Question

Using the Prandtl’s mixing length concept how is the turbulent shear stress expressed?

(a) $\rho l\frac{d\bar{u}}{dy}$

(b) $\rho l^{2}\frac{d\bar{u}}{dy}$

(c) $\rho l\left ( \frac{d\bar{u}}{dy} \right )^{2}$

(d) $\rho l^{2}\left ( \frac{d\bar{u}}{dy} \right )^{2}$