Study On Blocking Characteristics Of Overflow In Drainage Pipeline With Sedimentation

Sediment,as a common functional defect in drainage pipelines,easily leads to poor drainage in the pipeline,which reduces the flow capacity of the pipeline and adversely affects the realization of the pipeline function.Roughness coefficient is an important hydraulic parameter in the hydraulic calculation of drainage pipeline,which is affected by many factors such as the section form and hydraulic condition of the pipeline.And the flow capacity of the sediment pipeline will be affected to a certain extent when the flow condition and section shape of the bottom change.In order to explore the hydraulic characteristics of drainage pipeline with sedimentation and the influence of sediment on the flow capacity,this paper adopts the combination of experiments and numerical calculation to study the pipeline under different flow rates and different sedimentation degrees.The main contents and conclusions are as follows:(1)Based on the rule of particle size distribution of sediment in the pipeline and classification standard of functional defects of drainage pipeline,a test platform for pipeline under sediment was built,and overflow experiment of pipelines with different sedimentation degrees were carried out.Numerical simulations of different sedimentation degrees were carried out in pipelines of the same size.The results show that the average relative errors of the measured water level and velocity data are within5%,which verifies the accuracy of the numerical simulation.In other words,the numerical calculation method can be used to study the overflow of the drainage pipeline under the condition of sedimentation.(2)The sedimentation degree of drainage pipe was defined as the ratio of the height of the sediment at the bottom of the pipe to the diameter of the pipe.The results of water level under different flow conditions were obtained through numerical calculation of drainage pipeline under different sedimentation degree conditions.According to the dimensionality analysis of E.Buckingham theorem,the hydraulic factors related to roughness coefficient were obtained,and the relationship between roughness coefficient and flow rate,Reynolds number and relative roughness were further analyzed.In addition,the roughness coefficient equation of the pipeline with sedimentation in the turbulent rough area was obtained and statistically analyzed.The equation were tested by taking the test data at 0.3 sedimentation degree and results in the literature,which showed that the established equation was reliable in measuring the roughness coefficient of the pipeline with different sedimentation degrees.(3)The variation of water surface,velocity field and average wall shear stress in the sediment section of the pipeline were analyzed.The results show that the water level of the measuring point in the sediment section was relatively stable and the variation range was small,which belongs to uniform flow.Under the same flow rate,the water depth decreases with the increase of sedimentation degree.The flow velocity gradient at the wall was large,and the flow velocity distribution was related to the wall curvature and the bottom roughness.The sediment can exacerbate the secondary flow in the pipe,and the velocity gradient of 0.2 sedimentation degree is larger than that of0.4.The average wall shear stress is axially symmetrical about the center of the pipe,and increases with the increase of filling degree and sedimentation degree.(4)The flow rate change was used to represent the loss of pipeline flow capacity,and the influence of sedimentation degree on flow rate is quantitatively studied.For different filling degrees,the overflow capacity loss amount and sedimentation degree (3 can be expressed as an exponential function with a good correlation.The loss of pipeline overflow capacity increases significantly with the increase of sedimentation degree at the same degree of filling,and the change rate of pipeline overflow capacity loss decreases gradually with the increase of sedimentation degree at the same degree of filling.As the maximum design filling degree increases with the increase of pipe diameter,the flow capacity loss of large-diameter pipeline was smaller under the same sedimentation degree.The research results reflected the flow resistance calculation process and flow characteristics of the pipeline with sedimentation comprehensively.It provided a scientific basis for quantitative analysis of the change of roughness and design of index in pipeline with sedimentation,which has important practical value in engineering.