Flow over a cylinder in STAR-CCM+ and PointWise y+ calculator

Fluidy · May 8, 2020, 23:56

At the moment I am modelling a flow over a cylinder in STAR-CCM+ and therefore I need to calculate the prism layer thickness and the amount of prism layers. However, I have some questions and I would really appreciate it if someone could answer them. Thank you in advance!

Mesh

Surface Remesher
Automatic Surface Repair
Trimmed Cell Mesher
Prism Layer Mesher

Model

All y+ Wall Treatment
Constant Density
Gas(Air)
Gradients
K-Omega Turbulence
Reynolds-Averaged Navier-Stokes
Segregated Flow
Solution Interpolation
SST (Menter) K-Omega
Steady
Three-Dimensional
Turbulent
Wall Distance

Questions

1. The Reynolds number is 1.03E5, this results in laminar flow with turbulent wakes. Does this mean I need to define the model as steady & turbulent or implicit unsteady & laminar?

2. When using the K-Omega SST Turbulence Model is it true that I should aim for a y+ value around 1<4? Or should I use a y+>30 for the overal mesh and only a y+ of 1 for local refinements with volumetric control?

3. When using the y+ calculator (PointWise), is the calculated value of the wall spacing delta_s the distance from the wall to the center of the first boundary mesh cell or the height of the first boundary mesh cell(twice as big)?

4. Am I using the y+ calculator correctly for calculating the number of prism layers and the prism layer thickness?
(see inputs & outputs for details)

Inputs

Base size = 0.05 m (as fine as possible but with an acceptable calculation time)
Prism Layer Stretching ratio R = 1.3 (or perhaps 1.5?)
Desired y+ = 1
Wall Spacing delta_s = 1.947E-5 m (calculated with Pointwise y+ calculator)
Desired Prism Layer Thickness T = 0.1 m (double the base size)

Outputs

Number of Prism Layers n_exact = log(T/delta_s)/log(R) = 32,56
Number of Prism Layers n = 33 (I use this number for my STAR-CCM+ automated mesh default control settings)
Prism Layer Thickness = delta_s * R^n = 0,1121 m (I use this number for my STAR-CCM+ automated mesh default control settings)

Shayor · March 31, 2021, 13:24

Brother did you get your answer or solve your problem?I am kinda new to this field too.Your problem was related to mine.I wanted to know that those equations you used for the number of prism layers where you got those.If you could kindly tell me.Also how did you assume the stretch ratio?
Thanks in advance.Would greatly appreciate it.

May 8, 2020, 23:56	Flow over a cylinder in STAR-CCM+ and PointWise y+ calculator	#1
Fluidy New Member Nederland Join Date: May 2020 Posts: 3 Rep Power: 6	At the moment I am modelling a flow over a cylinder in STAR-CCM+ and therefore I need to calculate the prism layer thickness and the amount of prism layers. However, I have some questions and I would really appreciate it if someone could answer them. Thank you in advance! Mesh Surface Remesher Automatic Surface Repair Trimmed Cell Mesher Prism Layer Mesher Model All y+ Wall Treatment Constant Density Gas(Air) Gradients K-Omega Turbulence Reynolds-Averaged Navier-Stokes Segregated Flow Solution Interpolation SST (Menter) K-Omega Steady Three-Dimensional Turbulent Wall Distance Questions 1. The Reynolds number is 1.03E5, this results in laminar flow with turbulent wakes. Does this mean I need to define the model as steady & turbulent or implicit unsteady & laminar? 2. When using the K-Omega SST Turbulence Model is it true that I should aim for a y+ value around 1<4? Or should I use a y+>30 for the overal mesh and only a y+ of 1 for local refinements with volumetric control? 3. When using the y+ calculator (PointWise), is the calculated value of the wall spacing delta_s the distance from the wall to the center of the first boundary mesh cell or the height of the first boundary mesh cell(twice as big)? 4. Am I using the y+ calculator correctly for calculating the number of prism layers and the prism layer thickness? (see inputs & outputs for details) Inputs Base size = 0.05 m (as fine as possible but with an acceptable calculation time) Prism Layer Stretching ratio R = 1.3 (or perhaps 1.5?) Desired y+ = 1 Wall Spacing delta_s = 1.947E-5 m (calculated with Pointwise y+ calculator) Desired Prism Layer Thickness T = 0.1 m (double the base size) Outputs Number of Prism Layers n_exact = log(T/delta_s)/log(R) = 32,56 Number of Prism Layers n = 33 (I use this number for my STAR-CCM+ automated mesh default control settings) Prism Layer Thickness = delta_s * R^n = 0,1121 m (I use this number for my STAR-CCM+ automated mesh default control settings)

March 31, 2021, 13:24		#2
Shayor New Member Ahmed Abrar Shayor Join Date: Sep 2020 Location: Bangladesh Posts: 22 Rep Power: 6	Brother did you get your answer or solve your problem?I am kinda new to this field too.Your problem was related to mine.I wanted to know that those equations you used for the number of prism layers where you got those.If you could kindly tell me.Also how did you assume the stretch ratio? Thanks in advance.Would greatly appreciate it.