Unstructured Mesh Navier-Stokes Calculations of the Flow Field of a Helicopter Rotor in Hover

Three-dimensional viscous flow field around a lifting helicopter rotor in hover is calculated by using an unstructured mesh methodology. The flow solver utilizes a cell-centered finite-volume scheme that is based on the Roe’s flux-difference splitting and an implicit Jacobi/Gauss-Seidel time integration. The effect of turbulence is estimated by the Spalart-Allmaras one-equation model coupled with a wall function boundary condition. A solution-adaptive mesh refinement technique is used for efficient capturing of the tip vortex. Calculations are performed at two operating conditions with varying tip Mach number and collective pitch setting. Formation of the tip vortex is well captured through a series of adaptive mesh refinement procedure starting from a coarse initial mesh. Good agreements are obtained between the numerical result and the experiment for both the blade loading and the tip vortex behavior. It is demonstrated that the rotor performance and the flow field are significantly affected by viscosity. The process of tip vortex formation around the blade tip is also qualitatively investigated.

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