ASA 124th Meeting New Orleans 1992 October

2pPA4. The effect of turbulence on the loudness of sonic booms.

Kenneth J. Plotkin

Wyle Labs., 2001 Jefferson Davis Hwy., Ste. 701, Arlington, VA 22202

Turbulence is known to distort sonic booms in two ways: random perturbations occur at and following each shock, and the shock rise time increases. Both types of distortion affect the high-frequency content of a boom, and are therefore important to loudness. It is of particular interest whether this distortion will adversely affect the loudness of minimized sonic boom signatures that are associated with low-boom supersonic transport design. Available scattering theories for the magnitude of perturbations and for shock rise times were extended to provide estimates of the spectral content of the distortions. During this analysis, care was taken to recognize the interacting roles of turbulent scattering, absorption of sound by molecular relaxation, and weak nonlinear steepening. It was found that the perturbations at and following the shocks tend to increase the loudness, while the increased rise times tend to decrease the loudness by a comparable amount. Because turbulent scattering is random and three dimensional, an individual boom may be affected by one of these effects more than by the other. Turbulence can therefore cause significant variation in the loudness of individual booms. The change to the average loudness of a number of booms, which is primary to the assessment of cumulative community impact, will, however, be small. [Work supported by NASA---Langley Res. Ctr.]