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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 181 records · Page 10

Effect of ratio of wall boundary layer thickness to jet diameter on mixing of a normal hydrogen jet in a supersonic stream

A preliminary experimental program was conducted to determine the effect of the ratio of the free-stream boundary-layer thickness to jet diameter on the secondary jet penetration and mixing rate. Tests were conducted on a flat plate in a Mach number 4.05 airflow with sonic injection of hydrogen normal to the free-stream direction from circular underexpanded injectors. The ratio of boundary-layer thickness to jet diameter ranged from 1.25 to 6.5. Previous correlations of mixing performance were modified to account for the effect of the ratio of boundary-layer thickness to jet diameter.

Mcclinton, C. R.↗

On the existence of debris clouds in the Space Station orbit: Final results of the EuroMir 1995 impact detector

A flight experiment flown onboard the Mir space station as a part of the Euromir 95 mission is considered. The aim of the experiment was to develop a greater understanding of the effects of the space environment on materials. In addition to the active enumeration of particle impacts and trajectories, the aim was to capture hypervelocity particles for their return to earth. Postflight measurements were performed to determine the flux density, diameters and subsequent effects on various optical thermal control and structural materials. Sensors actively measured the atomic oxygen flux, the contamination depostion and their effects during the mission. Two clouds of small particles were detected during a period of 100 days onboard Mir. It is concluded that the measured momenta of these particles suggests that their size and velocity are such that they cause damage to optics and thermal control surfaces.

Maag, Carl R.↗

Hollow cathode restartable 15 cm diameter ion thruster

The effects of substituting high perveance dished grids for low perveance flat ones on performance variables and plasma properties within a 15 cm modified SERT II thruster are discussed. Results suggest good performance may be achieved as an ion thruster is throttled if the screen grid transparency is decreased with propellant flow rate. Thruster startup tests, which employ a pulsed high voltage tickler electrode between the keeper and the cathode to initiate the discharge, are described. High startup reliability at cathode tip temperatures of about 500 C without excessive component wear over 2000 startup cycles is demonstrated. Testing of a single cusp magnetic field concept of discharge plasma containment is discussed. A theory which explains the observed behavior of the device is presented and proposed thruster modifications and future testing plans are discussed.

Wilbur, P. J.↗

Cold air performance of a 12.766-centimeter-tip-diameter axial-flow cooled turbine. 2: Effect of air ejection on turbine performance

An air cooled version of a single-stage, axial-flow turbine was investigated to determine aerodynamic performance with and without air ejection from the stator and rotor blades surfaces to simulate the effect of cooling air discharge. Air ejection rate was varied from 0 to 10 percent of turbine mass flow for both the stator and the rotor. A primary-to-air ejection temperature ratio of about 1 was maintained.

Haas, J. E.↗

Life analysis of multiroller planetary traction drive

A contact fatigue life analysis was performed for a constant ratio, Nasvytis Multiroller Traction Drive. The analysis was based on the Lundberg-Palmgren method for rolling element bearing life prediction. Life adjustment factors for materials, processing, lubrication and traction were included. The 14.7 to 1 ratio drive consisted of a single stage planetary configuration with two rows of stepped planet rollers of five rollers per row, having a roller cluster diameter of approximately 0.21 m, a width of 0.06 m and a weight of 9 kg. Drive system 10 percent life ranged from 18,800 hours at 16.6 kW (22.2 hp) and 25,000 rpm sun roller speed, to 305 hours at maximum operating conditions of 149 kw (200 hp) and 75,000 rpm sun roller speed. The effect of roller diameter and roller center location on life were determined. It was found that an optimum life geometry exists.

Coy, J. J.↗

Tribological evaluation of an Al2O3-SiO2 ceramic fiber candidate for high temperature sliding seals

A test program to determine the relative sliding durability of an alumina-silica candidate ceramic fiber for high temperature sliding seal applications as described. This work represents the first reporting of the sliding durability of this material system. Pin-on-disk tests were used to evaluate the potential seal material by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Friction was measured during the tests and fiber wear, indicated by the extent of fibers broken in the tow or bundle, was measured at the end of each test. Test variables studied included ambient temperatures from 25 C to 900 C, loads from 1.3 to 21.2 Newtons, and sliding velocities from 0.025 to 0.25 m/sec. In addition, the effects of fiber diameter, elastic modulus, and a pretest fiber heat treatment on friction and wear were measured. In most cases, wear increased with temperature. Friction ranged from about 0.36 at 500 C and low velocity (0.025 m/s) to over 1.1 at 900 C and high velocity (0.25 m/s). The pretest fiber heat treatment, which caused significant durability reductions for alumina-boria-silica ceramic fibers tested previously, had little effect on the alumina-silica fibers tested here. These results indicate that the alumina-silica (Al2O3-SiO2) fiber is a good candidate material system for high temperature sliding seal applications.

Dellacorte, Christopher↗

Investigation of air flow in open-throat wind tunnels

Tests were conducted on the 6-inch wind tunnel of the National Advisory Committee for Aeronautics to form a part of a research on open-throat wind tunnels. The primary object of this part of the research was to study a type of air pulsation which has been encountered in open-throat tunnels, and to find the most satisfactory means of eliminating such pulsations. In order to do this it was necessary to study the effects of different variable on all of the important characteristics of the tunnel. This paper gives not only the results of the study of air pulsations and methods of eliminating them, but also the effects of changing the exit-cone diameter and flare and the effects of air leakage from the return passage. It was found that the air pulsations in the 6-inch wind tunnel could be practically eliminated by using a moderately large flare on the exit cone in conjunction with leakage introduced by cutting holes in the exit cone somewhat aft of its minimum diameter.

Jacobs, Eastman N↗

The effect of an on-orbit near encounter on the number flux density of micron sized particles

Many materials and techniques have been developed by the authors to sample the flux of particles in Low Earth Orbit (LEO), and through regular insitu sampling of the flux in LEO, the materials and techniques have produced data which complement the data now being amassed by the Long Duration Exposure Facility (LDEF) research activities. Recent flight experiments on STS-32, STS-44, STS-46, and STS-52 have been conducted to develop an understanding of the spatial density as a function of size (mass) for particle sizes 1x10(exp -6) cm and larger. In addition to the enumeration of particle impacts, it was also the intent of these experiments that hypervelocity particles be captured and returned intact. Measurements were performed post-flight to determine the flux density, diameters, and subsequent effects on various optical, thermal control, and structural materials. During the course of the STS-44 mission, the Space Shuttle corrected its altitude by 26 km to evade a spent upper stage. The results of this near encounter suggests that a cloud of micron sized particles exist in the vicinity of the object. Data also suggest that the flux density is nearly two (2) orders of magnitude higher than background flux. A comparison of the number flux density along with microphotographs of the captured particles will be presented for the referenced shuttle flights.

Maag, Carl R.↗

Reduction of crossflow shock-induced separation with a porous cavity at supersonic speeds

The effectiveness of wing surface porosity in reducing boundary-layer separation induced by a cross flow shock on a conical wing in a supersonic flow was investigated in tests conducted in the NASA Langley Research Center Unitary Plan Wind Tunnel, at a Reynolds number of 2 mln/ft at Mach numbers 1.62, 1.70, 1.86, and 2.00 and with the angle of attack varying between -2 and 10 deg. A porous cavity was installed in a 57 deg swept conical wing at a location where a cross flow shock had been observed in previous tests. The porosity was varied from 11 to 22 percent, the pore hole diameter was varied from 0.025 to 0.050 in., and the cavity depth varied from 0.067 to 0.255 in. It was found that a hole of 0.025 in. in diameter is more effective than a 0.050-in. hole. However, the effectiveness of the larger holes could be increased by reducing the cavity depth, causing a closed-cavity type flow condition.

Bauer, Steven X. S.↗

HiPEP Ion Optics System Evaluation Using Gridlets

Experimental measurements are presented for sub-scale ion optics systems comprised of 7 and 19 aperture pairs with geometrical features that are similar to the HiPEP ion optics system. Effects of hole diameter and grid-to-grid spacing are presented as functions of applied voltage and beamlet current. Recommendations are made for the beamlet current range where the ion optics system can be safely operated without experiencing direct impingement of high energy ions on the accelerator grid surface. Measurements are also presented of the accelerator grid voltage where beam plasma electrons backstream through the ion optics system. Results of numerical simulations obtained with the ffx code are compared to both the impingement limit and backstreaming measurements. An emphasis is placed on identifying differences between measurements and simulation predictions to highlight areas where more research is needed. Relatively large effects are observed in simulations when the discharge chamber plasma properties and ion optics geometry are varied. Parameters investigated using simulations include the applied voltages, grid spacing, hole-to-hole spacing, doubles-to-singles ratio, plasma potential, and electron temperature; and estimates are provided for the sensitivity of impingement limits on these parameters.

Willliams, John D.↗

Effect of the space environment on materials flown on the EURECA/TICCE-HVI experiment

The primary benefit of accurately quantifying and characterizing the space environmental effects on materials is longer instrument and spacecraft life. Knowledge of the limits of materials allows the designer to optimize the spacecraft design so that the required life is achieved. Materials such as radiator coatings that have excellent durability result in the design of smaller radiators than a radiator coated with a lower durability coating. This may reduce the weight of the spacecraft due to a more optimum design. Another benefit of characterizing materials is the quantification of outgassing properties. Spacecraft which have ultraviolet or visible sensor payloads are susceptible to contamination by outgassed volatile materials. Materials with known outgassing characteristics can be restricted in these spacecraft. Finally, good data on material characteristics improves the ability of analytical models to predict material performance. A flight experiment was conducted on the European Space Agency's European Retrievable Carrier (EuReCa) as part of the Timeband Capture Cell Experiment (TICCE). Our main objective was to gather additional data on the dust and debris environments, with the focus on understanding growth as a function of size (mass) for hypervelocity particles 1E-06 cm and larger. In addition to enumerating particle impacts, hypervelocity particles were to be captured and returned intact. Measurements were performed post-flight to determine the flux density, diameters, and subsequent effects on various optical, thermal control and structural materials. In addition to these principal measurements, the experiment also provided a structure and sample holders for the exposure of passive material samples to the space environment, e.g., the effects of thermal cycling, atomic oxygen, etc. Preliminary results are presented, including the techniques used for intact capture of particles.

Maag, Carl R.↗

Effect of Subsonic Inlet Lip Geometry on Predicted Surface and Flow Mach Number Distributions

The effect of subsonic inlet lip geometry on predicted surface and flow Mach number distributions is illustrated. The theoretical results were obtained from incompressible potential flow calculations corrected for compressibility. The major emphasis of this investigation is on the low-speed (takeoff and landing) operating conditions. The low-speed results were obtained for a range of three geometric variables of interest: contraction ratio, defined as the ratio of highlight area to throat area; internal lip major - to minor-axis ratio; and internal lip shape. The low-speed results were obtained at both static conditions and a free-stream velocity of 42.6m/sec, with incidence angles ranging from 0 deg to 50 deg. The results indicate that of the three geometric variables considered, contraction ratio had the largest effect on the surface Mach number distributions. The effects of inlet diameter ratio and blunting of the external forebody on maximum external surface Mach numbers are illustrated at a cruise Mach number of 0.8.

Albers, J. A.↗

Boundary-layer analysis of subsonic inlet diffuser geometries for engines nacelles

Theoretical Mach number distributions and boundary-layer parameters are presented for subsonic nacelle inlet diffuser geometries with length to exit diameter ratios ranging from 0.4 to 1.6 and diffuser exit area to throat area ratios ranging from 1.1 to 2.0. The major portion of the study was done with a cubic diffuser contour with the inflection point at the midpoint of the diffuser, a diffuser throat Mach number of 0.6, and a free-stream Mach number of 0.12. Calculations were performed at both model (diffuser exit diameter, 30.5 cm) and full-scale (diffuser exit diameter, 183 cm) sizes. Separation limits were defined by establishing a separation boundary on plots of diffuser area ratio as a function of diffuser length to diameter ratio. The effects of diffuser contour, inlet lip geometry, and throat Mach number on the boundary-layer characteristics are illustrated. The major results of the study indicate that the separation boundary is shifted to greater area ratios by (1) increasing the diffuser length, (2) increasing the scale of the diffuser and, (3) moving the inflection point of the diffuser contour to or ahead of the midpoint of the diffuser.

Albers, J. A.↗

Wind tunnel tests of modified cross, hemisflo, and disk-gap-band parachutes with emphasis in the transonic range

Transonic wind-tunnel studies were conducted with modified cross, hemisflo, and disk-gap-band parachute models in the wake of a cone-cylinder shape forebody. The basic cross design was modified with the addition of a circumferential constraining band at the lower edge of the canopy panels. The tests covered a Mach number range of 0.3 to 1.2 and a dynamic pressure range from 479 Newtons per square meter to 5746 Newtons per square meter. The parachute models were flexible textile-type structures and were tethered to a rigid forebody with a single flexible riser. Different size models of the modified cross and disk-gap-band canopies were tested to evaluate scale effects. Model reference diameters were 0.30, 0.61, and 1.07 meters (1.0, 2.0, and 3.5 ft) for the modified cross; and nominal diameters of 0.25 and 0.52 meter (0.83 and 1.7 ft) for the disk-gap-band; and 0.55 meter (1.8 ft) for the hemisflo. Reefing information is presented for the 0.61-meter-diameter cross and the 0.52-meter-diameter disk-gap-band. Results are presented in the form of the variation of steady-state average drag coefficient with Mach number. General stability characteristics of each parachute are discussed. Included are comments on canopy coning, spinning, and fluttering motions.

Foughner, J. T., Jr.↗

Shock shapes on blunt bodies in hypersonic-hypervelocity helium, air, and CO2 flows, and calibration results in Langley 6-inch expansion tube

Shock shape results for flat-faced cylinders, spheres, and spherically blunted cones in various test gases, along with preliminary results from a calibration study performed in the Langley 6-inch expansion tube are presented. Free-stream velocities from 5 to 7 km/sec are generated at hypersonic conditions with helium, air, and CO2, resulting in normal shock density ratios from 4 to 19. Ideal-gas shock shape predictions, in which an effective ratio of specific heats is used as input, are compared with the measured results. The effect of model diameter is examined to provide insight to the thermochemical state of the flow in the shock layer. The regime for which equilibrium exists in the shock layer for the present air and CO2 test conditions is defined. Test core flow quality, test repeatability, and comparison of measured and predicted expansion-tube flow quantities are discussed.

Miller, C. G., III↗