Highly Efficient Unsteady Panel Time-Marching Free Wake for Aerodynamics of Rotorcraft

Abstract

A highly efficient unsteady panel time-marching free wake is established to achieve fast and accurate prediction of the unsteady aerodynamics of a helicopter. The unsteady panel method is used to calculate the airload of rotor blades, and the free-wake method is applied to simulate the dynamics of rotor wake. The two methods are tightly coupled by convecting panels to vortex filaments, and the rotor wake is divided into three parts to reduce the computational cost. The first is shed wake indicated by doublet panels. The second is near-wake filaments, which are described by a series of vortex filaments attaching to the shed wake. The third is far-wake filaments connecting to the near-wake filaments. A velocity-field integration technique is adopted to overcome the singularity problem during the interaction of the rotor wake with blades. Helicopter rotors including the Caradonna–Tung and the AH-1G rotors are simulated in hover and forward flight to validate the accuracy and efficiency of the present approach. The predicted blade pressure and load distribution agree well with the measured data and computational-fluid-dynamics results in hover and low-speed forward flight. Compared to computational fluid dynamics and the traditional panel/vortex-rings free-wake method, the present method is more efficient.