Numerical Investigation of the Aerodynamics and Acoustics of Head-On Blade-Vortex Interaction

With the aim of obtaining detailed insight into the physical mechanism of blade-vortex interaction (BVI) and to comprehensively assess the capability of state-of-the art modelling tools in predicting the same, the present work attempts to simulate the flow-field around an isolated rotor undergoing a head-on parallel interaction with an independently generated vortex. The simulations are performed within a moving overset mesh framework that is readily extendable to realistic helicopter configurations. The resulting flow field is investigated, and the blade surface pressures and near and far-field acoustic pressures are compared directly against the experiments of Caradonna et al. (Ref. 1). Simulation results are first presented for the problem of a highly resolved two dimensional direct impact aerofoil-vortex interaction (2-D AVI) in which an idealised vortex model is initialised in the flow and allowed to freely convect and interact with the aerofoil. The vortex is observed to split into two halves that convect above and below the aerofoil surface at varying speeds. The aerofoil surface pressures from the 2-D AVI simulation are found to correlate well with measurements. A three dimensional simulation - in which the formation, convection and interaction of the vortex is resolved - is then attempted, with specific attention devoted to studying the ability of the methodology to accurately transfer vortical structures across moving mesh interfaces. While the flow solution is shown to be highly sensitive to errors that originate near mesh interfaces, the computed surface pressure and acoustics are shown to agree extremely well with measurements, thus establishing the viability of the methodology as an accurate predictive tool for the aerodynamics and acoustics of BVI.