K-Epsilon troublesome
 

I am simulating a fully turbulent flow inside a bifurcated pipe with the K_Epsilon model and Near wall equilibrium Function.

But I have noticed after doing the balance of Mass and Total Energy that the total energy is not conserved. Moreover there is a great amount of total energy created inside my domain.

What is happening? Why?

Thanks in advance.

Re: K-Epsilon troublesome
 

Are you sure about the way you looked at the energy conservation? Have you counted everything? Borrowing the analogy of sugar cubes I read about in a thermodynamics book, have you counted the sugar cubes that your child ate and ones he threw out of the window? More possibly, by any chance, is your conclusion based on the observation that the total energy (or total pressure) locally (at some cells) exceeds the averaged inlet total energy (or rpessure)? If you are, you're not correctly understanding what the energy conservation is about.

Re: K-Epsilon troublesome
 

I have checked it with Fluent. It gives you the surface integral along inlet/outlet sections:

Mass Flow Rate (kg/s) -------------------------------- --------------------

inlet 17.340075

outlet_primary -17.250082

Net 0.08999189

Mass-Weighted Average

Total Energy (j/kg) -------------------------------- --------------------

inlet 180861.2

outlet_primary 182157.09

Net 181507.45

That's what I obtained.

Re: K-Epsilon troublesome
 

You haven't counted the sugar cubes your children ate.

Re: K-Epsilon troublesome
 

Maybe I haven't count how stupid you are.

Re: K-Epsilon troublesome
 

This is a little too harsh for someone trying to help you ;) My apology if I annoyed you. Maybe I should've been more direct.

What I was trying to say was that you did not count the work done by the fluid against wall-shear and volumetric dissipation of energy, which drains the energy from the flow. You counted the energy-in and energy-out only. Checking conservation of "conserved" variables is a good idea. However, please keep in mind that the velocity field obtained by solving the momentum equations does not necessarily conserve energy unless you solve the equation for total energy.

Re: K-Epsilon troublesome
 

Thanks, I like that very much. Sorry for my last reply.