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May 3, 2016, 11:40 |
mass in is not equal in transient simulation
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#1 |
Senior Member
yaseen
Join Date: Oct 2015
Location: Hawler
Posts: 174
Rep Power: 10 |
hello
I simulated free surface by transient simulation with 10 sec total time and time step with 0.06 sec. but the result of mass flowrate (kg/s) at outlet does not equal to inlet. is it better to increase total time or reduce time step thanks for your suggestion. |
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May 3, 2016, 21:27 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,706
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We cannot tell with the small amount of information you have posted. This FAQ discusses some general issues: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
Note that in transient simulations the flow in does not have to equal the flow out. In transient simulations you can gain or loose material by having it build up or reduce in the simulation domain. So an imbalance between flow in and out does not necessarily mean you have a problem. I would recommend you look at the final results file in CFD-Post and see what is going on. When you understand what is happening you will know whether your simulation is correctly set up, whether it needs to run longer or whether what you have is correct. |
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May 6, 2016, 11:11 |
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#3 | |
Senior Member
yaseen
Join Date: Oct 2015
Location: Hawler
Posts: 174
Rep Power: 10 |
Quote:
but in modeling spillway, after a certain time the flow must become steady (inflow = outflow) |
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May 6, 2016, 15:20 |
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#4 |
Senior Member
Join Date: Jun 2009
Posts: 1,806
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That is only true when the solution reaches a state where all the transient/temporal derivatives are exactly 0. Otherwise, it is difficult to tell.
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