Investigation of Rotor-Rotor Interactions for Two Helicopters in Forward Flight Using Free-Vortex Wake Methodology

Abstract

This paper presents an investigation of the aerodynamic interactions between two UH-1H helicopter rotors in forward flight. The wake flow structure and performance characteristics of the rotors are investigated when the rear rotor is operating within the wake of the front rotor. A 3-D unsteady vortex-panel method potential flow solver based on a free-vortex-wake methodology is used for this purpose. The solver is validated using the experimental data from the Caradonna-Tung experiments. The interactional analyses are performed for 10 different positions of the rear rotor with respect to the front rotor. The wake of the front rotor, which is generated due to the mutual interactions of the wake and tip vortices, is significantly asymmetric and non-uniform. Therefore the rear rotor operates within a complex and vortical free-stream flow. The interaction of the incoming wake flow and the rear rotor generates a large, asymmetric wake region downstream of the rear rotor. The wake-rotor interactions cause substantial variations in the forces generated by the rear rotor. These variations also depend on the lateral location of the rear rotor with respect to the front one. © 2010 by Nilay Sezer Uzol.