[amey169]

Hello,


I am simulating a flow through a cooling jacket of motor. The fluid path is spiral along the circumference of the motor with inlet and outlets.


I am using the Segregated Flow and Energy model, BC's are mass flow inlet with a Total temperature of 303 K and at outlet - Pressure outlet with a Static temperature of 340 K. The inner wall of jacket has a heat source and it is a Conjugate Heat transfer simulation which I am running with solid region as transient state and fluid region as steady state.


The energy residuals of fluid region has converged and are in the range of 10^-6 and I am also monitoring the pressure drop which is also kind of constant, and hence can be said converged.


But the aforementioned error still exists after a long time even though energy residuals are low.



Error message : Static temperature did not converge 588 times on model-part "Outlet"
Static temperature did not converge 4094795 times on model-part "Fluid Region"


Why is this happening and what does this error exactly mean?


Thank you.

[fluid23]

Basically, the solver doesn't like your choice of boundary conditions. It doesn't play well with the outflow you have described. When you see something like this its a good bet that your boundary conditions are at fault.

You might try changing the pressure outlet option to 'radial equilibrium'. This is better suited for rotational (or spiral) outflow as you have described.

I also tend to stay away from the segregated solver for thermal problems. Try switching to the coupled solver and see if that doesn't also help.

Good luck. These sorts of errors can be tough to chase down sometimes.

[amey169]

Hi, Thank you for replying.

But I don't think that the radial equilibrium BC is available in Star-CCM, but can I add a target mass flow at the pressure outlet boundary? Will that in any way affect the stability?

One more question I have is, should I trust this solution as the energy residuals are down to the magnitude of -6?

Also, one thing I observed is - When I run just the solid region with the specified heat source on the inner wall, the temperature of that wall at a steady state is near about 2000 K, which I cross-checked with manual calculations.

But while running CHT, the temperature at the inner wall does not go that high, it is highest at the start - value being the static temperature at which it is initialized (800 K), and then decreases there onwards.

[amey169]

Originally Posted by fluid23

Basically, the solver doesn't like your choice of boundary conditions. It doesn't play well with the outflow you have described. When you see something like this its a good bet that your boundary conditions are at fault.

You might try changing the pressure outlet option to 'radial equilibrium'. This is better suited for rotational (or spiral) outflow as you have described.

I also tend to stay away from the segregated solver for thermal problems. Try switching to the coupled solver and see if that doesn't also help.

Good luck. These sorts of errors can be tough to chase down sometimes.

I tried by switching to a coupled solver, but the error still persists. Also, I checked the energy balance in both the cases, it was correct in case of segregated solver, i.e whatever was coming in was going out. But it was not so in case of coupled solver.