Introduction to CFD Chapter 8: Advanced meshing and automation
This chapter consolidates advanced meshing and automation concepts that elevate CFD from a tool-based activity to an engineering workflow. It introduces structured and unstructured advanced meshing strategies, highlights when expert meshing tools become necessary, and frames scripting as a productivity and robustness mechanism rather than a programming exercise.
Why This Chapter Exists
Up to this point, CFD workflows rely on:
Clean geometry
Robust default meshing tools
Standard solver practices
Real industrial problems often violate these assumptions:
Geometry is incomplete, dirty, or overly complex
Mesh quality requirements exceed automatic capabilities
Parametric studies and repeated analyses dominate project time
This chapter addresses how experienced CFD engineers handle these realities.
Advanced Meshing as an Engineering Skill
Meshing is not a preparatory step; it is a numerical modeling decision.
Advanced meshing becomes relevant when:
Flow accuracy depends strongly on near-wall resolution
Complex topology limits automatic mesh generation
Mesh quality controls convergence robustness
Large cell counts are required efficiently
Different tools exist because no single meshing strategy fits all problems.
Advanced Unstructured Meshing: Fluent Meshing
Conceptual Role
Fluent Meshing focuses on maximum flexibility with faceted geometry.
It is designed to work even when CAD quality is poor or geometry connectivity is unreliable.
This makes it especially useful for:
Large assemblies
STL or scanned geometries
Multi-region industrial systems
Late-stage geometry changes
Faceted Geometry Philosophy
Geometry is treated as a surface approximation rather than a perfect CAD entity.
This allows:
Repair and connection at the mesh level
Wrapping-based fluid extraction
Decoupling mesh quality from CAD quality
Physically, this shifts effort from geometry perfection to numerical suitability.
Volume Meshing Strategies
Fluent Meshing supports multiple volume mesh types, often combined:
Tetrahedral cores for geometric flexibility
Prism layers for boundary layer resolution
Hexcore or CutCell approaches for efficiency in large domains
Hybrid meshes balance accuracy, robustness, and computational cost.
When Fluent Meshing Makes Sense
Fluent Meshing is typically chosen when:
CAD cleanup is too costly
Connectivity issues break traditional meshing
Large industrial assemblies are involved
Manual local mesh control is required
It rewards experience and offers transparency rather than automation.
Structured Hexahedral Meshing: ICEM CFD Hexa
Why Structured Hexa Still Matters
Hexahedral meshes provide:
Superior numerical accuracy per cell
Lower numerical diffusion
Better convergence behavior
Predictable near-wall resolution
These benefits become critical in:
Turbomachinery
Internal flows
Boundary-layer-dominated problems
Blocking as a Modeling Process
Hex meshing relies on blocking, which is a topological abstraction of the flow domain.
Blocking:
Defines flow-aligned mesh structure
Encodes expected flow paths
Forces the engineer to reason about geometry simplification
This makes hex meshing a modeling exercise, not just meshing.
Engineering Trade-Off
Structured hex meshing:
Requires more upfront effort
Demands deeper understanding of geometry and flow
Delivers superior solution quality when done correctly
As complexity increases, automation decreases and expertise matters more.
Automation and Scripting in CFD Workflows
Why Automation Matters
Scripting is not about replacing engineers — it supports:
Repeatability
Parametric studies
Design space exploration
Reduction of manual errors
In CFD, time is often lost before solving starts.
Scripting as Workflow Control
Scripting enables:
Geometry generation driven by parameters
Consistent boundary condition assignment
Reproducible meshing strategies
Robust regeneration after geometry changes
Physically, this maintains model intent across iterations.
Recorded vs Engineered Scripts
Recording-based scripting lowers the entry barrier:
User actions are translated into commands
Scripts can later be cleaned and generalized
Advanced users refine scripts to:
Remove hard-coded geometry dependencies
Introduce parameters
Create reusable templates
Named Selections and Robustness
A key scripting principle is decoupling physics from geometry identity.
Using named selections:
Preserves boundary condition assignment
Prevents failures when geometry regenerates
Enables parametric workflows
This is critical for reliable automated studies.
How This Chapter Ties CFD Together
This final chapter reframes CFD as:
A controlled numerical experiment
A reproducible engineering process
A balance between automation and expertise
It emphasizes that:
Meshing quality governs solver behavior
Tool choice reflects problem nature
Engineering judgment remains central
CFD maturity is defined by workflow reliability, not by solver sophistication.
Engineering Intuition
Automatic tools are excellent until they are not
Geometry perfection is less important than numerical suitability
Hex meshes reward understanding; unstructured meshes reward flexibility
Automation protects engineering intent
Robust CFD workflows scale with project complexity
Study Priorities
If short on time, focus on:
When advanced meshing becomes necessary
Differences between structured and unstructured philosophies
Why faceted geometry is acceptable in CFD
Role of blocking in hex meshing
Purpose of scripting in CFD workflows
Importance of named selections for automation
Key Takeaways
Advanced meshing is about control, not complexity.
Tool choice reflects geometry, physics, and project constraints.
Structured hex meshes maximize accuracy per cell.
Fluent Meshing excels with complex, imperfect geometry.
Automation ensures repeatability and robustness.
CFD expertise lies in workflow design, not button knowledge.