Accurate and efficient vortex-capturing for a helicopter rotor in hover

This investigation has been carried out under a contract awarded by the Boeing/McDonnell Douglas Helicopter Company, Purchase Order Number 689578. The Boeing Company (Mesa) has granted NLR permission to publish this report. Summary A numerical method has been developed for predicting from first principles, the complex vortex-wake for a helicopter rotor in hover. The method is based on the solution of the three-dimensional, compressible Euler equations expressed in an Arbitrary Lagrangian Eulerian (ALE) reference frame. A second-order accurate discontinuous Galerkin (DG) finite-element method is used to discretize the governing equations on a hexahedral mesh. Unstructured, local mesh refinement is performed to enable prediction of the structure of the vortex wake while computational efficiency is retained through a mesh de-refinement process. Convergence acceleration is achieved using a multi-grid technique. While this study emphasizes the wake system for a hovering rotor, the developed method, when applied on a dynamically-deforming mesh, is equally applicable for predicting the vortex-wake for a rotor in forward flight. Accuracy of the predictions are assessed using the wind tunnel data for the two-bladed Caradonna-Tung rotor in hover.

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