Y+ value

totocros · July 22, 2015, 05:14

Hello everyone,
I am doing aeroacoustic simulation on a axial fan. In a first time I need to perform steady simulation to get the steady aerodynamic parameters.
To simulate the turbulence, I used "all y+ wall treatment" "K-omega turbulence" "sst (menter) k-omega" physics model on STAR CCM+.
I don't which time I am supposed to input a y+ value and how can I chose it. I need this value for the first cell size of my BL meshing.

Thanks a lot for your help by advance.
Thomas

fluid23 · July 22, 2015, 08:52

you don't input a y+ value. you have to size the prism cells at your wall boundaries such that your y+ is within an acceptable range. essentially, this ensures that you are modeling the boundary layer properly. for your selections you will want to keep y+ between 1 and 5 or 30 and 60. you can also have values that are between 5 and 30, but they will yield less accurate results as you are interpreting between a near wall and far wall treatments (hence the name all wall y+). avoid anything larger than 60 unless you can justify not caring about your boundary layer.

to see what your y+ is, create a scalar scene that has only wall type boundaries and assign wall y+ as the field function.

there is a tool on this site that will help you estimate the first cell height for a given y+ value, but its just a rough estimate. you will probably have to solve your model, adjust your mesh and continue solving until your residuals, figures of merit (i.e. things you are interested in getting out of the model) and y+ all reach acceptable levels of convergence.

totocros · July 23, 2015, 15:38

Thanks a lot for this complete answer, it helps me a lot.

Cheers

July 22, 2015, 05:14	Y+ value	#1
totocros New Member thomas Join Date: Jul 2015 Posts: 8 Rep Power: 10	Hello everyone, I am doing aeroacoustic simulation on a axial fan. In a first time I need to perform steady simulation to get the steady aerodynamic parameters. To simulate the turbulence, I used "all y+ wall treatment" "K-omega turbulence" "sst (menter) k-omega" physics model on STAR CCM+. I don't which time I am supposed to input a y+ value and how can I chose it. I need this value for the first cell size of my BL meshing. Thanks a lot for your help by advance. Thomas

July 22, 2015, 08:52		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	you don't input a y+ value. you have to size the prism cells at your wall boundaries such that your y+ is within an acceptable range. essentially, this ensures that you are modeling the boundary layer properly. for your selections you will want to keep y+ between 1 and 5 or 30 and 60. you can also have values that are between 5 and 30, but they will yield less accurate results as you are interpreting between a near wall and far wall treatments (hence the name all wall y+). avoid anything larger than 60 unless you can justify not caring about your boundary layer. to see what your y+ is, create a scalar scene that has only wall type boundaries and assign wall y+ as the field function. there is a tool on this site that will help you estimate the first cell height for a given y+ value, but its just a rough estimate. you will probably have to solve your model, adjust your mesh and continue solving until your residuals, figures of merit (i.e. things you are interested in getting out of the model) and y+ all reach acceptable levels of convergence.

July 23, 2015, 15:38		#3
totocros New Member thomas Join Date: Jul 2015 Posts: 8 Rep Power: 10	Thanks a lot for this complete answer, it helps me a lot. Cheers