Influence of boundary layer transition on the flutter behavior of a supercritical airfoil

Abstract

This paper presents a flutter analysis for the supercritical CAST 10-2 airfoil in a flow with free boundary layer transition based on CFD computations with the γ-Reθ transition model. The results are compared to fully turbulent results obtained with the SST k-ω turbulence model. Unsteady RANS computations at Rec=2×106 are used to determine the aerodynamic derivatives. These derivatives are required to identify the flutter boundary for a 2 degree-of-freedom model by a k method. The transonic flutter boundary decreases for a flow with free boundary layer transition compared to a fully turbulent flow in the vicinity of the transonic dip. However, the flutter boundary at subsonic Mach numbers is raised for a transitional flow. In addition, the transitional frequency response is discussed: an aerodynamic resonance in connection with an instability of the transition region is observed and the possibility of a 1 degree-of-freedom flutter for transitional flows is shown.