Real-Time simulation of dynamic stall with unsteady free-stream velocity

We show that a simple enhancement to the Peters et al. dynamic-stall model (an ONERA-Type model) results in large improvements in the correlation of experimental data with unsteady free-stream velocity. The core of the enhancement is that the free-stream velocity in the governing differential equation (for phase-lag and overshoot of the loads) is frozen when the dynamic-stall vortex is shed to reflect the constant strength of the shed vortex. To use the enhanced model, one need only train the new model on data for a steady free stream, and the resultant model then gives good correlation for results with unsteady free-stream as well. This improvement is demonstrated by comparisons with experimental data from Favier et al. (American Helicopter Society 48th Annual Forum Proceedings, Washington, DC, June 3-5, 1992, pp. 1385-1407) for CL under various pitch angles and free-stream velocities. Correlation with limited data for pitching-moment coefficient is also presented, which indicates that the methodology can also be used for modeling the moment coefficient, CM, under unsteady free-stream velocity.