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Troubleshooting Guide

This guide helps you diagnose and resolve common issues encountered during CFD simulations on the Navier AI Platform.

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Geometry Issues

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Upload and Import Problems

Symptoms:
  • Upload progress stalls
  • Error message during upload
  • File appears corrupted
Solutions:
  1. Check file size - Keep under 100MB for optimal performance
  2. Verify file format - Use STL files (binary preferred)
  3. Test file integrity - Open in CAD software to verify
  4. Simplify geometry - Reduce triangle count if too complex
  5. Check internet connection - Ensure stable upload connection
Symptoms:
  • Missing surfaces in 3D viewer
  • Incorrect scale or orientation
  • Geometry appears inside-out
Solutions:
  1. Scale verification - Check export units (use meters)
  2. Normal orientation - Fix inverted normals in CAD
  3. Coordinate system - Ensure proper X/Y/Z alignment
  4. File re-export - Use higher resolution settings
  5. Geometry repair - Use mesh repair tools (Netfabb, Meshlab)
Symptoms:
  • Volume calculation fails
  • Meshing errors occur
  • Inconsistent boundary patches
Solutions:
  1. Close holes in original CAD model
  2. Remove coincident surfaces that overlap
  3. Check intersection lines between components
  4. Use CAD repair functions before export
  5. Verify export settings for watertight output

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Mesh Generation Issues

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Mesh Quality Problems

Poor Orthogonality

Symptoms: Orthogonality < 0.1 Solutions:
  • Reduce refinement level jumps
  • Improve geometry quality
  • Adjust refinement zone positions
  • Use geometry-based refinement carefully

High Aspect Ratio

Symptoms: Aspect ratio > 1000 Solutions:
  • Reduce boundary layer refinement
  • Check domain aspect ratio
  • Adjust mesh transition zones
  • Consider different refinement strategy

Negative Volumes

Symptoms: Mesh generation fails Solutions:
  • Fix geometry intersections
  • Reduce refinement levels
  • Check for inverted surfaces
  • Verify domain boundaries

Excessive Cell Count

Symptoms: > 20M cells, memory issues Solutions:
  • Reduce base mesh density
  • Lower refinement levels
  • Remove unnecessary zones
  • Use symmetry when possible

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Mesh Generation Failures

Error Messages:
  • “Mesh generation failed”
  • “No cells in final mesh”
  • “Surface intersection errors”
Debugging Steps:
  1. Check geometry quality - Ensure watertight surfaces
  2. Reduce refinement levels - Start with lower levels
  3. Verify domain size - Ensure geometry inside domain
  4. Check overlapping zones - Remove conflicting refinement
  5. Examine surface normals - Verify outward-facing normals
Error Messages:
  • “Out of memory”
  • “Resource limit exceeded”
  • “Process killed”
Solutions:
  1. Reduce mesh density - Lower base cell size
  2. Limit refinement zones - Remove non-essential zones
  3. Use fewer cores - Reduce parallel mesh generation
  4. Simplify geometry - Remove complex features
  5. Consider splitting - Break large assemblies into parts

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Simulation Convergence Issues

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Slow or Poor Convergence

Symptoms:
  • Residuals plateau above 1e-3
  • Force coefficients oscillating
  • Mass flow imbalance > 1%
Diagnostic Steps:
  1. Check mesh quality - Review orthogonality and skewness
  2. Examine boundary conditions - Verify physical realism
  3. Monitor Y+ values - Ensure appropriate for turbulence model
  4. Review domain size - Check for boundary effects
Solutions:
  1. Enable potential flow initialization
  2. Reduce relaxation factors (pressure: 0.2, momentum: 0.5)
  3. Improve mesh quality in critical regions
  4. Extend iteration count - Some cases need more time
  5. Check boundary condition compatibility
Symptoms:
  • Residuals increasing rapidly
  • Extreme velocity/pressure values
  • Simulation crashes or stops
Immediate Actions:
  1. Stop simulation to prevent resource waste
  2. Check mesh quality metrics
  3. Verify boundary condition values
  4. Review domain setup
Solutions:
  1. Fix mesh quality issues (negative volumes, high skewness)
  2. Reduce relaxation factors significantly
  3. Check for realistic boundary values
  4. Verify proper units in all inputs
  5. Use more conservative solver settings

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Force Coefficient Issues

Unrealistic Values

Drag coefficient > 2.0 or < 0:
  • Check reference area calculation
  • Verify velocity magnitude
  • Review coordinate system alignment
  • Validate boundary conditions

Oscillating Forces

Coefficients varying > ±5%:
  • Extend simulation runtime
  • Check for mesh quality issues
  • Review time step (if transient)
  • Consider physical unsteadiness

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Boundary Condition Problems

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Inlet/Outlet Configuration

Symptoms:
  • Inlet ≠ Outlet mass flow
  • Continuity residuals high
  • Unphysical pressure build-up
Causes:
  • Inappropriate outlet boundary type
  • Pressure outlet with backflow
  • Closed flow circuit without proper outlet
Solutions:
  1. Use pressure outlet for external flows
  2. Check outlet boundary type compatibility
  3. Verify domain closure - no flow leaks
  4. Monitor mass flow rates at boundaries
  5. Adjust outlet pressure if needed
Symptoms:
  • Negative velocities at outlet
  • Unphysical flow patterns
  • Convergence difficulties
Solutions:
  1. Increase domain size (especially downstream)
  2. Use pressure outlet instead of velocity outlet
  3. Check flow direction specification
  4. Verify realistic velocity magnitudes
  5. Consider different boundary placement

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Wall Boundary Issues

For wall functions (y+ = 30-300):
  • Too low: y+ < 11 (inefficient)
  • Too high: y+ > 500 (inaccurate)
Solutions:
  1. Adjust first cell height in boundary layer
  2. Modify mesh density near walls
  3. Use appropriate turbulence model for y+ range
  4. Consider wall integration (y+ < 1) if needed
Symptoms:
  • Unrealistic temperatures
  • Poor thermal convergence
  • Energy imbalance
Solutions:
  1. Check thermal boundary conditions specification
  2. Verify material properties (specific heat, conductivity)
  3. Ensure energy equation is enabled
  4. Review reference temperatures

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Performance and Resource Issues

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Computational Performance

Slow Simulation

Runtime > Expected:
  • Check mesh size vs. cores
  • Monitor CPU utilization
  • Review memory usage
  • Consider mesh optimization

Memory Problems

Out of memory errors:
  • Reduce mesh density
  • Use fewer cores
  • Close other applications
  • Consider system upgrade

Stalled Progress

Simulation not advancing:
  • Check system resources
  • Monitor error logs
  • Verify internet connection
  • Contact support if persistent

Poor Scaling

Adding cores doesn’t help:
  • Mesh too small for cores used
  • Memory bandwidth limited
  • Check parallel efficiency
  • Optimize core count

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Results and Visualization Issues

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Unexpected Results

Symptoms:
  • Unphysical separation
  • Missing expected features
  • Asymmetric flow (should be symmetric)
Investigation:
  1. Check boundary conditions - Verify inlet/outlet setup
  2. Review mesh resolution - Ensure adequate for features
  3. Validate geometry - Confirm proper orientation
  4. Compare with theory - Basic flow physics
  5. Check convergence - Ensure simulation completed
Solutions:
  1. Increase mesh refinement in critical areas
  2. Extend simulation time for better convergence
  3. Verify boundary condition types and values
  4. Check for geometry errors or artifacts
Symptoms:
  • Drag much higher/lower than expected
  • Pressure patterns incorrect
  • Force directions wrong
Validation Steps:
  1. Order of magnitude check - Are values reasonable?
  2. Units verification - Consistent throughout?
  3. Reference area - Correct for coefficient calculation?
  4. Coordinate system - Proper force directions?
  5. Comparison data - What are expectations based on?
Debugging:
  1. Simplify case - Start with basic validation
  2. Check similar geometries - Literature comparison
  3. Review all inputs - Systematic verification
  4. Consider mesh independence - Try finer mesh

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Getting Help

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Self-Diagnosis Tools

Built-in Diagnostics

Platform Features:
  • Mesh quality reports
  • Convergence monitoring
  • Real-time diagnostics
  • Automatic validation

Manual Checks

Your Analysis:
  • Compare with known cases
  • Check order of magnitude
  • Verify conservation laws
  • Review all inputs

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When to Contact Support

Contact support when:
  • Platform errors prevent simulation setup
  • Unexpected crashes or failures occur
  • Results are consistently unreasonable despite troubleshooting
  • You need guidance on complex flow physics
  • Performance issues persist after optimization

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Information to Provide

When contacting support, include:
  1. Project name and simulation details
  2. Error messages (screenshots helpful)
  3. Geometry description and file details
  4. Simulation settings used
  5. Expected vs. actual results
  6. Troubleshooting steps already attempted
Remember: Most CFD issues are systematic. Work through problems methodically, starting with the most basic checks (geometry, mesh, boundary conditions) before moving to complex diagnostics.