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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Hovering model helicopter rotor testing

A relatively large test chamber, chosen to minimize room interference effects during helicopter hovering rotor tests, was found in initial operations to exhibit large, random variations of thrust, torque, and blade flapping. The source of these problems, unsteady recirculation of test chamber flow, was addressed by the addition of a 'flow straightener' that reduced these parameter variations to 1.5 percent of mean values. Rotor performance was then measured outside the chamber in calm, free air conditions and compared with chamber results obtained before and after modifications. Attention is given to wake flow visualization conducted in the test chamber, as well as outside.

Piziali, R. A.↗
NASA NTRS1985

Simplex finite element analysis of viscous incompressible flow with penalty function formulation

Viscous flow calculations are important for the determination of separated flows, recirculating flows, secondary flows and so on. This paper presents a penalty function approach for the finite element analysis of steady incompressible viscous flow. A simplex element is used with linear velocity and constant pressure in contrast to other works which usually employ higher order elements. Simplex elements yield analytical expressions for the element matrices which in turn lead to efficient solutions. Earlier works have partially indicated how constraint and lock-up problems might be avoided for simplex elements. This paper extends the earlier works by indicating the approach in detail and verifying that it is successful for several applications not discussed in the literature so far. Solution times and accuracy considerations are discussed for Couette flow, plane Poiseuille flow, a driven cavity problem, and laminar and turbulent flow over a step.

Allaire, P. E.↗
NASA NTRS1986

Dual throat thruster test results

Test results are presented for a dual throat thruster burning gaseous oxygen and hydrogen at primary (inner) chamber pressures from 380 to 680 psia. Heat flux profiles were obtained from calorimetric cooling channels in the inner nozzle, outer or secondary chamber and the tip of the inner nozzle. Data were obtained for two nozzle spacings over a chamber pressure ratio (secondary/primary) range of 0.45 to 0.83 with both chambers firing (Mode I). Fluxes near the end of the inner nozzle were significantly higher than in Mode II when only the inner chamber was fired, due to flow separation and recirculation caused by the back pressure imposed by the secondary chamber. As the pressure ratio increased, these heat fluxes increased and the region of high heat flux relative to Mode II extended farther upstream. The use of a gaseous hydrogen bleed flow in the secondary chamber to control heat fluxes in the primary plume attachment region was investigated in Mode II testing. A bleed flow of less than two percent of the primary chamber flow was required.

Ewen, R. L.↗
NASA NTRS1986

Turbulence energy and diffusion transport in a separating and reattaching flow

For accurate prediction of the turbulent flow in separated and reattaching regions, it is necessary to incorporate the second- and third-moments of turbulent fluctuations. The turbulence energy and the energy dissipation rate equations are modified by incorporating the second-order closure. Moreover, the third-order closure with near-wall correction is developed for the evaluation of the diffusive action of the second-moments. After comparison of the results with experimental data, it is shown that the models developed here improve the prediction of triple-velocity correlations in both recirculating and developing flow regions.

Amano, R. S.↗
NASA NTRS1986

Atomization and combustion characteristics of antimisting fuels using JT8D and air-boost injectors

The atomization levels of antimisting fuels are presently determined for a JT8D fuel injector, a low emission airblast JT8D injector, and an air-boost injector, at operating conditions simulating engine operating conditions. The effects of the use of antimisting kerosene (AMK) on component performance are also studied in the case of an in-service JT8D engine. The use of the AMK fuel causes a decline in the quality of the spray, most notably as a large increase in the Sauter mean diameter for all three injector types. In addition, the idle patternation data obtained indicate that the low emission injector fuel distribution changed from a hollow cone Jet A spray having no fuel at its center to a semihollow spray cone in the case of AMK; this change could disrupt the combustor primary zone recirculation pattern.

Kennedy, J. B.↗
NASA NTRS1985

Ground effect aerodynamics

The results of experimental and analytical studies on an isolated lifting rotor in ground effect at low advance ratios are discussed. The experiments show that the favorable effect of ground proximity in hover disappears rapidly with small increases in advance ratio. Two flow regimes occur, a recirculation of the rotor wake is present at the low end of the advance ratio range investigated and a ground vortex is formed as advance ratio increases, causing irregular changes in the hub moments with advance ratio. Experimental results also show that translational acceleration has a significant effect on the ground effect of a lifting rotor. Hot wire measurements of the flow field under the ratio in ground effect are also presented. The experimental data are analyzed to determine effective values of the inflow in ground effect.

Curtiss, H. C., Jr.↗
NASA NTRS1986

A single-board preprocessor and pulse generator

The Aeronomy Lab. of NOAA has designed and built a single board, programmable radar controller for use with VHF ST (stratosphere troposphere) radars. The controller consists of a coherent integrator preprocessor and a radar pulse generator, both of which are described, as well as interfaces to an antenna beam switch and a receiver bandwidth switch. The controller occupies a single slot in a Data General Nova of Eclipse computer. The integrator and pulse generator take advantage of high density, dual port FIFO chips such as the 512 x 9 Mostek MK 4501. These FIFOs have separate input and output ports and independent read and write cycles with cycle times of less than 200 ns, making them very fast and easy to interface. A simple block diagram of the coherent integrator is shown. The integrator is designed to handle inputs from one receiver (2 channels) with 1 sec sample spacing. The pulse generator is based on controllers designed by R. F. Woodman for the Arecibo and SOUSY radars us a recirculating memory scheme.

Carter, D. A.↗
NASA NTRS1984

Aerothermal modeling program, phase 2

The accuracy and utility of current aerothermal models for gas turbine combustors must be improved. Three areas of concern are identified: improved numerical methods for turbulent viscous recirculating flows; flow interaction; and fuel injector-air swirl characterization. Progress in each area is summarized.

Mularz, E. J.↗
NASA NTRS1984

Mass and Momentum Turbulent Transport Experiments

An experimental study of mixing downstream of axial and swirling coaxial jets is being conducted to obtain data for the evaluation and improvement of turbulent transport models currently employed in a variety of computational procedures used throughout the propulsion community. Effort was directed toward the acquisition of length scale and dissipation rate data that will provide more accurate inlet boundary conditions for the computational procedures and a data base to evaluate the turbulent transport models in the near jet region where recirculation does not occur. Mass and momentum turbulent transport data with a blunt inner-jet inlet configuration will also be acquired.

Johnson, B. V.↗
NASA NTRS1986

A description of the active and passive sidewall-boundary-layer removal systems of the 0.3-meter transonic cryogenic tunnel

Results are presented for an operational checkout and shakedown of the active sidewall-boundary-layer removal system newly installed in the Langley 0.3-meter Transonic Cryogenic Tunnel (0.3-m TCT). Prior to the installation of this active removal system, the sidewall-boundary layer was removed passively by exhausting directly to the atmosphere (i.e., no reinjection). With the active removal system using the reinjection compressor, the removal capability is greatly expanded to cover the entire operating envelope of the 0.3-m TCT. Details of the active removal system are presented including the compressor reinjection circuit, the compressor pressure ratio/surge control, and the compressor recirculation loop. The control logic and features of the compressor surge control are explained. Initial tests covering critical operating conditions show mass flow removal rates of about 5 percent at lower Mach numbers can be obtained with the active system. Measured performance characteristics of the compressor are presented. As part of the validation of the active system, limited airfoil tests were made using the new system.

Johnson, C. B.↗
NASA NTRS1986

Third-moment closure of turbulence for predictions of separating and reattaching shear flows: A study of Reynolds-stress closure model

A numerical study of computations in backward-facing steps with flow separation and reattachment, using the Reynolds stress closure is presented. The highlight of this study is the improvement of the Reynold-stress model (RSM) by modifying the diffusive transport of the Reynolds stresses through the formulation, solution and subsequent incorporation of the transport equations of the third moments, bar-u(i)u(j)u(k), into the turbulence model. The diffusive transport of the Reynolds stresses, represented by the gradients of the third moments, attains greater significance in recirculating flows. The third moments evaluated by the development and solution of the complete transport equations are superior to those obtained by existing algebraic correlations. A low-Reynolds number model for the transport equations of the third moments is developed and considerable improvement in the near-wall profiles of the third moments is observed. The values of the empirical constants utilized in the development of the model are recommended. The Reynolds-stress closure is consolidated by incorporating the equations of k and e, containing the modified diffusion coefficients, and the transport equations of the third moments into the Reynolds stress equations. Computational results obtained by the original k-e model, the original RSM and the consolidated and modified RSM are compared with experimental data. Overall improvement in the predictions is seen by consolidation of the RMS and a marked improvement in the profiles of bar-u(i)u(j)u(k) is obtained around the reattachment region.

Amano, R. S.↗
NASA NTRS1986

Advanced Gas Turbine (AGT) Technology Project

Engine testing, ceramic component fabrication and evaluation, component performance rig testing, and analytical studies comprised AGT 100 activities during the 1985 year. Ten experimental assemblies (builds) were evaluated using two engines. Accrued operating time was 120 hr of burning and 170 hr total, bringing cumulative total operating time to 395 hr, all devoid of major failures. Tests identified the generator seals as the primary working fluid leakage sources. Power transfer clutch operation was demonstrated. An alpha SiC gasifier rotor engine test resulted in blade tip failures. Recurring case vibration and shaft whip have limited gasifier shaft speeds to 84%. Ceramic components successfully engine tested now include the SiC scroll assembly, Si3N3 turbine rotor, combustor assembly, regenerator disk bulkhead, turbine vanes, piston rings, and couplings. A compressor shroud design change to reduce heat recirculation back to the inlet was executed. Ceramic components activity continues to focus on the development of state-of-the-art material strength characteristics in full-scale engine hardware. Fiber reinforced glass-ceramic composite turbine (inner) backplates were fabricated by Corning Glass Works. The BMAS/III material performed well in engine testing. Backplates of MAS material have not been engine tested.

Source record↗
NASA NTRS1986

Dual-throat thruster thermal model

The dual-throat engine is one of the dual nozzle engine concepts studied for advanced space transportation applications. It provides a thrust change and an in-flight area ratio change through the use of two concentric combustors with their throats arranged in series. Test results are presented for a dual throat thruster burning gaseous oxygen and hydrogen at primary (inner) chamber pressures from 380 to 680 psia. Heat flux profiles were obtained from calorimetric cooling channels in the inner nozzle, outer or secondary chamber and the tip of the inner nozzle. Data were obtained for two nozzle spacings over a chamber pressure ratio (secondary/primary) range of 0.45 to 0.83 with both chambers firing (Mode I). Fluxes near the end of the inner nozzle were significantly higher than in Mode II when only the inner chamber was fired, due to the flow separation and recirculation caused by the back pressure imposed by the secondary chamber. As the pressure ratio increased, these heat fluxes increased and the region of high heat flux relative to Mode II extended farther upstream. The use of the gaseous hydrogen bleed flow in the secondary chamber to control heat fluxes in the primary plume attachment region was investigated in Mode II testing. A thermal model of a dual throat thruster was developed and upgraded using the experimental data.

Ewen, R. L.↗
NASA NTRS1986

Estimation of absolute water surface temperature based on atmospherically corrected thermal infrared multispectral scanner digital data

Airborne remote sensing systems, as well as those on board Earth orbiting satellites, sample electromagnetic energy in discrete wavelength regions and convert the total energy sampled into data suitable for processing by digital computers. In general, however, the total amount of energy reaching a sensor system located at some distance from the target is composed not only of target related energy, but, in addition, contains a contribution originating from the atmosphere itself. Thus, some method must be devised for removing or at least minimizing the effects of the atmosphere. The LOWTRAN-6 Program was designed to estimate atmospheric transmittance and radiance for a given atmospheric path at moderate spectral resolution over an operational wavelength region from 0.25 to 28.5 microns. In order to compute the Thermal Infrared Multispectral Scanner (TIMS) digital values which were recorded in the absence of the atmosphere, the parameters derived from LOWTRAN-6 are used in a correction equation. The TIMS data were collected at 1:00 a.m. local time on November 21, 1983, over a recirculating cooling pond for a power plant in southeastern Mississippi. The TIMS data were analyzed before and after atmospheric corrections were applied using a band ratioing model to compute the absolute surface temperature of various points on the power plant cooling pond. The summarized results clearly demonstrate the desirability of applying atmospheric corrections.

Anderson, James E.↗
NASA NTRS1987

A Comparison of Experimental and Theoretical Results for Labyrinth Gas Seals

The basic equations are derived for a two control volume model for compressible flow in a labyrinth seal. The flow is assumed to be completely turbulent and isoenergetic. The wall friction factors are determined using the Blasius formula. Jet flow theory is used for the calculation of the recirculation velocity in the cavity. Linearized zeroth and first order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth order pressure distribution is found by satisfying the leakage equation. The circumferential velocity distribution is determined by satisfying the momentum equations. The first order equations are solved by a separation of variable solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients. The results of this analysis are compared to experimental test results.

Scharrer, Joseph Kirk↗
NASA NTRS1987

Flowfield measurements in a separated and reattached flat plate turbulent boundary layer

The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.

Patrick, William P.↗
NASA NTRS1987

A transport model of the turbulent scalar-velocity

Performance tests of the third-order turbulence closure for predictions of separating and recirculating flows in backward-facing steps were studied. Computations of the momentum and temperature fields in the flow domain being considered entail the solution of time-averaged transport equations containing the second-order turbulent fluctuating products. The triple products, which are responsible for the diffusive transport of the second-order products, attain greater significance in separating and reattaching flows. The computations are compared with several algebraic models and with the experimental data. The prediction was improved considerably, particularly in the separated shear layer. Computations are further made for the temperature-velocity double products and triple products. Finally, several advantages were observed in the usage of the transport equations for the evaluation of the turbulence triple products; one of the most important features is that the transport model can always take the effects of convection and diffusion into account in strong convective shear flows such as reattaching separated layers while conventional algebraic models cannot account for these effects in the evaluation of turbulence variables.

Amano, R. S.↗
NASA NTRS1987

Groundwater sapping channels: Summary of effects of experiments with varied stratigraphy

Experiments in the recirculating flume sapping box have modeled valley formation by groundwater sapping processes in a number of settings. The effects of the following parameters on sapping channel morphology were examined: surface slope; stratigraphic variations in permeability cohesion and dip; and structure of joints and dikes. These kinds of modeling experiments are particularly good for: testing concepts; developing a suite of distinctive morphologies and morphometries indicative of sapping; helping to relate process to morphology; and providing data necessary to assess the relative importance of runoff, sapping, and mass wasting processes on channel development. The observations from the flume systems can be used to help interpret features observed in terrestrial and Martian settings where sapping processes are thought to have played an important role in the development of valley networks.

Kochel, R. Craig↗