Numerical Simulations of Turbulent Combustion and Combustion Engines
Reynolds-Averaged Navier Stokes (RANS)
Solve for the mean values of all quantities, the predominant approach in engineering CFD packages.
Large Eddy Simulations (LES)
The turbulent large scales are explicitly calculated whereas the effects of smaller ones are modelled using subgrid closure rules. LES is particularly appealing for IC engine applications, which is attracting more research efforts.
Direct Numerical Simulations (DNS)
Solve the full instantaneous Navier-Stokes equations without any model for turbulent motions. DNS of IC engine flows is possible, but has not been performed.
Comparison of Approaches
| Approach||Advantages || Disadvantages|
- "Coarse" numerical grid
- Geometrical simplifications (2D Flows...)
- "Reduced" numerical cost
- Only mean flow field
- Models required
- Unsteady features
- Reduced modelling impact (compared to RANS)
- Subgrid models required
- 3D simulations required
- Needs precise codes
- High numerical cost
- No models for turbulence/ combustion interaction
- Tool to study models
- Prohibitive numerical cost (fine grids, precise codes)
- Limited to academic problems