Hermanson, James Carl
A new experimental facility was designed and constructed to test a coflow seeding technique for the study of turbulent mixing in steady and unsteady axisymmetric jets in a coflow. The coflow seeding method includes injecting oil smoke or other seed material into the coflow and then illuminating the flow field with a laser light sheet for flow visualization. The facility consisted of a wind tunnel containing a two sided contraction, six turbulence management stations, a 6 inch square test section, and an exhaust system. Images of the steady and unsteady turbulent jet flows were taken at 30 frames per second with a progressive scan CCD camera. Jet concentrations were then determined from the images using an image processing program (WiT). The steady state jet flow cases served as a baseline in order to validate the coflow seeding method prior to exploring unsteady jet flows. In the steady flow case the entrainment increased with a decreasing coflow velocity, as expected. Concentration profiles within the jet were used to determine jet widths and jet growth rates. These results validated the coflow method as an effective tool in flow visualization. Results for the pulsed jet cases were rather qualitative. This was due to solenoid response time and camera exposure speed inefficiencies. The average concentration, taken from an ensemble of unsteady jets, did suggest higher entrainment rates than for corresponding steady jets, as expected, but the amount of the increase could not be quantified. In order to obtain better unsteady jet information a faster solenoid and camera will need to be utilized. The detailed steady jet information attained, along with other detailed flow field images taken, established the coflow seeding method as a viable flow visualization technique. The coflow seeding technique also has the unique benefit of allowing visualization of both the jet flow and the surrounding flow field, which will contribute to the understanding of the fundamental characteristics of jet flow.
Worcester Polytechnic Institute
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