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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Influence of the number of vehicles in the emergence of sound events on the annoyance expressed - experimental study

The acoustical index leg was studied to determine its accuracy in predicting annoyance from traffic noise. Annoyance was tested in experimental situations where the frequency of the number of heavy vehicles varied from 3 to 30 HV/30 min for different classes of the Leg level at 50, 55, 60 dB(A) of traffic noise. The results showed that: (1) for a constant Leg level the annoyance increases as a function of the number of HV up to a certain threshold at which the annoyance is stabilized; (2) for a constant frequency of passage of HV, the annoyance increases with the Leg level; (3) composite indexes of the type Leg + Log NHV, L1 + EMER or L1 + L10 give a predictive value greater than that of the Leg pr Log nHV taken alone.

Vallet, M.↗
NASA NTRS1982

Experimental investigation of two nonaxisymmetric wedge nozzles at free stream Mach numbers up to 1.20

Forces and pressures on two nonaxisymmetric wedge nozzles were measured in a 16 foot transonic tunnel. Tests were conducted at static conditions and at free stream Mach numbers of 0.60, 0.80, 0.90, 0.94, and 1.20. The range of nozzle pressure ratios varied with configuration and Mach number. The internal and external geometry of the nozzles and the test model are defined in detail. Nozzle performance data are presented as discharge coefficients, internal thrust ratios, thrust minus nozzle drag ratios, and ideal thrust coefficients. Extensive internal and external pressure measurements are presented.

Mason, M. L.↗
NASA NTRS1982

Computation of two-dimensional turbulent flow at subsonic Mach numbers over thick trailing edges

An implicit time marching finite difference method is used to predict two dimensional turbulent flow at a Reynolds number of 440,000 and a Mach number of 0.574 over a shortened NACA 0012 airfoil with a trailing edge of 4.5% thickness and semicircular shape. The flow is found to be unsteady but periodic in the trailing edge region. Thus, lift and drag fluctuate at small amplitudes around mean values and at distinct frequencies.

Drescher, P.↗
NASA NTRS1981

Methods for the calculation of axial wave numbers in lined ducts with mean flow

A survey is made of the methods available for the calculation of axial wave numbers in lined ducts. Rectangular and circular ducts with both uniform and non-uniform flow are considered as are ducts with peripherally varying liners. A historical perspective is provided by a discussion of the classical methods for computing attenuation when no mean flow is present. When flow is present these techniques become either impractical or impossible. A number of direct eigenvalue determination schemes which have been used when flow is present are discussed. Methods described are extensions of the classical no-flow technique, perturbation methods based on the no-flow technique, direct integration methods for solution of the eigenvalue equation, an integration-iteration method based on the governing differential equation for acoustic transmission, Galerkin methods, finite difference methods, and finite element methods.

Eversman, W.↗
NASA NTRS1982

Separated trailing-edge flow at a transonic Mach number

Results from an experimental investigation of a small-scale separated flow at a sharp trailing edge are presented. The separated flow was a result of sustained adverse pressure gradients. Experiments were carried out at a transonic Mach number, without any shock wave in the flow, and at a high Reynolds number. Measurements include surface pressure distributions, mean velocity, turbulent shear stress, turbulent kinetic energy, and some streamwise turbulence intensity profiles in the region from just upstream of separation to downstream into the near-wake, following wake-closure. The results show noticeable changes in the mean and turbulent quantities in the separated region although the wall adverse pressure gradients are relatively weak. Turbulent normal stress becomes important in the vicinity of separation and in the separated zone with regard to both mean-flow development and turbulence-energy production. The experimental data are used to assess the performance of two boundary-layer calculation methods.

Viswanath, P. R.↗
NASA NTRS1982

Experimental studies of the Eppler 61 airfoil at low Reynolds numbers

The results of an experimental study to document the effects of separation and transition on the performance of an airfoil designed for low Reynolds number operation are presented. Lift, drag and flow visualization data were obtained for the Eppler 61 airfoil section for chord Reynolds numbers from about 30,000 to over 200,000. Smoke flow visualization was employed to document the boundary layer behavior and was correlated with the Eppler airfoil design and analysis computer program. Laminar separation, transition and turbulent reattachment had significant effects on the performance of this airfoil.

Burns, T. F.↗
NASA NTRS1984

Pseudo-Random Number Generators

Package features comprehensive selection of probabilistic distributions. Monte Carlo simulations resorted to whenever systems studied not amenable to deterministic analyses or when direct experimentation not feasible. Random numbers having certain specified distribution characteristic integral part of simulations. Package consists of collector of "pseudorandom" number generators for use in Monte Carlo simulations.

Howell, L. W.↗
NASA NTRS1982

An experimental documentation of a separated trailing-edge flow at a transonic Mach number

A detailed experiment on the separated flow field at a sharp trailing edge is described and documented. The separated flow is a result of sustained adverse pressure gradients. The experiment was conducted using an elongated airfoil-like model at a transonic Mach number and at a high Reynolds number of practical interest. Measurements made include surface pressures and detailed mean and turbulence flow quantities in the region just upstream of separation to downstream into the near-wake, following wake closure. The data obtained are presented mostly in tabular form. These data are of sufficient quality and detail to be useful as a test case for evaluating turbulence models and calculation methods.

Viswanath, P. R.↗
NASA NTRS1983

High Reynolds number tests of the CAST 10-2/DOA 2 airfoil in the Langley 0.3-meter transonic cryogenic tunnel, phase 1

A wind tunnel investigation of an advanced technology airfoil, the CAST 10-2/DOA 2, was conducted in the Langley 0.3 meter Transonic Cryogenic Tunnel (0.3 m TCT). This was the first of a series of tests conducted in a cooperative National Aeronautics and Space Administration (NASA) and the Deutsche Forschungs- und Versuchsanstalt fur Luft- und Raumfahrt e. V. (DFVLR) airfoil research program. Test temperature was varied from 280 K to 100 K to pressures from slightly above 1 to 5.8 atmospheres. Mach number was varied from 0.60 to 0.80, and the Reynolds number (based on airfoil chord) was varied from 4 x 10 to the 8th power to 45 x 10 to the 6th power. This report presents the experimental aerodynamic data obtained for the airfoil and includes descriptions of the airfoil model, the 0.3 m TCT, the test instrumentation, and the testing procedures.

Dress, D. A.↗
NASA NTRS1983

An efficient algorithm for generating random number pairs drawn from a bivariate normal distribution

An efficient algorithm for generating random number pairs from a bivariate normal distribution was developed. Any desired value of the two means, two standard deviations, and correlation coefficient can be selected. Theoretically the technique is exact and in practice its accuracy is limited only by the quality of the uniform distribution random number generator, inaccuracies in computer function evaluation, and arithmetic. A FORTRAN routine was written to check the algorithm and good accuracy was obtained. Some small errors in the correlation coefficient were observed to vary in a surprisingly regular manner. A simple model was developed which explained the qualities aspects of the errors.

Campbell, C. W.↗
NASA NTRS1983

Effect of tail-fin span on stability and control characteristics of a Canard-controlled missile at supersonic Mach numbers

An experimental wind-tunnel investigation was conducted at Mach numbers from 1.60 to 3.50 to obtain the longitudinal and lateral-directional aerodynamic characteristics of a circular, cruciform, canard-controlled missile with variations in tail-fin span. In addition, comparisons were made with the experimental aerodynamic characteristics using three missile aeroprediction programs: MISSILE1, MISSILE2, and NSWCDM. The results of the investigation indicate that for the test Mach number range, canard roll control at low angles of attack is feasible on tail-fin configurations with tail-to-canard span ratios of less than or equal to 0.75. The conards are effective pitch and yaw control devices on each tail-fin span configuration tested. Programs MISSILE1 and MISSILE2 provide very good predictions of longitudinal aerodynamic characteristics and fair predictions of lateral-directional aerodynamic characteristics at low angles of attack, with MISSILE2 predictions generally in better agreement with test data. Program NSWCDM provides good longitudinal and lateral-directional aerodynamic predictions that improve with increases in tail-tin span.

Blair, A. B., Jr.↗
NASA NTRS1983

An experimental investigation of the low Reynolds number performance of the Lissaman 7769 airfoil

A Lissaman 7769 airfoil, used on the Gossamer Condor and Gossamer Albatross human-powered aircraft, was tested in a low turbulence subsonic wind tunnel. Lift and drag data were collected at chord Reynolds numbers of 100,000, 150,000, 200,000, 250,000, and 300,000; at angles of attack from -10 to +20 deg by using an external strain gage force balance. Lift curves, drag curves, and drag polars were generated from both uncorrected data and data corrected for wind tunnel blockage effects. A flow visualization study was performed to correlate with the force data. The results of the investigation have shown that the airfoil exhibits a significant degradation in performance for chord Reynolds numbers below 150,000.

Conigliaro, P. E.↗
NASA NTRS1983

Flow in a differentially rotated cylindrical drop at low Reynolds number

A liquid drop held captive between parallel disks that are differentially rotated is a model for the swirling flows induced by crystal rotation in the floating-zone process for growing semiconductor materials. An asymptotic analysis for a cylindrical drop is presented that elucidates the structure of the axisymmetric cellular motions caused by disk rotation at low Reynolds number. Variations of meniscus shape induced by these flows are described in the limit of small capillary number. Most cellular flow fields break the bifurcation point that corresponds to the Plateau-Rayleigh limit for the length of a static drop into two disjoint shape families and lower the maximum stable drop length. This effect is studied by a singular bifurcation analysis.

Harriott, G. M.↗
NASA NTRS1983

Optimum actuator placement, gain, and number for a two-dimensional grillage

A technique for determining the best actuator locations, actuator gains, and number of actuators is presented with results obtained for a two-dimensional grillage model. The technique minimizes the sum of the actuator gains and it is shown for the example studied that this minimum is constant for a large variation in the number of actuators. Comparisons are made between force and torque actuators, and system stability is guaranteed throughout the design process.

Horner, G. C.↗
NASA NTRS1983

On the wave number spectrum of oceanic mesoscale variability observed by the SEASAT altimeter

The wave number spectrum of mesoscale variability in various parts of the oceans is computed on the basis of sea surface height variations measured by the SEASAT altimeter in nearly repeat orbits during the last 24 days of its mission, and it is noted that oceanic spectrum characteristics are dependent on the energy level of the mesoscale variability. On the basis of an assumed horizontal isotropy of mesoscale variability, scalar-wave number spectra of sea surface height and geostrophic kinetic energy are presented and the dynamical implications of these spectra are discussed. A rigorous examination of the effects of residual geoid and atmospheric water vapor on the computed oceanic spectra indicates that the general characteristics of the spectra were not significantly affected by them.

Fu, L.-L.↗
NASA NTRS1983

Number of terms required in the Fourier expansion of the reflection function for optically thick atmospheres

Computational results are presented for the separate terms in the Fourier expansion of the phase function and the reflection function of a semiinfinite, conservatively scattering atmosphere composed of cloud particles. The calculations involve successive applications of invariant imbedding, doubling, and asymptotic fitting methods to cover the range from very thin to very thick atmospheres. From the results, the ratio of the total reflection function to the first-order reflection function is determined as well as the number of terms required to describe the reflection function to an accuracy of 0.1 percent. The number of terms required depends strongly on the zenith angles of incidence and reflection as well as on details of the phase function. These results are compared with similar results obtained for a Henyey-Greenstein phase function having the same asymmetry factor as in the cloud model.

King, M. D.↗
NASA NTRS1983

Magnus effects at high angles of attack and critical Reynolds numbers

The Magnus force and moment experienced by a yawed, spinning cylinder were studied experimentally in low speed and subsonic flows at high angles of attack and critical Reynolds numbers. Flow-field visualization aided in describing a flow model that divides the Magnus phenomenon into a subcritical region, where reverse Magnus loads are experienced, and a supercritical region where these loads are not encountered. The roles of the spin rate, angle of attack, and crossflow Reynolds number in determining the boundaries of the subcritical region and the variations of the Magnus loads were studied.

Seginer, A.↗
NASA NTRS1983

An experimental documentation of trailing-edge flows at high Reynolds number

Experiments documenting attached trailing-edge and near-wake flows at high Reynolds numbers are described. A long, airfoil-like model was tested at subsonic and low transonic Mach numbers, and both symmetrical and asymmetrical flows with pressure gradients upstream of the trailing edge were investigated. Model surface pressures and detailed mean and turbulence flow qualities were measured in the vicinity of the trailing edge and in the near-wake. The data obtained are of sufficient quality and detail to be useful as test cases in assessing turbulence models and calculation methods.

Viswanath, P. R.↗