Analysis of a Passive Flow Control Device via Flow Visualization Techniques

This report details an experiment done to verify the effectiveness of a passive flow control system on a two-dimensional bluff body, blunt trailing edge model in controlling wake dimension and Karman vortex sheds. An earlier experiment by Park, et.al. [1] performed analysis via wind tunnel pressure testing and computerized model to determine the ideal proportions of such a tab design and identify the flow properties responsible for the potential drag reduction. To obtain visual verification of the existence of these concepts, a bluff body model proportionally identical to the one used by Park, et.al., was designed and tested in a water tunnel. The model incorporated a distribution system to dispense the colored dye that allowed visualization of the Karman vortices and related flow characteristics. Two endplates, one with the passive control system and one without, were each tested on the bluff body. Comparison of images captured from the two tests revealed the tab system induced flow characteristics indicative of 3D forcing and drag reduction. Additional investigation of the system performed by varying the angle of attack revealed a decrease in the tab device’s effectiveness as angle to the flow increased. Further experimentation could be done to investigate if modifications exist to improve the performance of the system in conditions not parallel to freestream flow; such a system would expand the potential applications of this passive flow control device in aerodynamic applications.