Flow-induced noise in turbulent pipe flow with aeroacoustic source terms from Large-Eddy Simulation

Modern product development processes rely strongly on novel simulation techniques for accurately predicting physical phenomena relevant for the design. The method of Large-Eddy Simulation (LES) has increasingly gained popularity, as it allows to capture directly a major part of the turbulent motion, thus limiting the uncertainty of the modelled contributions from the unresolved sub-grid scales (SGS). This characteristic feature makes LES a powerful candidate for predicting flow-induced sound sources for use in Hybrid Computational Aeroacoustics (CAA). The possible sound emission generated by turbulent vortical motion is of growing importance in the design of flow-guiding components. This is especially the case in electric vehicles, where the masking noise of the combustion engine is absent and limited space in the engine compartment of the vehicle may lead to unfavorable flow-conditions.
The present work applies incompressible LES to the generic test case of fully developed turbulent pipe flow. The predicted instantaneous flow field is used to compute aeroacoustic source terms to be supplied to different acoustic equations, such as Lighthill’s acoustic analogy or PCWE. The LES predictions are validated against results from measurements and Direct-Numerical Simulation (DNS), where a particular focus is put on the contribution from the unresolved scales to the aeroacoustic source term, which is provided by the SGS-model. The accurate computation of Lighthill’s source term poses a numerical challenge, as it involves by definition second-order spatial derivatives of the non-linear advective fluxes of momentum. Different approaches for computing a numerically discretized representation of this term are presented and discussed.