Energy Dissipation Of Propeller Type Baffle Block At Low Froude Number

Small hydropower is an important direction of our country’s hydropower developmentThe reliable discharge structure and energy dissipation device are important safetyguarantee of hydropower project.Low head, low froude number and less dissipated energyrate are characteristics of small hydropower.The discharged flow with large energy mayscoure downstream bed and bank seriously.What’s more,it might endanger the safety of theengineering.Therefore,research on energy dissipation characteristics under low froudenumber,development new economic and convenient supplementary dissipater are the greatsignificance of small hydropower development.Based on the principle of turbine,the energy of tail water is very few.In addition,therotation of propeller can enhance the mixing strength and adjust the distribution of velocity.Propeller type baffle block,a new type of supplementary dissipater is proposed.Design theenergy dissipation experiment model,through generalized model experiment andtheoretical analysis,main conclusions gained are as follows:(1)The study does a comparative analysis on hydraulic characteristics of downstreamflow,such as state fluid,maximum kinetic energy of single flow,velocity distribution,velocity coefficient near the floor,mean square deviation of velocity,the center of gravity of velocity,energy loss coefficient and so on.The results show that flow adjustment is obviously andenergy dissipation effect is significant when the stilling basin add propeller type baffleblock. The maximum velocity of out pool can reduce30%, the velocity near floor canreduce40~60%,mean square deviation of velocity which characteristed uniformity in velocitydistribution can reduce about50%,the average energy loss coefficient is increased from0.277to0.395~0.426,the maximum kinetic energy of single flow is decreased rapidly,thebiggest proportion of decrease reaches76.91%,the average is52.32%.(2)Based on test results,considered adjust velocity distribution,reduce the bottomvelocity,increase energy loss coefficient,baffle wall style as another form of supplementarydissipater has an optimal hight.In this paper the hight is3.5cm,0.5cm higher than the tail.(3)Through contrast test for mutiple supplementary dissipaters,analysis the effect onadjusment velocity and energy dissipation comprehensively,their quality order is baffle wall style、propeller and baffle block、baffle block、propeller type baffle block.The ratio ofmaximum velocity out pool is0.83:0.84:0.87:1.00,the ratio of mean square deviation ofvelocity is0.12:0.44:0.42:1.00,the ratio of energy loss coefficient is1.03:1.01:0.98:1.00.Therefore,compared with the other supplementary dissipaters,the propeller type baffleblock’s effect on adjusment velocity and energy dissipation is worse.(4)When adding propeller in front of baffle block,effect on adjustment flow in verticalis better than the other supplementary dissipaters,but in horizontal is not obvious,energy losscoefficient increases rarely.Therefore,in order to achieve turbine’s energy effect,moreresearch need to carry out.