Numerical simulation of turbulent flow around helicopter ducted tail rotor

As compared with helicopter conventional tail rotors, ducted tail rotors have a higher aerodynamic efficiency, smaller size and higher security. Therefore, ducted tail rotors have been extensively used in the world. Flow field of ducted tail rotors includes complex turbulent flow phenomena such as blade-vortex interaction and shroud-vortex interaction. The usual way to study the turbulent flow is the CFD numerical simulation. For ducted tail rotors both the fan and duct can yield thrust. In order to get flow field details and the total thrust of ducted tail rotors, a new numerical simulation technique for ducted tail rotor flow is established. In this paper, the flow field and performance of a helicopter ducted tail rotor in hover and sideward flight were analyzed using CFD technique. The general governing equations of turbulent flow around ducted tail rotors were first set up, and then directly solved by finite volume approach and SIMPLE approach in an axisymmetric coordinate system. The spinning fan was represented as time-averaged momentum source terms distributed along the span of the fan with functional relationship to the local flow conditions in N-S equations. The calculation method also included a stairstep representation of the shroud, staggered grid system, K-ɛ turbulence model and wall function method on the shroud. This unique CFD numerical simulation technique developed here not only can predict the flow field but also analyze the performance of ducted tail rotors. The calculated results for flow field and performance correlation show good agreement with the measured data. Therefore, it is concluded that the numerical simulation technique in this paper is proved to be feasible for analyzing design issues of ducted tail rotors.