Detailed Computational Investigation of a Hovering Microscale Rotor in Ground Effect

A compressible, structured, overset Reynolds-averaged Navier-Stokes-based solver is used to simulate a microhovering rotor in ground effect to demonstrate the capability of the code to provide accurate tip-vortex-flowfleld predictions, and to provide a good understanding of the ground wake interactions in conditions prevalent in helicopter brownout. The performance validation at different rotor heights above the ground shows good correlation with the experimental thrust and power measurements. A detailed comparison of the predicted tip-vortex flowfield shows good agreement with the vorticity contours and radial-velocity profiles obtained from the particle-image-velocimetry measurements during experiments. The examination of the in ground effect tip-vortex flowfield suggests high degree of instabilities close to the ground. The induced velocities arising from the proximity of the rotor tip vortices cause flow separation at the ground. An analysis of the eddy-viscosity contours near the ground indicates higher turbulence levels in the flowfield at smaller rotor heights above the ground. With a decreasing rotor height, the increased interactions between the tip vortices and the ground boundary layer result in the intermixing of eddy viscosity from the tip vortex to the ground boundary layer.