| Circulating water pumping station is an indispensable part of coal-fired power plant or nuclear power plant,and its hydraulic performance will directly affect the operational safety and work efficiency of the power plant.The water intake construction structure of the circulating water pumping station includes: forward water intake forebay and open water inflow channel.The main function of the forebay is to connect the water diversion channel and the inlet flow channel,and smoothly introduce the water flow into the inflow channel,providing a smooth and uniform flow pattern for the inflow channel.The main function of the inflow channel is to make further adjustments to the incoming flow of the forebay,and to set gates and filters in the flow path to control the incoming flow and prevent debris from entering the pump,so as to optimize the inlet conditions of the pump and ensure the pump efficient operation.Therefore,the hydraulic performance design of the forebay and inflow channel of the circulating water pump station has a great influence on the performance and reliability of the circulating water pump.This paper takes the inlet structure of a circulating water pump station in a coal-fired power plant as an example,the combination of numerical calculation and model test is used to study and analyze the flow characteristics,hydraulic structure optimization,vortex characteristics,and vortex resistance measures in the forebay and inflow channel of the pumping station.The specific research work and results are as follows:1.Based on the hydraulic similarity criterion,the normal physical model test platform for the intake structure of the circulating water pump station with a geometric scale of 1:10 and the corresponding three-dimensional calculation model are established.The RNG k-? turbulence model is used to numerically calculate the water flow characteristics in the forebay and inflow channel of the circulating water pumping station,and part of the calculation results are compared with the model test results,which verifies the accuracy and feasibility of the numerical calculation method.2.Numerical analysis is carried out on the inlet flow patterns of different water levels and different pump combinations scheme in the circulating water pumping station without rectification measures,supplemented by model test tests.The research results show that:under the design water level conditions and the combined operation scheme of each pump,the flow pattern in the forebay and the inflow channel is stable,there is no obvious skewed flow and large-area backflow,and the throat section of the inlet bell mouth of the circulating water pump(CW)is measured.The relative deviation of the each measuring point flow velocity with respect to the average flow velocity of eight measuring point,the horizontal deviation of the velocity distribution at the suspended height of the suction bell mouth of the 1.5D section upstream of the center line of each pump,and the pre-swirl angle in the inlet pipe all meet the corresponding test specifications.Compared with the design water level conditions,the low water level conditions are affected by the impact of the high-speed incoming flow of the diversion channel,and the flow pattern characteristic sections of each pump combination scheme have different degrees of largescale de-wall backflow,especially in the middle of the forebay.At the same time,the flow velocity distribution at the outlet section of the inflow channel is turbulent,and there is no obvious regularity.Circulating water pump(CW)inlet bell mouth throat section of the relative deviation of the flow velocity of each measuring point with respect to the average flow velocity of eight measuring point,and the horizontal deviation of the flow velocity distribution at the suspended height of the suction bell mouth of the 1.5D section upstream of the pump centerline,and the pre-swirl angle in the inlet pipe is higher than the critical value of the specification,the corresponding test index of the auxiliary sewage pump(AW)conforms to the hydraulic design specification.3.In view of the unfavorable flow patterns such as skewed flow and large-scale reflux in the forebay of each pump combination scheme under low water level operating conditions,the diversion grid and double bottom sill rectification measures are adopted respectively,and the influence of each rectification measure on the flow pattern of the forebay is studied and analyzed by numerical calculation methods.The calculation results show that the installation of diversion grids and double bottom sills in the forebay can significantly weaken the impact of the mainstream and reduce the reflux area in the forebay.Compared with the original plan:(a)the flow velocity distribution of section S1 under each pump combination scheme is even,the flow velocity distribution uniformity of the cross-section CW-S2 has increased by about 6%,and the average value is above87% and 84% respectively,while the uniformity of the flow velocity distribution of the cross-section AW-S2 remains basically unchanged;(b)Under each pump combination scheme,the flow velocity weighted deviation angle of the outlet section of the CW inflow channel are kept within 1?2°,and the flow velocity weighted deviation angle of the outlet section of the AW inflow channel are all less than 0.1°,which meets the hydraulic design criteria;However,affected by the working conditions and the geometrical size of the pump station prototype,these two types of rectification measures only weaken the area of the reflux zone and the lateral cross flow in the forebay.After optimized rectification,the reflux vortex structure of different small scales still exists.Therefore,according to the actual working status of the circulating water pump station,the circulating water pump is the main working unit.At the same time,adding the bottom sill must also consider the problem of later forebay dredging.It is recommended to choose the guide grid to optimize and rectify the forebay flow pattern.4.Taking the inflow channel of the circulating water pump(CW)as the research object,using the Realizable k-? turbulence model and the VOF(volume of fluid)twophase flow model to study and analyze the vortex characteristics in the inflow channel at the minimum submergence depth,and the influence of the guide cone + cross baffle vortex blocking device and the triangular cone vortex blocking device on the vortex flow of the inflow channel is compared.The research results show that at the minimum submergence depth,the flow pattern in the inflow channel of the circulating water pump is symmetrically distributed,and a clear free surface vortex is generated on the back side of the inlet pipe,and the free surface vortex has a tendency to extend and diffuse toward the bell mouth,which is easy to form an air-entrained vortex.In addition to the free surface vortex,a high-strength wall vortex structure is formed under the water inlet bell mouth and on both side walls,and the vortex directly enters the bell mouth from the wall surface,which will seriously affect the water inlet conditions and working stability of the circulating water pump.Compared with the solution of no blocking vortex device under the minimum submergence depth,the addition of a blocking vortex device in the inflow channel can effectively weaken the strength and distribution area of the submerged wall vortex,but the suppression effect on the free surface vortex is not obvious. |
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