Abstract:

Supersonic aircraft, particularly the projected high speed civil transport (HSCT), fly over the ocean to minimize the sonic boom noise impact on land. This noise interacts with the ocean surface, causing an underwater pressure disturbance. In steady, level supersonic flight at less than Mach 4.4 over a homogeneous ocean, the underwater disturbance is a decaying evanescent wave persisting in depth to 100 m or more. Realistically, however, the ocean is not homogeneous and contains wind-wave generated bubble clouds near the surface. In the current research, a two-dimensional finite difference simulation is used to predict underwater sound levels due to a sonic boom impinging on an ocean with bubble layers near the surface. Each of the bubble layers has an approximate sound speed appropriate for its corresponding depth; bubbles in the ocean can cause the sound speed to drop as low as the speed of sound in air. In this presentation the effects of bubble layers on the sonic boom noise penetration will be described. Preliminary results show that one can get propagating waves in the upper bubble layers but only evanescent waves below the layers. [Work supported by NASA Langley Research Center, under Grant NAG 1-1638.]