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What is the difference between the RANS model and the Reynolds stress model?

What is the difference between the RANS model and the Reynolds stress model? Correct Answer The Reynolds stress model needs 7 extra transport equations

The most common RANS turbulence models are classified on the basis of the number of extra transport equations they need. These models form the basis of the current procedures for turbulence problems in CFD packages. The Reynolds stress model needs seven more equations.

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