[Musaab Kadem]

Hello everyone,

I'm trying to study the velocity distribution of diesel fuel in a rotating disk apparatus using CFX. The cylindrical fluid container of this apparatus is filled by diesel and the disk is rotated by 2000 rpm. I used one fluid domain for diesel and subtract the solid disk from the fluid. Then I defined the solid walls as rotating wall. I got the velocity distribution results but I think is not correct. Because the velocity of the fluid around the disk is zero and that is not accurate.
The attached file involves photo the velocity distribution using contour on yz plane.
I would like to know what the correct method of setting the boundary condition to obtain the correct velocity distribution for the whole apparatus.

Any help will be much appreciated.

[ghorrocks]

But there is a velocity around what appears to be the disc. If I have misunderstood your question then please post some images of what you are modelling with labels and your output file.

[Musaab Kadem]

Dear Sir,
Thank you for your reply. I'm talking about the fluid under the disk (blue coulor), which means the velocity approximatly zero as shown in Picture 1.
While when I used immersed solid domain without subtract the solid disk the velocity distriution is different as shown in picture 2 and I think is more accuarate. But the main issue with the immersed solid domain was when I used vectors in CFX post to visualize the eddy motion above the disk, these vectors seems to pass throuh the solid disk as shown in picture 3.

[ghorrocks]

Do not use immersed solids for a simulation like this. If the rotor is axisymmetric then use a tangential wall velocity, or if not axisymmetric then used rotating frames of reference.

Once you have fixed that we can look at the velocities you talk about.

[Musaab Kadem]

Dear Sir,
The rotor in my work is axisymmetric. But please dear do you mean I used the tangential wall velocity in CFX setup (CFX pre) or in the results (CFX post). Because I tried to find the tangential wall velocity in CFX set up but i can't find it.
Thank you for your time

[ghorrocks]

Tangential wall velocities can be set in the boundary condition tab, in the mass and momentum settings.

[Musaab Kadem]

Dear Sir,
I only find three options in mass and momentuem when I activated the wall velocity, which are: cartesian components, cylindrical components and rotating wall. In my case I used rotating wall and set the angular velocity value. Is it mean the tanential velocity??

[ghorrocks]

You have to make sure the velocity you define is a tangential velocity. I cannot access CFX at the moment and check the option but you will need to define a rotation axis somewhere as well.