Lift and Drag Forces of a High Efficiency Airfoil With an Embedded Rotating Cylinder

Numerical investigations of an optimized thin airfoil with an active flow control device (rotating cylinder) embedded into the airfoil have been performed. The objective of the study was to investigate the possibility of using a rotating cylinder to maintain performance of micro aerial vehicles, MAVs, when significant and sudden variation in wind speed (example: gust) is present. The airfoil has a chord length of 19.66 cm and a span of 25 cm. The free stream mean velocity was 20 m/s which corresponds to a chord length Reynolds number of 2.54×105. Simulations were performed at 17 degrees angle of attack which include the initial angle that the cambered leading edge makes with the incoming axial flow. Simulation results for the airfoil without the embedded cylinder have shown flow separation at approximately 85% chord length. Then, a rotating cylinder with a 0.51 cm diameter was embedded into the airfoil, spanning the width of the airfoil at slightly downstream of the location of flow separation, i.e. at x/c = 0.848. There was 1 mm spacing between the cylinder and the airfoil, to allow cylinder’s rotation. Investigations were performed at different rotation speeds, corresponding to corresponding tangential velocities being higher than, equal to and less than the local axial freestream mean velocity. Results showed approximately 10% improvement in lift to drag ratio (L/D), when the tangential velocity was the same or higher than the local axial mean velocity.