City Research Online

Abstract

An explicit density-based solver suitable for multiphase flows has been developed and implemented in OpenFOAM. Phase change is predicted through the density variation under the HEM assumption and different thermodynamic models that have been utilized, starting from barotropic EoS to more complicated ones that include real fluid thermodynamics (Helmholtz EoS). In the latter, a tabulated data technique has been followed aiming to reduce the computational cost; the value of each thermodynamic quantity within each thermodynamic element is approximated by a finite element interpolation. Apart from the liquid and vapour phases, the non-condensable gas is modelled by adding a transport equation for the gas mass fraction (2-phase model). Finite volume discretization is employed in conjunction with high order Runge-Kutta methods for time integration. A Mach number consistent numerical flux, based on approximate Riemann solvers, is proposed and renders the solver suitable for low subsonic flows of the liquid regime, up to highly supersonic flow conditions noticed in the vapour phase. The validity of the developed models has been assessed against the exact solution of the Riemann problem, experimental data, other numerical tools and parametric studies.

Different multiphase flow simulations have been performed, from fundamental studies of bubble dynamics and droplet impacts on a solid surface to industrial applications such as Diesel injectors, needle-free devices and nozzles in cryogenic flows. Concerning the real fluid thermodynamics model, n-Dodecane bubble dynamics simulations in the proximity of a wall have been performed. The effect of the initial conditions and the different thermodynamic models utilized was investigated. The methodology has been also applied to cryogenic flows inside converging-diverging nozzles and demonstrated satisfactory agreement with prior experimental studies. The 2-phase solver was employed for modelling the wave dynamics and the cavitation regime inside a droplet which impacts a solid surface. Finally, the influence of the initial bubble pressure and the meniscus geometry on the developed jet velocity of a needle-free device is studied.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General)
Departments:	Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses School of Science & Technology School of Science & Technology > Engineering

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