Page 31 - TransAT_Tutorial_Manual

TransAT Tutorial Manual 1.2. Backward Facing Step

Simulation Parameters
This tab is used to define the numerical properties of the simulation.

• Click Simulation Parameters on the left-hand side of the TransATUI

• Set the following parameters to run a steady simulation with an implicit method.

Simulation Type : Steady
Number of I t e r a t i o n s : 800
ENABLE Autorelaxation
Relaxation Factor : 0.90

In this example, the value of the Relaxation Factor has been increased compared to the default
value of 0.6 in order to increase the speed of convergence of the simulation.

Note that increasing the Relaxation Factor is not a foolproof method to accelerate the con-
vergence of a simulation. Indeed, a simulation may become unstable with high values of the
Relaxation Factor. In such a simulation, it might be required to decrease the Relaxation
Factor to stabilise it.

Equations
In this section the convergence threshold is defined, as well as the convection scheme and other
parameters of the solvers used by TransAT.

• Select All Quantities in the equation tree and set the value of the Convergence Tolerance
field as follows

Convergence Tolerance : 1.0 e−6

Initial Conditions
In this tab simple initial conditions can be set. In this case, initial values for all the relevant
quantities will be set to 0 except the velocity component in the x-direction.

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

• Click U-Velocity in the quantity tree

• Set Method to Constant and Value to 0.1

• Proceed as above to set the initial state of the remaining quantities as follows

c
Ascomp AG Switzerland 21 Version 5.7