Numerical Methods in Computational Aeroacoustics (CAA)

Course Objective

The reduction of noise generated by turbulent flow has become an important topic in various engineering areas such as automotive, civil, or aeronautical engineering. The field of aeroacoustics concerns the noise generation and propagation in turbulent flow and has matured dramatically in the past three decades, especially through the increasingly stringent limits imposed on the noise emissions of civil aircraft. For a continuous progress in the reduction of aircraft noise emissions numerical tools will become essential in the future to achieve an optimized low-noise design of critical aircraft components. In the last years numerical techniques evolved in the framework of Computational Aeroacoustics (CAA) that are optimized for the simulation of wave-propagation and generation in non-uniform flows. CAA can be deemed to be a subdiscipline of Computational Fluid Dynamics (CFD). However, the main objective of CAA to understand the physics of noise generation and propagation differs considerably from that of CFD such that own numerical issues and methods became neccessary. This lecture aims at introducing into the new numerical concepts of CAA. Furthermore the lecture mediates the skills that are neccessary to enable further studies of the topic with the help of current scientifical literature. A prior attendance at the lecture ‘Grundlagen der Aeroakustik’ that introduces into the physical and mathematical concepts of aeroacoustics is useful but not mandatory for an understanding of the lecture.

Course Content

• Basic equation of aeroacoustics, dispersion relation, numerical discretization by means of finite differences, stability and von Neumann method
• Dispersion relation preserving schemes of high order on structured computation grids, formulation of equations on curvi-linear structured grids, low dissipation and dispersion Runge-Kutta methods, damping and filtering of non-physical waves, highly accurate non-reflecting boundary conditions
• Overview about CAA methods for nonstructured grids, particularly Discontinuous Galerkin FE scheme, stochastic and deterministic source description for CAA
• Integral methods for the extrapolation of simulation data to the farfield

Along with the lecture a field trip to the “Acoustic Windtunnel Braunschweig” (AWB) of DLR (MB-ISM-103) is recommended.