Numerical investigation of communicating turbulent boundary layers through porous media

Abstract

The reduction of trailing edge noise can be achieved through the use of porous trailing edges. It has been found that the unsteady interaction between the suction and pressure side of the airfoil is of relevance for noise reduction. Therefore, this study aims at investigating such ow physics. The proposed numerical setup consists of two vertically stacked temporally developing channel ows (4 ˇ (2 + t) ˇ 4, where and t are the half-charnnel height and the porous medium thickness respectively). The ow eld is solved using the lattice Boltzmann method through PowerFLOW. The two channel ows communicate through a fully resolved porous medium. In this work, the porous medium is a 75% porous Schwarz' P triply periodic minimal surface. Results show span-wise coherent turbulent structures developing on both sides of the porous medium. This is consistent with previous work on turbulent channels over porous media which enable ow in the stream-wise direction. However, the communication between both turbulent boundary layers results in these span-wise structures to be out-of-phase on either side of the permeable material. This phenomenon occurs at a frequency range where the noise reduction of porous trailing edges is the highest when compared to previous studies. A shift in turbulent kinetic energy carrying scales, with more energy being present in larger scales, is also observed. It can be concluded that this would increase the likelihood of interference occurring in the various locations of hydrodynamic pressure uctuation scattering and as such increase the noise reduction of porous trailing edges.