Computational Techniques for Improved Blade Vortex Interaction Modeling

As part of the Langley Computational Fluid Dynamics-based Blade-Vortex Interaction (BVI) prediction system, a rotor CFD code called FPRBVI was developed by combining the McDonnell Douglas Helicopter Systems (MDHS) wake tracking system and the full potential rotor (FPR) CFD analysis program. This new code, FPRBVI, has been a useful tool in investigating rotor blade-vortex interactions. Several enhancements have been recently added to improve the BVI modeling within the FPRBVI code. A wake interpolation method is discussed which interpolates and smooths the tip vortex wake information obtained from external free wake analyses. A method for modifying extremely oblique blade-vortex interactions to eliminate airloads impulses is presented. A technique for reducing the computation time of BVI calculations without loss in accuracy is discussed. A model for azimuthally-varying tip vortex core size was implemented to allow investigation of more realistic vortex behavior. Both aerodynamic and acoustic predictions using the four methods are presented and compared with OLS rotor wind tunnel measurements.