Dropshafts are vertical structures widely used in urban drainage systems and buildings for water transportation.In this paper,a physical model study was conducted to investigate the air entrainment in the dropshaft un...Dropshafts are vertical structures widely used in urban drainage systems and buildings for water transportation.In this paper,a physical model study was conducted to investigate the air entrainment in the dropshaft under various flow regimes with and without air ventilation.Observed from the experiments,the air entrainment mechanisms varied with the water flow regimes in the dropshaft.When there was no water plug formed in the dropshaft,air could be supplied directly from downstream.Once the water plug was formed,while without venting,the air was replenished only from downstream intermittently and then in the form of large air bubble traveling upwards to the airspace at the top;while with venting,air was mainly replenished from the dropshaft top and no large air bubble was observed.The experimental results also showed that the amount of entrained air in the dropshaft with venting was greater than that without venting.展开更多
Due to limited flow capacity and the instability of the asymmetric structure of traditional baffle dropshafts,a novel baffle dropshaft with a symmetric structure,adopting the construction shield well directly,is propo...Due to limited flow capacity and the instability of the asymmetric structure of traditional baffle dropshafts,a novel baffle dropshaft with a symmetric structure,adopting the construction shield well directly,is proposed for large-range flow discharge in deep tunnel drainage systems.In this study,a two-phase flow field of the novel baffle dropshaft with three different baffle spacings was simulated at seven different flow rates with a three-dimensional(3D)numerical model verified with experiments,to study hydraulic characteristics of this novel baffle dropshaft.The results show that the novel baffle dropshaft has a remarkable energy dissipation effect.Baffle spacing of the novel baffle dropshaft has a greater effect on flow patterns and baffle pressure distributions than the comprehensive energy dissipation rate.Flow rate is a critical issue for the selection of baffle spacing in the design.Some guidance on baffle spacing selection and structure optimization for the application of this novel baffle dropshaft in deep tunnel drainage systems is proposed.展开更多
Nowadays, "Sponge Cities" are being built to provide a valid solution to the glaring drainage problems in the urban areas of China. The hydraulics of a dropshaft, especially discharge capacity, energy dissip...Nowadays, "Sponge Cities" are being built to provide a valid solution to the glaring drainage problems in the urban areas of China. The hydraulics of a dropshaft, especially discharge capacity, energy dissipation and cavitation damage control, evidently affect its safety and the city's underground tunnel system, due to the high dropshaft and large discharge. The hydraulic characteristics of stepped spillway dropshafts are experimentally investigated for the variable step rotation angles and end sill heights. Flow regimes inside the dropshafts are classified under the different approach flow discharges. The results illustrate that there is high energy dissipation in the present dropshafts with the stepped spillway and the cavitation damage could be effectively avoided thanks to the effect of the air entrainment to the flow.展开更多
Standing waves occur frequently at the inlet due to the change of the flow direction from an approach channel to the dropshaft.The performance of the standing wave,characterized by the relative height,the location and...Standing waves occur frequently at the inlet due to the change of the flow direction from an approach channel to the dropshaft.The performance of the standing wave,characterized by the relative height,the location and the extent,is theoretically and experimentally investigated in the present paper.It is shown that the height of the standing wave decreases with the increases of the approach flow Froude number and the sub-channel number in the inlet,but increases with the increase of the curvature of the dropshaft.The errors of the expressions for the relative height,the location and the extent of the standing wave,are 9.7%,7.8%and 13.1%,respectively,as compared with the experimental data.展开更多
深层隧道排水系统(深隧)是布置于深层地下的大型排水工程,一般由调蓄隧道、入流竖井、通风设施(排气井)及排水泵站组成,具有调蓄雨洪及控制溢流污染的作用。其中调蓄隧道为避开地铁等城市地下工程往往布置于距离地面30~60 m深处,入流竖...深层隧道排水系统(深隧)是布置于深层地下的大型排水工程,一般由调蓄隧道、入流竖井、通风设施(排气井)及排水泵站组成,具有调蓄雨洪及控制溢流污染的作用。其中调蓄隧道为避开地铁等城市地下工程往往布置于距离地面30~60 m深处,入流竖井连接地表浅层管网和深层隧道。深隧系统竖井内部的水力学特性复杂,具有单宽流量大、落差高及大量掺气等特点,处理不当将造成较大的破坏。而极端降雨期间,由于未能充分排气而产生的间歇喷涌,也会对设施造成损害。本研究采用物理模型试验和水-气两相流数学模型CLSVOF(Coupling Level Set and Volume Of Fluid),研究了不同结构竖井(旋流式竖井和螺旋阶梯式竖井)水力学特性和调蓄隧道中的间歇喷涌问题。根据施工条件设计的两种竖井方案的消能率接近,旋流竖井存在负压及较大震动、排气不畅,而螺旋阶梯式竖井流速较低且流态稳定。在对调蓄隧道中"间歇喷涌"的数值模拟研究中,排气井管径对间歇喷涌的影响十分显著,模拟情景中最剧烈的喷涌会产生5.35倍初始状态下的测压管水头和38.2 m/s的喷涌速度。展开更多
The velocities at given points in the volute chamber,the contracted section and the vertical dropshaft of a discharge tunnel with vortex drop were measured by a small specially designed L-shaped tube,as Laser Doppler ...The velocities at given points in the volute chamber,the contracted section and the vertical dropshaft of a discharge tunnel with vortex drop were measured by a small specially designed L-shaped tube,as Laser Doppler Velocimetry（LDV） or Particle Image Velocimetry（PIV） would not work there due to the special structure of the discharge tunnel with vortex drop.Hydraulic empirical formulas were proposed to predict the velocities and the angles of the velocities made with the vertical direction θ.The theoretical analysis results were in good agreement with experimental data.Therefore,the method proposed in this paper can be used to analyze related characteristics of discharge tunnels with vortex drop.Additionally,different model scales were considered to predict the cavitation characteristics on the wall of a dropshaft in practical engineering.展开更多
基金the financial support from the China Scholarship Councilthe Natural Sciences and the Engineering Research Council (NSRC) of Canada
文摘Dropshafts are vertical structures widely used in urban drainage systems and buildings for water transportation.In this paper,a physical model study was conducted to investigate the air entrainment in the dropshaft under various flow regimes with and without air ventilation.Observed from the experiments,the air entrainment mechanisms varied with the water flow regimes in the dropshaft.When there was no water plug formed in the dropshaft,air could be supplied directly from downstream.Once the water plug was formed,while without venting,the air was replenished only from downstream intermittently and then in the form of large air bubble traveling upwards to the airspace at the top;while with venting,air was mainly replenished from the dropshaft top and no large air bubble was observed.The experimental results also showed that the amount of entrained air in the dropshaft with venting was greater than that without venting.
基金This work was supported by the National Natural Science Foundation of China(Grants No.51709087 and 51839008)the Fifth“333 Project”of Jiangsu Province(Grant No.BRA2018061).
文摘Due to limited flow capacity and the instability of the asymmetric structure of traditional baffle dropshafts,a novel baffle dropshaft with a symmetric structure,adopting the construction shield well directly,is proposed for large-range flow discharge in deep tunnel drainage systems.In this study,a two-phase flow field of the novel baffle dropshaft with three different baffle spacings was simulated at seven different flow rates with a three-dimensional(3D)numerical model verified with experiments,to study hydraulic characteristics of this novel baffle dropshaft.The results show that the novel baffle dropshaft has a remarkable energy dissipation effect.Baffle spacing of the novel baffle dropshaft has a greater effect on flow patterns and baffle pressure distributions than the comprehensive energy dissipation rate.Flow rate is a critical issue for the selection of baffle spacing in the design.Some guidance on baffle spacing selection and structure optimization for the application of this novel baffle dropshaft in deep tunnel drainage systems is proposed.
基金supported by the National Natural Science Foundation of China(Grant No.51779081)
文摘Nowadays, "Sponge Cities" are being built to provide a valid solution to the glaring drainage problems in the urban areas of China. The hydraulics of a dropshaft, especially discharge capacity, energy dissipation and cavitation damage control, evidently affect its safety and the city's underground tunnel system, due to the high dropshaft and large discharge. The hydraulic characteristics of stepped spillway dropshafts are experimentally investigated for the variable step rotation angles and end sill heights. Flow regimes inside the dropshafts are classified under the different approach flow discharges. The results illustrate that there is high energy dissipation in the present dropshafts with the stepped spillway and the cavitation damage could be effectively avoided thanks to the effect of the air entrainment to the flow.
基金supported by the National Natural Science Foundation of China(Grant No.51479057)
文摘Standing waves occur frequently at the inlet due to the change of the flow direction from an approach channel to the dropshaft.The performance of the standing wave,characterized by the relative height,the location and the extent,is theoretically and experimentally investigated in the present paper.It is shown that the height of the standing wave decreases with the increases of the approach flow Froude number and the sub-channel number in the inlet,but increases with the increase of the curvature of the dropshaft.The errors of the expressions for the relative height,the location and the extent of the standing wave,are 9.7%,7.8%and 13.1%,respectively,as compared with the experimental data.
文摘深层隧道排水系统(深隧)是布置于深层地下的大型排水工程,一般由调蓄隧道、入流竖井、通风设施(排气井)及排水泵站组成,具有调蓄雨洪及控制溢流污染的作用。其中调蓄隧道为避开地铁等城市地下工程往往布置于距离地面30~60 m深处,入流竖井连接地表浅层管网和深层隧道。深隧系统竖井内部的水力学特性复杂,具有单宽流量大、落差高及大量掺气等特点,处理不当将造成较大的破坏。而极端降雨期间,由于未能充分排气而产生的间歇喷涌,也会对设施造成损害。本研究采用物理模型试验和水-气两相流数学模型CLSVOF(Coupling Level Set and Volume Of Fluid),研究了不同结构竖井(旋流式竖井和螺旋阶梯式竖井)水力学特性和调蓄隧道中的间歇喷涌问题。根据施工条件设计的两种竖井方案的消能率接近,旋流竖井存在负压及较大震动、排气不畅,而螺旋阶梯式竖井流速较低且流态稳定。在对调蓄隧道中"间歇喷涌"的数值模拟研究中,排气井管径对间歇喷涌的影响十分显著,模拟情景中最剧烈的喷涌会产生5.35倍初始状态下的测压管水头和38.2 m/s的喷涌速度。
基金supported by the Key National Science and Technology Projects (Grant No. 2008BAB29B04)the National Natural Science Foundation of China (Grant Nos. 50709020,50909067)
文摘The velocities at given points in the volute chamber,the contracted section and the vertical dropshaft of a discharge tunnel with vortex drop were measured by a small specially designed L-shaped tube,as Laser Doppler Velocimetry（LDV） or Particle Image Velocimetry（PIV） would not work there due to the special structure of the discharge tunnel with vortex drop.Hydraulic empirical formulas were proposed to predict the velocities and the angles of the velocities made with the vertical direction θ.The theoretical analysis results were in good agreement with experimental data.Therefore,the method proposed in this paper can be used to analyze related characteristics of discharge tunnels with vortex drop.Additionally,different model scales were considered to predict the cavitation characteristics on the wall of a dropshaft in practical engineering.
