Flow Stability And Heat Transfer Characteristics Of Flow Past A Cylinder

As one of the classic problem of flow around a bluff body,flow past a circular cylinder has been widely studied by numbers of researchers for its massive engineering application and theoretical value.Moreover,the inhibition of Vortex Induced Vibration,drag reduction and the enhancement of comprehensive heat transfer performance of the cylinder is the key in actual engineering.Therefore,it is of great importance for flow control and improvement of heat transfer performance to explore the flow mechanism and related physical nature of flow past a circular cylinder,and then to realize the suppression of vortex shedding by passive control and strength the flow stability.While confirming the unstable area and realizing the control of the cylinder wake flow with the least amount of energy consumption is the key to the research.In this paper,two-dimensional flow past a circular cylinder under low Reynolds number is investigated based on Lattice Boltzmann Method.Based on the results of numerical simulation,various velocity profile at different distance from the cylinder center has been chosen and analyzed.Through introducing small disturbance in the basic flow field,the stability of the flow field can be calculated by the change of disturbance over time.The investigation shows that the results based on Lattice Boltzmann Method have good agreement with the results based on Computational Fluid Dynamics.Besides,by introducing small disturbance in the basic flow field,Orr-Sommerfeld perturbation equation is solved by spectral method and we can obtain the complex eigenvalues at different locations at given Reynolds numbers,which can determine whether the flow is stable.For three-dimensional characteristic of flow past a circular cylinder,the aim of present work is to control the wake flow and suppress the three-dimensional characteristic with a passive method by placing a couple of slits which connects the upper and lower separation zone to rear stagnation zone of cylinder,respectively.Numerical results indicated that transition critical Reynolds number from two-dimensional flow characteristic to three-dimensional flow characteristic increased with the augment of slits width,flow stability of the cylindrical downstream area is strengthened,and the three-dimensional characteristics of wake flow is well suppressed.Meanwhile,heat transfer characteristic of the cylinder with slits is enhanced significantly compared with the cylinder without slits at the same Reynolds number.The local Nusselt number distribution shows three-dimensional characteristic in the downstream area of cylinder at the critical Reynolds number,which proves the appearance of the three-dimensional characteristic of the flow past circular cylinder from another view.