Low-frequency extension of Amiet׳s theory for compact airfoil noise predictions

Amiet׳s theory is an airfoil noise prediction technique adopted in the industrial design of applications such as wind-turbines, turbomachinery, ventilation systems and drones. This methodology uses Schwarzschild׳s technique in an iterative procedure where the second calculation can only be computed in terms of approximate analytical expression. After two iterations Amiet׳s noise prediction is precise at high-frequencies, however generally overestimated in the frequency range where the airfoil is considered a compact noise source – acoustic wavelength comparable to the chord. This paper applies two extra iterations of Schwarzschild׳s technique to improve the methodology convergence in the compact airfoil regime. This approach is combined with analytical correction formulas derived to maintain the solution accuracy after four iterative application of Schwarzschild׳s technique. Results show that, in the compact airfoil regime, two extra iterations contribute to improved noise prediction convergence and enhanced agreement with experimental data.