Evaluation of Flexible Rotor Hover Performance in Extreme Ground Effect
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Motivated by the Sikorsky Human Powered Helicopter Challenge, an attempt to further study ground influence on a hovering rotor of highly elastic blades in extreme ground proximity has been carried out. This study presents two computational approaches for prediction of elastic blade behavior in ground effect, using finite element analysis (FEM) for deflections while modeling ground effect on a blade element level.The first approach is based on classical blade element momentum theory, correcting for ground effect based on empirical models.The second method uses a newly tailored rigid prescribed wake model alongside blade element analysis. As both methods account for local height off the ground at each blade element, they allow for more detailed insight regarding property distributions along the highly elastic blade in extreme ground effect conditions and thus improved performance prediction capabilities. This study includes experimental results from both a rigid blade sub-scale set-up and elastic blade full scale set-up, operating in extreme ground effect, which are subsequently used to validate the proposed methods. This work concludes that careful consideration of blade deflections when modeling flexible rotor performance in extreme ground effect is key to a successful prediction capability, and thus design parameters which influence variation in thrust distribution will have an increased effect on performance in these conditions.