Direct Simulation of Trailing-edge Noise Generated by a Controlled Diffusion Airfoil Using a Lattice-boltzmann Method

Broadband noise produced by the trailing-edge of a controlled diffusion (CD) airfoil is directly simulated using a Lattice-Boltzmann method (PowerFlow) which resolves both the aerodynamic and acoustic field around the airfoil. A proper DNS resolution is achieved in the vicinity of the airfoil for quasi-2D slice of the mock-up. Two numerical setups of the anechoic open-jet facility where both aerodynamic and acoustic data have been collected are investigated to capture the installation effects: in a first numerical setup (called free), the CD airfoil is set in an uniform flow, while in the second setup (lips) the real jet nozzle geometry is considered. While in the free-field configuration the boundary layer rapidly detaches on the suction side, in the lips the jet shear layers modify the pressure load on the airfoil and the boundary layer keeps attached in the configuration with nozzle. In both setups a laminar recirculation bubble is captured on the suction side near the leading edge. At the reattachment point vortices are emitted and convected either in the wake for the detached flow or along the suction side for the lips setup. The wallpressure and noise spectra for the free configuration are spread over a large band of frequencies and agree with similar experimental records at higher angle of attack for which the flow is detached. The spectra for the lips configuration better agree with the experimental record, despite a shift to low frequency caused by a lack of stretching due to the limited span-wise extent.