[snappyHexMesh] addlayercontrol

humber11 · September 5, 2021, 17:22

i'm just starting in cfd and i was testing k-epislon and y+ would have to be between 30 and 100, but how do i specify these values in snappyhexmesh?

Another question is why do I have to put more than one layer for the boundary layer?

thanks

AtoHM · September 6, 2021, 03:40

You cannot specify y+ directly in the mesher, as it depends on your Re-Number, which is unknown here. Normally you go and estimate the y+, e.g. with this tool: https://www.cfd-online.com/Tools/yplus.php
Then you have the spacing you need and can pass that to the mesher.

You want multiple layers, cause you want to resolve the transition continuously from the first cell upwards and also your mesh quality would be quite bad, if you had only 1 small layer and then the free stream spacing next to it.

September 5, 2021, 17:22	addlayercontrol	#1
humber11 New Member Humberto Join Date: Mar 2021 Location: Brasil Posts: 23 Rep Power: 5	i'm just starting in cfd and i was testing k-epislon and y+ would have to be between 30 and 100, but how do i specify these values in snappyhexmesh? Another question is why do I have to put more than one layer for the boundary layer? thanks

September 6, 2021, 03:40		#2
AtoHM Senior Member M Join Date: Dec 2017 Posts: 642 Rep Power: 12	You cannot specify y+ directly in the mesher, as it depends on your Re-Number, which is unknown here. Normally you go and estimate the y+, e.g. with this tool: https://www.cfd-online.com/Tools/yplus.php Then you have the spacing you need and can pass that to the mesher. You want multiple layers, cause you want to resolve the transition continuously from the first cell upwards and also your mesh quality would be quite bad, if you had only 1 small layer and then the free stream spacing next to it.