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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Navier-Stokes Simulation of the Canard-Wing-Body Longitudinal Dynamic Stability Characteristics

Many modern aircraft are canard-configured for aircraft control and improved aerodynamic performance. Canards can often enhance aircraft cruise performance, maneuverability and agility. For close-coupled canard configurations, the aerodynamic interaction between the canard and wing significantly changes the flow characteristics of the wing. In unsteady flow, such changes in the flow structure and performance of wings can be quite pronounced. Accurate modeling of the unsteady aerodynamics is essential for potential CFD design and analysis of such configurations. A time-accurate numerical simulation is performed to study the unsteady aerodynamic interaction between a canard and wing with emphasis on the effects of the canard on the configuration's dynamic response characteristics. The thin-layer Reynolds-averaged Navier-Stokes Equations with various turbulence models are used in this study. Computations are made on a generic, analytically-defined, close-coupled canard-wing-body configuration which has been the subject of numerous previously published experimental studies during the 1970's to mid-80's. More recently, a series of steady-flow simulations has been performed and published by the author. In the current study, the configuration is given prescribed ramp and oscillatory motions in order to predict characteristics such as the damping-in-pitch and oscillatory longitudinal stability parameters. The current computations are made at high-subsonic and transonic Mach numbers, moderate angles-of- attack from -4 to 20 degrees, and at various pitch rates and reduced frequencies. Comparisons of pressures and integrated force quantities (e.g. lift, drag, pitching moment and selected dynamic parameters) are made with other published computational results and available experimental data. Results showing the unsteady effects of the canard on surface pressures, integrated forces, canard-wing vortex interaction and vortex breakdown will be presented.

Tu, Eugene L.↗
NASA NTRS1979

Origin of longitudinal grooving in Tiu Vallis, Mars - Isolation of responsible fluid-types

Fluid instability analysis developed for the growth or decay of large, longitudinal roller vortex perturbations imposed at the base of fluids of exponentially stratified viscosities is presented. The origin of longitudinal grooving and fluting in a region of converging flow in Tiu Vallis, Mars, is analyzed, and the propensity of fluids, such as water, mudflow/debris flow, and lava, to develop longitudinal roll patterns as part of their flow field is tested. It is found that the grooving pattern in Tiu Vallis was probably formed by vortex motion in a mudflow or debris-laden slurry, but exact representation of sediment/debris concentration or sediment transport machanism is not yet possible. It is concluded that longitudinal vortex motion modelled in this analysis can develop in water, lava, or ice, but that the specific flow characteristics of these models which include the vortex motion are unreasonable for flow in Tiu Vallis.

Thompson, D. E.↗
NASA NTRS1952

Experimental Investigation of Flow in an Annular Cascade of Turbine Nozzle Blades of Constant Discharge Angle

The experimental performance of turbine nozzle blades designed for a constant discharge angle was investigated at discharge hub Mach numbers of 1.18, 1.31, and 1.41. Flow characteristics are presented in terms of energy losses, angle gradients, and secondary flow effects. Blade efficiency decreased from 0.983 to 0.978 with increasing Mach number in the range investigated while angle variations in the loss regions became very large, indicating poorer blade performance than efficiency implies.

BOUNDARY LAYER CHARACTERISITCS-INTERNAL AERODYNAMI↗
NASA NTRS1994

Towards Understanding the Fluid Dynamic Phenomenon of Interest to Rocket Base Heating: A Review

The significance of the base heating problem for rockets during ascent is due to the complex interaction between the rocket nozzle plumes and the external-flow which can change the flow characteristics in the base region dramatically. At lower altitudes the external-flow merges with the plume-flow, without the formation of a large separated flow region, and the cooler external-flow promotes convective cooling of the base wall. Under these conditions the majority of the base heating is due to radiative heating from the shock heated plume gases. At higher altitudes, however, the process of base heating is not so straightforward. The plume and the base flow expands dramatically and separated flow regions occur in the base area. Hot exhaust gases from the rocket nozzle will be entrained into the separated flow regions and produce a convective component to the base wall heating. Further, if the rocket exhaust-gas contains soot, the soot can increase the emission from the gas and dramatically increase the wall absorption coefficient for radiative heating if it is deposited on the walls . In addition, if the rocket exhaust gas is fuel rich, the fuel can bum in the separated flow regions and further increase the base heating. The base burning phenomenon, and the increased base heating caused by it at higher altitudes, have been observed for the Space Shuttle and Saturn Rocket. Under these conditions, the total heating is significantly higher than the heating without separated flow in the base region, and the increase in heating is directly attributable to the fluid dynamic complexity of the base region. Realistic simulation of the base heating requires that the calculated flow environment reproduce the fluid dynamic flow features accurately. Thus, it will be necessary to introduce into the CFD codes the capability for the flow to respond to the complex vehicle geometry, the effect of turbulence, the ability to accurately reproduce the plume shock/shear layer structures and capture such phenomenon as shock induced base separation and base-burning phenomenon. A survey of experimental, theoretical and computational work that details the fluid dynamics of the base flow environment will be presented in the proposed paper. CFD simulations of rocket base flows using standard CFD codes such as OVERFLOW or GASP will be explored to capture these phenomenon accurately. Merits and limitations of these codes for base flow environment predictions will be explored.

Venkatapathy, E.↗
NASA NTRS2004

Inlet Housing for a Partial-Admission Turbine

An inlet housing for a partial-admission turbine has been designed to cause the inlet airflow to make a smooth transition from an open circular inlet to an inlet slot. The smooth flow is required for purposes of measuring inlet flow characteristics and maximizing the efficiency of the turbine. A partial-admission turbine is a turbine in which the inlet slot occupies less than a complete circle around the rotor axis. In this case, the inlet slot occupies a 90 arc. The present special inlet-housing design is needed because the "bull nose" shape of a conventional turbine inlet housing fails to provide the required smooth transition in a partial-admission configuration and thereby gives rise to a loss of turbine efficiency and inaccuracies in inlet flow measurements. Upon entering the inlet housing through the circular opening, the flow encounters a "tongue"-shaped passageway, which serves as a ramp that diverts the flow to the first of two straight passages. This first passageway occupies a 90 arc and has a length equal to two passage heights. Instrumentation rakes for measuring the characteristics of the inlet flow are installed in this passageway. Just past the first straight passageway is the second one, which is narrower and leads to the 90 turbine inlet slot. This passageway is used to smooth the flow immediately prior to its passage through the turbine inlet slot. The length of this second passageway equals the length of the chord of a turbine vane. The inlet housing incorporates small ports for measuring static pressures at various locations of the flow, and incorporates bosses for the installation of the instrumentation rakes. The inlet housing also includes a flange at its inlet end for attachment to a circular inlet duct and a flange at its outlet end for attachment to the outer casing of the turbine.

Moye, Ralph↗
NASA NTRS1981

Novel improved PMR polyimides

The development of a class of high-temperature-resistant resins known as PMR polyimides has been reported by Serafini et al. (1972). Serafini and Vannucci (1975) found that the lower formulated molecular weight (FMW) compositions exhibited increased resin flow, but with some sacrifice in elevated temperature thermo-oxidative stability. Vannucci (1977) reported that the resin flow characteristics of the PMR composition having an FMW of 1500 could be varied by controlling the degree of resin advancement or imidization. The current investigation is concerned with an alternative approach to obtain improved flow PMR polyimides without sacrificing the desirable thermo-oxidative characteristics. The new approach is based on the utilization of a chemically compatible flow modifying agent. This agent is N-phenylnadimide (PN). The determination of the processing characteristics and properties of PN modified PMR/Celion 6000 composites is discussed.

Pater, R. H.↗
NASA NTRS1978

A critical examination of expansion tunnel performance

An experimental study of the performance of the expansion tunnel for various test gases and range of quiescent acceleration section and nozzle pressure, nozzle geometric area ratio, and nozzle axial station has been performed. Flow diagnostics used to examine expansion tunnel flow characteristics were time histories and profiles of pitot pressure and axial component of flow velocity. The purpose of this study was to determine experimentally what limitations might restrict predicted operational flexibility and the advantages and disadvantages of this mode of operation as compared to the expansion tube. Results are presented which demonstrate the expansion tunnel offers several advantages over the expansion tube, but the severity of the disadvantages of the tunnel makes the expansion tube mode of operation the more desirable for performing hypersonic-hypervelocity aerothermodynamic studies of proposed entry configurations.

Miller, C. G.↗
NASA NTRS1980

Scale model studies for establishing the flow patterns of a low-speed tunnel

Experiments were conducted in a model tunnel scaled down in a ratio of 1:24 from the full size prototype V/STOL tunnel at NASA Langley Research Center. The flow characteristics around the tunnel were studied and the location and causes of local flow separation and local recirculation were documented. The study of the interaction between the various components from which the tunnel is built, an experimental setup similar to the sequence of tunnel circuit components was constructed which enabled the various components to be tested either individually or in combination. The components were tested by the simple technique of blowing air through them, then measuring the velocity distribution at relevant sections.

Barna, P. S.↗
NASA NTRS1985

Emplacement of Long Lava Flows on Mauna Loa (hawaii) and Alba (mars)

Spacecraft images revealed that extremely long lava flows (more than 200 km long) exist on the surface of Mars and Io. Compared to terrestial volcanic eruptions, the occurrence of these long flows is very unusual, and may hint at a different style of either magma production or eruption. Attempts to model the emplacement of the long flows on other planets, using a Bingham rheological model, were only partially successful. The objective is to conduct field measurements on long lava flows in Hawaii (where individual flows such as those of 1859 and 1881 exceed 40 km in length) in order to document and interpret their flow characteristics. In this way, a better understanding of the formation of long lava flows is sought as well as a determination of whether the Mauna Loa flows are terrestrial analogs to the long flows seen on Mars and Io.

Mouginismark, P. J.↗
NASA NTRS1988

Space Cryogenics Workshop, University of Wisconsin, Madison, June 22, 23, 1987

Papers are presented on liquid helium servicing from the Space Station, performance estimates in the Superfluid Helium On-Orbit Transfer Flight Experiment, an analytical study of He II flow characteristics in the SHOOT transfer line, a Dewar to Dewar model for superfluid helium transfer, and mechanical pumps for superfluid helium transfer in space. Attention is also given to the cavitation characteristics of a small centrifugal pump in He I and He II, turbulent flow pressure drop in various He II transfer system components, slip effects associated with Knudsen transport phenomena in porous media, and an integrated fountain effect pump device for fluid management at low gravity. Other papers are on liquid/vapor phase separation in He-4 using electric fields, an enclosed capillary device for low-gravity management of He II, cavitation in flowing superfluid helium, the long-term performance of the passive thermal control systems of the IRAS spacecraft, and a novel approach to supercritical helium flight cryostat support structures.

Source record↗
NASA NTRS1994

Computed Flow Through An Artificial Heart Valve

Report discusses computations of blood flow through prosthetic tilting disk valve. Computational procedure developed in simulation used to design better artificial hearts and valves by reducing or eliminating following adverse flow characteristics: large pressure losses, which prevent hearts from working efficiently; separated and secondary flows, which causes clotting; and high turbulent shear stresses, which damages red blood cells. Report reiterates and expands upon part of NASA technical memorandum "Computed Flow Through an Artificial Heart and Valve" (ARC-12983). Also based partly on research described in "Numerical Simulation of Flow Through an Artificial Heart" (ARC-12478).

Rogers, Stewart E.↗
NASA NTRS1981

Dual nozzle aerodynamic and cooling analysis study

Analytical models to predict performance and operating characteristics of dual nozzle concepts were developed and improved. Aerodynamic models are available to define flow characteristics and bleed requirements for both the dual throat and dual expander concepts. Advanced analytical techniques were utilized to provide quantitative estimates of the bleed flow, boundary layer, and shock effects within dual nozzle engines. Thermal analyses were performed to define cooling requirements for baseline configurations, and special studies of unique dual nozzle cooling problems defined feasible means of achieving adequate cooling.

Meagher, G. M.↗
NASA NTRS1984

Assessment of preliminary prediction techniques for wing leading-edge vortex flows at supersonic speeds

The applicability of existing theoretical models for predicting wing leading edge separated flow characteristics for high-lift supersonic flight was examined with regard to previous experimental force, pressure and flow visualization data. Correlations of data on uncambered delta wings revealed that the upper surface normal force and minimum pressure coefficients decreased nonlinearly with increasing angles of attack. The attainable vacuum pressure decreased with increasing Mach number, while the lower surface normal force increased nonlinearly with increasing speed. The LISTAR and VORCAM linear theory aerodynamic codes generated predictions for comparison with the data. LISTAR displayed better agreement with measured vortex strength and position and lifting characteristics than did VORCAM. The Euler code SWINT was ill-suited to calculating wing performance in separated flows at high lift and low supersonic speeds.

Wood, R. M.↗
NASA NTRS1985

Quasi non-intrusive sampling and analysis of gases associated with the boundary layer on the tethered satellite and similar supersonic and hypersonic research vehicles

The effect that one candidate inlet, an assembly of capillary openings in a thin glass plate (a multichannel plate), might have on the overall sampling process is considered. The flow characteristics of the plate, under a variety of conditions of external pressure and mass flow, is evaluated. A review of capillary flow theory is presented with some development of the pertinent equations. The predicted mass flow will be compared to that determined perimentally to assess the effect that mass flow through one capillary might have upon a neighboring capillary. Mass spectrometric measurements of mixtures flowing through the multichannel plate (MCP) is also considered. In the first part of the experiments, the flow was in a direction normal to the surface of the plate. The experimental gases were Argon and mixtures of carbon dioxide in air. Ongoing experiments are discussed which are conducted with the flow parallel to the surface of the plate, a simulation of the kind of flow that a flight vehicle would experience.

Fishel, C.↗
NASA NTRS1955

Effect of surface roughness on characteristics of spherical shock waves

An investigation has been conducted on a small-scale test layout in which direct observation of the shock wave movement with time could be made in order to determine the effects of surface roughness on the characteristics of spherical shock waves. Data were obtained with 15-gram pentolite charges at four heights of burst, both for a smooth surface and for a surface completely covered with pyramid-shaped roughness elements. The observations resulted in determinations of shock peak overpressure and Mach stem height as a function of distance for each test. Comparison of the smooth-surface data with those obtained for the extremely rough condition showed a small net effort of roughness on the shock peak overpressures at the surface for all burst heights, the effect being to lower the overpressures. The effect of surface roughness on the Mach stem formation and growth was to delay the formation at the greatest charge height and to lower the height of the Mach stem for all heights.Comparison of the free-air shock peak overpressures with larger scale data showed good similarity of the overpressure-distance relationships. The data did not fit a geometrical similarity parameter for the path of the triple point at different heights of burst suggested by other investigators. A simple similarity parameter (relating the horizontal distance to the theoretical point of Mach formation) was found which showed only a small influence of burst height on the path of the triple point. While the data presented provide knowledge of the effect of many surface-roughness elements on the overall shock characteristics, the data do not provide insight into the details of the air-flow characteristics along the surface, nor the relative contribution of individual roughness elements to the results obtained.

Huber, Paul W↗
NASA NTRS1953

Performance Characteristics of Plane-Wall Two-Dimensional Diffusers

Experiments have been made at Stanford University to determine the performance characteristics of plane-wall, two-dimensional diffusers which were so proportioned as to insure reasonable approximation of two-dimensional flow. All of the diffusers had identical entrance cross sections and discharged directly into a large plenum chamber; the test program included wide variations of divergence angle and length. During all tests a dynamic pressure of 60 pounds per square foOt was maintained at the diffuser entrance and the boundary layer there was thin and fully turbulent. The most interesting flow characteristics observed were the occasional appearance of steady, unseparated, asymmetric flow - which was correlated with the boundary-layer coalescence - and the rapid deterioration of flow steadiness - which occurred as soon as the divergence angle for maximum static pressure recovery was exceeded. Pressure efficiency was found to be controlled almost exclusively by divergence angle, whereas static pressure recovery was markedly influenced by area ratio (or length) as well as divergence angle. Volumetric efficiency. diminished as area ratio increased, and at a greater rate with small lengths than with large ones. Large values of the static-pressure-recovery coefficient were attained only with long diffusers of large area ratio; under these conditions pressure efficiency was high and. volumetric efficiency low. Auxiliary tests with asymmetric diffusers demonstrated that longitudinal pressure gradient, rather than wall divergence angle, controlled flow separation. Others showed that the addition of even a short exit duct of uniform section augmented pressure recovery. Finally, it was found that the installation of a thin, central, longitudinal partition suppressed flow separation in short diffusers and thereby improved pressure recovery

Reid, Elliott G↗
NASA NTRS1997

Cavity Unsteady-Pressure Measurements at Subsonic and Transonic Speeds

An experimental investigation was conducted in the Langley 8-Foot Transonic Pressure Tunnel to determine the flow characteristics of rectangular cavities with varying relative dimensions at subsonic and transonic speeds. Cavities were tested with width-to-depth ratios of 1, 4, 8, and 16 for length-to-depth ratios l/h of 1 through 17.5. The maximum cavity depth was 2.4 in., and the turbulent boundary layer approaching the cavity was approximately 0.5 in. thick. Unsteady- and mean static-pressure measurements were made at free-stream Mach numbers from 0.20 to 0.95 at a unit Reynolds number per foot of approximately 3 x 10(exp 6); however, only unsteady-pressure results are presented in this paper. Results indicate that as l/h increases, cavity flows changed from resonant to nonresonant with resonant amplitudes decreasing gradually. Resonant spectra are obtained largely in cavities with mean static-pressure distributions characteristic of open and transitional flows. Resonance sometimes occurred for closed flow. Increasing cavity width or decreasing cavity depth while holding l/h fixed had the effect of increasing resonant amplitudes and sometimes induced resonance. The effects due to changes in width are more pronounced. Decreasing Mach number has the effect of broadening the resonances.

Tracy, Maureen B.↗