This article uses the flow of cigarette smoke to illustrate the basic principles and applications of fluid dynamics. It covers fluid motion and various hydrodynamic phenomena, such as laminar flow, turbulence, and detachment, using everyday examples to emphasize their importance and applications.

Fluid Dynamics Through Cigarette Smoke

We all have memories of watching our father’s cigarette smoke or incense smoke from a ritual ascend into the sky as a child. At first, it clings to an object, then it separates from it and rises in a straight line, then it forms a vortex, and finally it disperses. You’ve probably wondered about this behavior at one point or another. Why does it behave the way it does, and why can’t it just swirl and disperse in the first place? The science that studies these reasons is called fluid dynamics.
The word hydrodynamics may not sound familiar. However, the importance of fluids like air and water in our environment is not negligible, so analyzing the relationships between them and other objects numerically is very important. While it’s not possible to cover all the examples and calculations in this article, we’ll talk about the behavior of fluids through a few representative examples.

Basic concepts of fluid dynamics

Fluid mechanics is the study of fluids in motion or at rest, as well as their behavior when they come into contact with solids or other fluids. In general, matter is divided into solids and fluids. The distinction between the two is based on their behavior when subjected to shear stress. Solids can deform when subjected to shear stress, but they don’t flow. Fluids, on the other hand, cannot resist shear stress and will move. We see this motion and say that the fluid is flowing.
The no-slip condition refers to the property that fluid particles in contact with a wall will stick to the wall and not move. For fluids with low viscosity, you can solve the problem as if it were an idealized fluid with no viscosity in a region far enough away from the object to avoid significant errors. However, in the immediate vicinity of an object’s surface, viscosity cannot be ignored. This boundary region is called the boundary layer, and the effects of viscosity must be considered inside the boundary layer.

Laminar Flow and Turbulence

Laminar flow is a very orderly flow in which the fluid moves parallel to the wall surface. There are no particles entering perpendicular to the direction of flow, and no vortices occur. A good example of laminar flow is when you run water through a thin pipe and add ink to observe the flow. If the Reynolds number is small, the ink flows in a straight line, and each part of the water moves parallel to the pipe wall.
Turbulent flow, on the other hand, unlike laminar flow, is highly irregular, complex, and continuously changing over time. In turbulent flow, there are many small eddies called vortices, and large vortices gradually break into smaller ones and dissipate. Turbulence exhibits a complex flow that is difficult to predict, and because of this irregularity, the study of turbulence remains one of the most important unsolved problems in physics.

Applications of fluid dynamics

Despite its complex principles, fluid dynamics is closely connected to our daily lives. It plays an important role not only in the flow of smoke or water, but also in the design of our cars and airplanes. For example, it is crucial that the wings of an airplane optimize their interaction with the air to generate lift and minimize drag. These designs are all based on the principles of fluid dynamics, and especially in aerospace, it is essential to study the flow of air and control it effectively. The principles of fluid dynamics are applied to the geometry of the wing, as well as the air intake and exhaust of the engine.
In recent years, the application of fluid dynamics has also become prominent in sports science. In particular, the design of sporting goods, such as swimwear, is centered on minimizing fluid resistance. The full-body swimsuits worn by famous swimmers reduce resistance in the water, helping them to break records. The design of these sports equipment is all based on hydrodynamics.
Separation is when a fluid breaks away from its boundary layer. This happens when a fluid passes over a solid surface, such as an airplane wing. When separation occurs, pressure drag, which is a component of drag, increases dramatically and lift decreases. Delamination is an important issue in airplane design, and research is ongoing to reduce it.

Conclusion

Fluid dynamics can seem a bit abstract because it deals with the invisible dynamics of fluids. Nevertheless, fluid dynamics has practical applications in a variety of fields, including cars, airplanes, and sporting goods, and contributes to making our daily lives easier and safer. Even now, many scientists and engineers are working on solving unsolved problems in fluid dynamics, and the results will enrich our lives.