[halowine]

Hello everyone,

I am currently testing some BC's with Fluent 17.
I'm using a simple test case for now (2D).

My current case is a cylinder D=0.1 in 2D with an outflow at U=1 (fluid is water). Here's a picture of it:

https://imgur.com/RoFIcfr

I'm having trouble to find the correct BC to apply for this simple external flow.

At the inlet (left BC), I use Velocity-inlet with ux=1.
At the outlet (right BC), I use pressure-outlet.

My problem is for the top and bottom BC.
I tested 2 method but it doesn't give me the same result.

1. Top and Bottom BC are velocity inlet at ux=1.
2. Top and Bottom BC are slip wall (I use a moving wall at ux=1).

If I look at the velocity field, it seems to be the same. But my pressure field is different:
1.
https://imgur.com/bvr9Rqq
2.
https://imgur.com/B71fqJX

If I look at the drag coefficient
Cd1=47
Cd2=50

Which method is the right one? pressure inlet perhaps?

Thank you

[ICEMgod]

My approach would be a standard "no-slip" Wall BC for top and bottom. Just make sure the boundarys are far enough from your cylinder.

Moving wall (ux=1) should also work and give the same results for your cylinder flow. The BC shouldn't have an influence on the flow around the cylinder.

Velocity-In wouldn't be correct because there is no mass entering the domain here.

How did you specify the drag? Did you plot the variable over iterations?

Correct me if I'm wrong!

Edit: Your drag seems a bit high. Your Re-number should be: 0,1m*1m/s*1000kg/m^3/0,001Pa*s=100000. Drag should be ~1