Study On Flow Field Characteristics Of Suction Water-Intake And Its Influence On Raw Water Turbidity

In this paper,the sution water-intake of Taihu waterwork in Huzhou was taken as the research object.The flow field characteristics around the intake under the pumping action and the wind power and its influence on sediment particles movement were studied by means of model test and numerical simulation.On this basis,how the flow field affects the turbidity of raw water was analyzed.The main research contents are as follws:1.A 50:1 scale model test of the intake was carried out,and the velocity around the intale was measured by the Particle Image Velocimetry(PIV).In the mean time,FLUENT was used to conduct single-phase flow numerical simulation analysis of the flow field around the 1:1 intake,whose design was the same as the model test with pumping action only,and the results were compared with the model teste results.The comparision shows that the data of the model test are close to the numerical simulation resulds after scale conversion.Their distribution shape of the velocity field conforms to a high degree under some working conditions,but the others conforms to a low degree.This indicates the limitations of scale model test and additional research needs to be done by numerical simulation analysis.By analyzing the numerical simulation results of single-phase flow,it can be seen that in increase of water depth will weaken the strength of pupmping action.2.The numerical model of gas-liquid two-phase transient flow field of intake was established to calculate the flow field around the intake under the coupling effect of wind and pumping action.After continuous optimization of the numerical model and comparison with relevant literature,an applicative model for the flow field aroud the intake was obtained.The numerical simulation results show that the flow field is generally periodic,and the dominant direction of flow is determined by the wind direction.When the calculation tends to be stable,the change range of the maximum flow velocity is fixed.By comparing the calculation results of single-phase flow and two-phase flow,it shows that the wind plays an important role in the change of field overall velocity.There is a certain correlation between the wind and turbidity,so the movement of sediment particles can be analyzed by the calculation results of two-phase flow.3.The raw water around the intake was collected,and the size of suspended particles in it was measured with the Laser Particle Size Analyzer(LPSA).The measurement results show that the median particle size of suspended particles is about 9 microns,which is consistent with the measured date of Taihu lake sediment in scholars' literatures.The incipient and non-depositing velocity of these particles are discussed based on previous studies on sediment movement.And they can be the judgment basis of analyzing sediment movement.4.The incipient and non-depositing velocity of suspended particles in raw water were compared with the calculation results of two-phase flow numerical simulation.The influence of water depth,wind speed and wind direction on raw water turbidity was comprehensively analyzed.Results show that the flow velocity around the intake is small under dominant wind conditions and the bottom sediment is hard to start.But most of the flow velocity above the water inlet reaches the non-depositing velocity of suspended particles,proving that the non-depositing of suspended particles is the primary cause for the drastic change of raw water turbidity.And larger wind causes higher raw water turbidity.Combining images analysis and velocity distribution,the area of different non-depositing velocity in different sections under each working condition were counted.And the amount of continuously moving sediment was estimated by using the data of particle size distribution and the area,which was conducted on the correlation analysis with turbidity for all working conditions.