Impact of Porous Media on Boundary Layer Turbulence

Abstract

The subsonic flows around NACA 0012 aerofoils with a solid, a porous, and a poro-serrated trailing edge (TE) at a Reynolds number of 1 × 106 are investigated by a hybrid Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) approach. The porosity is treated by the method-of-volume averaging. In the RANS, a two-equation low Reynolds number k-ε turbulence model is modified to include the porous treatment. Similarly the equations in the LES are extended by the Darcy–Forchheimer model. The simulation is set up with the broadband turbulent boundary layer trailing edge (TBL-TE) noise prediction as a future objective in mind, i.e., the noise sources in the trailing edge region are captured by the LES. To enforce a physically realistic transition from an averaged RANS solution towards a resolved turbulent flow field, at the inflow of the LES coherent structures are generated by means of the reformulated synthetic turbulence generation (RSTG) method. For the poro-serrated TE, turbulence statistics vary in the spanwise direction between the two extremes of a pure solid and a rectangular porous TE, where porosity locally increases the level of turbulence intensity and alters the near wall turbulence anisotropy.

Towards extending the aircraft flight envelope by mitigating transonic airfoil buffet

“…The different aerodynamic performance of the porous trailing edge designs can be explained by the previous observations summarized in Table 1 . The time-averaged boundary layer thickening of around 10.2% induced by PTE1 increases the aerodynamic drag, which was observed for other porous materials as well 58 , 60 , 64 , 70 , 71 . Furthermore, a minor increase of the Reynolds shear stress within the boundary layer of 2.2% could contribute to the aerodynamic performance deficit.…”

“…This two-fold benefit is in great contrast to the other buffet control strategies discussed above. These devices typically increase the noise emissions because the additional components disturb the flow field 58 , 59 . Moreover, porous trailing edges have the advantages of low cost, low operational complexity, and robustness.…”