The shear stress for laminar or viscous flow is given by Newton's law of viscosity as:-

$\tau_v=\mu\dfrac{du}{dy}$

Similarly for the expression of viscous shear, J. Bossinesq expressed the turbulent shear in mathematical form as,

$\tau_t=\eta\dfrac{d\overline{u}}{dy}.............................(1)$

Where,

$\tau_t$ = Shear stress due to turbulence

$\eta$ = Eddy viscosity

$\overline{u}$ = Average …