A difficulty in turbulence
theory caused by more unknowns than equations.
The closure problem of turbulence is alternately described as the requirement for an infinite number of equations, which would also be impossible to solve. This problem is apparently associated with the nonlinear
nature of turbulence, and the traditional analytical approach of Reynolds averaging
the governing equations to eliminate linear
terms while retaining the nonlinear
terms as statistical
correlations of various orders (i.e., consisting of the product of multiple dependent variables
). The closure problem is a long-standing unsolved problem of classical (Newtonian) physics. While no exact solution has been found to date, approximations called closure assumptions
can be made to allow approximate solution of the equations for practical applications.
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