Control Panel
Initial Conditions Introduction
The Initial Condition panel enables you to set the initial values required for the computation. The following methods available: For All Volumes, Mixed, and Volume by Volume. Select the method from the pull-down menu labeled Initial Condition.
• IC Option Menu
o Initial Conditions-Constant
o Initial Conditions-Previous Solution
o Initial Conditions-Previous Solution + Constant
• IC Applied Menu
o Initial Conditions-For All Volumes
o Initial Conditions-Volume by Volume Mode
• Reset, Apply, and OK Buttons
Although the Initial Conditions selected should not affect the final solution, they can affect the path to convergence. Therefore, we recommend that you use realistic values. For more information on initial conditions, see the Module section.
Control Panel
Initial Conditions-Constant
The Constant option enables you to set a constant value as an initial condition for every cell in the computational domain or to indicate that values will be provided by a user subroutine (uinit). The Initial Conditions panel is shown in the For All Volumes mode ready to accept Constant Values.
Initial Conditions Panel - Constant Option
A tabbed list is shown for each Module that has been activated. Under each tab is a list of
variables that require initialization. These will be listed in a separate section and each section has several elements. Shown in the figure below is a typical Initial Condition value section (this one is for X-Direction Velocity).
All of the value sections contain a title that describes the value represented in the section. An Evaluation Method pull-down menu displays the Constant and User Sub(uinit) options. The Variable Name is the same name used for graphical output. A field enables you to add user-supplied values.
Initial Condition Values Section
Control Panel
Initial Conditions-Previous Solution
The Previous Solution option enables you to use the results from a previously run simulation as the initial condition for the current simulation.
Initial Conditions Panel - Previous Solution Option
A field requests the filename of a previously run solution. The solver reads the initial fields from the specified file.
When you are performing a steady-state simulation, and you click the Continuation Run button, the solver begins the run with the iteration count set to one more than the last iteration from the previous solution. The solver appends the new residual values to the old residual data sets so that you can see a continuous residual history, uninterrupted by the restart.
When you are performing a transient calculation, and you click the Continuation Run button, the solver sets the start time of the transient run equal to the time in the restart file. Additionally, the solver appends residuals and monitor point data to existing files rather than writing to new files.
When starting from a previous solution, also called a restart run, CFD-ACE-GUI imposes the following restrictions:
• The grid size must be the same in the current model and in the previous solution data set. This does not mean that the physical domains must be identical, but that the number of grid blocks must be the same and the number of cells in each block must be the same.
• The variables solved, as dictated by the Modules selected in the Problem Type settings and Model Options, should be the same. Otherwise, a smooth restart may not be possible.
Control Panel
Initial Conditions-Previous Solution + Constant
The Previous Solution + Constant option enables you to use constant values, a user subroutine, or specify that results of a previous solution be used for initial values. You can specify this for each variable.
Initial Conditions Panel - Previous Solution + Constant Option
In this mode the option of taking initial values as constants is pushed down to the level of the individual variables. This option is useful for models in which you have added one or more dependent variables to a previous simulation and wish to take all dependent variables, except the new ones, from the previous solution.
The Continuation Run option is still allowed in this mode but should not be selected for cases in which the number of dependent variables changes. For these cases, the residual and monitor value plotters will not behave properly.
Control Panel
Initial Conditions-For All Volumes
The For All Volumes option has two additional ways to define the initial conditions (listed under the IC Source pull-down menu).
Control Panel
Initial Conditions-Volume By Volume
The Volume by Volume option enables you to set different initial conditions on each individual volume condition region. When you switch the IC setting mode to Volume By Volume, you can set different initial conditions on each of the available volume conditions. The Model Explorer
switches to an IC Explorer view and lists all of the available volume conditions. Recall that (in CFD-GEOM terms) for 3D grid systems, every structured or unstructured domain is a separate volume condition. In 2D grid systems every structured face or unstructured loop is a separate volume condition.
Before any initial condition settings can be made, you need to pick a volume conditions to make it active. This can be done through several methods. The most common are picking from the viewer window and picking from the Model Explorer.
Picking from the viewer window is done by placing the mouse cursor over a Volume Condition handle (usually cross-hairs or normal vectors) and pressing the left mouse button. To select more than one volume condition at the same time, hold down the Ctrl key while picking with the left mouse button.
Picking from the Model Explorer can be done by selecting a Volume Condition entry from the Model Explorer list with the left mouse button. Discrete multiple picking can be done by holding down the Ctrl key while picking multiple entries with the left mouse button. A continuous multiple pick can be made by picking one item from the Model Explorer and then holding down the Shift-key and picking another item. In this case every item between the first and second items will be picked. See Graphics Area-Picking Operations for more details on picking.
If several volume conditions have been selected, you may make them part of a permanent group by pressing the Group button located on the lower toolbar.
After one or more volume conditions have been selected, you may set the initial conditions using the methods as described above in the section Constant Values.