Study On Shape Parameters Of Dovetail Flip Bucket Based On Guxian Energy Dissipation Optimization

For High-head gravity dams with ski-jump energy dissipation,flip bucket shape and shape parameters are particularly important for the stability of the floor of the plunge pool and the downstream energy dissipation and erosion prevention.Based on the method of hydraulic model test,the hydraulic model of the Yellow River Guxian Water Control Project with geometric scaleλ_l=60 is used to optimize the flood discharge and energy dissipation system.The main research contents and results of this paper are as follows:（1）The article studied the characteristics of waterjet and pressure characteristics of the floor of the plunge pool of six flip bucket shapes,including continuous,narrow slit,differential,dovetail,straight edge narrow-slit dovetail and curved narrow-slit dovetail flip bucket shape.The results show that the continuous flip bucket waterjet is continuous and dense.The narrow-slit flip bucket is applied to a 30°angle,and it does not show alongitudinally stretched waterjet shape.The differential flip bucket waterjet presents the morphological of stratified and split strands.The dovetail flip bucket waterjet is longitudinally shaped like a broom.The area of waterjet and inlet width are greatly increased.There is no impact pressure along the time-averaged pressure,and the root mean square peak value of the pulsating pressure is reduced by 59.5%,69.8%,and 39.4%,respectively,compared with the continuous,narrow slit and differential flip bucket.The horizontal contraction and longitudinal stretching effect of the curved narrow-slit dovetail flip bucket is better than that of the straight-sided narrow-slit dovetail flip bucket,and the lateral contraction is conducive to the turbulence of the water near the dam and weakens the turbulence of the water in the second dam area.The dovetail flip bucket is conducive to the stability of the floor of the plunge pool and the safety of the downstream energy dissipation and erosion prevention.It has certain reference value for the selection of the flip bucket shape of similar high-head gravity dams.（2）The article studied the outlet position of dovetail cutout.The results show that the root mean square of pulsating pressure increases with the increase of outlet elevation.The root mean square of the pulsating pressure at the bottom of the water cushion pool decreases with the decrease of the pile number at the exit of the cantilever.At the same time,the change of the elevation of the outlet and pile number may cause negative pressure in the original flow passage,and air holes and other facilities should be added to avoid cavitation and cavitation erosion.（3）Based on the orthogonal test method,the article studied the sensitivity and significance of the inner edge angleθ₁,opening ratioβ₁ of dovetail head and opening ratioβ₂ of dovetail end.The results show thatθ₁ are the greatest factor of sensitivity/significance,β₂ are the secondary factor,andβ₁ are the least secondary factor,namely,the order of sensitivity/significance of factors are as follows:θ₁＞β₂＞β₁.（4）Based on orthogonal test method and single factor test method,the article studied the hydraulic characteristics of the inner edge pick angleθ₁,the outer edge pick angleθ₂,the dovetail head opening ratioβ₁,the dovetail end opening ratioβ₂ and the reverse arc radius R of dovetail flip bucket shape parameters.The results show that:1)With the increase ofθ₁（θ₁=10°→20°）,the root mean square peak valueσ_max of the pulsating pressure on the floor of the water cushion pond,the pick distance of the inner edge of the water tongue L_n and the pick distance of the outer edge of the water tongue L_w increase significantly,and the inlet width L decreases significantly.2)With the increase ofθ₂（θ₂=30°→50°）,the distance L_n from the inner edge of the tongue is basically the same,and the distance L_w from the outer edge of the tongue and inlet width L increases first and then decreases trend.The L_w of the dovetail tongue is not the maximum when the angle of the outer edge of the tongue is 45°,and the impact force of the water tongue on the water cushion is not the strongest whenθ₂ is too large.3)With the increase ofβ₁（β₁=0.2→0.8）,the pick distance L_n at the inner edge increases first and then decreases,the pick distance L_w at the outer edge of the water tongue and the water inlet width L gradually decrease,and the overall change of the pick height H is not large.The peak valueσ_max of the root mean square of the pulsating pressure decreases first and then increases.The relative position x of the measurement point in the impact zone decreases,and the impact zone is close to the upstream.Whenθ₁=10°/15°,the best opening ratioβ₁ is 0.4/0.5.4)With the increase ofβ₂（β₂=0.3→0.7）,the peak valueσ_max of the root mean square of the pulsating pressure first decreases and then increases,the inner edge pick distance L_n first decreases and then increases,and the outer edge pick distance L_w and the inlet width L both show a decreasing trend.5)With the increase of R（R=30 m→60 m）,the inner edge pick distance L_n increases,the outer edge pick distance L_w increases first and then decreases,the inlet width L decreases,and the pick height H decreases.The larger R is,the greater kinetic energy carried by the waterjet tongue is,and the greater the impact force on the water cushion is.（5）Based on the optimization combination of dovetail type carpeting shape parameters,the article studied the optimization of"3 surface holes+2 bottom holes"flood discharge system.The results show that the dovetail type is adopted in all the spillway structures,and the combined spillway tongue has good transverse contraction and longitudinal tensile properties.The tongue smoothly converges and stretches,ensuring the smooth transition of water flow.Compared with the original continuous type,the interaction between water tongues decreases,the falling points of water tongues on the inner and outer edges are stagger distributed,the flow state in the water cushion pond is greatly improved,energy dissipation is sufficient,and no impact pressure is generated on all pressure measuring lines.And the root mean square peak valueσ_max=3.88 m is 74%smaller than the root mean square control standard 6.75 m.