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138

Jun 2, 2011
06/11

by
Singh, Hanwant B.; Eilers, Jame

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The enormous growth in aviation has given rise to concerns that emissions from aircraft may be modifying the atmosphere in important ways. SONEX (Subsonic Assessment Ozone Nitrogen Oxide Experiment), a NASA-sponsored DC-8 aircraft mission, was conducted in October-November 1997 in the vicinity of the North Atlantic flight corridor to study the effect of aircraft emissions on the nitrogen oxide families (NOx), and ozone (O3). SONEX was managed by Ames Research Center. The major SONEX science...

Topics: K-EPSILON TURBULENCE MODEL, K-OMEGA TURBULENCE MODEL, AERODYNAMICS, SHEAR FLOW, BOUNDARY LAYER...

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226

May 23, 2011
05/11

by
Allamandola, L. J

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Spectroscopic studies of the following potential diffuse interstellar band (DIB) carriers are reviewed: unspecified organics, carbon chains, polycyclic aromatic hydrocarbons (PAHs), fullerenes and derivatives, as well as porphyrins and related material. An assessment of each is given, along with suggestions for further experimental studies needed to fully test each candidate. Of the experimental techniques in common use matrix isolation spectroscopy with neon matrices is the most appropriate...

Topics: AERODYNAMICS, TURBULENT FLOW, K-EPSILON TURBULENCE MODEL, COMPUTATIONAL FLUID DYNAMICS, ALGEBRA,...

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196

May 23, 2011
05/11

by
Mazuruk, K.; Su, Ching-Hua; Sha, Yi-Gao; Lehoczky, S. L

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An oscillating-cup viscometer was developed to measure viscosity of molten HgZnTe ternary semiconductor alloys. Data were collected for the pseudobinary Hg(0.84)Zn(0.16)Te melt between 770 and 850 C. The kinematic viscosity was found to vary from approximately 1.1 to 1.4 x 10(sup -3)sq cm/s. A slow relaxation phenomena was also observed for temperatures from the melting point of 770 to approx. 800 C. Possible mechanisms for this effect are discussed.

Topics: FLOW DISTRIBUTION, AUGMENTATION, HEAT TRANSFER, DUCTS, MATHEMATICAL MODELS, SECONDARY FLOW, FINITE...

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536

Jul 23, 2010
07/10

by
Fleischman, G. L.; Peck, S. J.; Tanzer, H. J

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The feasibility of fabricating and processing moderate temperature range vapor chamber type heat pipes in a low mass honeycomb panel configuration for highly efficient radiator fins for potential use on the space station was investigated. A variety of honeycomb panel facesheet and core-ribbon wick concepts were evaluated within constraints dictated by existing manufacturing technology and equipment. Concepts evaluated include type of material, material and panel thickness, wick type and...

Topics: K-EPSILON TURBULENCE MODEL, MATHEMATICAL MODELS, NUMERICAL ANALYSIS, TURBULENT BOUNDARY LAYER,...

380
380

Jul 21, 2010
07/10

by
Hopkins, R. H

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Metallic impurities, both singly and in combinations, affect the performance of silicon solar cells. Czochralski silicon web crystals were grown with controlled additions of secondary impurities. The primary electrical dopants were boron and phosphorus. The silicon test ingots were grown under controlled and carefully monitored conditions from high-purity charge and dopant material to minimize unintentional contamination. Following growth, each crystal was characterized by chemical,...

Topics: CHANNEL FLOW, CLOSURE LAW, NAVIER-STOKES EQUATION, ROTATING FLUIDS, TURBULENCE MODELS, TURBULENT...

382
382

Jun 12, 2011
06/11

by
Singh, Mrityunjay; Morscher, Gregory N

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Ceramic matrix composites are leading candidate materials for a number of applications in aeronautics, space, energy, and nuclear industries. Potential composite applications differ in their requirements for thickness. For example, many space applications such as ''nozzle ramps'' or ''heat exchangers'' require very thin () 1 mm) structures whereas turbine blades would require very thick parts ( or = 1 cm). Little is known about the effect of thickness on stress-strain behavior or the elevated...

Topics: JET AIRCRAFT NOISE, NOISE MEASUREMENT, NOISE PREDICTION (AIRCRAFT), AEROACOUSTICS, ANALOGIES,...

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237

May 23, 2011
05/11

by
NON

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An acoustic sensor for measuring acoustic waves contained in fluid flow flowing over the sensor is introduced. The acoustic sensor reduces any unwanted self-noise associated with the flowing fluid by providing a nose cone having proper aerodynamic properties and by positioning the diaphragm of a microphone of the sensor at a location where any unwanted noise is at a relatively low level. The nose cone has a rounded, blunt or even sharp tip neither of which creates any major disturbances in the...

Topics: NOZZLE FLOW, JET EXHAUST, THROATS, NOZZLE GEOMETRY, FLOW VISUALIZATION, FLOW CHARACTERISTICS, MACH...

The problem of plane stagnation point flow with freestream turbulence is examined from a basic theoretical standpoint. It is argued that the singularity which arises from the standard kappa-epsilon model is not due to a defect in the model but results from the use of an inconsistent freestream boundary condition. The inconsistency lies in the implementation of a production equals dissipation equilibrium hypothesis in conjunction with a freestream mean velocity field that corresponds to...

Topics: NASA Technical Reports Server (NTRS), FREE FLOW, PLANE STRAIN, STAGNATION POINT, TURBULENT FLOW,...

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749

May 27, 2011
05/11

by
Vaidyanathan, Hari; Rao, Gopalakrishn

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The 18650 type lithium ion cells are characterized by a cell resistance of 130 m Omega, capacity of 1.27 Ah at 25C, and a mid-discharge voltage of 3.6 V. The capacity loss in the 72-hour stand test was 3.39 percent. The heat dissipation properties were determined by a radiative calorimeter. During charge, initial endothermic cooling and subsequent exothermic cooling beyond 55 percent state-of-charge were observed. At C/2 rate of discharge (which is considered medium rate), the heat dissipated...

Topics: AEROACOUSTICS, NOISE SPECTRA, NOISE PREDICTION, JET AIRCRAFT NOISE, SUBSONIC FLOW, NOISE INTENSITY,...

173
173

Jul 12, 2010
07/10

by
Katow, M. S.; Khan, I.; Williams, W. F

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Using a Cassegrainian geometry, the 64-meter antenna with its distorted paraboloidal reflecting surface is forced to produce a uniform phase wavefront by a pathlength-compensating subreflector. First, the computed distortion vectors at the joints or nodes of the main reflector structure supporting the surface panels are best fitted to a paraboloid. Second, the resulting residual distortion errors are used to determine a compensating subreflector surface by ray tracing using geometric optics...

Topics: BACKWARD FACING STEPS, INCOMPRESSIBLE FLOW, REATTACHED FLOW, TURBULENT FLOW, EQUATIONS OF MOTION,...

235
235

Jun 15, 2011
06/11

by
NON

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The invention is a miniature, remote, computer-controlled dead weight calibrator. This device which is comprised of an interlocking rod and dead weight assembly, a motorized lifting mechanism, a controller, and a microcomputer, allows automatic calibration of force transducers needed for wind tunnel operations while the transducers are located within a cryogenic chamber. The operation of a cryogenic transonic wind tunnel requires calibration of force transducers at cryogenic operating...

Topics: CHANNEL FLOW, REYNOLDS NUMBER, VISCOSITY, VORTICES, ENERGY BUDGETS, FLOW DISTRIBUTION, K-EPSILON...

The National PARC (NPARC) Alliance was established by the NASA Lewis Research Center and the Air Force Arnold Engineering Development Center to provide the U.S. aeropropulsion community with a reliable Navier-Stokes code for simulating the nonrotating components of propulsion systems. Recent improvements to the turbulence model capabilities of the NPARC code have significantly improved its capability to simulate turbulent flows. Specifically, the Chien k-epsilon and Wilcox k-omega turbulence...

Topics: NASA Technical Reports Server (NTRS), NAVIER-STOKES EQUATION, K-EPSILON TURBULENCE MODEL, K-OMEGA...

249
249

May 23, 2011
05/11

by
Everhart, Joel L

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Orifice-to-orifice inconsistencies in data acquired with an electronically-scanned pressure system at the beginning of a wind tunnel experiment forced modifications to the standard, instrument calibration procedures. These modifications included a large increase in the number of calibration points which would allow a critical examination of the calibration curve-fit process, and a subsequent post-test reduction of the pressure data. Evaluation of these data has resulted in an improved...

Topics: AEROACOUSTICS, K-EPSILON TURBULENCE MODEL, COMPUTER PROGRAMS, JET AIRCRAFT NOISE, GAS DYNAMICS,...

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 characteristics of the recirculation zones in confined coaxial turbulent jets are investigated numerically employing the kappa - epsilon turbulence model. The geometrical arrangement corresponds to the experimental study of Owen (AIAA J. 1976) and the investigation is undertaken to provide information for isothermal flow relevant to combustor flows. For the first time, the shape, size, and location of the recirculation zones for the above experimental configuration are correctly predicted....

Topics: NASA Technical Reports Server (NTRS), COMBUSTION CHAMBERS, ISOTHERMAL FLOW, PREDICTIONS,...

The full text of a paper presented at the Whither Turbulence Workshop (Cornell University, March 22-24, 1989) on past and future trends in turbulence modeling is provided. It is argued that Reynolds stress models are likely to remain the preferred approach for technological applications for at least the next few decades. In general agreement with the Launder position paper, it is further argued that among the variety of Reynolds stress models in use, second-order closures constitute by far the...

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

The main objective of this paper is to construct a turbulence model with a more reliable second equation simulating length scale. In the present paper, we assess the length scale equation based on Menter s modification to Rotta s two-equation model. Rotta shows that a reliable second equation can be formed in an exact transport equation from the turbulent length scale L and kinetic energy. Rotta s equation is well suited for a term-by-term modeling and shows some interesting features compared...

Topics: NASA Technical Reports Server (NTRS), TURBULENCE MODELS, NAVIER-STOKES EQUATION, REYNOLDS...

221
221

May 23, 2011
05/11

by
Cios, K. J.; Berke, L.; Vary, A.; Sharma, S

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Soft computing techniques of neural networks and genetic algorithms are used in the design of superalloys. The cyclic oxidation attack parameter K(sub a), generated from tests at NASA Lewis Research Center, is modelled as a function of the superalloy chemistry and test temperature using a neural network. This model is then used in conjunction with a genetic algorithm to obtain an optimized superalloy composition resulting in low K(sub a) values.

Topics: AEROACOUSTICS, TURBULENCE, KINETIC ENERGY, MATHEMATICAL MODELS, SUPERSONIC JET FLOW, ACOUSTIC...

This report documents the changes that were made to the two-equation k-epsilon turbulence model in the NPARC (National-PARC) code. The previous model based on the low Reynolds number model of Speziale, was replaced with the low Reynolds number k-epsilon model of Chien. The most significant difference was in the turbulent Prandtl numbers appearing in the diffusion terms of the k and epsilon transport equations. A new inflow boundary condition and stability enhancements were also implemented into...

Topics: NASA Technical Reports Server (NTRS), K-EPSILON TURBULENCE MODEL, LOW REYNOLDS NUMBER, TURBULENCE,...

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...

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715

Jul 21, 2010
07/10

by
NON

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For the years beyond FY 1986, the plan consists of activities that are technologically possible and considered to be in the national interest. Its implementation will ensure logical and continued progress in reaching the Nation's goals in aeronautics and space, consistent with the responsibilities assigned NASA by the National Aeronautics and Space Act of 1958, as amended. The major features of the programs are described in detail and the nature of the aeronautics and space programs beyond the...

Topics: COMBUSTION CHAMBERS, INTERPOLATION, K-EPSILON TURBULENCE MODEL, MATHEMATICAL MODELS, TURBULENCE,...

This viewgraph presentation discusses geometry and flow configuration, effect of y+ on heat transfer computations, standard and extended k-epsilon turbulence model results with wall function, low-Re model results (the Lam-Bremhorst model without wall function), a criterion for flow reversal in a radially rotating square duct, and a summary.

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, HEAT TRANSFER, K-EPSILON...

466
466

Jul 26, 2010
07/10

by
Poinsatte, Philip E.; Vanfossen, G. James; Dewitt, Kenneth J

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Local heat transfer coefficients were measured on a smooth and roughened NACA 0012 airfoil. Heat transfer measurements on the 0.533 m chord airfoil were made both in flight on the NASA Lewis Twin Otter Icing Research Aircraft and in the NASA Lewis Icing Research Tunnel (IRT). Roughness was obtained by the attachment of uniform 2 mm diameter hemispheres to the airfoil surface in 4 distinct patterns. Flight data were taken for the smooth and roughened airfoil at various Reynolds numbers based on...

Topics: COMPUTATIONAL GRIDS, EIGENVALUES, FLOW DISTRIBUTION, REYNOLDS NUMBER, K-EPSILON TURBULENCE MODEL,...

The turbulent mass flux, or equivalently the fluctuating Favre velocity mean, appears in the first and second moment equations of compressible kappa-epsilon and Reynolds stress closures. Mathematically it is the difference between the unweighted and density-weighted averages of the velocity field and is therefore a measure of the effects of compressibility through variations in density. It appears to be fundamental to an inhomogeneous compressible turbulence, in which it characterizes the...

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE FLOW, ISOTROPIC TURBULENCE, K-EPSILON TURBULENCE...

Several two-equation models were proposed and tested against benchmark flows by various researchers. For each study, different numerical methods or codes were used to obtain the results which were reported to be an improvement over other models. However, these comparisons may be overshadowed by the different numerical schemes used to obtain the results. With this in mind, several existing two-equation turbulence models, including k-epsilon, k-tau, k-omega, and q-omega models, are implemented...

Topics: NASA Technical Reports Server (NTRS), FLUID DYNAMICS, K-EPSILON TURBULENCE MODEL, NUMERICAL...

This viewgraph presentation discusses the following: introduction to CFD Research Corporation; experiences with two-equation models - models used, numerical difficulties, validation and applications, and strengths and weaknesses; and answers to three questions posed by the workshop organizing committee - what are your customers telling you, what are you doing in-house, and how can NASA-CMOTT (Center for Modeling of Turbulence and Transition) help.

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, K-EPSILON TURBULENCE MODEL,...

Models employed in the computation of turbulent flows are described and their application to internal flows is evaluated by examining the predictions of various turbulence models in selected flow configurations. The main conclusions are: (1) the k-epsilon model is used in a majority of all the two-dimensional flow calculations reported in the literature; (2) modified forms of the k-epsilon model improve the performance for flows with streamline curvature and heat transfer; (3) for flows with...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, MATHEMATICAL MODELS, TURBULENCE...

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890

Jul 25, 2010
07/10

by
Huh, Oscar Karl; Leibowitz, Scott G.; Dirosa, Donald; Hill, John M

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The use of NOAA Advanced Very High Resolution Radar/High Resolution Picture Transmission (AVHRR/HRPT) imagery for earth resource applications is provided for the applications scientist for use within the various Earth science, resource, and agricultural disciplines. A guide to processing NOAA AVHRR data using the hardware and software systems integrated for this NASA project is provided. The processing steps from raw data on computer compatible tapes (1B data format) through usable qualitative...

Topics: COMPUTATIONAL FLUID DYNAMICS, MOMENTUM THEORY, NAVIER-STOKES EQUATION, NUSSELT NUMBER, HEAT...

This viewgraph presentation provides a brief review of two-equation eddy-viscosity models (TEM's) from the perspective of applied CFD. It provides objective assessment of both well-known and newer models, compares model predictions from various TEM's with experiments, identifies sources of modeling error and gives historical perspective of their effects on model performance and assessment, and recommends directions for future research on TEM's.

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

This paper compares temperature field measurements from selected experiments on a single row, and opposed rows, of jets injected into a ducted crossflow with profiles calculated using an empirical model based on assumed vertical profile similarity and superposition, and distributions calculated with a 3-D elliptic code using a standard K-E turbulence model. The empirical model predictions are very good within the range of the generating experiments, and the numerical model resultings, although...

Topics: NASA Technical Reports Server (NTRS), COMPUTER PROGRAMS, DILUTION, DUCTED FLOW, FLOW DISTRIBUTION,...

In a recent paper, the authors compared the performance of a variety of turbulence models including the k-epsilon model and the second-order closure model based on Renormalization Group (RNG) Methods. The performance of these RNG models in homogeneous turbulent shear flow was found to be quite poor, apparently due to the value of the constant C(sub epsilon1) in the modeled dissipation rate equation which was substantially lower than its traditional value. However, recently a correction has been...

Topics: NASA Technical Reports Server (NTRS), K-EPSILON TURBULENCE MODEL, RENORMALIZATION GROUP METHODS,...

An experimental program to characterize the spray from candidate nozzles for icing-cloud simulation is discussed. One canidate nozzle, which is currently used for icing research, has been characterized for flow and drop size. The median-volume diameter (MVD) from this air-assist nozzle is compared with correlations in the literature. The new experimental spray facility is discussed, and the drop-size instruments are discussed in detail. Since there is no absolute standard for drop-size...

Topics: NASA Technical Reports Server (NTRS), FUEL SPRAYS, ICE FORMATION, SPRAY NOZZLES, TWO PHASE FLOW,...

A numerical study of incompressible turbulent separated flows is carried out by using two-equation turbulence models of the K-epsilon type. On the basis of realizability analysis, a new formulation of the eddy-viscosity is proposed which ensures the positiveness of turbulent normal stresses - a realizability condition that most existing two-equation turbulence models are unable to satisfy. The present model is applied to calculate two backward-facing step flows. Calculations with the standard...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, COMPUTATIONAL FLUID DYNAMICS,...

The physical properties of the commonly used second-order closure models are examined theoretically for rotating turbulent flows. Comparisons are made with results which are a rigorous consequence of the Navier-Stokes equations for the problem of a fully-developed turbulent channel flow in a rapidly rotating framework. It is demonstrated that all existing second-order closures yield spurious physical results for this test problem of rotating channel flow. In fact, the results obtained are shown...

Topics: NASA Technical Reports Server (NTRS), CHANNEL FLOW, CLOSURE LAW, NAVIER-STOKES EQUATION, ROTATING...

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276

Jul 25, 2010
07/10

by
Sandham, N. D.; Mungal, M. G.; Broadwell, J. E.; Reynolds, W. C

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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...

Topics: DYNAMIC CHARACTERISTICS, NAVIER-STOKES EQUATION, SHEAR STRESS, TURBINE PUMPS, FINITE DIFFERENCE...

Our research involves study of the behavior of k-epsilon turbulence models for simulation of bypass-level transition over flat surfaces and turbine blades. One facet of the research has been to assess the performance of a multitude of k-epsilon models in what we call "natural transition", i.e. no modifications to the k-e models. The study has been to ascertain what features in the dynamics of the model affect the start and end of the transition. Some of the findings are in keeping...

Topics: NASA Technical Reports Server (NTRS), K-EPSILON TURBULENCE MODEL, SHEAR FLOW, SIMULATION,...

A two-equation turbulence model of the K-epsilon type was recently derived by using Renormalization Group (RNG) methods. It was later reported that this RNG based model yields substantially better predictions than the standard K-epsilon model for turbulent flow over a backward facing step - a standard test case used to benchmark the performance of turbulence models in separated flows. The improvements obtained from the RNG K-epsilon model were attributed to the better treatment of near wall...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, K-EPSILON TURBULENCE MODEL,...

A transport equation for eddy viscosity is proposed for wall bounded turbulent flows. The proposed model reduces to a quasi-homogeneous form far from surfaces. Near to a surface, the nonhomogeneous effect of the wall is modeled by an elliptic relaxation model. All the model terms are expressed in local variables and are coordinate independent; the model is intended to be used in complex flows. Turbulent channel flow and turbulent boundary layer flows with/without pressure gradient are...

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

A primitive pressure-velocity variable finite difference computer code was developed to predict swirling recirculating inert turbulent flows in axisymmetric combustors in general, and for application to a specific idealized combustion chamber with sudden or gradual expansion. The technique involves a staggered grid system for axial and radial velocities, a line relaxation procedure for efficient solution of the equations, a two-equation k-epsilon turbulence model, a stairstep boundary...

Topics: NASA Technical Reports Server (NTRS), COMBUSTION CHAMBERS, COMPUTER PROGRAMS, ISOTHERMAL PROCESSES,...

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567

May 23, 2011
05/11

by
Santoro, Robert J

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A series of uni-element rocket injector studies were completed to provide benchmark quality data needed to validate computational fluid dynamic models. A shear coaxial injector geometry was selected as the primary injector for study using gaseous hydrogen/oxygen and gaseous hydrogen/liquid oxygen propellants. Emphasis was placed on the use of nonintrusive diagnostic techniques to characterize the flowfields inside an optically-accessible rocket chamber. Measurements of the velocity and species...

Topics: REYNOLDS STRESS, CUBIC EQUATIONS, ROTATING FLUIDS, STRESS ANALYSIS, AIRCRAFT ENGINES, TURBULENT...

This report covers the third year research effort of the project. The research work focussed on the fine scale mixing noise of both subsonic and supersonic jets and the effects of nozzle geometry and tabs on subsonic jet noise. In publication 1, a new semi-empirical theory of jet mixing noise from fine scale turbulence is developed. By an analogy to gas kinetic theory, it is shown that the source of noise is related to the time fluctuations of the turbulence kinetic theory. On starting with the...

Topics: NASA Technical Reports Server (NTRS), AEROACOUSTICS, NOISE PREDICTION, JET AIRCRAFT NOISE, SUBSONIC...

A formalism will be presented that allows the transformation of two-equation eddy viscosity turbulence models into one-equation models. The transformation is based on an assumption that is widely accepted over a large range of boundary layer flows and that has been shown to actually improve predictions when incorporated into two-equation models of turbulence. Based on that assumption, a new one-equation turbulence model will be derived. The new model will be tested in great detail against a...

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

For modelling the turbulent flow in a seal the Navier-Stokes equations in connection with a turbulence (kappa-epsilon) model are solved by a finite-difference method. A motion of the shaft round the centered position is assumed. After calculating the corresponding flow field and the pressure distribution, the rotor-dynamic coefficients of the seal can be determined. These coefficients are compared with results obtained by using the bulk flow theory of Childs and with experimental results.

Topics: NASA Technical Reports Server (NTRS), AERODYNAMIC COEFFICIENTS, COMPUTATION, FINITE DIFFERENCE...

This work investigates the turbulent constitutive relation when turbulence is subjected to solid body rotation. Laws regarding spectra and asymptotic decay of rotating homogeneous turbulence were confirmed through large-eddy simulation (LES) computations. Rotating turbulent flows exist in many industrial, geophysical, and astrophysical applications. From Lagrangian analysis a relation between turbulent stress and strain in rotating homogeneous turbulence was inferred. This relation was used to...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, COMPUTERIZED SIMULATION, ENERGY...

A numerical simulation is presented of an axisymmetric turbulent jet discharging axially from below into a cylindrical tank and directed towards the liquid vapor interface. The liquid vapor interface is assumed to be flat and shear free. The k-epsilon turbulence model is used to calculate the eddy viscosity. The turbulence intensity distribution and the length scale associated with the k-epsilon model are calculated as functions of jet flow rates and systems parameters. Numerical results are...

Topics: NASA Technical Reports Server (NTRS), K-EPSILON TURBULENCE MODEL, LIQUID-VAPOR INTERFACES,...

A multigrid method is presented for calculating turbulent jets in crossflow. Fairly rapid convergence is obtained with the k-epsilon turbulence model, but computations with a full Reynolds stress turbulence model (RSM) are not yet very efficient. Grid dependency tests show that there are slight differences between results obtained on the two finest grid levels. Computations using the RSM are significantly different from those with k-epsilon model and compare better to experimental data. Some...

Topics: NASA Technical Reports Server (NTRS), CLOSURE LAW, COMPUTATIONAL GRIDS, CROSS FLOW, K-EPSILON...

This research brief contains the progress reports of the research staff of the Center for Modeling of Turbulence and Transition (CMOTT) from July 1993 to July 1995. It also constitutes a progress report to the Institute of Computational Mechanics in Propulsion located at the Ohio Aerospace Institute and the Lewis Research Center. CMOTT has been in existence for about four years. In the first three years, its main activities were to develop and validate turbulence and combustion models for...

Topics: NASA Technical Reports Server (NTRS), COMBUSTION PHYSICS, COMPUTATIONAL FLUID DYNAMICS, REACTING...

This paper demonstrates how well the k-omega turbulence model describes the nonlinear growth of flow instabilities from laminar flow into the turbulent flow regime. Viscous modifications are proposed for the k-omega model that yield close agreement with measurements and with Direct Numerical Simulation results for channel and pipe flow. These modifications permit prediction of subtle sublayer details such as maximum dissipation at the surface, k approximately y(exp 2) as y approaches 0, and the...

Topics: NASA Technical Reports Server (NTRS), CHANNEL FLOW, COMPUTATIONAL FLUID DYNAMICS, INCOMPRESSIBLE...

A numerical study of a prototypical vortex controlled diffuser is performed. The basic diffuser geometry consists of a step expansion in a pipe of area ratio 2.25:1. The incompressible Reynolds averaged Navier-Stokes equations, employing the K-epsilon turbulence model, are solved. Results are presented for bleed rates ranging from 1 to 7 percent. Diffuser efficiencies in excess of 80 percent are obtained. Reattachment lengths are reduced by a factor of up to 3. These results are in qualitative...

Topics: NASA Technical Reports Server (NTRS), DIFFUSERS, FLOW DISTRIBUTION, INCOMPRESSIBLE FLOW, K-EPSILON...

The flowfields of gas turbine combustion chambers were investigated. Six flowfield configurations with sidewall angles alpha = 90 and 45 deg. and swirl vane angles phi = 0, 45 and 70 deg. are characterized. Photography of neutrally-buoyant helium-filled soap bubbles, tufts, and injected smoke helps to characterize the time-mean streamlines, recirculation zones and regions of highly turbulent flow. Five-hole pitot probe pressure measurements allow the determination of time-mean velocities u, v...

Topics: NASA Technical Reports Server (NTRS), COMBUSTION CHAMBERS, FLOW DISTRIBUTION, FLOW GEOMETRY, GAS...