Gas and liquid flows (fluid flows) can be described as being in one of three states; turbulent, transitional, or laminar.
Turbulent flow is by nature chaotic. The fluid mixes irregularly during turbulent flow. Constant changes in the flow’s behavior (wakes, vortexes, eddies) make flow rates difficult, if not impossible, to accurately measure. Turbulent flow usually occurs at high flow rates and/or in larger diameter pipes. Turbulent flow is usually desirable when solids must remain suspended in the fluid to prevent settling or blockages.
Transitional flow exhibits characteristics of both laminar and turbulent flow. The edges of the fluid flow in a laminar state, while the center of the flow remains turbulent. Like turbulent flows, transitional flows are difficult, if not impossible, to accurately measure.
Laminar flow layers
Laminar or Smooth flow tends to occur at lower flow rates through smaller pipes. In essence, the fluid particles flow in cylinders. The outermost cylinder, touching the pipe wall, does not move due to viscosity. The next cylinder flows against the unmoving fluid cylinder, which exhibits less frictional “pull” than the pipe wall. This cylinder will move the slowest. This continues, with the centermost cylinder having the greatest velocity.