Use of aerofoil section dynamic stall synthesis methods in rotor design

Abstract

AbstractThe introduction of the original time delay method of Beddoes, an engineering model for the unsteady response of an aerofoil section including dynamic stall, had a profound effect on the design and development of rotor systems in the UK. Over the years, the model expanded to include more and more features of the unsteady flow, with many contributors. It is now in use throughout the world as part of rotor analysis packages. Nevertheless, it retains its essential simplicity. Work to confirm the ability of the most recent version of the dynamic stall model from the University of Glasgow to replicate the complicated behaviour of an advanced rotor aerofoil section at full scale Reynolds and Mach numbers provides an opportunity to review the use of this new engineering model in the helicopter rotor design environment.This note discusses the application of dynamic stall synthesis methods to the problem of classifying and comparing aerofoil sections when designing rotors for the retreating blade stall condition that determines the rotor blade area requirement of the helicopter. The development of the dynamic stall models employed in UK rotor designs is reviewed in this paper and their use in the design process explained, with emphasis on the assumptions that overcome the limitations of the models and exploit their simplicity, enabling accurate and conservative rotor designs. The paper shows how the model may be used to structure the analysis of complex sets of dynamic aerofoil data. It illustrates how structured comparison between the model and the data yields a concise appreciation of the behaviour of the aerofoil and an understanding of the physical processes involved. Some previously unappreciated effects are identified and the model is used to transfer experience of the aerofoil section behaviour from the non-rotating wind-tunnel environment to that of the rotor. Finally, the application of the new engineering model developed at Glasgow University in the rotor design process is outlined. Some remarks on the use of engineering models in comparison with CFD models in the design context are included.