AN EVALUATION OF THE METHOD FOR DETERMINING THE WHITHAM F-FUNCTION USING DISTRIBUTIONS OF DOWNWASH AND SIDEWASH ANGLES

摘要

The method (due to Landahl et al.) of computing the Whitham F-function using distributions of downwash and sidewash angles was evaluated with two different models. F-functions which were calculated for a 4° (half angle) cone cylinder at M∞ = 2.01, using theoretically and experimentally derived flow angles, show that the method of Landahl et al. is sensitive to small inaccuracies in the measured flow angles. An oblique wing transport model was tested at 0° angle of attack at M∞ = 2.01. In this test, two different probes were used at two different distances from the model (one probe measured flow angularity and the other static pressures). The pressure signa¬ture derived from the F-function (computed using distributions of downwash and sidewash angles measured at the distance of 0.32 body lengths) was extrapolated and compared to the pressure signature measured at the distance of 0.87 body lengths with the static pressure probe. The agreement between the two pressure signatures is poor, and the discrepancy is believed to be due largely to the many inaccuracies involved in using a probe designed to measure flow angularity.