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Results for “Critical Velocity”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Aerodynamic performance of a ceramic-coated core turbine vane tested with cold air in a two-dimensional cascade

The aerodynamic performance of a core turbine vane with a ceramic coating was investigated experimentally in a two-dimensional cascade of 10 vanes. The vane was first tested with a rough coating and then retested after the coating had been smoothed. The test fluid was atmospheric air. The cascade tests covered a range of pressure ratios corresponding to ideal exit critical velocity ratios of 0.6 to 0.95. The principal measurements were cross-channel surveys of exit total pressure, static pressure, and flow angle. The results presented include exit survey results and overall performance in terms of flow angle, weight flow, and kinetic energy loss. The performance of the ceramic-coated vanes is compared with the performance of an uncoated vane having a similar profile.

Stabe, R. G.↗
NASA NTRS1976

Cold-air annular-cascade investigation of aerodynamic performance of core-engine-cooled turbine vanes. 2: Pressure surface trailing edge ejection and split trailing edge ejection

The aerodynamic performance of two trailing edge ejection cooling configurations of a core-engine stator vane were experimentally determined in an ambient inlet-air full-annular cascade where three-dimensional effects could be obtained. The tests were conducted at the design mean-radius ideal aftermixed critical velocity ratio of 0.778. Overall vane aftermixed thermodynamic and primary efficiencies were obtained over a range of coolant flows to about 10 percent of the primary flow at a primary to coolant total temperature ratio of 1.0. The radial variation in efficiency and the circumferential and radial variations in vane-exit total pressure were determined. Comparisons are made with the solid (uncooled) vane.

Mclallin, K. L.↗
NASA NTRS1975

Mass loss from the region of Mars and the asteroid belt

Models of the solar nebula suggest that the mass of solid matter which condensed in the region of Mars and the asteroids was much greater than the amount now present. Bombardment by a primordial population of asteroidal bodies originating near Jupiter's orbit could preferentially remove matter from this region, without significant effects in the earth's zone. A critical velocity exists, for which they can be ejected from the solar system by Jupiter. The minimum perihelion attainable at this velocity lies between the orbits of Mars and the earth. The lifetimes of Mars-crossing bodies are limited by collisions with Jupiter; earth-crossers are ejected on a much shorter time scale. The total bombardment flux was at least two orders of magnitude greater in the zone of Mars than in that of the earth. The flux at Venus and Mercury from this source was negligible.

Weidenschilling, S. J.↗
NASA NTRS1975

Structure and evolutionary history of the solar system

General principles and observational facts concerning the solar system are examined, taking into account the orbits of planets and satellites, the small bodies, the resonance structure, spin and tides, and postaccretional changes in the solar system. A description is given of the accretion of celestial bodies and the plasma phase is considered. Aspects of chemical differentiation and the matrix of the groups of bodies are also discussed, giving attention to chemical compositions in the solar system, meteorites and their precursor states, mass distribution and the critical velocity, and the structure of the groups.

Alfven, H.↗
NASA NTRS1977

Effect of endwall cooling on secondary flows in turbine stator vanes

The effect of endwall cooling on the secondary flow behavior and the aerodynamic performance of a core turbine stator vane was determined. The investigation was conducted in a cold-air, full-annular cascade, where three-dimensional effects were obtained. Two endwall cooling configurations were tested. In the first configuration, the cooling holes were oriented so that the coolant was injected in line with the inviscid streamline direction. In the second configuration, the coolant was injected at an angle of 15 deg to the inviscid streamline direction and oriented towards the vane pressure stator. In both cases the stator vanes were solid and uncooled so that the effect of endwall cooling was obtained directly. Total-pressure surveys were taken downstream of the stator vanes over a range of cooling flows at the design, mean-radius, critical velocity ratio of 0.778. Changes in the total-pressure contours downstream of the vanes were used to obtain the effect of endwall cooling on the secondary flows in the stator.

Goldman, L. J.↗
NASA NTRS1977

Recent activity in the moon; Proceedings of the Special Symposium, Houston, Tex., March 16, 1976

The papers review evidence for recent activity within the moon as manifested by lunar grid system, transient phenomena, moonquakes, and episodic emissions of radiogenic gases. Topics include a survey of lunar transient phenomena, possible causes of such phenomena, evidence that high-frequency seismic events may be shallow moonquakes, lunar seismicity and tectonics, a hypothesis on the nature of sites of lunar gas venting, and a search for sporadic gas emissions from the moon. Other contributions discuss the release of radiogenic argon-40 from the moon, radon-222 emission as an indicator of current activity on the moon, upper limits to gas emission from sites of lunar transient phenomena, physical processes that could produce transient changes on the lunar surface, critical-velocity gas-plasma interaction as a mechanism for lunar transient phenomena, and tidal triggering of moonquakes, transient phenomena, and radiogenic-gas emissions.

Runcorn, S. K.↗
NASA NTRS1977

Effect of coolant flow ejection on aerodynamic performance of low-aspect-ratio vanes. 2: Performance with coolant flow ejection at temperature ratios up to 2

The aerodynamic performance of a 0.5 aspect ratio turbine vane configuration with coolant flow ejection was experimentally determined in a full annular cascade. The vanes were tested at a nominal mean section ideal critical velocity ratio of 0.890 over a range of primary to coolant total temperature ratio from 1.0 to 2.08 and a range of coolant to primary total pressure ratio from 1.0 to 1.4 which corresponded to coolant flows from 3.0 to 10.7 percent of the primary flow. The variations in primary and thermodynamic efficiency and exit flow conditions with circumferential and radial position were obtained.

Hass, J. E.↗
NASA NTRS1977

Effect of endwall cooling on secondary flows in turbine stator vanes

An experimental investigation was performed to determine the effect of endwall cooling on the secondary flow behavior and the aerodynamic performance of a coreturbine stator vane. The investigation was conducted in a cold-air, full-annular cascade, where three-dimensional effects could be obtained. Two endwall cooling configurations were tested. In the first configuration, the cooling holes were oriented so that the coolant was injected in line with the inviscid streamline direction. In the second configuration, the coolant was injected at an angle of 15 deg to the inviscid streamline direction and oriented toward the vane pressure surface. In both cases the stator vanes were solid and uncooled so that the effect of endwall cooling could be obtained directly. Total-pressure surveys were taken downstream of the stator vanes over a range of cooling flows at the design, mean-radius, critical velocity ratio of 0.778. Changes in the total-pressure contours downstream of the vanes were used to obtain the effect of endwall cooling on the secondary flows in the stator. Comparisons were made between the two cooled-endwall configurations and with the results obtained previously for solid endwalls.

Goldman, L. J.↗
NASA NTRS1978

A cometary ionosphere model for Io

A source for the ionosphere of Io is proposed based on the assumption that the satellite is rather moonlike but continuously bombarded by intense fluxes of energetic particles, which makes its surface electrically conducting so that a significant Birkeland current is drawn up along magnetic field lines from Jupiter's ionosphere. It is suggested that the ion current is neutralized upon contact with Io's surface and that subsequent sputtering of this material from the surface supplies the satellite's neutral atmosphere. A model for the generation and maintenance of Io's ionosphere is outlined, according to which the structure of the ionosphere is determined by the impact of energetic trapped electrons from the Jovian magnetosphere and the ram pressure of the corotational magnetospheric wind. The first of these two processes provides the main ionization mechanism, while the second compresses the upstream (or 'nighttime') ionosphere via Alfven's critical-velocity phenomenon. It is concluded that Io's ionosphere is more nearly analogous to the coma and tail of a comet in the solar wind than to the earthlike case of a permanent gravitationally bound ionosphere.

Cloutier, P. A.↗
NASA NTRS1979

On the detection of lunar volatile emissions

This letter shows that the Apollo lunar-surface Suprathermal Ion Detection Experiment (SIDE) instruments lack the sensitivity to detect even large emissions of radiogenic gases from the moon if the venting of these gases occurs primarily at a few-well-defined sites of lunar transient phenomena (LTPs). It is suggested that specific flight instruments for the proposed ESA Polar Orbiting Lunar Observatory (POLO) mission, which could detect active venting, would help determine the energy source for LTPs and would increase knowledge of lunar geophysics. A critical-velocity model for the LTP energy source is briefly discussed.

Srnka, L. J.↗
NASA NTRS1981

The use of AntiMisting Kerosene (AMK) in turbojet engines

The effect of antimisting kerosene (AMK) flow characteristics on fan jet engines and the impact of degradation requirements on the fuel system was evaluated. It was determined from the present program that AMK fuel cannot be used without predegradation, although some degradation occurs throughout the fuel feed system, expecially in the fuel pumps. There is a tendency toward FM-9 AMK additive agglomeration and gel formation when the liquid flows at a critical velocity through very small passages. The data indicate this phenomenon to be a function of the degree of degradation, the passage size, the differential pressure, the fluid temperature, and the accumulated flow time. Additionally, test results indicate that the long term cumulative effects of this phenomenon may require more degradation than the theoretical requirement determined from short term tests.

Schmidt, H. W.↗
NASA NTRS1982

Laser anemometer measurements in an annular cascade of core turbine vanes and comparison with theory

Laser measurements were made in an annular cascade of stator vanes operating at an exit critical velocity ratio of 0.78. Velocity and flow angles in the blade to blade plane were obtained at every 10 percent of axial chord within the passage and at 1/2 axial chord downstream of the vanes for radial positions near the hub, mean and tip. Results are presented in both plot and tabulated form and are compared with calculations from an inviscid, quasi three dimensional computer program. The experimental measurements generally agreed well with these theoretical calculations, an indication of the usefulness of this analytic approach.

Goldman, L. J.↗
NASA NTRS1982

The electrothermal ramjet

An electrothermal ramjet configuration is examined as a possible alternative to rail guns and mass drivers for high acceleration launch missions. For a specific mission (earth escape) the idealized performance of the electrothermal ramjet, the electrothermal rocket and the electromagnetic acceleration system are compared. This comparison indicates that the gross performance of the ramjet compares favorably with that of the ideal electromagnetic acceleration system. A specific configuration for the ramjet is chosen and models for the dynamics, thermodynamics and fluid mechanics are presented. Results of calculations for a typical supersonic launch cycle suggest that pressure, temperature and power demand profiles associated with ramjet operation should be reasonable. A light gas gun is proposed to accelerate the vehicle to the critical velocity where efficient ramjet operation can begin. The theoretical performance of the ramjet is also shown to be substantially better than that of the light gas gun at high velocities.

Wilbur, P. J.↗
NASA NTRS1983

Incidence loss for fan turbine rotor blade in two-dimensional cascade

The effect of incidence angle on the aerodynamic performance of a fan turbine rotor blade was investigated experimentally in a two dimensional cascade. The test covered a range of incidence angles from -15 deg to 10 deg and exit ideal critical velocity ratios from 0.75 to 0.95. The principal measurements were blade-surface static pressures and cross-channel survey of exit total pressure, static pressure, and flow angle. Flow adjacent to surfaces was examined using a visualization technique. The results of the investigation include blade-surface velocity distribution and overall kinetic energy loss coefficients for the incidence angles and exit velocity ratios tested. The measured losses are compared with those from a reference core turbine rotor blade and also with two common analytical methods of predicting incidence loss.

Kline, J. F.↗
NASA NTRS1983

Impact damage resistance of flat glass/cellular glass solar mirror experimental panels

An attempt is made to characterize the hail-impact behavior of a solar concentrator structural material which consists of thin, second-surface silvered glass sheets bonded to structural support panels of cellular glass. The resulting glass/cellular glass panel can be described as a thin, brittle plate supported by an elastic foundation, with the adhesive bonding the two as a third component. The plate will bend during impact. Attention is experimentally given to how variations in the characteristics or geometry of the flat glass, adhesive and cellular glass affect hail-impact damage resistance. The critical energy needed to cause impact damage is calculated from the critical velocity of the iceball by means of the kinetic energy formula. The complexity of this structural system and the variability of the specimens render it impossible to completely develop an analytical treatment for the prediction of impact damage resistance.

Varner, J. R.↗
NASA NTRS1985

What determines the location of satellites and planets?

The discrete structural pattern in the distribution of the satellites and planets around their primaries has since its discovery been thought to hold the key to the origin and evolution of the solar system. Different attempts to rationalize this distribution are reviewed with emphasis on theories with foundation in verifiable physical processes. Foremost among these is the band structure theory, which relates the emplacement of interstellar dust and gas source material around the magnetized primarily to the critical velocity for ionization of the four major interstellar gas components. The uncertainties, that are inevitable in all reconstructions, are in this theory compensated by the support from precise manifestations of the 2/3 effect in the Saturnian ring system and in the asteroid belt, and by the reproduction of related phenomena in laboratory and space experiments.

Arrhenius, G.↗
NASA NTRS1985

Initial results of SEPAC scientific achievement

Electron beam injection of 5 keV, 300 mA (1.5 kW) and MPD arcjet plasma injection of 2 kJ/shot were successfully performed together with various kinds of diagnostic instruments including a high sensitivity TV camera observation in the Spacelab 1. Major scientific results obtained are studies of: (1) vehicle charge-up due to the electron beam emission and its neutralization by the MPD arcjet plasma; (2) beam-plasma interaction including the plasma wave excitation; (3) beam-atmosphere interaction such as the verification of critical velocity ionization effect; and (4) anomalous enhancement of ionization associated with a neutral gas injection into space.

Obayashi, T.↗
NASA NTRS1985

Rossby waves in opposing currents

A barotropic Rossby wave incident to a region of increasing mean flow velocity opposing the wave group velocity undergoes a reversal of direction at a stopping point where the mean flow velocity and local wave group velocities are equal and opposite. Incident wave amplitude increases approaching this stopping point, which may be referred to as a group velocity critical layer, but eventually suffers a decrease along its trajectory so that the reflected wave amplitude and energy tend to zero on approach to a phase velociy critical layer located where the opposing flow vanishes. Some applications of this process to observations of synoptic scale Rossby waves are suggested and an axample of the interaction of an incident wave with a barotropic model of the Hadley circulation is presented to illustrate these ideas.

Farrell, B.↗