New Far-Field Boundary and Initial Conditions for Computation of Rotors in Vertical Flight Using Vortex Tube Model

Motivated by demands for improved far-field boundary condition and initial condition for computations of helicopter rotor aerodynamics, a theoretical model using a truncated vortex tube concept is applied to the Navier–Stokes computations. A helicopter rotor wake is represented by the truncated vortex tube of continuously distributed vorticity in this model. Velocity components induced by the vortex tube are used to specify the far-field boundary and initial conditions. Computations were done for the UH-60A model-rotor test cases in hover. The results of the vortex tube model boundary condition show good agreements with the measured performance values and provide a more accurate prediction of rotor wake than that of the source-sink boundary condition. In addition, the initial condition using the vortex tube model enables faster convergence and gives more stable solutions than an initial condition assuming quiescent flow fields. Its application is also easily extended to climbing/descending flights, because the vortex tube model was originally devised to calculate induced flows of a helicopter rotor in the vertical flight. Computed rotor performance values agree with experimental results for various vertical flight conditions. The overall results show that the vortex tube model can be used for the new far-field boundary condition and initial condition when performing helicopter rotor analysis.

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