The work reflected in this study includes a detailed study of co-flow jet (CFJ) technologies as they are applied to a typical thin airfoil, NACA 6415, at take-off and landing speeds. Numerical analysis and experimental testing were conducted on baseline and co-flow jet airfoils of the same plan form.
The CFJ mechanism employs high pressure air injected along the span at the leading edge while a low pressure source removes the same amount of air along the span at the trailing edge. Hence, the net mass flux of the system is zero energy loss is minimized. The jet produced along the upper surface of the airfoil mixes with and excites the free stream flow resulting in increased lift, augmented stall margin, and decreased drag. At certain angles of attack the decreased drag is negative and thrust is produced.
The research was comprised of four phases including computational fluid dynamics (CFD) simulations, design and manufacturing of a transformable baseline and adjustable slot size CFJ airfoil, implementation of a CFJ Wind Tunnel Laboratory, and wind tunnel testing.
A computational fluid dynamics code, developed at the University of Miami, was used to study flow fields and to obtain analytical results of aerodynamic properties for the baseline and CFJ airfoils. Modeling of both wing shapes utilized the baseline ordinates of a cambered NACA 6415 airfoil. The free stream steady state flow was set to Mach=0.1 to simulate take-off and landing speeds where the co-flow jet mechanism would demonstrate its largest increase in performance. CFD simulations of both models provided aerodynamic coefficients as well as mass flow and jet effect data specifically useful to the CFJ airfoil.
The NACA 6415 model used for wind tunnel testing was designed and produced to provide both baseline and CFJ results with adjustable injection and suction slot sizes. Connections for a side-mounted force balance and an air delivery system for the co-flow jet were included in the airfoil model. The design and manufacturing of a wind tunnel test section extension was necessary to provide support for the additional aerodynamic loads induced by the CFJ airfoil and to house various air connections and test sensors. A CFJ Wind Tunnel Laboratory was designed and constructed during the course of the research and included selection of proper air delivery apparatus for the injection and suction air for the CFJ jet.
All testing controls and sensor equipment were acquired and installed to obtain various data needed for experimental analysis. Finally, a data acquisition system was designed to consolidate all testing information for ease of use. Wind tunnel testing of the baseline and CFJ airfoils provided the aerodynamic loads and coefficients needed to demonstrate the performance enhancements of the co-flow jet flow control method. Experimental and numerical results were examined to understand the benefits of the co-flow jet as it compares to a similar baseline airfoil. The CFD simulations and experimental measurements agree fairly well. All results indicate that the CFJ flow control method is very effective for a typical thin airfoil with 15% maximum thickness.
Author: Kirk, Danah
Source: University of Miami