2.2. Internal Flow and External Flow

Now if you talk about when do I get 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.

This chunk highlights the importance of classifying fluid flow problems. Classification helps in simplifying complex fluid dynamics into manageable categories, thus allowing for effective problem-solving. By understanding whether the flow is viscous or inviscid, steady or unsteady, internal or external, we can apply appropriate principles and equations relevant to that specific type of flow.

Imagine you are sorting laundry. You separate whites from colors, heavy fabrics from lighter ones, and delicates from regular clothes. This makes it easier to wash each type correctly. Similarly, classifying fluid flow allows engineers to tackle each type of flow situation with the right methods, just as you choose the right wash cycle for different types of laundry.

Like first let me talk about that. When the as you know in a solid mechanics when two objects are moving it there will be the resistance force okay. 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... we can talk about the inviscid flow.

This chunk discusses two types of fluid flows: viscous and inviscid. Viscous flow occurs when the effects of viscosity are significant, leading to resistance against the motion of fluid. For instance, honey flows slowly due to its high viscosity. In contrast, inviscid flow refers to situations where viscosity is negligible compared to other forces, allowing the fluid to flow more freely, such as how air flows over a wing.

Think of pushing a thick syrup through a straw (viscous flow) compared to pushing water through the same straw (inviscid flow). The syrup represents a high-viscosity fluid requiring more force to move, while water flows easily with little resistance, representing inviscid flow.

If you look at a pipe flow. That means I know there is inlet, there is outlet and these are the boundary is defined by this the pipe boundary. So these are internal flow. So I know the boundaries defined by the solid surface there is an inflow, there is an outflow.

Internal flow occurs within boundaries, such as pipes or tubes, where the fluid has defined inlets and outlets. The flow behavior is influenced by the pipe walls, which causes friction and pressure drops. Understanding internal flow is crucial in engineering applications, like designing piping systems in buildings or chemical plants.

Imagine a garden hose. When you turn the faucet on, water flows from the tap, through the hose (internal flow), and out the nozzle. The hose boundaries influence how easily the water flows by creating friction. Knowing how water behaves in the hose helps you determine how strong a nozzle you need to control the water pressure.

If I have a tennis ball when you have the flow that means you may consider a tennis ball is moving with the velocity V or you can consider the wind is moving with velocity V. Both are the same conditions can prevail it... we call external flow.

External flow refers to fluid flow occurring around solid objects, without defined boundary constraints like in internal flow. This can include air flowing over a moving car or a ball. Understanding external flow is vital in fields like aerodynamics, where the design of vehicles for improved performance involves managing how the surrounding air interacts with them.

Picture a bicycle moving forward. The air that moves around the cyclist’s body and bicycle frame represents external flow. The shape of the bicycle influences how aerodynamic it is, just as a well-shaped ball minimizes drag when thrown through the air.

Let me consider that I have the wind movements of the velocity V, there is a hill and the flow is coming over that... we can classify them steady flow, periodic flow and unsteady flow.

This part introduces steady and unsteady flow classifications. Steady flow means that the fluid properties at a point do not change over time. Unsteady flow, however, varies over time. Understanding these categories is essential for engineers to predict how fluids will behave under different conditions.

Think of a calm lake (steady flow) where the water surface remains still. In contrast, during a storm, the lake's surface becomes turbulent (unsteady flow) and changes continuously, similar to how the wind changes direction and speed, affecting the flow pattern.

Another flow system which is very simple the gravity based or buoyancy based fluid systems... we can call a forced flow and the flow what we are dividing steady, unsteady and periodic.

Natural flow occurs due to natural forces like gravity or buoyancy without external energy input, while forced flow requires energy input, such as pumps or turbines. Grasping the differences helps engineers determine how to control fluid systems effectively.

Consider a waterfall (natural flow) where water freely falls due to gravity vs. a swimming pool pump (forced flow) directing water through filters. Understanding these dynamics allows pool maintenance to manage circulation and cleanliness.

If you talk about the flow, laminar flow, the turbulent flow, and transitional flow... which is in between. When the flow changes from the laminar to turbulence you will have a certain range.

This section clarifies the differences between laminar, turbulent, and transitional flows. Laminar flow is smooth and orderly, where layers slide past each other, while turbulent flow is chaotic, with eddies and fluctuations. Transitional flow occurs when the flow shifts from laminar to turbulent. Recognizing these flows is critical in applications ranging from flowing water in pipes to atmospheric flows.

Think of a smooth river (laminar flow) where water flows gently and silently. In contrast, a rapidly flowing river filled with white rapids represents turbulent flow. Transitional flow might occur when a smooth river suddenly hits a rocky section, creating chaotic movements of water.

Now let have a very interesting concept is that when you talk about a fluid flow systems and as I talk about that density is a mass of the fluid per unit volume... then we can say that this is what it happens it very different flow process.

This chunk discusses compressible and incompressible flow based on density changes. Compressible flows can have significant changes in density, especially at high speeds, while incompressible flows do not exhibit notable density changes. Most engineering problems can often be simplified assuming incompressibility unless dealing with high-speed flows, like jet propulsion.

Imagine blowing up a balloon (compressible flow) where the air inside can greatly change volume (density). In contrast, filling a water bottle (incompressible flow), where the water's density and volume remain relatively constant under normal conditions.

When you talk about any flow systems that flow is having a three dimensions okay... we can simplify this is a one dimensional, two dimensional or the three dimensional flow.

This section explains that fluid flows can be categorized as one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D), depending on the complexity of the velocity components involved. Simplifying flow to lower dimensions can make solving fluid dynamics problems more manageable.

Picture a straight river (1D flow) where water flows in one direction. If the river bends and has variations in depth and width (2D flow), you’ll need to consider those changes. Finally, during a rainstorm, water may flow everywhere – in depth, width, and length (3D flow), adding complexity to our calculations.

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