Velocity distribution is affected by several factors, including pipe surface roughness,
turbulence level, flow area changes. The shear stress of the fluid creates the velocity
distribution in the flow. The flow velocity very close to the pipe wall is zero. This results
in a significant change in velocity across the pipe cross section. The laminar and turbulent velocity distributions are significantly different as a result of different shear stresses
in the flow. In turbulent flow, the velocity gradient is greater near to the pipe wall than it
is in laminar flow. In laminar flow, the center line velocity is higher than in turbulent flow
of equal mean velocity .
With a smoothly shaped outlet from tank to pipe, the velocity profile is a function of distance. The fully developed profile is constant, if it is not disturbed. In a pipe elbow, the
fully developed velocity profile is disturbed by inertia forces in the fluid .
A more drastic change in velocity profile can be caused by an orifice or a valve that create a high velocity jet into a flow stream. On the downstream side of an orifice there are
strong vortices which cause flow pressure losses. High velocity jets are also accompanied by the noise, especially in the case of compressible flow. The velocity profile after
the valve is dependent on the valve type and design, and on valve travel. A fully open
ball valve behaves as an extension to the pipe and thus does not disturb the velocity
profile in the way that, for instance, butterfly and globe valves do