Characterization of vortex rope in draft tube of water turbine based on Omega vortex identification method
In order to study the vortex rope characteristics of the water turbine draft tube and the effec-tiveness of the Omega vortex identification method on the vortex rope of the draft tube,the Q and λ2 criteria and the Omega vortex identification method on the vortex rope of the draft tube were compared,and the vortex rope characteristics of the draft tube under different operating conditions based on the Omega method and the reduced dimensional Omgea method were analyzed.The results show that for ra-dial water turbines,the Q and λ2 criteria,as well as the Omega vortex identification method can iden-tify a clear and reasonable draft tube vortex by adjusting the threshold value reasonably,while the threshold selection interval of the Omega method is small and insensitive.The draft tube of the water turbine will have a long vortex rope in the flow condition,which is not conducive to the stability of the machinery.At the same time,using the reduced-dimensional Omega vortex identification method and the proposed vortex energy index,quantitative analysis of the monitoring surface of the tailpipe under different operating conditions was conducted to determine the area of high vortex concentration,as well as studying the energy dissipation patterns in draft tube.The results show that the area between the in-let and the bend of the draft tube has the highest vortex concentration,the highest energy dissipation and the most unstable flow pattern,which can provide a basis for optimizing the structure of this type of water turbine.
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