Research On Slip Mechanism And S-blade Hydraulic Characteristic Of Hydraulic Energy Recovery Turbines

Pumps as turbines(PAT)is an attractive and important alternative for energy recovery solution.The application of PAT have been developed in the processes of petro-chemical,metallurgy,desalination,et al.Despite the wide application of PAT,some problems have been exposed recently,such as biased prediction and selection,low efficiency,and unstable operating of PAT.The reason lies in the lack of flow mechanism of PAT,for instance,the effects of slip and vortex phenomenons on PAT's performance,which affect the performance prediction and blade optimization of PAT.As a consequence,the slip phenomenon within flow channels of PAT was revealed,and the optimization of blades was complemented considering slip factor.(1)The slip mechanisms of pump mode and turbine mode of PAT were revealed using theoretical and Computational Fluid Dynamics(CFD)methods.Slip factor were studied,and a theoretical prediction model was presented for PAT selection considering slip factors.Finally,an experiment was performed to verify the prediction model.Result shows the presented model is more accurate than Stepanoff,Alatorre-Frenk,Sharma,and Derakhshan models.(2)A optimization scheme of large inflow angle impeller for PAT was presented considering slip factor and flow matching between volute and impeller.The S-blade impeller for PAT was proposed finally.A 80-50-315 PAT with different inflow angles(30°,60°,90°,120°,150°,175°)were simulated by CFD,and results show the best efficiency point of PAT was related to inflow angle of 120°.For PAT with high efficiency,the inflow angle of balde was recommended for 90°-150°.Furthermore,the efficiency of PAT with S-blade is higher than back-ward blade and original blade.(3)Steady numerical simulation of PAT with S-blade was performed using CFX17.0 based on RNG k-? turbulence model.The large vortexes within flow channels was researched,which induced by slip phenomenon.Result shows that the large vortexes occur near the inlet of impeller for PAT,it causes the disorder distribution of velocity and pressure in flow channels.Besides,the vortexes weaken when PAT operating at large flow rate.In the next step,the DES model was applied for unsteady numerical simulation of PAT,result shows that the structure of vortexes is steady,but swirling strength of vortexes change with 0.5 period of PAT rotating.Furthermore,the vortexes make a subordinate contribution to the pressure fluctuation of PAT.(4)Generally,the blades and van wrap are related to shrink angle of flow channels.Sblade PAT with different blades and van wraps were simulated by CFX17.0,the effect of shrink angle of flow channel on velocity slip was revealed,and the relationship between shrink angle and slip factor was conducted as quadratic function.Besides,the effect of rotating speed on slip factor was studied,and its relationship was conducted as cubic equation.To verify the efficiency of S-blade PAT is higher than others,3 PATs with S-balde,back-ward blade,and original blade impellers were manufactured and tested respectively.Results show that the efficiency of PAT with S-blade is higher than back-ward and original blades,and its average efficiency in tested region is 3% higher than PAT with original blade.The study provides a theoretical basis for the selection and performance prediction of PAT,as well as the blade optimization of PAT.