When entering into the subject of turbulent flow, it is essential to understand that the kind of flow with which we deal belongs to a particular class known as shear flow. These types of flow comprise flow fields in which relative velocities have been induced by shear stresses rather than by the action of pressure forces. In pipe flow, when the fluid enters through the well-rounded bell from a reservoir or from the calm open air, a uniform velocity distribution occurs at the pipe entrance. Immediately down stream from the entrance of the pipe, the flow is structured with a boundary layer near the wall, and is of uniform velocity profile in the central part. Due to the action of wall friction, the boundary layer grows thicker and thicker downstream. As the mass flux is constant throughout the pipe,’ the central stream must accelerate to compensate for this retardation of the flow near the wall. Finally, the boundary layer thickness reaches the value of pipe radius. The free stream, therefore, disappears from the central part of the pipe. Furthermore, Barbin and Jones (1)* pointed out that following the disappearance of the free stream, further changes in the velocity profile and turbulence structure occur before a fully developed condition is reached* The flow in the inlet region of a pipe is, therefore, a transition from a boundary layer type flow at the entrance to a fully developed flow downstream. The change of the free stream velocity in the entry region causes a greater reduction of the static pressure than that in the fully developed region.



College and Department

Mechanical Engineering



Date Submitted


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Hydraulics, Boundary layer, Fluid dynamics