Unsteady Actuating Blade Model for CFD/CSD Analysis of a Tiltrotor

The paper presents an effective method to evaluate the unsteady flow field around a rotor through a Computational Fluid Dynamics model based on the actuator blade approach. The actuator blade extends the classical actuator disk model without the necessity to perform time or azimuth averaging operations. In this way, a time accurate investigation of the influence of the rotor wake on the rotor itself and on other non-rotating parts (fuselage, wings) can be performed. The method exploits the overset grid technique to allow an easy identification of the location of the sources distributed in the flow field to enforce the correct blade loads. The kinematics and the dynamics of the rotating parts is computed thought the coupling with a multibody solver and transmitted to the CFD as movement of the independent surface grids associated with each actuator blade. This allows to keep into account both rigid and elastic movements, including those related to movable surfaces. A comparison with experimental results obtained for a four blade tiltrotor are shown to verify the quality of the prediction of the flow field. Additionally, a comparison with the results obtained through a classical actuator disk allows to quantify the effects of the employment of the time-accurate approach with respect to the time-averaged results of the actuator disk model.