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Lattice Structure Wind Load STAR-CCM+

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Old   May 15, 2020, 22:19
Question Lattice Structure Wind Load STAR-CCM+
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Join Date: May 2020
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For my final year bachelor project, I need to make a CFD-model to calculate the wind load on a lattice structure/crane arm. As comparison material, I have the real wind tunnel measurements with a net force of around 4.05 N. I made the lattice structure in SW, saved it as Parasolid, imported it through 3D-CAD Models, and then made a new geometry part from it. Also, the model is made with part-based meshing. For the calculation of the number of prism layers and the prism layer thickness. The results after 1000 iterations are around 4.14 N which is great, however I am unsure if this is accurate or just pure luck because the mesh does not look great. I currently have a few problems/questions that I would like to have your insights on, thank you in advance!

Parts:
Lattice Structure (only half with a symmetry plane)
Wind tunnel
Volume of Refinement Wind Tunnel
Volume of Refinement Wake
Volume of Refinement Offset of Lattice Structure

Models:
All y+ Wall Treatment
Constant Density
Gas (Air)
Gradients
K-Omega Turbulence (SST)
RANS
Segregated Flow
Solution Interpolation
Steady
Three Dimensional
Turbulent
Wall Distance

Settings:
https://imgur.com/bWuKP2q

Volume Mesh Inside:
https://imgur.com/7M4ug1u

Volume Mesh Outside:
https://imgur.com/2GQomkd


Questions:
1. There are weird lines on the tubes of my mesh because of the prism layers. How can I solve this?
https://imgur.com/Uv5alm0


2. I made an Excel table/calculation for the prism layer thickness and amount of prism layers and it works because if I measure the last prism layer it is exactly 1.3X smaller than the base size of the smallest volume of refinement (Offset). However, there is a smaller transition mesh between the last boundary layer and the volume of refinement mesh, how do I get rid of this?
https://imgur.com/nSO67do


3. After reading online that for a trimmed mesh you need to have custom sizes that are n * 0.5 * base size, I changed the following controls, but it made the boundary layers have a weird cone-like shape. I expected the mesh to improve after this change, so I am wondering what I did do wrong?
Old: https://imgur.com/LroApty
New: https://imgur.com/W524HqY
Base size: 0.1
Minimum Surface Size: 0.0002 -> 0.0001953125
VoR - Offset: 0.001 -> 0.0015625
VoR - Wake: 0.005 -> 0.00625
VoR - Windtunnel: 0.01 -> 0.0125
Number of Prism Layers: 17 -> 19
Prism Layer Total Thickness: 4.41E-3 -> 7.49E-3


4.The y+ calculation is based on a reference length of 4mm, which is the diameter of the diagonal V-tubes on the side of the lattice structure. I used 4 mm because that is the diameter of the diagonal V-tubes in the lattice structure that are the most common and therefore probably the most critical. Is this method acceptable or do I need to calculate the reference length by calculating Total Volume/Effective Area?
https://imgur.com/RockrMO
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Old   May 17, 2020, 14:33
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Quote:
Originally Posted by Fluidy View Post
For my final year bachelor project, I need to make a CFD-model to calculate the wind load on a lattice structure/crane arm. As comparison material, I have the real wind tunnel measurements with a net force of around 4.05 N. I made the lattice structure in SW, saved it as Parasolid, imported it through 3D-CAD Models, and then made a new geometry part from it. Also, the model is made with part-based meshing. For the calculation of the number of prism layers and the prism layer thickness. The results after 1000 iterations are around 4.14 N which is great, however I am unsure if this is accurate or just pure luck because the mesh does not look great. I currently have a few problems/questions that I would like to have your insights on, thank you in advance!

Parts:
Lattice Structure (only half with a symmetry plane)
Wind tunnel
Volume of Refinement Wind Tunnel
Volume of Refinement Wake
Volume of Refinement Offset of Lattice Structure

Models:
All y+ Wall Treatment
Constant Density
Gas (Air)
Gradients
K-Omega Turbulence (SST)
RANS
Segregated Flow
Solution Interpolation
Steady
Three Dimensional
Turbulent
Wall Distance

Settings:
https://imgur.com/bWuKP2q

Volume Mesh Inside:
https://imgur.com/7M4ug1u

Volume Mesh Outside:
https://imgur.com/2GQomkd


Questions:
1. There are weird lines on the tubes of my mesh because of the prism layers. How can I solve this?
https://imgur.com/Uv5alm0


2. I made an Excel table/calculation for the prism layer thickness and amount of prism layers and it works because if I measure the last prism layer it is exactly 1.3X smaller than the base size of the smallest volume of refinement (Offset). However, there is a smaller transition mesh between the last boundary layer and the volume of refinement mesh, how do I get rid of this?
https://imgur.com/nSO67do


3. After reading online that for a trimmed mesh you need to have custom sizes that are n * 0.5 * base size, I changed the following controls, but it made the boundary layers have a weird cone-like shape. I expected the mesh to improve after this change, so I am wondering what I did do wrong?
Old: https://imgur.com/LroApty
New: https://imgur.com/W524HqY
Base size: 0.1
Minimum Surface Size: 0.0002 -> 0.0001953125
VoR - Offset: 0.001 -> 0.0015625
VoR - Wake: 0.005 -> 0.00625
VoR - Windtunnel: 0.01 -> 0.0125
Number of Prism Layers: 17 -> 19
Prism Layer Total Thickness: 4.41E-3 -> 7.49E-3


4.The y+ calculation is based on a reference length of 4mm, which is the diameter of the diagonal V-tubes on the side of the lattice structure. I used 4 mm because that is the diameter of the diagonal V-tubes in the lattice structure that are the most common and therefore probably the most critical. Is this method acceptable or do I need to calculate the reference length by calculating Total Volume/Effective Area?
https://imgur.com/RockrMO

What is the max. skewness angle, face validity and min. face quality for your mesh? Also, have you checked your imported geometry for errors before creating mesh?
mazhar16823 is offline   Reply With Quote

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Tags
boundary layer, mesh, star ccm, trimmer, volumetric control

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