Page 365 - TransAT_Tutorial_Manual

TransAT Tutorial Manual 9.1. Water suction

Initial Conditions
In this tab initial conditions can be set. In this case, initial values of the velocity components
will all be set to 0m.s −1 . The remainig quantities, namely pressure and phase volume fractions
will be set up using advanced initial conditions.

• Select the Initial Conditions tab on the left-hand side of the TransAT user interface

• Click Momentum in the quantity tree

• Set Method to Constant and Value to 0.0

This will set both the U-Velocity and V-velocity components to 0 over the whole domain.

Advanced Initial Conditions
It is necessary to initialise the simulation, in order to give the initial location of the different
phases and set the initial pressure distribution. In this simulation, the region defined by y < y c
is initially filled with water while the region defined by y ≥ y c is filled with air with y c = 0.25m.

Pressure is initialised over the domain with the following equation to get a reference pressure
0 at the interface between the two phases:

p(x, y) = ρg(y c − y) (9.1)

with ρ the density of the mixture (ρ = ρ water if y < y c and ρ = ρ air if y ≥ y c ) and g the component
of the gravity vector in the y-direction.

A ready-made initial condition file, initialconditions.cxx, can be found in the reference folder
(9.1 - water suction in the Tutorials folder).

• Copy the file initialconditions.cxx from the subfolder Tutorials/9.1 - water suction of the
Public/Documents/TransAT5.7 folder to your project folder.

• Select Advanced Initial Conditions

• Click to compile the initial conditions. This step is optional and only checks that
the initialcondition.cxx file is written properly and can be compiled. The flow field will be
initialised later in the Execute window.

c
Ascomp AG Switzerland 355 Version 5.7