Acceleration of High-Fidelity Simulation for Unsteady Flows with Low Reduced Frequency Using Harmonic Balance Method: Application for Airfoil Flows

This paper presents an application of harmonic-balanced large-eddy simulation(HB-LES) to a transonic buffet flow around OAT15 airfoil. HB-LES is a novel numerical technique developed by the authors, which combines LES with the harmonic balance method using the difference in timescales between the periodic flow and the turbulent fluctuations to accelerates high-fidelity simulation of low reduced frequency unsteady flows. In HB-LES, both the periodic component and the turbulent fluctuations as well as their nonlinear mutual interaction are resolved by iterating short-time LES and harmonic balance method. Numerical results show that HB-LES predicted both the mean and fluctuation amplitude of pressure and velocity in the separated boundary layer quantitatively well. HB-LES successfully reproduced the unsteady behaviour of the shock-wave and the separated boundary layer reported in the conventional time-accurate Wall-Modeled LES. The computation time of HB-LES is reduced by a factor of 0.067 compared to the conventional time-accurate LES.