Prediction of Helicopter Rotor Loads Using Time-Spectral Computational Fluid Dynamics and an Exact Fluid-Structure Interface

Abstract

The objectives of this paper are to introduce time-spectral computational fluid dynamics (CFD) for the analysis of helicopter rotor flows in level flight and to introduce an exact fluid-structure interface for coupled CFD/computational structural dynamics (CSD) analysis. The accuracy and efficiency of time-spectral CFD are compared with conventional time-marching computations. The exact interface is equipped with an exact delta coupling procedure that bypasses the requirement for sectional airloads. Predicted loads are compared between time-spectral and time-marching CFD using both interfaces and validated using UH-60A flight data for high-vibration and dynamic stall conditions. It is concluded that time-spectral CFD can indeed predict rotor performance and peak-to-peak structural loads efficiently, and hence, open opportunity for blade shape optimization. The vibratory and dynamic stall loads, however, require a large number of time instances, which reduces its efficiency. The exact interface and delta procedure allow coupling to be implemented for arbitrary grids and advanced structural models exactly, without the requirement for two-dimensional sectional airloads.