general considerations

When is compressibility important?

How is turbulence modeling affected?

Favre averaging

What is effect of density fluctuations (mathematically)?

summary

• density fluctuations often negligible
  $\rightarrow$ turbulence modeling remains almost unchanged
• Favre averaging transforms transport equation
  $\rightarrow$ recovers generic form of transport equations
• Favre averaging if only a mathematical transformation (not a simplification)