[Araash]

hello everyone,
i have a simple 2D problem (i attach a picture of the problem).
left side is velocity-inlet and the right side is pressure-outlet. circle has a constant temperature and the fluid is only water. i want to add hydrophobic boundary condition to the wall(circle) then compare the shear stress on it with the hydrophilic one.
how can i add this boundary condition in fluent?? pls help.

[force_95]

Originally Posted by Araash

hello everyone,
i have a simple 2D problem (i attach a picture of the problem).
left side is velocity-inlet and the right side is pressure-outlet. circle has a constant temperature and the fluid is only water. i want to add hydrophobic boundary condition to the wall(circle) then compare the shear stress on it with the hydrophilic one.
how can i add this boundary condition in fluent?? pls help.

I guess you have to solve this problem with the help of a User defunded function (UDF)

[LuckyTran]

You need to translate "hydrophobic" into a physical parameter that can be modeled.

Usually this means setting the wettability using the contact angle from a multiphase model.

[Araash]

thank you @LuckyTran for your reply.
yes I need to change the contact angle between water and wall.
in the multiphase model we have 2 phases: primary phase and secondary phase and that means we should have 2 fluids.
but in my problem, I only have one fluid and that is water.
is there a way that I can change the contact angle between water and wall?
I really need help...

[Araash]

Originally Posted by LuckyTran

You need to translate "hydrophobic" into a physical parameter that can be modeled.

Usually this means setting the wettability using the contact angle from a multiphase model.

thank you @LuckyTran for your reply.
yes I need to change the contact angle between water and wall.
in the multiphase model we have 2 phases: primary phase and secondary phase and that means we should have 2 fluids.
but in my problem, I only have one fluid and that is water.
is there a way that I can change the contact angle between water and wall?
I really need help...

[LuckyTran]

A hydrophobic phase exists only when there is also an immiscible hydrophilic phase. There is no "contact angle" when you only have water.

[Araash]

Originally Posted by LuckyTran

A hydrophobic phase exists only when there is also an immiscible hydrophilic phase. There is no "contact angle" when you only have water.

thank you for your answer,
if I put air and water in this problem...what should be the volume fractions?? for example if I give 0.7 for water would it be ok??
I have another question and i really appreciate it if you answer...
can I put this hydrophobic boundary condition with slip boundary condition on the wall?