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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN:
1-56700-135-1 (Print)

NOVEL PHENOMENA IN TURBULENT ELLIPTIC WAKES

Masaru Kiya
Division of Mechanical Science, Hokkaido University Sapporo 060-8628, Japan

Yukinobu Abe
Division of Mechanical Science, Hokkaido University Sapporo 060-8628, Japan

Osamu Mochizuki
Faculty of Science and Engineering, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585, Japan

Hitoshi Ishikawa
Division of Mechanical Science, Hokkaido University Sapporo 060-8628, Japan

Abstract

Novel phenomena have been found in the wake of an elliptic disk set normal to the uniform approaching flow. There exist two periodic components of velocity fluctuations in the wake. One is centred around the minor plane, being due to alternate shedding of hairpin-like vortices. The other is centred around the major plane, being due to a meandering motion of the hairpin-like vortices. The axis switching, which is similar to that in ellitic jets (Ho & Gutmark 1987), occurrs at approximately 4 minor diameters downstream of the disk. Mechanism of the axis switching is completely different from that in the elliptic jets, being likely to be due to difference in growth rates of fundamental Fourier modes of global instability in the minor and major planes. Structure of the wake is studied by flow visualization, a direct numerical simulation, and a survey of the time-mean velocity and turbulence intensities.