Flow And Heat Transfer Characteristics Of Flow Past A Slit-cylinder

As a classic problem of flow around a bluff body, flow past a circular cylinder has always been the focus of attention and research for its important engineering significance and theoretical value. Moreover, drag reduction and inhibition of Vortex-Induced-Vibration are the key in actual engineering application. Therefore, it is of great importance to explore the flow mechanism and related physical nature, and then to find an effective method to reduce the drag, control the flow and improve heat transfer performance based on the relevant physical mechanism.A passive method is proposed in present work, which placing a pair of slits, each one extends from the upper or lower separation region to the rear stagnation zone of cylinder. It's expected to realize the control of circular cylinder wake and the decrease of drag forces by finding appropriate geometrical parameter of circular cylinder.In present work, Computational Fluid Dynamics is used to investigate the features of flow past a slit-cylinder based on the Finite Volume Method. The flow and heat transfer characteristics of flow past slit-cylinders with different ratios of slit width to the diameter of circular cylinder s/D are conducted. The ratio varies from 0.01 to 0.1 and the Reynolds number based on the diameter of circular cylinder varies from 60 to 200. Furthermore, three-dimensional numerical simulations have been performed in order to probe the transition feature from two-dimensional model to three-dimensional model when Reynolds number is 200, 230, 250 and 1000. The maintenance effect of slit on two-dimensional model of flow past a circular cylinder is probed as well.The present numerical results show that the drag and lift forces of slit-cylinder cases are much lower than that of unmodified cylinders in considered cases. The vortex shedding from the circular cylinder surface is effectively suppressed by the slits. The most significant result is obtained when s/D=0.02. Moreover, the comprehensive heat transfer performance of cylinder surface is significantly increased with the augment of the slit size, which is superior to that of circular cylinder without slits when Re is relatively lower. Compared with the unmodified cylinder, the comprehensive heat transfer performance of circular cylinder with slit width of 0.02 D is increased by 29.1% when Re=60. Within a certain Re range, the slit-cylinder with slit width of 0.02 D can prompt the vortex transition towards three-dimensional flow model. The transition is effectively suppressed when the slit width is enlarged to 0.1D. However, the slit-cylinder structure could strengthen the three-dimensional characteristics when Re is near to subcritical value. The energy has been scattered to the whole flow field, which result in the drag reduction. Moreover, heat transfer performance is enhanced while the flow drag is reduced effectively, which caused by the slits. Consequently, the comprehensive heat transfer performance is significantly improved.