Q. I am running a thermal solution in CFX 5.7 with only specified temperatures as the thermal boundary conditions. The resulting temperature field contains values that are out of bounds, with temperatures out of bounds values where the temperature was specified. Why is this and what can I do to ensure that the displayed results are within bounds?
A. At the intersection of a specified temperature boundary and an adiabatic wall, there is ambiguity as to which condition should prevail.
CFX solves the conservation equation for the nodes on all these boundaries all the time, and uses the specified temperature to close the flux through the boundary faces. (The faces are either in one boundary or the other, so there is no ambiguity...). However, this closure can support negative coefficients (and hence out-of-bound temperature) when the boundary face area is arger than the 'interior' face area (ie, concave surfaces).
To obtain bounded values, the following three steps are necessary.
- Set the expert parameter (not in the GUI):
boundary diffusion scheme = 3
- Make the adiabatic planes symmetry planes.
- Display hybrid values.
|
Q. I am running a thermal solution in CFX 5.7 with only specified temperatures as the thermal boundary conditions. The resulting temperature field contains values that are out of bounds, with temperatures out of bounds values where the temperature was specified. Why is this and what can I do to ensure that the displayed results are within bounds? A. At the intersection of a specified temperature boundary and an adiabatic wall, there is ambiguity as to which condition should prevail. CFX solves the conservation equation for the nodes on all these boundaries all the time, and uses the specified temperature to close the flux through the boundary faces. (The faces are either in one boundary or the other, so there is no ambiguity...). However, this closure can support negative coefficients (and hence out-of-bound temperature) when the boundary face area is arger than the 'interior' face area (ie, concave surfaces). To obtain bounded values, the following three steps are necessary. - Set the expert parameter (not in the GUI): boundary diffusion scheme = 3 - Make the adiabatic planes symmetry planes. - Display hybrid values. |
||
|