The CFD driven optimisation of a modified venturi for cavitational activity

Abstract

This work presents CFD-based optimisation of the important geometrical parameters of a cavitating venturi. The parameters for optimisation were selected based on the analysis of the steps involved in the cavitation process like cavity inception, cavity growth, and cavity collapse. It was seen that the ratio of the perimeter of the venturi to the cross-sectional area of its constriction quantifies the possible location of the inception of the cavity. The ratio of the throat length to its height (in the case of a slit venturi) controls the maximum size of the cavity and the angle of the divergence section controls the rate of collapse of a cavity. Based on the numerical study, it was concluded that a slit venturi (˛= 2.7) with the slit length equal to its height (1:1) and a half angle of divergence section of 5.5 • is an optimum geometry for best cavitational activity.Ce travail présente l'optimisation CFD-basée des paramètres géométriques importants d'un venturi cavitation. Les paramètres d'optimisation ontété choisis basés sur l'analyse desétapes impliquées dans le processus de cavitation comme la création de cavité, la croissance de cavité et l'écroulement de cavité. On l'a vu que le rapport du périmètre du venturià la section transversale de sa constriction (˛) quantifie l'emplacement possible de la création de la cavité. Le rapport de la longueur de gorgeà sa hauteur (dans le cas d'une fente venturi) contrôle la taille maximale de la cavité et l'angle de la section de divergence contrôle la vitesse de l'écroulement d'une cavité. Basé sur l'étude numérique, on a conclu qu'une fente venturi (˛= 2,7) avec la longueur de la fenteégaleà sa hauteur (1:1) et un demi-angle de la section de divergence de 5,5 est une géométrie optimum pour la meilleure activité de cavitation.

Hydrodynamic cavitation: an advanced oxidation process for the degradation of bio-refractory pollutants

“…Some experimental studies (Padoley et al 2012, Gore et al 2014) have also used the same configuration of venturi having half divergent angle of 5.5° for slit and 6.5° for circular venturi to produce desirable physicochemical changes in wastewater treatment application. Therefore, for a better cavitational yield, it is recommended to use optimum divergent angle in the range of 11°-13° as estimated in the CFD studies (Bashir et al 2011, Jain et al 2014) and validated through various experimental studies (Saharan et al , 2013. Chavan et al (2015) defined a cavitation efficacy parameter as "maximum collapse pressure/permanent pressure drop", maximized the same using numerical studies of venturi CFD and cavity dynamics, and have proposed optimum configurations.…”

“…The geometrical parameters play an important role when the focus is on achieving higher cavitational yield for producing the desirable transformation. For an optimum cavitational yield, parameters such as number of cavitational events, cavitational intensity, the residence time of the cavities in a low-pressure region, and the pressure recovery rate in the downstream section are very important (Bashir et al 2011). These parameters significantly depend on the geometry of the cavitating device.…”

“…the divergent angle, can greatly affect the life of cavity and the generated collapse pressure. Bashir et al (2011) have studied the different half divergent angles in the range of 5.5° to 8.5° and have optimized the factor based on the obtained cavitation number and density profile in the divergent section. It was observed that on increasing the angle from 5.5° to 8.5° the optimum cavitation number was increased from 0.23 to 0.28.…”

“…In this instance, it is necessary to optimize the ratio of throat height/diameter to its length. Bashir et al (2011) have carried out computational fluid dynamics (CFD) analysis of venturi at different perimeter to cross-sectional area ratios such as 1:0.5, 1:1, 1:2, and 1:3. The optimum ratio was found to be 1:1 based on the length of the cavitation zone and the velocity achieved at the throat.…”

An Automatic Method for Optimizing Venturi Shape in Cavitation Flows

“…To counter this effect and obtain a cavitation flow centred in the geometry an obstruction was added to the venturi. The concept can be seen as a development of the ideas put forward in [11]. The modified venturi design is shown in Fig.…”