty-warm waters. Fresh waters are frequently derived from glacial melting that influences the fjord either directly or through rivers. Salty waters are associated with Modified Subantarctic (MSAAW) and Subantarctic Water (SAAW). Double-diffusive convection occurred as layering in 40% of the year-round data and as salt fingering in <1% of the time. The most vigorous layering, was found at depths between 20 and 70 m, as quantified by (a) Turner angles, (b) density ratios, and (c) heat diffusivity (with maximum values of 5 × 10-5 m2 s-1). Diffusive-layering events presented a meridional gradient with less layering within the 41-47°S northern region, relative to the southern region between 47° and 56°S. Layering occupied, on average, 27% and 56% of the water column in the northern and southern regions, respectively. Thermohaline staircases were detected with microprofile measurements in Martinez and Baker channels (48°S), showing homogeneous layers (2-4 m thick) below the pycnocline (10-40 m). Also in this area, increased vertical mixing coincided with the increased layering events. High values of Thorpe scale (LT ∼ 7 m), dissipation rate of TKE (ε = 10-5-10-3 W kg-1) and diapycnal eddy diffusivity (Kρ = 10-6-10-3 m-2 s-1) were associated with diffusive layering. Implications of these results are that diffusive layering should be taken into account, together with other mixing processes such as shear instabilities and wind-driven flows, in biological and geochemical studies.
Internal wave energy radiated from a turbulent mixed layer
NASA Astrophysics Data System (ADS)
Munroe, James R.; Sutherland, Bruce R.
2014-09-01
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.
Internal wave energy radiated from a turbulent mixed layer
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.
Three-dimensional plastic flow of anisotropic layer compressed by flat dies
NASA Astrophysics Data System (ADS)
Maksimova, Ljudmila A.
2016-06-01
Three-dimensional flow of anisotropic plastic layer compressed by parallel rough flat dies is considered. Ideal plastic material model with Hill anisotropic yield criterion modification of Mises isotropic model is used with associated plastic flow rule. General solution of a thin layer plastic flow problem with Prandtl linear velocity and shear stress variation in layer thickness direction is presented. Effects of contact friction force vector module and direction on the layer pressure on the dies and the layer plastic flow are considered.
Mixing layers and coherent structures in vegetated aquatic flows
NASA Astrophysics Data System (ADS)
Ghisalberti, Marco; Nepf, Heidi M.
2002-02-01
To date, flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow, with vegetative drag treated as an extension of bed drag. However, recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer. This paper presents laboratory measurements, obtained from a scaled seagrass model, that demonstrate the applicability of the mixing layer analogy to aquatic systems. Specifically, all vertical profiles of mean velocity contained an inflection point, which makes the flow susceptible to Kelvin-Helmholtz instability. This instability leads to the generation of large, coherent vortices within the mixing layer (observed in the model at frequencies between 0.01 and 0.11 Hz), which dominate the vertical transport of momentum through the layer. The downstream advection of these vortices is shown to cause the progressive, coherent waving of aquatic vegetation, known as the monami. When the monami is present, the turbulent vertical transport of momentum is enhanced, with turbulent stresses penetrating an additional 30% of the plant height into the canopy.
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.
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.
Calculation of external-internal flow fields for mixed-compression inlets
NASA Technical Reports Server (NTRS)
Chyu, W. J.; Kawamura, T.; Bencze, D. P.
1987-01-01
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.
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.
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).
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.
Mixing Layer Excitation by Dielectric Barrier Discharge Plasma Actuators
NASA Astrophysics Data System (ADS)
Ely, Richard; Little, Jesse
2012-11-01
The response of a mixing layer with velocity ratio 0.28 to perturbations near the high-speed side (U2=11 m/s, ReL = 0.26 × 106) of its origin from dielectric barrier discharge plasma actuators is studied experimentally. Both alternating current (ac) and nanosecond (ns) pulse driven plasma are investigated in an effort to clarify the mechanisms associated with each technique as well as the more general physics associated with flow control via momentum-based versus thermal actuation. Ac-DBD plasma actuators, which function through electrohydrodynamic effects, are found to generate an increase in mixing layer momentum thickness that is strongly dependent on forcing frequency. Results are qualitatively similar to previous archival literature on the topic employing oscillating flaps. Ns-DBD plasma, which is believed to function through thermal effects, has no measureable influence on the mixing layer profile at similar forcing conditions. In the context of previous archival literature, these results suggest different physical mechanisms govern active control via ac- and ns-DBD plasma actuation and more generally, momentum versus thermal perturbations. Further investigation of these phenomena will be provided through variation of the boundary/mixing layer properties and forcing parameters in the context of spatially and temporally resolved experimental data. Supported by: AFOSR and Raytheon Missile Systems.
An experimental study of scalar mixing in curved shear layers
NASA Technical Reports Server (NTRS)
Karasso, P. S.; Mungal, M. G.
1990-01-01
This report describes the work being undertaken to study the scalar mixing in curved shear layers. First, the motivation for this work and its objectives are described. Second, a description of the experimental rig that has been built is given. Third, some preliminary results (flow visualizations) are discussed, and finally, future steps that will be taken to complete the study are outlined.
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.
Photoionized Mixing Layer Models of the Diffuse Ionized Gas
NASA Astrophysics Data System (ADS)
Binette, Luc; Flores-Fajardo, Nahiely; Raga, Alejandro C.; Drissen, Laurent; Morisset, Christophe
2009-04-01
It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer (TML) models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated, and mixed. The emission spectrum of such layers is compared with observations of Rand of the DIG in the edge-on spiral NGC 891. We generate two sequence of models that fit the line ratio correlations between [S II]/Hα, [O I]/Hα, [N II]/[S II], and [O III]/Hβ reasonably well. In one sequence of models, the hot wind velocity increases, while in the other, the ionization parameter and layer opacity increase. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.
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.
Direct simulation of shock-induced mixing layer
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.
Modeling the iron cycling in the mixed layer
NASA Astrophysics Data System (ADS)
Weber, L.; Voelker, C.; Schartau, M.; Wolf-Gladrow, D.
2003-04-01
We present a comprehensive model of the iron cycling within the mixed layer of the ocean, which predicts the time course of iron concentration and speciation. The speciation of iron within the mixed layer is heavily influenced by photochemistry, organic complexation, colloid formation and aggregation, as well as uptake and release by marine biota. The model is driven by mixed layer dynamics, dust deposition and insolation, as well as coupled to a simple ecosystem model (based on Schartau at al.2001: Deep-Sea Res.II.48,1769-1800) and applied to the site of the Bermuda Atlantic Time-series Study (BATS). Parameters in the model were chosen to reproduce the small number of available speciation measurements resolving a daily cycle. The model clearly reproduces the available Fe concentration at the BATS station but the annual balance of Fe fluxes at BATS is less constrained, due to uncertainties in the model parameters. Hence we discuss the model's sensitivity to parameter uncertainties and which observations might help to better constrain the relevant model parameters. Futher we discuss how the most important model parameters are constrained by the data. The mixed layer cycle in the model strongly influences seasonality of primary production as well as light dependency of photoreductive processes and therefore controlls iron speciation. Futhermore short events within a day (e.g. heavy rain, change of irradiance, intense dust deposition and temporary deepening of the mixed layer) may push processes like colloidal aggregation. For this reason we compare two versions of the model: The first one is forced by monthly averaged climatological variables, the second one by daily climatological variabilities.
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.
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.
Measurements of Molecular Mixing in a High Schmidt Number Rayleigh-Taylor Mixing Layer
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
The Saharan atmospheric boundary layer: Turbulence, stratification and mixing
NASA Astrophysics Data System (ADS)
Garcia-Carreras, Luis; Parker, Douglas J.; Marsham, John H.; Rosenberg, Philip D.; Marenco, Franco; Mcquaid, James B.
2013-04-01
High-resolution large-eddy model simulations, combined with aircraft and radiosonde observations from the Fennec observational campaign are used to describe the vertical structure of the Saharan atmospheric boundary layer (SABL). The SABL, probably the deepest dry convective boundary layer on Earth, is crucial in controlling the vertical redistribution and long-range transport of dust, heat, water and momentum in the Sahara, with significant implications for the large-scale Saharan heat low and West African monsoon systems. The daytime SABL has a unique structure, with an actively growing convective region driven by high sensible heating at the surface, capped by a weak (≤1K) temperature inversion and a deep, near-neutrally stratified Saharan residual layer (SRL) above it, which is mostly well mixed in humidity and temperature and reaches a height of ~500hPa. Large-eddy model (LEM) simulations were initialized with radiosonde data and driven by surface heat flux observations from Fennec supersite-1 at Bordj Bardji Mokhtar (BBM), southern Algeria. Aircraft observations are used to validate the processes of interest identified in the model, as well as providing unprecedented detail of the turbulent characteristics of the SABL. Regular radiosondes from BBM during June 2011 are used to generate a climatology of the day-time SABL structure, providing further evidence that the processes identified with the LEM are recurrent features of the real SABL. The model is shown to reproduce the typical SABL structure from observations, and different tracers are used to illustrate the penetration of the convective boundary layer into the residual layer above as well as mixing processes internal to the residual layer. Despite the homogeneous surface fluxes and tracer initialization, the large characteristic length-scale of the turbulent eddies leads to large horizontal changes in boundary layer depth (which control the formation of clouds) and significant heterogeneity in tracer
Autumnal Mixed-Phase Cloudy Boundary Layers in the Arctic.
NASA Astrophysics Data System (ADS)
Pinto, James O.
1998-06-01
Two mixed-phase cloudy boundary layer events observed over the Arctic ice pack in autumn are extensively analyzed. The local dynamic and thermodynamic structure of the boundary layers is determined from aircraft measurements including analysis of turbulence, longwave radiative transfer, and cloud microphysics. The large-scale forcing is determined from the National Centers for Environmental Prediction reanalysis fields while mesoscale forcing is estimated from 40-km aircraft box patterns. The two cases differed somewhat in their local static stability, surface characteristics, and large-scale forcing. One case was characterized by a stably stratified cloudy boundary layer over a heterogeneous surface containing numerous open leads. The other case occurred over a fairly homogenous surface of multiyear ice and consisted of a surface-based stable layer surmounted by a low-level jet and a cloud-topped mixed layer. An important large-scale factor in the development of low clouds appears to have been water vapor advection. Low clouds formed irrespective of the sign of the large-scale vertical velocity. Observed flux profiles indicate that both cloudy boundary layers are cooled through turbulent eddies except at cloud top where entrainment of warm moist air aloft occurs. Maximum turbulent kinetic energy occurs near cloud top where turbulent motions are driven by strong radiative cooling (>70 K day1) and in the vicinity of the low-level jet where turbulence is shear induced. The presence of both liquid and ice in the cloud layers appears to be a nearly steady-state feature at temperatures between 13° and 20°C. Results of a simple condensed water budget indicate that these colloidally unstable mixed-phase clouds may be maintained through strong cloud-top radiative cooling. The isobaric cooling rate required to maintain the presence of both liquid and ice in a stratiform cloud is quite sensitive to variations in the highly uncertain concentration of ice-forming nuclei.
Ion mixing of III-V compound semiconductor layered structures
Xia, W.; Pappert, S.A.; Zhu, B.; Clawson, A.R.; Yu, P.K.L.; Lau, S.S. ); Poker, D.B.; White, C.W. ); Schwarz, S.A. )
1992-03-15
Compositional disordering of III-V compound superlattice structures has received considerable attention recently due to its potential application for photonic devices. The conventional method to induce compositional disorder in a layered structure is to implant a moderate dose of impurity ions ({similar to}10{sup 15}/cm{sup 2}) into the structure at room temperature, followed by a high-temperature annealing step (this process is referred to as IA here). Ion irradiation at room temperature alone does not cause any significant intermixing of layers. The subsequent high-temperature annealing step tends to restrict device processing flexibility. Ion mixing (IM) is capable of enhancing compositional disordering of layers at a rate which increases exponentially with the ion irradiation temperature. As a processing technique to planarize devices, ion mixing appears to be an attractive technology. In this work, we investigate compositional disordering in the AlGaAs/GaAs and the InGaAs/InP systems using ion mixing. We found that the ion mixing behavior of these two systems shows a thermally activated regime as well as an athermal regime, similar to that observed for metal-metal and metal-semiconductor systems. Ion mixing is observed to induce compositional disordering at significantly lower temperatures than that for the IA process. We have compared the two processes in terms of five parameters: (1) irradiation temperature, (2) dose dependence, (3) dose rate dependence, (4) annealing, and (5) ion dependence (including electrical effects and mass dependence). We found that the IM process is more efficient in utilizing the defects generated by ion irradiation to cause disordering. Both the physical mechanism of ion mixing and possible device implications will be discussed.
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.
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.
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.
Vortical structure in a forced plane mixing layer
NASA Technical Reports Server (NTRS)
Leboeuf, Richard L.
1993-01-01
The objective of this phase of an ongoing study is to obtain detailed three dimensional phase-averaged measurements of forced mixing layer vorticity development and evolution. Acoustic forcing is being used to phase-lock the initial development and subsequent pairing of the span wise vortical structures. Phase averaged measurements of the three velocity components will permit the study of three dimensional vorticity distributions without invoking Taylor's hypothesis which is known to introduce uncertainty. Currently two sine waves, one at the fundamental roll-up frequency and the second, its subharmonic, are being used to force the initial roll-up and first pairing of the span wise rollers. The two dimensional measurements described in this report were obtained in order to determine the best operating conditions for the detailed three dimensional study of the mixing layer undergoing pairing via various pairing mechanisms.
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.
Seasonal variability of mixed layer depth in Indonesian Seas
NASA Astrophysics Data System (ADS)
Radjawane, Ivonne M.; Nurdjaman, Susanna; Apriansyah
2015-09-01
This research is conducted to analyzed seasonal variation of mixed layer depth (MLD) in Indonesian Seas using monthly temperature average data from World Ocean Atlas (WOA) 2009 with the 0.25 degree grid resolution and wind data from NCEP. The results of this study indicate that seasonal variation of MLD are closely related to seasonal monsoonal wind pattern prevail in Indonesia region especially at south of west Java, central of Banda Sea and Sulawesi Sea. The MLD is deeper during Southeast (SE) Monsoon. The stronger wind blowing over ocean surface caused stronger ocean dynamics and stronger mixing process that effect deeper mixing region. In contrary, during SE Monsoon, the location of strong upwelling such as in the coastal area of east Java and from eastern Banda Sea till Arafura Sea showed the MLD is shallower compare during the Northwest (NW) Monsoon.
Dependence of Boundary Layer Mixing On Lateral Boundary Conditions
NASA Astrophysics Data System (ADS)
Straub, D.
Ocean circulation models often show strong mixing in association with lateral bound- ary layers. Such mixing is generally considered to be artifactual rather than real. Fur- thermore, the severity of the problem is boundary condition dependent. For example, an inconsistency between geostrophy and insulating boundary conditions on tempera- ture and salinity cause many modelers to opt for the no slip, rather than slip boundary condtion on the tangential component of momentum. As modellers increasingly move into the eddy revealing regime, biharmonic, rather than harmonic dissipative operators are likely to become more common. Biharmonic operators, however, require specifi- cation of additional boundary conditions. For example, there are several `natural ex- tensions' to each of the slip and no slip conditions. Here, these various possiblities are considered in the context of a simple model. Particular attention is payed to how mixing (and the associated overturning cell) is affected by the choice of boundary condition.
Thermal mixing layer downstream of half-heated turbulence grid
NASA Astrophysics Data System (ADS)
Larue, J. C.; Libby, P. A.
1981-04-01
Experimental and theoretical results are presented concerning the temperature in the thermal mixing layer downstream of a partially heated turbulence grid. Temperatures were measured by platinum wire thermometers located upstream and downstream of a turbulence grid consisting of 18 horizontal and 18 vertical heating rods, with the uppermost nine horizontal rods heated to a temperature about 200 C above ambient. Experimental results are presented for the mean temperature distribution, the distribution of relative temperature intensity, the distributions of the skewness and kurtosis of the temperature fluctuations, probability density functions for the temperature, the skewness of the temperature derivative and the thickness of the thermal interface in the thermal mixing layer, and are compared with previous experimental results where available. As in previous investigations, the measured intensity of the temperature fluctuations in the center of the mixing layer is found to disagree with that predicted by the analysis of Libby (1975) by 40%, and it is concluded that experiments simultaneously yielding the velocity and temperature characteristics are required to explain the discrepancy.
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.
Thermodynamic-biological-optical coupling in the oceanic mixed layer
NASA Astrophysics Data System (ADS)
Simonot, Jean-Yves; Dollinger, Eric; Le Treut, Hervé
1988-07-01
In order to quantitatively investigate the role of phytoplanktonic blooms in the open ocean on sea surface temperature (SST) prediction, the mixed layer model of Gaspar (1985, 1988) is coupled to a primary production model adapted from Agoumi (1985), allowing an interactive prediction of the upper ocean turbidity, over two seasonal cycles at Ocean Weather Station (OWS) R (Romeo). (In this paper we use "turbidity" for total optical content, thus including mineral and phytoplanktpnic content.) The validity of Gaspar's model, originally tested at OWS P (Papa), is first demonstrated for OWS R in its only thermodynamic version. Agoumi's (1985) model, developed for multiyear simulations over the English Channel, is then adapted to the case of the open ocean upper layers. It is shown how turbulent mixing is an important factor regulating primary production and nutrient fluxes, in order to obtain spring and autumn phytoplanktonic blooms and winter decay. Finally, it is shown how the typical spring and autumn errors in SST prediction from the mixed-layer model can be changed in sign in the thermodynamic-biological-optical coupled version of the model. These results confirm that the phytoplanktonic seasonal cycle has a significant impact on sea surface temperature simulation. It is therefore reasonable to consider taking this factor into account in future upper ocean simulation experiments, and some recommendations are suggested for further studies.
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.
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
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.
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.
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.
Spatial three-dimensional secondary instability compressible boundary-layer flows
NASA Technical Reports Server (NTRS)
El-Hady, Nabil M.
1989-01-01
Three-dimensional linear secondary instability theory is extended for compressible and high Mach number boundary layer flows. The small but finite amplitude compressible Tollmien-Schlichting wave effect on the growth of 3-D perturbations is investigated. The focus is on principal parametric resonance responsible for the strong growth of subharmonic in low disturbance environment. The effect of increasing Mach number on the onset, growth, the shape of eigenfunctions of the subharmonic is assessed, and the resulting vortical structure is examined.
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
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.
Nonlinear stability of non-stationary cross-flow vortices in compressible boundary layers
NASA Astrophysics Data System (ADS)
Gajjar, J. S. B.
1995-05-01
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.
DNSs of Multicomponent Gaseous and Drop-Laden Mixing Layers Achieving Transition to Turbulence
NASA Technical Reports Server (NTRS)
Bellan, Josette; Selle, Laurent
2007-01-01
A paper describes direct numerical simulations (DNSs) of three-dimensional mixing-layer flows undergoing transition to turbulence; the mixing layers may or may not be laden with evaporating liquid drops.
NASA Astrophysics Data System (ADS)
Fair, Geoff Eric
Threshold strength behavior and flaw insensitivity have recently been observed in laminar ceramic composites containing thick stress-free layers and thin layers in residual compression (due to thermal expansion mismatch). The threshold strength behavior is due to a crack tip shielding effect in which the stress intensity factor cracks initiating in the thick layers and propagating through the thin layers is reduced by the compressive stresses. Consequently, a well-defined level of stress (the threshold strength) is required to cause the cracks to propagate entirely through the compressive layers to cause failure of the specimens regardless of the initial flaw size. The threshold strength behavior is only observed in one loading orientation relative to the layers. The current work describes the processing procedures and fracture behavior of ceramic composites with three-dimensional architectures of thin compressive layers which are expected to exhibit threshold strength behavior in any tensile loading orientation and possess higher threshold strengths than laminates of similar architectural dimensions. Processing of the composites consists of producing spherical agglomerates, coating these agglomerates with a thin layer of material which upon heat treatment develops a residual compressive stress, and consolidating the coated agglomerates into bars suitable for mechanical testing. Finite element modeling of the residual stresses in the composite architecture is used to explain fracture behavior of the composites which is shown to depend on the architectural variables. Fractography of failed specimens is instrumental in elucidating the processing flaws within the architectures, one of the most pervasive of which is inter-agglomerate voids due to incomplete consolidation; additional processing steps are developed to remove these flaws and produce flaw-free composites suitable for a study of a flaw-insensitivity through the introduction of controlled flaws. Mechanical
A comparison of hydrographically and optically derived mixed layer depths
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.
Evaluation of some compression aids in tableting of roller compacted swellable core drug layer.
Golchert, D; Bines, E; Carmody, A
2013-09-10
Swellable core technology (SCT) represents a broadly applicable oral osmotic drug delivery platform for the controlled release of drugs. SCT tablets control drug delivery by using osmosis to regulate the influx of water into the tablet's core. The tablet consists of two layers; drug layer and sweller layer, with a semi-permeable membrane coating and delivery port located in the drug layer side of the tablet. The key component of SCT formulations is polyethylene oxide (PEO), which is typically wet granulated with organic solvents to prevent rapid gel hydration observed during contact with aqueous environments. However, the use of organic solvents has their own environmental and cost considerations which make this form of processing undesirable. To overcome this issue, dry granulation can be employed. However, PEO is a very plastic material and problems may be encountered during the tableting process, when work hardening occurs upon double compression. The addition of compression aids to the drug layer will help to increase the roll force when generating ribbons - reducing fines and segregation potential - while also reducing work hardening effects which impact tablet friability. The five compression aids used in this study were microcrystalline cellulose (MCC), xylitol, di-calcium phosphate (anhydrous), lactose monohydrate and starch. The work undertaken here studies the compression properties of the drug layer blends with different levels of the five compression aids as part of the formulation. Roller compaction properties are also varied to provide granules with differing solid fractions. The results of this study indicate that addition of microcrystalline cellulose in the formulation in levels between 10% and 30% significantly improve the tablet hardness at lower tablet compression forces. Further work is required to investigate the impact on dissolution. PMID:23796839
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
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.
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.
Water Vapor Turbulence Profiles in Stationary Continental Convective Mixed Layers
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.
Vertical and horizontal mixing in the tropical tropopause layer
NASA Astrophysics Data System (ADS)
Glanville, Anne Alexandra
Nearly all air enters the stratosphere through a single layer in the tropics. The tropical tropopause layer (TTL) is a transition region between the troposphere and stratosphere and its roles include regulating stratospheric chemistry and surface climate. Multiscale dynamics existing in the TTL range from transient convection to the hemispheric wave-driven circulation and the relative influences of these processes still remain unclear. This study pays special attention to vertical and horizontal mixing which are associated with breaking gravity waves and Rossby waves, respectively. Our study quantifies the roles of these dynamics by taking advantage of the conservative nature of water vapor in the lower stratosphere. Unable to change concentration in the lowermost stratosphere after passing through the cold point, water vapor becomes a tracer for total transport and its signal is known as the tape recorder. This tape recorder is studied using observations, reanalysis data, a chemistry-climate model (CCM), and simple idealized modeling. Modifying past methods, we are able to capture the seasonal cycle of effective transport in the TTL and we introduce seasonally-dependent dynamics to a one-dimensional model and perform a parameter-sweep to test all possible dynamical combinations. Simulating with unrealistic annual mean transports results in bimodality where either vertical advection or vertical mixing dominate. The solutions that depend on amplified vertical advection disappear when seasonally-dependent transports are used. Overall, all datasets show that vertical mixing is as important to TTL transport as vertical advection itself even during boreal winter when advection peaks. The reanalysis and CCM have increased effective transport compared to observations, however, they rely on different dynamics. The reanalysis has amplified vertical mixing while the CCM has amplified vertical advection. This hints at the possible influence of spurious diffusion from data
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.
Diurnal Variation in Radon Concentration and Mixing-Layer Depths
NASA Astrophysics Data System (ADS)
Kataoka, Toshio
Variation of 222Rn, its short-lived daughters and 212Pb concentrations in the atmosphere, and conditions of the lower atmosphere were observed simultaneously at Kamisaibara Village in Japan. The variation of 222Rn concentration and the ratio of the concentrations of 212Pb and the short-lived daughters of 222Rn during nighttime is explained by sodar echoes and temperature profiles obtained by an instrumented tethered balloon. Depths of the convective mixing layer estimated using the 222Rn concentration, using the surface sensible heat flux, and obtained by low-level sondes are compared and found to be in approximate agreement.
Large-eddy simulation of a spatially-evolving turbulent mixing layer
NASA Astrophysics Data System (ADS)
Capuano, Francesco; Catalano, Pietro; Mastellone, Andrea
2015-11-01
Large-eddy simulations of a spatially-evolving turbulent mixing layer have been performed. The flow conditions correspond to those of a documented experimental campaign (Delville, Appl. Sci. Res. 1994). The flow evolves downstream of a splitter plate separating two fully turbulent boundary layers, with Reθ = 2900 on the high-speed side and Reθ = 1200 on the low-speed side. The computational domain starts at the trailing edge of the splitter plate, where experimental mean velocity profiles are prescribed; white-noise perturbations are superimposed to mimic turbulent fluctuations. The fully compressible Navier-Stokes equations are solved by means of a finite-volume method implemented into the in-house code SPARK-LES. The results are mainly checked in terms of the streamwise evolution of the vorticity thickness and averaged velocity profiles. The combined effects of inflow perturbations, numerical accuracy and subgrid-scale model are discussed. It is found that excessive levels of dissipation may damp inlet fluctuations and delay the virtual origin of the turbulent mixing layer. On the other hand, non-dissipative, high-resolution computations provide results that are in much better agreement with experimental data.
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.
Mix Degradation in DT Filled Capsules When Shock and Compression Yields are Resolved
NASA Astrophysics Data System (ADS)
Wilson, D. C.; Herrmann, H. W.; Mack, J. M.; Young, C. S.; Kyrala, G. A.; Cooley, J. H.; Welser-Sherrill, L.; Langenbrunner, J. R.; Evans, S. C.; Sedillo, T. J.; Horsfield, C. J.; Drew, D. W.; Miller, E. K.; Glebov, V. Yu.
2007-11-01
1100μm dia. DT(5atm) + 3He (0,1,or 5 atm) filled glass capsules were directly driven on the Omega laser to measure yield, X-ray images, and especially the burn time history. The 600ps square pulse increases time separation between the ``shock'' yield (before the reflected shock reaches the incoming shell) and later ``compression'' yield. Matching the timing and amount of this early ``shock'' yield in the implosions fixes the electron conduction flux limiter. The Scannapieco and Cheng mix model results are compared with measured yield, burn temperatures and histories, and gated X-ray images. The experiment shows degradation of both the shock and compression yield, but relatively more degradation of the compression yield than explained by the model. The first gated images, which occur when the reflected shock reaches the incoming shell, show significant mixing has already occurred. But the lack of X-ray emission 60ps earlier suggests no mixing then. Work supported by US DOE/NNSA, performed by LANL, operated by LANS LLC under Contract DE-AC52-06NA25396. LA-UR-07-4929.
Decoupling and Multicriticality in the Mixed Phase of Layered Superconductors
NASA Astrophysics Data System (ADS)
Rodriguez, Jose P.
2000-03-01
The mixed phase of extremely type-II layered superconductors is studied theoretically through an analysis of the corresponding layered XY model with uniform frustration. The latter is carried out by a partial duality transformation to a neutral layered Coulomb gas ensemble (CGE). The CGE is dilute in the weak-coupling limit at high perpendicular fields, in which case we obtain a second-order melting transition that separates a coupled phase at low temperatures composed of 2D vortex lattices from a decoupled vortex-liquid phase at high temperatures. This indicates that neither the Friedel scenario nor the ``line-liquid'' phase are likely in clean layered superconductors. It is also argued on the basis of the CGE description that the above second-order melting line converts itself into a first-order decoupling transition at perpendicular fields that lie below the dimensional cross-over scale. Comparison with available results from Monte Carlo simulation of the frustrated XY model and from experiments in high-temperature superconductors is made where possible.
A mixing layer theory for flow resistance in shallow streams
NASA Astrophysics Data System (ADS)
Katul, Gabriel; Wiberg, Patricia; Albertson, John; Hornberger, George
2002-11-01
A variety of surface roughness characterizations have emerged from nineteenth and twentieth century studies of channel hydraulics. When the water depth h is much larger than the characteristic roughness height ks, roughness formulations such as Manning's n and the friction factor f can be explicitly related to the momentum roughness height zo in the log-law formulation for turbulent boundary layers, thereby unifying roughness definitions for a given surface. However, when h is comparable to (or even smaller than) ks, the log-law need not be valid. Using a newly proposed mixing layer analogy for the inflectional velocity profile within and just above the roughness layer, a model for the flow resistance in shallow flows is developed. The key model parameter is the characteristic length scale describing the depth of the Kelvin-Helmholtz wave instability. It is shown that the new theory, originally developed for canopy turbulence, recovers much of the earlier roughness results for flume experiments and shallow gravel streams. This study is the first to provide such a unifying framework between canopy atmospheric turbulence and shallow gravel stream roughness characterization. The broader implication of this study is to support the merger of a wealth of surface roughness characterizations independently developed in nineteenth and twentieth century hydraulics and atmospheric sciences and to establish a connection between roughness formulations across traditionally distinct boundary layer types.
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.
NASA Technical Reports Server (NTRS)
Strong, Stuart L.; Meade, Andrew J., Jr.
1992-01-01
Preliminary results are presented of a finite element/finite difference method (semidiscrete Galerkin method) used to calculate compressible boundary layer flow about airfoils, in which the group finite element scheme is applied to the Dorodnitsyn formulation of the boundary layer equations. The semidiscrete Galerkin (SDG) method promises to be fast, accurate and computationally efficient. The SDG method can also be applied to any smoothly connected airfoil shape without modification and possesses the potential capability of calculating boundary layer solutions beyond flow separation. Results are presented for low speed laminar flow past a circular cylinder and past a NACA 0012 airfoil at zero angle of attack at a Mach number of 0.5. Also shown are results for compressible flow past a flat plate for a Mach number range of 0 to 10 and results for incompressible turbulent flow past a flat plate. All numerical solutions assume an attached boundary layer.
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.
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.
Estimating mixed layer nitrate in the North Atlantic Ocean
NASA Astrophysics Data System (ADS)
Steinhoff, T.; Friedrich, T.; Hartman, S. E.; Oschlies, A.; Wallace, D. W. R.; Körtzinger, A.
2009-09-01
Here we present an equation for the estimation of nitrate in surface waters of the North Atlantic Ocean (40° N to 52° N, 10° W to 60° W). The equation was derived by multiple linear regression (MLR) from nitrate, sea surface temperature (SST) observational data and model mixed layer depth (MLD) data. The observational data were taken from merchant vessels that have crossed the North Atlantic on a regular basis in 2002/2003 and from 2005 to present. It is important to find a robust and realistic esitmate of MLD because the deepening of the mixed layer is crucial for nitrate supply to the surface. We compared model data from two models (FOAM and Mercator) with MLD derived from float data (using various criteria). The Mercator model gives a MLD estimate that is close to the MLD derived from floats. MLR was established using SST, MLD from Mercator, time and latitude as predictors. Additionally a neural network was trained with the same dataset and the results were validated against both model data as a "ground truth" and an independent observational dataset. This validation produced RMS errors of the same order for MLR and the neural network approach. We conclude that it is possible to estimate nitrate concentrations with an uncertainty of ±1.5 μmol L-1 in the North Atlantic.
Estimating mixed layer nitrate in the North Atlantic Ocean
NASA Astrophysics Data System (ADS)
Steinhoff, T.; Friedrich, T.; Hartman, S. E.; Oschlies, A.; Wallace, D. W. R.; Körtzinger, A.
2010-03-01
Here we present an equation for the estimation of nitrate in surface waters of the North Atlantic Ocean (40° N to 52° N, 10° W to 60° W). The equation was derived by multiple linear regression (MLR) from nitrate, sea surface temperature (SST) observational data and model mixed layer depth (MLD) data. The observational data were taken from merchant vessels that have crossed the North Atlantic on a regular basis in 2002/2003 and from 2005 to the present. It is important to find a robust and realistic estimate of MLD because the deepening of the mixed layer is crucial for nitrate supply to the surface. We compared model data from two models (FOAM and Mercator) with MLD derived from float data (using various criteria). The Mercator model gives a MLD estimate that is close to the MLD derived from floats. MLR was established using SST, MLD from Mercator, time and latitude as predictors. Additionally a neural network was trained with the same dataset and the results were validated against both model data as a "ground truth" and an independent observational dataset. This validation produced RMS errors of the same order for MLR and the neural network approach. We conclude that it is possible to estimate nitrate concentrations with an uncertainty of ±1.4 μmol L-1 in the North Atlantic.
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.
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.
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.
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.
Dynamic negative compressibility of few-layer graphene, h-BN, and MoS2.
Barboza, Ana Paula M; Chacham, Helio; Oliveira, Camilla K; Fernandes, Thales F D; Ferreira, Erlon H Martins; Archanjo, Braulio S; Batista, Ronaldo J C; de Oliveira, Alan B; Neves, Bernardo R A
2012-05-01
We report a novel mechanical response of few-layer graphene, h-BN, and MoS(2) 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 MoS(2)), but it is absent in single-layer graphene and in few-layer mica and Bi(2)Se(3). 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. PMID:22468807
NASA Astrophysics Data System (ADS)
Dykhovskii, I. A.; Kovalev, P. I.
Supersonic heterogeneous gas flows colliding with blunt-nosed objects are examined by studying the effects of water droplets colliding with similar objects. Various optical techniques are applied to the study of the effects to capitalize on the advantages and efficiency of each. The patterns of disturbance are visualized and described qualitatively to isolate the mechanisms of interaction in compressed layers.
Secondary instability of compressible boundary layer to subharmonic three-dimensional disturbances
NASA Technical Reports Server (NTRS)
El Hady, Nabil M.
1989-01-01
Three-dimensional linear secondary instability theory is extended for compressible boundary layers on a flat plate in the presence of finite amplitude Tollmien-Schlichting (T-S) waves. The focus is on principal parametric resonance responsible for the strong growth of harmonics in a low disturbance environment.
Secondary instability of compressible boundary layer to subharmonic three-dimensional disturbances
NASA Technical Reports Server (NTRS)
El-Hady, Nabil M.
1988-01-01
Three-dimensional linear secondary instability theory is extended for compressible boundary layers on a flat plate in the presence of finite amplitude Tollmien-Schlichting (T-S) waves. The focus is on principal parametric resonance responsible for the strong growth of harmonics in a low disturbance environment.
CVS Filtering of 3D Turbulent Mixing Layers Using Orthogonal Wavelets
NASA Technical Reports Server (NTRS)
Schneider, Kai; Farge, Marie; Pellegrino, Giulio; Rogers, Michael
2000-01-01
Coherent Vortex Simulation (CVS) filtering has been applied to Direct Numerical Simulation (DNS) data of forced and unforced time-developing turbulent mixing layers. CVS filtering splits the turbulent flow into two orthogonal parts, one corresponding to coherent vortices and the other to incoherent background flow. We have shown that the coherent vortices can be represented by few wavelet modes and that these modes are sufficient to reproduce the vorticity probability distribution function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of CVS filtering, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.
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.
Passive scalar entrainment and mixing in a forced, spatially-developing mixing layer
NASA Technical Reports Server (NTRS)
Lowery, P. S.; Reynolds, W. C.; Mansour, N. N.
1987-01-01
Numerical simulations are performed for the forced, spatially-developing plane mixing layer in two and three dimensions. Transport of a passive scalar field is included in the computation. This, together with the allowance for spatial development in the simulations, affords the opportunity for study of the asymmetric entrainment of irrotational fluid into the layer. The inclusion of a passive scalar field provides a means for simulating the effect of this entrainment asymmetry on the generation of 'products' from a 'fast' chemical reaction. Further, the three-dimensional simulations provide useful insight into the effect of streamwise structures on these entrainment and 'fast' reaction processes. Results from a two-dimensional simulation indicate 1.22 parts high-speed fluid are entrained for every one part low-speed fluid. Inclusion of streamwise vortices at the inlet plane of a three-dimensional simulation indicate a further increase in asymmetric entrainment - 1.44:1. Results from a final three-dimensional simulation are presented. In this case, a random velocity perturbation is imposed at the inlet plane. The results indicate the 'natural' development of the large spanwise structures characteristic of the mixing layer.
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
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)
On the effect of boundary layer growth on the stability of compressible flows
NASA Technical Reports Server (NTRS)
El-Hady, N. M.
1981-01-01
The method of multiple scales is used to describe a formally correct method based on the nonparallel linear stability theory, that examines the two and three dimensional stability of compressible boundary layer flows. The method is applied to the supersonic flat plate layer at Mach number 4.5. The theoretical growth rates are in good agreement with experimental results. The method is also applied to the infinite-span swept wing transonic boundary layer with suction to evaluate the effect of the nonparallel flow on the development of crossflow disturbances.
Growth of Goertler vortices in compressible boundary layers along curved surfaces
NASA Technical Reports Server (NTRS)
El-Hady, N. M.; Verma, A. K.
1983-01-01
An investigation of the growth of the three-dimensional, counter-rotating, longitudinal type vortices is considered in two-dimensional laminar compressible boundary-layer flow. The basic approximation of the disturbance equations that includes the terms due to boundary layer growth is considered and solved numerically. These terms are shown to have large local effects near the neutral stability region. The study shows that the instability of the boundary layer with respect to the three-dimensional vortices sets in at higher Goertler number as Mach number increases. Also the maximum amplitude ratio of the vortices is reduced by about 20 percent as Mach number increases from 0 to 5.
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.
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.
NASA Astrophysics Data System (ADS)
Cervera, M.; Lafontaine, N.; Rossi, R.; Chiumenti, M.
2016-06-01
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 (P1P1 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.
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.
Estimation of atmospheric mixing layer height from radiosonde data
NASA Astrophysics Data System (ADS)
Wang, X. Y.; Wang, K. C.
2014-06-01
Mixing layer height (h) is an important parameter for understanding the transport process in the troposphere, air pollution, weather and climate change. Many methods have been proposed to determine h by identifying the turning point of the radiosonde profile. However, substantial differences have been observed in the existing methods (e.g. the potential temperature (θ), relative humidity (RH), specific humidity (q) and atmospheric refractivity (N) methods). These differences are associated with the inconsistency of the temperature and humidity profiles in a boundary layer that is not well mixed, the changing measurability of the specific humidity and refractivity with height, the measurement error of humidity instruments within clouds, and the general existence of clouds. This study proposes a method to integrate the information of temperature, humidity and cloud to generate a consistent estimate of h. We apply this method to high vertical resolution (~ 30 m) radiosonde data that were collected at 79 stations over North America during the period from 1998 to 2008. The data are obtained from the Stratospheric Processes and their Role in Climate Data Center (SPARC). The results show good agreement with those from N method as the information of temperature and humidity contained in N; however, cloud effects that are included in our method increased the reliability of our estimated h. From 1988 to 2008, the climatological h over North America was 1675 ± 303 m with a strong east-west gradient: higher values (generally greater than 1800 m) occurred over the Midwest US, and lower values (usually less than 1400 m) occurred over Alaska and the US West Coast.
Estimation of atmospheric mixing layer height from radiosonde data
NASA Astrophysics Data System (ADS)
Wang, X. Y.; Wang, K. C.
2014-02-01
Mixing layer height (h) is an important parameter for understanding the transport process in the troposphere, air pollution, weather and climate change. Many methods have been proposed to determine h by identifying the turning point of the radiosonde profile. However, substantial differences have been observed in the existing methods (e.g., the potential temperature (θ), relative humidity (RH), specific humidity (q) and atmospheric refractivity (N) methods). These differences are associated with the inconsistency of the temperature and humidity profiles in a boundary layer that is not well mixed, the changing measurability of the specific humidity and refractivity with height, the measurement error of humidity instruments within clouds, and the general existence of clouds. This study proposes a method to integrate the information of temperature, humidity and cloud to generate a consistent estimate of h. We apply this method to high vertical resolution (~ 30 m) radiosonde data that were collected at 79 stations over North America during the period from 1998 to 2008; the data are obtained from the Stratospheric Processes and their Role in Climate Data Center (SPARC). The results show good agreement with those from N method as the information of temperature and humidity contained in N; however cloud effects that are included in our method increased the reliability of h. Furthermore, our results agree well with the independent h that was determined from lidar observations. From 1988 to 2008, the climatological h over North America was 1675± 303 m with a strong east-west gradient: higher values (generally greater than 1800 m) occurred over the Midwest US, and lower values (usually less than 1400 m) occurred over Alaska and the US west coast.
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
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.
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
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
Tactical application of an atmospheric mixed-layer model
NASA Astrophysics Data System (ADS)
Graves, R. M.
1982-12-01
Modern Naval weapon and sensor systems are strongly influenced by the marine environment. Foremost among the atmospheric effects is ducting of electromagnetic energy by refractive layers in the atmosphere. To assess the effect of ducting on electromagnetic emissions, the Navy developed the Integrated Refractive Effects Prediction System (IREPS). Research at Naval Postgraduate School (NPS) has led to development of a state-of-the-art model which can be used to predict changes to the refractive profile of the lower atmosphere. The model uses radiosonde data and surface meteorological observations to predict changes in refractive conditions and low level cloud/fog formation over 18 to 30 hour periods. The model shows some skill in forecasting duct regions when subsidence rates can be specified to within +/-.0015 m/s. This thesis shows the applicability of the NPS marine atmospheric mixed layer model to fleet tactics. Atmospheric refractive effects on specific emitters can be predicted when model predictions are used in conjunction with IREPS.
Seaglider observations of surface mixed layer physics and biogeochemistry
NASA Astrophysics Data System (ADS)
Damerell, Gillian; Heywood, Karen; Thompson, Andrew; Henson, Stephanie; Rumyantseva, Anya
2013-04-01
The Ocean Surface Mixing, Ocean Sub-mesoscale Interaction Study (OSMOSIS) aims to develop new, physically-based parameterisations of processes that deepen and shoal the ocean surface boundary layer. As part of this project, 2 Seagliders were deployed in September 2012 at the Porcupine Abyssal Plain (PAP) site in the North Atlantic, to measure the structure and evolution of the ocean surface boundary layer over the seasonal cycle. The gliders measured temperature, salinity, dissolved oxygen, dive-averaged currents, chlorophyll fluorescence, CDOM fluorescence and PAR. We present results from the first 6 months of the Seaglider deployments, examining particular case studies of deepening/shoaling events and their impact on the biogeochemistry. Shoaling events appear to be more abrupt than deepening events. We also discuss the water masses found in the area, in particular, the occurrences of Mediterranean Water observed at a depth of approximately 800 m. As a contribution to the GROOM project, we assess the advantages and challenges of maintaining a continuous glider-based multidisciplinary observing system at the PAP site, with 2 gliders being turned around approximately every 4 months.
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.
Tolerance of Mach 2.50 axisymmetric mixed-compression inlets to upstream flow variations
NASA Technical Reports Server (NTRS)
Choby, D. A.
1972-01-01
An investigation of the tolerances of two Mach 2.50 axisymmetric mixed-compression inlets to upstream flow variations was conducted. Tolerances of each inlet to angle of attack as a function of decreasing free-stream Mach number were obtained. A local region of overcompression was formed on the leeward side of the inlet at maximum angle of attack before unstart. This region of overcompression corresponded to local subsonic flow conditions ahead of the geometric throat. A uniform Mach number gradient of 0.10 at the cowl lip plane did not affect the inlet's pressure recovery, mass flow ratio, or diffuser exit total-pressure distortion.
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
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.
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.
Particle transport and flow modulation in particle-laden mixing layers
NASA Astrophysics Data System (ADS)
Tong, Xiao-Ling
Shear flows provide a means to rapidly mix and disperse discrete solid particles and droplets in natural and industrial processes. Moderate mass loadings of particles in a gas mixing layer may also alter the gas shear flow. While the modeling of single-phase shear flows has undergone several decades of development and validation, the consideration of the corresponding problem in two- phase shear flows has just began. This dissertation represents a systematic effort to use a tool known as direct numerical simulations (DNS) to advance our understanding of particle transport and flow modulation in a gas mixing layer laden with solid particles. In DNS, almost all dynamically important flow scales are directly resolved. Previously, DNS of three-dimensional (3D) particle-laden shear flows have not been possible due to their high computational cost. Therefore, we first set out to develop and validate a computationally efficient and numerically accurate DNS methodology for particle-laden mixing layer. The method relies on a Fourier vorticity-based formulation together with a divergence-free decomposition. While almost all previous numerical studies adopted the trajectory approach for the dispersed phase in the context of DNS, a continuum approach has been developed and shown to reduce the computational time by a factor of 15 for the simulations of 3D particle-laden mixing layers. The validity and interpretation of the continuum approach were illustrated analytically with a stagnation point flow model. Detailed comparisons showed that the continuum approach and the trajectory approach yielded very similar results. Since the particulate field is compressible, numerical diffusion must be applied to remove local singularities. A dynamic-diffusion model has been developed as an optimum numerical diffusion model to ensure spectral resolution of particulate continuum fields. The numerical method was then used to study the interactions of finite-inertia particles with 3D flow
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.
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.
Efficient computation of the stability of three-dimensional compressible boundary layers
NASA Technical Reports Server (NTRS)
Malik, M. R.; Orszag, S. A.
1981-01-01
Methods for the computer analysis of the stability of three-dimensional compressible boundary layers are discussed and the user-oriented Compressible Stability Analysis (COSAL) computer code is described. The COSAL code uses a matrix finite-difference method for local eigenvalue solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used initial-value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed which may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black-box stability code. Sample stability calculations are presented for the boundary layer profiles of an LFC swept wing.
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).
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.
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.
Influence of hydrophobic treatment on the structure of compressed gas diffusion layers
NASA Astrophysics Data System (ADS)
Tötzke, C.; Gaiselmann, G.; Osenberg, M.; Arlt, T.; Markötter, H.; Hilger, A.; Kupsch, A.; Müller, B. R.; Schmidt, V.; Lehnert, W.; Manke, I.
2016-08-01
Carbon fiber based felt materials are widely used as gas diffusion layer (GDL) in fuel cells. Their transport properties can be adjusted by adding hydrophobic agents such as polytetrafluoroethylene (PTFE). We present a synchrotron X-ray tomographic study on the felt material Freudenberg H2315 with different PTFE finishing. In this study, we analyze changes in microstructure and shape of GDLs at increasing degree of compression which are related to their specific PTFE load. A dedicated compression device mimicking the channel-land pattern of the flowfield is used to reproduce the inhomogeneous compression found in a fuel cell. Transport relevant geometrical parameters such as porosity, pore size distribution and geometric tortuosity are calculated and consequences for media transport discussed. PTFE finishing results in a marked change of shape of compressed GDLs: surface is smoothed and the invasion of GDL fibers into the flow field channel strongly mitigated. Furthermore, the PTFE impacts the microstructure of the compressed GDL. The number of available wide transport paths is significantly increased as compared to the untreated material. These changes improve the transport capacity liquid water through the GDL and promote the discharge of liquid water droplets from the cell.
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
The behaviour of a compressible turbulent boundary layer under incipient separation conditions
NASA Technical Reports Server (NTRS)
Muck, K. C.; Smits, A. J.
1984-01-01
This paper presents an experimental study of a turbulent boundary-layer/shock-wave interaction. The interaction was generated by a two-dimensional compression corner, and the flow was on the point of separating. Measurements were made using both normal and inclined hot wires, and the data include measurements of the longitudinal mass-flow fluctuation intensity and the mass-weighted Reynolds shear stress.
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.
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.
NASA Technical Reports Server (NTRS)
Beckwith, I. E.
1974-01-01
The purpose of the present note is to show that on a flat plate where both the wall temperature and mean wall pressure are constant, neither of the limitations of parallel flow or of unity for the turbulent Prandtl number are required in order for the Crocco solution to apply to the turbulent boundary-layer flow. It is shown herein that this result is subject to restrictions on the magnitude of pressure fluctuations. The same analysis is generalized to show that the compressible turbulent boundary layer on an isothermal swept flat plate is independent of the spanwise flow if the molecular Prandtl number is unity.
Surface-cooling effects on compressible boundary-layer instability, and on upstream influence
NASA Technical Reports Server (NTRS)
Seddougui, S. O.; Bowles, R. I.; Smith, F. T.
1991-01-01
The influence of surface cooling on compressible boundary-layer instability is discussed theoretically for both viscous and inviscid modes, at high Reynolds numbers, with related questions on upstream influence being considered in an Appendix. The cooling enhances the surface heat transfer and velocity gradient, crating a high-heat-transfer sublayer. This has the effect of distorting and accentuating the viscous Tollmien-Schlichting modes to such an extent that their spatial growth rates becomes comparable with, and can even exceed, the growth rates of inviscid modes, including those found previously. This is for moderate cooling, and it applies at any Mach number. In addition, the moderate cooling destabilizes otherwise stable viscous or inviscid modes, in particular triggering outward-traveling waves at the edge of the boundary layer in the supersonic regime. Severe cooling is also discussed as it brings compressible dynamics directly into play within the viscous sublayer. All the new cooled modes found involve the heat-transfer sublayer quite actively, and they are often multistructured in form and may be distinct from those observed in previous computational and experimental investigations. The corresponding nonlinear processes are also pointed out with regard to transition in the cooled compressible boundary layer. Finally, comparisons with Lysenko and Maslov's (1984) experiments on surface cooling are presented.
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.
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.
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.
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
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.
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
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.
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.
Inhomogeneous relaxation of a molecular layer on an insulator due to compressive stress.
Bocquet, F; Nony, L; Mannsfeld, S C B; Oison, V; Pawlak, R; Porte, L; Loppacher, Ch
2012-05-18
We discuss the inhomogeneous stress relaxation of a monolayer of hexahydroxytriphenylene (HHTP) which adopts the rare line-on-line (LOL) coincidence on KCl(001) and forms moiré patterns. The fact that the hexagonal HHTP layer is uniaxially compressed along the LOL makes this system an ideal candidate to discuss the influence of inhomogeneous stress relaxation. Our work is a combination of noncontact atomic force microscopy experiments, density functional theory and potential energy calculations, and a thorough interpretation by means of the Frenkel-Kontorova model. We show that the assumption of a homogeneous molecular layer is not valid for this organic-inorganic heteroepitaxial system since the best calculated energy configuration correlates with the experimental data only if inhomogeneous relaxations of the layer are taken into account. PMID:23003159
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.
Experimental investigation of terminal shock sensors in mixed-compression inlets
NASA Technical Reports Server (NTRS)
Sajben, Miklos; Donovan, John F.; Morris, Martin J.
1990-01-01
This paper describes experimental investigations of devices designed for the nonintrusive detection of terminal shock location in mixed-compression inlets at high supersonic flight speeds. Systems based on sensing wall pressures by an array of wall-mounted transducers were selected for detailed study. Pressure signals were processed by three different methods: (1) interpretation of instantaneous pressure distributions, (2) detection of the turbulent intensity amplification occurring at the shock, and (3) determination of the upstream limit to which a search-tone, introduced at the downstream end of the channel, can propagate. The first two of these methods were tested in real time. The third method appeared feasible for weak shocks only; at high shock strengths, propagation upstream of the source could not be detected.
Nature of Mixed-Layer Clays and Mechanisms of their Formation and Alteration
NASA Astrophysics Data System (ADS)
Srodon, Jan
Mixed-layer clay minerals are intermediate products of reactions involving pure end-member clays. They come from natural environments ranging from surface to low-grade metamorphic and hydrothermal conditions. Most often mixed layering is essentially two component, but more complicated interstratifications have also been documented. Variable tendency to form regular 1:1 interstratifications has been observed and explanations of this phenomenon have been proposed. Mixed-layer clays are either di- or trioctahedral; di/trioctahedral interstratifications are rare. Most mixed-layer clays contain smectite or vermiculte as a swelling component. Exceptions are all trioctahedral: serpentine/chlorite in low-temperature environments, and mica/chlorite and talc/chlorite at high temperatures. Solid state transformation and dissolution/crystallization are the two mechanisms responsible for the formation of different mixed-layer clays. In general, the weathering reactions that produce mixed layering are reversals of the corresponding high-temperature reactions, but the reaction paths are quite different. Weathering reactions alter smectite into kaolinite via mixed-layer kaolinite/smectite. Illite, chlorite, and micas react into mixed-layer clays involving vermiculite layer, then into vermiculite, and finally smectite. Interstratifications of smectite and glauconite, serpentine and chlorite, and smectite and talc are characteristic of early diagenesis and indicative of sedimentary environments. Three reactions involving mixed-layer clays-smectite to illite, smectite to chlorite, and serpentine/chlorite to chlorite-proceed gradually during burial diagenesis and are used for reconstructing maximum burial conditions, illite/smectite being the most useful tool. Rectorite, tosudite, talc/chlorite, and mica/chlorite are mixed-layer minerals indicative of temperatures higher than diagenetic, characteristic of low-temperature metamorphism or hydrothermal alteration.
Processing mixed-waste compressed-gas cylinders at the Oak Ridge Reservation
Morris, M.I.; Conley, T.B.; Osborne-Lee, I.W.
1998-05-01
Until recently, several thousand kilograms of compressed gases were stored at the Oak Ridge Reservation (ORR), in Oak Ridge, Tennessee, because these cylinders could not be taken off-site in their state of configuration for disposal. Restrictions on the storage of old compressed-gas cylinders compelled the Waste Management Organization of Lockheed Martin Energy Systems, Inc. (LMES) to dispose of these materials. Furthermore, a milestone in the ORR Site Treatment Plan required repackaging and shipment off-site of 21 cylinders by September 30, 1997. A pilot project, coordinated by the Chemical Technology Division (CTD) at the Oak Ridge National Laboratory (ORNL), was undertaken to evaluate and recontainerize or neutralize these cylinders, which are mixed waste, to meet that milestone. Because the radiological component was considered to be confined to the exterior of the cylinder, the contents (once removed from the cylinder) could be handled as hazardous waste, and the cylinder could be handled as low-level waste (LLW). This pilot project to process 21 cylinders was important because of its potential impact. The successful completion of the project provides a newly demonstrated technology which can now be used to process the thousands of additional cylinders in inventory across the DOE complex. In this paper, many of the various aspects of implementing this project, including hurdles encountered and the lessons learned in overcoming them, are reported.
An analytical study of the effects of surface roughness on a compressible turbulent boundary layer
NASA Astrophysics Data System (ADS)
Khan, Z. H.
1983-12-01
A previous study on the effect of surface roughness on the turbulent boundary layer, using a FORTRAN code, ITRACT, solved for the characteristics of a laminar, transitional and turbulent boundary layer on smooth surfaces. The present study investigates the influence of surface roughness on a compressible turbulent boundary layer and then extends the usefulness of ITRACT by including in it the optional capability of rough-surface boundary-layer calculations. Surface roughness was represented by distributed sources and sinks in the appropriate governing equations. The most important term is a sink term in the mean momentum equation, representing the form drag due to the roughness element. Governing boundary-layer equations for continuity, momentum, and energy were derived in a form to account for blockage effects due to roughness elements. The modified governing equations were then transformed using Probstein-Elliott and Levy-Lees transformations. The resulting equations, with appropriate boundary conditions, were solved by finite-difference techniques to determine the nondimensional velocity components and temperature at a finite number of nodes in the boundary-layer flow field.
Inter-Layer Prediction of Color in High Dynamic Range Image Scalable Compression.
Le Pendu, Mikael; Guillemot, Christine; Thoreau, Dominique
2016-08-01
This paper presents a color inter-layer prediction (ILP) method for scalable coding of high dynamic range (HDR) video content with a low dynamic range (LDR) base layer. Relying on the assumption of hue preservation between the colors of an HDR image and its LDR tone mapped version, we derived equations for predicting the chromatic components of the HDR layer given the decoded LDR layer. Two color representations are studied. In a first encoding scheme, the HDR image is represented in the classical Y'CbCr format. In addition, a second scheme is proposed using a colorspace based on the CIE u'v' uniform chromaticity scale diagram. In each case, different prediction equations are derived based on a color model ensuring the hue preservation. Our experiments highlight several advantages of using a CIE u'v'-based colorspace for the compression of HDR content, especially in a scalable context. In addition, our ILP scheme using this color representation improves on the state-of-the-art ILP method, which directly predicts the HDR layer u'v' components by computing the LDR layers u'v' values of each pixel. PMID:27244738
A defect stream function, law of the wall/wake method for compressible turbulent boundary layers
NASA Technical Reports Server (NTRS)
Barnwell, Richard W.; Dejarnette, Fred R.; Wahls, Richard A.
1989-01-01
The application of the defect stream function to the solution of the two-dimensional, compressible boundary layer is examined. A law of the wall/law of the wake formulation for the inner part of the boundary layer is presented which greatly simplifies the computational task near the wall and eliminates the need for an eddy viscosity model in this region. The eddy viscosity model in the outer region is arbitrary. The modified Crocco temperature-velocity relationship is used as a simplification of the differential energy equation. Formulations for both equilibrium and nonequilibrium boundary layers are presented including a constrained zero-order form which significantly reduces the computational workload while retaining the significant physics of the flow. A formulation for primitive variables is also presented. Results are given for the constrained zero-order and second-order equilibrium formulations and are compared with experimental data. A compressible wake function valid near the wall has been developed from the present results.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Jeon, Dong Hyup; Kim, Hansang
2015-10-01
The effect of the compression ratio on the dynamic behavior of liquid water transport in a gas diffusion layer (GDL) is studied both experimentally and numerically. We experimentally study the emergence and growth of liquid droplets in a channel at various compression ratios by adopting a direct visualization device. The results of the experiment show that water breakthrough occurs at the channel for a low compression ratio, whereas it is observed at the channel/rib interface for a high compression ratio. To determine the mechanism of water transport in the GDL, a multiphase lattice Boltzmann method (LBM) is developed for a simplified porous structure of the GDL. The observation of lattice Boltzmann (LB) simulation shows that the compression ratio significantly affects the water transport in the GDL. The results indicate that the lower compression ratio reduces the water saturation in the GDL. The simulation and experimental result are similar.
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.