Aerodynamic noise simulation of an airfoil in a periodically fluctuating freestream

A numerical simulation of NACA0015 airfoil is performed to investigate the effect of periodically fluctuating freestream on the generated noise. A three-dimensional grid is constructed for the computation. Fluctuating freestream is modelled as a sinusoidal fluctuation of its velocity magnitude from its average value U_avg = 20 m/s, resulting in an average Reynolds number of 400,000. As such, the time-varying freestream velocity can be defined as U(t) = U_avg(1 + σ sin(ωt)), where σ is the relative amplitude of fluctuation and ω being its angular frequency. Large eddy simulation was used for the aerodynamic computation while Ffowcs-Williams Hawkings acoustic analogy was used to compute acoustic results. Current results at 8° angle of attack show tonal noise increase at freestream oscillation frequency as well as a significant broadband noise increase above 2000 Hz.