Research On Flow Field And Response Of Flexible Flat Roof Based On Particle Imaging Velocimetry And Digital Image Correlation Method

Flexible thin membrane roof structure is one of the large-span flexible structures widely used in recent years,this kind of structure will produce wind-induced large-amplitude vibration,instability and even damage under the action of wind load.The reason is that the airflow through the flexible membrane roof not only changes the surrounding flow field,but also changes the dynamic characteristics of the structure itself,the unsteady aerodynamic effect of the flow field and the unsteady aeroelastic response of the membrane caused by this wind-induced coupling effect cannot be ignored.Because the characteristic flow field and vibration state of the membrane roof are the most intuitive representations of the wind-induced coupling effect,obtaining quantitative data of the characteristic flow field and vibration state of the thin membrane roof is also the basis for understanding the wind-induced coupling effect from the mechanism,so that the wind-induced instability and even damage of the thin membrane roof can be explained from the principles of aerodynamics.In this paper,based on the wind tunnel test,the particle imaging velocimetry(PIV)and digital image correlation(DIC)methods are mainly used to study characteristic flow field and the wind-induced responses of the flexible flat roof model under different inflow conditions.The main contents include:(1)The PIV is firstly used to study the flow field around the rigid flat roof model under different inflow conditions,parameters such as the position of the vortex core,the length of the reattachment point,and vortex shedding frequency are obtained according to the corresponding wind tunnel tests.The disciplines of the flow field parameters and vortex shedding frequency of the rigid flat roof model changing with the inflow conditions are concluded.(2)The PIV is also carried out on the flexible flat roof model under the same inflow conditions as those of the rigid flat roof model tests.The influence of the unsteady aeroelastic response of the flexible flat roof model on its characteristic flow field are concluded by comparison with the flow field characteristics of the rigid roof model.(3)The DIC is used to reconstruct the three-dimensional topography of the flexible flat roof model under different inflow conditions,and then the wind-induced responses of the flexible flat roof model are extracted from this,the disciplines of the wind-induced responses of the flexible flat roof model changing with the flow characteristics are concluded.The influence of the unsteady aerodynamic effect of characteristic flow field on the vibrationlevel and shape of the flexible flat roof model are concluded by comparison with the characteristic flow field.The research results show that,as the incoming wind velocity increases slowly,the height of the vortex core from the roof,the horizontal distance between the vortex core and the front edge and the reattachment length of the rigid flat roof gradually decrease,and the vortex shedding frequency gradually increases.Moreover,as the incoming turbulence intensity increases,the height of the vortex core from the roof,the reattachment length and the vortex shedding frequency of the rigid flat roof gradually decrease,but the horizontal distance between the vortex core and the front edge gradually increases.Flow field parameters around the flexible flat roof model shows the similar changes as rigid flat roof ones,due to the influence of unsteady aeroelastic responses of the flexible flat roof model,the height of the vortex core from the roof,the horizontal distance between the vortex core and the front edge and the reattachment length of the flexible flat roof are much smaller than the corresponding parameters of those of the rigid flat roof ones under the same inflow conditions,while the vortex shedding frequency is much greater than that of the rigid flat roof model.As the incoming wind velocity increases,the aeroelastic response magnitudes and wind-induced frequency of the flexible flat roof model increase gradually.As the incoming turbulence intensity increases,the aeroelastic response magnitudes of the flexible flat roof model increases but the wind-induced frequency gradually decreases.It is also concluded that the characteristic flow field around the flexible flat roof have great influences on the aeroelastic magnitude and shape of the structural deformation due to the unsteady aerodynamic effect of characteristic flow field.