- In analogy with the coefficient of viscosity for laminar flow, J. Boussinesq introduced a mixing coefficient
 for the Reynolds stress term, defined as
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- Using the shearing stresses can be written as
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such that the equation
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may be written as
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| (33.13) |
The term νt is known as eddy viscosity and the model is known as eddy viscosity model .
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- Unfortunately the value of νt is not known. The term ν is a property of the fluid whereas νt is attributed to random fluctuations and is not a property of the fluid. However, it is necessary to find out empirical relations between νt, and the mean velocity. The following section discusses relation between the aforesaid apparent or eddy viscosity and the mean velocity components
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