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At least 1,189 records · Page 66

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NASA NTRS1976

Frequency modulation at a moving material interface and a conservation law for wave number

An integral conservation law for wave numbers is considered. In order to test the validity of the proposed conservation law, a complete solution for the reflection and transmission of an acoustic wave impinging normally on a material interface moving at a constant speed is derived. The agreement between the frequency condition thus deduced from the dynamic equations of motion and the frequency condition derived from the jump condition associated with the integral equation supports the proposed law as a true conservation law. Additional comparisons such as amplitude discontinuities and Snells' law in a moving media further confirm the stated proposition. Results are stated concerning frequency and wave number relations across a shock front as predicted by the proposed conservation law.

Kleinstein, G. G.↗

NASA NTRS1976

Results of wind tunnel RCS interaction tests on a 0.010-scale space shuttle orbiter model (51-0) in the Calspan Corporation 48-inch hypersonic shock tunnel (test 0A93)

A hypersonic shock tunnel test on a 0.010 scale SSV orbital configuration was performed to determine the effects of RCS jet/flow field interactions on SSV aerodynamic stability and control characteristics at various hypersonic Mach and Reynolds numbers. Flow field interaction data were obtained using pitch and roll jets. In addition, direct impingement data were obtained at a Mach number of zero with the test section pumped down to below 10 microns of mercury pressure.

Daileda, J. J.↗

NASA NTRS1976

Rock failure analysis by combined thermal weakening and water jet impact

The influence of preheating on the initiation of fracture in rocks subjected to the impingement of a continuous water jet is studied. Preheating the rock is assumed to degrade its mechanical properties and strength in accordance with existing experimental data. The water jet is assumed to place a quasi-static loading on the surface of the rock. The loading is approximated by elementary functions which permit analytic computation of the induced stresses in a rock half-space. The resulting stresses are subsequently coupled with the Griffith criteria for tensile failure to estimate the change, due to heating, in the critical stagnation pressure and velocity of the water jet required to cause failure in the rock.

Nayfeh, A. H.↗

NASA NTRS1976

Elasto-plastic impact of hemispherical shell impacting on hard rigid sphere

An analysis of plastic stress waves for cylindrical metallic projectile in impact is extended to an analysis of a hemispherical shell suffereing plastic deformation during the process of impact. It is assumed that the hemispherical shell with a prescribed launch velocity impinges a fixed rigid sphere of diameter equal to the internal diameter of the shell. The dynamic biaxial state of stress present in the shell during deformation is investigated. The analysis is valuable for studying the state of stress during large plastic deformation of a hemispherical shell.

Raftopoulos, D. D.↗

NASA NTRS1976

Shock wave-turbulent boundary layer interactions in transonic flow

The method of matched asymptotic expansions is used in analyzing the structure of the interaction region formed when a shock wave impinges on a turbulent flat plate boundary layer in transonic flow. Solutions in outer regions, governed by inviscid flow equations, lead to relations for the wall pressure distribution. Solutions in the inner regions, governed by equations in which Reynolds and/or viscous stresses are included, lead to a relation for the wall shear stress. Solutions for the wall pressure distribution are reviewed for both oblique and normal incoming shock waves. Solutions for the wall shear stress are discussed.

Adamson, T. C., Jr.↗

NASA NTRS1976

Calculation of a separated turbulent boundary layer

The properties of a Navier-Stokes solution of a shock-separated turbulent flow over a flat wall are investigated. Refinements of an algebraic relaxation turbulence model previously shown to be of value for the simulation of separated flows are presented. A simplified analysis applicable near an adiabatic wall is developed and used to help verify the accuracy of the numerical solution. Features of the time-dependent response of a turbulent boundary layer to shock impingement are presented.

Baldwin, B.↗

NASA NTRS1976

An analytical study of noise generation by subsonic flows in the presence of rigid surfaces

A general analytical method is developed for determination of the radiated noise field from highly sheared, subsonic flows in the presence of rigid surfaces. The method is specifically formulated to use measurable flow field properties as the basis input data for calculations. The governing equations of a viscous, incompressible fluid are employed to determine approximately the so-called shear noise source strength distribution in the flow. Mean rates of strain and fluctuating velocity covariances are the fundamental input data for calculations. The method is applied to the wall jet region of a circular jet impinging at 45 deg to an infinite plane surface. Velocity field measurements of Foss are used to describe the required flow properties. Comparisons of calculated results with measured surface pressures and sound pressure levels are given and discussed.

Wooley, J. P.↗

NASA NTRS1976

Calculation of the longitudinal aerodynamic characteristics of wing-flap configurations with externally blown flaps

A theoretical investigation was carried out to extend and improve an existing method for predicting the longitudinal characteristics of wing flap configurations with externally blown flaps (EBF). Two potential flow models were incorporated into the prediction method: a wing and flap lifting-surface model and a turbofan engine wake model. The wing-flap model uses a vortex-lattice approach to represent the wing and flaps. The jet wake model consists of a series of closely spaced vortex rings normal to a centerline which may have vertical and lateral curvature to conform to the local flow field beneath the wing and flaps. Comparisons of measured and predicted pressure distributions, span load distributions on each lifting surface, and total lift and pitching moment coefficients on swept and unswept EBF configurations are included. A wide range of thrust coefficients and flap deflection angles is considered at angles of attack up to the onset of stall. Results indicate that overall lift and pitching-moment coefficients are predicted reasonably well over the entire range. The predicted detailed load distributions are qualitatively correct and show the peaked loads at the jet impingement points, but the widths and heights of the load peaks are not consistently predicted.

Mendenhall, M. R.↗

NASA NTRS1976

Space shuttle contamination due to backflow from control motor exhaust

Spacecraft contamination of the space shuttle orbiter and accompanying Spacelab payloads is studied. The scattering of molecules from the vernier engines and flash evaporator nozzle after impingement on the orbiter wing surfaces, and the backflow of molecules out of the flash evaporator nozzle plume flow field due to intermolecular collisions in the plume are the problems discussed. A method was formulated for dealing with these problems, and detailed results are given.

Robertson, S. J.↗

NASA NTRS1976

Outdoor performance results for NBS Round Robin collector no. 1

The efficiency of a PPG flat-plate solar collector was evaluated utilizing an outdoor solar collector test facility at the NASA-Lewis Research Center, as part of the National Bureau of Standards 'round robin' collector test program. The correlation equation for collector thermal efficiency Eta curve fit of the data was: Eta = 0.666 - 1.003(Btu/hr-sq ft-F) Theta, where the parameter Theta is the difference between the average fluid temperature and the ambient temperature, all divided by the total flux impinging on the collector.

Miller, D. R.↗

NASA NTRS1977

Air cooling of disk of a solid integrally cast turbine rotor for an automotive gas turbine

A thermal analysis is made of surface cooling of a solid, integrally cast turbine rotor disk for an automotive gas turbine engine. Air purge and impingement cooling schemes are considered and compared with an uncooled reference case. Substantial reductions in blade temperature are predicted with each of the cooling schemes studied. It is shown that air cooling can result in a substantial gain in the stress-rupture life of the blade. Alternatively, increases in the turbine inlet temperature are possible.

Gladden, H. J.↗

NASA NTRS1977

Numerical solution for the temperature distribution in a cooled guide vane blade of a radial gas turbine

A two dimensional finite difference numerical technique is presented to determine the temperature distribution of an internal cooled blade of radial turbine guide vanes. A simple convection cooling is assumed inside the guide vane blade. Such cooling has relatively small cooling effectiveness at the leading edge and at the trailing edge. Heat transfer augmentation in these critical areas may be achieved by using impingement jets and film cooling. A computer program is written in FORTRAN IV for IBM 370/165 computer.

Hosny, W. M.↗

NASA NTRS1977

Sun direction detection system

One of the detectors is an illumination detector consisting of two spaced apart elongated strips with a strip of cadmium sulphide (Cds) deposited therebetween. Whenever the line image impinges the CdS strip, the resistance between the two other strips is relatively low, while being high when the line image is outside the field of view of the illumination detector. Also included is a sun angle detector which consists of a vapor deposited resistor strip connected at one end to plus 10v and at the other end to minus 10v. Spaced apart from the resistor strip is an elongated strip of low resistance material acting as an output strip, with a CdS strip between the two strips. When the line image is within the field of view of the sun angle detector, the output voltage at the output strip depends on the position of the line image across the sun angle detector.

Schmidt, L. F.↗

NASA NTRS1963

Spectral emissivity of metals after damage by particle impact

The reflectance, R, solar absorption, alpha, thermal emittance epsilon, and the alpha/epsilon ratio were determined for several metals before and after bombardment by high velocity microprojectiles. Observed decreases of 1 to 26 percent in the reflectance of various metals were apparently dependent on the amount of surface area damaged as well as on the velocity of the impinging projectiles. The thermal emittance was observed to increase more than the solar absorptance, which resulted in a net decrease in the alpha/epsilon ratio in all metals investigated except stainless steel 304. In the case of stainless steel 304, alpha and epsilon were observed to increase equally, resulting in an alpha/epsilon ratio apparently insensitive to microprojectile bombardment. Recommendations for the continuation of these investigations are outlined.

Laszlo, T. S.↗

NASA NTRS1977

Gregorian all-reflective optical system

An optical heterodyne receiver comprises a system of reflectors forming a folded Gregorian configuration for collecting a signal beam, and an optical detector located at the focus of the system. A paraboloidal primary reflector and an elipsoidal secondary reflector face each other on an optical axis with the focus of the secondary reflector coinciding with the focus of the primary reflector. An auxiliary laser generates a local oscillator beam that is combined with the signal beam after the signal beam emerges from the exit pupil (which is also the aperture stop) of the system, and the resultant is impinged on the detector. A pair of image motion compensators is located as close to the exit pupil as possible for aligning off-axis inputs to the detector.

King, W. L.↗

NASA NTRS1977

Comparison of jet Mach number decay data with a correlation and jet spreading contours for a large variety of nozzles

Small-scale circular, noncircular, single- and multi-element nozzles with flow areas as large as 122 sq cm were tested with cold airflow at exit Mach numbers from 0.28 to 1.15. The effects of multi-element nozzle shape and element spacing on jet Mach number decay were studied in an effort to reduce the noise caused by jet impingement on externally blown flap (EBF) STOL aircraft. The jet Mach number decay data are well represented by empirical relations. Jet spreading and Mach number decay contours are presented for all configurations tested.

Groesbeck, D. E.↗

NASA NTRS1977

High performance N2O4/amine elements: Blowapart

The mechanisms controlling hypergolic propellant reactive stream separation (RRS) were studied and used to develop design criteria for injectors free from both steady state RSS and cyclic propellant stream separation. This was accomplished through the analysis of single element injectors using N204/MMH propellants; the injectors were representative of the space shuttle orbit maneuvering engine and space tug applications. A gas phase/surface reaction mechanism which controls RSS was identified. Injector design criteria were developed, which defined a critical chamber pressure for those operating conditions above which RSS occurs. It was found that the amount of interfacial surface area at impingement is controlled by injector hydraulics.

Lawver, B. R.↗

NASA NTRS1976

Gasdynamics of the cryogenic cooler of the Nimbus F spacecraft

This paper presents a theoretical study of the gasdynamic behavior of the system used to vent methane gas from an open-cycle cryogenic cooler carried on the Nimbus F satellite. The flow of this gas from the cryogen tank to the vent-line exit takes place at very low Reynolds number, and is strongly affected by variations in the tube cross-sectional area, substantial heat addition, and important frictional effects. All three of these factors play a role in determining the choking mass flow. Finite-difference calculations are used to establish the mass flow rates for a range of cryogen temperatures. Finite-difference calculations are also used to determine the flowfield in the plume that results when the vented gas exits from the spacecraft. The momentum-flux distributions within the plume are then used to estimate the torques applied to the spacecraft when the plume impinges on several surfaces near the exit point. These torque estimates compare favorably with flight data.

Rae, W. J.↗