Proceedings of the 6 th World Congress on Mechanical, Chemical, and Material Engineering (MCM'20) Prague, Czech Republic Virtual Conference – August, 2020 Paper No. HTFF 170 DOI: 10.11159/htff20.170 HTFF170-1 Bubbly Cavitating Flow Through a Converging Nozzle Mohammed ZAMOUM 1 , Rachid BOUCETTA 1 , Mohand KASSEL 1 Laboratoire Génie Physique des Hydrocarbures LGPH, Faculté des Hydrocarbures et de la Chimie FHC, Université M’hamed Bougara Boumerdes UMBB Boulevard de l’indépendance, Boumerdes 35000, Algeria m.zamoum@univ-boumerdes.dz; r.boucetta@univ-boumerdes.dz m.kessal@univ-boumerdes.dz Abstract- In the present work, the bubbly cavitating flow phenomena after passing through the converging nozzle is numerically investigated. The dynamic of the cavitating bubbles is modeled by the use of the mass and momentum phase’s equations, which are coupled with the Rayleigh-Plesset equation of the N bubbles dynamics. However, assuming that the same initial conditions of all bubbles are identical and that all bubbles are equi-distant from each other simplifies the governing equations. Equation set is numerically resolved by the use of a fourth order Runge-Kutta scheme. The numerical resolution of the previous equations set let us found that the bubble radius distribution, fluid velocity and fluid pressure change dramatically with upstream void fraction and an instability appeared just after the passing the converging nozzle for both cases one bubble N=1 and two bubbles N=2. Indeed, for the case of one bubble N=1, the flashing flow phenomena occurs for an upstream void fraction α s =11.2x10 -3 , which corresponds to a critical bubble radius R c =1.8. Whereas, for bubble number N=2, the same phenomenon occurs for α s = 8.9x10 -3 , with R c =2. This difference is due to the bubble interaction. Also, we found that, the bubble number N strongly affect the bubble frequency. However, with increase the bubble number, the maximum size of the bubbles increases and bubble frequency oscillation decrease. Keywords: Bubbly flow, Converging nozzle, Two phase flow, Cavitation 1. Introduction Bubbly cavitating flows in ducts and nozzles represent an important problem in many engineering applications such as propelling nozzles in jet engines. The converging nozzle flow is one of any cavitating flow in which a low pressure region causes the flow to accelerate. The investigations of homogeneous steady-state cavitating nozzle flows, using spherical bubble dynamics with a polytropic thermal process [1, 2], have shown some flow instabilities illustrated by flashing flow phenomenon. The flow model, a generally used, is a nonlinear continuum bubbly mixture which is coupled with the dynamics equation of the bubble. A three equations model was first proposed by van Wijngaarden [3, 4] and has been used for studying steady and transient shock wave propagation in bubbly liquids, by omitting the acceleration of the mean flow. This model has been also considered by Wang and Brennen [1], in the case of converging-diverging nozzle, with an upstream variable void fraction. It was observed that significant change of the flow characteristics depends strongly on the latter and a critical bubbles radius have been obtained. A. Ooi and R. Manasseh [5] have studied coupling effects on acoustic signature from non-linear oscillations of a group of micro bubbles by the use of Rayleigh-Plesset equation, where bubbles number and their natural frequency are significantly dependant. Several numerical and experimental studies have been carried out on the effect of the geometrical parameters [6, 9], such as throat diameter, throat length, and diffuser angle, on the mass flow rate, critical pressure ratio and application rang of small-sized cavitating venturi. Also, Tian et al [10] have designed and investigated a variable area cavitating venture. They have realised four sets of experiments to investigate the effect of the pintle stroke, the upstream pressure and downstream pressure as well as the dynamic motion of the pintle on the performance of the variable area cavitating venture. They concluded that the variable area cavitating venturi can control and measure the mass flow rate dynamically. More recently, Zamoum et al [11] have numerically investigated the dynamical of a bubbly flows converging- diverging nozzle (Venturi). The mass and momentum phases equations, which are coupled with the Rayleigh-Plesset