How to set up transient simulation for rotating parts

rusham · July 27, 2017, 16:31

Hi,

I am new in FLUENT. Can anybody help how to correctly set up transient simulation on a wind turbine? As it is shown in the figure below, the geometry consists of two parts: enclosure, which is fixed and rotating frame( inside of which geometry of the wind turbine subtracted). Inlet wind velocity is 12 m/s and angular rotation of the rotating frame is 72 rpm. I will be very glad if somebody can answer for following questions:
1. Which solver to use: pressure based or density based?
2. How can I monitor the Courant number at cell during transient simulation (it should be less 1)?
3. Which method to use: sliding mesh, dynamic mesh or moving frame of reference?
4. How can I obtain animation of the flow?

many thanks

zobekenobe · July 27, 2017, 19:12

Hey I hope this helps, I've done this with a stirred tank.

Terminology:
Rotating Zone: Inner Zone
Outer Domain: Outer Zone

Geometry and Meshing
Firstly, you should have subtracted the inner zone from the outer zone and there would be two faces at the same location. Normally ANSYS would consider them as contacting faces and continue but you would have to define an interface over there.

Select the face from the inner zone Name it Interface-inner-zone
Select the face from the outer zone Name it Interface-outer-zone.

Setup

In fluent, go to mesh interfaces and define an interface using these two faces.

In the cell zone conditions, select the Frame motion for the inner zone. There would be a drop down below where you can select the outer zone (relative to which the inner zone moves). Define the axis of rotation and the speed of rotation.

All other parameters are pretty much the same.

This is the moving frame of reference (MRF).

Sliding mesh is usually more computationally intensive.

zobekenobe · July 28, 2017, 06:58

Why do you have so subtract the inner zone from the outer zone?

Here is a visualization, imagine a glass of water filled to its brim and in that glass you place your inner volume. (there would be an overflow) and the level is back at its brim.

Now freeze these two till the water is solid ice. Now if you had to remove the inner volume you would find there is a gap in the volume of the water.

This is how it is.

Inner volume domain + outer volume domain should equal to the total domain.
If you don't subtract it would imply the water did not overflow or in other words there would be an overlap of the domains.

(hope this explains a bit)

As to find the all the intermediate time-steps. If you post process in CFX post, in the animate option you can have all the time steps (I guess).

But in order to get all the result files at every time step in the autosave option you could set to save every 1 time-step and do not over write the files.
After you initialize your case in the Calculation Activities menu -> Automatic Export you can select all the entities you want saved and the format you want it saved in.

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July 27, 2017, 19:12		#2
zobekenobe Member zobekenobe Join Date: Mar 2009 Location: Dublin, Ireland Posts: 72 Rep Power: 17	Hey I hope this helps, I've done this with a stirred tank. Terminology: Rotating Zone: Inner Zone Outer Domain: Outer Zone Geometry and Meshing Firstly, you should have subtracted the inner zone from the outer zone and there would be two faces at the same location. Normally ANSYS would consider them as contacting faces and continue but you would have to define an interface over there. Select the face from the inner zone Name it Interface-inner-zone Select the face from the outer zone Name it Interface-outer-zone. Setup In fluent, go to mesh interfaces and define an interface using these two faces. In the cell zone conditions, select the Frame motion for the inner zone. There would be a drop down below where you can select the outer zone (relative to which the inner zone moves). Define the axis of rotation and the speed of rotation. All other parameters are pretty much the same. This is the moving frame of reference (MRF). Sliding mesh is usually more computationally intensive.

July 28, 2017, 06:58		#3
zobekenobe Member zobekenobe Join Date: Mar 2009 Location: Dublin, Ireland Posts: 72 Rep Power: 17	Why do you have so subtract the inner zone from the outer zone? Here is a visualization, imagine a glass of water filled to its brim and in that glass you place your inner volume. (there would be an overflow) and the level is back at its brim. Now freeze these two till the water is solid ice. Now if you had to remove the inner volume you would find there is a gap in the volume of the water. This is how it is. Inner volume domain + outer volume domain should equal to the total domain. If you don't subtract it would imply the water did not overflow or in other words there would be an overlap of the domains. (hope this explains a bit) As to find the all the intermediate time-steps. If you post process in CFX post, in the animate option you can have all the time steps (I guess). But in order to get all the result files at every time step in the autosave option you could set to save every 1 time-step and do not over write the files. After you initialize your case in the Calculation Activities menu -> Automatic Export you can select all the entities you want saved and the format you want it saved in.