The instantaneous stream-wise velocity of a turbulent flow is given as follows:
$u(x,y,z,t)=\overline{u}(x,y,z)+{u}'(x,y,z,t)$
The time-average of the fluctuating velocity ${u}'(x,y,z,t)$ is
- $\displaystyle{\frac{u'}{2}} \\$
- $\displaystyle{\frac{-\overline{u}}{2}} \\$
- $\text{zero}\\$
- $\displaystyle{\frac{\overline{u}}{2}}$
