Steady and unsteady flow simulation of a combined jet flap and Coanda jet effects on a 2D airfoil aerodynamic performance (2007)

Two-dimensional numerical flow simulations were per formed to investigate the combined effects of two types of trailing edge blowing jets upon the aerodynamic performance of a supercritical airfoil. One of the two (Coanda jet) was blown tangentially around a Coanda surface (round trailing edge) while the other one (jet flap ) was blown normally off the Coanda surface at a given angle. Steady and time-accurate viscous flow simulations were performed and demonstrated stable flow solutions. Results obtained for four di fferent airfoil configurations (no-jets, Coanda jet only, jet flap only, combined Coanda jet and jet fl ap) showed that the combined jets configuration presented the best aerodynamic performance. In the continuing search for improvements in the ae rodynamic efficiency of wind turbines, many aerodynamic enhancements to the blades of conventional turbines have been proposed and studied. Numerous techniques have been studied to i ncrease the lift to drag ratio of the blades and hence their overall efficiency at extracting power from the wind. To this end, techniques such as blowing air over the blade trailing edge (1), blowi ng air through the trailing edge (jet flap) (2) and the use of a Coanda surface at the trailing edge wit h tangential blowing (3) are known to produce substantial increases in lift. Many experimental in vestigations have also been conducted on these three types of concepts in the past (2, 3). A jet flap is characterized by a high-velocity air jet that is blown straight out of the airfoil trailing edge at a controlled angle. Its potential benefits originate in the more global influence tha t the deflected jet sheet has upon the surrounding fl owfield. An aerodynamic Coanda effect is generated when a high-velocity air jet is blown tan gentially along a curved surface. The circumferential air jet remains attached to the sur face owing to the balance between the low static pressures generated by the jet itself on the surfac e and the centrifugal force acting on the jet. These two aerodynamic techniques are classically well established for aeronautical applications (2). Extending circulation control towards wind tur bine applications, there is ongoing research in this topic with an aim towards increased power gene ration (1). More recently, the availability of convenient and economic modeling, to study larger p erformance matrices due to increased (and lower cost) computational power, has meant that the investigation of trailing edge blowing (jet flap) and Coanda surfaces using Computational Fluid Dynamics has received greater attention (1). In the current numerical investigation, we believe that a combination of jet flap and Coanda effect may lead to an additive effect and substanti al increase in the airfoil lift. To prove the concept, the present investigation was carried out on low Mach number flow over a supercritical airfoil with a round trailing edge, where a jet fla p and a Coanda jet are applied concurrently. Results in terms of Mach number distribution, pressu re coefficient profiles and force coefficients (lift and drag) are presented.