Investigation on Dissimilarity between Heat and Momentum Transport Processes and Its Numerical Modeling

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This research project was conducted for investigation on the mechanism of dissimilarity between heat and momentum transport processes and its numerical modelling. The head investigator originally found the dissimilarity in a flat plate turbulent boundary layr disturbed by a circular cylinder, which means wall heat transfer enhancement and wall skin friction reduction simultaneously occur down stream of the cylinder. Such a bluff body, however, is not a suitable geometrical shape because of a relatively large momentum loss due to its form drag. A thin LEBU (Large Eddy Break-Up) plate, on the other hand, is one of the effective shapes to reduce the skin friction without a serious form drag, although the heat transfer is not enhanced with the plate.In this project, therefore, a flatten cylinder (Case 1) or a square rod attached with a splitter plate (Case 2) were inserted in a flat plate turbulent boundary layr in order to find the best shape to generate strong dissimilarity most effectiv … More ely and also to investigate how the dissimilarity is produced related to Karman vortices generated behind the inserted bodies. It was found for Case 1 that the degree of heat transfer enhancement decreases with an increase in the flatness of the cylinder, while the degree of skin friction reduction does not decreases in such a monotonous way. For Case 2, Karman vortex shed behind the rod was controlled by the splitter plate and suppressed with an increase in the plate length. Quadrant analysis, spectral analysis and wavelet analysis of monitored turbulent signals revealed for both cases that selective intensification of the interactive fluid motions was produced intermittently, synchronized with the Karman vortices. Such a selective intensification could be related to the generation mechanism of the dissimilarity.Unsteady flow and thermal numerical computations were also performed for both laminar and turbulent boundary layrs disturbed by a square rod. It was found that flow unsteadiness strongly depends on the ratio of the clearance between the rod and the plate to the side length of the rod. The dissimilarity was observed statistically in such a manner that heat transfer enhancement and skin friction reduction occur instantaneously at the same region, accompanied with the Karman vortex shedding. Less