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338

Aug 1, 2010
08/10

by
Caroglanian, Arme

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A frequency selective surface (FSS) composed of apertures in a metallic sheet is known as the inductive FSS. The infinite inductive FSS theory is derived and the aperture fields are solved by a spectral domain formulation with method of moments solution. Both full domain and subsectional basis functions are studied. A locally planar technique (LPT) is used to determine the forward scattered field from a generally shaped inductive FSS with arbitrary illumination.

Topics: COMPRESSIBILITY EFFECTS, REYNOLDS STRESS, STRESS ANALYSIS, TURBULENT FLOW, DECOMPOSITION, HIGH SPEED

402
402

May 23, 2011
05/11

by
Banerjee, Nana S.; Geer, James F

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The problem of accurately reconstructing a piece-wise smooth, 2(pi)-periodic function f and its first few derivatives, given only a truncated Fourier series representation of f, is studied and solved. The reconstruction process is divided into two steps. In the first step, the first 2N 1 Fourier coefficients of f are used to approximate the locations and magnitudes of the discontinuities in f and its first M derivatives. This is accomplished by first finding initial estimates of these...

Topics: REYNOLDS STRESS, HOMOGENEOUS TURBULENCE, STRESS ANALYSIS, TURBULENCE MODELS, COEFFICIENTS, SYSTEMS...

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183

May 29, 2011
05/11

by
Bolotin, Gary; Boyce, Le

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This paper will present several methods for adjusting clock skew variations that occur in a n accumulative z-axis interconnect system. In such a system, delay between modules in a function of their distance from one another. Clock distribution in a high-speed system, where clock skew must be kept to a minimum, becomes more challenging when module order is variable before design.

Topics: MATHEMATICAL MODELS, TURBULENCE, TURBULENT FLOW, METHOD OF MOMENTS, REYNOLDS STRESS, KOLMOGOROV...

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223

Jun 11, 2011
06/11

by
NON

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This custom bibliography from the NASA Scientific and Technical Information Program lists a sampling of records found in the NASA Aeronautics and Space Database. The scope of this topic includes technologies to allow robust, affordable access of cargo, particularly to low-Earth orbit. This area of focus is one of the enabling technologies as defined by NASA s Report of the President s Commission on Implementation of United States Space Exploration Policy, published in June 2004.

Topics: AIRFOILS, LASER DOPPLER VELOCIMETERS, TURBULENCE, VELOCITY DISTRIBUTION, BUBBLES, REYNOLDS STRESS,...

In recent years, many researchers have used numerical simulation to investigate scramjet engine because, setting up of testing facilities for scramjet engine is very expensive. Completion of simulation work in less time is cost-effective but, it is also important to achieve good outcome from the simulation work. In this context, the use of appropriate turbulent model for the simulation for DLR scramjet engine is a vital aspect. From the available literature, it is seen that many researchers...

Topics: DLR Scramjet Engine, Reynolds Stress, SST k- ω, RNG k-ε & CFD

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202

May 23, 2011
05/11

by
NON

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Production of an electric voltage in response to mechanical excitation (piezoelectricity) or thermal excitation (pyroelectricity) requires a material to have a preferred dipole orientation in its structure. This preferred orientation or polarization occurs naturally in some crystals such as quartz and can be induced into some ceramic and polymeric materials by application of strong electric or mechanical fields. For some materials, a combination of mechanical and electrical orientation is...

Topics: COMPUTATIONAL FLUID DYNAMICS, PARAMETERIZATION, REYNOLDS STRESS, TURBULENCE MODELS, TURBULENT FLOW,...

276
276

Jun 11, 2011
06/11

by
Yu, Jin-Yi; Lau, K. M

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In this study, we perform experiments with a coupled atmosphere-ocean general circulation model (CGCM) to examine ENSO's influence on the interannual sea surface temperature (SST) variability of the tropical Indian Ocean. The control experiment includes both the Indian and Pacific Oceans in the ocean model component of the CGCM (the Indo-Pacific Run). The anomaly experiment excludes ENSOs influence by including only the Indian Ocean while prescribing monthly-varying climatological SSTs for the...

Topics: LASER DOPPLER VELOCIMETERS, LEADING EDGES, FLOW VELOCITY, FLOW DISTRIBUTION, VECTOR ANALYSIS,...

118
118

Jun 2, 2011
06/11

by
Eshow, Michelle M

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The Federal Aviation Administration (FAA) has decided to field major elements of the Center/TRACON (Terminal Radar Approach Control) Automation System (CTAS) to many air traffic control facilities across the United States. To facilitate the deployment, NASA, the FAA, and their contractors have conceived and implemented an innovative software development approach known as Joint Development. Under joint Development, NASA and the FAA are working in a common baseline of software that combines the...

Topics: JET AIRCRAFT NOISE, NOISE PREDICTION, AEROACOUSTICS, PREDICTION ANALYSIS TECHNIQUES, COMPUTATIONAL...

Analytical methods for the development of Reynolds stress models in turbulence are reviewed in detail. Zero, one and two equation models are discussed along with second-order closures. A strong case is made for the superior predictive capabilities of second-order closure models in comparison to the simpler models. The central points are illustrated by examples from both homogeneous and inhomogeneous turbulence. A discussion of the author's views concerning the progress made in Reynolds stress...

Topics: NASA Technical Reports Server (NTRS), CLOSURES, HOMOGENEOUS TURBULENCE, REYNOLDS STRESS, STRESS...

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231

Jul 21, 2010
07/10

by
NON

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A television camera apparatus is disclosed in which bright objects are attenuated to fit within the dynamic range of the system, while dim objects are not. The apparatus receives linearly polarized light from an object scene, the light being passed by a beam splitter and focused on the output plane of a liquid crystal light valve. The light valve is oriented such that, with no excitation from the cathode ray tube, all light is rotated 90 deg and focused on the input plane of the video sensor....

Topics: COMPUTATIONAL FLUID DYNAMICS, TURBULENCE MODELS, TURBULENT FLOW, TWO FLUID MODELS, CONTINUUM FLOW,...

In this paper, we establish the causality between the model coefficients in the standard pressure-strain correlation model and the predicted equilibrium states for homogeneous turbulence. We accomplish this by performing a comprehensive fixed point analysis of the modeled Reynolds stress and dissipation rate equations. The results from this analysis will be very useful for developing improved pressure-strain correlation models to yield observed equilibrium behavior.

Topics: NASA Technical Reports Server (NTRS), REYNOLDS STRESS, HOMOGENEOUS TURBULENCE, STRESS ANALYSIS,...

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445

May 28, 2011
05/11

by
NON

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This Fabrication and Assembly Flow Plan is submitted in response to CDRL 023 for the Advanced Microwave Sounding Unit-A (AMSU-A). In response to the CDRL instructions, this document presents the fabrication, assembly, inspection, and test sequences, locations, operations, and controls for hardware articles at all levels of assembly to be manufactured by Aerojet.

Topics: AIRFOILS, WAKES, PRESSURE DISTRIBUTION, VELOCITY DISTRIBUTION, REYNOLDS STRESS, BOUNDARY LAYER...

232
232

Sep 20, 2010
09/10

by
Thorpe, Arthur N.; Barkatt, Aaro

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Experiments carried out during the progress period are summarized. Experiments carried out involving glass samples exposed to solutions of Tris have shown the appearance of 'spikes' upon monitoring glass dissolution as a function of time. The periodic 'spikes' observed in Tris-based media were interpreted in terms of cracking due to excessive stress in the surface region of the glass. Studies of the interactions of silicate glasses with metal ions in buffered media were extended to systems...

Topics: ROCKET THRUST, REYNOLDS STRESS, STRESS ANALYSIS, THRUST CHAMBERS, TURBULENCE EFFECTS, TURBULENCE...

A Galilean invariant weak-equilbrium hypothesis that is sensitive to streamline curvature is proposed. The hypothesis leads to an algebraic Reynolds stress model for curved flows that is fully explicit and self-consistent. The model is tested in curved homogeneous shear flow: the agreement is excellent with Reynolds stress closure model and adequate with available experimental data.

Topics: NASA Technical Reports Server (NTRS), TURBULENCE MODELS, MATHEMATICAL MODELS, REYNOLDS STRESS,...

Dynamic subgrid models have proved to be remarkably successful in predicting the behavior of turbulent flows. Part of the reasons for their success are well understood. Since they are constructed to generate an effective viscosity which is proportional to some measure of the turbulent energy at the high wavenumber end of the spectrum, their eddy viscosity vanishes as the flow becomes laminar. This alone would justify their use over simpler models. But beyond this obvious advantage, which is...

Topics: NASA Technical Reports Server (NTRS), SCALE MODELS, DYNAMIC MODELS, TURBULENT FLOW, ROBUSTNESS...

241
241

Jun 26, 2011
06/11

by
Nakamiya, M.; Scheeres, D. J.; Yamakawa, H.; Yoshikawa, M

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Spacecraft capture trajectories to the periodic orbits of the L1 and L2 points in the restricted Hill three-body problem are studied. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future proposals to place ''Deep Space ports'' at the Earth and Mars L1 or L2 points. These spaceports are considered as candidate gateways for interplanetary transfers in the future. We utilize stable manifolds for capture trajectories to...

Topics: ACOUSTICS, REYNOLDS STRESS, TURBULENT FLOW, MATHEMATICAL MODELS, FLOW EQUATIONS, AEROACOUSTICS,...

In order to develop more quantitative measures of coherent structures that would have comparative value over a range of experiments, it is essential that such measures be independent of the observer. It is only through such a general framework that theories with a fundamental predictive value can be developed. The triple decomposition phi = bar-phi + phi(c) + phi(r) (where bar-phi is the mean, phi(c) is the coherent part, and phi(r) is the random part of any turbulent field phi) serves this...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, EQUATIONS OF MOTION, FLOW...

219
219

Jul 23, 2010
07/10

by
Allen, Bradley P.; Holtzman, Peter L

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An overview of the knowledge acquisition component of the Bauhaus, a prototype computer aided software engineering (CASE) workstation for the development of domain-specific automatic programming systems (D-SAPS) is given. D-SAPS use domain knowledge in the refinement of a description of an application program into a compilable implementation. The approach to the construction of D-SAPS was to automate the process of refining a description of a program, expressed in an object-oriented domain...

Topics: CHANNEL FLOW, STOKES LAW (FLUID MECHANICS), TRANSPORT THEORY, WALLS, DISSIPATION, ENERGY BUDGETS,...

261
261

May 23, 2011
05/11

by
Kurucz, Robert L

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Convective model atmospheres must be used with caution when the properties predicted by the model, such as those listed may not represent the space-time average of the real properties of stars.

Topics: PARTICLE IMAGE VELOCIMETRY, SHEAR LAYERS, JET AIRCRAFT NOISE, GAS JETS, TURBULENCE, VELOCITY...

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311

Jun 9, 2011
06/11

by
Hollis, Brian R.; Thompson, Richard A.; Murphy, Kelly J.; Nowak, Robert J.; Riley, Christopher J.; Wood, William A.; Alter, Stephen J.; Prabhu, Ramadas K

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This report provides an overview of hypersonic Computational Fluid Dynamics research conducted at the NASA Langley Research Center to support the Phase II development of the X-33 vehicle. The X-33, which is being developed by Lockheed-Martin in partnership with NASA, is an experimental Single-Stage-to-Orbit demonstrator that is intended to validate critical technologies for a full-scale Reusable Launch Vehicle. As part of the development of the X-33, CFD codes have been used to predict the...

Topics: COMPUTATIONAL FLUID DYNAMICS, TWO DIMENSIONAL MODELS, COUNTERFLOW, FLUIDICS, TEST FACILITIES,...

134
134

Jul 26, 2010
07/10

by
Bezdek, James C

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Kohonen's feature maps approach to clustering is often likened to the k or c-means clustering algorithms. Here, the author identifies some similarities and differences between the hard and fuzzy c-Means (HCM/FCM) or ISODATA algorithms and Kohonen's self-organizing approach. The author concludes that some differences are significant, but at the same time there may be some important unknown relationships between the two methodologies. Several avenues of research are proposed.

Topics: AXISYMMETRIC FLOW, MODULATION, REYNOLDS STRESS, SUPERSONIC SPEED, BOUNDARY LAYER FLOW, BOUNDARY...

368
368

Jul 23, 2010
07/10

by
Dunagan, Stephen E.; Norman, Thomas R

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A wind tunnel experiment simulating a steady three-dimensional helicopter rotor blade/vortex interaction is reported. The experimental configuration consisted of a vertical semispan vortex-generating wing, mounted upstream of a horizontal semispan rotor blade airfoil. A three-dimensional laser velocimeter was used to measure the velocity field in the region of the blade. Sectional lift coefficients were calculated by integrating the velocity field to obtain the bound vorticity. Total lift...

Topics: AERODYNAMIC CHARACTERISTICS, REYNOLDS STRESS, BOUNDARY LAYER SEPARATION, COMPUTATIONAL FLUID...

Experiments have been performed to investigate the effects of elevated free-stream turbulence and streamwise acceleration on flow and thermal structures in transitional boundary layers. The free-stream turbulence ranges from 0.5 to 6.4% and the streamwise acceleration ranges from K = 0 to 0.8 x 10(exp -6). The onset of transition, transition length and the turbulent spot formation rate are determined. The statistical results and conditionally sampled results of th streamwise and cross-stream...

Topics: NASA Technical Reports Server (NTRS), BOUNDARY LAYERS, HEAT TRANSFER, TEMPERATURE DISTRIBUTION,...

No abstract available

Topics: NASA Technical Reports Server (NTRS), REYNOLDS STRESS, STRESS ANALYSIS, SPHERICAL HARMONICS,...

Leslie's perturbative treatment of the direct interaction approximation for shear turbulence (Modern Developments in the Theory of Turbulence, 1972) is applied to derive a time dependent model for the Reynolds stresses. The stresses are decomposed into tensor components which satisfy coupled linear relaxation equations; the present theory therefore differs from phenomenological Reynolds stress closures in which the time derivatives of the stresses are expressed in terms of the stresses...

Topics: NASA Technical Reports Server (NTRS), RELAXATION (MECHANICS), REYNOLDS STRESS, SHEAR FLOW,...

Equations for the mean and turbulent quantities for compressible turbulent flows are derived. Both the conventional Reynolds average and the mass-weighted, Favre average were employed to decompose the flow variable into a mean and a turbulent quality. These equations are to be used later in developing second order Reynolds stress models for high speed compressible flows. A few recent advances in modeling some of the terms in the equations due to compressibility effects are also summarized.

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBILITY EFFECTS, REYNOLDS STRESS, STRESS ANALYSIS,...

242
242

Jun 12, 2011
06/11

by
Yep, Tze-Wing; Agrawal, Ajay K.; Griffin, DeVo

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Experiments were conducted in earth gravity and micro gravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2 s drop tower at NASA John H. Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique suited for the microgravity environment. The flow structure was characterized by distribution of helium mole...

Topics: CIRCULATION CONTROL AIRFOILS, REYNOLDS AVERAGING, NAVIER-STOKES EQUATION, NUMERICAL ANALYSIS,...

295
295

May 29, 2011
05/11

by
Tarokh, M.; Shiller, Z.; Hayati, S

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The paper presents two path planners suitable for planetary rovers. The first is based on fuzzy description of the terrain, and genetic algorithm to find a traversable path in a rugged terrain. The second planner uses a global optimization method with a cost function that is the path distance divided by the velocity limit obtained from the consideration of the rover static and dynamic stability. A description of both methods is provided, and the results of paths produced are given which show...

Topics: BIOMASS, LAGRANGIAN FUNCTION, PARTICULATES, REYNOLDS STRESS, VAPOR PHASES, MULTIPHASE FLOW,...

The addition of small amounts of long chain polymer molecules to wall-bounded flows can lead to dramatic drag reduction. Although this phenomenon has been known for about fifty years, the action of the polymers and its effect on turbulent structures are still unclear. Detailed experiments have characterized two distinct regimes (Warholic et al. 1999), which are referred to as low drag reduction (LDR) and high drag reduction (HDR). The first regime exhibits similar statistical trends as...

Topics: NASA Technical Reports Server (NTRS), ADDITIVES, ENERGY TRANSFER, DRAG REDUCTION, CHANNEL FLOW,...

Second order turbulence models describe the effect of mean flow and external agencies (such as buoyancy) on the evolution of turbulence. Therefore, in principle, these models give a more accurate description of complicated flow fields (e.g. flows with large anisotropy in turbulence, such as near the leading edge of a turbine blade) than the two equation models. The objectives of this document are to assess the performance of the various second order turbulence models in benchmark flows and to...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, REYNOLDS STRESS, TRANSPORT...

A numerical method is presented to solve the three-dimensional Navier-Stokes equations in combination with a full Reynolds-stress turbulence model. Computations will be shown for three complex flowfields. The results of the Reynolds-stress model will be compared with those predicted by two different versions of the k-omega model. It will be shown that an improved version of the k-omega model gives as accurate results as the Reynolds-stress model.

Topics: NASA Technical Reports Server (NTRS), FLOW DISTRIBUTION, THREE DIMENSIONAL FLOW, TURBULENCE MODELS,...

285
285

Jun 1, 2011
06/11

by
Shea, M. A

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The purpose of this grant was to locate, catalog, and assemble, in standard computer format, ground-level solar cosmic ray data acquired by cosmic ray detectors for selected events in the 19th solar cycle. The events for which we initially proposed to obtain these data were for the events of 23 February 1956,4 May 1960, 12 and 15 November 1960 and 18 and 20 July 1961. These were the largest events of the 19th solar cycle. However, a severe (more than 50%) reduction in the requested funding,...

Topics: COMPUTATIONAL FLUID DYNAMICS, PRESSURE DISTRIBUTION, TURBULENCE MODELS, INTERNAL FLOW, SPACE...

This progress report covers the grant period from March until the end of January 1993. Extensive data reduction and analysis of single and two-point measurements for a backward-facing experiment were performed. Pertinent results are presented in two conference papers which are appended to this report. The titles of the papers are as follows: (1) 'Two-point correlation measurements in a recovering turbulent boundary layer'; and (2) 'An experimental study on the recovery of a turbulent boundary...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, REATTACHED FLOW, SEPARATED FLOW,...

Low subsonic and incompressible wake flow downstream of lightly loaded rotor was studied. Measurements of mean velocity, turbulence intensity, Reynolds stress, and static variations across the rotor wake at various axial and radial locations were investigated. Wakes were measured at various rotor blade incidences to discern the effect of blade loading on the rotor wake. Mean velocity and turbulence measurements were carried out with a triaxial hot wire probe both rotating with the rotor and...

Topics: NASA Technical Reports Server (NTRS), ROTOR AERODYNAMICS, ROTOR BLADES (TURBOMACHINERY), WAKES,...

Recent theoretical and experimental results demonstrating the interaction between force fields and density inhomogeneities as they arise in premixed turbulent flames are discussed. In such flames, the density fluctuates between two levels, the high density in reactants rho sub r and the low density in products rho sub p, with the ratio rho sub r/rho sub p on the order of five to ten in flows of applied interest. The force fields in such flames arise from the mean pressure drop across the flame...

Topics: NASA Technical Reports Server (NTRS), DIFFUSION, FIELD THEORY (PHYSICS), PREMIXED FLAMES, TURBULENT...

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302

May 22, 2011
05/11

by
Schmidt, G. R.; Chung, T. J.; Nadarajah, A

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The free surface behavior of a volatile wetting liquid at low gravity is studied using scaling and numerical techniques. An open cavity model, which was applied in part 1 to investigate fluid flow and heat transfer in non-deforming pores, is used to evaluate the influence of convection on surface morphology with length scales and subcooling/superheating limits of 1 less than or equal to D less than or equal to 10(exp 2) microns and approximately 1 K, respectively. Results show that the menisci...

Topics: FLOW STABILITY, FLOW DISTORTION, INCOMPRESSIBLE FLOW, KINETIC ENERGY, ROTATING FLUIDS, FLOW THEORY,...

A turbulence was envisioned whose energy containing scales would be Gaussian in the absence of inhomogeneity, gravity, etc. An equation was constructed for a function equivalent to the probability density, the second moment of which corresponded to the accepted modeled form of the Reynolds stress equation. The third moment equations obtained from this were simplified by the assumption of weak inhomogeneity. Calculations are presented with this model as well as interpretations of the results.

Topics: NASA Technical Reports Server (NTRS), MATHEMATICAL MODELS, PROBABILITY DENSITY FUNCTIONS, REYNOLDS...

The progress is reported of the Center for Modeling of Turbulence and Transition (CMOTT). The main objective of the CMOTT is to develop, validate and implement the turbulence and transition models for practical engineering flows. The flows of interest are three-dimensional, incompressible and compressible flows with chemical reaction. The research covers two-equation (e.g., k-e) and algebraic Reynolds-stress models, second moment closure models, probability density function (pdf) models,...

Topics: NASA Technical Reports Server (NTRS), CHEMICAL REACTIONS, REYNOLDS STRESS, THREE DIMENSIONAL FLOW,...

Three mean velocity components and six Reynolds stresses were measured at two streamwise stations in a juncture flow using hot-wire anemometer techniques.

Topics: NASA Technical Reports Server (NTRS), REYNOLDS STRESS, VELOCITY MEASUREMENT, WIND TUNNEL TESTS,...

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475

Jul 23, 2010
07/10

by
Murray, James E.; Maine, Richard E

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This report is a user's manual for version 2.1 of pEst, a FORTRAN 77 computer program for interactive parameter estimation in nonlinear dynamic systems. The pEst program allows the user complete generality in definig the nonlinear equations of motion used in the analysis. The equations of motion are specified by a set of FORTRAN subroutines; a set of routines for a general aircraft model is supplied with the program and is described in the report. The report also briefly discusses the scope of...

Topics: CLOSURE LAW, TEMPERATURE DISTRIBUTION, VELOCITY DISTRIBUTION, COMPUTATIONAL FLUID DYNAMICS, FINITE...

A system for measuring momentum flux in a turbulently flowing fluid includes: a sensing apparatus for dynamically sensing the mainstream and the cross velocity components of the fluid, a transducer operative to provide two electrical output signals representative of the velocity components in the mainstream and in the cross direction, and signal processors to derive the Reynolds stress wave and the Reynolds stress.

Topics: NASA Technical Reports Server (NTRS), LIQUID FLOW, REYNOLDS STRESS, SIGNAL PROCESSING, TURBULENT...

A simple parameterization scheme for a complex turbulent flow using nondimensional parameters coming from the Reynolds stress equations is given. Definitions and brief descriptions of the physical significance of several nondimensional parameters that are used to characterize turbulence from the viewpoint of single-point turbulence closures are given. These nondimensional parameters reflect measures of (1) the spectral band width of the turbulence; (2) deviations from the ideal Kolmogorov...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, PARAMETERIZATION, REYNOLDS...

Turbulence models are necessary in numerical simulations because of the impracticality of computing all scales of turbulent motion. Approximate methods, or turbulence models, are introduced to simplify and make the computations practical. There are several approaches to turbulence modeling: subgrid scale modeling; modeling of all the scales of turbulent motion; eddy viscosity; and Reynolds stress turbulence closure models. In many instances, computations based on turbulence models are compared...

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE FLOW, COMPUTER PROGRAMS, HIGH SPEED, TURBULENCE...

The requirement that physical quantities not vary with a hybrid LESRANS model's blending parameter imposes conditions on the computation that lead to better results across LES-RANS transitions. This promises to allow placement of those transitions so that LES is performed only where required by the physics, improving computational efficiency. The approach is applied to separated flow past periodic hills, where good predictions of separation-bubble size are seen due to the gradual, controlled,...

Topics: NASA Technical Reports Server (NTRS), MATHEMATICAL MODELS, SEPARATED FLOW, EDDY VISCOSITY,...

A new approach to Reynolds averaged turbulence modeling is proposed which has a computational cost comparable to two equation models but a predictive capability approaching that of Reynolds stress transport models. This approach isolates the crucial information contained within the Reynolds stress tensor, and solves transport equations only for a set of 'reduced' variables. In this work, Direct Numerical Simulation (DNS) data is used to analyze the nature of these newly proposed turbulence...

Topics: NASA Technical Reports Server (NTRS), MATHEMATICAL MODELS, TURBULENCE MODELS, PREDICTION ANALYSIS...

The interaction between a turbulent flow and certain types of structures which respond to its excitation is investigated. One-dimensional models were used to develop the basic ideas applied to a second model resembling the fuselage construction of an aircraft. In the two-dimensional case a simple membrane, with a small random variation in the membrane tension, was used. A decaying turbulence was constructed by superposing infinitely many components, each of which is convected as a frozen...

Topics: NASA Technical Reports Server (NTRS), PERTURBATION THEORY, REYNOLDS STRESS, SOUND WAVES, STRUCTURAL...

Direct numerical simulations are performed for homogeneous turbulence with a mean flow having elliptic streamlines. This flow combines the effects of rotation and strain on the turbulence. Qualitative comparisons are made with linear theory for cases with high Rossby number. The nonlinear transfer process is monitored using a generalized skewness. In general, rotation turns off the nonlinear cascade; however, for moderate ellipticities and rotation rates the nonlinear cascade is turned off and...

Topics: NASA Technical Reports Server (NTRS), CASCADE FLOW, HOMOGENEOUS TURBULENCE, LAMINAR FLOW, REYNOLDS...

The CTR numerical data base generated by direct simulation of homogeneous anisotropic turbulence was used to calculate all of the terms in the spectral balance equations for the turbulent Reynolds stresses. The aim in not only to test the main closure assumptions used in the split-spectrum models, but also to try to devise improved hypotheses deduced from the statistical information. Numerical simulations of turbulent flows provide a large amount of data, a thought provoking wealth of...

Topics: NASA Technical Reports Server (NTRS), ANISOTROPIC FLUIDS, CLOSURE LAW, ENERGY TRANSFER, REYNOLDS...

Direct numerical simulations of compressible, homogeneous, turbulent shear flows are used to evaluate Reynolds stress models. Three pressure-strain models, which are either linear, quadratic, or cubic in the anisotropy tensor are considered. Dilatational dissipation and pressure-strain correlation models do not correctly capture the compressibility effects seen in the direct simulations. In particular, the increase in the anisotropy of normal stresses and the reduction in the shear stress are...

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE FLOW, COMPUTATIONAL FLUID DYNAMICS, HOMOGENEOUS...

A study is made to improve the predictions of Reynolds stresses in backward facing step flows, through modifications of the pressure-strain correlation. The mean-strain term of the pressure-strain correlation is formulated only in terms of nonisotropic turbulence in order to take the severe nonisotropic effect caused by a separating flow. This model is compared with other models and results are verified with experimental results.

Topics: NASA Technical Reports Server (NTRS), MODELS, PRESSURE RATIO, REYNOLDS STRESS, STRESS-STRAIN...