Experimental and computational investigation of passive surface flow control for aerodynamic efficiency

A passive surface flow tailoring methodology, inspired by nature, is proposed and studied, under the long-term goal of achieving greater aerodynamic efficiency and stability for wall bounded flows pertinent to systems such as wind turbines and low-speed small unmanned aircraft. In this paper, passive surface features are designed as ridge-lines parallel to the leading edge of the airfoil/wing, with a cross section given by Gaussian curve(s). Subsonic wind tunnel experiments were conducted with a wing section comprised of the symmetric NACA 0012 airfoil; the experiments were run at different angles of attack for incoming Re of about 1e05-2e05. The experiments showed that promising gains can be achieved for lift-to-drag ratios at low angles of attack and in delaying stall angles by using ridges that are close to the leading edge, in comparison to the baseline wing section with no ridges. On the other hand, CFD simulations conducted (using the FLUENT package) on a NACA 4412 airfoil demonstrated that ridges located further away from the leading edge can significantly delay (by > 10% of chord length) flow separation compared to the baseline airfoil with no ridges (for incoming Re of about 2e05).