Experimental investigation of aerodynamic sound radiated from flow around an airfoil placed in the turbulent flow generated by active turbulence generator

Abstract

Sound generated aerodynamically from a flow around an airfoil subjected to inflow turbulence is investigated experimentally to identify the dominant source of the sound. The test airfoil has NACA0012 wing section. The wind speed is set to 30 m/s, which results in an airfoil Reynolds number of 300000. Its lift and drag coefficient are 0.78 and 0.06 when the angle of attack is 9 degrees. Wind tunnel experiments are conducted with Active Turbulence Generator (ATG) set at the nozzle exit. The ATG is controlled by the swing angles and rotation speeds of the stepping motors 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. 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. Therefore, the higher the turbulence intensity, the higher the sound, and the higher the correlation between the power of the flow velocity fluctuation and the sound pressure level at each frequency.