Numerical study of pressure distribution in entrance pipe flow

This article describes the computation of pipe flow in the entrance region. The pressure distribution and flow characteristics, particularly the effect of vorticity in the vicinity of the wall, were analyzed for moderate Reynolds numbers (Re) ranging from 500 to 10,000. It was found, for the first time, that a large pressure gradient in the radial direction exists near the pipe inlet. The pressure gradient is caused by the radial component of the curl of vorticity, which decreases as Re increases. The pressure at the wall is lower than that at the central core for Re ≤$\le$ 5000. This result is beyond the scope of the boundary-layer assumption for pressure, although it applies to flows at high Reynolds numbers.