Learning Forum

[MRMR]

Hi, 
In my case I'm simulating an air flow through a nozzle - and the problem is that in energy balance which I try to define I have some missing values and I cannot understand where is the problem - nozzle drawing included (c - velocity, i - enthalpy, Q - heat added, t - temperature). 
So I have the boundary conditions and no matter what kind of mesh I use (RMS heat transfer residual always lower than 10^(-4) and most often lower than 10^(-5) or reaching 10^(-6); velocity and other residual nearly always reaching 10^(-6) I'm missing something in energy balance.  
I use CFX, SST with incl. viscous heat term, pressure inlet and outlet as boundary conditions, air as ideal gas, outside wall of nozzle is heated - defined by a temperature of wall. No wall thickness - simple model. 
So I start with CFD-post calculator to get massflowAve  enthalpy and velocity for inlet and outlet. Then I check what is the mass flow and by multiplating it with enthalpy values I get the values to the energy balance. Then I calculate kinetic energy (mv^2)/2 and to get the wall heat flux first I calculate it for the wallave and then multiple it with wall area.

And in this way I get every needed values on the left and right side of the equation, but there is always a little bit missing (maybe 1 to 10J heat more is added - in the whole energy balance is nearly nothing). I thought about friction but it should only create heat which is included in energy balance (pressure losses also counted). I also thought about some approximation mistakes but the bigger model is - the bigger are these "losses" so it's not a coinsidence.

If you dont know the answer, could you help me where should I look to get to know where to search to fill my lack of knowledge?

Kinds Regards
Martin

[DrAmine]

Do rely on the solver out file for checking imbalances. 

In Post use the Heat Flux variable in post processing which is available on walls and non wall boundaries.

[MRMR]

Thank you Amine for your answer. 

In CFD-post I checked the areaAve heat flux for inlet, outlet and wall and multiplied them with the area of each surface - the differences in the whole balance are very little so it works, thank you. 
Do you/anyone else have an idea why the values of massflow doesnt work? Approximation mistakes?

Kind Regards 
Martin