Turbulent kinetic energy dissipation rate ($ϵ=2\nu \overline{s_{ij}^{\prime }{s}_{ij}^{\prime }}$)

The positive rate per unit mass at which molecular viscosity removes turbulent kinetic energy, with $s_{ij}^{\prime }$ the fluctuating symmetric velocity-gradient tensor. Its dimensions are velocity squared per time. The integral-scale estimate is $ϵ\sim q^3/L$, expressing transfer over turnover time $L/q$; numerical constants depend on the convention for the turbulent velocity and length scales.