Turbulence dissipation rate

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Turbulence dissipation, $\epsilon$ is the rate at which turbulence kinetic energy is converted into thermal internal energy. The SI unit of $\epsilon$ is $\mathrm{J} / (\mathrm{kg} \cdot \mathrm{s}) = \mathrm{m}^2 / \mathrm{s}^3$ .

$\epsilon \, \equiv \, \nu \overline{\frac{\partial u_i'}{\partial x_k}\frac{\partial u_i'}{\partial x_k}}$

For compressible flows the definition is most often slightly different:

$\epsilon \, \equiv \, \frac{1}{\overline{\rho}} \overline{\tau_{ij} \frac{\partial u_i''}{\partial x_j}}$

Where the viscous stress, $\tau_{ij}$ , using Stokes law for mono-atomic gases, is given by:

$\tau_{ij} = 2 \mu S^*_{ij}$

where

$S^*_{ij} \equiv \frac{1}{2} \left( \frac{\partial u_i}{\partial x_j} + \frac{\partial u_j}{\partial x_i} \right) - \frac{1}{3} \frac{\partial u_k}{\partial x_k} \delta_{ij}$

Turbulence dissipation rate

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