Influence of turbulence inflow conditions on aeroacoustics of wall-bounded flows

A scale-resolving simulation of a turbulent boundary layer (TBL) requires an inflow condition that introduces turbulence into the domain. The boundary values must accurately approximate real turbulent structures in order to minimize the inflow adaption and to allow for sustained growth of the TBL. In practice, all inflow conditions incur an error on the flow field directly downstream. This error is typically quantified as the distance from the inlet at which the velocity statistics recover correct values. However, this measure is insufficient for simulations where evaluating acoustic pressure is an important outcome, necessitating a quantification of the error in the pressure field. This aspect of inflow generation is currently not addressed in the literature and constitutes the main topic of this article. We show that violation of the continuity equation near the inflow region generates spurious pressure fluctuations over the entire domain, leading to poor sound prediction results in low Mach number regimes. In particular, we look at three known inflow generation methods (namely, precursor simulations, the synthetic eddy method, and recycling using an upstream open channel flow) and evaluate how silent they are. For evaluation, the sensitive case of a TBL developing over a flat plate is used as the test case. The recycling method satisfies the divergence-free condition and introduces the least amount of spurious numerical noise to the sound field while giving reasonably good agreement in terms of the overall development of the TBL. • Several spatially evolving boundary layers with different inflow conditions. • Quantification of the divergence condition at the inflow. • Assessment of the acoustics of different inflow conditions. • Recycling method satisfies the divergence-free condition and introduces the least amount of spurious numerical noise.