Abstract
The objective of the present study is to modify mixing and heat transfer in impinging jets using a single-frequency excitation imposed at the jet exit. The excitation frequency is selected to be St θ = fθ/U J,max = 0.017 where θ is the jet-exit momentum thickness and U J,max is the jet-exit maximum velocity. In free jets, this excitation results in turbulence suppression in a downstream location. On the other hand, in impinging jets, the effect of excitation significantly depends on the distance (H) between the jet exit and the impinging wall. For large H (e.g. H / D = 10, D is the jet exit diameter), the Nusselt number near the stagnation point (Nu stag ) decreases due to turbulence suppression by the excitation. For small H (e.g. H / D = 2), Nu stag is almost unchanged but the secondary peak much suppressed. On the other hand, Nu stag increases for H / D = 6 due to turbulence enhancement by the excitation. The different behaviors of Nusselt number with respect to H / D are closely related to the changes in vortical structures by excitation.
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Jungwoo Kim obtained his B.S., M.S. degrees and Ph.D. at the Department of Mechanical Engineering, Seoul National University, Korea, in 1999, 2001 and 2005, respectively. Dr. Kim is currently an assistant professor at the Department of Mechanical System Design Engineering, Seoul National University of Science and Technology.
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Kim, J. Active control of impinging jet for modification of mixing. J Mech Sci Technol 28, 927–935 (2014). https://doi.org/10.1007/s12206-013-1160-1
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DOI: https://doi.org/10.1007/s12206-013-1160-1