## Fluids

#### Eulerian-Eulerian Model: Unreasonable Prediction of Temperature Field for Secondary Phase

• 5435426346dsfa
Subscriber

Greetings,

I'm currently doing a simple test using the Eulerian-Eulerian model to simulate the jet injected into a box.

My primary phase is air with another gas as the secondary phase. At domain inlet, the BCs for the primary phase are: velocity 5 m/s, temperature 2000 K, volume fraction 1, and BCs for the secondary phase are velocity 0 m/s, temperature 300 K, volume fraction 0. The simulation domain is initially full of air (primary phase) at room temperature (300 K).

I noticed that I got an unreasonable prediction of the temperature field for the secondary phase:

• I didn't inject any secondary phase through the inlet, however, the secondary phase can still be heated up even without the consideration of the heat transfer between two phases.

• There is no secondary phase inside the simulation domain (volume fraction of the secondary phase is 0 everywhere). According to the energy equation mentioned in the theory manual, the secondary phase shouldn't be heated up in the region whose volume fraction is 0.

• The temperature profiles for the primary and secondary phases are similar to each other.

I made many of my classmates to simulate the same case, and it seems like they all have the same issue. Can anybody help me out?

• DrAmine
Ansys Employee
Why multiphase model if you have two gases? Wrong model.
• 5435426346dsfa
Subscriber

Hi Amine,

Thank you so much for your reply. In order to answer your question, I ran one more case to achieve the multiphase scenario. The attached figure is the problem I'm going to simulate: using the air jet injected through the pipe to stir the water in the vessel.

Noticed that only air is injected through the pipe. The vessel is initially filled with water at the bottom, and the rest part is air. My primary phase is water with the air as the secondary phase. At domain inlet, the BCs for the water phase are: velocity 0 m/s, temperature 300 K, volume fraction 0, and BCs for the air phase are velocity 0.1 m/s, temperature 2000 K, volume fraction 1.

Again, the same results can be detected for my water phase: I didn't inject the water through the inlet, and only air is injected (as you can tell from my BCs and velocity/VOF contours). However, there is a high-temperature "jet" of water phase near the inlet. But when I check the VOF contour and the velocity contour for my water phase, there is nothing near the inlet. It is no reason for the region without the water phase to have such a high-temperature jet.

Not sure is it one of the bugs of the model or is there some wrong with my model setup? Could you please help me out?

Air Phase - Contours

Water Phase - Contours

• DrAmine
Ansys Employee
No the results are okay. You might scale with water volume fraction to understand the principle of interpenetrating continua. There is no water at the nozzle.
• 5435426346dsfa
Subscriber

Dear Amine,

Thanks for your reply. A UDF was developed to mark out the cells whose water phase volume fraction is strictly equal to 0. The red cell represents the cell that is full of air, which means there has no reason to have the water phase temperature since there has no water phase in that cell! Could you please tell me why I would have these results?

• DrAmine
Ansys Employee
There is no water so why creating a problem from it. Are you using an actual version?
• H2015
Subscriber

What do you mean by "scale with water volume fraction" ?

Best regards

• DrAmine
Ansys Employee

multiply with water volume fraction.

• H2015
Subscriber

I got it, thanks

This is because Eulerian model is considered as an NON HOMOGENEOUS model, right ? so, it solve energy (Temperature) and momentum (velocity) equation for BOTH phases.

Best regards