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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 235 records · Page 13

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NASA NTRS1978

Low-speed test limit of V/STOL model located vertically off-center

A vertically off-centered V/STOL model - a 2-ft-diam three-bladed aluminum propeller operating in a rotor mode - is tested in an 8 by 12 ft wind tunnel with and without ground plane along with an associated 3 by 4.5 ft test section insert. The objective was to assess the effect of the vertically off-centered model on the low-speed test limit. The aerodynamic data of the model at a constant negative angle of attack (-3 deg) are recorded at selected tunnel dynamic pressures to provide adequate data points to define the model lift variation with respect to the tip speed ratio. The adverse effect of the rotor low-speed test limit is observed in the form of lift change with respect to the tip speed ratio. A major conclusion is that for rotors tested with a ground plane or in the vicinity of the floor, the ratio of distance between floor and model to rotor radius defines the low-speed test limits.

Shindo, S.↗

NASA NTRS1979

Computer-assisted high-speed balancing of T53 and T55 power turbines

Standard overhaul procedures for U.S. Army helicopter engines require operational vibration acceptance testing after rebuild. Engines frequently experience vibrations which exceed allowable overhaul work requirement limits. The rework/retest cycle for these engines constitute a significant cost penalty to the overhaul center. This paper reviews both analytical and test data which indicate bending critical speeds within the operating speed range of the low-speed power turbine rotor as the cause of most test cell rejections. High-speed balancing techniques are applicable and are capable of significantly reducing this reject rate. A complete prototype computer-assisted high-speed balancing system for assembled T53 and T55 power turbine rotors is described.

Pojeta, T. J.↗

NASA NTRS1979

NASA low- and medium-speed airfoil development

The status of NASA low and medium speed airfoil research is discussed. Effects of airfoil thickness-chord ratios varying from 9 percent to 21 percent on the section characteristics for a design lift coefficient of 0.40 are presented for the initial low speed family of airfoils. Also, modifications to the 17-percent low-speed airfoil to reduce the pitching-moment coefficient and to the 21-percent low speed airfoil results are shown for two new medium speed airfoils with thickness ratios of 13 percent and 17 percent and design-lift coefficients of 0.30. Applications of NASA-developed airfoils to general aviation aircraft are summarized.

Mcghee, R. J.↗

NASA NTRS1980

Forward acoustic performance of a shock-swallowing high-tip-speed fan (QF-13)

Forward noise and overall aerodynamic performance data are presented for a high-tip-speed fan having rotor blade airfoils designed to alter the conventional leading-edge bow shocks to weak, oblique shocks which are swallowed within the interblade channels. It was anticipated that the swallowed shocks would minimize the generation of multiple-pure-tone noise. In the speed range where the shocks presumably were swallowed, the multiple-tone noise was lowered only about 3 decibels. Comparison with several high-speed fans on a thrust-corrected basis indicates that the present fan was the quietest in total forward noise at low speeds but offered no advantage at high speeds.

Lucas, J. G.↗

NASA NTRS1980

A numerical technique for calculation of the noise of high-speed propellers with advanced blade geometry

A numerical technique and computer program were developed for the prediction of the noise of propellers with advanced geometry. The blade upper and lower surfaces are described by a curvilinear coordinate system, which was also used to divide the blade surfaces into panels. Two different acoustic formulations in the time domain were used to improve the speed and efficiency of the noise calculations: an acoustic formualtion with the Doppler factor singularity for panels moving at subsonic speeds and the collapsing sphere formulation for panels moving at transonic or supersonic speeds. This second formulation involves a sphere which is centered at the observer position and whose radius decreases at the speed of sound. The acoustic equation consisted of integrals over the curve of intersection for both the sphere and the panels on the blade. Algorithms used in some parts of the computer program are discussed. Comparisons with measured acoustic data for two model high speed propellers with advanced geometry are also presented.

Nystrom, P. A.↗

NASA NTRS1980

Results of a low-speed wind tunnel test of the MDC 2.2M supersonic cruise aircraft configuration

Results of a low speed test conducted in the Full Scale Tunnel at NASA Langley using an advanced supersonic cruise vehicle configuration are presented. These tests used a 10 percent scale model of a configuration that had demonstrated high aerodynamic performance at Mach 2.2 during a previous test program. The low speed model has leading and trailing edge flaps designed to improve low speed lift to drag ratios at high lift and includes devices for longitudinal and lateral/directional control. The results obtained during the low speed test program have shown that full span leading edge flaps are required for maximum performance. The amount of deflection of the leading edge flap must increase with C sub L to obtain the maximum benefit. Over 80 percent of full leading edge suction was obtained up to lift off C sub L's of 0.65. A mild pitch up occurred at about 6 deg angle of attack with and without the leading edge flap deflected. The pitch up is controllable with the horizontal tail. Spoilers were found to be preferable to spoiler/deflectors at low speeds. The vertical tail maintained effectiveness up to the highest angle of attack tested but the tail on directional stability deteriorated at high angles of attack. Lateral control was adequate for landing at 72 m/sec in a 15.4 m/sec crosswind.

Yip, L. P.↗

NASA NTRS1980

Gravitational radiation and the ultimate speed in Rosen's bimetric theory of gravity

In Rosen's bimetric theory of gravity the (local) speed of gravitational radiation is determined by the combined effects of cosmological boundary values and nearby concentrations of matter. It is possible for the speed of gravitational radiation to be less than the speed of light. It is here shown that the emission of gravitational radiation prevents particles of nonzero rest mass from exceeding the speed of gravitational radiation. Observations of relativistic particles place limits on the speed of gravitational radiation and the cosmological boundary values today, and observations of synchroton radiation from compact radio sources place limits on the cosmological boundary values in the past.

Caves, C. M.↗

NASA NTRS1981

Unsteady fan blade pressure and acoustic radiation from a JT15D-1 turbofan engine at simulated forward speed

Tests have been conducted on a JT15D-1 turbofan engine both statically and at simulated forward speed in the Ames 12 x 24 Meter Wind Tunnel. Both far-field acoustic data and unsteady pressure data from transducers mounted on the fan blades were acquired. Results showed a sound power reduction of about 10 dB in the far-field acoustic levels with simulated forward speed over those measured without forward speed. Blade mounted transducer results showed rotor-turbulence interaction dominated the noise field at very low speeds while an interaction between the rotor and internal struts dominated at higher speeds. Results are presented to show the effects of varying engine rpm, changing the angle-of-attack of the engine inlet to tunnel flow and mounting an aircraft wing to simulate an installation condition on an actual aircraft.

Preisser, J. S.↗

NASA NTRS1981

Magnitude and frequency of wind speed shears from 3 to 150 meters

An analysis is presented of high resolution wind profile measurements recorded at the NASA 150-m ground winds tower facility, showing wind speed shear frequency and magnitude distributions for six vertical layers of the atmosphere and one vertical distance. Vertical wind shear is defined as the change of wind speed with height, and its magnitudes were derived by algebraically subtracting lower level wind speeds from those of higher levels and dividing the distance between levels. Horizontal wind shear is understood to be change of wind speed with horizontal distance, and its magnitudes were derived by algebraically subtracting the wind speed at a short tower from that at a tall one and dividing by the distance between towers.

Alexander, M. B.↗

NASA NTRS1981

Advanced superposition methods for high speed turbopump vibration analysis

The small, high pressure Mark 48 liquid hydrogen turbopump was analyzed and dynamically tested to determine the cause of high speed vibration at an operating speed of 92,400 rpm. This approaches the design point operating speed of 95,000 rpm. The initial dynamic analysis in the design stage and subsequent further analysis of the rotor only dynamics failed to predict the vibration characteristics found during testing. An advanced procedure for dynamics analysis was used in this investigation. The procedure involves developing accurate dynamic models of the rotor assembly and casing assembly by finite element analysis. The dynamically instrumented assemblies are independently rap tested to verify the analytical models. The verified models are then combined by modal superposition techniques to develop a completed turbopump model where dynamic characteristics are determined. The results of the dynamic testing and analysis obtained are presented and methods of moving the high speed vibration characteristics to speeds above the operating range are recommended. Recommendations for use of these advanced dynamic analysis procedures during initial design phases are given.

Nielson, C. E.↗

NASA NTRS1982

Summary and recent results from the NASA advanced High Speed Propeller Research Program

Advanced high-speed propellers offer large performance improvements for aircraft that cruise in the Mach 0.7 to 0.8 speed regime. The current status of the NASA research program on high-speed propeller aerodynamics, acoustics, and aeroelastics is described. Recent wind tunnel results for five 8- to 10-blade advanced models are compared with analytical predictions. Test results show that blade sweep was important in achieving net efficiencies near 80 percent at Mach 0.8 and reducing near-field cruise noise by dB. Lifting line and lifting surface aerodynamic analysis codes are under development and some initial lifting line results are compared with propeller force and probe data. Some initial laser velocimeter measurements of the flow field velocities of an 8-bladed 45 deg swept propeller are shown. Experimental aeroelastic results indicate that cascade effects and blade sweep strongly affect propeller aeroelastic characteristics. Comparisons of propeller near-field noise data with linear acoustic theory indicate that the theory adequate predicts near-field noise for subsonic tip speeds but overpredicts the noise for supersonic tip speeds. Potential large gains in propeller efficiency of 7 to 11 percent at Mach 0.8 may be possible with advanced counter-rotation propellers.

Mitchell, G. A.↗

NASA NTRS1984

The status of analytical preparation for 2-dimensional testing at high transonic speeds in the University of Southampton transonic self-streamlining wind tunnel

Validation data from the Transonic Self-Streamlining Wind Tunnel has proved the feasibility of streamlining two dimensional flexible walls at low speeds and up to transonic speeds, the upper limit being the speed where the flexible walls are just supercritical. At this condition, breakdown of the wall setting strategy is evident in that convergence is neither as rapid nor as stable as for lower speeds, and wall streamlining criteria are not always completely satisfied. The only major step necessary to permit the extension of two dimensional testing into higher transonic speeds is the provision of a rapid algorithm to solve for mixed flow in the imagery flow fields. The status of two dimensional high transonic testing in the Transonic Self-Streamlining Wind Tunnel is outlined and, in particular, the progress of adapting an algorithm, which solves the Transonic Small Perturbation Equation, for predicting the imagery flow fields is detailed.

Lewis, M. C.↗

NASA NTRS1984

An Automated Stall-Speed Warning System

The NASA Dryden Flight Research Facility embarked upon a project with the United States Army Aviation Engineering Flight Activity (USAAEFA) to develop and test a stall-speed warning system. NASA designed and built an automated stall-speed warning system which presents both airspeed and stall speed to the pilot. The airspeed and stall speed are computed in real time by monitoring the basic aerodynamic parameters {dynamic pressure, horizontal and vertical accelerations, and pressure altitude) and other parameters (elevator and flap positions, engine torques, and fuel flow). In addition, an aural warning at predetermined stall margins is presented to the pilot through a voice synthesizer. Once the system was designed and installed in the aircraft, a flight-test program of less than 20 hr was anticipated to determine the stall-speed software coefficients. These coefficients would then be inserted in the system's software and then test flown over a period of about 10 hr for the purposes of evaluation.

Pilot↗

NASA NTRS1983

An Automated Stall-Speed Warning System

The NASA Dryden Flight Research Facility embarked upon a project with the United States Army Aviation Engineering Flight Activity (USAAEFA) to develop and test a stall-speed warning system. NASA designed and built an automated stall-speed warning system which presents both airspeed and stall speed to the pilot. The airspeed and stall speed are computed in real time by monitoring the basic aerodynamic parameters (dynamic pressure, horizontal and vertical accelerations, and pressure altitude) and other parameters (elevator and flap positions, engine torques, and fuel flow). In addition, an aural warning at predetermined stall margins is presented to the pilot through a voice synthesizer. Once the system was designed and installed in the aircraft, a flight-test program of less than 20 hr was anticipated to determine the stall-speed software coefficients. These coefficients would then be inserted in the system's software and then test flown over a period of about 10 hr for the purposes of evaluation.

Dynamic Pressure↗

NASA NTRS1983

Solar wind iron abundance variations at speeds greater than 600 km/s, 1972-1976

An analysis has been conducted of the Fe/H ratios in the peaks of high-speed streams during the decline of solar cycle 20 and the following minimum (October 1972-December 1976). The response of the 50- to 200-keV ion channel of The Johns Hopkins University Applied Physics Laboratory energetic particle experiments (EPE) on IMP 7 and 8, which is (in the absence of energetic ions) dominated by solar wind iron ions at high solar wind speeds (V approximately equal to or greater than 600 km/s) as inferred from calibrations of flight spare detectors. The conducted Fe measurements have been compared with solar wind H and He parameters from the Los Alamos National Laboratory instruments on the same spacecraft. In general, the Fe distribution parameters (bulk velocity, flow direction, temperature) are found to be similar to the He parameters. Although the average Fe/H ratios found in the peaks of many steady high-speed streams agree within observational uncertainties with the nominal coronal ratio of 4.7 x 10 to the -5th, abundance variations of a factor of up to 6 are obtained across a given coronal-hole associated high-speed stream. There are, as well, a factor of 2 variations between stream-averaged abundances for recurrent high-speed streams emanating from different coronal holes occurring on the sun on the same solar rotation. Flare-related solar wind flows sometimes show Fe/H ratios enhanced by factors of 4-5 more than in coronal-hole associated, quiet-time streams, while in one case the Fe/H enhancement was still observable one rotation after the flare activity. Over the period 1973-1976, a steady decrease in the average quiet time Fe/H ratio by a factor of approximately 4 is measured on both IMP 7 and 8.

Mitchell, D. G.↗

NASA NTRS1984

Loss reduction in axial-flow compressors through low-speed model testing

A systematic procedure for reducing losses in axial-flow compressors is presented. In this procedure, a large, low-speed, aerodynamic model of a high-speed core compressor is designed and fabricated based on aerodynamic similarity principles. This model is then tested at low speed where high-loss regions associated with three-dimensional endwall boundary layers flow separation, leakage, and secondary flows can be located, detailed measurements made, and loss mechanisms determined with much greater accuracy and much lower cost and risk than is possible in small, high-speed compressors. Design modifications are made by using custom-tailored airfoils and vector diagrams, airfoil endbends, and modified wall geometries in the high-loss regions. The design improvements resulting in reduced loss or increased stall margin are then scaled to high speed. This paper describes the procedure and presents experimental results to show that in some cases endwall loss has been reduced by as much as 10 percent, flow separation has been reduced or eliminated, and stall margin has been substantially improved by using these techniques.

Wisler, D. C.↗

NASA NTRS1985

Design and lubrication of high-speed rolling-element bearings

The speed capability of rolling element bearings has increased from speeds of less than two million DN to speeds of three million DN. The life and reliability of these bearings also increased where they are equal to, or greater than, those of bearings with limited speed capability. Design parameters must be carefully chosen and optimized based upon sophisticated bearing computer programs. Material and lubricant selection must be integrated into the bearing design. Bearing thermal management must be implemented through proper lubrication and cooling. Parameters which can be used to design, specify, and lubricate high speed bearings are discussed.

Zaretsky, E. V.↗

NASA NTRS1985

On the determination of laminar flame speeds from stretched flames

The effects of stretch on the determination of the laminar flame speed are experimentally studied by using the positively-stretched stagnation flame and negatively-stretched bunsen flame, and by using lean and rich mixtures of methane, propane, butane, and hydrogen with air whose effective Lewis numbers are either greater or less than unity. Results demonstrate that flame speed determination can be influenced by stretch through two factors: (1) Preferential diffusion which tends to increase or decrease the flame temperature and burning rate depending on the effective Lewis number, and (2) Flow divergence which causes the flame speed to assume higher values when evaluated at the upstream boundary of the preheat zone instead of the reaction zone. Recent data on flame speed including the present ones are then examined from the unified viewpoint of flame stretch, leading to satisfactory resolution of the discrepancies between them. The present study also proposes a methodology of determining the laminar flame speeds by using the stagnation flame and linearly extrapolating the data to zero stretch rate.

Wu, C. K.↗