Numerical simulation of cavitation and atomization using a fully compressible three-phase model

Abstract

The aim of this paper is to present a fully compressible three-phase (liquid, vapour and air) model and its application to the simulation of in-nozzle cavitation effects on liquid atomization. The model employs a combination of homogeneous equilibrium barotropic cavitation model with an implicit sharp interface capturing VoF approximation. The numerical predictions are validated against the experimental results obtained for injection of water into the air from a step-nozzle, which is designed to produce asymmetric cavitation along its two sides. Simulations are performed for three injection pressures, corresponding to three different cavitation regimes, referred to as cavitation inception, developing cavitation and hydraulic-flip. Model validation is achieved by qualitative comparison of the cavitation, spray pattern and spray cone angles. The flow turbulence in this study is resolved using the Large Eddy Simulation approach. The simulation results indicate that the major parameters that influence the primary atomization are cavitation, liquid turbulence and, to a smaller extent, the Rayleigh-Taylor and Kelvin-Helmholtz aerodynamic instabilities developing on the liquid/air interface. Moreover, the simulations performed indicate that periodic entrainment of air into the nozzle occurs at intermediate cavitation numbers, corresponding to developing cavitation (as opposed to incipient and fully-developed cavitation regimes); this transient effect causes a periodic shedding of the cavitation and air clouds and contributes to improved primary atomization. Finally, the cone angle of the spray is found to increase with increased injection pressure but drops drastically when hydraulic-flip occurs, in agreement with the relevant experiments.

Numerical study of cavitation regimes in flow over a circular cylinder

“…Numerical methods which include the effects of NCG were often based on the incompressible Navier-Stokes equations (Kunz et al 2000;Singhal et al 2002;Ji et al 2010;Lu, Bark & Bensow 2012). More recently, fully compressible formulations have been employed (Orley et al 2015;Mithun, Koukouvinis & Gavaises 2018). In the present work, the numerical method of Gnanaskandan & Mahesh (2015), based on a fully compressible formulation for the vapour-water mixture, is extended to account for NCG.…”

“…Presence of NCG can influence cavitating flows in various ways (Briancon-Marjollet, Franc & Michel 1990;Kawakami, Gin & Arndt 2005;Orley et al 2015;Makiharju, Ganesh & Ceccio 2017;Vennig et al 2017;Brandao, Bhatt & Mahesh 2018;. Influence of dissolved and injected NCG in partial cavitation over a wedge has been considered by Makiharju et al (2017).…”

Simulation and Measurement of Transient Fluid Phenomena within Diesel Injection

“…The computational methodology is based on a sharp interface 'volume of fluid' (VOF) technique including several customized models, which can track the liquid/non-condensable gas interface [19]. A three-phase fully compressible barotropic cavitation model is employed [19], where pressure is related to density, capturing phase change at saturation pressure, combined with non-condensable gases. K-omega turbulence modelling with corrections in presence of cavitation was implemented, is discussed in [23], the original model is from Reboud et al [21].…”

“…These data will compliment studies with both ECN and full geometry injector with simulation and experimental comparison for diesel injection events. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The images shown of the end of the injection event indicate that it is likely that the large ligaments of liquid fuel which emerge in this period with poor combustion characteristics [36] or lead to wetting of the surface of the fuel injector. Images are also included which show the discharge of fuel from the nozzle after the injection event wetting the surface of the fuel injector.…”

Combined visualisation of cavitation and vortical structures in a real-size optical diesel injector

“…high discharge coefficient, enhanced spray-plume atomisation, minimal shot-to-shot variation, as well as exceptional durability considering cycling over several years (Karathanassis et al 2020). It has been firmly established by the relevant research community that phasechange phenomena occurring in the internal flow-path of fuel injectors are strongly linked to the emerging spray morphology and dynamics (Payri et al 2004;Mithun et al 2018). The occurrence of cavitation, i.e.…”