Analysis of the Turbulent Wake Generated by a Micro Air Vehicle Hovering near the Ground with a Lattice Boltzmann Method

Abstract

This paper presents numerical investigations undertaken to analyze the turbulent flow produced in the wake of a micro air vehicle rotor interacting with the ground. Two configurations are investigated: a free rotor and a shrouded rotor. The Reynolds number based on the chord and tip speed is Retip = 0.86 × 105, which corresponds to a challenging flow where leading-edge separations are commonly observed. The numerical simulations are performed with a Reynolds-averaged Navier–Stokes approach and a large-eddy simulation (by means of a lattice-Boltzmann method), combined with an immersed boundary approach. The comparison of numerical data with measurements shows that the mean flow and the turbulent shear stresses are accurately predicted close to the ground and in the rotor wake. However, some discrepancies remain in the prediction of the rotor torque and thrust, mainly due to the difficulty to reproduce the flow near the rotor walls. An analysis is conducted to identify and understand the different sources of turbulent production. The numerical simulations show also that the presence of a shroud contributes, at a given thrust, to reduce the velocity and the turbulent intensity at
the ground.