A study of aerodynamic sound generated from an airfoil placed in a flow with turbulence (1^st report: In the case of airfoil subjected to homogeneous turbulence)

Abstract

Sound generated aerodynamically from a flow around an airfoil subjected to inflow turbulence is investigated experimentally as well as numerically to identify the dominant source of the sound. The test airfoil has NACA0012 wing section with a chord length of 150 mm and a spanwise length of 500 mm. The wind speed is set to 30 m/s, which results in an airfoil Reynolds number of 3.0×10⁵. Wind tunnel experiments are conducted with Active Turbulence Generator (ATG) set at the nozzle exit to control the turbulence intensity and the eddy scale of the inflow turbulence, independently. The former is varied from 10 % to 20 % while the latter is varied from 300 mm to 1600 mm. Large eddy simulation (LES) with turbulent grids is also performed to investigate the flow field around the airfoil in further detail, for which the turbulence intensity is 10 % and the eddy scale is 3.75 mm. As a result, we have found that the pressure fluctuation near the leading edge of the airfoil is remarkably high, and therefore, it is most likely the cause of the considerable increase in the sound generated from the airfoil. In addition, the correlation between the airfoil lift force and the angle of attack for the airfoil subjected to the inflow turbulence is not very high, and therefore, the change in the lift force due to the change in the angle of attack is least likely to the cause of increase in the sound.