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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Effect of afterbody geometry on aerodynamic characteristics of isolated nonaxisymmetric afterbodies at transonic Mach numbers

A parametric study was conducted in the Langley 16-Foot Transonic Tunnel on an isolated nonaxisymmetic fuselage model that simulates a twin-engine fighter. The effects of aft-end closure distribution (top/bottom) nozzle-flap boattail angle versus nozzle-sidewall boattail angle) and afterbody and nozzle corner treatment (sharp or radius) were investigated. Four different closure distributions with three different corner radii were tested. Tests were conducted over a range of Mach numbers from 0.40 to 1.25 and over a range of angles of attack from -3 to 9 degrees. Solid plume simulators were used to simulate the jet exhaust. For a given closure distribution in the range of Mach numbers tested, the sharp-corner nozzles generally had the highest drag, and the 2-in. corner-radius nozzles generally had the lowest drag. The effect of closure distribution on afterbody drag was highly dependent on configuration and flight condition.

Bangert, Linda S.↗
NASA NTRS1991

A finite Reynolds number approach for receptivity due to rapid variations in surface boundary conditions

A new approach to the prediction of instability generation due to the interaction of free-stream disturbances with regions of short-scale variations in surface boundary conditions is presented which accounts for the finite Reynolds number effects while providing a framework for studying receptivity in a variety of flows. The approach is demonstrated for the case of Tollmien-Schlichting wave generation in a Blasius boundary layer due to the interaction of a free-stream acoustic wave with a localized wall inhomogeneity. The results obtained by the finite Reynolds number approach are compared with predictions of the asymptotic approach.

Choudhari, Meelan↗
NASA NTRS1991

Waves and thermodynamics in high Mach number propulsive ducts

The propulsive effects of waves in ducts, especially at high Mach numbers, are investigated, focusing on drag and thrust and on the conversion of heat into waves which produce thrust. It is shown that essentially all of the work done by an expanding fluid passing through a duct at high Mach number is delivered in the form of waves, and that duct surface angles exist that are optimum for the production of thrust from a wave. The effects of wave phenomena on drag and thrust are considered by extending the concept of a Busemann biplane into that of a 'Busemann scramjet, taking 'off-design' performance into account. An idealized model of a streamtube with heat addition is developed, and flow mechanisms involved in generating thrust by the expansion of this streamtube in an exhaust nozzle are examined.

Stalker, R. J.↗
NASA NTRS1992

Plasma wave profiles of earth's bow shock at low Mach numbers - ISEE 3 observations on the far flank

A survey of selected crossings far downstream from the subsolar shock is presented in which the overall plasma wave (PW) behavior of a selected set of nearly perpendicular crossings and another set of limited Mach number but broad geometry are delinated. The result is a generalizable PW signature, or signatures, of low Mach number shocks and some likely implications of those signatures for the weak shock's plasma physical processes on the flank. The data are found to be consistent with the presence of ion beam interactions producing noise ahead of the shock in the ion acoustic frequency range. The presence or absence, and the amplitudes, of PW activity are explainable by the presence or absence of a population of upstream ions controlled by the component of the interplanetary magnetic field normal to the solar wind flow.

Greenstadt, E. W.↗
NASA NTRS1992

On the drag of model dendrite fragments at low Reynolds number

An experimental study of low Reynolds number drag on laboratory models of dendrite fragments has been conducted. The terminal velocities of the dendrites undergoing free fall along their axis of symmetry were measured in a large Stokes flow facility. Corrections for wall interference give nearly linear drag vs Reynolds number curves. Corrections for both wall interference and inertia effects show that the dendrite Stokes settling velocities are always less than that of a sphere of equal mass and volume. In the Stokes limit, the settling speed ratio is found to correlate well with the primary dendrite arm aspect ratio and a second dimensionless shape parameter which serves as a measure of the fractal-like nature of the dendrite models. These results can be used to estimate equiaxed grain velocities and distance of travel in metal castings. The drag measurements may be used in numerical codes to calculate the movement of grains in a convecting melt in an effort to determine macrosegregation patterns caused by the sink/float mechanism.

Zakhem, R.↗
NASA NTRS1993

On the drag of model dendrite fragments at low Reynolds number

An experimental study of low Reynolds number drag on laboratory models of dendrite fragments has been conducted. The terminal velocities of the dendrites undergoing free fall along their axis of symmetry were measured in a large Stokes flow facility. Corrections for wall interference give nearly linear drag vs Reynolds number curves. Corrections for both wall interference and inertia effects show that the dendrite Stokes settling velocities are always less than that of a sphere of equal mass and volume. In the Stokes limit, the settling speed ratio is found to correlate well with primary dendrite arm aspect ratio and a second dimensionless shape paremeter which serves as a measure of the fractal-like nature of the dendrite models. These results can be used to estimate equiaxed grain velocities and distance of travel in metal castings. The drag measurements may be used in numerical codes to calculate the movement of grains in a convecting melt in an effort to determine macrosegregation patterns caused by the sink/float mechanism.

Zakhem, R.↗
NASA NTRS1993

Performance characteristics of two multiaxis thrust-vectoring nozzles at Mach numbers up to 1.28

The thrust-vectoring axisymmetric (VA) nozzle and a spherical convergent flap (SCF) thrust-vectoring nozzle were tested along with a baseline nonvectoring axisymmetric (NVA) nozzle in the Langley 16-Foot Transonic Tunnel at Mach numbers from 0 to 1.28 and nozzle pressure ratios from 1 to 8. Test parameters included geometric yaw vector angle and unvectored divergent flap length. No pitch vectoring was studied. Nozzle drag, thrust minus drag, yaw thrust vector angle, discharge coefficient, and static thrust performance were measured and analyzed, as well as external static pressure distributions. The NVA nozzle and the VA nozzle displayed higher static thrust performance than the SCF nozzle throughout the nozzle pressure ratio (NPR) range tested. The NVA nozzle had higher overall thrust minus drag than the other nozzles throughout the NPR and Mach number ranges tested. The SCF nozzle had the lowest jet-on nozzle drag of the three nozzles throughout the test conditions. The SCF nozzle provided yaw thrust angles that were equal to the geometric angle and constant with NPR. The VA nozzle achieved yaw thrust vector angles that were significantly higher than the geometric angle but not constant with NPR. Nozzle drag generally increased with increases in thrust vectoring for all the nozzles tested.

Wing, David J.↗
NASA NTRS1992

Statistics of the cosmic Mach number from numerical simulations of a cold dark matter universe

Results are presented of an analysis of the cosmic Mach number, M, the ratio of the streaming velocity, v, to the random velocity dispersion, sigma, of galaxies in a given patch of the universe, which was performed on the basis of hydrodynamical simulations of the cold dark matter scenario. Galaxy formation is modeled by application of detailed physical processes rather than by the ad hoc assumption of 'bias' between dark matter and galaxy fluctuations. The correlation between M and sigma is found to be very weak for both components. No evidence is found for a physical 'velocity bias' in the quantities which appear in the definition of M. Standard cold-dark-matter-dominated universes are in conflict, at a statistically significant level, with the available observation, in that they predict a Mach number considerably lower than is observed.

Suto, Yasushi↗
NASA NTRS1993

On streamwise vortices in high Reynolds number supersonic axisymmetric jets

Streamwise vortices previously observed in underexpanded jets were studied using pitot pressure measurements and flow visualizations. A simple model was developed that gives reasonable agreement with the pressure measurements. A convergent nozzle and a convergent-divergent nozzle of design Mach number 1.5 were employed to generate jet flows of equivalent Mach numbers up to 2.5. By operating the nozzles fully expanded, overexpanded, and underexpanded, insight into both the occurrence and the cause of formation of the vortices was gained.

Arnette, S. A.↗
NASA NTRS1993

Ion and electron heating at the low-Mach-number, quasi-parallel bow shock

The study examines the magnetic structure and energy dissipation at low-Mach-number, quasi-parallel collisionless shocks on the basis of observations obtained by the ISEE 1 and 2 spacecraft at seven crossings of the earth's dayside bow shock. All the shocks exhibit a fairly short-scale-length ramp where the principal jumps in the electron temperature, ion temperature, and magnetic field strength take place. Large-amplitude LF transverse waves in the magnetic field are present in and downstream from the ramp, with more modest waves upstream. The amplitude of the downstream waves is typically larger than can be accounted for by shock compression of the upstream waves. The electron heating represents about 6 percent of the dissipated bulk flow energy, consistent with observations in other parameter regimes, and suggesting that the dominant electron heating process is the same. It is suggested that the low-Mach-number shocks are reforming but do not exhibit downstream variability because of the relatively low levels of reflected ions.

Thomsen, M. F.↗
NASA NTRS1993

Plume structures in the hard-turbulent regime of three-dimensional infinite Prandtl number convection

Numerical simulations of three-dimensional infinite Prandtl number thermal convection with Rayleigh number (Ra) up to 10 exp 8 are reported. Convection with Ra higher than 10 exp 7 is characterized by the appearance of disconnected thermal plumes. The smaller plumes are detached by the currents produced by the larger plumes. The low wavenumber portion of a thermal power spectrum near the boundary layer becomes flat at high Ra, while the spectrum measured in the interior shows a positive slope for low wavenumbers. Differences are found in the thermal spectra between 2D and 3D models.

Malevsky, A. V.↗
NASA NTRS1993

The cosmic Mach number - Direct comparisons of observations and models

A robust method is used to derive the cosmic Mach number, M, from existing peculiar velocity data sets. For the IR Tully-Fisher distances of spirals in the Local Supercluster of Aaronson et al. (1979, 1982), M of 1.03 and a characteristic distance from the Local Group of 1464 km/s are found. For the elliptical galaxy sample of Faber et al. (1987, 1988), M of 0.57, with a characteristic distance of 2572 km/s is found. These results are compared with Monte Carlo simulations of the observational realizations drawn from numerical simulations of the universe based on various scenarios, including the standard cold dark matter (CDM) scenario. The effect of velocity bias on the derived Mach number is found to be small. Only 5 percent of the CDM simulations have M as large as or larger than that derived for the Aaronson et al. sample.

Strauss, Michael A.↗
NASA NTRS1993

Heat Transfer from Radiatively Heated Material in a Low Reynolds Number Microgravity Environment

A mathematical model of the transient three-dimensional heat transfer between a slowly moving ambient gas stream and a thermally thick or thin flat surface heated by external radiation in a microgravity environment is presented. The problem is motivated in part by fire safety issues in spacecraft. The gas phase is represented by variable property convection-diffusion energy and mass conservation equations valid at low Reynolds numbers. The absence of gravity and low Reynolds number together permit the flow to be represented by a self-consistent velocity potential determined by the ambient velocity and the thermal expansion in the gas. The solid exchanges energy with the gas by conduction/convection and with the surroundings by surface absorption and re-emission of radiation. Heat conduction in the solid is assumed to be one dimensional at each point on the surface as a consequence of the limited times (of order of 10 seconds) of interest in these simulations. Despite the apparent simplicity of the model, the results show a complex thermally induced flow near the heated surface. The thermal exchange between the gas and solid produces an outward sourcelike flow upstream of the center of the irradiated area and a sinklike flow downstream. The responses of the temperature fields and the associated flows to changes in the intensity of the external radiation and the ambient velocity are discussed.

Yamashita, H.↗
NASA NTRS1993

Low Reynolds number k-epsilon modelling with the aid of direct simulation data

The constant C sub mu and the near-wall damping function f sub mu in the eddy-viscosity relation of the k-epsilon model are evaluated from direct numerical simulation (DNS) data for developed channel and boundary layer flow at two Reynolds numbers each. Various existing f sub mu model functions are compared with the DNS data, and a new function is fitted to the high-Reynolds-number channel flow data. The epsilon-budget is computed for the fully developed channel flow. The relative magnitude of the terms in the epsilon-equation is analyzed with the aid of scaling arguments, and the parameter governing this magnitude is established. Models for the sum of all source and sink terms in the epsilon-equation are tested against the DNS data, and an improved model is proposed.

Rodi, W.↗
NASA NTRS1984

Comparative wind tunnel tests at high Reynolds numbers of NACA 64 621 airfoils with two aileron configurations

An experimental program to measure the aerodynamic characteristics of the NACA 64-621 airfoil when equipped with plain ailerons of 0.38 chord and 0.30 chord and with 0.38 chord balanced aileron has been conducted in a pressurized 6 x 12-inch High Reynolds Number Wind Tunnel. Surface pressures were measured and integrated to yield lift and pressure drag coefficients for angles of attack from -3 deg to +42 deg, and for selected aileron deflections from 0 to -90 deg at nominal Mach and Reynolds numbers of 0.25 and 5 x l0 exp 6, respectively. When resolved into thrust coefficient for wind turbine aerodynamic control applications, the data indicated the anticipated decrease in thrust coefficient with negative aileron deflection at low angles of attack; however, as angle of attack increased, thrust coefficients eventually became positive. All aileron configurations, even at -90 deg deflections, showed this trend. Hinge moments for each configuration complete the data set.

Gregorek, G. M.↗
NASA NTRS1993

Flowfield measurements about a multi-element airfoil at high Reynolds numbers

This paper describes experimental data obtained with a multi-element airfoil at flight Reynolds numbers and lift coefficients including Clmax. The wind tunnel test was conducted in the NASA Langley Low Turbulence Pressure Tunnel as part of a cooperative effort between McDonnell Douglas Aerospace and NASA Langley. The airfoil model is a supercritical design configured with a leading-edge slat and a single-segment trailing-edge flap. Data include surface static-pressure distributions (integrated to obtain lift), drag data obtained with wake-rake surveys, and fbwfield surveys obtained with a flat-tube and five-hole probe at nine stations on the configuration's upper surface. Effects of variations in Reynolds number and flap gap on airfoil performance and flowfield survey data are presented.

Chin, Vincent D.↗
NASA NTRS1939

Propeller Tests to Determine the Effect of Number of Blades at Two Typical Solidities

Propellers with equal total blade area, but with different numbers, were tested at Stanford University. The tests show generally that, for equal total blade area, propellers with the larger number of blades absorb the greater power and, provided hubs have equal drag, develop the higher efficiency. It is shown that the differences found are in agreement, qualitatively, with what might be predicted from simple blade-element theory.

Lesley, E P↗
NASA NTRS1956

Drag Interference Between a Pointed Cylindrical Body and Triangular Wings of Various Aspect Ratios at Mach Numbers of 1.50 and 2.02

The drag of a body alone, six triangular wings of various aspect ratios, and the combinations were measured at Mach numbers of 1.50 and 2.02 at a Reynolds number of 5.5 million (based on the body length). The experimental drag-interference results were in accordance with calculations based on NACA RM A9E19, 1949, with skin-friction effects taken into account, the interference effect being principally the result of fixing transition on the body by adding a wing.

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