Wall Modeling Effects in Transitional Airfoil Flows Using the Lattice-Boltzmann Method

The present study aims to assess wall modeling effects on transitional airfoil flows with laminar separation bubbles. Here, the lattice-Boltzmann method (LBM) is employed to investigate the flow over two NACA airfoil profiles. The first, a NACA0012 airfoil at an angle of attack of 3 deg, Mach number M = 0.3, and Reynolds number Re = 5 X 10^4, and the second, a NACA4412, with Re = 9.4 X 10^4}, M = 0.17 and 7 deg. AoA. The moderate Reynolds number configurations at hand are relevant in the context of small scale eVTOL vehicles. For both cases, a laminar separation bubble forms on the airfoil suction side, being responsible for complex dynamics including the shedding of coherent structures that scatter on the trailing edge, being important sources of airfoil tonal noise. The LBM in Direct Numerical Simulation (DNS) mode has shown to properly capture the unsteady flow physics in a NACA0012 simulation compared to a wall-resolved large eddy simulation (LES) of the Navier-Stokes equations. In this paper, we will quantify the performance of wall models within the LBM approach in the software PowerFLOW. The main goal is to assess the capability of wall-modeled LES in resolving near-wall features of transitional boundary layers. The results show that the different wall model strategies implemented in PowerFLOW provide similar metrics for the NACA0012 airfoil, but different statistics are observed for the NACA4412, which could be justified by the higher adverse pressure gradients on the suction side.