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171

Jun 9, 2011
06/11

by
Hankins, Genevieve; Vahala, Linda; Beggs, John H

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Electromagnetic propagation models for signal strength prediction within aircraft cabins are essential for evaluating and designing a wireless communication system to be implemented onboard aircraft. A model was developed using Wireless Valley's SitePlanner; which is commercial grade software intended for predictions within office buildings. The performance of the model was evaluated through a comparison with test data measurements taken on several aircraft. The comparison concluded that the...

Topics: LARGE EDDY SIMULATION, BOUNDARY LAYER TRANSITION, SWEPT WINGS, EDDY VISCOSITY, CROSS FLOW

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246

Jun 9, 2011
06/11

by
Brandon, Jay M.; Foster, John V.; Shah, Gautam H.; Gato, William; Wilborn, James E

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Improvements in testing and modeling of nonlinear and unsteady aerodynamic effects for flight dynamics predictions of vehicle performance is critical to enable the design and implementation of new, innovative vehicle concepts. Any configuration which exhibits significant flow separation, nonlinear aerodynamics, control interactions or attempts maneuvering through one or more conditions such as these is, at present, a challenge to test, model or predict flight dynamic responses prior to flight....

Topics: AIRFOILS, EDDY VISCOSITY, STRESS ANALYSIS, TURBULENCE MODELS, FLOW DISTRIBUTION, NONLINEARITY,...

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293

May 29, 2011
05/11

by
Lau, K. M.; Weng, Hengy

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Major droughts and floods over the U.S. continent may be related to a far field energy source in the Asian Pacific. This is illustrated by two climate patterns associated with summertime rainfall over the U.S. and large-scale circulation on interannual timescale. The first shows an opposite variation between the drought/flood over the Midwest and that over eastern and southeastern U.S., coupled to a coherent wave pattern spanning the entire East Asia-North Pacific-North America region related...

Topics: CONVECTIVE FLOW, EDDY VISCOSITY, SUN, TURBULENCE, COMPUTERIZED SIMULATION, RAYLEIGH NUMBER, STELLAR...

249
249

Jul 6, 2010
07/10

by
Wiley, H. G.; Kilgore, R. A.; Hillje, E. R

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No Abstract Available

Topics: BOUNDARY LAYER FLOW, FINITE DIFFERENCE THEORY, INJECTION, TURBULENT BOUNDARY LAYER, EDDY VISCOSITY,...

A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.

Topics: NASA Technical Reports Server (NTRS), EDDY VISCOSITY, ANISOTROPIC FLUIDS, SIMPLIFICATION, SYMMETRY,...

A correlation function, derived on the basis of self similar variable eddy viscosity decay, is introduced and utilized to correlate aircraft trailing vortex velocity data from ground and flight experiments. The correlation function collapses maximum tangential velocity data from scale model and flight tests to a single curve. The resulting curve clearly shows both the inviscid plateau and the downstream decay regions. A comparison between experimental data and numerical solution shows closer...

Topics: NASA Technical Reports Server (NTRS), AIRCRAFT WAKES, TURBULENT FLOW, VORTEX BREAKDOWN, EDDY...

A method is presented for estimating the dispersion and dilution of jet aircraft exhaust from aircraft passage through times on the order of weeks thereafter. In the near wake of the aircraft, the solution is that for round turbulent jets in a parallel flow. More rapid dispersion due to atmospheric effects begins when the scale-dependent eddy viscosity becomes larger than the turbulent jet eddy viscosity. In the far wake region, the solution approaches that for scale-dependent dispersion from a...

Topics: NASA Technical Reports Server (NTRS), DILUTION, DISPERSING, JET AIRCRAFT, JET EXHAUST, AIRCRAFT...

403
403

Jun 9, 2011
06/11

by
Korte, J. J.; Salas, A. O.; Dunn, H. J.; Alexandrov, N. M.; Follett, W. W.; Orient, G. E.; Hadid, A. H

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A model of a linear aerospike rocket nozzle that consists of coupled aerodynamic and structural analyses has been developed. A nonlinear computational fluid dynamics code is used to calculate the aerodynamic thrust, and a three-dimensional fink-element model is used to determine the structural response and weight. The model will be used to demonstrate multidisciplinary design optimization (MDO) capabilities for relevant engine concepts, assess performance of various MDO approaches, and provide...

Topics: MATHEMATICAL MODELS, AERODYNAMIC DRAG, ROTATING CYLINDERS, SEPARATED FLOW, TURBULENCE MODELS,...

Diagnostically determined three dimensional trajectories were used to reveal some of the scale interaction processes that occur between convective storms and their environment. Data from NASA's fourth Atmospheric Variability Experiment are analyzed. Two intense squall lines and numerous reports of severe weather occurred during the period. Convective storm systems with good temporal and spatial continuity are shown to be related to the development and movement of short wave circulation systems...

Topics: NASA Technical Reports Server (NTRS), ATMOSPHERIC CIRCULATION, CLIMATOLOGY, THUNDERSTORMS,...

256
256

Jun 12, 2011
06/11

by
Bailey, Sheila G.; Castro, Stephanie L.; Raffaelle, Ryne P.; Fahey, Stephen D.; Gennett, Thomas; Tin, Padeth

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There has been considerable investigation recently regarding the potential for the use of nanomaterials and nanostructures to increase the efficiency of photovoltaic devices. Efforts at the NASA Glenn Research Center have involved the development and use of quantum dots and carbon nanotubes to enhance inorganic and organic cell efficiencies. Theoretical results have shown that a photovoltaic device with a single intermediate band of states resulting from the introduction of quantum dots offers...

Topics: TURBULENT FLOW, HEAT TRANSFER, K-OMEGA TURBULENCE MODEL, BALDWIN-LOMAX TURBULENCE MODEL, SHEAR...

Lam's phenomenological epsilon-renormalization group (RNG) model is quite different from the other members of that group. It does not make use of the correspondence principle and the epsilon-expansion procedure. We demonstrate that Lam's epsilon-RNG model is essentially the physical space version of the classical closure theory in spectral space and consider the corresponding treatment of the eddy viscosity and energy backscatter.

Topics: NASA Technical Reports Server (NTRS), NAVIER-STOKES EQUATION, RENORMALIZATION GROUP METHODS,...

The major points are described of a turbulent transport model of the classical, gradient transport, eddy viscosity type. The relationship is discussed of the developed model to the Prandtl (jet mixing) model, the Schlichting (wake) model, and the Clauser (boundary layer) model. Limitations of the model and test cases are summarized.

Topics: NASA Technical Reports Server (NTRS), MATHEMATICAL MODELS, TURBULENT MIXING, EDDY VISCOSITY, FREE...

The hypersonic turbulent wake produced by a wedge was studied experimentally and its properties were compared with predictions obtained from a numerical computation procedure. In the computation procedure several models for the eddy viscosity formulation of the turbulent transport were examined. Conventional-defect models and a modified mixing-length model were found to yield good predictions of the experimental data. The classical mixing-length model gave unrealistic results. The experimental...

Topics: NASA Technical Reports Server (NTRS), FLOW CHARACTERISTICS, HYPERSONIC WAKES, TURBULENT WAKES,...

Presented is a re-derivation of the eddy viscous dissipation tensor commonly used in present oceanographic general circulation models. When isotropy is imposed, the currently-used form of the tensor fails to return to the laplacian operator. In this paper, the source of this error is identified in a consistent derivation of the tensor in both rectangular and earth spherical coordinates, and the correct form of the eddy viscous tensor is presented.

Topics: NASA Technical Reports Server (NTRS), DISSIPATION, EDDY VISCOSITY, OCEAN CURRENTS, OCEAN MODELS,...

247
247

Jun 2, 2011
06/11

by
Queen, Eric M

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An aerocapture guidance algorithm based on a calculus of variations approach is developed, using angle of attack as the primary control variable. Bank angle is used as a secondary control to alleviate angle of attack extremes and to control inclination. The guidance equations are derived in detail. The controller has very small onboard computational requirements and is robust to atmospheric and aerodynamic dispersions. The algorithm is applied to aerocapture at Neptune. Three versions of the...

Topics: TURBULENT FLOW, HIGH REYNOLDS NUMBER, FLOW DISTRIBUTION, EDDY VISCOSITY, ANGLE OF ATTACK, CROSS...

Use of the Smagorinsky eddy-viscosity formulation and related schemes for subgrid-scale parameterization of large eddy simulation models requires specification of a single length scale, earlier related by Lilly to the scale of filtering and/or numerical resolution. An anisotropic integration of the Kolmogoroff enstrophy spectrum allows generalization of that relationship to anisotropic resolution. It is found that the Deardorff assumption is reasonably accurate for small anisotropies and can be...

Topics: NASA Technical Reports Server (NTRS), ANISOTROPY, EDDY VISCOSITY, PARAMETERIZATION, VORTICITY,...

The application of deductive turbulence theory for validity determination of turbulence phenomenology at the level of second-order, single-point moments is considered. Particular emphasis is placed on the phenomenological formula relating the dissipation to the turbulence energy and the Rotta-type formula for the return to isotropy. Methods which deal directly with most or all the scales of motion explicitly are reviewed briefly. The statistical theory of turbulence is presented as an expansion...

Topics: NASA Technical Reports Server (NTRS), MATHEMATICAL MODELS, STATISTICAL MECHANICS, TURBULENT FLOW,...

265
265

May 23, 2011
05/11

by
Li, Xi-Zeng; Su, Bao-Xi

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It is found that the field of the combined mode of the probe wave and the phase-conjugate wave in the process of non-degenerate four-wave mixing exhibits higher-order squeezing to all even orders. And the generalized uncertainty relations in this process are also presented.

Topics: AIRFOILS, AERODYNAMIC STALLING, LIFT, STRESS ANALYSIS, TURBULENCE MODELS, TURBULENT FLOW, REYNOLDS...

Since its first application, the dynamic procedure has been recognized as an effective means to compute rather than prescribe the unknown coefficients that appear in a subgrid-scale model for Large-Eddy Simulation (LES). The dynamic procedure is usually used to determine the nondimensional coefficient in the Smagorinsky (1963) model. In reality the procedure is quite general and it is not limited to the Smagorinsky model by any theoretical or practical constraints. The purpose of this note is...

Topics: NASA Technical Reports Server (NTRS), VORTICES, DYNAMIC MODELS, EDDY VISCOSITY, SCALE MODELS,...

278
278

Jul 11, 2010
07/10

by
BETHOUX, J. P.; IVANOFF, A

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THE ANNUAL CYCLE OF THE VERTICAL THERMOCLINE CORRESPONDING TO THE ABSORPTION OF SOLAR ENERGY WAS INVESTIGATED BY UNDERWATER PHOTOMETRY. IT IS SHOWN THAT SOLAR ENERGY GIVES RISE TO A DENSITY GRADIENT RESULTING IN THE VERTICAL STABILITY OF THE WATER. MATHEMATICAL MODELS ARE PROPOSED ON THE ASSUMPTION THAT THE THERMOCLINE CONSTITUTES AN EFFECTIVE BARRIER AND CONSIDERS THE TURBULENT CONDUCTION OF HEAT TO BECOME NEGLIGIBLE.

Topics: ATMOSPHERIC MODELS, TEMPERATURE GRADIENTS, COMPRESSIBLE FLOW, FLOW CHARACTERISTICS, MARS...

The generalized eddy viscosity approach is described and results are presented of test cases which show that predictions obtained by this approach are adequate for most engineering applications. Because of the importance of starting computations from the injection station where experimentally determined mean and turbulence parameters are rarely available, a very simple core model applicable to simple step-type (slug) profiles was developed. Agreement between predicted and experimental mean...

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

The large-eddy simulation of the spatial evolution of a stationary crossflow vortex packet in a three-dimensional boundary layer was performed. Although a coarse grid was used (compared to that required by a direct numerical simulation) the essential features of the disturbance evolution, such as the spanwise disturbance spreading and the vortex rollover, were captured accurately. The eddy viscosity became significant only in the late nonlinear stages of the simulation.

Topics: NASA Technical Reports Server (NTRS), LARGE EDDY SIMULATION, BOUNDARY LAYER TRANSITION, SWEPT...

A general method for computing laminar and turbulent boundary layers for two-dimensional time-dependent flows is presented. The method uses an eddy-viscosity formulation to model the Reynolds shear-stress term and a very efficient numerical method to solve the governing equations. The model was applied to steady two-dimensional and three-dimensional flows and was shown to give good results. A discussion of the numerical method and the results obtained by the present method for both laminar and...

Topics: NASA Technical Reports Server (NTRS), LAMINAR BOUNDARY LAYER, TIME DEPENDENCE, TURBULENT BOUNDARY...

Some experiments on turbulent free shear layers in pressure gradients are discussed. Topics covered in the discussion include: (1) two dimensional vortex structures, (2) the effect of channel walls, and (3) the case of a mixing layer in pressure gradient.

Topics: NASA Technical Reports Server (NTRS), PRESSURE GRADIENTS, SHEAR LAYERS, TURBULENT FLOW, CHANNEL...

It is suggested here that the laminar character of the large-scale deep convective flows appearing in numerical simulations of the Sun's convective envelope arises from the effect of turbulent eddy viscosity. Previously, M. Schwarzchild suggested the same idea to explain the observed surface granulation in the Sun.

Topics: NASA Technical Reports Server (NTRS), CONVECTIVE FLOW, EDDY VISCOSITY, SUN, TURBULENCE,...

Direct numerical simulations show that the triadic transfer function T(k,p,q) peaks sharply when q (or p) is much smaller than k. The triadic transfer function T(k,p,q) gives the rate of energy input into wave number k from all interactions with modes of wave number p and q, where k, p, q form a triangle. This observation was thought to suggest that energy is cascaded downscale through non-local interactions with local transfer and that there was a strong connection between large and small...

Topics: NASA Technical Reports Server (NTRS), DECOMPOSITION, EDDY VISCOSITY, ENERGY TRANSFER, TRANSFER...

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 computer program was developed to do the calculations for two-dimensional or axisymmetric configurations from low speeds to hypersonic speeds with arbitrary streamwise pressure, temperature, and Mach number distributions. Options are provided for obtaining initial conditions either from experimental information or from a theoretical similarity solution. The transition region can be described either by an arbitrary distribution of intermittency or by a function based on Emmons' probability...

Topics: NASA Technical Reports Server (NTRS), BOUNDARY LAYERS, COMPUTER PROGRAMS, FLOW CHARACTERISTICS,...

Strong nonlinear interactions among unstable waves and the mean flow occur in a simplified quasigeostrophic spectral model of the upper troposphere of Jupiter. The upper boundary of the layer inhibits vertical motion while at the lower boundary perturbations of the potential temperature are not permitted. On an infinite beta plane the forced flow of alternating zones of prograde and retrograde zonal winds, decreasing with height, are linearly unstable and it is shown that the nonlinear terms...

Topics: NASA Technical Reports Server (NTRS), ATMOSPHERIC TEMPERATURE, EDDY VISCOSITY, GEOSTROPHIC WIND,...

Explicit algebraic stress models that are valid for three-dimensional turbulent flows in noninertial frames are systematically derived from a hierarchy of second-order closure models. This represents a generalization of the model derived by Pope who based his analysis on the Launder, Reece, and Rodi model restricted to two-dimensional turbulent flows in an inertial frame. The relationship between the new models and traditional algebraic stress models -- as well as anistropic eddy visosity...

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

The objective is to understand and extend a recent theory of turbulence based on dynamic renormalization group (RNG) techniques. The application of RNG methods to hydrodynamic turbulence was explored most extensively by Yakhot and Orszag (1986). An eddy viscosity was calculated which was consistent with the Kolmogorov inertial range by systematic elimination of the small scales in the flow. Further, assumed smallness of the nonlinear terms in the redefined equations for the large scales results...

Topics: NASA Technical Reports Server (NTRS), EDDY VISCOSITY, HYDRODYNAMICS, ITERATION, K-EPSILON...

The three-dimensional time dependent equations of motion were numerically integrated for fully-developed turbulent channel flow. A large scale flow field was obtained directly from the solution of these equations, and small scale field motions were simulated through an eddy viscosity model. The calculations were carried out on the ILLIAC 4 computer. The computed flow patterns show that the wall layer consists of coherent structures of low speed and high speed streaks alternating in the spanwise...

Topics: NASA Technical Reports Server (NTRS), CHANNEL FLOW, EDDY VISCOSITY, TURBULENT FLOW, COMPUTERIZED...

Three-dimensional transonic flow over a delta wing is investigated using several turbulence models. The performance of linear eddy viscosity models and an explicit algebraic stress model is assessed at the start of vortex flow, and the results compared with experimental data. To assess the effect of transition location, computations that either fix transition aft of the leading edge or are fully turbulent are performed. These computations show that grid resolution, transition location and...

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

The question is considered of how complex a model should be used for the calculation of turbulent shear flows. At the present time there are models varying in complexity from very simple eddy-transport models to models in which all the equations for the nonzero second-order correlations are solved simultaneously with the equations for the mean variables. A discussion is presented of the relationship between these two models of turbulent shear flow. Two types of motion are discussed: first,...

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

A three dimensional study of convection in a self gravitating sphere of Boussinesq fluid with a Rayleigh number of 10 to the 10th power and a Prandtl of 1 is presented. The velocity and temperature of the fluid are computed at the largest wavelengths using spectral methods. A confirmation that the fluid is anisotropic and that the energy spectra are not smooth functions of wavelength but have a large amount of fine structure is discussed. The parameterization of the transport properties of the...

Topics: NASA Technical Reports Server (NTRS), CONVECTION, CONVECTIVE FLOW, RAYLEIGH NUMBER, STELLAR...

Experimental investigations of the wake flow of a hemisphere and cylinder show that such memory effects can be substantial and have a significant influence on momentum transport. Memory effects are described in terms of suitable memory functions.

Topics: NASA Technical Reports Server (NTRS), MOMENTUM TRANSFER, RHEOLOGY, TURBULENT FLOW, VORTICES, WAKES,...

Two fundamentally different views of the general circulation of Jovian atmospheres have emerged. According to one view, the observed jet streams at the cloud tops are controlled by the vorticity transfers of small scale eddies generated by planetary wave instabilities within a shallow atmospheric layer. According to the alternate point of view, the zonal jets are surface manifestations of deep interior convection organized into cylindrical motion with axes parallel to the planetary rotation...

Topics: NASA Technical Reports Server (NTRS), ATMOSPHERIC CIRCULATION, EDDY VISCOSITY, GEOSTROPHIC WIND,...

The behavior of vortex-flow, accompanied with breakdown, formed above sharp-edged delta wings, was studied experimentally as well as theoretically. Emphasis is placed particularly on the criterion for the breakdown at sufficiently large Reynolds numbers

Topics: NASA Technical Reports Server (NTRS), DELTA WINGS, FLOW DISTRIBUTION, REYNOLDS NUMBER, VORTEX...

Off-body pressure, forces, and moments for the Gulfstream Low Boom Model are computed with a Reynolds Averaged Navier Stokes solver coupled with the Spalart-Allmaras (SA) turbulence model. This is the first application of viscous output-based adaptation to reduce estimated discretization errors in off-body pressure for a wing body configuration. The output adaptation approach is compared to an a priori grid adaptation technique designed to resolve the signature on the centerline by stretching...

Topics: NASA Technical Reports Server (NTRS), AERODYNAMIC CONFIGURATIONS, EDDY VISCOSITY, TURBULENCE...

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637

May 23, 2011
05/11

by
NON

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The following summaries of major reports are presented: (1) 'Scientific Opportunities in the Human Exploration of Space;' (2) 'A Space Physics Paradox;' (3) 'An Integrated Strategy for the Planetary Sciences;' and (4) 'ONR (Office of Naval Research) Research Opportunities in Upper Atmospheric Sciences.' Short reports on the following topics are also presented: life and microgravity sciences and the Space Station Program, the Space Infrared Telescope Facility and the Stratospheric Observatory...

Topics: TURBULENCE, PRESSURE DISTRIBUTION, DENSITY DISTRIBUTION, FOURIER TRANSFORMATION, ENTROPY, VELOCITY...

378
378

May 23, 2011
05/11

by
Tan, C. M.; Carr, L. W

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A variety of empirical and computational fluid dynamics two-dimensional (2-D) dynamic stall models were compared to recently obtained three-dimensional (3-D) dynamic stall data in a workshop on modeling of 3-D dynamic stall of an unswept, rectangular wing, of aspect ratio 10. Dynamic stall test data both below and above the static stall angle-of-attack were supplied to the participants, along with a 'blind' case where only the test conditions were supplied in advance, with results being...

Topics: SUBSONIC FLOW, OSCILLATING FLOW, PRESSURE REDUCTION, BOUNDARY CONDITIONS, UNSTEADY FLOW, TURBULENT...

The selection of inflow values at boundaries far upstream of an aircraft is considered, for one- and two-equation turbulence models. Inflow values are distinguished from the ambient values near the aircraft, which may be much smaller. Ambient values should be selected first, and inflow values that will lead to them after the decay second; this is not always possible, especially for the time scale. The two-equation decay during the approach to the aircraft is shown; often, the time scale has...

Topics: NASA Technical Reports Server (NTRS), UPSTREAM, BOUNDARY LAYERS, TURBULENCE MODELS, MATHEMATICAL...

An improved k-epsilon model for low Reynolds number turbulence near a wall is presented. The near-wall asymptotic behavior of the eddy viscosity and the pressure transport term in the turbulent kinetic energy equation is analyzed. Based on this analysis, a modified eddy viscosity model, having correct near-wall behavior, is suggested, and a model for the pressure transport term in the k-equation is proposed. In addition, a modeled dissipation rate equation is reformulated. Fully developed...

Topics: NASA Technical Reports Server (NTRS), CHANNEL FLOW, COMPUTERIZED SIMULATION, EDDY VISCOSITY, FLUID...

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...

Topics: NASA Technical Reports Server (NTRS), CHEMICAL REACTIONS, EDDY VISCOSITY, GAS INJECTION, TURBULENT...

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262

May 29, 2011
05/11

by
Clowdsley, Martha S.; Wilson, John W.; Heinbockel, John H.; Tripathi, R. K.; Singleterry, Robert C., Jr.; Shinn, Judy L

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A neutron transport algorithm including both elastic and nonelastic particle interaction processes for use in space radiation protection for arbitrary shield material is developed. The algorithm is based upon a multiple energy grouping and analysis of the straight-ahead Boltzmann equation by using a mean value theorem for integrals. The algorithm is then coupled to the Langley HZETRN code through a bidirectional neutron evaporation source term. Evaluation of the neutron fluence generated by the...

Topics: TRANSONIC FLOW, MACH NUMBER, FLOW DISTRIBUTION, DELTA WINGS, BOUNDARY LAYER SEPARATION, ANISOTROPY,...

Proceedings of conference on free turbulent shear flows - Vol. 1

Topics: NASA Technical Reports Server (NTRS), CONFERENCES, MATHEMATICAL MODELS, SHEAR FLOW, TURBULENT FLOW,...

Analysis for the turbulent mixing of free jets is presented in this paper and compared to recent experimental results. A turbulent mass diffusion model is presented and is based on the concentration potential core. The model yielded good results when compared with the experimental results except for low-speed flows where few experimental data are available. A review of recent experimental results verifies again that the three diffusion processes in turbulent mixing are interrelated; however, no...

Topics: NASA Technical Reports Server (NTRS), FREE JETS, MATHEMATICAL MODELS, TURBULENT DIFFUSION,...

We have performed Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) of forced isotropic turbulence at moderate Reynolds numbers. The subgrid scale model used in the LES is based on an eddy viscosity which adjusts instantaneously the energy spectrum of the LES to that of the DNS. The statistics of the large scales of the DNS (filtered DNS field or fDNS) are compared to that of the LES. We present results for the transfer spectra, the skewness and flatness factors of the...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, EDDY VISCOSITY, ISOTROPIC...

Program goals at the Center for Modeling of Turbulence and Transition (CMOTT), NASA Lewis Research Center, are (1) to develop reliable turbulence (including bypass transition) and combustion models for complex flows in propulsion systems and (2) to integrate developed models into deliverable CFD tools for propulsion systems in collaboration with industry. This viewgraph presentation covers the following topics: development of turbulence and combustion models; collaboration with industry and...

Topics: NASA Technical Reports Server (NTRS), COMBUSTION PHYSICS, PROPULSION, TURBULENCE, TURBULENCE...

A general formulation of some effects of swirl on turbulent mixing is given. The basis for the analysis is that momentum transport is enhanced by turbulence resulting from rotational instability of the fluid field. An appropriate form for the turbulent eddy viscosity is obtained by mixing length type arguments. The result takes the form of a corrective factor that is a function of the swirl and acts to increase the eddy viscosity. The factor is based upon the initial mixing conditions implying...

Topics: NASA Technical Reports Server (NTRS), MATHEMATICAL MODELS, SUPERSONIC COMBUSTION, SWIRLING,...