Increase of trailing-edge noise due to inflow turbulence

Abstract

Altough the regulatory imposition of low-noise limits, airframe noise currently limits the design space of several applications, such as, wind energy, marine, and aeronautics. The noise of those applications is significantly increased by the presence of inflow turbulence. It has been believed that only the leading-edge component is increased. However, recent results show that the trailing-edge noise is also increased because of the free-stream turbulence penetration in the airfoil boundary layer. This research measures the increase of trailing-edge noise due to inflow turbulence for NACA 63018 and NACA 0008 airfoils. Noise measurements were conducted for velocities ranging from 15 to 40 m/s, with and without inflow turbulence. A rod installed upstream of the airfoils generated an inflow turbulence of ≈ 12%. The wall-pressure fluctuations were measured close to the trailing edge to analyze the near-field phenomenon. The inflow turbulence increases the wall-pressure spectrum level in the entire frequency range and the spanwise correlation length in the low-frequency range. The trailing-edge noise increases due to the inflow turbulence in the entire frequency range at least 2 db up to more than 15 dB for all the cases. The contribution of leading- and trailing-edge noise to the total noise varies with the airfoil geometry, with the trailing-edge noise dominating in a larger frequency range for the thickest airfoil.