[aja1345]

Hi, I modeled an air turbine and I want to mesh a model of air turbine(Wells turbine). This turbine have 6 blades((360/6)=60 deg=angle between blades). Due to the circumferential symmetry, only one sixth of the annulus has been computed, imposing periodic boundary conditions in the tangential direction. The computational domain has been restricted in the axial direction to six chord lengths upstream and ten chord lengths downstream of the blade.





Also, the effects of separation, boundary layer interaction and vortex on the hub and surfaces of blade and Tip clearance are important in this modeling.





Now, I should obtain optimum first cell height value. The Reynolds number based on the blade chord was approximately equal to 2.4*10^5 that I found this Re number from a paper. I have some equations.
Firstly, I have a question that how to calculate this number for this model? Is this number calculated from relative velocity in this type of turbines? If so, How to calculate relative velocity for this model?
How to mesh on surfaces of blade and hub, casing and Tip clearance of turbine in Gambit? In other word, how do we know our acceptable Y+ value and inflation growth rate?
In fact, I want to obtain optimum first cell height values of hub, Casing and surfaces of blade. But How? I have to find optimum Y+ value, since the cost of a CFD evaluation obviously increases rapidly with the number of grid cells.
What do I the turbulence model use?
Could you please also tell me how to determine the boundary layer thickness on the surfaces of blade and hub and Casing?
I am grateful for guide me. Thanks for your help


Thanks,

Best,

Amir

[-mAx-]

You have to check the theory for your Re
Regarding the y+ you have a online tool, for setting the first cell height:
http://www.cfd-online.com/Tools/yplus.php
In Gambit you also have a tool for meshing the BL. Gambit will create prismatic layers around your body.
Check Tutorial 13 from Gambit:
https://www.sharcnet.ca/Software/Gam...uide/tgtoc.htm

[aja1345]

Hi max,

Thanks.

But this online tool is valid for flat plate. Is this tool also valid for turbo machinary?

[aja1345]

NO one answer my question?

I really dont know that this online tool is valid for the turbo machinery, especially these type of turbines.

I am grateful that some one explain about this online tools. Do use this tool have many errors?

[-mAx-]

This is an estimation.
Once you solution converged, you have to check your y+ to be sure your mesh is ok with your wall function.
If not then you need to adapt your mesh

[aja1345]

Originally Posted by -mAx-

This is an estimation.
Once you solution converged, you have to check your y+ to be sure your mesh is ok with your wall function.
If not then you need to adapt your mesh

Hi Max,

Ok, if I use wall function, I dont know range of Y+. Please guide me about this range.

Also, How to do this check in Fluent?

Thanks,

Best.

Amir

[-mAx-]

please check the theory
http://www.cfd-online.com/Wiki/Intro...urbulent_flows

Then in fluent you have the possibility to display the contour of turbulence (Y+) or something like that.