Wall-Modelled LES on Hierarchical Cartesian Mesh for Trailing Edge Noise Prediction

The use of Wall-Modelled LES (WMLES) for the Direct Noise Computation (DNC) of airfoil trailing-edge is successfully demonstrated for an DU96-180 airfoil. Macroscopic flow equations are solved with low dispersive and dissipative finite-difference and finite-volume methods on hierarchical Cartesian meshes. In the first approach, the incompressible Navier-Stokes equations are solved for flow and a coupled APE-1 system is solved for acoustics, which operates with different explicit time step sizes for incompressible flow and acoustics. Although usage of WMLES implies a characteristic frequency at the trailing edge of order �� := ����/�� ≃ 450���� on the pressure-side and 64���� on the suction-side, the results reveal a very good agreement with measured spectra for high frequencies up to 15kHz, proving that WMLES is suitable for acoustic predictions across wide range of frequencies. The far-field acoustics is a resultant of the scattering of resolved eddies structures convecting past the trailing edge and this scattering can happen over a wide range of frequencies, not restricted by the time scale ��������/��. In the second part of this contribution, Direct Noise Computations (DNC) of a proprietary wind turbine profile EC135F are carried out within the Zonal-LES (ZLES) framework of DLR’s CAA code PIANO. The code solves the fully compressible Navier-Stokes equations in non-linear disturbance equation (NLDE) form over a given RANS background flow with low dispersive and dissipative fourth-order Dispersion Relation Preserving (DRP) scheme and explicit fourth-order Runge-Kutta time integration. The inflow forcing required for the zonal LES is obtained via Fast Random Particle Mesh method (FRPM). The computed power spectral density of unsteady surface pressure fluctuations and the far-field sound pressure level show very good agreement with the experimental data, for both, tonal and broadband noise.