5.2. Introduction to Flow Analysis

First let us talk what is the system, what is the control volume. The system is a quantity of matter or the region in a space chosen for the study. For example, I have considered a 2 kg of gas which is having 1 meter cube volumes. And if I heat this gas, if I give a temperature to this gas, then what will happen? This gas will be expanded. So this is a system, that means we have a fixed amount of the mass of gas we consider it is a system and this system has a boundary and the surroundings.

In fluid mechanics, a 'system' refers to a specific amount of fluid or matter that we study to analyze its behaviors and properties. For instance, if we take 2 kg of gas contained in 1 cubic meter and heat it, we observe the gas expanding. This expansion is due to the energy added to the gas, which increases its temperature and affects its volume. The 'boundary' is the surface enclosing this gas, separating it from its surroundings, which can change when the gas expands. Understanding systems helps us explore how fluids react under different conditions.

Think of a balloon filled with air. The air inside the balloon represents the system, while the rubber of the balloon acts as the boundary. If you heat the balloon (like warming it in the sun), the air warms up, expands, and can even cause the balloon to pop if the pressure exceeds the elasticity of the boundary.

But many of the times we cannot solve the problems within system approach which in generally follow in thermodynamics. But in case of the fluid flow problems, we go for a space defined by a particular volume, okay. Like for example, I have this problem. If you look it this is what my control volume. This is the space what I have considered as a control volume and the fluid is coming from this sides and this piston is moving in this conditions.

In fluid flow analysis, we often use the concept of a 'control volume.' This is a defined space where we can analyze fluid flow and its interactions with boundaries. Unlike a system, which is a fixed quantity of matter, a control volume can adjust to changing conditions, allowing for mass, energy, and momentum to flow in and out from its boundaries. This flexibility makes it easier to apply the conservation laws that are crucial in analyzing fluid behavior.

Imagine a water tank with an inlet pipe for filling and an outlet pipe for draining. The tank represents the control volume. As water flows in and out, we can study the levels, pressures, and velocities to understand the behavior of water in different scenarios, such as changing the inlet speed or the tank size.

So we have a control volume the fixed regions or the movable regions on the space that what we consider it and it is confined by the surface we call the control surface. That is what the control surface. The control surface can be a fixed surface or can be a movable boundary conditions.

The 'control surface' acts as the boundary for our control volume. This surface can either be fixed in place or it can move, which is important for analyzing dynamic systems. Understanding whether our control surface is fixed or flexible helps determine how we model the fluid flow, especially in situations where the flow interacts with moving machinery (like pistons or fans).

Consider a suitcase on a conveyor belt (the suitcase is the control volume). While the suitcase remains in one location on the belt (fixed surface), the belt moves underneath it, which is akin to a moving boundary. If you were to open it, things on the inside (pressure, items) interact with the environment outside the suitcase, similar to how fluids move across control surfaces.

Then I will give a very interesting examples of a bird under the wind flow conditions. Then we will talk about what type of flow analysis techniques are available and how we solve very complex flow problems using these analysis techniques.

Flow analysis techniques include methods to study how fluids (like air or water) move and interact with objects. These techniques can help us understand real-life scenarios, such as how a bird can remain on a branch while facing wind or how engineers design structures that withstand wind forces. Methods include theoretical calculations, numerical simulations, and experiments, each offering valuable insights depending on the situation.

Consider a kite flying in the wind. Engineers can analyze the kite’s shape and stability using flow analysis techniques to ensure it stays airborne. By assessing wind speed and direction, they can predict the necessary adjustments to keep it flying steadily, similar to how birds manage their position against the force of wind.

--