考虑拦污栅影响的河床式电站进水口水力特性OA

[Objective]The power generation efficiency of low-head,large-discharge hydropower stations is highly sensitive to head loss.Reducing the head loss at the intake of such stations is essential to improve their hydraulic energy utilization.This study aims to 1)investigate the distribution of flow velocity,pressure,and turbulent kinetic energy in low-head riverbed-type intakes,2)examine the sources of head loss at the intake,3)quantify head los-ses in different sections of the intake and the head loss coefficients of the trash racks,and 4)finally provide guid-ance for the design and optimization of similar intakes.[Methods]We established a three-dimensional model en-compassing the intake(including the trash rack),the flow passage from the intake to the turbine spiral case,and the upstream intake channel.Hydraulic simulations of these regions were performed using the k-ε turbulence model in ANSYS Fluent.A hydrostatic pressure boundary condition was applied at the inlet,while a flow velocity bounda-ry condition was specified at the outlet of the turbine spiral case.[Results](1)When the bottom sediment outlets were not in operation,the flow velocity before the trash rack at the middle orifice was the highest(ranging from 1.4 m/s to 2.7 m/s),while the velocities before the trash rack at the left and right orifices were lower(ranging from 0.5 m/s to 1.9 m/s).After the left bottom sediment outlet was activated,the flow area in front of the trash rack at the left orifice decreased,with the maximum flow velocity increasing to approximately 2 m/s.(2)The overall pres-sure was slightly higher before the trash rack and slightly lower after it.The maximum pressure differences across the beams,intermediate support,and rack bars were 0.3 m,0.3 m,and 0.08 m,respectively.(3)Across the op-erating conditions,the head losses at the intake were 0.121 m,0.229 m,0.385 m,and 0.376 m,respectively.The corresponding average head losses for the trash rack sections were 0.078 m,0.120 m,0.172 m,and 0.174 m.(4)When the bottom sediment outlets were not in operation,the head loss coefficients for the trash racks of the left,middle,and right orifices were 2.1,0.9,and 1.7,respectively.After the bottom sediment outlet was activa-ted,the head loss coefficient for the trash rack at the corresponding orifice decreased to 1.2.[Conclusion]The op-eration of a bottom sediment outlet reduces the flow area before the trash rack of the corresponding orifice,making the velocity distribution more uniform and increasing the average flow velocity.Low-pressure zones and high turbu-lent kinetic energy zones occur at the tails of beams,intermediate support,and rack bars,as well as at the turning corners of the separation pier heads for each orifice and at the intake sill.These regions are the primary locations of head loss in the intake and trash rack.As a result,head losses in the intake entrance section and trash rack section are significant,with the trash rack section accounting for approximately 50％of the total head loss at the intake.When the bottom sediment outlets are not in operation,the head loss coefficient for the left orifice's trash rack is the highest,followed by the right orifice,with the middle orifice being the smallest.After the bottom sediment outlet is activated,the flow velocity distribution at the pre-rack cross-section becomes more uniform,resulting in an approxi-mately 43％reduction in the head loss coefficient for the trash rack at the corresponding orifice.