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Results for “Coefficient of performance”

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 595 records · Page 33

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NASA NTRS1985

Rolling, slip and traction measurements on low modulus materials

Traction and wear tests were performed on six low modulus materials (LMM). Three different traction tests were performed to determine the suitability of the material for use as traction rollers. These were the rolling, slip and endurance traction tests. For each material the combination LMM on LMM and LMM on steel were evaluated. Rolling traction test were conducted to determine the load - velocity limits, the rolling traction coefficient of the materials and to establish the type of failures that would result when loading beyond the limit. It was found that in general a simple constant rolling traction coefficient was enough to describe the results of all the test. The slip traction tests revealed that the peak traction coefficients were considerably higher than for lubricated traction contacts. The endurance traction tests were performed to establish the durability of the LMM under conditions of prolonged traction. Wear measurements were performed during and after the test. Energetic wear rates were determined from the wear measurements conducted in the endurance traction tests. These values show that the roller wear is not severe when reasonable levels of traction are transmitted.

Tevaarwerk, J. L.↗

NASA NTRS1970

Solid state bistable power switch

Tin and copper provide high current and switching time capabilities for high-current resettable fuses. They show the best performance for trip current and degree of reliability, and have low coefficients of thermal expansion.

Bartko, J.↗

NASA NTRS1972

Study of blade clearance effects on centrifugal pumps

A program of analysis, design, fabrication, and testing has been conducted to develop and experimentally verify analytical models to predict the effects of impeller blade clearance on centrifugal pumps. The effect of tip clearance on pump efficiency, and the relationship between the head coefficient and torque loss with tip clearance was established. Analysis were performed to determine the cost variation in design, manufacture, and test that would occur between unshrouded and shrouded impellers. An impeller, representative of typical rocket engine impellers, was modified by removing its front shroud to permit variation of its blade clearances. It was tested in water with special instrumentation to provide measurements of blade surface pressures during operation. Pump performance data were obtained from tests at various impeller tip clearances. Blade pressure data were obtained at the nominal tip clearance. Comparisons of predicted and measured data are given.

Hoshide, R. K.↗

NASA NTRS1969

Probabilistic-graphical and phenomenological analysis of combined bending-torsion fatigue reliability data

Fatigue data generated by three combined bending-torsion fatigue reliability research machines at The University of Arizona are probabilistic-graphically and phenomenologically analyzed. Distributions that are applicable to fatique life and static strength data are discussed. Phenomenological justifications for the use of these distributions are presented. It is found that the normal distribution represents the cycles-to-failure data at the highest stress levels best. The lognormal distribution appears to fit the cycles-to-failure data at the lower stress levels best and quite well at all stress levels including the highest. A regression analysis and least-squares goodness-of-fit test was performed for normal and lognormal plots. In most cases, the correlation coefficient gave a better fit to the data using the normal distribution, but the difference between the two was so slight that positive discrimination could not be made.

Kececioglu, D.↗

NASA NTRS1977

Documentation of GEMASS entry to touchdown simulation

The entry-to-touchdown space shuttle orbiter simulation capability incorporated into the GEMASS subprogram 33 (3-DOF) is documented. A digital autopilot interfaces between GEMASS and the guidance. Vehicle attitude is determined by use of the ability of GEMASS to integrate differential equations in addition to the equations of motion. Vehicle aerodynamic characteristics are obtained from an aerodynamic data tape and control surface deflections required to trim the vehicle, and trimmed aerodynamic coefficients are determined internally. Several indicators to allow evaluation of subsystem performance are included; as is the ability of the user to activate any of several error dispersion sources. The performance of the simulation compares well with more sophisticated simulations.

Waibel, R. H.↗

NASA NTRS1978

Flat-plate liquid solar collector

Report presents test procedures and results of program to obtain thermal performance data on liquid, incident-angle-modifier, heat-loss-coefficient, and stagnation tests.

Shih, K.↗

NASA NTRS1976

Summary of low-speed aerodynamic characteristics of upper-surface-blown jet-flap configurations

The results of recent wind tunnel investigations to provide fundamental information on the upper surface blown (USB) jet flap concept demonstrated that the USB concept provides good high-lift performance. It is shown that the low speed performance is dependent upon the jet turning angle and turning efficiency and on the use of proper leading and trailing edge treatment to prevent premature flow separation. The best means of achieving good turning performance in any particular USB application must be determined from overall operational considerations in which high speed performance, structures and noise, as well as low speed performance, are evaluated. The large diving moments generated at high lift coefficients can be trimmed satisfactorily with a large, conventional horizontal tail; a high tail position is best from longitudinal stability considerations. Large rolling and yawing moments are introduced with the loss of an engine, but these moments can be trimmed satisfactorily through the use of asymmetrical boundary layer control and through the use of spoiler and rudder deflection as needed.

Phelps, A. E., III↗

NASA NTRS1979

LDV measurements on propellers

Laser Doppler velocimeter (LDV) measurements of the flow velocity around high-efficiency propeller blades for high disk loading turboprop propulsion systems are reported. The wind-tunnel flow around sets of eight straight and swept propeller blades with the same twist and chord distributions was measured using a conventional two-color dual scatter LDV system. The measurements of the axial flow velocities a small distance in front of the propeller blade, between the blade row, and downstream of the propeller are shown to provide information necessary for the determination of overall performance, swirl angle distribution, blade loading distributions, local lift and drag coefficients, interference effects, shock location, local induced velocities, wake characteristics and stall pattern.

Sullivan, J. P.↗

NASA NTRS1981

Evaluation of a method for heat transfer measurements and thermal visualization using a composite of a heater element and liquid crystals

Commercially available elements of a composite consisting of a plastic sheet coated with liquid crystal, another sheet with a thin layer of a conducting material (gold or carbon), and copper bus bar strips were evaluated and found to provide a simple, convenient, accurate, and low-cost measuring device for use in heat transfer research. The particular feature of the composite is its ability to obtain local heat transfer coefficients and isotherm patterns that provide visual evaluation of the thermal performances of turbine blade cooling configurations. Examples of the use of the composite are presented.

Hippensteele, S. A.↗

NASA NTRS1981

Evaluation of a method for heat transfer measurements and thermal visualization using a composite of a heater element and liquid crystals

Hippensteele, S. A.↗

NASA NTRS1981

Erosion of Galilean satellite surfaces by Jovian magnetosphere particles

The effects on the surfaces of the Galilean satellites Europa, Ganymede and Callisto of impacts by particles of the Jupiter magnetosphere in which they are immersed are estimated. Differential ion fluxes measured by the Voyager low-energy magnetosphere particle analyzer as a function of ion energy were used to calculate ice erosion fluxes for the satellites under the assumption that each is 50% ice covered. Calculations were performed on the basis of laboratory data concerning the ice sputtering coefficients of protons and oxygen ions of various energies. A water erosion rate of greater than 10 to the 10th/sq cm per sec is obtained for Europa, which implies a total erosion over 1 billion years of an ice layer 100 m deep. Atmospheric column densities of the H2O molecules sputtered from the surface but not escaping the satellites are also calculated for the three satellites assuming a sputtered ion temperature of 2000 K, and are found to dominate those produced by sublimation. Finally, estimates are presented of the source and loss processes for an oxygen atmosphere around Ganymede created by sputtering or sublimation.

Johnson, R. E.↗

NASA NTRS1981

A study of model parameters associated with the urban climate using HCMM data

The use of infrared and visible data from the Heat Capacity Mapping Mission (HCMM) and in situ data to study the intensity of the urban heat island of Saint Louis is described. Analysis of HCMM data shows that an urban heat island exists day and night in all seasons when clear skies prevail. The lower albedo value of the urban region during the day suggests that the higher temperatures are due to more absorption of solar radiation. Preliminary analysis of in situ meteorological data was performed after merging with HCMM data, and surface roughness, the exchange coefficient, and the soil moisture were calculated.

Source record↗

NASA NTRS1986

Scaling of helicopter main rotor noise in hover

A 2.1-m-diam, one-sixth-scale model helicopter main rotor was tested in hover at the NASA Ames Outdoor Aerodynamic Research Facility. It had previously been tested in hover in the NASA Ames 40- by 80-Foot Wind Tunnel test section. The primary objective of the tests was to obtain acoustic and performance data on a medium-scale rotor at various thrust coefficients and tip Mach numbers to compare to similar existing data on a full-scale helicopter main rotor. Information is presented on the effects of thrust- and tip-speed variation, the effects of boundary-layer trip strips, and the effects of wind conditions. In addition, a preliminary evaluation of the scaling of helicopter main-rotor noise in hover is presented. A secondary objective was to contribute to a data base that will permit the estimation of facility effects on acoustic testing.

Kitaplioglu, C.↗

NASA NTRS1987

Maximum survival capability of an aircraft in a severe windshear

The performance of constant-alpha, maximum-alpha, constant-velocity, constant-absolute-inclination, constant-climb-rate, and constant-pitch (CP) vertical-plane guidance schemes for aircraft taking off under horizontal-windshear conditions with a downdraft is compared by means of numerical simulations; the results are presented in tables and graphs, and it is found that CP guidance gives the best aircraft survivability. Optimal, gamma-guidance, and simplified-gamma trajectories are then evaluated to improve the performance of CP, and the correct selection of the feedback gain coefficient and the time delay for response to windshear onset is shown to be of great importance for maximizing survivability.

Miele, A.↗

NASA NTRS1991

The NASA aircraft noise prediction program improved propeller analysis system

The improvements and the modifications of the NASA Aircraft Noise Prediction Program (ANOPP) and the Propeller Analysis System (PAS) are described. Comparisons of the predictions and the test data are included in the case studies for the flat plate model in the Boundary Layer Module, for the effects of applying compressibility corrections to the lift and pressure coefficients, for the use of different weight factors in the Propeller Performance Module, for the use of the improved retarded time equation solution, and for the effect of the number grids in the Transonic Propeller Noise Module. The DNW tunnel test data of a propeller at different angles of attack and the Dowty Rotol data are compared with ANOPP predictions. The effect of the number of grids on the Transonic Propeller Noise Module predictions and the comparison of ANOPP TPN and DFP-ATP codes are studied. In addition to the above impact studies, the transonic propeller noise predictions for the SR-7, the UDF front rotor, and the support of the enroute noise test program are included.

Nguyen, L. Cathy↗

NASA NTRS1992

A periodic moment method solution for TM scattering from lossy dielectric bodies with application to wedge absorber

The periodic moment method (PMM) solution for the scattering from two-dimensional lossy dielectric bodies is developed in this paper. The purpose is to design microwave wedge absorber for low reflectivity so that one can improve the performance of anechoic chamber measurements. With PMM, the reflection and transmission coefficients of periodically distributed bodies illuminated by a plane wave have been accurately calculated using a Cray Y-MP supercomputer. Through these studies, some wedge absorber configurations have been designed, fabricated, and then tested in the OSU/ESL compact range measurement facility. Two 8 in. commercial wedges, a curved wedge, and a four-layer wedge are studied in this paper. In all cases, good agreement between calculations and measurements has been obtained.

Yang, Chang-Fa↗

NASA NTRS1937

Full-scale Wind-tunnel and Flight Tests of a Fairchild 22 Airplane Equipped with External-airfoil Flaps

Wind-tunnel and flight tests have been made of a Fairchild 22 airplane equipped with a wing having external-airfoil flaps that also perform the function of ailerons. Lift, drag, and pitching-moment coefficients of the airplane with several flap settings, and the rolling- and yawing-moment coefficients with the flaps deflected as ailerons were measured in the full-scale tunnel with the horizontal tail surfaces and propeller removed. The effect of the flaps on the low speed and on the take-off and landing characteristics, the effectiveness of flaps when used as ailerons, and the forces required to operate them as ailerons were determined in flight. The wind-tunnel tests showed that the flaps increased the maximum lift coefficient of the airplane from 1.51 with the flap in the minimum drag position to 2.12 with the flap in the minimum drag position to 2.12 with the flap deflected 30 degrees. In the flight tests the minimum speed decreased from 46.8 miles per hour with the flaps up to 41.3 miles per hour with the flaps deflected. The required take-off run to attain a height of 50 feet was reduced from 820 to 750 feet and the landing run from a height of 50 feet was reduced from 930 to 480 feet. The flaps for this installation gave lateral control that was not entirely satisfactory. Their rolling action was good but the adverse yaw resulting from their use was greater than is considerable, and the stick forces required to operate them increased too rapidly with speed.

Reed, Warren D↗

NASA NTRS1994

Temperature dependence of ultraviolet absorption cross-sections of alternative hydrochlorofluorocarbons

Ultraviolet absorption cross-section of six alternative hydrochlorofluorocarbons (HCFC-21 HCFC-22, HCFC-123, HCFC-124, HCFC-141b and HCFC-142b1) have been measured between 170 and 260 nm for temperature ranging from 210 to 295 K. These data are compared with other available determinations performed at room temperature and their temperature dependence is discussed. Photodissociation coefficients are estimated and their temperature dependence is discussed. Impact of the photodissociation on the total atmospheric destruction of these compounds is illustrated.

Gillotay, D.↗