Numerical Study of Wind-Tunnel Sidewall Effects on Circulation Control Airfoil Flows

摘要

Two- and three-dimensional numerical simulations are performed of the flow around a circulation control airfoiln(using aCoanda jet blowing over a rounded trailing edge) placed in a rectangularwind-tunnel test section.The airfoilnmodel spans the entire tunnel and the span-to-chord ratio of themodel is 3.26. The objective of this numerical study,nin which we solve the compressible Reynolds-averaged Navier–Stokes equations in a time-resolved manner (but thensolutions eventually converge to steady states), is to investigate the physical mechanisms of wind-tunnel sidewallneffects on the flow, especially in the midspan region. The three-dimensional simulations predict that the Coanda jetnflowis quasi-two-dimensional until the flowseparates fromthe trailing edge of the airfoil; however, the spanwise endsnof this Coanda jet sheet then three-dimensionally roll up on the side walls of the wind tunnel to form two largenstreamwise vortices downstream. Careful comparisons between the two- and three-dimensional simulations revealnthat the wind-tunnel stream goes below the airfoil more in the three-dimensional cases than in the two-dimensionalncases due to the presence of these two streamwise vortices downstream. This results in smaller lift and larger dragnbeing produced at the midspan of the airfoil in the three-dimensional cases than in the two-dimensional cases.