SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Temperature-control apparatus mixes pulses of liquid nitrogen into smoothly flowing nitrogen gas to produce flow of nitrogen gas at controlled low temperature. Mixing chamber provides turbulence, thermal mass, and thermal conductance to promote thermal and mechanical mixing of liquid and gaseous flows and thereby suppresses large transient deviations from set-point temperature.
The present experimental study was conducted in order to determine the existence of streamwise vortex meander in a mixing layer, and if present, its significance on the measured properties. The dependence of the velocity cross-correlation on the fixed probe location was shown to be a good indicator of the stationarity of the streamwise vortex location. The cross-correlation measurements obtained here indicate that spanwise meander is negligible, although transverse apparent meander (normal to the plane of the mixing layer) was indicated. The transverse meander, exemplified by the elliptical shape of the mean streamwise vorticity contours, was expected, since the streamwise vorticity in the braid region is essentially inclined, with respect to the streamwise direction. These conclusions were supported by results of estimated spanwise profiles of the transverse velocity component. The balance of evidence suggests that the measured mean streamwise vorticity decay is representative of the decay of the vorticity rather than an artifact of meander.
Experiments have been conducted to investigate the effect of fluid mixing on the depressurization of a large liquid hydrogen storage tank. The test tank is approximately ellipsoidal, having a volume of 4.89 m(exp 3) and an average wall heat flux of 4.2 W/m(exp 2) due to external heat input. A mixer unit was installed near the bottom of the tank to generate an upward directed axial jet flow normal to the liquid-vapor interface. Mixing tests were initiated after achieving thermally stratified conditions in the tank either by the introduction of hydrogen gas into the tank or by self-pressurization due to ambient heat leak through the tank wall. The subcooled liquid jet directed towards the liquid-vapor interface by the mixer induced vapor condensation and caused a reduction in tank pressure. Tests were conducted at two jet submergence depths for jet Reynolds numbers from 80,000 to 495,000 and Richardson numbers from 0.014 to 0.52. Results show that the rate of tank pressure change is controlled by the competing effects of subcooled jet flow and the free convection boundary layer flow due to external tank wall heating. It is shown that existing correlations for mixing time and vapor condensation rate based on small scale tanks may not be applicable to large scale liquid hydrogen systems.
Six headplate modules in a flame-tube combustor were evaluated. Unburned hydrocarbons, carbon monoxide, and oxides of nitrogen were measured for three types of fuel injectors both with and without a mixing venturi. Tests were conducted using jet A fuel at an inlet pressure of 0.69 megapascal, an inlet temperature of 478 K, and an isothermal static pressure drop of 3 percent. Oxides of nitrogen were reduced by over 50 percent with a mixing venturi with no performance penalties in either other gaseous emissions or pressure drop.
We report here on the details of the first, in situ, real-time measurements of H-1211 (CBrClF2) and sulfur hexafluoride (SF6) mixing ratios in the stratosphere up to 20 km. Stratospheric air was analyzed for these gases and others with a new gas chromatograph, flown aboard a National Aeronautics and Space Administration ER-2 aircraft as part of the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission conducted in 1994. The mixing ratio of SF6, with its nearly linear increase in the troposphere, was used to estimate the mean age of stratospheric air parcels along the ER-2 flight path. Measurements of H-1211 and mean age estimates were then combined with simultaneous measurements of CFC-11 (CCl3F), measurements of brominated compounds in stratospheric whole air samples, and records of tropospheric organic bromine mixing ratios to calculate the dry mixing ratio of total bromine in the lower stratosphere and its partitioning between organic and inorganic forms. We estimate that the organic bromine-containing species were almost completely photolyzed to inorganic species in the oldest air parcels sampled. Our results for inorganic bromine are consistent with those obtained from a photochemical, steady state model for stratospheric air parcels with CFC- I I mixing ratios greater than 150 ppt. For stratospheric air parcels with CFC-11 mixing ratios less than 50 ppt (mean age greater than or equal to 5 years) we calculate inorganic bromine mixing ratios that are approximately 20% less than the photo-chemical, steady state model. There is a 20% reduction in calculated ozone loss resulting from bromine chemistry in old air relative to some previous estimates as a result of the lower bromine levels.
The dual-pump coherent anti-Stokes Raman spectroscopy (CARS) method was used to measure temperature and the absolute mole fractions of N2, O2 and H2 in a supersonic non-reacting fuel-air mixing experiment. Experiments were conducted in NASA Langley Research Center s Direct Connect Supersonic Combustion Test Facility. Under normal operation of this facility, hydrogen and air burn to increase the enthalpy of the test gas and O2 is added to simulate air. This gas is expanded through a Mach 2 nozzle and into a combustor model where fuel is then injected, mixes and burns. In the present experiment the O2 of the test gas is replaced by N2. The lack of oxidizer inhibited combustion of the injected H2 fuel jet allowing the fuel/air mixing process to be studied. CARS measurements were performed 427 mm downstream of the nozzle exit and 260 mm downstream of the fuel injector. Maps were obtained of the mean temperature, as well as the N2, O2 and H2 mean mole fraction fields. A map of mean H2O vapor mole fraction was also inferred from these measurements. Correlations between different measured parameters and their fluctuations are presented. The CARS measurements are compared with a preliminary computational prediction of the flow.
The influence of shear layer excitation on the mixing of supersonic rectangular jets was studied experimentally. Two methods of excitation were used to control the jet mixing. The first used the natural screech of an underexpanded supersonic jet from a converging nozzle. The level of the screech excitation was controlled by the use of a pair of baffles located to block the acoustic feedback path between the downstream shock structure and the nozzle lip. A screech level variation of over 30 decibels was achieved and the mixing was completely determined by the level of screech attained at the nozzle lip. The second form of self-excitation used the induced screech caused by obstacles or paddles located in the shear layers on either long side of the rectangular jet. With sufficient immersion of the paddles intense jet mixing occurred and large flapping wave motion was observed using a strobed focused Schlieren system. Each paddle was instrumented with a total pressure tap and strain gages to determine the pressure and drag force on the square cross-section paddle. Considerable drag was observed in this initial exploratory study. Future studies using alternate paddle geometries will be conducted to maximize jet mixing with minimum drag.
An experimental investigation was conducted to determine the effect of bleed on a shock wave-boundary layer interaction in an axisymmetric mixed-compression supersonic inlet. The inlet was designed for a free-stream Mach number of 2.50 with 60-percent supersonic internal area contraction. The experiment was conducted in the NASA Lewis Research Center 10-Foot Supersonic Wind Tunnel. The effects of bleed amount and bleed geometry on the boundary layer after a shock wave-boundary layer interaction were studied. The effect of bleed on the transformed form factor is such that the full realizable reduction is obtained by bleeding of a mass flow equal to about one-half of the incident boundary layer mass flow. More bleeding does not yield further reduction. Bleeding upstream or downstream of the shock-induced pressure rise is preferable to bleeding across the shock-induced pressure rise.
The seventh long-duration expedition crew is currently in residence aboard International Space Station (ISS), continuing a permanent human presence in space that began in October 2000. During that time, expedition crews have been operators and subjects for 16 Human Life Sciences investigations, to gain a better understanding of the effects of long-duration space flight on the crew members and of the environment in which they live. Investigations have been conducted to study the radiation environment in the station as well as during extravehicular activity (EVA); bone demineralization and muscle deconditioning; changes in neuromuscular reflexes, muscle forces and postflight mobility; causes and possible treatment of postflight orthostatic intolerance; risk of developing kidney stones; changes in pulmonary function caused by long-duration flight as well as EVA; crew and crew-ground interactions; and changes in immune function. The experiment mix has included some conducted in flight aboard ISS as well as several which collected data only pre- and postflight. The conduct of these investigations has been facilitated by the Human Research Facility (HRF). HRF Rack 1 became the first research rack on ISS when it was installed in the US laboratory module Destiny in March 2001. The rack provides a core set of experiment hardware to support investigations, as well as power, data and commanding capability, and stowage. The second HRF rack, to complement the first with additional hardware and stowage capability, will be launched once Shuttle flights resume. Future years will see additional capability to conduct human research on ISS as International Partner modules and facility racks are added to ISS . Crew availability, both as a subject count and time, will remain a major challenge to maximizing the science return from the bioastronautics research program.
Chemical mixing laser investigations were conducted (1) to investigate the properties of a bimolecular exchange laser system pumped by the H + Cl2 yields HCl(v) + Cl reaction, initiated by arc-dissociated H2, with lasing occurring between wavelengths of 3.4 and 4.0 microns, and (2) to establish the feasibility of an atom recombination-transfer laser employing recombination of arc-dissociated nitrogen with subsequent transfer of vibrational energy to CO2 for lasing at 10.6 microns. One-dimensional analytical results indicate higher results should be obtained with up to v = 3 to 2 transitions participating. Diagnostic and analytical results show that the reaction mechanism during mixing, a back reaction of HCl(v) with H atoms, reaction of Cl with H2(v), moderately fast V-V, V-T processes, and possible HCl(o) initial contaminant level may explain the low performance. N2-CO2 thermal mixing laser studies were extended to measure the efficiency of transfer of recombination energy in such a nonequilibrium N2 source to 10.6 microns optical energy. The low level of efficiency suggests that V-T decay processes may prevent vibrational energy freezing until much lower temperatures are achieved and that trapping of energy in long-lived electronic excitation of N2 may be a factor.
Computational fluid dynamics analyses and experimental data are presented for the Mach 6 facility nozzle used in the Arc-Heated Scramjet Test Facility for the Enhanced Injection and Mixing Project (EIMP). This project, conducted at the NASA Langley Research Center, aims to investigate supersonic combustion ramjet (scramjet) fuel injection and mixing physics relevant to flight Mach numbers greater than 8. The EIMP experiments use a two-dimensional Mach 6 facility nozzle to provide the high-speed air simulating the combustor entrance flow of a scramjet engine. Of interest are the physical extent and the thermodynamic properties of the core flow at the nozzle exit plane. The detailed characterization of this flow is obtained from three-dimensional, viscous, Reynolds-averaged simulations. Thermodynamic nonequilibrium effects are also investigated. The simulations are compared with the available experimental data, which includes wall static pressures as well as in-stream static pressure, pitot pressure and total temperature obtained via in-stream probes positioned just downstream of the nozzle exit plane.
As part of the NASA Energy Efficient Engine program, scale-model performance tests of a mixed flow exhaust system were conducted. The tests were used to evaluate the performance of exhaust system mixers for high-bypass, mixed-flow turbofan engines. The tests indicated that: (1) mixer penetration has the most significant affect on both mixing effectiveness and mixer pressure loss; (2) mixing/tailpipe length improves mixing effectiveness; (3) gap reduction between the mixer and centerbody increases high mixing effectiveness; (4) mixer cross-sectional shape influences mixing effectiveness; (5) lobe number affects mixing degree; and (6) mixer aerodynamic pressure losses are a function of secondary flows inherent to the lobed mixer concept.
Experiments were conducted to explore the effects of vortex generators, in the form of tabs projecting normally into the jet, on the mixing and the far-field noise characteristics of a jet. A converging-diverging nozzle with a design Mach number of 1.36 was used in the experiments. The flow regimes from subsonic to highly underexpanded supersonic conditions were studied. One, two, and four tabs were used and some of the findings of previous investigators were examined and confirmed. The tabs eliminated screech noise from moderately overexpanded cases to highly underexpanded cases. Detailed flow visualizations and measurements showed that two tabs bifurcated the jet at all Mach numbers. While the effect of two tabs was persistent and the jet remained bifurcated, the distortions produced by one and four tabs disappeared by a streamwise distance of approximately 16 jet diameters. Two and four tabs significantly increased the entrainment of ambient air into the jet.
Thermal conductivity of multilayer and mixed powder high temperature insulation systems over wide temperature range and vacuum conditions
An investigation of vane-induced flow rotation to modify distorted steady-state total-pressure patterns in the subsonic diffuser of a supersonic mixed-compression inlet was conducted. Radial static-pressure gradients generated by the rotation was the mechanism used to modify the total-pressure distributions. Significant redistribution of circumferential distortion patterns into more compatible radial patterns was realized, but flow problems near the duct walls reduced the general effectiveness of the technique. Total-pressure losses associated with the swirl vanes were slight. Limited turbulence data indicated that vane istallation resulted in reduced turbulence levels.
Results of experimental tests conducted on a supersonic, mixed compression, axisymmetric inlet are presented. The inlet is designed for operation at Mach 2.5 with a turbofan engine (TF-30). The inlet was terminated with either a choked-orifice plate or a long pipe with variable area choked exit plug. Frequency responses were obtained for selected static pressures in the diffuser. These pressures were selected as potential control signals for terminal shock control. Frequency responses were obtained for the Mach 2 and 2.5 conditions for different terminations. Responses also were obtained with and without cowl bleed. Internal disturbances were produced by sinusoidally varying the inlet overboard bypass doors at frequencies out to 100 hertz.
The aerodynamic design of an inlet stage for a two-stage, 10/1 pressure ratio, 2 lb/sec flow rate compressor is discussed. Initially a performance comparison was conducted for an axial, mixed flow and centrifugal second stage. A modified mixed flow configuration with tandem rotors and tandem stators was selected for the inlet stage. The term conical flow compressor was coined to describe a particular type of mixed flow compressor configuration which utilizes axial flow type blading and an increase in radius to increase the work input potential. Design details of the conical flow compressor are described.
A performance test of several experimental afterburner configurations was conducted with a mixed-flow turbofan engine in an altitude facility. The simulated flight conditions were for Mach 1.4 at two altitudes, 12,190 and 14,630 meters. Turbine discharge temperatures of 889 and 1056 K were used. A production afterburner was tested for comparison. The research afterburners included partial forced mixers with V-gutter flameholders, a carburetted V-gutter flameholder, and a triple ring V-gutter flameholder with four swirl-can fuel mixers. Fuel injection variations were included. Performance data shown include augmented thrust ratio, thrust specific fuel consumption, combustion efficiency, and total pressure drop across the afterburner.