On Modeling and Simulation of Airwake and Airwake-Downwash Turbulence for Helicopter Shipboard Operations

This paper reviews the statistical treatment of both airwake and airwake-downwash turbulence in the ship-helicopter dynamic interface; airwake refers to the turbulence shed from the ship superstructure and airwake-downwash turbulence, to the coupled flowfield of airwake and rotor downwash. The paper also addresses non-real-time simulation of both flow-fields through shaping filters driven by white noise. Throughout, the focus is on the one-point statistics of autocorrelation and autospectrum and on the two-point statistics of cross-correlation and cross-spectrum. Specifically, the review covers experimental and CFD-based investigations, and also perturbation-theory approach of extracting analytical models from a database of autospectral and cross-spectral points of flow velocity data from these investigations. The state of the art has reached the point of reliably predicting and simulating the one-point statistics of airwake. By comparison, the database on the two-point statistics of airwake and on the one-point statistics of airwake-downwash turbulence is much too limited; this virtually precludes passing a judgment on the current capabilities for predicting and simulating the respective statistics. As to the two-point statistics of airwake-downwash turbulence, no database is available in the open literature. Future research should address the one-point and two-point statistics of airwake-downwash turbulence and also the two-point statistics of airwake.