Large-Eddy Simulations of Owl-Like Wing Under Low Reynolds Number Conditions

Flow fields around an owl-like wing and aerodynamic characteristics at a chord Reynolds number of 23,000 are investigated using three-dimensional implicit large-eddy simulation. The cross sectional profile of the owl wing model named “owl-like wing” is constructed based on the owl wing at 40% of the span length from the root. It consists of flat upper surface, large camber, and thin geometry. Results show that at low angles of attack (α), separation, transition, and reattachment are observed in the instantaneous flow fields on the pressure side. The laminar separation bubbles can be seen in time- and span-averaged flow fields. It is likely that lift and drag generation is correlated with the location of separation points on the suction side. However, it has little influence on behavior of C_L-α curve. On the other hand, at high angles of attack, the flow on the pressure side is fully attached. The flow on the suction side is similar to that of the pressure side at low angles of attack. It is found that unlike the case of the flow at the low angles of attack, the laminar separation bubble on the suction side affects the response of C_L to variation of α. Furthermore, it is possible to decrease the drag and to increase the lift when the location of the laminar separation bubble is well organized by an appropriate airfoil surface geometry. Also, the deeply concaved lower surface contributes to lift enhancement. From those factors mentioned above, the owl-like wing gains higher lift-to-drag ratio comparing with conventional thin and thick symmetrical airfoils such as NACA0002 and NACA0012. Indeed, maximum lift-to-drag ratio of the owl-like wing is approximately 23 at the angle of attack of 6.0 degrees at Reynolds number of 23,000.