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Strawn, Roger C.

Publications and source records attributed to Strawn, Roger C..

26 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Correlation of Puma airfoils - Evaluation of CFD prediction methods

A cooperative program was undertaken by research organizations in England, France, Australia and the U.S. to study the capabilities of computational fluid dynamics codes (CFD) to predict the aerodynamic loading on helicopter rotor blades. The program goal is to compare predictions with experimental data for flight tests of a research Puma helicopter with rectangular and swept tip blades. Two topics are studied. First, computed results from three CFD codes are compared for flight test cases where all three codes use the same partial inflow-angle boundary conditions. Second, one of the CFD codes (FPR) is iteratively coupled with the CAMRAD/JA heilcopter performance code. These results are compared with experimental data and with an uncoupled CAMRAD/JA solution. The influence of flow field unsteadiness is found to play an important role in the blade aerodynamics. Alternate boundary conditions are suggested in order to properly model this unsteadiness in the CFD codes.

Strawn, Roger C.↗
NASA NTRS1989

Advanced rotor computations with a corrected potential method

An unsteady Full-Potential Rotor code (FPR) has been enhanced with modifications directed at improving its drag prediction capability. The potential code has been rewritten with modifications to increase the code accuracy. Also, the shock generated entropy has been included to provide solutions comparable to the Euler equations. Two different weakly interacted boundary layer models have also been coupled to FPR in order to estimate skin-friction drag. One is a two-dimensional integral method and the other is a three-dimensional finite-difference scheme. The new flow solver is able to find accurate inviscid drags without recourse to numerical error tares. This permits the resolution of drag distributions resulting from rotor geometric variations. Good comparisons have been obtained between computed and measured torque for a rectangular and a highly swept model rotor.

Bridgeman, John O.↗
NASA NTRS1988

An entropy and viscosity corrected potential method for rotor performance prediction

An unsteady Full-Potential Rotor code (FPR) has been enhanced with modifications directed at improving its drag prediction capability. The shock generated entropy has been included to provide solutions comparable to the Euler equations. A weakly interacted integral boundary layer has also been coupled to FPR in order to estimate skin-friction drag. Pressure distributions, shock positions, and drag comparisons are made with various data sets derived from two-dimensional airfoil, hovering, and advancing high speed rotor tests. In all these comparisons, the effect of the nonisentropic modification improves (i.e., weakens) the shock strength and wave drag. In addition, the boundary layer method yields reasonable estimates of skin-friction drag. Airfoil drag and hover torque data comparisons are excellent, as are predicted shock strength and positions for a high speed advancing rotor.

Bridgeman, John O.↗
NASA NTRS1988

An experimental and computational study of rotor-vortex interactions

An experimental and computational study has been performed on a close rotor-blade/vortex interaction. Surface pressure data was obtained from a rotor operating close to the tip-vortex from an upstream wing in a wind tunnel. Data was obtained for a wide range of blade-vortex proximities, orientations, and blade-tip Mach numbers (up to the transonic regime). A numerical model of these interactions was constructed using the unsteady, three-dimensional, full-potential rotor code called FPR. The model employed an undistorted full-field representation of the measured vortex. This simple model gave excellent comparisons with the data for a wide range of conditions, including parallel head-on interactions. Computational studies have also been performed on the manner of vortex representation and the influence of vortex-core size.

Caradonna, Francis X.↗
NASA NTRS1987

Geometrical acoustics and transonic helicopter sound

A new method is presented for predicting the impulsive noise generated by a transonic rotor blade. The method is a combined approach involving computational fluid dynamics and geometrical acoustics. A full-potential finite-difference method is used to obtain the pressure field close to the blade. A Kirchhoff integral formulation is then used to extend these finite-difference results into the far field. This Kirchhoff formula is based on geometrical acoustics approximations. It requires initial data across a plane at the sonic radius in a blade-fixed coordinate system. This data is provided by the finite-difference solution. Acoustic pressure predictions show good agreement with hover experimental data for cases with hover tip Mach numbers of 0.88 through 0.96. The cases above 0.92 tip Mach number are dominated by non-linear transonic effects seen as strong shocks on and off the blade tip. This paper gives the first successful predictions of far-field acoustic pressures for high-speed impulsive noise over a range of Mach numbers after delocalization.

Isom, Morris↗
NASA NTRS1987

Prediction of high-speed rotor noise with a Kirchhoff formula

A new methodology has been developed to predict the impulsive noise generated by a transonic rotor blade. The formulation uses a full-potential finite-difference method to obtain the pressure field close to the blade. A Kirchhoff integral formulation is then used to extend these finite-difference results into the far-field. This Kirchhoff formula is written in a blade-fixed coordinate system. It requires initial data across a plane at the sonic radius. This data is provided by the finite-difference solution. Acoustic pressure predictions show excellent agreement with hover experimental data for two hover cases of 0.88 and 0.90 tip Mach number, the latter of which has delocalized transonic flow. These results represent the first successful prediction technique for peak pressure amplitudes using a computational code.

Purcell, Timothy W.↗
NASA NTRS1987

Prediction of unsteady transonic rotor loads with a full-potential rotor code

A new version of the full-potential rotor code (FPR) is described. This revised version contains improvements in code structure, algorithm implementation, and input/output options over the earlier version. The FPR code is coupled to a rotor-wake and trim model and the resulting combined code is used to predict surface pressures for three experimentally tested helicopter rotors. Generally good agreement is seen between computed and experimental results.

Strawn, Roger C.↗