Experimental Study of Co-Flow Jet Airfoil Performance Enhancement Using Discreet Jets

This paper demonstrates a new performance enhancement methodology for Co-Flow Jet (CFJ) airfoils using discrete injection jets. This research is motivated by the hypothesis that a discrete CFJ (DCFJ) airfoil will generate both streamwise and spanwise vortex structures to achieve more effective turbulent mixing than an open slot CFJ airfoil. Aerodynamic forces and DPIV measurements show that the DCFJ airfoil can achieve up to a 250% increase of maximum lift, and simultaneously generates a tremendous thrust. Nearly 80% of the injection momentum is converted to drag reduction, which indicates that CFJ airfoils are highly energy efficient. The stall angle of attack is also significantly increased. In other words, a DCFJ airfoil is a high lift system and at the same time is also a high thrust propulsion system with low energy expenditure. Best performances are achieved with small discrete holes and large obstruction factor. Power consumption is analyzed and is found to be low compared with the performance gain. Thus, the DCFJ airfoil concept appears to be very promising for the development of integrated airframe-propulsion systems and rotorcraft systems with high performance and high efficiency.