Features Of Hydraulics And Flow Past Cylinder(s) On Staircase

Underground flooding has become a new challenge due to the rapid expansion of underground space and frequent occurrence of extreme precipitation events. The underground space suffers high risk of flooding intrusion. As the critical paths, the entrance/exit staircase to the underground space has becoming a high risky area for people evacuating from underground space when flooding occurs. To evaluate the evacuation safety of people walking through the flooding staircase, the Features of hydraulics and flow past cylinde(s) on staircase have been investigated experimentally and numerically. The main contents are as follows.Firstly, the classification of aerated flow was introduced and the mechanism of aerated flow was discussed. It follows the concepts of the aerated flow with a clear water core and aerated flow with a fully aerated core, and the diffusion equations of the aerated flow with one air-water interface. Based on that and the superposition principle, the diffusion equation and calculation method of hydraulic parameters of aerated flow with two air-water interfaces was derived.Secondly, a physical model of a staircase with the rest platform was assembled based on the Froude similarity. The hydraulic features of the flooding flow on the staircase, flow velocity field, point of inception, air concentration distribution, air-water mixture velocities and jet characteristics downstream the rest platform were investigated, the diffusion equation of aerated flow with two air-water interfaces was verified by the measured data.Thirdly, according to the results of the test and the theory of numerical simulation, a numerical model of flooding flow on the staircase with rest platform was developed. Based on the flexibility of the numerical model, the influence of the existence of rest platform, different slopes and different forms of the staircase on the flow field on the flow pattern, velocity distribution and the evaluation of the safe evacuation of people walking on the flooding staircase were analyzed numerically.Finally, a new force measurement instrument used to measure the hydrodynamic force on the free surface-piercing cylinder under complex flow conditions was developed and its precision was calibrated. As the simplified model of the flow past human body(s), the flow past a single surface-piercing cylinder on the staircase and a cylinder array were experimentally investiagted. The hydrodynamic forces and drag coefficients on an isolated circular cylinder located at different steps of the staircase under different ground water depth, and on a single cylinder in a cylinder groups arranged in different arrays were discussed.The innovation points of the paper are:the diffusion equation of aerated flow with two air-water interfaces was derived based on the theory of aerated water and the superposition principle and verified by the experimental data; the influence of the existence of the rest platform, different slopes and different forms of the staircase (straight-run staircase, L-shaped staircase with a90°-turn and U-shaped staircase with a180°-turn) on the hydraulic features of flooding flow on staircase were discussed; a new force measurement instrument used to measure the hydrodynamic force on the free surface-piercing cylinder under complex flow conditions was developed and calibrated, and then used to measure the hydrodynamic forces acting on cylinder(s) on the staircase; the characteristics of flow past cylinder(s) on the staircase were experimentally investigated and the drag coefficients of the flow past cylinder(s) on the staircase were discussed.