| The flow around circular cylinder structure group are widely encountered in many engineering applications,such as high-rise buildings,transmission tower,cable and bridge tower,to name but a few.The fluid load has an effect on the strength,stability and safety of the circular cylinder structure.Based on Fluent software,the flow around three-dimensional circular cylinders have been investigated numerically under subcritical Reynolds number by using large eddy simulation method(LES).The flow field characteristics of the two tandem circular cylinders,four square-arranged cylinders and five X-arranged cylinders were analyzed emphatically,and the mechanism of interference effect between them were illustrated,providing a reference for design of practical engineering.Main research work are reflected as follows:(1)The three dimensional flow around a double cylinder at Re=3900 is studied.The influence of the different spacing on the hydrodynamic parameters and the distribution characteristics of the surrounding flow field is analyzed,and the flow interference mechanisms around the cylinders are clarified.The study shows that the flow characteristics of both cylinders in tandem arrangement have significant changes with the increasing of the spacing ratio,and the flow patterns transform from reattachment mode to wake impact one.(2)The flow past three-dimensional four circular cylinders in an in-line square configuration have been investigated at Re=3900.The effects of incidence angle and spacing ratio on the fluid force coefficients and flow pattern of four square-arranged circular cylinders are analyzed emphatically,while the interference and intrinsic mechanisms of flow around the cylinders are clarified.The study shows that the incidence angle and spacing ratio have a significant impact on the fluid force coefficients,flow pattern and interference effects of the flow around four square-arranged cylinders.On the one hand,the critical spacing ratios are 3.5(?=0°),3.5(?=22.5°)and 3.0(?=45.0°),respectively.And the interference effect changes from promixity effect to wake one.On the other hand,the phenomenon of high-speed flow can be observed in the gap region at the small spacing ratio.For the large spacing ratio case,the effect of the wake of the upstream cylinders on the downstream ones is significant.And the flow characteristics of the upstream cylinders is similar with those of the single cylinder case.(3)The flow past three-dimensional five X-arranged circular cylinders have been investigated at Re=3900.The effects of incidence angle and spacing ratio on the fluid force coefficients and flow pattern of five X-arranged circular cylinders are analyzed emphatically,while the interference and intrinsic mechanisms of flow around the cylinders are clarified.The study shows that the incidence angle and spacing ratio have a significant impact on the fluid force coefficients,flow pattern and interference effects of the flow around five X-arranged cylinders.The critical spacing ratios are 5.0(?=0°),6.0(?=22.5°)and 6.0(?=45.0°),respectively.When ?=0° and L/D=5.0-7.0,the gap flow effect is stronger than the wake effect.However,for the case of ?=22.5° and L/D=7.0,the fluid flow characteristics on both sides are different between the downstream cylinder and the middle one.When ?=45° and L/D=5.0,there is no vortex shedding in the wake region of the upstream cylinder,while there is the vortex street behind the middle one.Additionally,as the spacing ratio increases to 6.0-7.0,the vortex street is formed in the wake of the upstream and middle cylinders. |
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