Investigating the impact of using CFD generated unsteady mach number dynamic stall data for numerical rotor analysis of helicopter forward flight

This paper investigates whether the accuracy of the blade airload prediction by current comprehensive rotor analysis methods are compromised by the exclusion of the unsteady nature of the freestream velocity in semi-empirical dynamic stall models. First, the current industry practice of rotor analysis utilizing semi-empirical dynamic stall models is reviewed, and the deficiencies in the accuracy of this method is demonstrated by comparing its results to the flight test data obtained from the UH-60A Airloads Program. To study the impact of including the unsteady nature of the freestream in dynamic stall, Computational Fluid Dynamics (CFD) was used to generate the unsteady 2D dynamic stall aerodynamic data representative of the conditions in the steady-level flight validation case (CT/σ = 0.129, μ = 0.24) from the UH-60A Airloads program whose counter designation is c9017. The CFD data served as inputs to the in-house rotor analysis code called Qoptr to generate blade airload results. The Qoptr blade airload results generated with the unsteady CFD dynamic stall data showed considerably better agreement with the flight test data than the results generated with semi-empirical dynamic stall models, especially in the sectional moment results