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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 217 records · Page 12

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NASA NTRS1976

Acoustic radiation and surface pressure characteristics of an airfoil due to incident turbulence

The noise and unsteady surface pressure characteristics of an isolated airfoil in a uniform mean velocity, homogeneous, nearly isotropic turbulence field were investigated. Experiments were performed with a 23 cm chord, two-dimensional airfoil over a Mach number range of 0.1 to 0.5. Far-field noise spectra and directivity as well as surface pressure spectra and cross-spectra were obtained. Incident turbulence statistics were documented. Theory applied to predict far-field noise and surface pressure characteristics from measured inflow turbulence statistics showed good agreement with measurement. The theoretical formulation represents a first-principles solution providing absolute level prediction without recourse to empirical or adjustable constants, and takes into account compressibility as well as source noncompactness effects. All chordwise portions of the airfoil radiated directly to the far-field, the leading edge to the dominant noise producing region. The effect of angle of attack on noise and surface pressures is small. The interaction of incident turbulence of approximately 4 percent intensity with an airfoil was found to be a broadband noise source of high intensity relative to other noise sources.

Paterson, R. W.↗

NASA NTRS1977

A theory of sea scatter at large incident angles

Radar sea scatter at large incident angles (30 deg or greater) is investigated using a model which takes into account theoretically-calculated small- and large-scale wave perturbations as well as measured sea surface slope densities and sea spectra obtained from empirical observations. Effects of incident angle, polarization, frequency, wind speed and anisotropic characteristics of the sea surface may be studied by application of the model. In particular, it is found that the increase in backscattering coefficients with wind velocity is due primarily to the growth of the sea spectrum and secondarily to the interaction between small- and large-scale perturbations. Furthermore, differences in upwind and downwind observations may be attributed to anisotropic properties of the sea spectrum. Theoretical findings derived from the model are compared with experimental data, and good agreement is found.

Chan, H. L.↗

NASA NTRS1977

Performance analysis of grazing incidence imaging systems

An exact expression relating the coordinates of a point on the incident ray, a point of reflection from an arbitrary surface, and a point on the reflected ray is derived. The exact relation is then specialized for the case of grazing incidence, and first order and third order systematic analyses are carried out for a single reflective surface and then for a combination of two surfaces. The third order treatment yields a complete set of primary aberrations for single element and two element systems. The importance of a judicious choice for a coordinate system in showing field curvature to clearly be the predominant aberration for a two element system is discussed. The validity of the theory is verified through comparisons with the exact ray trace results for the case of the telescope.

Winkler, C. E.↗

NASA NTRS1977

Method of and means for testing a glancing-incidence mirror system of an X-ray telescope

An apparatus was designed for measuring the resolution and efficiency of a glancing-incidence mirror system having an even number of coaxial and confocal reflecting surfaces for use in an X-ray telescope. A collimated beam of X-rays is generated by an X-ray laser and directed along the axis of the system so that the beam is incident on the reflecting surfaces and illuminates a predetermined area. An X-ray detector, such as a photographic film, is located at the common focus of the surfaces so that the image produced by the X-rays may be compared with a test pattern interposed between the laser and the system.

Dailey, C. C.↗

NASA NTRS1977

Design, fabrication and performance of two grazing incidence telescopes for celestial extreme ultraviolet astronomy

The design and performance of grazing incidence telescopes for celestial extreme ultraviolet (EUV) astronomy are described. The telescopes basically consist of a star tracker, collimator, grazing incidence mirror, vacuum box lid, vacuum housing, filters, a ranicon detector, an electronics box, and an aspect camera. For the survey mirror a Wolter-Schwarzschild type II configuration was selected. Diamond-turning was used for mirror fabrication, a technique which machines surfaces to the order of 10 microns over the required dimensions. The design of the EUV spectrometer is discussed with particular reference to the optics for a primarily spectroscopic application and the fabrication of the f/10 optics.

Lampton, M.↗

NASA NTRS1978

Methods for calculating the transonic boundary layer separation for V/STOL inlets at high incidence angles

A semi-empirical scheme for the prediction of transonic pressure distribution on the surface of V/STOL inlets at high incidence angles has been developed. The investigation is intended to improve the boundary layer calculation and separation prediction by including the effects of shock wave-boundary layer interaction into the Lewis Inlet Viscous Computer Program. Wind-tunnel results and theoretical pressure calculation for critical cases are used in constructing the transonic pressure distribution. The program, which describes the development of the boundary layer and predicts the possible flow separation, can handle the cases of inlets at high incidence angles where local supersonic region may occur in the flow.

Chou, D. C.↗

NASA NTRS1979

Investigation of flexible nozzle wall-flutter incidents in the NASA-Ames Research Center 11- by 11-foot transonic wind tunnel

Twice during the spring of 1978, the two steel-plate 'flex-walls' that form the variable-geometry nozzle of the 11- by 11-foot tunnel at Ames Research Center experienced a severe dynamic instability. Both walls fluttered in the fundamental beam-bending mode and experienced stresses approaching the yield strength of the material. Both flutter incidents occurred at Mach numbers of about 1.15. The tunnel, operational for 24 years, had no history of such an instability. The cause of these flutter incidents, the steps taken to prevent a recurrence, and the requalification of the facility are described.

Erickson, L. L.↗

NASA NTRS1967

Review of the Lightning Strike Incident at Launch Complex 37 on July 27, 1967, and Comparison to a Gemini Lightning Strike

The Launch Complex 37 lightning strike of July 27, 1967, was reviewed and compared to a similar incident on the Gemini Program. Available data indicate little likelihood of damaging currents having been present in SA-204 Launch Vehicle or the ground equipment during the July 27th incident. Based on the results of subsystem and system testing after the strike, anticipated results of future testing, the six months elapsed time between the strike-and launch, and the fact that much of the critical airborne electrical/electronic equipment has been removed since the strike for other reasons, no new actions are considered necessary at this time in the Gemini case, significant failures occurred in both airborne and ground circuits. Due to the resultant semi, condlictor uncertainty, and the relatively' short time prior to planned launch, all critical airborne components containing semiconduetors were replaced, and a sophisticated data comparison task was implemented.

Llewellyn, J. A.↗

NASA NTRS1980

Analysis of general aviation single-pilot IFR incident data obtained from the NASA aviation safety reporting system

Data obtained from the NASA Aviation Safety Reporting System (ASRS) data base were used to determine problems in general aviation single pilot IFR operations. The data examined consisted of incident reports involving flight safety in the National Aviation System. Only those incidents involving general aviation fixed wing aircraft flying under IFR in instrument meteorological conditions were analyzed. The data were cataloged into one of five major problem areas: (1) controller judgement and response problems; (2) pilot judgement and response problems; (3) air traffic control intrafacility and interfacility conflicts; (4) ATC and pilot communications problems; and (5) IFR-VFR conflicts. The significance of the related problems, and the various underlying elements associated with each are discussed. Previous ASRS reports covering several areas of analysis are reviewed.

Bergeron, H. P.↗

NASA NTRS1979

Design of stigmatic grazing incidence telescopes with non-parabolic primaries

A two-mirror grazing-incidence telescope having a non-parabolic primary, and designed to be free of spherical aberration has been investigated. A method for determining the second surface equation is described, when the surface equation for one mirror is given. Application to grazing incidence systems such as used in X-ray and planed for EUV astronomy is discussed. Of special interest is the design of a secondary mirror when the hyperboloid of a conventional Wolter type I system is taken as the primary.

Winkler, C. E.↗

NASA NTRS1979

Solar radiation incident on the Martian surface

Calculations indicate that the maximum daily solar radiation reaching the Martian surface is about 325 cal/sq cm during southern hemisphere summer at latitude of about 40 deg S. In the ultraviolet region of the spectrum, the radiation reaching the surface at wavelengths greater than 2800 A is within 10% of the radiation incident on the atmosphere. There is significant extinction of radiation in the spectral region near 2500 A in mid and high latitudes due to absorption of radiation by ozone; radiation reaching the surface may be reduced to one one-thousandth of that incident on the atmosphere during winter. Virtually no radiation of wavelengths less than 1900 A reaches the surface because of absorption by the large column abundance of carbon dioxide. Daily and latitudinal distributions of radiation are presented for wavelengths of 3000, 2500 and 2000 A.

Kuhn, W. R.↗

NASA NTRS1981

Scale effects on turbulent boundary layer development and flow separation around V/STOL inlets at high incidence

Numerical methods for calculating laminar and turbulent boundary layers development around V/STOL engine inlets at high incidence angles, along with the procedures for predicting flow separation, are presented. Results of scale-effects, which are obtained by a numerical scaling procedure on the boundary layer characteristics and incidence angles at onset of separation are discussed. The interesting 'cross-over' phenomena, where the full-scale models actually exhibit earlier separation than the scaled-models, is illustrated for a typical V/STOL inlet at a certain operating condition. Some of the numerical results are compared with the existing wind-tunnel test data for a 1/6 scale inlet model to demonstrate the validity of the numerical approach.

Chou, D. C.↗

NASA NTRS1981

Flow separation in inlets at incidence angles

Wind-tunnel pressure data and flow pictures obtained for two two-dimensional inlet models have been examined to study the internal flow structure and separation at large incidence angles. The inlet models were 12-in. high (diffuser exit height) and had internal contraction ratio of 1.21 and 1.17. They were tested at low forward speeds over a wide range of throat Mach numbers (inlet mass flow rates) and angles of incidence. Characteristic features of the internal flow such as a drastic change of pressure gradient near the highlight, local separation bubbles and shock/boundary-layer interactions have been indicated and discussed. For a few specific cases, the experimental surface pressure distributions have been compared with theoretical predictions.

Jakubowski, A. K.↗

NASA NTRS1981

Effects of rotation and blade incidence on the properties of turbomachinery rotor wake

An experimental investigation of the effects of the speed of rotation on a turbomachinery rotor blade wake was conducted using a fan rotor in incompressible flow. Measurements were made at two different rotational speeds (1753 and 1010 rpm) but keeping the same blade loading. This was achieved by maintaining the same incidence angle to the rotor blades in both sets of measurements. The blade incidence angle was also varied to discern the effect of blade loading. A tri-axial hot wire probe mounted in a stationary frame of reference was used for the measurements made at several radial and axial stations in the near- and far-wake regions. The three dimensional mean velocity and turbulence profiles, the wake defect, wake decay rate, turbulence intensities and turbulence stresses are appreciably altered when the speed of rotation and the blade loading are changed. The wake defect is substantially reduced and the radial velocity increased when the rotational speed is increased.

Lakshminarayana, B.↗

NASA NTRS1983

Estimating Insolation Incident on Tilted Surfaces

ASHMET computer program estimates amount of solar insolation incident on surfaces of several types of solar collectors, including fixed-position flat-plate, monthly-tilt-adjusted flat-plat, beam-tracting, and fixed-azimuthtracker. Basic methodology employed in ASHMET is to use ASHRAE relationships to obtain clear-day total daily insolation incident on collector surface of representative day of each month of year. ASHMET is interactive program and prompts user for all required data.

Elkin, R. E.↗

NASA NTRS1982

Echelle spectrographs at grazing incidence

It is shown that by using the conical diffraction mount, existing echelle gratings can be used at grazing incidence to achieve high spectral resolution in the extreme UV and soft X rays. Design considerations for grazing incidence echelle spectrographs are examined, and two sample designs are discussed. The first, for use in the extreme UV, has a primary mirror and an entrance slit to the spectrograph. The system has a resolution of 10,000, operates at any wavelength longward of 100 A, and covers 30% of the spectrum at a single setting. The X-ray spectrograph uses objective gratings to obtain spectral resolution of 28,000 over any factor of 2 in. wavelength. It operates to wavelengths as short as 4 A.

Cash, W.↗

NASA NTRS1982

Wave scattering from a periodic dielectric surface for a general angle of incidence

Electromagnetic waves scattered from a periodic dielectric and perfectly conducting surface are studied for a general angle of incidence. It is shown that the one-dimensional corrugated surface can be solved by using two scalar functions: the components of the electric and magnetic fields along the row direction of the surface, and appropriate boundary conditions to obtain simple matrix equations. Results are compared to the case where the incident angle wave vector is perpendicular to the row direction. Numerical results demonstrate that energy conservation and reciprocity are obeyed for scattering by sinusoidal surfaces for the general case, which checks the consistency of the formalism.

Chuang, S. L.↗

NASA NTRS1982

Incidence angle considerations for spacecraft imaging radar

The value of radar imagery for most geologic applications is greatest when obtained with relatively large incidence angles. It is infeasible to attain these large angles from spacecraft altitudes. A study is being conducted to assess the usefulness of imagery collected at smaller angles. Radar image simulation is employed to create imagery for platform scenarios at numerous angles of incidence for specific geologic features. Preliminary analyses and results are provided.

Kaupp, V. H.↗