Impact of multi-species gas injection on trailing-edge noise

An investigation of a prospective technique to reduce trailing-edge noise is presented. The computational approach based on large-eddy simulations (LES) and solutions of the acoustic perturbation equations (APE) is applied to trailing-edge noise of a flat plate at a freestream Mach number 0.6 and a Reynolds number of 12,000 based on the boundary-layer thickness at the inflow boundary. At two locations, i.e., upstream of and at the trailing edge, gases at different thermodynamic properties, i.e., air, carbon dioxide, and helium, are injected as a silencing fluid into the external flow field. The modified velocity and density fields influence the corresponding acoustic sources. The results include the analysis of turbulent structures, which are responsible for the noise generation and the mechanism defining the noise source. The injection at the trailing edge yields a reduced rate of change of the turbulent scales in the streamwise and spanwise direction defining an acoustically soft trailing edge. For the same mass flow rate of injected fluid the largest noise reduction is achieved by the light fluid, i.e., the helium mixture. The overall sound pressure level decreases by 2 dB compared to the no-injection configuration.

► The reduction of trailing-edge noise is presented by using a hybrid LES/CAA method. ► The injection at the trailing edge reduces the rate of change of the turbulent scale. ► The sudden increase/decrease of the turbulence correlation length is prevented. ► The low-density injection achieves more reduction than the high-density injection.