| The unique patterns of concave bank erosion and convex bank sedimentation in curved channels can lead to migration in the river,making the river more curved.Excessive bending is not conducive to flood discharge,navigation,and agricultural production,and river regulation is necessary at this time.Groynes are a multifunctional river training structure that is widely used in waterway regulation,ecological restoration,and riverbank protection projects.The local erosion phenomenon at the head of traditional impermeable groyne is relatively serious,and it is easy to cause structural instability under long-term action.It is a trend to renovate existing groynes or adopt groynes with more reasonable design forms.Geometric factors are an important reference principle for groyne design.This article considers the influence of various geometric factors and uses numerical simulation methods to study the effects of different types of single groyne on the flow characteristics of 180° bend and different types of groynes on continuous bend.The changes in flow velocity,recirculation zone,turbulent kinetic energy,and bed shear stress in the bend after the layout of groyne are analyzed,and the following conclusions are obtained:(1)In 180° bend,large bed shear stress is generated near the traditional impermeable groyne head and opposite bank,which is prone to high erosion.As the permeability rate increases,the flow velocity behind the single permeable groyne increases,while the flow velocity at the center and opposite bank of the channel decreases accordingly.The streamline behind the groyne gradually tends to be gentle,and the backflow phenomenon becomes less obvious.The degree of turbulence in the bend continuously decreases,and the bed shear stress near the head and convex bank of the permeable groyne significantly decreases compared to the traditional impermeable groyne.When the permeability rate is high,the flow velocity on the concave bank behind the groyne is relatively high,and the effect of groyne protection is weak.When the permeability rate is 30%,the improvement effect of permeable groyne is better.Under the same maximum water discharge rate of the groyne body,the bank protection effect and water diversion effect of the single notched groyne are better than those of the permeable groyne.The degree of water turbulence in the bend decreases with the decrease of the notched length,and the high bed shear stress near the groyne head and convex bank is significantly reduced.Keeping the notched length unchanged,as the decreases of notched depth,the water retaining effect of the groyne increases,and the flow velocity at channel center and opposite bank gradually increases.The turbulence degree of the water flow in the bend first increases and then decreases,and the bed shear stress near the groyne head and convex bank significantly increases.When the notched depth approaches the height of the water surface,the distribution of bed shear stress is close to that of the impermeable groyne.(2)In continuous bend,compared to the equal-length impermeable groynes,the descending arrangement of impermeable groynes performs better in increasing the flow velocity of the main channel,which can improve river navigation,but also brings higher turbulence energy and bed shear stress.The ascending arrangement of impermeable groynes helps to reduce erosion and reduce the flow velocity near the downstream river bank,protecting the river bank for a longer distance,and is suitable as a bank protection structure in channel bend.Both permeable and notched groynes can alleviate the erosion of the groyne head and the erosion of the inner bank in continuous bend.Permeable groynes have a good slow flow effect,helping to reduce the turbulence of water flow in bend.They can also serve as energy dissipation structures.Notched groynes enrich the terrain near the groyne fields,facilitate the habitat of aquatic organisms,and can be applied in ecological restoration projects. |
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