Numerical simulation of vertical intermittent flows
File(s)
Author(s)
Galleni, Francesco
Type
Thesis
Abstract
The present research extends the application of the “slug capturing” technique,
already extensively validated for the prediction of horizontal slug flow, to the
case of vertical pipes. In this technique, the one-dimensional two fluid model is
solved numerically in order to simulate mechanistically the growth and
development of the structures which characterise the vertical intermittent flow,
such as slugs and waves.
In this work the technique is first successfully applied to the prediction of
vertical slug flow: it is shown here that, when the appropriate correlation for the
interfacial friction forces is used, the slug capturing technique is able to simulate
correctly – even in vertical configurations - the complete evolution of the slugs
and to predict their key characteristics with a notable accuracy when compared
against experimental data. This represents certainly the most important
achievement of this work.
The one-dimensional two-fluid model is well known to be ill-posed and hence,
as the mesh is refined, artificial instabilities may grow so as to render the
simulation unreliable. For this reason, a Von Neumann analysis of the discretized
form of the model is presented. It is shown that the discretization introduces a
cut-off limit for short wavelengths, below which all the perturbations are damped.
It is suggested here that this effect, for practical sizes of the mesh, is sufficient
to stabilize the system.
Furthermore, this work presents preliminary results of the application of the
technique to churn flow. It is shown that, although the results may be considered
promising, the model still needs development.
already extensively validated for the prediction of horizontal slug flow, to the
case of vertical pipes. In this technique, the one-dimensional two fluid model is
solved numerically in order to simulate mechanistically the growth and
development of the structures which characterise the vertical intermittent flow,
such as slugs and waves.
In this work the technique is first successfully applied to the prediction of
vertical slug flow: it is shown here that, when the appropriate correlation for the
interfacial friction forces is used, the slug capturing technique is able to simulate
correctly – even in vertical configurations - the complete evolution of the slugs
and to predict their key characteristics with a notable accuracy when compared
against experimental data. This represents certainly the most important
achievement of this work.
The one-dimensional two-fluid model is well known to be ill-posed and hence,
as the mesh is refined, artificial instabilities may grow so as to render the
simulation unreliable. For this reason, a Von Neumann analysis of the discretized
form of the model is presented. It is shown that the discretization introduces a
cut-off limit for short wavelengths, below which all the perturbations are damped.
It is suggested here that this effect, for practical sizes of the mesh, is sufficient
to stabilize the system.
Furthermore, this work presents preliminary results of the application of the
technique to churn flow. It is shown that, although the results may be considered
promising, the model still needs development.
Version
Open Access
Date Issued
2017-02
Date Awarded
2017-06
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Issa, Raad
Van Wachem, Berend
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)