[Jiricbeng]

Hello,
my simulation is a steady state including fluid domain only using total energy option. The boundary conditions applied on the boundary faces are:

S1: mass flow inlet
S2: pressure opening
S3: wall constant temperature
S4: wall constant temperature, wall velocity included.


Should the sum of heat flow on all bounding surfaces be zero?

Symbolically written: areaInt(Heat Flux)@S = 0, where S=S1+S2+S3+S4 ?

Is this the energy conservation equation in CFX ?

[Opaque]

Answer: NO.

The sum of the fluxes over all the surfaces = 0.

Fluxes at wall = areaInt(Heat Flux)@Surface
Fluxes at inlet/outlet/opening = massFlowInt(Total Enthalpy)@Surface

Note: I have neglected the diffusion transport at inlet/outlet/opening for simplification. In advection dominated flows, the diffusion transport is second-order compared to the advected energy.

[Jiricbeng]

Thank you for the answer. Could you please tell, what does the energy conservation equation looks like when using CFX variables?



My case does not satisfy the equations you mentioned, although it is converged.

[Opaque]

If you look at the end of the output file, there is a section with the flow summaries for each equation, as well as the imbalance.

You can then compute each one of them from the equations I described previously. From your initial question, I assumed there was no additional physics or interaction between the equations, i.e. plain vanilla flow with energy.

I already included the CFX variables and integration details required to complete the conservation balance check. Once you go through the summary you should be able to identify additional quantities (not always present for vanilla flows)

[Jiricbeng]

Thank you again for the answer. Well, I checked the imbalance and they are below 1%. Also monitored expressions are stable. Attached, please find the part of the out file. The simulation is two phase (air and oil) and I also checked modifications of the expressions, e.g. massFlowInt(oil.Total Enthalpy)@Surface or oil.massFlowInt(oil.Total Enthalpy)@Surface, the same for air etc.