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RESEARCH PAPERS

Streak Characteristics and Behavior Near Wall and Interface in Open Channel Flows

[+] Author and Article Information
M. Rashidi, S. Banerjee

Department of Chemical and Nuclear Engineering, University of California, Santa Barbara, CA 93106

J. Fluids Eng 112(2), 164-170 (Jun 01, 1990) (7 pages) doi:10.1115/1.2909383 History: Received January 26, 1989; Online May 23, 2008

Abstract

Turbulent structures near the boundaries (solid wall and gas-liquid interface) have been studied in open channel flows. Experiments with no shear, countercurrent shear, and cocurrent shear at the gas-liquid interfaces were conducted. Results indicate that near the sheared interfaces, the mean nondimensional span wise streak-spacing, lambda+ , appears to be essentially invariant with shear Reynolds number, exhibiting consistent values of lambda+ ≈ 100 at y1 + = 5, while increasing with distance from the interface. Observation of the streaks near the interface indicates that the process of streak merging is active even for y1 + < 5. Further studies show that the low-speed streaks frequently occur as regions between longitudinal vortices separated by Deltaz+ ≈ 50 near the boundaries. These vortices generally originate from the boundaries at an angle of about 20–25 deg (for y+ <20), then lift up or eject chaotically at an angle of about 40–50 deg (for y+ >20). Based on these observations, a conceptual mechanism of streak breakdown near the sheared boundaries has been provided.

Copyright © 1990 by The American Society of Mechanical Engineers
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