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Mesh independence study for transient simulation

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Old   September 21, 2015, 10:06
Default Mesh independence study for transient simulation
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Tom
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Hello,
I want to set up a simulation in transient mode and to get good results I want to do a mesh independence study.

Do I have to do the mesh study in transient mode or can I select a value and do the study in steady mode?

Thank you!
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Old   September 21, 2015, 17:32
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You have to have a flow with the same characteristics as your intended flow. If you can do this with steady state then do so because it is much quicker.
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Old   September 22, 2015, 02:21
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Quote:
Originally Posted by ghorrocks View Post
You have to have a flow with the same characteristics as your intended flow. If you can do this with steady state then do so because it is much quicker.
sorry dear, I didnt get the answer,,,
You mean that mesh independence study for transient study can be validated on Steady state problem... As steady state problem is quicker..
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Old   September 22, 2015, 03:11
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Yes, that is correct.

If the transient flow is a boundary layer flow with a BL thickness of Xmm then over a bluff body, and if your steady state flow is also a BL with thickness about Xmm then over a bluff body - then a mesh sensitivity study on the steady state flow should be valid for the transient flow.

But if your flow is inherently transient (eg some shock waves, free surface waves, natural convection) then you cannot use the steady state flow.
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Old   September 22, 2015, 04:19
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Quote:
Originally Posted by ghorrocks View Post
Yes, that is correct.

If the transient flow is a boundary layer flow with a BL thickness of Xmm then over a bluff body, and if your steady state flow is also a BL with thickness about Xmm then over a bluff body - then a mesh sensitivity study on the steady state flow should be valid for the transient flow.

But if your flow is inherently transient (eg some shock waves, free surface waves, natural convection) then you cannot use the steady state flow.
Thanks for your quick help..
Sir , I am a bit new here and also have a lot of searching and browsing..but still confuse in few areas...
How we can find BL thickness?
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Old   September 22, 2015, 06:20
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https://en.wikipedia.org/wiki/Boundary_layer_thickness
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Old   September 22, 2015, 08:06
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First of all: thank you for the information guys.

My setup is actually the air flow through a diffuser with some impacts on velocity and pressure that can only be seen in a transient simulation. So I guess I have to do the mesh study in transient mode.
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Old   November 17, 2022, 01:04
Default steady mesh study instead of transient for fsi case
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HI guys
im doing a fsi modelling which i should first do the mesh study and then continue
ive been told i can do it in reynolds max condition,i dont know how?
from which type of solution should i get max Reynolds? at first?
and what does max Reynolds condition mean overally? just to enter max velocity and run the solution? how does it make difference?
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Old   November 17, 2022, 01:09
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I do not understand your question.

Are you asking whether you should check the mesh sensitivity at the maximum Reynolds Number you are interested in? If so the answer is yes, you should check that condition if other Reynolds numbers goes into other regimes (eg transitional turbulence) then you should check them as well. But often just checking the highest Reynolds Number is OK, as that is likely to require the finest mesh.
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Old   November 17, 2022, 01:12
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thanks for your quick reply.
sorry i will ask it on fluent forum i made a mistake again.
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