Aero-Acoustic Source Terms from Large-Eddy Simulation in Turbulent Pipe Flow

In the acoustic design of flow guiding components, novel simulation concepts for predicting relevant sound sources in the early design state become increasingly important. This requires accurate numerical methods to describe the involved phenomena. The present study computationally investigates the flow-induced aeroacoustic sound sources, generated in turbulent pipe flow. The analysis follows a hybrid approach, where the acoustic sound field is predicted separately from the underlying turbulent flow field, supplied with acoustic source terms from an incompressible flow simulation of the considered configuration in the limit of low Mach number. Source terms for use as input into different acoustic wave equations, the Lighthill wave equation, the vortex sound theory, and the Perturbed Convective Wave Equation (PCWE) are computed performing incompressible Direct Numerical Simulations (DNS) and Large-Eddy Simulations (LES) of fully developed pipe flow. The predictions for the different source terms are analyzed in physical and spectral space. The comparison of the LES results against the corresponding highly resolved DNS data particularly highlights the marked effect of the applied spatial resolution as well as the contributions from the subgrid-scale model, met with different LES grids. The source terms for Lighthill and vortex sound theory are shown as highly different in magnitude reflecting the diffusion of the kinetic energy included in the latter. The transient and the convective component of the PCWE source term are shown to be strongly negative correlated, which significantly reduces the predicted amplitudes of the sound source at all frequencies.