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International Heat Transfer Conference 10

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Mechanism of Heat Transfer Augmentation by Longitudinal Vortices in a Flat Plate Boundary Layer

Kahoru Torii
Department of Mechanical Engineering and Materials Science, Yokohama National University, Yokohama 240, Japan

Koichi Nishino
Department of Mechanical Engineering and Materials Science, Yokohama National University, Yokohama 240, Japan

Ken Nakayama
Yokohama National University, Tokiwadai 156, Hodogaya, Yokohama 240, JAPAN

DOI: 10.1615/IHTC10.2420
pages 123-128

Abstract

Mechanisms of heal transfer augmentation achieved by the artificial introduction of large-scale longitudinal vortices were experimentally investigated. The vortices were generated by placing a single half-delta wing vortex generator in an otherwise laminar boundary layer on a flat plate. A rotation probe technique with a miniature slant hot-wire sensor was employed for the measurement of highly skewed velocity fields downstream of the vortex generator. It was shown that the position of the local peak of the heat transfer corresponded well to the downwash side of each vortex, where boundary layer thinning took place as a result of the entrainment of the high-speed outer layer fluid. On the upwash side, where the local heat transfer augmentation was less significant, energetic velocity fluctuations were found to appear as a result of the onset of the local turbulence transition, which then contributed to the overall improvement of heat transfer farther downstream. Prom a detailed analysis of the streamwise velocity fluctuations, it was revealed that the turbulence characteristics in the localized turbulent regions were similar to those reported for a turbulent boundary layer, particularly when the wall normal positions were normalized appropriately to take the Reynolds number difference into account.

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