21.2 : 파이프 흐름의 일반적 특성 II

As fluid enters a pipe, it first flows through an entrance region where the velocity profile adjusts, forming a boundary layer along the walls. This boundary layer grows until it fills the pipe, creating a fully developed flow with a steady velocity profile across the pipe's cross-section.

The distance required to reach this fully developed state, known as the entrance length, depends on the flow type and the Reynolds number. Laminar flow reaches this state over a shorter distance, while turbulent flow requires a longer entrance length due to mixing and irregularities.

In the fully developed flow, motion is driven by pressure differences. In horizontal pipes, this pressure difference counteracts viscosity and maintains steady flow.

In the entrance region, a more significant pressure gradient is needed to balance acceleration as the flow adjusts, but this gradient becomes constant once fully developed.

Shear stress differs by flow type: in laminar flow, it results from molecular interactions, while in turbulent flow, it arises from the momentum transfer between more significant, randomly moving fluid particles. This difference affects the pressure distribution and overall flow behavior.