Before revision: In the above picture, can be expressed in terms of the mixing length considering a fluid parcel moving with in the z-direction: The fluctuating components of velocity, , , and , can also be expressed in a similar fashion: although the theoretical justification for doing so is weaker, as the pressure gradient force can significantly alter the fluctuating components.
After revision: In the above picture, can be expressed in terms of the mixing length considering a fluid parcel moving in the z-direction: The fluctuating components of velocity, , , and , can also be expressed in a similar fashion: although the theoretical justification for doing so is weaker, as the pressure gradient force can significantly alter the fluctuating components.