Gunilla Efraimsson
Department of Aeronautical and Vehicle Engineering
KTH
SE-100 44 Stockholm
In the first part of the talk I will give a brief overview of the activities in computational aeroacoustics at the Department of Aeronautical and Vehicle Engineering, KTH.
In the second part talk we will in detail analyze the performance of a higher order accurate finite difference scheme on aeroacoustic applications. The focus of the talk will be on the effect of grid-stretching, especially for the purpose of damping out outgoing acoustic waves. Via the use of a very simple model problem, which is a solution to the linearized Euler equations in two space dimensions, the upstream and downstream acoustic waves can be analyzed in more detail than what is mostly possible for common test cases. The numerical solutions of the model problem, together with theoretical analysis of a fourth order accurate operator in space, enables a detailed understanding of the effect of grid stretching on the group velocity, phase speed and the influence of artificial viscosity. The analysis is illustrated by the flow over a cavity in two space dimension, where acoustic waves are generated and propagate upstream of the cavity. Finally, the effect of Mach number variation on the order of accuracy is investigated, where also very low Mach numbers are considered.