The Study On Flow Field Characteristics Of Two-tooth Block Inner Dissipater

The tooth block internal energy dissipater belongs to a special type of sudden dispersal and dissipative energy dissipater.It sets up tooth blocks in pressurized pipelines or tunnels to suddenly contract and expand the over-current section,resulting in drastic changes in the flow streamline.Rolls are generated to eliminate the energy in the water stream.In the early stage of the research group,a series of studies were conducted on the hydraulic characteristics of tooth block internal energy dissipaters,which mainly included factors such as the number of blocks,area contraction ratio,height of blocks,and relative length,and their over-flow capacity,energy dissipation rate,and pressure characteristics.The effect of cavitation characteristics.This paper is based on the research of the first-stage secondary block-type internal energy dissipater,and chooses the same two-level body(area shrinkage ratio of 0.5,the number of blocks is 4)of the block,Doppler flow meter on the block The flow field of an energy dissipater with a distance of 40cm was measured to analyze the distribution rules of its mean flow velocity and pulsating strength.Numerical simulations were then performed to numerically calculate the spacing between blocks with different tooth blocks and second-stage blocks,and the distance between blocks was analyzed.The effect of the changes on the average flow velocity and turbulent energy distribution.The main research contents and conclusions are as follows:1.Through the measurement and measurement of the instantaneous flow velocity at each measurement cross section of a secondary block type internal energy dissipater with a 40cm pitch between blocks and blocks at different flow rates(3L/s-18L/s),the water flow along the longitudinal direction is analyzed in detail.The average flow velocity distribution and pulsating intensity distribution rule of the gap profile and the toothed block profile have the following main flow field characteristics:(1)The maximum value of the time-averaged flow velocity along the central axis of the pipe flow direction appears in the two-stage tooth block segment,that is,0.5D and 3.2D from the first-stage tooth block entrance,where the maximum time average of the first-order tooth block is The flow rate is 2.2times the average cross-sectional flow velocity,the maximum mean flow velocity at the second-order tooth block is 2.5 times the cross-sectional average flow velocity,and the maximum time-averaged flow velocity of the secondary tooth block is greater than the first-order tooth block.(2)There is a longitudinal section where the tooth block are located in the direction of the water flow,and it can be observed that the water flow exists in the back of the tooth block,and no reverse flow phenomenon is observed in the longitudinal section where the gaps are located.(3)As the flow rate increases,the range of the backflow area at the rear of the block is also greater.When the flow rate is 18L/s,the recirculation zone is30mm away from the pipe wall,and the maximum reverse flow velocity appears at 0.4D behind the first gear block,which is 0.449m/s.(4)As the flow rate increases,both the axial and radial pulsation strengths increase.The most obvious area of change is in the shear layer of the exit recirculation zone of the block,and after the second stage block is greater than the first-degree tooth.After the block,the axial direction is larger than the radial one.(5)In the direction of water flow,the pulsation strength is most violent at the position 0.4D behind the block and the height of the block,and the maximum pulsation strength of the first block is 0.65 times the mean flow velocity.The pulsation strength is greater than the first-order tooth block,which is about 0.83 times the average flow velocity.2.Comparing the numerical calculation results of the block-type internal energy dissipater with a spacing of 40cm with the test,the results are in good agreement with each other.On this basis,the block-type energy dissipater for each distance(40cm,60cm,80cm,100cm)is The numerical calculation and analysis of the flow rate of 18L/s,27L/s,and 36L/s can obtain the effect of the distance between blocks and blocks on each flow:(6)The average flow velocity of the second-stage tooth block internal energy dissipater with different spacings has the same tendency in the direction of the flow in the pipeline,which is reflected in the rapid increase through the two-stage tooth block entrance,through the block.At the exit section,there is a jet flow,the average flow velocity gradually decreases,and there are vortices on both sides.(7)The variation of block spacing has almost no effect on the average flow velocity distribution near the first-order tooth block entrance and exit,and affects the average flow velocity distribution near the entrance and exit of the second-order tooth block.The larger the distance,the greater the influence.(8)As the distance between blocks increases,the average flow velocity distribution at the second-order gear blocks at each flow is closer to the first-order block,when the distance is 100cm,the second-level block and the first-level block are at the same time.Average flow velocity distribution is approximate.(9)With the increase of the distance between the blocks,the average turbulent energy at the outlet of the secondary blocks increases gradually,the distance increases from 40cm to 100cm,and the turbulent energy is 0.428m~2/s~2,0.561m~2/s~2,0.574m~2/s~2,0.581 m~2/s~2.In this paper,through the measurement and calculation of the flow field of the different pitch blocks,the overall change law of the flow field is obtained,which can provide the basis for the follow-up to explore the energy dissipation mechanism and the optimal arrangement of the second tooth block internal energy dissipater.