Flow-Control Mechanisms Associated with a Circular Cylinder with a Normal Slit

• Main Authors: Huai-Lung Ma, 馬淮龍
• Other Authors: 郭正雄
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/wqr2fm

博士 === 國立中興大學 === 機械工程學系所 === 106 === Flow simulation around circular cylinder with a normal slit at Reynolds number (Re) 200 is conducted using Ansys/Fluent, and the theoretical analysis on an oscillatory slit flow is also presented. The slit ratio (S/D) ranges from 0.03 to 0.3. Some critical outcomes are outlined. The oscillatory slit flow is driven by alternate variations of the pressure difference between two slit openings (or exits), in form of periodic blowing/suction with zero net mass flux (ZNMF). Blowing/suction is regarded as the periodic perturbation to the boundary layer-flow to delay the flow separation along the rear surface and reduce the formation length of the Kármán vortex street. For all slit ratios studied, the frequency and amplitude responses, as well as the slight phase shift clearly demonstrate the primary lock-on of the wake. Nevertheless the one-sided lock-on frequency range lies only within f_a⁄(f_so>1). The results indicate that the optimal S/D is limited to S⁄D=0.21 at Re = 200. When applied to the novel vortex flowmeter, the non-dimensional parameter η can be related to S/D, Strouhal number (St) and Re. In the design stage, the range 0.97<η<20 is suggested for Re=2×〖10〗^2~8.5×〖10〗^4. The optimal value η_opt can be obtained by experiments and simulation, and the optimal S/D can be estimated for a fixed applied Re at the design stage.