Dear Experts
I am analyzing the flow around circular cylinder(dia=0.1m, Vel=0.5275m/s, dyn visc=1.6e-5kg/m/s, density=1.185kg/m^3)
I calculated first cell height for y+ value of 1 which is 0.3mm.
Now in order to ensure the 15nodes with in BL or in order to ensure 20 layers to cover BL..what setting should i do in INFLATION option of meshing??
In inflation option, should I use first layer thickness option and input the first cell height value at "First layer hight value??
2nd point is about the "TOTAL THICKNESS option in inflation...how to use that to validate the above conditions....
Thanks in advance
hi Niaz,
You can use total thickness option, where you can specific the total thickness and no: of layer required (20). It will generate 20 layers in boundary layer.
Hope this helps you.
Thanks and regards,
Rajesh.
Thanks Rajesh
What will be value of total thickness in this case?... I have to ensure 2 conditions... 1st is to have 20layers in Boundary layer and 2nd is to ensure y+ value equal to 1..
If you are using ICEM CFD, it is better to generate one prism layer of the total thickness of the boundary layer. You can use Edit Mesh > Split Mesh >Split Prisms to divide this layer into 20 layers. To ensure the first layer is 0.3mm (y+ = 1) use Fixed initial height option.
Thank you Yasser Ahmed
I am using ANSYS Workbench (fluent)...
In FLUENT TOTAL thickness option...we have to define 3 parameters
1. number of layer (which will be 20 in my case)
2. Growth rate (1.2)
3. Maximum thickness (which will be boundary layer)
There is no option of (FIXED INITIAL HEIGHT)...
so I am unable to define first layer height....when I vary GROWTH RATE, it automatically vary first layer thickness value so that it can accomodate 20layers in BL... But I have no control to put first layer on desired location.
I will try to find a solution for this problem in Ansys meshing. However, my advice is to use ICEM CFD for the grid generation which give you good control for the computational grid.
Regards,
Dr. Yasser M. Ahmed
Thank you Sir,
I never used ICEM CFD, but now thinking to shift to ICEM CFD,,, Thanks for the guidance.
ICEM CFD is a powerful grid generator especially (in my point of view) for unstructured mesh.
Hello,
Indeed, if you use "Inflation Option: First Layer Thickness", the parameter "First Layer Height" gives you a fixed height of an initial meshing layer.
So you set Maximum Layers = 20, Growth Rate = 1.2 and adjust the First Layer Height value to meet your requirements.
You are right N.V Koziov..
By following your suggestion, we can ensure the first node position as per y+1 condition but how we can ensure that all the 20 layers will be with-in boundary layer... -since the growth rate is 1.2... so the the first node will be at 0.3, then 0.3*1.2,then 0.3*1.2*1.2 then 0.3*1.2*1.2*1.2 and so on,,,
So in this case we will not be sure that the all the 20layers will come inside the Boundary layer.. One possible option is to vary the growth rate...
I also have one more query,,is then any formula to get the Boundary layer thickness in case of flow around cylinder??
In literature we have alot of formulas for plate...but I couldn't find formula for cylinder...
Niaz,
If 20 layers is obligatory, you will have to adjust either the "Growth Rate" or the "First Layer Height".
Usually, the thickness of a boundary layer is defined in a manner it is valid for different geometries, it may be flat or cylindrical surface. Probably, this is your case, too.
There is a formula in the attached file (first two pages) from Schlichting book ((Boundary layer theory)/ flow around cylinder, it might be useful.
- Badges
- Science topic