Parametric Study of Separation and Reattachment in Transonic Airfoil Flows

Abstract

Shock and boundary-layer interactions in transonic airfoils are investigated by means of wall-modeled large-eddy simulation. A distinctive flow model, organized and chaotic, occurs in this regime driven by the transition from laminar to turbulent flow, and therefore the appearance of coherent structures such as the Kelvin–Helmholtz instability. This phenomenon is crucial for designing transonic airfoils because it leads to a high rise in drag. Experimental observations show that the main variables of transonic airfoil flow are the freestream Mach number, the Reynolds number, and boundary-layer thickness. Simulations are performed to investigate the relation of various components of the shock/boundary-layer interaction, that is, the pressure rise to shock-induced separation, the length of the separation bubble, and the rear separation to the unit Reynolds number and the boundary-layer condition upstream of the shock. Flow around NACA0012 is investigated in a range of transonic Mach numbers at various unit Reynolds numbers. It is found that the bubble length on the airfoil changes rapidly with relatively small changes in the freestream Mach number. Simulation results show that the separation length decreases with increasing of the unit Reynolds number; however, increasing the boundary-layer thickness results in an increase in the bubble’s extent. Evaluation of the rear-separation region shows that, as the Reynolds number increases, the length of the rear separation declines at a given Mach number.