Study Of Influence Of Upstream Corner Cutting And Recession Of Tandem Square Cylinders On Aerodynamic Performance On Large Eddy Simulation

Two tandem square cylinders is a kind of common combination structure and has been widely used in many engineering applications.Being strongly related to the flow characteristics,the aerodynamic performance of two tandem square cylinders will be significantly affected by the corner modification of the square cylinder,minor modification of the corner shape of the square cylinder will induce the remarkable change of the flow field in the wake,affecting the aerodynamic performance of the square cylinder in the downstream,however,there is still lack of the relevant research.In this study,the spatial averaged large eddy simulation was carried out for the two tandem square cylinder cases at the upstream corner cutting and recession.The influence of the corner cutting and recession effect on the aerodynamic performance of the two tandem cylinders was analyzed in detail.The influence mechanism was also discussed by analyzing the time-averaged and transient flow fields around the cylinders.The main research aspects are as follows:(1)Unsteady flow around quasi-three-dimensional two tandem square cylinders at spacing ratio(defined by the ratio of the central distance and the depth of the cylinders)of 2.0was numerically simulated by the spatial averaged large eddy simulation technique with corner cutting and recession of the upstream square cylinder and that without corner modification,respectively.The present numerical method and parameter setting was verified by comparing the results between the present simulation and previous studies for the tandem square cylinders without corner modification.The influence of corner cutting and recession was discussed by comparing the simulated aerodynamic coefficients and wind pressure distribution of the three cases.The flow mechanism was also discussed by analyzing the time-averaged and transient flow fields around the cylinders.The results show that flow reattachment on the downstream square cylinder is affected by the upstream corner cutting and recession,resulting in decreases of the mean and fluctuating wind load.The corner cutting on the upstream square cylinder can remarkably reduce mean wind load in the streamwise direction,while the corner recession treatment can weaken the transversal fluctuating wind load.(2)The unsteady flow around two-dimensional model of two tandem cylinder with and without considering corner cutting and recession was firstly simulated at spacing ratios ranges from 2.0 to 5.0.The critical spacing ratios were observed for the two tandem cylinder cases with and without corner cutting and recession by analyzing the abrupt changes of the aerodynamic forces.The large eddy simulation was then carried out for the two tandem square cylinder cases at the above critical spacing ratios.The influence of upstream corner cutting and recession on the aerodynamic performance of tandem square cylinders is discussed in detail from the aspect of wind pressure and flow mechanism.The results show that corner cutting and recession on the upstream cylinder will change the separation point and flow pattern of the square cylinder,thus narrowing the wake flow,shortening the critical spacing and reducing the aerodynamic coefficients.Furthermore,the corner cutting and recession on the upstream cylinder makes the aerodynamic coefficient and wind pressure coefficient of the tandem square cylinders lower than that of the tandem square cylinders without corner modification at the same spacing.(3)By adopting the combined self-maintaining boundary condition and vortex synthesis method to generate inflow turbulence for LES,the flow around three-dimensional tandem square cylinders with breadth-to-height aspect ratio of 1:6 are numerically simulated by LES in turbulence boundary layer.The spacing ratio is set to be as same as that of quasi-three-dimensional tandem square cylinders.The results show that the flow pattern of three-dimensional tandem square cylinders is also changed by upstream corner cutting and recession,affecting the distribution of wind pressure and flow field between the two tandem square cylinders,resulting in decreases of the wind load,which is same as the quasi-three-dimensional tandem square cylinders.However,the flow separation occurs on the top of three-dimensional tandem square cylinders,forming an integrated vortex structure.Furthermore,spiral vortex occurs on the side of the three-dimensional tandem cylinders due to the friction effect on the ground.When considering the corner cutting and recession for the upstream cylinder,the flow separation on the top of the three-dimensional tandem square cylinders is restrained and the separation vortex gets more close to the wall,making the distribution more dispersed,which affecting wind load at these locations.