ASA 124th Meeting New Orleans 1992 October

2pPA5. Flight test measurements of the effect of turbulence on sonic boom peak overpressure and rise time.

William L. Willshire, Jr.

NASA---Langley Res. Ctr., M.S. 460, Hampton, VA 23666

Donald P. Garber

David W. DeVilbiss

Lockheed Eng. and Sci. Co.

Sonic boom bow shock amplitude and rise time statistics from a sonic boom propagation flight test experiment are presented. The experiment consisted of flying two types of aircraft, the T-38 and F-15, at speeds of Mach 1.2 to 1.3 over a ground-based microphone array with concurrent meteorological measurements. Bow shock overpressure and rise time distributions measured under low and moderate atmospheric turbulence conditions for the same test aircraft are quite different. The peak overpressure distributions are skewed positively, indicating a tendency toward positive deviations from the mean. Standard deviations of overpressure distributions measured under moderate turbulence were slightly larger than those measured under low turbulence. Under moderate turbulence conditions the mean rise time was larger by a factor of 3.7 and the standard deviation was larger by a factor of 3.2 from the low turbulence values. These changes resulted in a transition from a peaked appearance of the low-turbulence rise time distribution to a flattened appearance for moderate turbulence rise time distributions.