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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

A heat exchanger computational procedure for temperature-dependent fouling

A novel heat exchanger computational procedure is described which provides a means of rapidly calculating the distributions of fluid and wall temperatures, deposit formation, and pressure loss at various points in a heat exchanger. The procedure is unique in that it is capable of treating wide variations in heat exchanger geometry without recourse to restrictive assumptions concerning heat exchanger type (e.g., co-flow, counterflow, cross flow devices, etc.). The analysis has been used extensively to predict the performance of cross-counterflow heat exchangers in which one fluid behaves as a perfect gas (e.g., air) while the other fluid is assumed to be a distillate fuel. The model has been extended to include the effects on heat exchanger performance of time varying inflow conditions. Heat exchanger performance degradation due to deposit formation with time can be simulated, making this procedure useful in predicting the effects of temperature-dependent fouling.

Chiappetta, L. M.↗
NASA NTRS1982

A vectorized, finite-volume, adaptive grid algorithm applied to planetary entry problems

An adaptive grid, finite-volume method has been applied to problems in planetary entry for computing complete flowfields. The adaption algorithm is implicit in nature and is keyed to resolve user specified gradients. The finite-volume algorithm is explicit, utilizing a maximum time step advancement at each grid point to accelerate convergence to the steady state. The present version of the code is for the laminar flow of a perfect gas. The role of the adaption algorithm in resolving various features of blunt body/wake flow for planetary entry conditions is emphasized.

Gnoffo, P. A.↗
NASA NTRS1982

'Coriolis resonance' within a rotating duct

An investigation of the unsteady disturbances of a fixed frequency within a radial duct rotating at a set speed is presented. The flow is assumed to be compressible, inviscid, and of a fluid which is a perfect gas. Equations are developed for the steady and the unsteady parts of the flow in cylindrical coordinates. The unsteady disturbances are expressed by Fourier decomposition in angular position, distance into the duct, and in time. It is found that a resonance is possible when the frequency of flow disturbances is twice the shaft-rotation frequency, considering only the radial and tangential disturbances and not the radial and circumferential disturbances. The particular point at which the resonance occurs indicates the occurrence is due to the Coriolis force, which is only present in the radial and tangential directions. It is noted that the Coriolis force can only be present in open-ended ducts, such as those found in centrifugal compressors.

Kurosaka, M.↗
NASA NTRS1982

Computer program for solving laminar, transitional, or turbulent compressible boundary-layer equations for two-dimensional and axisymmetric flow

A numerical algorithm and computer program are presented for solving the laminar, transitional, or turbulent two dimensional or axisymmetric compressible boundary-layer equations for perfect-gas flows. The governing equations are solved by an iterative three-point implicit finite-difference procedure. The software, program VGBLP, is a modification of the approach presented in NASA TR R-368 and NASA TM X-2458, respectively. The major modifications are: (1) replacement of the fourth-order Runge-Kutta integration technique with a finite-difference procedure for numerically solving the equations required to initiate the parabolic marching procedure; (2) introduction of the Blottner variable-grid scheme; (3) implementation of an iteration scheme allowing the coupled system of equations to be converged to a specified accuracy level; and (4) inclusion of an iteration scheme for variable-entropy calculations. These modifications to the approach presented in NASA TR R-368 and NASA TM X-2458 yield a software package with high computational efficiency and flexibility. Turbulence-closure options include either two-layer eddy-viscosity or mixing-length models. Eddy conductivity is modeled as a function of eddy viscosity through a static turbulent Prandtl number formulation. Several options are provided for specifying the static turbulent Prandtl number. The transitional boundary layer is treated through a streamwise intermittency function which modifies the turbulence-closure model. This model is based on the probability distribution of turbulent spots and ranges from zero to unity for laminar and turbulent flow, respectively. Several test cases are presented as guides for potential users of the software.

Harris, J. E.↗
NASA NTRS1983

A comparative study of time-marching and space-marching numerical methods

Menees (1981) has conducted an evaluation of three different flowfield codes for the Jupiter entry conditions. However, a comparison of the codes has been made difficult by the fact that the three codes use different solution procedures, different computational mesh sizes, and a different convergence criterion. There are also other differences. For an objective evaluation of the different numerical solution methods employed by the codes, it would be desirable to select a simple no-blowing perfect-gas flowfield case for which the turbulent models are well established. The present investigation is concerned with the results of such a study. It is found that the choice of the numerical method is rather problem dependent. The time-marching and the space-marching method provide both comparable results if care is taken in selecting the appropriate mesh size near the body surface.

Gupta, R. N.↗
NASA NTRS1982

Thermal structure of the atmosphere of Venus from Pioneer Venus radio occultations

The processing and analysis results from 87 radio occultation experiments performed with the Pioneer Venus Orbiter are detailed. Atmospheric structure data were obtained with S-band (2293 MHz) and X-band (8407 MHz) signals transmitted through the 40 and 85 km levels of the Venus atmosphere. Latitudes of -68 to 88 deg at solar zenith angles of 8-166 deg were explored. The conversion of the data into acceptable form for the barometric equation to use the perfect gas law to obtain the temperature profiles is described. The temperature structures were more dependent on latitude than solar illumination conditions, with the greatest changes occurring in the circumpolar region. The polar tropopause altitude was about 4.8 km above its value at lower altitudes, with a temperature drop of 60 K and a pressure drop of 240 mb.

Kliore, A. J.↗
NASA NTRS1983

Heating analysis of bent-nose biconics at high angles of attack using the parabolized Navier-Stokes equations

A method based on the Parabolized Navier-Stokes equations is used to calculate the flow field and heat transfer of lifting entry vehicles. The method is based on the Bean and Warming implicit algorithm and uses a new procedure for preventing departure solutions. Calculations are carried out for blunt on-axis and bent biconics, assuming a perfect gas and laminar flow, and compared with available heat transfer, surface pressure and shock shape measurements for a range of Mach numbers and angles of attack. In all calculations presented here, the starting solution is obtained from available inviscid and boundary layer codes. Good agreement with experiment is indicated. Thus, the method provides an accurate and rather inexpensive procedure for calculating three-dimensional flows at supersonic Mach numbers.

Stephenson, B. L.↗
NASA NTRS1983

The computation of inviscid rotational gasdynamic flows using an alternate velocity decompositon

The present investigation has the objective to present a method which can be considered to be a modification of existing potential flow algorithms. The method can be employed for the accurate and efficient solution of rotational gasdynamic flows. The general approach to computing inviscid rotational flows considered makes use of a velocity decomposition discussed by Clebsch (1859). Recent applications of the Clebsch representation in inviscid flows have involved the convection of an externally generated vorticity. Attention is given to the case of a steady, inviscid flow of a perfect gas with a uniform incoming stream. The developed procedure makes it possible to obtain a rapid solution to inviscid, compressible, rotational flows with solution algorithms which are a modification of existing potential flow codes. An application of the procedure to supersonic rotational conical flow is discussed.

Grossman, B.↗
NASA NTRS1985

Three-dimensional viscous-shock-layer applications for the Space Shuttle orbiter

A nonorthogonal three-dimensional viscous-shock-layer code was modified and used to compute the windward surface flowfield over a Shuttle-like configuration. Code modifications were made in the methods used to evaluate shock boundary conditions and in the implementation of the equilibrium air models. Additional viscous terms were also retained in the governing equations. Effects of these modifications are demonstrated. Three-dimensional flowfield solutions obtained with the modified code showed good comparison of surface heating and pressure with actual flight data. An apparently three-dimensional effect, characterized by a drop in surface heating on the Shuttle windward centerline in the wing root area, was predicted by the present method. A preliminary review of Shuttle ground-based experimental and flight data confirmed this trend. The present three-dimensional solutions were also compared with the predictions of several approximate methods. Those comparisons showed the approximate methods to be valid for predicting heating along the Shuttle windward centerline uner both perfect gas and equilibrium air conditions.

Thompson, R. A.↗
NASA NTRS1985

A three-dimensional Navier-Stokes/Euler code for blunt-body flow computations

The formulation computation method of an improved version of the three-dimensional Navier-Stokes/Euler computation algorithm of Li (1981) for the numerical simulation of blunt-body reentry flows are discussed, and results for five sample problems are presented graphically. The vector notation of the coordinate systems is defined; the governing equations are presented in full; the Jacobian matrices and damping terms of the factorization technique (based on the alternating-direction implicit procedure of Beam and Warming, 1978) are explained; and the capabilities, limitations and proper use of the code are summarized. Examples presented include the equilibrium-flow problem for Shuttle-orbiter reentry at Mach 22 and angle of attack 40.8 deg and the perfect-gas problem of an aerobraking orbital-transfer vehicle with an ellipsoidal/60-deg cone and a toroidal sonic shoulder. The advantages of the improved code in terms of accuracy and computation time are indicated.

Li, C. P.↗
NASA NTRS1985

The effect of aerodynamic and structural detuning on turbomachine supersonic unstalled torsional flutter

The effects of alternate-blade structural detuning and adjacent-blade alternate-circumferential-spacing aerodynamic detuning on the supersonic unstalled torsional flutter stability of a turbomachine rotor are investigated analytically. An unsteady aerodynamic model employing influence coefficients is constructed for the case of a flat-plate-airfoil cascade in torsion-mode harmonic oscillation in a supersonic inviscid isentropic adiabatic irrotational perfect-gas inlet flow with a subsonic leading-edge locus. The influence coefficients and equations of motion are derived; the model is verified by applying it to the 12-blade cascade-B flow geometry studied by Verdon and McCune (1975); and the results are presented graphically. It is found that the rotor can be stabilized over the entire reduced frequency range by applying a combination of structural and aerodynamic detuning as the passive flutter-control mechanism.

Hoyniak, D.↗
NASA NTRS1985

Thermodynamic evaluation of transonic compressor rotors using the finite volume approach

Research at NASA Lewis Research Center gave the opportunity to incorporate new control volumes in the Denton 3-D finite-volume time marching code. For duct flows, the new control volumes require no transverse smoothing and this allows calculations with large transverse gradients in properties without significant numerical total pressure losses. Possibilities for improving the Denton code to obtain better distributions of properties through shocks were demonstrated. Much better total pressure distributions through shocks are obtained when the interpolated effective pressure, needed to stabilize the solution procedure, is used to calculate the total pressure. This simple change largely eliminates the undershoot in total pressure down-stream of a shock. Overshoots and undershoots in total pressure can then be further reduced by a factor of 10 by adopting the effective density method, rather than the effective pressure method. Use of a Mach number dependent interpolation scheme for pressure then removes the overshoot in static pressure downstream of a shock. The stability of interpolation schemes used for the calculation of effective density is analyzed and a Mach number dependent scheme is developed, combining the advantages of the correct perfect gas equation for subsonic flow with the stability of 2-point and 3-point interpolation schemes for supersonic flow.

Moore, J.↗
NASA NTRS1986

Application of program LAURA to three-dimensional AOTV flowfields

Program LAURA (Langley Aerothermodynamic Upwind Relaxation Algorithm) is a robust, finite volume, single-level storage, implicit upwind differencing algorithm which has been documented and tested on several three-dimensional blunt-body flows. The algorithm can run at unlimited Courant numbers (relaxing the steady-state equations) but requires the inversion of only a 5 x 5 matrix per computational cell. An alternating directional sweep Gauss-Seidel substitution strategy is used to relax the governing equations. At present, the Euler and thin-layer Navier-Stokes equations using Sutherland's law for viscosity have been modeled for a perfect gas, equilibrium air, and nonequilibrium air chemistry neglecting diffusion. The equilibrium and nonequilibrium air chemistry options have been described in a companion paper. Good comparisons with experimental data and another calculation method for pressure distributions, aerodynamic coefficients, and heat-transfer distributions have been demonstrated for three-dimensional blunt-body flows.

Gnoffo, P. A.↗
NASA NTRS1986

Intercomparison of numerical models of flaring coronal loops

The proposed Benchmark Problem consists of an infinitesimal magnetic flux tube containing a low-beta plasma. The field strength is assumed to be so large that the plasma can move only along the flux tube, whose shape remains invariant with time (i.e., the fluid motion is essentially one-dimensional). The flux tube cross section is taken to be constant over its entire length. In planar view the flux tube has a semi-circular shape, symmetric about its midpoint s = s sub max and intersecting the chromosphere-corona interface (CCI) perpendicularly at each foot point. The arc length from the loop apex to the CCI is 10,000 km. The flux tube extends an additional 2000 km below the CCI to include the chromosphere, which initially has a uniform temperature of 8000 K. The temperature at the top of the loop was fixed initially at 2 X 1 million K. The plasma is assumed to be a perfect gas (gamma = 5/3), consisting of pure hydrogen which is considered to be fully ionized at all temperatures. For simplicity, moreover, the electron and ion temperatures are taken to be everywhere equal at all times (corresponding to an artificially enhanced electron-ion collisional coupling). While there was more-or-less unanimous agreement as to certain global properties of the system behavior (peak temperature reached, thermal-wave time scales, etc.), no two groups could claim satisfactory accord when a more detailed comparison of solutions was attempted.

Kopp, R. A.↗
NASA NTRS1987

Enhancements to Program LAURA for computation of three-dimensional hypersonic flow

Changes to Program Laura (Langley Aerothermodynamic Upwind Relaxation Algorithm) are presented which enhance both stability and accuracy of the algorithm. A discussion of iteration/sweeping strategies and their relation to computer architectures is included to best exploit the capabilities of serial, vector, and parallel processor machines. Test cases for Mach 10 perfect gas flow and Mach 32 real gas flow in chemical nonequilibrium over a blunt, raked elliptic cone using the thin-layer Navier-Stokes equations are presented in order to demonstrate the current improved capabilities. Algorithm changes include the use of volume averaging, application of a symmetric total variation diminishing (TVD) scheme, and stronger interaction between the grid/shock alignment routine and the relaxation algorithm. Good comparisons with heat transfer and pitching moment data at three different angles of attack for the Mach 10 tests serve to further validate the present algorithm. Parameters are defined which control the coupling of the specie continuity equations with the solution of the mixture conservation equations. A discussion of the consequences involved in the choice of strong versus weak coupling is presented, and a sample nonequilibrium calculation on a fine grid over a full scale model of the Aeroassist Flight Experiment (AFE) demonstrates current capabilities.

Gnoffo, Peter A.↗
NASA NTRS1987

Computational fluid dynamics near the continuum limit

Two dimensional Navier-Stokes equations for a perfect gas are solved for hypersonic flow over a flat plate at Reynolds numbers ranging from continuum to the free molecule flow. In the transition flow regime, new slip boundary conditions are introduced, which reduce to the well-known slip conditions of Maxwell at small Knudsen numbers and yield the correct shear stress and heat transfer in the limiting case of free molecule flow. Comparison of the computed results with the existing experimental data and Monte Carlo calculations indicates that the continuum Navier-Stokes equations give surprisingly realistic results throughout the transition flow regime, when the new slip boundary conditions are used.

Maccormack, Robert W.↗
NASA NTRS1987

Experimental study of shock wave interference heating on a cylindrical leading edge at Mach 6 and 8

This paper presents the details of an experimental study of shock wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet. The study was conducted at Mach numbers of 6.3, 6.5 and 8.0. This study has provided the first (1) detailed pressure and heat transfer rate distributions for a two-dimensional shock wave interference on a cylinder and (2) insight into the effects of temperature dependent specific heats on the phenomena. The peak pressure and heat transfer rates were 10 times the undisturbed flow stagnation point levels. The peak levels and their gradients increased with Mach number. Variation in specific heats and hence the ratio of specific heats with temperature manifest in slightly lower loads and amplification factors than for corresponding perfect gas conditions.

Wieting, Allan R.↗
NASA NTRS1987

Navier-Stokes simulation of a hypersonic generic wing/fuselage

An unsteady thin-layer Navier-Stokes code is used to calculate a generic wing/fuselage configuration at a Mach number of 25 and freestream conditions corresponding to an altitude of 220,000 feet. Calculations were performed with the assumptions of a perfect gas and with chemical equilibrium, and the boundary layer was assumed to be turbulent and to have a surface temperature prescribed at 1255 K. Results for the two different gas assumptions were compared in terms of distributions of pressure, density, temperature, Mach number, ratio of specific heat, and heat transfer. Numerical problems arising in the calculations were identified.

Wai, John C.↗