Semi-Empirical Modeling of Two-Dimensional and Three-Dimensional Dynamic Stall.

摘要

Helicopters are generally limited in their performance by the phenomenon of dynamic stall. The purpose of this work is to develop a method for modeling dynamic stall that is appropriate to preliminary design and flight simulator applications. Unlike other semi-empirical dynamic stall models, the model developed in this thesis, not only counts for the well-known, three-dimensional flow effects on the stalled loads but also captures the secondary vortex-shedding phenomenon that has been seen in experiments. The fundamental physics that modify dynamic-stall behavior and that have been extended from two-dimensional to three-dimensional flow are, namely: 1.) yawed flow, 2.) time-varying velocity, 3.) the rotational environment and 4.) the radial blade coupling. For the reduced-order modeling, extra nonlinear states have been added to the dynamic stall model in order to simulate the double-dynamic-stall phenomenon. The results of this study will have practical applications to aerospace systems, such as compliant or morphing surfaces in rotary-wing systems that encounter transient or periodic separation and reattachment during phenomena such as dynamic stall.