Study On The Flow Characteristics And Influencing Factors Of Cavitation-Induced Choked Flow In Venturi Tube

Cavitation is a complex flow phenomenon and phase change phenomenon that occurs in a liquid medium.The occurrence of cavitation often leads to vibration,noise,and material performance degradation.However,recent studies have found that cavitation in the venturi can be useful in some occasions.The fill pump of the chemical and volume control system(CVS)and the feed water pump of the feed water system(FWS)are key equipments in the CAP1400 safe nuclear power technology.A cavitating venturi tube is installed downstream of these two pumps in the nuclear power plant,which is used to protect the pump by cavitationinduced choked flow in venturi tube.Based on the research methods of numerical simulation,high-speed camera experiment and theoretical analysis,the present paper uses the scaled model of the cavitating venturi from CAP1400 nuclear power plant as the research object to study the phenomenon of cavitation-induced choked flow in venturi tube,and the macroscopic development law,micro-flow characteristics and its influencing factors are also analyzed.The present paper establishes a numerical model suitable for the study of cavitation-induced choked flow in venturi tube.Through numerical simulation and experimental research,it is found that: the whole process of cavitation-induced choked flow in venturi tube can be divided into cavitation development,cavitation-induced choked flow and stable periodic cavitation,each of the three stages has its own iconic characteristics;with the increase of the choked flowrate corresponding to the working conditions,the cavitation period shows an increasing trend,and the cavity volume and the cavity length continue to increase;in the process of the cavitation-induced choked flow,shedding of small bubbles,tail bubbles and the vapor cavity will occur in the throat under the action of the re-entrant jet;it is also found in the experiment that large-scale cavities will collapse instantaneously and the rope-like bubbles will appear under the influence of the shock wave effect.Micro flow characteristics of cavitation-induced choked flow are numerically simulated by the large eddy simulation method in the present paper.It is found that the pressure pulsation and cavity movement at the venturi throat and diffusion section are obviously periodic;the shedding and collapse of a large number of unsteady and small bubbles will affect the periodic characteristics of pressure pulsation and cavitation movement.The present paper also carried out numerical simulation studies on the possible influencing factors of the choked flowrate,analyzed the influence of different venturi structure parameters and flow field parameters on the choked flow,and finally obtained the flow prediction formula of the cavitation-induced choked flow which can be used to guide the engineering practice.