If you have been around smokers, you probably noticed that the cigarette
smoke rises in a smooth plume for the first few centimeters and then starts
fluctuating randomly in all directions as it continues its rise. Other plumes
behave similarly (Fig. 8–3). Likewise, a careful inspection of flow in a pipe
reveals that the fluid flow is streamlined at low velocities but turns chaotic
as the velocity is increased above a critical value, as shown in Fig. 8–4. The
flow regime in the first case is said to be laminar, characterized by smooth
streamlines and highly ordered motion, and turbulent in the second case,
where it is characterized by velocity fluctuations and highly disordered
motion. The transition from laminar to turbulent flow does not occur suddenly;
rather, it occurs over some region in which the flow fluctuates
between laminar and turbulent flows before it becomes fully turbulent. Most
flows encountered in practice are turbulent. Laminar flow is encountered
when highly viscous fluids such as oils flow in small pipes or narrow
passages.
If you have been around smokers, you probably noticed that the cigarettesmoke rises in a smooth plume for the first few centimeters and then startsfluctuating randomly in all directions as it continues its rise. Other plumesbehave similarly (Fig. 8–3). Likewise, a careful inspection of flow in a pipereveals that the fluid flow is streamlined at low velocities but turns chaoticas the velocity is increased above a critical value, as shown in Fig. 8–4. Theflow regime in the first case is said to be laminar, characterized by smoothstreamlines and highly ordered motion, and turbulent in the second case,where it is characterized by velocity fluctuations and highly disorderedmotion. The transition from laminar to turbulent flow does not occur suddenly;rather, it occurs over some region in which the flow fluctuatesbetween laminar and turbulent flows before it becomes fully turbulent. Mostflows encountered in practice are turbulent. Laminar flow is encounteredwhen highly viscous fluids such as oils flow in small pipes or narrowpassages.
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