User Guide

Status: Skeleton — to be expanded as tutorials are written.

This guide covers running DNDSR simulations from mesh generation through to post-processing.

---

Overview

DNDSR is a compressible Navier-Stokes solver using high-order Compact Finite Volume (CFV) / Variational Reconstruction (VR) on unstructured meshes. It supports:

• 2D and 3D inviscid and viscous flows
• RANS turbulence models (Spalart-Allmaras, k-omega SST, Realizable k-epsilon)
• MPI parallelism for multi-node clusters
• Optional CUDA GPU acceleration (EulerP module)

Workflow

Mesh generation (Pointwise / Gmsh / other) → CGNS
       ↓
Solver configuration (JSON)
       ↓
Run solver (C++ executable or Python script)
       ↓
Post-processing (ParaView / VisIt / Tecplot)

---

Mesh Generation

DNDSR reads CGNS format meshes. We currently use Pointwise for mesh generation.

‍TODO: Add recommended Pointwise export settings (CGNS version, zone organization, boundary condition naming).

Supported Element Types

Dimension	Linear (O1)	Quadratic (O2)
2D	Tri3, Quad4	Tri6, Quad9
3D	Tet4, Hex8, Prism6, Pyramid5	Tet10, Hex27, Prism18, Pyramid14

‍TODO: Notes on mesh quality requirements (skewness, aspect ratio, minimum cell size) for high-order VR.

</blockquote>

Running a Simulation

C++ Solver

# Build first (see @ref building)
cmake --build build -t eulerSA -j8
 
# Run
mpirun -np 4 ./build/app/Euler/eulerSA cases/naca0012/eulerSA_config.json

‍TODO: Add notes on:

• Choosing the correct executable (euler, euler3D, eulerSA, euler2EQ, ...)
• MPI rank count vs. mesh size guidelines
• Setting OMP_NUM_THREADS for hybrid parallelism
• Wall time and checkpoint restart

Python Solver (EulerP)

‍TODO: Add minimal Python script example using DNDSR.EulerP.

</blockquote>

Post-Processing

DNDSR outputs VTK (.vtu / .pvtu) and Tecplot (.plt) formats.

ParaView / VisIt

• Open the .pvtu (parallel VTK) or .vtu (serial) files
• Available fields: density, velocity, pressure, temperature, Mach number, turbulence quantities (for RANS models)

‍TODO: Add screenshots or a brief ParaView pipeline description.

Tecplot

• Open .plt files directly
• > TODO: Any Tecplot-specific notes

---

Tutorials

‍TODO: Add step-by-step tutorials:

1. Periodic Vortex — 2D inviscid, validation case
2. NACA 0012 — 2D RANS, airfoil at angle of attack
3. 3D Cylinder — laminar / turbulent cylinder flow
4. Custom case — adapting an existing config to a new mesh

</blockquote>

Tips and Best Practices

‍TODO: Collect practical advice:

• Starting from a lower-order solution
• CFL ramping for stiff cases
• Monitoring residuals and convergence
• When to use elevation + bisection vs. native O2 mesh
• Memory usage estimates

</blockquote>

See Also

• Building DNDSR — build instructions
• Solver Configuration — JSON configuration reference
• Python Geom Module - Mesh Reader Guide — mesh reading in Python
• Troubleshooting and FAQ — common issues and fixes