Input Y+ values into Fluent

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  • Last Post 16 November 2018
melalisa96 posted this 15 November 2018

Hi

I'm not hitting the expected range of y+ values for my simulation. Is there a way in Fluent that will allow me to input my desired y+ values to obtain the first layer cell size?

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rwoolhou posted this 15 November 2018

No, what is happening is the flow (and probably first cell height) is not uniform and so y+ will drift. You could take that result and then try to remesh based on the y+ to find the cell height at each location: that's not a good idea.   I'd look at using adaption to refine the mesh where it's needed. 

melalisa96 posted this 15 November 2018

Hi rwoolhou

How do I go about using adaption to refine the mesh where it's required?

kkanade posted this 15 November 2018

Can you please insert images of your mesh? Also let us know the boundary conditions and models you are using.

What y+ value you are targeting? Are you using and prism layer? 

 

melalisa96 posted this 15 November 2018

Hi Kkanade

I am simulating a rotating propeller and am using K-epsilon standard wall function. The range of y+ values which I'm targeting are between 30 to 300. 

kkanade posted this 15 November 2018

Mesh looks ok to me. What y+ values you are getting after solving?

Can you please give more details about your set up?

melalisa96 posted this 16 November 2018

Hi Kkanade

My y+ values are 8-175 for the default adaptive meshing. I tried to refine the mesh by diving the size of each mesh by 2 and got between 10-212. However, in doing so, my values drifted further from the wind tunnel experiment result which I found online as a means to validate my methodology. The link can be found here: https://m-selig.ae.illinois.edu/props/volume-1/propDB-volume-1.html 

Basically, I am simulating an apc 8x3.8 slow flyer propeller. As you can see from the images above, I have enclosed the propeller in a rotating region followed by the body of influence and them the control volume domain. I am using k-epsilon standard wall function which requires me to target a range of 30-300 for the y+ values. It appears I'm not reliably catching the flow and I'm guessing it's due to the mesh. How do I go about implementing the inflation layers using the adaptive meshing approach?

kkanade posted this 16 November 2018

When you use k-e with standard wall function, you will need y+ 30 to 300. 

Please check contours - turbulence - y+. Please identify the regions where y+ is less than 30 and then coarsen the mesh. 

If you use adaptive meshing to refine, it will further refine mesh and will further reduce y+

 

 

 

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