# General CFD FAQ

(Difference between revisions)
 Revision as of 08:14, 5 December 2005 (view source)Tsaad (Talk | contribs)← Older edit Revision as of 08:16, 5 December 2005 (view source)Tsaad (Talk | contribs) Newer edit → Line 2: Line 2: == Physics == == Physics == === What is the Reynolds decomposition? === === What is the Reynolds decomposition? === - The Reynolds decomposition is used to separate the scales in a turublent flow and resolve the velocity field as the sum of an average component and a fluctuating component. + The Reynolds decomposition is used to separate the scales in a turublent flow and resolve the velocity field (or any other scalar field) as the sum of an average component and a fluctuating component. The time average of the fluctuating field is identically zero. === What is the difference between the Reynolds decomposition and LES filtering? === === What is the difference between the Reynolds decomposition and LES filtering? ===

## Revision as of 08:16, 5 December 2005

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## Physics

### What is the Reynolds decomposition?

The Reynolds decomposition is used to separate the scales in a turublent flow and resolve the velocity field (or any other scalar field) as the sum of an average component and a fluctuating component. The time average of the fluctuating field is identically zero.

### What is the difference between the Reynolds decomposition and LES filtering?

The Reynolds decomposition separates the velocity field into an average component and a fluctuating component. The time average of the fluctuating component is identically zero. In LES, a filtering operation is performed to decompose the velocity field into a filtered velocity field and a filtered residual field. The crucial difference between both methods is

• The filtered velocity field is a random variable while the average field (Reynolds) is not
• The time average of the residual field is generally nonzero while it is identically zero for fluctuating component in the Reynolds decomposition.

## Numerics

### What is the difference between FEM, FVM and FDM?

Describe differences between the finite volume method, the finite element method and the finite difference method...