Mitch Wolff (Advisor)
Master of Science in Engineering (MSEgr)
The use of small jets of air has proven to be an effective means of flow control on low Reynolds number turbine blades. Pulsing of these jets has also shown benefits in reducing the amount of air needed to achieve the same level of flow control. An experiment using Hot Wire Anemometry and Particle Image Velocimetry (PIV) has been used to investigate how these pulsed jets interact with the boundary layer to help keep the flow attached. A 25x scaled jet in a flat plate has been utilized. The 25.4 mm diameter jet has a pitch angle of 30° and a skew angle of 90°. Pitch angle is defined as the angle the jet makes with the surface of the plate, and the skew angle is the angle that the projection of the jet on the surface makes with the crossflow. The jet was pulsed at both 0.5 Hz and 4 Hz with varying pulse durations (duty cycles), as well as various blowing ratios (ratio of the jet velocity to the freestream velocity). Duty cycles of 10, 25, 50, and100 percent were implemented at a blowing ratio of unity. Blowing ratios of 0.5, 1, 2, and 4 were implemented at a 50% duty cycle and at 0.5 Hz. Velocity and vorticity planes were obtained at various spanwise locations and used in the characterization of the jetflow. Both the free jet as well as the jet in crossflow were studied. A calibration experiment was also performed using PIV on a rotating disk. The calibration experiment was successful and the PIV results averaged a 1.56% error. The hot wire experiment with the free jet showed that the starting vortex is a key event at the beginning of each cycle, and the end of each cycle included a “kick-back” and a suction effect that could also have an influence on the boundary layer. The PIV experiment was performed first on the free jet, and results were comparable to the hot wire results. When the PIV experiment was performed on the jet in crossflow, it was clear that both the beginning and ending events of the jet cycle were keys to eliminating or delaying flow separation.The effect of the beginning and ending events can be used to keep the flow attached for longer periods of time by increasing the frequency of the jet pulse. Due to limitations of the setup, higher frequency cases could not be studied. However, the experiment was successful in controlling a separated crossflow for blowing ratios greater than unity. The larger blowing ratios resulted in larger attachment size, and were able to sustain attachment for longer time periods.
Department or Program
Department of Mechanical and Materials Engineering
Year Degree Awarded
Copyright 2005, all rights reserved. This open access ETD is published by Wright State University and OhioLINK.