Hover Performance in Ground Effect Prediction Using a Dual Solver Computational Methodology

Rotorcraft operation in ground effect is an essential phase of every rotorcraft mission. Accurate prediction of this aerodynamic regime has implications for the design of the rotor, vehicle, and mission guidelines. Modern rotorcraft designs require higher fidelity predictions of the aerodynamics beyond the capabilities of momentumbased or algebraic models of ground effect, but high-fidelity computational fluid dynamics (CFD) remains intractably expensive. A hybrid CFD-free-wake solver OVERFLOW-CHARM has been developed for application to this problem. It was validated against thrust, power, and flow visualization data obtained experimentally for a micro-scale rotor hovering out of ground effect and in ground effect at a range of heights between h/R = 0.5 and h/R = 2.5. A study of numerical options was performed to ensure confidence in the computational simulations. The results demonstrated that OVERFLOW-CHARM was able to capture the integrated rotor loads within three percent of a conventional OVERFLOW simulation at twenty percent the computational cost, and that qualitative agreement in the predicted flow fields was observed between OVERFLOW-CHARM, OVERFLOW, and experiment.