2..1. Viscous Flow and Inviscid Flow

Now if you talk about when do I get a problems of the fluid flow problems, first it comes it that we should classify it. The classification means you will try to understand that we are simplifying or categorizing the fluid flow in that category. So we can solve that particular category class of the fluid flow problems.

When faced with fluid flow problems, the first step is to classify or categorize the flow. This helps in simplifying the complexities of the problems, allowing us to apply specific methods and solutions that are relevant to the category of flow we are dealing with. In essence, classification helps to break down the problem into more manageable pieces, making it easier to analyze and solve.

Think of fluid flow classification like organizing a library. Just as books are categorized into fiction, non-fiction, science, and history to help find information easily, fluid flows can be categorized to help engineers apply the right theories and solutions. For instance, knowing that a problem involves viscous flow allows the engineer to use models that address viscosity effects, similar to how a librarian would go to the non-fiction section for science books.

And exact same way the resistance in a fluid flow we call the viscous. So that viscosity, viscous flow when we have the flow resistance are dominated, are significant then we call the viscous flow.

Viscous flow refers to the scenario in fluid dynamics where the resistance due to viscosity is significant. Viscosity is a measure of a fluid’s resistance to deform or flow. In a viscous flow, the fluid experiences significant internal friction as molecules slide past each other, slowing down the flow. This is particularly noticeable when the moving fluid interacts with solid boundaries, creating drag.

Imagine trying to push a thick syrup through a narrow straw. The syrup moves slowly, and you feel the resistance of the syrup as you push the straw. In this case, the thick syrup represents a viscous fluid, and the resistance you feel is due to its high viscosity, illustrating viscous flow.

But there are the reasons where you may not have the viscous is going to dominated or comparatively it is a less as compared to other force component, those reasons we can talk about the inviscid flow.

In contrast, inviscid flow refers to fluid flow where the effects of viscosity are negligible. This occurs under conditions where other forces, such as pressure or inertial forces, dominate the flow dynamics. In these scenarios, the fluid can be treated as having no internal shear resistance, simplifying the analysis significantly.

Consider a water jet from a garden hose. As the water shoots out at high speed, the flow can be approximated as inviscid because the impact of viscosity is minimal compared to the kinetic energy of the flowing water. In this analogy, you can think of it as a race car zooming down a track—at such high speeds, the air’s resistance is minimal compared to the car's momentum.

Now you take it this example. This is very interesting examples here, okay. If you look at a two pipes are there. One is a bigger pipe, another is a smaller pipe, okay.

In the example of two pipes—one larger and one smaller—we can observe both viscous and inviscid flow. Inside the larger pipe, the flow is predominantly viscous near the walls where the fluid interacts with the pipe material, but as we move towards the center, the effects of viscosity become less significant, leading to conditions that can be considered inviscid. Conversely, in the smaller pipe, the influence of viscosity may dominate throughout, altering the flow dynamics.

Think about how your sink has both wide and narrow pipes. When water flows into the wider pipe, it moves more freely and quickly in the center (inviscid), but near the sides, it slows down due to friction with the walls (viscous). In contrast, a narrower pipe restricts flow throughout, showing higher viscous effects.

The second component what we will talk it now is the internal flow external flow. Here I am talking about the boundary.

Internal flow occurs when the fluid flow is confined within boundaries, such as a pipe, where the later stages are defined by solid walls. External flow refers to fluid flow occurring freely without these specific boundaries, such as air flowing around an object, like a tennis ball. Understanding the distinction is crucial for predicting flow behavior and the forces acting on the fluid.

Consider a river (external flow), where the water flows freely and is affected by natural boundaries like riverbanks. In contrast, when water travels through a pipe (internal flow), it is contained and thus experiences different dynamics influenced heavily by the pipe’s walls.

So we can simple way categorize viscous flow, inviscid flow, external flow and the internal flow.

In conclusion, understanding fluid flow involves categorizing whether the flow is viscous or inviscid and recognizing the external or internal boundaries of the flow. This classification aids in identifying the appropriate analysis methods and simplifications needed to solve fluid mechanics problems.

Imagine you are planning a road trip. Knowing the type of roads (smooth highways vs. rough terrain) helps you choose the right vehicle and plan your route. Similarly, knowing whether fluid flows are viscous or inviscid and if they are internal or external helps engineers select the right approach for analyzing fluid dynamics.

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