High performance airfoil using co-flow jet flow control

The wind tunnel tests in this research have proved the superior performance of co-flow jet(CFJ) airfoil to dramatically increase lift, stall margin, and drag reduction. Two airfoils with different injection slot size are tested to study the effect of geometry. The airfoil with smaller injection slot size (0.65% chord length) performs significantly better than the one with twice larger slot size. With the momentum coefficient varying from 0.1 to 0.30, compared with the baseline airfoil, the maximum lift of the smaller size CFJ airfoil is increased by 113% to 220%, the angle of attack (AoA) operating range (stall margin) is increased by 100% to 153%. The minimum drag coefficient is reduced by 30% to 127% with the momentum coefficient varying from 0.055 to 0.192. Large negative drag (thrust) is produced when the momentum coefficient is high. A coefficient of jet kinetic energy is introduced, which apperas to correlate better with the maximum lift and stall margin than the momentum coefficient when CFJ airfoil geometry varies. The momentum coefficient correlates well with drag reduction. It is observed that the thicker injection slot airfoil has smaller stall AoA and hence less maximum lift. To achieve the same lift coefficient of 4.42, the power required for the thicker injection slot is 3.9 times of that required for the thinner injection slot airfoil. No optimization of the airfoil configuration is done in this research and hence it is believed that there is a great potential for further CFJ airfoil performance improvement. In the experiment, it is observed that there is a limit of the jet mass flow rate to maintain the stability of the flow. Below the limit, increasing the jet mass flow rate (momentum coefficient) will make the flow attached and increase the lift and stall AoA. However, if the jet mass flow rate exceeds the limit, the whole flow field breaks down. This research also has conducted a concept study by CFD simulation indicating that it is possible for the CFJ airfoil to exceed the inviscid limit of maximum lift coefficient due to the high jet velocity inducing high suction velocity of the airfoil.