In turbulent flows, the small scale turbulent "eddies" present in the flow can act like a viscosity, creating a gradient in the velocity. In most turbulent flows, this "eddy diffusivity of momentum" or "eddy viscosity" is larger in magnitude than the actual viscosity. Looking at these figures, we can see that the distributions of the turbulent stress u'v' and du/dy are closely matched, as are the distributions of u'w' and du/dz. From these data, estimates of the magnitude of the eddy diffusivity of momentum are possible, information which is important to turbomachinery engineers and modellers.
Like the streamwise data, the lateral injection data shows the same agreement between the turbulent shear stresses and the resulting velocity gradients.