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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Hingeless rotor vibration and loads at high advance ratio

Experimental values of mean and oscillatory shaft force aeroelastic derivatives with respect to cyclic pitch are presented in dimensionless coefficient form for stiff-bladed hingeless rotors operating at high advance ratio. Good agreement with theory is obtained for the 2P components, in rotating axes, of the oscillatory hub moment derivatives. Trends were predicted for the mean components. Experimental plots of the azimuthal distribution of blade flap bending moment due to cyclic pitch are compared with theoretical for high values of flap frequency ratio and advance ratio. Good agreement is found near the blade root. The similarity parameters that should be preserved in the scale model testing of stiff-bladed hingeless rotors at high advance ratio are reviewed, and some aspects of hingeless rotor wind tunnel testing are considered.

Watts, G. A.↗
NASA NTRS1974

Shock shapes of blunt bodies in hypersonic helium, air, and CO2 flows

A primary factor governing hypersonic flowfield characteristics of blunt vehicles entering planetary atmospheres is the normal shock density ratio. Hence, a means of duplicating or simulating the high density ratios experienced during planetary entry is needed. One facility having the capability of generating a range of hypersonic-hypervelocity flow conditions in arbitrary test gases is the expansion tube. Preliminary shock shape results obtained in the Langley 6-in. expansion tube at hypersonic conditions are presented. Normal shock density ratios from approximately 4 to 19 were generated using helium, air, and CO2 test gases at freestream velocities from 5 to 7 km/sec. Test models were a flat-faced cylinder and the Viking aeroshell.

Miller, C. G.↗
NASA NTRS1974

Development of the Viking Mars lander thermal control subsystem design

Two Viking spacecraft, each consisting of a lander capsule coupled to an orbiter, will be launched toward Mars during the summer of 1975. About a year later, the orbiters will go into orbit around Mars and the landers will descend to the surface for 90-day landed missions. The lander must withstand a wide variety of environmental and operational conditions during all phases of the mission, including prelaunch sterilization. On the surface of Mars, the lander internal temperatures must be controlled under widely varying thermal environments and atmospheric conditions. The lander thermal design is based on the maximum use of passive techniques and is integrated into the overall vehicle design and operation. The solutions to the unusual combinations of design problems and a summary of the results of full scale model testing under simulated mission conditions are presented.

Morey, T. F.↗
NASA NTRS1974

Performance of an inlet for an integrated scramjet concept

Review of the results of an experimental investigation of the performance of an inlet for an integrated scramjet engine concept at Mach 6. Following a description of the inlet design and test model, the Mach 6 experimental results obtained are presented in terms of integrated performance parameters.

Trexler, C. A.↗
NASA NTRS1974

The prediction of structural response to buffet flow: A state-of-the-art review

Certain aspects of the dynamic system being discussed are reviewed and important structural and aerodynamic quantities of the system are discussed. A theoretical model is presented which relates these quantities to each other. These quantities are then each, in turn, considered in terms of the state of the art of determining the quantities and in terms of areas where further research is needed. The similarity laws and scaling relationships applicable to determining buffet structural response are then discussed, and areas where simplification is required or may be permissible are mentioned. Finally, the various types of model tests pertinent to predicting response of the aircraft structure to buffet flow are discussed.

Hanson, P. W.↗
NASA NTRS1974

A new technique for inducing a turbulent boundary layer in a supersonic flow

The feasibility of using slot injection to establish a turbulent boundary layer corresponding to a known Reynolds number was investigated. The basic concept consists of injecting secondary air through a slot. The air is injected at the same local static pressure at a selected stagnation temperature to simulate a given up-stream heat conduction. The mass of the injected air is controlled to match a desired Reynolds number. Secondary air was injected through a supersonic nozzle over a flat plate model. Tests were conducted with different injection air conditions. Heat transfer rates were measured behind the slot and results were compared with theoretical estimates. Static pressure measurements were made over the surface in the streamwise direction. Velocity and Mach number profiles were determined downstream of the slot. Laminar and turbulent profiles were calculated to compare with the results of measurements. Experimental results indicate that this is an effective method for establishing a turbulent boundary layer having a prescribed value of R sub e Theta.

Miyazawa, M.↗
NASA NTRS1974

Shuttle extravehicular activity signal processor pulse amplitude modulation decommutator

To provide data with long-term stability and accuracy, the pulse amplitude modulation (PAM) decommutator was synchronized to the PAM-return to zero wavetrain, and each channel was sampled with a common sample and hold circuit and digitized sequentially. The digital value of each channel was then scaled by the digital value of the calibration channels. The corrected digital value of each channel was stored for one complete frame and then transferred to the multiplexer-demultiplexer at a high rate in one block of serial digital data. A test model was built to demonstrate this design approach taken for the PAM decom and performance data was provided. The accuracies obtained with various signal to noise ratios are shown.

Noble, D. E.↗
NASA NTRS1974

High-temperature earth-storable propellant acoustic cavity technology

Design criteria, methods and data, were developed to permit effective design of acoustic cavities for use in regeneratively cooled OME-type engines. This information was developed experimentally from two series of motor firings with high-temperature fuel during which the engine stability was evaluated under various conditions and with various cavity configurations. Supplementary analyses and acoustic model testing were used to aid cavity design and interpretation of results. Results from this program clearly indicate that dynamic stability in regeneratively cooled OME-type engines can be ensured through the use of acoustic cavities. Moreover, multiple modes of instability were successfully suppressed with the cavity.

Oberg, C. L.↗
NASA NTRS1975

Composite reinforced propellant tanks

Design studies involving weight and cost were carried out for several structural concepts applicable to space shuttle disposable tankage. An effective design, a honeycomb stabilized pressure vessel, was chosen. A test model was designed and fabricated.

Brown, L. D.↗
NASA NTRS1975

Effect of entry-lip design on aerodynamics and acoustics of high throat Mach number inlets for the quiet, clean, short-haul experimental engine

Results of scale model tests of high-throat-Mach-number inlets designed to suppress inlet-emitted engine machinery noise produced in a V/STOL wind tunnel are presented. A vacuum system was used to induce inlet airflow with a siren as a noise source. Inlet mass flow was 11.68 kilograms (25.75 lb. min) per second at a throat Mach number of 0.79. The effect of entry-lip design (contraction ratio and diameter ratio) on inlet total-pressure recovery, steady-state pressure distortion, performance at high incidence angles, and noise suppression was determined. With proper entry-lip design, total-pressure recovery in excess of 0.988 could be obtained statically at an average throat Mach number of 0.79. Total-pressure distortion was 5 percent. The reduction in the siren tone sound pressure level transmitted through the inlet was 10 to 14 db relative to that measured at throat Mach 0.6.

Miller, B. A.↗
NASA NTRS1975

Estimates of saltation threshold and erosion rates on Mars

The Mariner 9 photographs of the Martian surface include many which show crater-associated streaks caused by atmospheric winds. Due to the low density atmosphere of Mars, the wind speeds necessary to move surface particles and thus cause the streaks are apparently very high. The atmospheric-boundary-layer wind tunnel has been used to determine threshold speeds for particles of varying density and diameter and the results for small particles have been extrapolated to estimate somewhat lower threshold speeds on Mars than previous estimates. A series of streak modeling tests is used to derive an erosion-rate correlation function, which is in turn used to estimate erosion rates to the lee of some of the craters on Mars which exhibited time-dependent streak behavior during the mission.

Iversen, J. D.↗
NASA NTRS1975

A method for the evaluation of damage on the surface of carbon-carbon ablation samples

The effect of weave geometry on the onset of transition from laminar to turbulent flow around a sample of an orthogonally woven fine weave carbon-carbon material tested in an arc-jet is investigated. Seventeen post-test models which had undergone only partial transition around the circumference were examined as to location of turbulent regions relative to the weave axes. It was statistically shown that the weave axes had the lowest probability of being a position of initial transition onset. The probability generally increased with distance from a major axis, with some rays, notably the 45 deg rays, showing better transition resistance than the adjacent rays. The incidence of initial transition onset correlated well with the number of X or Y fibers that the flow passes over from stagnation point to the shoulder.

Heinonen, E. W.↗
NASA NTRS1976

Three dimensional thrust chamber life prediction

A study was performed to analytically determine the cyclic thermomechanical behavior and fatigue life of three configurations of a Plug Nozzle Thrust Chamber. This thrust chamber is a test model which represents the current trend in nozzle design calling for high performance coupled with weight and volume limitations as well as extended life for reusability. The study involved the use of different materials and material combinations to evaluate their application to the problem of low-cycle fatigue in the thrust chamber. The thermal and structural analyses were carried out on a three-dimensional basis. Results are presented which show plots of continuous temperature histories and temperature distributions at selected times during the operating cycle of the thrust chamber. Computed structural data show critical regions for low-cycle fatigue and the histories of strain within the regions for each operation cycle.

Armstrong, W. H.↗
NASA NTRS1976

Experiments with a self-correcting wind tunnel

The feasibility of controlling the flow actively through the walls of a transonic, porous wall wind tunnel in order to minimize wall interference effects on a test model is demonstrated. The method is based upon measuring the components of the disturbance velocity at discrete points along an imaginary surface in the flow field within the tunnel. A mathematical formulation of the flow field exterior to the surface including the boundary condition for unconfined flow, i.e., that all disturbance vanish at infinite, is used to determine if these measured velocity components are consistent with that boundary condition. If they are not, the theory provides a better approximation to the velocity component for unconfined flow, and the flow through the tunnel walls is readjusted iteratively until the measured quantities are consistent with unconfined flow. A brief review of theoretical methods is followed by a description of the Calspan self correcting wind tunnel design and operation, calibration with and without active wall control. Typical results obtained by approximating a conventional porous wall wind tunnel for an 0012 airfoil show that active wall control largely reproduces the correct shock wave position, eliminates wall interference of lift and drag, and reduces the interference effects on pitching moment to 10%.

Vidal, R. J.↗
NASA NTRS1976

A methodology for producing reliable software, volume 1

An investigation into the areas having an impact on producing reliable software including automated verification tools, software modeling, testing techniques, structured programming, and management techniques is presented. This final report contains the results of this investigation, analysis of each technique, and the definition of a methodology for producing reliable software.

Stucki, L. G.↗
NASA NTRS1976

Aeroelastic stability and control of an oblique wing

Dynamic model tests were staged to compare the aeroelastic stability of a free-flying oblique-winged aircraft and the known divergent instability characterizing swept-forward wing configurations, to test the effect of wing elasticity on aileron control and trim. The aircraft fuselage was clamped in some tests and left free to roll in others. Two rigid wing panels were hinged near the wing center with elastic restraining springs. It is found that the aeroelastic divergence affecting swept-forward wings does not occur with an oblique wing, whose aeroelastic instability sets in at a dynamic pressure exceeding that for static divergence of swept-forward wings, and appears in the form of undamped oscillations. Oblique wing stability is sensitive to the moment of inertia of the fuselage in roll. Roll control and lateral trim are attainable with conventional ailerons, even at speeds at which divergence of a clamped forward wing shows up.

Jones, R. T.↗
NASA NTRS1976

Coannular nozzle noise characteristics and application to advanced supersonic transport engines

Recent programs in the field of jet noise, sponsored by the NASA Lewis Research Center, have indicated that the variable stream control engines (VSCE) which are being considered for advanced supersonic cruise aircraft have inherent jet noise advantages over earlier engines. This characteristic is associated with the exit velocity profile produced by such an engine. The high velocity fan stream, on the outer periphery, is acoustically dominant while the primary stream is held to a low velocity and therefore contributes little to the overall noise. Scale model tests have indicated low noise levels. Operation under static conditions, as well as in a relative velocity field (simulating take-off speeds) has indicated large reductions are available from the coannular nozzle and the VSCE. The inherently low levels of jet noise prompted changes in the cycle, which allowed an increase in the amount of augmentation incorporated in the fan stream, without exceeding the suggested noise guidelines, thereby allowing the use of a considerably smaller engine, with obvious vehicle advantages.

Kozlowski, H.↗
NASA NTRS1976

Coannular plug nozzle noise reduction and impact of exhaust system designs

Reducing the noise generated by high velocity jets has confronted engine designers and acoustics workers alike for the past fifteen years. Some of the jet noise suppressor configurations that are investigated are shown. With the exception of the early CJ-805 daisy suppressor nozzle which found successful application on the Convair 990 airplane, the others were developmental hardware at different stages of the effort in the past eight years - all aiming at potential supersonic cruise aircraft applications. Some significant progress was made as the result of work supported by NASA and FAA in the past two to three years. This work pertains to the concept demonstration and scale model testing of coannular plug nozzles with inverted velocity profile, and to the preliminary study of its application to advanced variable cycle engines (VCE) appropriate for supersonic cruise aircraft.

Lee, R.↗