| Recycling the surplus pressure energy head in liquid has a great significance to save energy and reduce consumption and promote sustainable development.How to convert the surplus pressure energy head into t he energy of other forms by pump as turbine(PAT)has gradually become a popular direction in the area of energy recovery in recent years.Based on the self-designed centrifugal pump with space diffuser,this paper try to take the condition of hydraulic tu rbine as the research object.Then the Three-dimensional(3D)flow was simulated based on the large-eddy simulation(LES)and Mixture multiphase flow model under different flow conditions with the medium of water and sand water.Firstly,the steady 3D flow was simulated based on the standard k-? turbulence model and Mixture multiphase flow model,got the external characteristic curve of the hydraulic turbine from 0.7QBEP to 1.4QBEP(QBEP is the best efficiency flow).Compared and analyzed the pressure,velocity,vorticity,streamline and the distribution of particles in the conditions of 0.7 QBEP,1.0QBEP and 1.3QBEP with the medium of water and sand water.The results of steady calculation showed that: the energy pressure head of the solid-liquid two-phase is higher than that of the water under the condition of small flow rate,and when the flow rate increases to 1.0 QBEP,The energy pressure head of the solid-liquid two-phase begins to be lower than that of water The efficiency of solid-liquid two-phase is always lower than that of water,and the flow rate of the highest efficiency is greater than that under water.The pressure distribution and velocity distribution shows the law of stepwise decline along the flow direction.The pressure drop of solid-liquid two-phase is higher than that of water,and the flow rate of the highest efficiency is greater than that under water.The presence of particles has a great influence on the degree of disorder in the flow field under the condition of small flow rate,however,the presence of particles has a great little influence on the degree of disorder under the condition of large flow rate.Secondly,the unsteady 3D flow was simulated based on the LES turbulence model and Mixture multiphase flow model,Compared and analyz ed the pressure fluctuation in the conditions of 0.7QBEP,1.0QBEP and 1.3QBEP with the medium of water and sand water.Carried out tracking the variation of vorticity distribution in stator and rotor cascades of the channel under the conditions of 1.0QBEP?The results of unsteady calculation showed that: the periodicity of the pressure fluctuations of the point between the stator and the rotor and the point in the guide vane influenced by the change of the pressure gradient in the impeller is obvious,and consistent with blade passing period.The pressure coefficient of the monitoring point increases and the amplitude decreases with the increase of flow rate.The closer the channel is,the larger the amplitude of pressure fluctuation and the higher the frequency components.The main frequency are the blade pass frequency(BPF)and the harmonic frequency is a multiple of the BPF under different conditions,and its amplitude is exponential decay.The vortex induce second harmonic in the impeller obviously.The particles enhances the high-frequency pressure fluctuation under small flow rate condition,and particles weakens the high-frequency pressure fluctuation under the large flow rate condition.As the impeller blades rotate close to the outlet of the guide vanes,A large number of vortices appeared on the concave surface of impeller blade,and experienced a variety of complex evolution,such as stretching,merging,then gradually dissipated along the flow direction.Due to the larger viscosity of the solid-liquid two-phase flow,the large scale vortex in the flow field and the extinction of the small scale vortex are accelerated. |
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