###### Abstract  
Cavitation is a typical physical process that has shown to be highly valuable in the wastewater treatment field. This study aims to investigate the effects of the converging and diverging sections of a Venturi tube on the cavitation flow field. Multiphase flows in tubes are presented using the mixture model and the standard k-\(\epsilon\) model. And the Schnerr and Sauer cavitation model is employed to simulate the vapor-liquid phase transition process. Both grid independence and the numerical method's feasibility were validated before the research. The results showed that the influence of the divergence section length on Venturi cavitation characteristics depends on the provided pressure conditions. As the pressure increases, shorter divergence sections result in more significant cavitation effects. The length of the convergence section displays various cavitation behaviors under different pressure situations. A small contraction section length can achieve better cavitation effects in high-pressure applications, whereas the opposite is true in low-pressure cases. Within the scope of this study, it was observed that the Venturi tube with a divergent section of 14 Lt and a convergent one of 2.4 Lt provided enhanced cavitation performance when subjected to inlet pressures ranging from 0.8 to 1.2 MPa. Our findings indicate that the selection of converging and diverging section lengths in Venturi tubes should consider the corresponding operational pressure conditions, which provides valuable guidance and engineering significance in the research and development of Venturi cavitation devices in hydraulic engineering. V 2  
generates cavitation in a thin water layer in order to investigate the effect of hydrodynamic cavitation on the disinfection of E. coli. Experiments have demonstrated that hydrodynamic cavitations are particularly efficient in reducing bacterial division capacity. [PERSON] et al. [11] used a cavitation device that included a stator and a rotor assembly to clean effluent from the wood finishing sector within a specific rotating speed range, and they discovered that the chemical oxygen demand (COD) in real wastewater may be significantly lowered. Therefore, it is evident that hydraulic cavitation has shown considerable promise in the realm of wastewater treatments. However, the design of hydrodynamic cavitation reactors has a substantial impact on their cavitation performance. At present, there exist four main types of cavitation reactors that are typically utilized in a laboratory setting: the orifice plate, the Venturi tube, vortex, and rotary types [12; 13]. While the latter two types exhibit low pressure loss, their intricate structure and high maintenance costs serve as limiting factors for their widespread adoption. In contrast, both the orifice plate and Venturi tube cavitation reactors operate on similar principles of cavitation and offer the advantages of simple design, ease of use, and strong controllability. Nevertheless, the orifice plate cavitation reactors are more prone to blockages at sudden changes in the flow channel section and experience greater pressure losses than the Venturi tube counterparts. Therefore, the Venturi tube cavitation reactors are more widely applied in the field of hydraulic cavitation. Until recently, researchers' interest in Venturi cavitation characteristics has not waned. Most of them focus on the cavitation inception, evolution process, cavitation instability, and the structural parameters of Venturi tubes. [PERSON] et al. [14] analyzed the effect of key geometric parameters, such as the throat length and diffuser angle of Venturi tubes on cavitation inception. Further, [PERSON] et al. [15] investigated the impact of various geometric parameters on cavitation inception using a numerical simulation and experimental methods and discovered that flow resistance determines cavitation inception. [PERSON] et al. [16] used a high-speed video camera to visualize the behavior of a moving bubble cavitation in a Venturi from the inception to collapse process.