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At least 919 records · Page 51

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NASA NTRS1983

Aeroelastic analysis for propellers - mathematical formulations and program user's manual

Mathematical development is presented for a specialized propeller dedicated version of the G400 rotor aeroelastic analysis. The G400PROP analysis simulates aeroelastic characteristics particular to propellers such as structural sweep, aerodynamic sweep and high subsonic unsteady airloads (both stalled and unstalled). Formulations are presented for these expanded propeller related methodologies. Results of limited application of the analysis to realistic blade configurations and operating conditions which include stable and unstable stall flutter test conditions are given. Sections included for enhanced program user efficiency and expanded utilization include descriptions of: (1) the structuring of the G400PROP FORTRAN coding; (2) the required input data; and (3) the output results. General information to facilitate operation and improve efficiency is also provided.

Bielawa, R. L.↗

NASA NTRS1983

A possible explanation for the present difference between linear noise theory and experimental data for supersonic helical tip speed propellers

High speed turboprops are attractive candidates for future aircraft because of their high propulsive efficiency. However, the noise of their propellers may create a cabin environment problem for the aircraft powered by these propellers. The noise of some propeller models was measured, and predictions of the noise using a method based on the Ffowcs Williams-Hawkins equation were made. The predictions and data agree well at lower helical tip Mach numbers but deviate above Mach 1.0. Some possible reasons why the theory does not predict the data and focuses on improvement of the aerodynamic inputs as the most likely remedy are investigated. In particular, it is proposed that an increase in the drag and a decrease in the lift near the tip of the blade where the majority of the noise is generated, is warranted in the input to the theory.

Dittmar, J. H.↗

NASA NTRS1984

An experimental investigation of the effect of boundary layer refraction on the noise from a high-speed propeller

Models of supersonic propellers were previously tested for acoustics in the Lewis 8- by 6-Foot Wind Tunnel using pressure transducers mounted in the tunnel ceiling. The boundary layer on the tunnel ceiling is believed to refract some of the propeller noise away from the measurement transducers. Measurements were made on a plate installed in the wind tunnel which had a thinner boundary layer than the ceiling boundary layer. The plate was installed in two locations for comparison with tunnel ceiling noise data and with fuselage data taken on the NASA Dryden Jetstar airplane. Analysis of the data indicates that the refraction increases with: increasing boundary layer thickness; increasing free stream Mach number; increasing frequency; and decreasing sound radiation angle (toward the inlet axis). At aft radiation angles greater than about 100 deg there was little or no refraction. Comparisons with the airplane data indicated that not only is the boundary layer thickness important but also the shape of the velocity profile. Comparisons with an existing two-dimensional theory, using an idealized shear layer to approximate the boundary layer, showed that the theory and data had the same trends. Analysis of the data taken in the tunnel at two different distances from the propeller indicates a decay with distance in the wind tunnel at high Mach numbers but the decay at low Mach numbers is not as clear.

Dittmar, J. H.↗

NASA NTRS1983

Propeller tone bursts

Intense high frequency (25-38 kHz) tone bursts have been observed in acoustic tests of a scale model of a general aviation propeller. The amplitude of the tone burst is approximately equal to the amplitude of the propeller noise signature. The conditions necessary for the production of these tone bursts are described. The experiments indicate that the origin of these bursts is a periodic flow oscillation on the suction surface of the propeller blade tips which may be due to the interaction between an oscillating shock wave and a laminar boundary layer.

Succi, G. P.↗

NASA NTRS1984

Ignition characterization of the GOX/ethanol propellant combination

This paper describes the results of a study to define the ignition characteristics and thruster pulse mode capabilities of the GOX/ethanol propellant combination. Ignition limits were defined in terms of mixture ratio and cold flow pressure using a spark initiated torch igniter. Igniter tests were run over a wide range of cold flow pressure, propellant temperature and mixture ratio. The product of cold flow pressure and igniter chamber diameter was used to correlate mixture ratio regimes of ignition and nonignition. Engine ignition reliability and pulse mode capability were demonstrated using a 620 lbF thruster with an integrated torch igniter. The nominal chamber pressure and mixture ratio were 150 psia and 1.8, respectively, thruster tests were run over a wide range of chamber pressures and mixture ratios. The feasibility of thruster pulse mode operation with the non-hypergolic GOX/ethanol propellant combination was demonstrated.

Lawver, B. R.↗

NASA NTRS1985

Wingtip Vortex-Augmented Turbopusher Propeller Thrust

Thrust of propeller enhanced by tip vortex. Wingtip-Mounted Nacelle provides turboprop vortex velocity recovery. Thrust of turbopusher propeller increased by flow of lift-induced vortex. As result of weaker vortex, reduction in induced drag of wing afforded by propeller-wake mass injection into core of vortex, causing it to break down.

Patterson, J. C., Jr.↗

NASA NTRS1984

Propellant transfer: Tethered depot

Spacebasing of orbital transfer vehicles at a space station requires a depot that safely and efficiently stores and transfers the resupply propellants. In order to transfer propellants, a method effectively acquire only liquid and vent only gas must exist. A method that produces a low gravity to settle propellants would bypass these weaknesses, while allowing ground-like operations. This low gravity can be passively produced using gravity gradient techniques. A satellite with a large length to diameter ratio, such as a depot attached to a space station with a tether, stabilizes along on Earth radial because of an outward acceleration proportional to the distance from the satellite's center of gravity. Analysis indicates that liquid can be setteled with relatively short tether lengths. The feasibility, design requirements, and operational limitations of a tethered refueling depot were investigated with special emphasis on slosh control.

Kroll, K.↗

NASA NTRS1985

Towards a renewal of the propeller in aeronautics

The reasons for reconsidering the propeller for aircraft propulsion, the areas of application, and necessary developments are considered. Rising fuel costs and an increasing theoretical and experimental data base for turboprop engines have demonstrated that significant cost savings can be realized by the use of propellers. Propellers are well-suited to powering aircraft traveling at speeds up to Mach 0.65. Work is progressing on the development of a 150 seat aircraft which has a cruise speed of Mach 0.8, powered by a turboprop attached to an engine of 15,000 shp. Aeroelasticity analyses ae necessary in order to characterize the behavior of thin profile propfan blades, particularly to predict the oscillations through the entire functional range. High-power reducers must be developed, and the level of cabin noise must be controlled to less than 90 dB. Commercial applications are predicted for turboprops in specific instances.

Berger, D.↗

NASA NTRS1985

Compatibility experiments of facilities, materials, and propellants for electrothermal thrusters

Experiments were performed to determine the compatibility of materials and propellants for electro-thermal thrusters. Candidate propellants for resistojet propulsion include carbon dioxide, methane, hydrogen, ammonia, and hydrazine. The materials being examined are grain stabilized platinum for resistojets for Space station and rhenium for high performance resistojets for satellites. Heater mass loss and deterioration of materials were evaluated. A coiled tube of platinum, with yttria dispersed throughout the base material to inhibit grain growth, was tested in carbon dioxide at 1300 C for 2000 hr. Post-test examination indicated the platinum-yttria heater would last over 100 000 hr with less than 10 percent mass loss. Short-term compatibility tests were conducted to test the integrity of the platinum-yttria in hydrogen, methane, carbon dioxide/methane mixtures and ammonia environments. In each of these 100 hr tests, the platinum-yttria mass change indicated a minimum coil life of 100 000 hr. Facility related effects were investigated in materials tests using rhenium heated to high tempertures. Vacuum facility water reduction was monitored using a mass spectrometer. In vacuum environments obtained using only diffusion pumping and those obtained with the assistance of cryogenic equipment there were mass gains in the rhenium heaters. These mass gains were the result of the high amount of oxygen and water contained in the gas. Propellant purity and preferred test facility environments are discussed.

Whalen, M. V.↗

NASA NTRS1984

Tethered propellant resupply technique for space stations

One of the primary functions of the space station is related to the propellant resupply of orbital transfer vehicles, orbital maneuvering vehicles, and satellites. Difficulties arise in the case of an acquisition of cryogenic propellants by means of a use of zero-gravity techniques. The use of the 'tethered propellant resupply technique' is, therefore, considered. A study is being conducted to determine the feasibility, design requirements, and operational limitations of this technique. Attention is given to aspects of gravity feed, transfer method selection, requirements related to the orbital transfer vehicle, hazard clearance, attitude control, depot operations, end mass velocity, the microgravity laboratory, and concept evaluation activities.

Kroll, K. R.↗

NASA NTRS1986

Measuring Combustion Advance in Solid Propellants

Set of gauges on solid-propellant rocket motor with electrically insulating case measures advance of combustion front and local erosion rates of propellant and insulation. Data furnished by gauges aid in motor design, failure analysis, and performance prediction. Technique useful in determining propellant uniformity and electrical properties of exhaust plum. Gauges used both in flight and on ground. Foilgauge technique also useful in basic research on pulsed plasmas or combustion of solids.

Yang, L. C.↗

NASA NTRS1986

Circulation-Control Variable-Pitch Propeller

Circulation-control variable-pitch propeller has large lift value at moderate blowing coefficients. Based on circulation-control airfoil concept, has no moving parts other than needed for propeller rotation. Substituted for conventional variable-pitch propeller airfoil, lowers manufacturing costs, reduces maintenance, and improves reliability.

Garner, H. D.↗

NASA NTRS1985

Compatibility of grain-stabilized platinum with candidate propellants for resistojets

Resistojets are candidates for space station auxiliary propulsion, and should be characterized by both long life and multipropellant operations, requirements limited by available materials. Grain stabilized platinum is examined for use as a resistojet thruster material. Use of platinum in other applications indicates it can be used at moderately high temperatures for extended periods of time. Past results indicate that grain-stabilized platinum should be sufficiently inert in candidate propellant environments. Therefore, compatibility of platinum-yttria (P/Y2O3) and platinum-zirconia (Pt/ZrO2) with carbon dioxide, methane, hydrogen and ammonia is examined. A series of 1000 hr tests in CO2, H2, and NH3 is conducted at 1400 C and a series of 1000 hr tests in CH4 is conducted at about 500 C. Scanning electron microscopy, Auger electron spectroscopy and depth profiling analysis are then used to determine the effects of propellants on the material surface, to evaluate possible material contamination and to evaluate grain growth. The results indicate that there is carbon deposition on the surface of the Pt/Y2O3 and Pt/ZrO2 in both the CO2 and CH4 environments. In the H2 environment, the Pt/Y2O3 and Pt/ZrO2 specimen surfaces are roughened. After exposure to the NH3 environment, the Pt/Y2O3 and Pt/ZrO2 are roughened and pitted over the entire heated area with some pitted areas along the grain boundaries. SEM photos show grain growth in cross-sectional views of all the Pt/Y2O3 samples and the Pt/ZrO2 samples, except that tested in methane. Mass loss measurements indicate that Pt/Y2O3 and Pt/ZrO2 would last in excess of 200,000 hr in each propellant environment. However, in NH3 both Pt/Y2O3 and Pt/ZrO2 are severely pitted, with voids up to 50 percent into the material. Pt/Y2O3 and Pt/ZrO2 are not recommended for high temperature service in NH3.

Whalen, M. V.↗

NASA NTRS1985

Compatibility experiments of facilities, materials, and propellants for electrothermal thrusters

Experiments were performed to determine the compatibility of materials and propellants for electro-thermal thrusters. Candidate propellants for resistojet propulsion include carbon dioxide, methane, hydrogen, ammonia, and hydrazine. The materials being examined are grain stabilized platinum for resistojets for space station and rhenium for high performance resistojets for satellites. Heater mass loss and deterioration of materials were evaluated. A coiled tube of platinum, with yttria dispersed throughout the base material to inhibit grain growth, was tested in carbon dioxide at 1300 C for 2000 hr. Post-test examination indicated the platinum-yttria heater would last over 100,000 hr with less than 10 percent mass loss. Short-term compatibility tests were conducted to test the integrity of the platinum-yttria in hydrogen, methane, carbon dioxide/methane mixtures and ammonia environments. In each of these 100 hr tests, the platinum-yttria mass change indicated a minimum coil life of 100,000 hr. Facility related effects were investigated in materials tests using rhenium heated to high temperatures. Vacuum facility water reduction was monitored using a mass spectrometer. In vacuum environments obtained using only diffusion pumping and those obtained with the assistance of cryogenic equipment there were mass gains in the rhenium heaters. These mass gains were the result of the high amount of oxygen and water contained in the gas. Propellant purity and preferred test facility environments are discussed.

Whalen, M. V.↗

NASA NTRS1986

Experimental and Theoretical Study of Propeller Spinner/Shank Interference

A fundamental experimental and theoretical investigation into the aerodynamic interference associated with propeller spinner and shank regions was conducted. The research program involved a theoretical assessment of solutions previously proposed, followed by a systematic experimental study to supplement the existing data base. As a result, a refined computational procedure was established for prediction of interference effects in terms of interference drag and resolved into propeller thrust and torque components. These quantities were examined with attention to engineering parameters such as two spinner finess ratios, three blade shank forms, and two/three/four/six/eight blades. Consideration of the physics of the phenomena aided in the logical deduction of two individual interference quantities (cascade effects and spinner/shank juncture interference). These interference effects were semi-empirically modeled using existing theories and placed into a compatible form with an existing propeller performance scheme which provided the basis for examples of application.

Cornell, C. C.↗

NASA NTRS1980

Solid-propellant rocket motor internal ballistics performance variation analysis, phase 5

The results of research aimed at improving the predictability of internal ballistics performance of solid-propellant rocket motors (SRM's) including thrust imbalance between two SRM's firing in parallel are presented. Static test data from the first six Space Shuttle SRM's is analyzed using a computer program previously developed for this purpose. The program permits intentional minor design biases affecting the imbalance between any two SMR's to be removed. Results for the last four of the six SRM's, with only the propellant bulk temperature as a non-random variable, are generally within limits predicted by theory. Extended studies of internal ballistic performance of single SRM's are presented based on an earlier developed mathematical model which includes an assessment of grain deformation. The erosive burning rate law used in the model is upgraded and made more general. Excellent results are obtained in predictions of the performances of five different SRM's of quite different sizes and configurations. These SRM's all employ PBAN type propellants with ammonium perchlorate oxidizer and 16 to 20% aluminum except one which uses carboxyl terminated butadiene binder. The only non-calculated parameters in the burning rate equations that are changed for the different SRM's are the zero crossflow velocity burning rate coefficients and exponents. The results, in general, confirm the importance of grain deformation. The improved internal ballistic model makes practical development of an effective computer program for application of an optimization technique to SRM design which is also demonstrated. The program uses a pattern search technique to minimize the difference between a desired thrust-time trace and one calculated based on the internal ballistic model.

Sforzini, R. H.↗

NASA NTRS1985

MPD thruster performance - Propellant distribution and species effects

Previous research has shown that MPD thruster performance, as measured by thrust, specific impulse, and efficiency, is limited by a so-called 'onset' current level. Experimental results are presented which show that the onset current level varies with the radial position of mass injection. Specifically, mass injection into either of two zones results in drastically different performance for both argon and xenon propellants. This difference in performance is evidenced by the onset current levels, the onset V-J signatures, and the overall V-J characteristics. The behavior of the thruster with the total mass flow split between the two zones follows a transition between the zonal behavioral limits. The behavior of propellant mixtures also follows a transition between the behavior of the individual propellant species. The flow region between the two zones is characterized by a particle number density discontinuity, a large axial current density, and a large electron Hall parameter, suggesting a possible correlation between observed onset phenomena and a shear-flow discontinuity located in the region between the two zones.

Kelly, A. J.↗

NASA NTRS1986

An experimental investigation of propeller wakes using a laser Doppler velocimeter

The results of experimental investigations on three single rotation propellers are summarized in this paper. Force measurements showed a definite improvement in efficiency at low advance ratios and in static operation due to use of proplets. Extensive velocity measurements were made using a LDV system. The large amounts of data gathered are presented to reveal clearly the tip vortex streaming back from the propeller. The velocities were also processed using momentum theorem to obtain the thrust and power radial distributions as well as the integrated thrust and power coefficients. The thrust coefficient compared well with force measurements and theoretical prediction from vortex lattice and Goldstein analysis. However, the power coefficient calculated from the momentum analysis was consistently lower than the theoretical or measured values. The measured velocities were also used to compute the vorticity and the trajectory of the tip vortex in the wake behind the propeller.

Sundar, R. M.↗