NUMERICAL STUDY ON FLOW PERFORMANCE OF DELAYING AIRFOILSTALL WITH INTERNAL SLOTS
In order for an airfoil blade to efficiently capture wind or current energy, its post-stall performance needs to improve. Flow separation associated with stall not only reduces performance but also increases damage from fatigue. This paper reports our numerical investigation of a passive flow control mechanism created by placing internal slots on an airfoil to allow flow from the positive pressure surface to move to the negative pressure side to remove separated flow. In the present study, the case of a NACA 0012 foil is reported, with Reynolds number ranging from 300,000 to 800,000, calculated from the incoming uniform flow speed and foil’s chord length. An angle of attack of up to 60 degrees is examined with the Spalart-Allaras turbulence model. Other airfoils were also investigated, but the essential results are similar. Our results show that a 70% increase in peak lift coefficient could be achieved with internal slots. At an angle of attack of 19 degrees, the lift-drag ratio is typically about 28 vs 6, in favor of a foil with an internal slot. Performance for larger angle of attacks can be improved with multiple internal slots. The conventional foil nevertheless performs better for lower angle of attacks. Our work demonstrates the possibility of improving airfoil performance for all angles of attack using internal slots with a control of their openings.