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Boundary layer airfoil5/28/2023 ![]() ![]() An empirical formula is derived to estimate the tonal frequencies produced by flow past the flat plate. Simultaneous measurements of the far-field noise and flow about the plate's trailing edge have been acquired in an anechoic wind tunnel at the University of Adelaide. This paper presents results of an empirical study on the tonal noise produced by a sharp-edged flat plate at low-to-moderate Reynolds number (0.7 × 10^5 ≤ Rec ≤ 2.3 × 10^5, based on chord). There is, however, limited experimental evidence to verify this proposed hypothesis. Many previous researchers have attributed airfoil tonal noise to a feedback loop between instabilities in the laminar boundary layer and the acoustic waves produced at the trailing edge. "Airfoils operating at low-to-moderate Reynolds number may produce noise that contains one or more high amplitude tonal components. The bubbles can cause vibration and noise at the wind turbine blade, hence they should be better known and eliminated, which aerodynamic performance and energy efficiency of turbine can be increased. At lower angles of attack, short bubble occurred, and frequency of vortex shedding due to short bubble were high whereas shedding frequency of long bubble at moderate angles of attack were low. Besides, mean and rms velocities showed that flow characteristics near wake were influenced by LSB and trailing-edge separation. Experiments indicated that location and formation of LSB were affected by variety of both Reynolds number and angle of attack. Hot-film experiment was performed to obtain more information with regards to progress and formation of LSB. Also, velocity measurements at near wake region were done to highlight coactions among LSB and trailing edge vortices. Furthermore, smoke-wire experiment was performed to clearly visualize flow patterns such as flow separation or laminar separation bubble (LSB) over the airfoil. Force measurement of NACA 4412 airfoil was conducted at various angles of attack and Reynolds numbers. Objective of this study is to elucidate relationship with aerodynamic properties and vortex shedding from suction surface and wake of wind turbine blade at low Reynolds numbers. ![]()
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