Hybrid Turbulence Model Simulations of Blade Section in Dynamic Stall

Dynamic stall on helicopter blades increases power consumption and causes unsteady aerodynamic loads, vibrations, and noise. The prediction of dynamic stall onset is of interest to designers and operators of helicopters. For Reynolds numbers up to one million and higher, dynamic stall can be initiated by the bursting of a laminar separation bubble. This has been demonstrated in experiments and simulations. The accurate prediction of bubble bursting in simulations requires that the separation bubble physics be captured accurately. While wall-resolved large-eddy simulations can fulfill that requirement, they are computationally expensive. This paper explores the feasibility of hybrid turbulence model simulations based on the Spalart–Allmaras and Menter shear-stress transport models in combination with the Coder transition model for predicting dynamic stall onset. Results from both two-dimensional and three-dimensional simulations with narrow spanwise domain extent are presented. While the present simulations can capture bubble bursting, the poststall aerodynamics are not accurately represented because the narrow domain favors spanwise structures. The case under consideration is a blade section with a NACA 0012 airfoil that is subjected to a constant-rate pitch-up maneuver and a harmonic pitching motion. The chord Reynolds number for the two cases is five hundred thousand and one million, respectively. With the Menter shear-stress model, bubble bursting and dynamic stall onset are captured in agreement with published data. While bubble bursting is delayed for the Spalart–Allmaras model, this problem can likely be overcome by a modification of the blending function.