= Solution
The <K-epsilon turbulence model> evolves <turbulent kinetic energy> $k$ and its <turbulent kinetic energy dissipation rate> $\epsilon$, rather than resolving turbulent fluctuations. It closes the <Reynolds stress> with an isotropic <eddy viscosity>, $\nu_T=C_\mu k^2/\epsilon$, and models transport of $k$ and $\epsilon$ by gradient diffusion with coefficients $\nu_T/\sigma_k$ and $\nu_T/\sigma_\epsilon$. Production is tied to mean strain; dissipation-equation production and destruction are modeled terms with empirical constants. The characteristic velocity and length are $\sqrt k$ and $k^{3/2}/\epsilon$. These assumptions are primarily for high <Reynolds number>, and strongly anisotropic flow, sharp interfaces and molecular-viscosity-dominated regions need additional treatment. The dissipation equation is a closure, not a second exact energy-conservation law.
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