Effect of Free-Stream Turbulence Intensity on Transonic Airfoil with Shock Wave

Airplanes regularly operate switching between various flight modes such as take-off, climb, cruise, descend and landing. During these flight conditions the free-stream approaching the wings undergo fundamental changes. In transonic flow conditions, typically in the military or aerospace applications, existence of nonlinear and unsteady effects of the airflow stream significantly alters the performance of an airfoil. This paper presents the influence of free-stream turbulence intensity on transonic flow over an airfoil in the presence of a weak shock wave. In particular, NACA 0012 airfoil performance at Ma(infinity)=0.7 is considered in terms of drag, lift, turbulence kinetic energy, and turbulence eddy dissipation parameters under the influence of varying angle of attacks and free-stream turbulence. The finite volume method in a commercial CFD package ANSYS-CFX is used to perform the numerical analysis of the flow. Mesh refinement using a mesh-adaption technique based on velocity gradient is presented for more accurate prediction of shocks and boundary layers. A Shear Stress Transport (SST) turbulence model is validated against experimental data available in the literature. Numerical simulations were performed, with free stream turbulence intensity ranging from low (1%), medium (5%) to high (10%) levels. Results revealed that drag and lift coefficients are approximately the same at every aforementioned value of turbulence intensity. However, turbulence kinetic energy and eddy dissipation contours vary as turbulence intensity changes, but their changes are disproportionally small, compared with values adopted for free-stream turbulence.