[esha]

Originally Posted by msaeedsadeghi

I have already written it. Email me please.

hi, can you please email me udf for this? I will highly appreciate for you help. tayyabakauser@yahoo.com

[pakk]

Don't use a UDF, just use the built-in slip!

[esha]

Originally Posted by pakk

Don't use a UDF, just use the built-in slip!

Actaully, I am simulating viscoelastic fluid over a circular cylinder and using udf to calculate polymers drag. but when I tried to give slip condition it diverges. So, I wanna test it. or could you please let me know what should I do? Thank u!

[Sadra.Forouzi]

Originally Posted by flotus1

Apply some under-relaxation.

Additionally, I can only emphasize once more that fluent comes with a BC of the type us=B*(du/dy).
It is called "Slip Boundary Formulation for Low-Pressure Gas System" and even includes the term for thermal creep.

Hi thank you for sharing this information how thermal creep term can be activated in the Fluent?

[FORGODSAKE]

Can you share UDF for slip in microchannels with me

[gluzdov]

Originally Posted by pakk

Don't use a UDF, just use the built-in slip!

could you please describe how to use the built-in slip?

Do you mean: for Density-Based solver type, under wall boundary condition -> shear condition: Partial Slip for Rarefied Gases? So, our "slip" is Momentum Accomodation Coefficient? In Theory Guide -> Slip Boundary Formulation for Low-Pressure Gas Systems. There is the formula:

Uw-Ug=(2-MAC)/MAC*Lambda*(Ug-Uc)/delta

If I want to implement this boundary condition to my solid wall, how should I choose MAC coefficient? For Betta=0 the equivalent would be MAC=2. For Betta->Infinity (Absolute Slip) MAC=0.Yes? But how to express Betta from MAC coefficient when I want to know slip length in mkm? There is Lambda coefficient, how to calculate it?

And I don't understand what is Uw-Ug, why we don't use just Uw here? like this:

Uw=(2-MAC)/MAC*Lambda*(Uw-Uc)/delta