Notorious Difference in Tdr Residual for two Simulations of the same Model

Lapidus · April 24, 2019, 03:51

Good Day everybody,

As the title states, I have come across a massive difference in the values for Tdr when I run a simulation on a very same model.

Do I run it as it is, the solution converges nicely, but I have reverse flow for 500 faces at the outlet.
Do I happen to extrude the inlet and outlet eight times the inlet/outlet diameter (as suggested by the steve portal), I do not have the reverse flow problem anymore, yet Tdr asymptotically approaches 0.1.

Has the simulation for the extruded model converged even though Tdr is not under 10^-3?
Any suggestions in this reguard would be very welcomed

steve lee · April 24, 2019, 19:52

Hi.
Did you show the residual plot which is normalized?
In STAR-CCM+ default setting of residual is normalized..
You should turn off normalized option and recheck residual.

Because of extruded mesh, the initial normalized value can be changed

Lapidus · April 25, 2019, 03:31

Yes, residuals are normalized in the "Auto" mode with maximum of 5000 plot samples.

In your opinion, I should switch the normalization off and see if the amount by which they vary is sufficiently small?

Thanks

steve lee · April 25, 2019, 04:30

Try it
In CCM+ normalize using first 5 step..(default)

If your residual still have too big gap, you should check BC and IC

Lapidus · April 25, 2019, 10:09

Yes, it worked like a charm! Now all residuals are at 5e-6 with the exception of Tdr that is at 5e-3. Assuming the convergence is a safe bet here. Thanks

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April 24, 2019, 19:52		#2
steve lee Member Steve Join Date: Mar 2018 Location: South Korea Posts: 69 Rep Power: 8	Hi. Did you show the residual plot which is normalized? In STAR-CCM+ default setting of residual is normalized.. You should turn off normalized option and recheck residual. Because of extruded mesh, the initial normalized value can be changed

April 25, 2019, 03:31		#3
Lapidus New Member Rod Lamar Join Date: Apr 2019 Posts: 19 Rep Power: 7	Yes, residuals are normalized in the "Auto" mode with maximum of 5000 plot samples. In your opinion, I should switch the normalization off and see if the amount by which they vary is sufficiently small? Thanks

April 25, 2019, 04:30		#4
steve lee Member Steve Join Date: Mar 2018 Location: South Korea Posts: 69 Rep Power: 8	Try it In CCM+ normalize using first 5 step..(default) If your residual still have too big gap, you should check BC and IC

April 25, 2019, 10:09		#5
Lapidus New Member Rod Lamar Join Date: Apr 2019 Posts: 19 Rep Power: 7	Yes, it worked like a charm! Now all residuals are at 5e-6 with the exception of Tdr that is at 5e-3. Assuming the convergence is a safe bet here. Thanks