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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A study of residual interference effects in adaptive wall testing of a 7-inch chord CAST-10-2/DOA 2 airfoil model

The residual interferences present in the testing of a CAST10-2/DOA2 airfoil model in the Langley 0.3 m Transonic Cryogenic Tunnel (0.3 m TCT) is examined. The 7.1 inch chord airfoil model was tested in the 0.3 m TCT adaptive wall test section with a nominal 13 inch square cross section. The test data obtained on the same model during different tunnel entries showed different levels of residual interference. The present study shows that for valid comparison of the test data from adaptive wall tunnels, it is necessary to account for residual interferences, in particular the blockage correction to the Mach number.

Murthy, A. V.↗
NASA NTRS1979

Pulsed radio frequency interference effects on data communications via satellite transponder

Power-limited communication links may be susceptible to significant degradation if intentional or unintentional pulsed high level radio frequency interference (RFI) is present. Pulsed RFI is, in fact, of current interest to NASA in studies relating to its Tracking and Data Relay Satellite System (TDRSS). The present paper examines the impact of pulsed RFI on the error probability performance of a power-limited satellite communication link: the assumed modulation scheme is PN coded binary PSK. The composite effects of thermal noise, pulsed CW and pulsed Gaussian noise are analyzed, where RFI arrivals are assumed to follow Poisson statistics. Under the assumption that the satellite repeater is ideal and that integrate and dump filtering is employed at the ground receiver, an exact error probability expression and associated approximations are derived. Computed results are generated using an arbitrarily specified RFI model.

Weinberg, A.↗
NASA NTRS1996

Quantum Interference Effects in Molecular Y- and Rhomb-Type Systems

In this paper we report the first observation of molecular population trapping in four level systems. Constructive and destructive quantum interferences between two sum-frequncy two-photon transitions in Y- and rhomb-type four-level systems, respectively, im sodium molecules have been experimentally achieved by using only one laser source. Their energy level schemes are featured by the extremely near-resonant enhancement of the equal-frequency two-photon transitions, sharing both the initial and the intermediate levels for the Y-type, and sharing both the initial and the final levels for the rhomb-type systems. Their novel spectral effects are to show seriously restrained Doppler-free UV peak at the nominal location of the induced two-photon transition with visible fluorescence in rhomb-type schems, and to show a strong extra UV peak but null visible fluorescence in the middle between the two dipole allowed two-photon transitions.

Xia, Hui-Rong↗
NASA NTRS1991

Radio frequency interference effect on PN code sequence lock detector

The authors find the probabilities of detection and false alarm of the pseudonoise (PN) sequence code lock detector when strong radio frequency interference (RFI) hits the communications link. Both a linear model and a soft-limiter nonlinear model for a transponder receiver are considered. In addition, both continuous wave (CW) RFI and pulse RFI are analyzed, and a discussion is included of how strong CW RFI can knock out the PN code lock detector in a linear or a soft-limiter transponder. As an example, the Space Station Freedom forward S-band PN system is evaluated. It is shown that a soft-limiter transponder can protect the PN code lock detector against a typical pulse RFI, but it can degrade the PN code lock detector performance more than a linear transponder if CW RFI hits the link.

Kwon, Hyuck M.↗
NASA NTRS1980

Theoretical and Experimental studies of aerodynamic interference effects

Theoretical studies of aerodynamic forces on winglets shed considerable light on the mechanism by which these devices can reduce drag at constant total lift and on the necessity for proper alignment and cambering to achieve optimum favorable interference. Results of engineering studies, wind tunnel tests and performance predictions are reviewed for installations proposed for the AMST YC-14 and the KC-135 airplanes. The other major area of aerodynamic interference discussed is that of engine nacelle installations. Slipper and overwing nacelles have received much attention because of their potential for noise reduction, propulsive lift and improved ground clearance. A major challenge is the integration of such nacelles with the supercritical flow on the upper surface of a swept wing in cruise at high subsonic speeds.

Rettie, I. H.↗
NASA NTRS1986

Transonic airfoil calculations including wind tunnel wall-interference effects

The results of Reynolds-averaged time-dependent inviscid and turbulent compressible Navier-Stokes computations using the implicit finite-difference approach of Steger (1978), modified by incorporating a pressure boundary condition, (PBC) to account for wall interference are compared with experimental data on a NACA 64A010 airfoil (Johnson and Bachalo, 1980) in graphs and briefly characterized. The computational approach is the same as that used by King and Johnson (1980), but a 137 x 50 mesh is used instead of a 97 x 35 mesh, and special care is taken in resolving the nose, shock, and trailing-edge regions. Imposition of PBC is shown to improve significantly the accuracy of the computations for the flowfield on the upper surface of the airfoil, shifting the shock forward to its experimentally measured position in the case of turbulent flow. The failure of the method, even with PBC, to match the experimental shock location in the case of a flow with a separation bubble is attributed to inadequacies in the algebraic turbulence model employed (Baldwin and Lomax, 1978).

King, L. S.↗
NASA NTRS1976

Wind tunnel wall interference effects on a supercritical airfoil at transonic speeds

Wind tunnel tests of a 10% supercritical airfoil have been conducted in the Lockheed Compressible Flow Facility at transonic speeds to determine the effects of varying wind tunnel wall porosity on airfoil performance. Wall configurations ranging in porosity from 1.3% to 10% were investigated at Reynolds numbers of 7 to 30 million. Experimental data presented to show the effect of varying wall porosity include airfoil surface pressures, airfoil forces, and wind tunnel wall pressures. Utilizing the experimental results, an assessment of the applicability of current subcritical theoretical methods to predict wall interference corrections in subsonic and transonic flows is made.

Blackwell, J. A., Jr.↗
NASA NTRS1972

Transonic wall interference effects on bodies of revolution.

Efforts to develop a near sonic transport have placed renewed emphasis on obtaining accurate aerodynamic force and pressure data in the near sonic speed range. Comparison of wind-tunnel and flight data obtained for a blunt-nose body of revolution showed significant discrepancies in drag levels near Mach 1 - apparently due to wind-tunnel wall interference. Subsequent tests of geometrically similar bodies of revolution showed that increasing the model-to-test-section blockage ratio from 0.00017 to 0.0043 resulted in altered drag curve shapes, delayed drag divergence, and 'transonic creep' from subsonic drag levels due to increased wall interference.

Couch, L. M.↗
NASA NTRS1989

Interference effects on scattering by parallel fibers

The present examination of radiative heat transfer through fibrous materials gives attention to the interactions between radiation scattered from individual parallel fibers for the case of a normally-incident plane EM wave and different representative geometries. Experimental results are obtained for the specific case corresponding to fibers in one plane. Analytical models are developed for the radiative scattering behavior of fibrous media when the interference mechanism is accounted for; the results obtained indicate that interference decreases the scattering efficiency of fibrous media containing a large number of randomly positioned fibers.

White, Susan M.↗