After rising a short distance, the smooth column of smoke from a cigarette breaks up into an irregular and random pattern. In a similar fashion, a stream of fluid flowing past an obstacle breaks up into eddies and vortices which give the flow irregular velocity components transverse to the flow direction. Other examples include the wakes left in water by moving ships, the sound produced by whistling and by wind instru- ments. These examples are the results of—

The phenomena described, such as the transition of a smooth cigarette smoke column into an irregular pattern and the formation of eddies and vortices behind obstacles, are classic characteristics of turbulent flow. In fluid mechanics, laminar or streamline flow occurs when fluid particles move in smooth, parallel layers. However, when the flow velocity increases or encounters obstacles, it becomes turbulent, characterized by random, chaotic fluctuations and transverse velocity components. This turbulence is responsible for the formation of wakes behind moving ships and the generation of sound in wind instruments through vortex shedding and instability-induced excitation [3]. While laminar flow is orderly, turbulent flow involves the breakdown of these layers into complex structures like eddies, which are essential for the acoustic resonances found in whistling [2].

Sources

1. [1] https://core.ac.uk/download/pdf/41826970.pdf
2. [2] https://ntrs.nasa.gov/api/citations/19950022299/downloads/19950022299.pdf
3. [3] https://archive.org/download/wavesripplesinwa00flemuoft/wavesripplesinwa00flemuoft.pdf