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ISSN Online: 2377-424X

ISBN CD: 1-56700-226-9

ISBN Online: 1-56700-225-0

International Heat Transfer Conference 13
August, 13-18, 2006, Sydney, Australia

MODELLING OF CAVITATION FLOW IN A NOZZLE AND ITS EFFECT ON SPRAY DEVELOPMENT

Get access (open in a dialog) DOI: 10.1615/IHTC13.p16.70
12 pages

Résumé

The experimental observations and theoretical models of spray formation due to the effect of cavitation development in injection nozzles are reviewed. Particular attention is focused on the effects of cavitation disturbances on jet and spray break-up. Models of jet and spray break-up which take into account the stochastic character and non-equilibrium spectrum of product droplets are essential when modelling the primary and secondary stages of break-up. Single-fluid models of cavitation are shown to be robust, but contain empirical rate parameters which require adjustments for specific flows. This study addresses the liquid quality and viscous shear stress effects on cavitation flow. In order to account for the liquid quality effect on cavitation a model derived from bubble dynamics theory is developed. The model for the concentration of cavitation nuclei in a liquid is derived by assuming hydrodynamic similarity of cavitation flows. The model accounts for the variation in the number density of cavitation bubbles as a function of liquid tension in the cavitation region. This model was developed using an analogy with the effect of liquid superheat on the number of nuclei in models for nucleate boiling. The model contains a parameter, which describes the liquid quality. This can be adjusted using one set of measurements for a given liquid. The influence of viscous shear stress on the cavitation threshold in high-speed flows, such as those observed in the nozzles of a direct-injection diesel engine, has been clarified. In order to describe this effect on hydrodynamic cavitation in high-speed turbulent flows a model that takes into account the critical vapour pressure was developed. The model was adjusted to describe sub-cavitation and super-cavitation flows in real-scale models of diesel injectors.