Y plus value

mithinga · October 27, 2016, 02:52

i am using ansys fluent for simulation, my value of y+ is coming about 2.5 its not coming near to 1.my first cell height of the model is 0.0692mm, with growth rate 0.5 and maximum layer of 4 at velocity 0.3 m/s. Can anyone suggest how to modify or reduce my y+ value.

scipy · October 27, 2016, 05:47

If your aimed y+ is 1 and your current y+ is 2.5 then you need to reduce the first cell height by 2.5x times. So, from 0.0692 mm to 0.0277 mm.

What do you mean with growth rate 0.5? Anything lower than 1 would mean the elements are not even growing in the normal to wall direction. Did you mean 50% growth rate (growth factor 1.5?) maybe?

Anyway, growth rate should be around 1.2 (anything up to 1.3 (30%) growth rate is OK for normal to wall direction of growth).

However, if your first layer is that small (wall resolving mesh) and you used only 4 layers in the boundary layer part of the mesh, I'm afraid to even ask what's the aspect ratio of the first element outside the boundary layer.

Maybe post a screenshot of your mesh near the wall area...

Far · October 27, 2016, 11:21

Quote:

If your aimed y+ is 1 and your current y+ is 2.5 then you need to reduce the first cell height by 2.5x times. So, from 0.0692 mm to 0.0277 mm.

Not necessary as it is non linear function. I would recommend to change first cell height by half and see the yplus value.

Shamoon Jamshed · October 28, 2016, 08:42

Sijal, may be you can help. I am comparing heat transfer and friction factor results for a pipe with grooves in it. I am comparing Nusselt and friction factor in the two cases. The results are very surprising. The nusselt is comparable to experiment with k epsilon while friction is good in case of k omega. Could you please tell me the discrepancy? Please help me as I am not getting why two models are behaving differently.

October 27, 2016, 02:52	Y plus value	#1
mithinga New Member mithinga Join Date: Oct 2016 Posts: 1 Rep Power: 0	i am using ansys fluent for simulation, my value of y+ is coming about 2.5 its not coming near to 1.my first cell height of the model is 0.0692mm, with growth rate 0.5 and maximum layer of 4 at velocity 0.3 m/s. Can anyone suggest how to modify or reduce my y+ value.

October 27, 2016, 05:47		#2
scipy Senior Member Alex Pasic Join Date: Aug 2011 Location: Croatia Posts: 199 Rep Power: 15	If your aimed y+ is 1 and your current y+ is 2.5 then you need to reduce the first cell height by 2.5x times. So, from 0.0692 mm to 0.0277 mm. What do you mean with growth rate 0.5? Anything lower than 1 would mean the elements are not even growing in the normal to wall direction. Did you mean 50% growth rate (growth factor 1.5?) maybe? Anyway, growth rate should be around 1.2 (anything up to 1.3 (30%) growth rate is OK for normal to wall direction of growth). However, if your first layer is that small (wall resolving mesh) and you used only 4 layers in the boundary layer part of the mesh, I'm afraid to even ask what's the aspect ratio of the first element outside the boundary layer. Maybe post a screenshot of your mesh near the wall area... __________________ If you're in need of some free quality CFD video tutorials - check out SiriusCFD @ YouTube

October 28, 2016, 08:42		#4
Shamoon Jamshed Senior Member Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 377 Rep Power: 18	Sijal, may be you can help. I am comparing heat transfer and friction factor results for a pipe with grooves in it. I am comparing Nusselt and friction factor in the two cases. The results are very surprising. The nusselt is comparable to experiment with k epsilon while friction is good in case of k omega. Could you please tell me the discrepancy? Please help me as I am not getting why two models are behaving differently.