Dynamic Stall Computations of a Double-Swept Rotor Blade with Rigid and Elastic Modelling

Kurzfassung

Innovative helicopter rotor blades with a combined forward-backward double-sweep at the outer part of the blade enable a reduction in noise emission and enhance the overall performance of a rotor. In this context, the influence of the aeroelastic behaviour in connection with the dynamic stall phenomenon is of great importance. It is accompanied by large aerodynamic load peaks, primarily seen in the lift and the pitching moment, impacting the structural integrity of the blades and adjacent control components. Double-swept model rotor blades were developed and investigated experimentally at the German Aerospace Center (DLR) in Göttingen regarding the dynamic stall behaviour in a four-bladed rotor configuration at the Rotor Test Facility Göttingen. Due to an axial inflow to the rotor disc a sinusoidal variation in pitch angle is introduced to trigger the dynamic stall phenomenon once per revolution. The numerical study simulates the conducted experiments utilizing two different blade modelling approaches: elastic and rigid bodies. The corresponding computations are carried out with the use of computational fluid dynamics (CFD) and a multibody system (MBS). With the inclusion of blade elasticity both domains are connected together by using a strong aeroelastic coupling scheme. Three test cases with a rotor speed of 23.6 Hz will be presented comprising two test cases with fixed collective pitch angle and one with a superposed cyclic variation in pitch angle in order to introduce the dynamic stall phenomenon. Finally, a comparison is carried out with experimental data including the measured rotor thrust as well as the displacements at the blade tips. They show good agreement with the numerical results in both of the considered fields comprising the structural behaviour of the blades as well as the surrounding fluid flow.