Effect of initial conditions on interaction between a boundary layer and a wall-mounted finite-length-cylinder wake
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作者:
Wang, H. F.
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机构:Hong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R China
Wang, H. F.
Zhou, Y.
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Hong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R ChinaHong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R China
Zhou, Y.
[1
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Chan, C. K.
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机构:Hong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R China
Chan, C. K.
Lam, K. S.
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机构:Hong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R China
Lam, K. S.
机构:
[1] Hong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R China
[2] Hong Kong Polytech Univ, Dept Appl Math, Kowloon, Hong Kong, Peoples R China
[3] Hong Kong Polytech Univ, Dept Civil & Struct Engn, Kowloon, Hong Kong, Peoples R China
[4] Huazhong Univ Sci & Technol, State Key Lab Coal Combust, Wuhan, Hubei, Peoples R China
The effects of initial conditions on interaction between a boundary layer over a flat plate and flow around a wall-mounted finite-length cylinder were experimentally investigated. A square cylinder with a characteristic width (d) of 20 mm and a length of H=5d was vertically mounted on a horizontal flat plate. Three different boundary layers were investigated, their momentum thickness being 0.07d, 0.13d, and 0.245d, respectively, measured at the cylinder axis in the absence of the cylinder. All the experiments were carried out in a closed-loop water tunnel at a Reynolds numbers of 11 500 based on d and the free-stream velocity U(infinity). It is found that initial boundary layer conditions have a profound effect on the near wake, including the flow near the cylinder free end that is well beyond the boundary layer. With increasing boundary layer thickness, the base vortex is enhanced, inducing a stronger upwash flow from the cylinder base, which acts to weaken the downwash free-end shear layer and the tip vortex. Consequently, spanwise vortices gain strength near the free end but impair near the wall, causing the ratio of symmetrically to antisymmetrically arranged vortices to vary and subsequently the Reynolds stresses to increase significantly in magnitude near the free end but to decrease near the wall.