## Fluids

#### Fluent/ Moving wall with specified shear condition

• Elham91
Subscriber

Hi,

I'm working on analyzing fluid flow around a rotating tool in 2D. First, I considered a constant rotating speed for tool by "no slip"condition and it worked. As my situation involves different shear stress on the wall-tool, I need to compile a UDF for "specified shear" for this wall. Therefore, I have a wall with "moving condition" and "specified shear". but in fluent when I choose moving wall, "specified shear"option will be deactive. I saw some tutorials from old versions of Fluent that didn't have this problem and you could use both conditions for one wall together. Could any one help me please to define my situation? I am using ANSYS 2019 R3.

Elham

• Karthik R

Hello,

Could you please help us understand why you would like to apply a specified shear on your rotating wall boundary? If the fluid is sticking to this moving wall, then you should be using a no-slip condition.

Thank you.

Karthik

• Elham91
Subscriber

Thank you for your answer. I have a rotating tool and a nozzle that a shear thinning metal flows between them. so when it flows between the tool and nozzle, friction causes to heat up until 450 degree Celsius or more. as a thermomechanical process is happenning on high temperature in some parts of wall we have stick condition and in some parts we have slip. for this reason I should write a UDF to consider stick/slip condition at the walls. its ok for wall of the nozzle because it is stationary, but for tool is impossible because it has rotating speed.

thank you

• Karthik R

When you specify shear stress, the Fluent solver uses this value to estimate the value of the velocity at the wall. This is the reason why the moving wall condition does not allow the specification of shear stress. This is the reason why this condition was removed in the newer versions.

I hope this helps.

Thank you!

Karthik.

• Elham91
Subscriber

Dear Karthik,

Thank you, now I understand the reason.

Best regards

• Karthik R

You're very welcome!

• Almuatasim Salameh
Subscriber

Hello,

I am facing a similar problem, I have two concentric cylinders, and one of them rotates, I have a non-newtonian fluid and I expect slip to occur at both walls, the question is: does this mean I have to define the wall rotation speed after subtracting the slip speed, i.e wall speed = actual fluid speed at wall?
if so, how shall I account for shear heating?

-ANSYS 2021 R2-

Thank you