Modelling of wave and turbulence induced secondary currents in stratified duct flow

摘要

In this thesis mathematical and numerical modelling of the flow field in the liquid phase in gas-liquid stratified duct flow is studied. The flow is turbulent, and the interface between the gas and the liquid is presumed to be deformed by regular gravity waves. The thesis mainly discusses mechanisms for generation of secondary currents known to exist in this flow regime. The work comprises three papers: (1) Waves, turbulence and the mean field in stratified duct flow, (2) Wave induced secondary currents in stratified duct flow, (3) Comparison between turbulence and wave induced secondary currents in stratified duct flow. Paper 1 derives a mathematical model of the three dimensional velocity field in the liquid phase and presents numerical calculations. In Paper 2 it is shown that the secondary velocities in the liquid phase may result from an interaction between wave pseudomomentum per unit mass and mean axial velocity. In Paper 3, the turbulence model ASM (Algebraic Stress Model) of Naot and Rodi is implemented and applied together with the wave field model of the present thesis. The mathematical model includes non-linear coupled equations which are solved simultaneously by a numerical method, subject to prescribed boundary conditions. The general purpose computer code PHOENICS of Rosten and Spalding are used as a modelling platform. The wave boundary value problem is not solved by means of the numerical techniques of PHOENICS, but rather by separate routines coded in FORTRAN and linked to the PHOENICS code. 136 refs., 70 figs., 25 tabs.