Noise reduction mechanism of a three-element airfoil with a swept-angle based on lattice Boltzmann method

This paper investigates the noise reduction mechanism of a three-element airfoil with a swept angle. It analyzes the impact of the swept angle on airfoil noise through numerical simulations validated by wind tunnel experiments. An in-house high-precision numerical scheme based on the lattice Boltzmann method combined with the parallel computing capabilities of graphics processing units is used to directly simulate the unsteady vortices around the airfoil. The study finds that the noise reduction effect of the swept angle is not solely attributed to the decrease in effective incoming flow velocity, the sweepback effect introduces a spanwise phase difference during vortex shedding, which weakens the spanwise coherence of the vortex structures. Meanwhile, the breakdown into smaller vortex structures leads to an increase in broadband noise which compensates exactly the additional reduction of the low frequency spectrum pressure level. Based on the Lamb vector ω×u in the vortex-acoustic theory and combined with the dynamic mode decomposition method, this paper conducts a study on the quantitative relationship between the evolution of vortex morphology and noise changes.