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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Computation of aerodynamic interference effects on oscillating airfoils with controls in ventilated subsonic wind tunnels

Lift interference effects are discussed based on Bland's (1968) integral equation. A mathematical existence theory is utilized for which convergence of the numerical method has been proved for general (square-integrable) downwashes. Airloads are computed using orthogonal airfoil polynomial pairs in conjunction with a collocation method which is numerically equivalent to Galerkin's method and complex least squares. Convergence exhibits exponentially decreasing error with the number n of collocation points for smooth downwashes, whereas errors are proportional to 1/n for discontinuous downwashes. The latter can be reduced to 1/n to the m+1 power with mth-order Richardson extrapolation (by using m = 2, hundredfold error reductions were obtained with only a 13% increase of computer time). Numerical results are presented showing acoustic resonance, as well as the effect of Mach number, ventilation, height-to-chord ratio, and mode shape on wind-tunnel interference. Excellent agreement with experiment is obtained in steady flow, and good agreement is obtained for unsteady flow.

Fromme, J. A.↗
NASA NTRS1993

Interference effects on Space Station Freedom and space shuttle orbiter Ku-band downlinks

The space shuttle orbiter (SSO) and Ku-band single access return (KSAR) link and the Space Station Freedom (SSF) KSAR link via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. Recently, Tsang and Su (1988, 1989) simulated the mutual interference effects, using a practical nonlinear bandlimited channel. The purpose of this paper is to demonstrate that a simplified (i.e., linear band-limited channel) analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit energy-to-thermal noise power spectral density ratio to achieve a 10 exp -5 coded bit-error-probability is determined to be 4 dB for the Ku-band SSO-to-TDRS I-channel return link with a 4.5 dB effective signal-to-interference total power ratio (S/I) when the Ku-band SSF-to-TDRS return link interferes, whereas Su's simulation yields approximately 5 dB degradation. For the Ku-band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I = 21.6 dB. In conclusion, interference on the Ku-band SSO-to-TDRS I-channel return link is significant, but on the Ku-band SSF-to-TDRS return link it is negligible.

Kwon, Hyuck M.↗
NASA NTRS1979

Radio frequency interference effects of continuous wave signals on telemetry data, part 2

The results of radio frequency interference tests and the derived telemetry bit SNR degradation model, which includes the telemetry data rate and the telemetry data power as independent variables for characterizing the continuous wave interference effects on telemetry data, are presented. The telemetry bit SNR degradation model was implemented in the second version of the Deep Space Interference Prediction software.

Low, P. W.↗
NASA NTRS2015

Wind Tunnel Interference Effects on Tilt Rotor Testing Using Computational Fluid Dynamics

Experimental techniques to measure rotorcraft aerodynamic performance are widely used. However, most of them are either unable to capture interference effects from bodies, or require an extremely large computational budget. The objective of the present research is to develop an XV-15 Tilt Rotor Research Aircraft rotor model for investigation of wind tunnel wall interference using a novel Computational Fluid Dynamics (CFD) solver for rotorcraft, RotCFD. In RotCFD, a mid-fidelity URANS solver is used with an incompressible flow model and a realizable k-ε turbulence model. The rotor is, however, not modeled using a computationally expensive, unsteady viscous body-fitted grid, but is instead modeled using a blade element model with a momentum source approach. Various flight modes of the XV-15 isolated rotor, including hover, tilt and airplane mode, have been simulated and correlated to existing experimental and theoretical data. The rotor model is subsequently used for wind tunnel wall interference simulations in the National Full-Scale Aerodynamics Complex (NFAC) at NASA Ames Research Center in California. The results from the validation of the isolated rotor performance showed good correlation with experimental and theoretical data. The results were on par with known theoretical analyses. In RotCFD the setup, grid generation and running of cases is faster than many CFD codes, which makes it a useful engineering tool. Performance predictions need not be as accurate as high-fidelity CFD codes, as long as wall effects can be properly simulated. For both test sections of the NFAC wall interference was examined by simulating the XV-15 rotor in the test section of the wind tunnel and with an identical grid but extended boundaries in free field. Both cases were also examined with an isolated rotor or with the rotor mounted on the modeled geometry of the Tiltrotor Test Rig (TTR). A 'quasi linear trim' was used to trim the thrust for the rotor to compare the power as a unique variable. Power differences between free field and wind tunnel cases were found from -7 % to 0 % in the 80- by 120-Foot Wind Tunnel test section and -1.6 % to 4.8 % in the 40- by 80-Foot Wind Tunnel, depending on the TTR orientation, tunnel velocity and blade setting. The TTR will be used in 2016 to test the Bell 609 rotor in a similar fashion to the research in this report.

CFD↗
NASA NTRS1974

Space shuttle launch vehicle (13 P-OTS) strut support interference effects study in the Rockwell International 7- by 7-foot trisonic wind tunnel (IA68)

Strut support interference investigations were conducted on an 0.004-(-) scale representation of the space shuttle launch vehicle in order to determine transonic and supersonic model support interference effects for use in a future exhaust plume effects study. Strut configurations were also tested. Orbiter, external tank, and solid rocket booster pressures were recorded at Mach numbers 0.9, 1.2, 1.5, and 2.0. Angle of attack and angle of sideslip were varied between plus or minus 4 degrees in 2 degree increments. Parametric variations consisted only of the strut configurations.

Rogge, R. L.↗
NASA NTRS1931

The Interference Effects on an Airfoil of a Flat Plate at Mid-span Position

This report gives the results of an investigation of the mutual interference of an airfoil and a flat plate inserted at mid-span position. The tests were conducted in the Variable-Density Wind Tunnel of the National Advisory Committee for Aeronautics at a high value of the Reynolds Number. The interference effects of this combination were found to be small. Supplementary tests indicated that the use of fillets decreases both the lift and drag slightly. A bibliography of publication dealing with interference between wings and bodies, and with the effects of cut-outs and fillets is included.

Ward, Kenneth E↗
NASA NTRS1979

Interference effects of aircraft components on the local blade angle of attack of a wing-mounted propeller

The aerodynamic interference effects on a propeller operating in the presence of different wing-body-nacelle combinations was studied. The unsteady blade angle of attack variation with azimuth angle by varying the pitch and yaw of the nacelle was minimized. Results indicate for the particular configuration of interest the minimum blade angle of attack variation occurred with the nacelle pitched downward 4.5 deg and yawed inward 3.0 deg.

Mendoza, J. P.↗