Assessment of computational techniques for the prediction of acoustic sources from lifting surfaces using LES and DNS

The acoustic field produced by the flow over a lifting surface is closely linked to the dynamics of the boundary layer. The location and mechanism of the transition strongly influences the character of the trailing edge flow and surface pressure fluctuations and so accurately predicting the transition process is critical for acoustic analyses. In this study, a comparison of DNS and LES is undertaken for a transitional boundary layer flow over a foil at a moderate Reynolds number. The effects of the of sub-filter scale model, discretisation scheme and mesh resolution are considered to better understand how LES can be used to accurately resolve external boundary layer and trailing edge flows. Significant differences are seen for the different modelling approaches and the reasons for this are explored. A second case is then considered using LES which has a very different boundary layer and trailing edge flow. This case highlights the important link between the transitional boundary layer dynamics, trailing edge flow and the acoustic field.