Q) I am running a case in which I want to have a pre-defined pressure at a
certain point of the computational domain. This is accomplished by
(manually) justifying the outlet pressure of the domain and keeping
everything else constant. I have created a monitoring point at that
location:
MONITOR POINT: p monitorinpoint
Cartesian Coordinates = -1.05 [m], 0 [m], 0.03 [m]
Option = Cartesian Coordinates
Output Variables List = Pressure
END
After a couple of trials I found an outlet pressure that leads to
desired pressure in the monitoring point (following this via the
CFX-Solver Manager). Surprisingly, looking at the results in POST and
probing a pressure at this point gives a pressure value that is about 10
Pa lower than according to the GUI of Solver Manager. Pressure level in
the monitoring point is around 46 500 Pa.
How is it possible that pressure in this particular point is somewhat
different in Solver Manager and in POST? This complicates the solution
procedure, as in the system slight pressure changes are of major
importance. Therefore I should always check the pressure in POST rather
than in Solver Manager.
A) This seems to be a difference between the interpolation in the solver and Post.
In the Solver Manager Gui the values are calculated using a nearest neighbour (vertex) calculation and in CFX-Post (the more accurate) a tri-linear interpolation.
The finer the grid, the smaller the difference between the results should be.
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Q) I am running a case in which I want to have a pre-defined pressure at a certain point of the computational domain. This is accomplished by (manually) justifying the outlet pressure of the domain and keeping everything else constant. I have created a monitoring point at that location: MONITOR POINT: p monitorinpoint Cartesian Coordinates = -1.05 [m], 0 [m], 0.03 [m] Option = Cartesian Coordinates Output Variables List = Pressure END After a couple of trials I found an outlet pressure that leads to desired pressure in the monitoring point (following this via the CFX-Solver Manager). Surprisingly, looking at the results in POST and probing a pressure at this point gives a pressure value that is about 10 Pa lower than according to the GUI of Solver Manager. Pressure level in the monitoring point is around 46 500 Pa. How is it possible that pressure in this particular point is somewhat different in Solver Manager and in POST? This complicates the solution procedure, as in the system slight pressure changes are of major importance. Therefore I should always check the pressure in POST rather than in Solver Manager. A) This seems to be a difference between the interpolation in the solver and Post. In the Solver Manager Gui the values are calculated using a nearest neighbour (vertex) calculation and in CFX-Post (the more accurate) a tri-linear interpolation. The finer the grid, the smaller the difference between the results should be. |
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