# How to set the gradient of scalar when using UDS

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 September 2, 2013, 10:39 How to set the gradient of scalar when using UDS #1 New Member   Y Zhao Join Date: Jan 2013 Posts: 2 Rep Power: 0 Hi everyone, I met a problem about adding UDS in Fluent. I would like to see the scalar transportation in a chamber. If I want to set the gradient of scalar at the outlet to be zero which means the scalar there has no change, how can I set it? The inlet and outlet boundary conditions are separately velocity inlet and pressure outlet. Thank you. All the best, Yuchun

 September 5, 2013, 03:02 #2 Senior Member     A-A Azarafza Join Date: Jan 2013 Posts: 226 Rep Power: 11 Hi dude Just go to the interest B.C, then click on UDS tab and finally select flux (gradient) scalar option from the left side and set zero value for the corresponding parameter. It's easy and straightforward. Good luck __________________ Regard yours

September 5, 2013, 04:31
#3
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Y Zhao
Join Date: Jan 2013
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Quote:
 Originally Posted by A CFD free user Hi dude Just go to the interest B.C, then click on UDS tab and finally select flux (gradient) scalar option from the left side and set zero value for the corresponding parameter. It's easy and straightforward. Good luck
Thanks a lot!
I still have a question: in the user's guide, it says "If you select Specified Flux, your input will be the value of the flux at the boundary". Here, is the flux the same as the gradient?

 September 5, 2013, 19:01 #4 Senior Member     A-A Azarafza Join Date: Jan 2013 Posts: 226 Rep Power: 11 Hi Definitely yup. It is actually Neumann boundary condition. __________________ Regard yours

April 26, 2018, 20:25
#5
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Tharanga Jayathungage Don
Join Date: Sep 2014
Location: Auckland
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Quote:
 Originally Posted by A CFD free user Hi Definitely yup. It is actually Neumann boundary condition.
Hi,
I have a question about the zero flux condition. When we consider the equation of UDS flux, diffusive flux should be equal to the advective flux a due to the zero flux condition. UC=Dxgradient(C). You were saying it should be zero gradients. It is confusing to me. Can you explain, please? Thanks