Numerical and experimental investigation to develop a prediction method for the flap noise

Abstract

This thesis is about using both simulation and experiment to measure flap noise. Flap noise happens at both low- and high-frequency ranges. It includes flap-edge noise and other sources inside the flap’s boundary layer. The main objective is to develop a method to predict the three-dimensional flap noise. Since both experiment and computational fluid dynamics have some limitations and difficulties, respectively, a developed semi-empirical Mach scaling method has been studied. Indeed, four different methods are applied to the same wing and flap configuration for the same Reynolds number including experiment at KAIST’s wind tunnel, URANS + acoustic analogy (FWH), applied Brooks, and RANS + Brooks. These all four methods showed a similar trend and pattern for both low and high frequencies. However, the sound pressure level is different due to each meth-od’s limitations. The trend and pattern correspond to the previous research by other people. The applied Mach scaling method shows that separation effect on the flap occurs at low frequencies. On the contrary, the edge vortex mainly contributes the sound pressure level at higher frequencies. Depending on the Reynolds number and flap’s edge side, the edge vortex might influence the sound spectrum at low frequencies. Edge-vortex main-ly happens above 1000 Hz. The low-frequency noise is between 20 to 500 Hz, which is primarily attributable to the separation effect and slight effect of the edge vortex.