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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Experimental and predicted aerodynamic characteristics of a proposed Assured Crew Return Vehicle (ACRV) lifting-body configuration at Mach 6 and 10

The effects of Mach number, Reynolds number, and ratio of specific heats on the aerodynamic characteristics of a proposed Assured Crew Return Vehicle (ACRV) lifting-body configuration were examined for a range of angles of attack from -5 deg to 50 deg. Predictions made with a Langley-developed, three-dimensional Navier Stokes solver known as LAURA, which was exercised as an Euler solver for the present study, are compared with the experimental results. Unlike the Shuttle Orbiter, which experienced a significant nose-up increment in pitching moment with decreasing specific heat ratio (i.e., real gas effects), the aerodynamic characteristics of this lifting-body configuration are insensitive to changes in specific heat ratio. The maximum trimmed lift-to-drag ratio achieved was about 1.5. Predicted inviscid values of aerodynamic coefficients were generally in good agreement with measurement.

Micol, John R.↗
NASA NTRS1989

Hypersonic CFD applications at NASA Langley using CFL3D and CFL3DE

The CFL3D/CFL3DE CFD codes and the industrial use status of the codes are outlined. Comparison of grid density, pressure, heat transfer, and aerodynamic coefficience are presented. Future plans related to the National Aerospace Plane Program are briefly outlined.

Richardson, Pamela F.↗
NASA NTRS1989

Conservation equations and physical models for hypersonic air flows over the aeroassist flight experiment vehicle

The code development and application program for the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA), with emphasis directed toward support of the Aeroassist Flight Experiment (AFE) in the near term and Aeroassisted Space Transfer Vehicle (ASTV) design in the long term is reviewed. LAURA is an upwind-biased, point-implicit relaxation algorithm for obtaining the numerical solution to the governing equations for 3-D, viscous, hypersonic flows in chemical and thermal nonequilibrium. The algorithm is derived using a finite volume formulation in which the inviscid components of flux across cell walls are described with Roe's averaging and Harten's entropy fix with second-order corrections based on Yee's Symmetric Total Variation Diminishing scheme. Because of the point-implicit relaxation strategy, the algorithm remains stable at large Courant numbers without the necessity of solving large, block tri-diagonal systems. A single relaxation step depends only on information from nearest neighbors. Predictions for pressure distributions, surface heating, and aerodynamic coefficients compare well with experimental data for Mach 10 flow over an AFE wind tunnel model. Predictions for the hypersonic flow of air in chemical and thermal nonequilibrium over the full scale AFE configuration obtained on a multi-domain grid are discussed.

Gnoffo, Peter A.↗
NASA NTRS1990

Analytical aerodynamic model of a high alpha research vehicle wind-tunnel model

A 6 DOF analytical aerodynamic model of a high alpha research vehicle is derived. The derivation is based on wind-tunnel model data valid in the altitude-Mach flight envelope centered at 15,000 ft altitude and 0.6 Mach number with Mach range between 0.3 and 0.9. The analytical models of the aerodynamics coefficients are nonlinear functions of alpha with all control variable and other states fixed. Interpolation is required between the parameterized nonlinear functions. The lift and pitching moment coefficients have unsteady flow parts due to the time range of change of angle-of-attack (alpha dot). The analytical models are plotted and compared with their corresponding wind-tunnel data. Piloted simulated maneuvers of the wind-tunnel model are used to evaluate the analytical model. The maneuvers considered are pitch-ups, 360 degree loaded and unloaded rolls, turn reversals, split S's, and level turns. The evaluation finds that (1) the analytical model is a good representation at Mach 0.6, (2) the longitudinal part is good for the Mach range 0.3 to 0.9, and (3) the lateral part is good for Mach numbers between 0.6 and 0.9. The computer simulations show that the storage requirement of the analytical model is about one tenth that of the wind-tunnel model and it runs twice as fast.

Cao, Jichang↗
NASA NTRS1991

Propulsion-induced aerodynamics of an ejector-configured STOVL fighter aircraft

Propulsion-induced aerodynamic effects are computed by using data obtained from tests of a full-scale model of the E-7A configuration that were run in the NASA Ames 40 x 80 and 80 x 120-foot tunnels. These effects are shown both in aerodynamic coefficients and nondimensionalized by thrust versus equivalent velocity. The test results show that the full-scale ventral nozzle-induced effects are smaller than scale model data, while the ejector-induced effects demonstrate fair agreement. The effect of tunnel test section size is primarily observed at low and static speed, high thrust conditions, as seen in comparisons of data from both tunnels. The 80 x 120-foot tunnel test gave better static thrust calibrations and permitted a greater range of test freestream velocities and angles-of-attack, extending the database provided by the full-scale model.

Poppen, William A.↗
NASA NTRS1990

A flight experiment to measure rarefied-flow aerodynamics

A flight experiment to measure rarefied-flow aerodynamics of a blunt lifting body is being developed by NASA. This experiment, called the Rarefied-Flow Aerodynamic Measurement Experiment (RAME), is part of the Aeroassist Flight Experiment (AFE) mission, which is a Pathfinder design tool for aeroassisted orbital transfer vehicles. The RAME will use flight measurements from accelerometers, rate gyros, and pressure transducers, combined with knowledge of AFE in-flight mass properties and trajectory, to infer aerodynamic forces and moments in the rarefied-flow environment, including transition into the hypersonic continuum regime. Preflight estimates of the aerodynamic measurements are based upon environment models, existing computer simulations, and ground test results. Planned maneuvers at several altitudes will provide a first-time opportunity to examine gas-surface accommondation effects on aerodynamic coefficients in an environment of changing atmospheric composition. A description is given of the RAME equipment design.

Blanchard, Robert C.↗
NASA NTRS1991

Three-dimensional rarefied flow simulations for the Aeroassist Flight Experiment vehicle

Hypersonic rarefied flow about the Aeroassist Flight Experiment vehicle has been investigated using a three-dimensional direct simulation Monte Carlo method. Calculations are performed for the transitional flows encountered during the vehicle's atmospheric entry for altitudes of 110 and 100 km with an entry velocity of 9.9 km/s. The simulations are performed using a five-species reacting gas model that account for rotational and vibrational internal energies. The solutions indicate that dissociation is important at altitudes of 110 km and below. Results are presented for surface pressures, convective heating, flowfield structure, and aerodynamic coefficient variations with altitude.

Celenligil, M. Cevdet↗
NASA NTRS1990

Prediction of vortical flows on wings using incompressible Navier-Stokes equations

Grid-density and Reynolds-number effects on integral values and static pressure distributions are presently studied in the steady-state Navier-Stokes solutions obtained for the flow around a round-edged double delta wing using an upwind-relaxation finite-difference algorithm. It is found that while the computed longitudinal aerodynamic coefficients are in good agreement with extant experimental data, the magnitudes of suction-pressure peaks are underpredicted in the vicinity of the trailing edge. It is judged that additional computations employing finer-grid solutions in the vortical flow region are required.

Hsu, C.-H.↗
NASA NTRS1991

The microgravity environment of the Space Shuttle Columbia payload bay during STS-32

Over 11 hours of three-axis microgravity accelerometer data were successfully measured in the payload bay of Space Shuttle Columbia as part of the Microgravity Disturbances Experiment on STS-32. These data were measured using the High Resolution Accelerometer Package and the Aerodynamic Coefficient Identification Package which were mounted on the Orbiter keel in the aft payload bay. Data were recorded during specific mission events such as Orbiter quiescent periods, crew exercise on the treadmill, and numerous Orbiter engine burns. Orbiter background levels were measured in the 10(exp -5) G range, treadmill operations in the 10(exp -3) G range, and the Orbiter engine burns in the 10(exp -2) G range. Induced acceleration levels resulting from the SYNCOM satellite deploy were in the 10 (exp -2) G range, and operations during the pre-entry Flight Control System checkout were in the 10(exp -2) to 10(exp -1) G range.

Dunbar, Bonnie J.↗
NASA NTRS1992

Effect of airfoil (trailing-edge) thickness on the numerical solution of panel methods based on the Dirichlet boundary condition

The practical limit of airfoil thickness ratio for which acceptable engineering results are obtainable with the Dirichlet boundary-condition-based numerical methods is investigated. This is done by studying the effect of thickness on the calculated pressure distribution near the trailing edge and by comparing the aerodynamic coefficients with available exact solutions. The first objective of this study, owing to the wide use of such computational methods, is to demonstrate the numerical symptoms that occur when the body or wing thickness approaches zero and to increase the awareness of potential users of these methods. Additionally, an effort is made to obtain the practical limits of the trailing-edge thickness where such problems will appear in the flow solution, and to propose some possible cures for very thin airfoils or those with cusped trailing edges.

Yon, Steven↗
NASA NTRS1992

Analysis of cascades using a two dimensional Euler aeroelastic solver

A two-dimensional unsteady aerodynamic Euler solver based on a flux differencing scheme is being developed to analyze oscillating cascades. The cascades can have subsonic, transonic, or supersonic flow with either subsonic or supersonic axial velocity. The aerodynamic solver is coupled with a typical section structural model for each blade of the cascade. Flutter analysis methods both in time and frequency domains are then implemented into the resulting aeroelastic solver. Methods that reduce computational time for calculating the unsteady aerodynamic coefficients, namely the influence coefficient method and the pulse response method, are also implemented and validated. The present solver showed good correlation with published results for all the flow regimes. It is shown that grid coarsening improved the accuracy of the predictions. A representative flutter calculation showed that both the frequency domain and time domain methods are implemented correctly into the aeroelastic solver.

Reddy, T. S. R.↗
NASA NTRS1991

Aerobrake aerothermodynamic environment predictions in support of the Aeroassist Flight Experiment

A computational fluid dynamic (CFD) simulation of the flow past an Aeroassist Flight Experiment (AFE) aerobrake under wind tunnel test conditions has been made. The Navier-Stokes equations in three dimensions were solved numerically using a finite-volume, implicit approach. Comparisons with experimental data include surface pressures and heat transfer rates and aerodynamic coefficients. Agreement with experiment is shown to be excellent. The dependence of the solution on the computational grid is explored. The present work is preliminary to simulation of the flow past the AFE under flight conditions, which at present cannot be duplicated with ground-based experimental facilities.

Fay, John F.↗
NASA NTRS1992

A hypersonic shock tunnel test of the Aeroassist Flight Experiment (AFE) vehicle at high altitude test conditions

The Aeroassist Flight Experiment (AFE) vehicle is a 4.26 m-diameter raked and blunted elliptic cone that is intended to obtain aerodynamic and aerothermodynamic data on blunt bodies at velocities near 10 km/s and altitudes above 75 km. Previous wind tunnel tests of this configuration have been at Mach numbers of 10 or lower. The present test program consisted of five test conditions at Mach numbers between 15 and 20 and simulated altitudes from 75 km to 97 km. Static longitudinal aerodynamic coefficients, the lift-to-drag ratio, and the trim angle-of-attack were obtained for angles-of-attack between 7 deg and 27 deg. The effects of angle-of-attack and shock Reynolds number, Re2, have been studied. These results indicate the AFE configuration is longitudinally stable. The variation of normal force slope, CNalpha and lift-to-drag slope, (L/D)alpha as well as the trim angle-of-attack with Re2 are documented. The trim angle-of-attack increases with decreasing values of shock Reynolds number (increasing altitude) while the lift-to-drag ratio at the trimmed conditions is relatively constant.

Wittliff, C. E.↗
NASA NTRS1992

Improved accuracy in ground-based facilities - Development of an automated film-reading system for ballistic ranges

Software for an automated film-reading system that uses personal computers and digitized shadowgraphs is described. The software identifies pixels associated with fiducial-line and model images, and least-squares procedures are used to calculate the positions and orientations of the images. Automated position and orientation readings for sphere and cone models are compared to those obtained using a manual film reader. When facility calibration errors are removed from these readings, the accuracy of the automated readings is better than the pixel resolution, and it is equal to, or better than, the manual readings. The effects of film-reading and facility-calibration errors on calculated aerodynamic coefficients is discussed.

Yates, Leslie A.↗
NASA NTRS1993

Hypersonic lateral and directional stability characteristics of aeroassist flight experiment configuration in air and CF4

Hypersonic lateral and directional stability characteristics measured on a 60 deg half-angle elliptical cone, which was raked at an angle of 73 deg from the cone centerline and with an ellipsoid nose (ellipticity equal to 2.0 in the symmetry plane), are presented for angles of attack from -10 to 10 deg. The high normal-shock density ratio of a real gas was simulated by tests at a Mach number of 6 in air and CF4 (density ratio equal to 5.25 and 12.0, respectively). Tests were conducted in air at Mach 6 and 10 and in CF4 at Mach 6 to examine the effects of Mach number, Reynolds number, and normal-shock density ratio. Changes in Mach number from 6 to 10 in air or in Reynolds number by a factor of 4 at Mach 6 had a negligible effect on lateral and directional stability characteristics. Variations in normal-shock density ratio had a measurable effect on lateral and directional aerodynamic coefficients, but no significant effect on lateral and directional stability characteristics. Tests in air and CF4 indicated that the configuration was laterally and directionally stable through the test range of angle of attack.

Micol, John R.↗
NASA NTRS1992

Concurrent processing adaptation of aeroelastic analysis of propfans

Discussed here is a study involving the adaptation of an advanced aeroelastic analysis program to run concurrently on a shared memory multiple processor computer. The program uses a three-dimensional compressible unsteady aerodynamic model and blade normal modes to calculate aeroelastic stability and response of propfan blades. The identification of the computational parallelism within the sequential code and the scheduling of the concurrent subtasks to minimize processor idle time are discussed. Processor idle time in the calculation of the unsteady aerodynamic coefficients was reduced by the simple strategy of appropriately ordering the computations. Speedup and efficiency results are presented for the calculation of the matched flutter point of an experimental propfan model. The results show that efficiencies above 70 percent can be obtained using the present implementation with 7 processors. The parallel computational strategy described here is also applicable to other aeroelastic analysis procedures based on panel methods.

Murthy, D. V.↗
NASA NTRS1993

Nonequilibrium effects on the aerothermodynamics of transatmospheric and aerobraking vehicles

A 3D CFD algorithm is used to study the effect of thermal and chemical nonequilibrium on slender and blunt body aerothermodynamics. Both perfect gas and reacting gas air models are used to compute the flow over a generic transatmospheric vehicle and a proposed lunar transfer vehicle. The reacting air is characterized by a translational-rotational temperature and a vibrational-electron-electronic temperature and includes eight chemical species. The effects of chemical reaction, vibrational excitation, and ionization on lift-to-drag ratio and trim angle are investigated. Results for the NASA Ames All-body Configuration show a significant difference in center of gravity location for a reacting gas flight case when compared to a perfect gas wind tunnel case at the same Mach number, Reynolds number, and angle of attack. For the same center of gravity location, the wind tunnel model trims at lower angle of attack than the full-scale flight case. Nonionized and ionized results for a proposed lunar transfer vehicle compare well to computational results obtained from a previously validated reacting gas algorithm. Under the conditions investigated, effects of weak ionization on the heat transfer and aerodynamic coefficients were minimal.

Hassan, Basil↗
NASA NTRS1992

An Aerodynamic Preliminary Analysis System (APAS) calibration report - Space Shuttle Orbiter

The Space Shuttle Orbiter is modelled and analyzed using the Aerodynamic Preliminary Analysis System (APAS). APAS predictions of Orbiter longitudinal and lateral-directional aerodynamics are compared to Shuttle Orbiter Aerodynamic Design Data Book (ADDB) values from Mach numbers of 0.3 to 20. Agreement between APAS results and the ADDB was good, especially in the case of the longitudinal aerodynamic coefficients. The results of this study establish a sense of confidence in the use of the APAS for conceptual and preliminary studies.

Cruz, Christopher I.↗