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 TURBULENT FLOW
LAMINAR (STREAMLINE) FLOW
FIGURE 3-1.
Laminar and Turbulent Flow Patterns
and the boundary values can vary significantly. The Reynolds number is
important because of the impact it may have on final meter selection.
4.2 Nonstable Flow. A nonstable flow can be defined as a fluid that is
swirling, pulsating, or changed in character by some projection into the fluid
flow or a change in pipe direction. Most meters are designed to tolerate
small amounts of nonstable flow and still register an accurate reading. To
ensure the highest accuracy, all meters specify varying lengths of straight
pipe before and after the meter. These lengths are usually expressed in
multiples of pipe diameters. The required length of straight pipe is found by
multiplying the pipe diameter by the multiple listed. Under some
circumstances, it may not be possible to install meters with the recommended
lengths of straight piping before and after the meters. If so, the flow
distortions may exceed the ability of the meter to absorb and still return a
reading with the required accuracy. If the velocity profile has been so
distorted or swirl induced to such a degree that meter accuracy is
compromised) installation of flow straighteners in the pipe run q ay correct
the situation. Figure 3-2 shows cross-sections of two devices used to
straighten fluid flows. Figure 3-2(a) is a section of pipe that is filled
with straight tubes which will correct most types of distortions. Figure
3-2(b) is a similar device except that instead of tubes, a grid device
assembled at 90 degree angles is inserted into the pipe. Some meters may also
3-3
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