|
Often, the data available to you is not in SI
units, but in other units like CGS or English, or a
combination of different units. Having different unit
systems available in the set-up process is helpful
since you do not have to convert the units yourself.
In CFD-ACE+, the Units menu allows you to choose the
unit system with which you would like to work.
The Units menu allows you to select the unit system
that will be used to display all physics-related dimensional
quantities displayed in the GUI. You may change the unit system at any time while
using CFD-ACE-GUI, so that you can input any value in your preferred unit system.
The Units menu offers the six choices shown in figure 1.
Figure 1. Units menu choices in CFD-ACE-GUI
The first selection, Default Display Units, is the
default setting and is provided for backward
compatibility with versions prior to V2004.
The next four selections are for standard unit
systems.
-
SI Units
-
CGS Units
-
English Units I
-
English Units II
The two English systems differ only in the unit of
length used (foot vs. inch).
The final selection, User
Defined, allows you to select the unit
to be used for 16 fundamental quantities, as shown in figure 2. You can use any combination of units.
Figure 2. User Defined unit system window
NOTE: Changing the unit system does
not modify stored values you have already input; only
the displayed values are updated to be consistent with
the selected unit system.
As an example, consider the Reference Pressure for
any give case. If the Reference Pressure is set to
101325Pa, and then the unit for pressure is changed to psi, the value for
the Reference Pressure will be changed accordingly to reflect the psi units
for pressure quantities:
-
Open a DTF file in CFD-ACE-GUI.
-
Click on Unit Menu and select User Defined.
-
Change the units of Pressure.
-
Set up the VC/BC/IC for the case using the units
specified in the User Defined unit system. In
Figure 3, you can see that the Reference Pressure
units are in Pascals by default, but we can change
them to psi in the User Defined unit system menu.
Figure 3. Pressure in Pascals
Figure 4. Pressure after changing the units from
Pascals to psi
-
Submit the DTF file to the CFD-ACE+ solver and post-process the results in CFD-VIEW.
NOTES:
-
Any data in the form of tables for settings options, such as "Profile in X",
"Profile in time", "Specify
Monitor Point", etc., must be provided in SI unit
system irrespective of the selected global unit system.
-
Any data provided from outside CFD-ACE-GUI, through options like "Profile
from File" or "Read from File", must be provided in
the SI unit system irrespective of the selected global
unit system.
-
CFD-ACE-SOLVER outputs all data in the SI unit system.
In order to post-process data in a particular unit
system, in CFD-VIEW click the Units menu and select the desired unit system.
- As stated above, changing the units through the Units menu will only affect
physics-related quantities, such as velocity, electric voltage,
temperature, density, thermal conductivity, etc. Model-related
(i.e. geometric) quantities will not be affected by the selected
unit system. Such model-related quantities include, but are not limited to: X, Y, Z
(when specifying position for, say, fans, spray injectors, macro particles),
fan thickness and radius, macro particle diameter and point spacing, monitor points
location.These model-related quantities will be affected by
the model scale.
If you have any questions about this tip or would like us to discuss other topics in the future,
please let us know.
Regards,
ESI CFD Support Team
|
