Abstract:
The control of flow separation is one of the important ways for the reduction of drag as well as the increase of lift to drag ratio. In the domain of aerospace technology the main focus of this study is the enhancement of lift force, the reduction of drag force and in combination the enhancement of lift to drag ratio. In order to achieve these objectives, both active and passive controls of flow separation on 2D NACA 0018 airfoil are considered and CFD simulation is performed on this configuration. The computational runs are made at Reynolds number 7.12x106 and angles of attack ranges from 0° ~ 25°. This investigation primarily focuses on the flow separation delay by suction with a slot of width 2% of the chord length placed at different locations of the airfoil to find optimum position. Suction pressures are expressed as the percentage of atmospheric pressure and accordingly four different suction pressures: 44%, 54%, 64% and 74% are considered to find out the best suction position based on the aerodynamic performances.
As a passive flow control of separation, two different configurations of internal slots are then introduced, one is tangential internal slot and the other is leading edge chordal slot. The result shows that the performance of tangential internal slot is better in comparison to that of leading edge chordal slot. For getting better result, the optimum position of tangential internal slot is sought and considered for further CFD simulation and analysis of the result.
Finally, the combined effects of tangential internal slot near the leading edge and suction near the trailing edge are studied. The result shows that the combination of suction and tangential internal slot moves the separation point from 46% to 72% of the chord length while for only tangential internal slot the separation occurs at 68% of the chord length. The detached flow reattaches at 97% of the chord length position for plain airfoil with and without the tangential internal slot and for the combined effect of suction and tangential internal slot the reattachment occurs at 73% of the chord length position. This modified configuration increases lift force, decreases drag force and increases lift to drag ratio significantly. The tangential internal slot increases lift to drag ratio as 9% compared with plain airfoil whereas the combination of tangential internal slot and suction increases 17% lift to drag ratio. The result also shows that the stall angle is increased by this modified configuration in airfoil. The outcome of this investigation might help the airfoil designers to achieve much better aerodynamic performance.
