Computation of flow noise using source terms in linearized Euler's equations

An acoustic analogy using linearized Euler's equations (LEE) forced with aerodynamic source terms is investigated to compute the acoustic far field. This hybrid method is applied to three model problems simulated by solving Navier-Stokes equations. In this way, its validity is estimated by comparing the predicted acoustic field with the reference solution given directly by the Navier-Stokes equations. The noise radiated by two corotating vortices is studied: first, in a medium at rest and, second, in a mean sheared flow with no convection velocity. Then the sound field generated by vortex pairings in a subsonic mixing layer is investigated. In this case, a simplified formulation of LEE is proposed to prevent the exponential growth of instability waves. The acoustic fields obtained by solving LEE are in good agreement with the reference solution. This study shows that the source terms introduced into the LEE are appropriate for free sheared flows and that acoustic-mean flow interactions are property taken into account in the wave operator.