| The water flow conditions of the long steep slope tunnel are complex,and the hydraulic problems such as inlet vortex,inlet suction in gate well and clear full flow in tunnel body are very unfavorable to the safe operation of hydraulic structures.At present,the research results on the hydraulic characteristics of the long steep slope tunnel are relatively rare,the flow pattern transformation mechanism of the long steep slope tunnel is not clear,and there are also many factors affecting the discharge capacity.Collected and sorted in this paper,on the basis of literature study,combining the reality of a long steep slope 1:50 tunnel project engineering model test,focuses on long steep tunnel flow pattern evolution,analysis of long steep cut-off tunnel flow pattern transition,the study of complex under the condition of water diversion tunnel in the flow regime,the change law of pressure analysis of long steep tunnel water flow movement characteristics inlaws.In order to further study the hydraulic characteristics of the long steep slope,a generalized model is added on the basis of the engineering model,and the results of the engineering model tests are mutually verified and supplemented,and the related factors affecting the discharge capacity of the long steep slope tunnel are analyzed and compared.Through model test analysis and comparison,the main research results of this paper are as follows:(1)The flow characteristics of long and steep slope tunnels are systematically studied,and the flow evolution laws of long steep slope tunnels are analyzed and summarized.The flow patterns of open and full flow transitions in long steep slope tunnels can be divided into four categories: intermittent top-out flow patterns,intense The flow state of the fold-shock wave water flow,the flow state of the large trapped air bag,the flow state of the paroxysmal small bubbles.In the process of rising and falling of the water level,the flow patterns in the cave are in different order,but they all belong to the above-mentioned types of flow patterns.(2)The flow regime transition limit law of long steep slope tunnel is studied.The analysis suggests that the boundary of free-surface-pressure flow in steep slope tunnels is related to the slope.With the increase of slope,the upper limit of open-full flow gradually rises.If the critical slope is exceeded,the upper limit of free-surface-pressure flow will decrease instead.The maximum open-full flow limit observed in the experiment The value H/D is approximately 2.72.The upper critical water level is unstable and the lower critical water level is stable.That is,the H/D value of the open flow is converted into a clear full flow,or the H/D value of a clear full flow is converted into a clear flow is about 1.1.There is a difference in the flow regime boundary between the water level rise process and the water level fall process of the steep slope tunnel,and the clear full flow range during the water level fall is smaller than the clear full flow range during the water level rise process.(3)The fluctuating pressure changes are related to the process of clear full flow.Thereare differences in the fluctuating pressure changes in the diversion tunnel between the rising process of the reservoir water level and the decline process of the reservoir water level.The fluctuating pressure changes more drastically during the rising process of the water level,which proves that the clear full flow is in There is a difference between the water level rising process and the water level falling process.The time-averaged pressure change law in the long steep slope tunnel is basically the same along the way.In the open flow,the pressure head line is basically parallel to the tunnel bottom slope with little change;when the flow is full,the pressure in the inlet section changes greatly,mainly due to the contraction of the inlet section and the local head The increase in loss is related to the negative pressure at the tail of the tunnel under full flow.In the open flow stage,the pressure gradient of the straight pipe section of the cave body is a constant value.The pressure head slope of the straight pipe section in the full flow cave increases with the increase of the reservoir water level.(4)The influence of the outlet topography,roughness,slope and curve on the discharge capacity is studied.Comprehensive analysis shows that the influence of various factors on roughness>slope>topography>curve.Among the four factors,the roughness has the greatest influence on the discharge capacity,which is mainly manifested in that the head loss along the way is proportional to the square of the roughness,so the change of the roughness has the greatest influence on the discharge capacity. |
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