AdvancedTopic 104 of 105Thermodynamics & Fluids
Large eddy simulation
Resolves large turbulent eddies and models only the small ones.
In depth
LES filters the Navier-Stokes equations: large energy-containing eddies are resolved on the grid and smaller ones modelled with a subgrid-scale model (Smagorinsky). More accurate than RANS for unsteady separated flows but costs much more; requires fine meshes and small time steps.
Key points
- Filter width
- Wall-modelled LES
- Hybrid RANS-LES
ExampleLES is used to study combustor flows and wind loading on buildings.
What is Large eddy simulation?
Resolves large turbulent eddies and models only the small ones.
Why is it important to understand large eddy simulation?
Large eddy simulation resolves the large turbulent structures and models only the smaller ones, which gives more detail than averaged models.
How does LES differ from RANS?
RANS models all turbulence in averaged equations, while LES resolves most of the energy-containing eddies and models only the small scales.
Why is LES expensive?
The mesh must be fine enough to resolve large eddies, which requires far more cells and time steps than averaged models.
How is Large eddy simulation used in practice?
Typical applications include simulating the flow around a bluff body where unsteady wakes matter, predicting the noise produced by a jet from its turbulent structures and studying the mixing in a combustor where large eddies control flame behaviour.
What should I learn before Large eddy simulation?
Study "Energy efficiency and sustainability" first (topic 103 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Large eddy simulation?
Filter width. Wall-modelled LES. Hybrid RANS-LES.
Can you give an example of Large eddy simulation?
LES is used to study combustor flows and wind loading on buildings.
What comes after Large eddy simulation?
The next topic is "Organic Rankine cycle", which builds directly on this one.
How difficult is Large eddy simulation?
It is classed as Advanced in Thermodynamics & Fluids (topic 104 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.