Numerical Simulation Of The Influence About The Discharge Capacity Of Piano Key Weirs With Different Overhang Angle

Piano Key Weirs(PKW)is a new labyrinth weir.Compared to conventional thin-walled weir,it Increasing the length of Overflow leading edge to improve the discharge capacity like other labyrinth weirs;On the other hand,Compared to conventional labyrinth weir,it make the traditional labyrinth weir units replaced by upstream and downstream overhang,and improving the discharge capacity further,the base area becomes drastically smaller at the same time.So the Piano Key Weirs collect the advantages of thin-walled weir and labyrinth weir,It can be widely used in building new concrete gravity dam or old dam’s expansion and alterations.Since the overhang angle is an important parameter which can affect PKW’s ability of discharge In this paper,we use 3D turbulent mathematical model,combining with the VOF free surface tracking method for physical experiment of this kind of size 3D numerical simulation research,combined with numerical simulation and physical experiment to study the Piano Key Weirs discharge characteristics..Simulation results of discharge and flow pattern are in good agreement with those obtained in the experiment,thus verify the reliability of the numerical simulation research.Therefore,this paper designed five different sets of PKW which have the same parameter except the overhang angle.Analyzes the changes in leakage flow with the increasing on the weir head through Numerical Simulation the 5 sets of PKW.The total discharge can be divided into three overflow outlet and inlet,and lateral front.And we find a large part of increasing discharge characteristics is from side edge discharge increasing after the analyze from the numerical simulation.If we keep changing the angle,even exceed the critical value of overhang angle,the PKW will become a conventional labyrinth weir.We have made a further study on the impact of overhang angles on the discharge capacity of PKW.In this paper,on the basis of previous design,we added 3 groups of overhang angle of PKW type,which are all beyond the critical value of overhang angle.Again,in order to facilitate comparison,the other parameters remain unchanged.We find that,through further simulations,the discharge capacity rules of these 3 group of overhang angle were different.Compared to the previous five group body,discharge capacity of the later three groups of PKW increased significantly,but the flow curves of the three groups are basically coincident.Specific performances:The discharge capacity of the three groups of PKW are stronger than the former five groups at a low water head and the situation is just the opposite at a high water head.Generally speaking,the discharge capacity of the later three groups of PKW is closed and better than the previous five group body.Since the PKW are usually installed on the dam.So in order to discuss the impact of the Deep reservoir on the PKW discharge capacity,we added 4 groups of Deep reservoir of PKW type,and the other parameters remain unchanged.Through simulations,we find with the increase in deep reservoir,the discharge capacity is decreasing.The reason may be similar to the thin-walled weir,Due to the increased shrinkage of water and the decrease of H/P,lead to discharge coefficient decrease.