Computational Study on the Effects of Unsteady Freestream on an Airfoil Performance at Low Reynolds Numbers

摘要

Computational studies of the response of a NACA0012 airfoil at varying angles of attack (a) to freestream turbulence at low Reynolds numbers (i.e., 12,000 based on the airfoil chord length) are conducted in this work. The unsteady freestream is generated by placing an array of circular cylinders upstream of the airfoil. The presence of moderate freestream turbulence (～5%) affected the formation of laminar separation bubbles near the leading edge of the airfoil, which has significant impacts on the aerodynamic performance. The study was able to recreate the maximum lift coefficient of the airfoil in unsteady freestream turbulence observed in experiments, which is higher than that for the airfoil in a uniform freestream. In general, the present numerical results agree reasonably well with those from experimental studies. This work also demonstrates that three-dimensional (3D) simulations with high-order accurate numerical methods predict the lift coefficient more accurately than lower dimension (i.e., 2D) or lower order 3D methods.