Mesh dependence study with wall law

franacosta · June 30, 2017, 07:13

Hi!

I am using a realizable k-epsilon turbulence model with the two-layer all y+ wall treatment in an internal flow geometry that presents sharp angles. I aim for 30< wall y+ <150, but I inevitably get low y+ values in the sharp angles. I am using a polyhedral mesh with 1 layer of prisms, with its thickness fixed at 45% of the base size. I want to conduct a mesh dependence study by changing the base size of the mesh but, if I do so, the wall y+ will change as the prism layer thickness changes. Due to this, a finer mesh might lead to erroneous results if the y+ becomes less adequate for the wall law used. My question is:
Is there a recommended practice for conducting the mesh dependence study varying the base size? Should I keep the prism layer thickness constant in all cases so that the y+ remains constant and the number of calculations points in the core of the volume (and not near the walls) is the only variable that changes as I decrease the base size?

Thanks in advance!

ashokac7 · July 22, 2017, 10:16

It's harder to control mesh size in star-ccm. You can use controls but they are not full proof. Instead star-ccm can import cas file as volume mesh. So if your geometry is simpler then you can mesh it in hypermesh and then import it in star ccm as .cas

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June 30, 2017, 07:13	Mesh dependence study with wall law	#1
franacosta New Member Francisco Join Date: Feb 2017 Posts: 1 Rep Power: 0	Hi! I am using a realizable k-epsilon turbulence model with the two-layer all y+ wall treatment in an internal flow geometry that presents sharp angles. I aim for 30< wall y+ <150, but I inevitably get low y+ values in the sharp angles. I am using a polyhedral mesh with 1 layer of prisms, with its thickness fixed at 45% of the base size. I want to conduct a mesh dependence study by changing the base size of the mesh but, if I do so, the wall y+ will change as the prism layer thickness changes. Due to this, a finer mesh might lead to erroneous results if the y+ becomes less adequate for the wall law used. My question is: Is there a recommended practice for conducting the mesh dependence study varying the base size? Should I keep the prism layer thickness constant in all cases so that the y+ remains constant and the number of calculations points in the core of the volume (and not near the walls) is the only variable that changes as I decrease the base size? Thanks in advance!

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July 22, 2017, 10:16		#2
ashokac7 Senior Member Ashok Chaudhari Join Date: Aug 2016 Location: Pune, India Posts: 260 Rep Power: 11	It's harder to control mesh size in star-ccm. You can use controls but they are not full proof. Instead star-ccm can import cas file as volume mesh. So if your geometry is simpler then you can mesh it in hypermesh and then import it in star ccm as .cas Sent from my Redmi Note 3 using CFD Online Forum mobile app