Problem with: WARNING: inflow at outflow boundary

Michal Krasowski

Good morning,

As a new Altair user I am trying to run some first simulations in SimLab- focused on the flow and heat transfer topics. For the purpose of checking the potentials of the software I took some manifold CAD, we use. I managed to run some simple flow simulations, but while running the simulation with heat transfer, there is some error.

 

MODEL DESCRIPTION:
Presented in the attached picture.

Manifold with 2 separate chambers (Cold and hot fluid side- Top and Bottom separately).
One inlet per chamber (2 in total) and 4 outlets per chamber (8 in total)

BOUNDARY CONDITIONS

Material:

Both fluid domains: Water
Solid- aluminium

Inlet_1: 0.22 m/s inflow with 90'C temperature (green in the picture)
Inlet_2: 0.35 m/s inflow with 10'C temperature (green in the picture)

Oulets: Without additional parameters specified (orange in the picture) 

Walls: All the outer walls of the manifold selected and Thermal Convection with Heat Transfer Coefficient of 20 W/m2'C and reference temperature of 20'C (blue in the picture)

SOLUTION TYPE:

 

ERROR:

1. First of all- is there some reason I cannot access Plot Convergence and View Solver Log at all while calculation is running (at any stage of the calculations)? I cannot see the status of computation at all.

2. The error message I get after unsuccessful simulation

After checking the notepad file in the solution folder I can see information

acuSolve:     temperature  sol ratio = 1.291179e-02
acuSolve: *** WARNING: inflow at outflow boundary: Outlet_9 (mass/time: in=-1.991674e-08, out=6.559069e-02)
acuSolve: *** WARNING: inflow at outflow boundary: Outlet_10 (mass/time: in=-1.480227e-05, out=4.121442e-02)

Outlet_9- this are all the outlet surfaces at the top part of manifold
Outlet_10- this are the outlet surfaces at the bottom part of manifold

Could you let me know what is potential reason for that and possible solution? Is it because of some backflow conditions and I should specify them in Outlet Boundary Conditions?

Thank you in advance!

Kind regards,

Michal K.

acupro

You may consider not using . in the problem name - underscore instead.

You likely have vortices forming and passing through the outlets - since they are close to the 'action' in the flow.  Try extending the outlet pipes so the outlets are farther away from the main body.  Also, I always recommend to put topologically separate (disconnected) outlets into their own sets rather than lumping them all into one.

You can activate backflow conditions on the outlets - this enables you to specify conditions (turbulence, temperature) on any flow that enters at the outlets.  I typically use exiting-average or exiting-area-average for both turbulence and temperature backflow.

What have you specified for turbulence at the inlets (from the turbulence drop-down on the inlet BC panel)?

acupro

You may consider not using . in the problem name - underscore instead.

You likely have vortices forming and passing through the outlets - since they are close to the 'action' in the flow.  Try extending the outlet pipes so the outlets are farther away from the main body.  Also, I always recommend to put topologically separate (disconnected) outlets into their own sets rather than lumping them all into one.

You can activate backflow conditions on the outlets - this enables you to specify conditions (turbulence, temperature) on any flow that enters at the outlets.  I typically use exiting-average or exiting-area-average for both turbulence and temperature backflow.

What have you specified for turbulence at the inlets (from the turbulence drop-down on the inlet BC panel)?

Michal Krasowski

acupro_21778 said:

You may consider not using . in the problem name - underscore instead.

You likely have vortices forming and passing through the outlets - since they are close to the 'action' in the flow.  Try extending the outlet pipes so the outlets are farther away from the main body.  Also, I always recommend to put topologically separate (disconnected) outlets into their own sets rather than lumping them all into one.

You can activate backflow conditions on the outlets - this enables you to specify conditions (turbulence, temperature) on any flow that enters at the outlets.  I typically use exiting-average or exiting-area-average for both turbulence and temperature backflow.

What have you specified for turbulence at the inlets (from the turbulence drop-down on the inlet BC panel)?

I though so, so I elongated the channels before simulation- but it turned out not to be enough.

You were right, that elongating it even further solved the issue.