Study On Boundary Layer Blowing Control Of Large Span Cantilever Structure Based On Vortex Model

With the development of building technology,large span cantilever structure is widely used in all aspects of life,especially the stadium.However,In the calculation of wind pressure of large span suspension structure,because the calculation method of wind pressure based on formulated constant assumption is often invalid,the simple method of wind pressure for large span suspension is only based on the empirical parameter method of wind tunnel test.However,this method is not suitable for the changeable form of structure,and is very inconvenient for the wind resistant design of structures.As a typical flexible structure,large span cantilever structures have long natural frequencies and are very sensitive to wind loads,the wind-induced response of large span cantilever structures can not be ignored.On the roof,the flow separation often produces large negative pressure.In view of these problems,this dissertation analyzes the causes of wind pressure on the roof,introduces the vortex model as the link,which links the characteristics of the flow and the wind pressure distribution,then puts forward the wind pressure model of the roof.Based on this,a new blowing control mode and an optimal control scheme under different conditions are proposed.The flow velocity model of the surface vortex of the large span cantilever structure is established by studying the relationship between the characteristics of the flow and the vortex.The CFD numerical simulation is used to simulate the actual flow around the large span cantilever structure,and determine the key parameters affecting the wind pressure distribution on the roof.The characteristics of the roof vortex shape,distribution characteristics and velocity profile of the large span cantilever structure are studied.Based on the numerical simulation results,the hypothesis of vortex drift is proposed.Based on this hypothesis,it is found that the vortex velocity profiles on the roof are similar,and the relationship between the characteristics of the flow and the vortex is determined.The vortex flow velocity model suitable for large span cantilevered structures is established.The wind pressure model of large span cantilever structure is established by studying the relationship between vortex shape and roof wind pressure characteristics.According to the differences of the vortex shape of roof and thevariation characteristics of wind pressure,the roof is divided into three regions: the leading-edge separation region,the vortex region and the vortex separation region.Through the introduction of the vortex center distance h variable and the correction of the radius of curvature of the existing wind pressure model,this dissertation slove three specificity problems: no peak value under the votex;the velocity of the potential flow field does not change along the axial direction;the center of vortex is closer to the roof.Based on the modified wind pressure model,the influence of the external shape parameters of large span cantilever structure is studied,included roof inclination,lowerstand ventilation rate,aspect ratio and high span ratio,and the influence coefficient of shape is analyzed quantitatively.Based on the previous theoretical research,the blowing control of the boundary layer is proposed.This method can reduce the wind pressure on the roof by controlling the shape of vortex.The effectiveness of the control method is verified by the CFD numerical simulation method.It is found that the blowing control effects are different in the three regions of the leading-edge separation region,the vortex region and the vortex separation region.The influence of the blowing velocity of three regions on the extreme pressure of roof of the large span cantilever structure and the influence of the layout position on the vortex elimination effect are studied,and the optimal control scheme is put forward.Considering the influence of external wind environment on the optimal control scheme,the corresponding improvement strategy is put forward to ensure that the blowing control of the surface layer has a wide range of engineering applications.