超音速後流からの音波発生機構について

A direct numerical simulation of a supersonic wake undergoing transition to turbulence has been performed. The compressible Navier-Stokes are solved to study the acoustic generation mechanism for a Mach 2 wake. High-order upwind-biased compact schemes are used for spatial derivatives and a fourth-order Runge-Kutta scheme for time advancement. Navier-Stokes characteristic boundary conditions are employed in the vertical direction and periodic boundary conditions in the streamwise and spanwise directions for a time-developing DNS. The laminar wake was forced with a combination of the 2-D most unstable mode and a pair of oblique subharmonic unstable modes, which were obtained from linear stability theory for the viscous compressible equations. Forcing with a pair of oblique subharmonic modes yields streamwise/vertical counter rotating vortices in the saddle region of the plane wake. As streamwise/vertical counter rotating vortices evolve outside, their self-induction causes inclined braidlike structures to form in the wake, which are similar to the observations in the experimental supersonic flat plate wake transition. Acoustic waves of the plane wake are generated when two-dimensional rollup structures appear and rotate in a coherent fashion in the wake. 3-D elliptical structures play an important role for sound generation in the plane wake.
資料番号: AA0063154018
レポート番号: JAXA-SP-06-010