Single- and Dual-Rotor Flowfield and Outwash Predictions

摘要

An empirical method and a computational fluid dynamics (CFD) modeling of single- and dual-rotor outwash flow characteristics are presented. The empirical approach is based on the classical treatment of outwash flows for single and dual-rotor systems hovering in proximity to ground surface. But, whereas the classical method predicts outwash only along orthogonal directions, forward and aft and outboard of the sides of the aircraft, the present research generalizes the approach to outwash determination at any azimuth. A numerical flow computational method is also investigated for predicting the complex In Ground Effect (IGE) flowfield surrounding dual rotor systems. This approach takes advantage of some recent developments in Navier-Stokes flow solution scheme that involve efficient coupling of the flow solver with a blade-element rotor analysis. The scheme substantially reduces computational time while preserving reasonable accuracy, making it a feasible method for practical application to prediction of multirotor near-field and outwash characteristics. Outwash predictions for a single-rotor helicopter and a tiltrotor using the empirical method and the CFD method are compared with predictions based on the current Federal Aviation Administration (FAA) method. Correlation of the predictions from the empirical method with single-rotor helicopter flight test measured data is also presented.