Boussinesq eddy viscosity hypothesis

Summary

The Boussinesq eddy viscosity hypothesis models the Reynolds stress of a turbulent flow as proportional to the mean rate of strain. It has the same form as the viscous stress of a Newtonian fluid. The coefficient, the eddy viscosity, is a property of the flow, not of the fluid, and is usually much larger than the molecular viscosity. Joseph Boussinesq proposed it in 1877. It is the basis of most engineering turbulence models, which differ in how they compute the eddy viscosity. It is one approach to the closure problem.