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# Basics of Compressible Fluid Flow

“Compressible fluid” is known as those fluids if its density varies with pressure caused by the flow. If density does not change or changes slightly then it is known as an "incompressible fluid".

“Compressible or incompressible fluid” is a subject of gas dynamics or chemical engineering. This is often considered to be the branch of “fluid mechanics”. Fluids are classified into two forms such as “compressible and incompressible fluid”. There is no significant change in density as “incompressible fluid flow”. Generally, fluids(Liquid) are considered to be “incompressible”. Water is a perfect example of “incompressible fluid”.

## Fluid flow

Particular types of fluids deal with fluid statistics and different fluid dynamics. Fluid is not stationary; it is always in motion. Fluid flow is a subject of “fluid mechanics” and is particularly related to “fluid dynamics”. In general, fluid flow is motion or movement of fluid that is due to numerous unbalanced forces. Fluid continues to be in motion until all unbalanced forces are applied to it.

## Types of fluid flow

Whenever a fluid is in motion it has certain characteristics, nothing but the fluid has a certain amount of volume, density, pressure, direction, and velocity. Based upon these characteristics of fluid, fluid is divided into certain types:

In case of “steady flow”, fluids have certain sorts of attributes such as pressure, density, volume, and velocity. All these physical characteristics of fluids remain constant with respect to time in a fluid flow at a given point v. For example, we can take flow of fluid through a pipe which is having pressure or has a density and has no velocity so that the flow of fluid through the pipe is having the same cross-sectional area from inlet to outlet. Note that, there will be no change in the physical properties of fluid over the period of time. So this type of fluid is termed as “steady flow”. In case of “unsteady flow”, all these physical characteristics can change with respect to time, that is why it is termed as “unsteady flow”.

### Uniform and non-uniform flow:

In case of “uniform flow,” the particular flowing fluid is having a certain amount of velocity which is proportionally greater than the flowing fluid. The condition of the uniformity or non-uniformity of fluid flow can be stated as:

### Flowing fluid >> Velocity

If the velocity of a fluid is constant over the period of time, then it is termed as “uniform flow”. If the velocity of fluid does not change over a period of time, then it is termed as “non-uniform flow”. For example, let us consider a pipe that has the same cross-sectional area from inlet to outlet. In this case, suppose it tapered cross-section so when a particular fluid flows through the pipe then the pressure at inlet will not be equal to pressure at outlet. It means the velocity of inlet and outlet is not equal so the flow becomes “non-uniform flow”. “Uniform flow” only deals with velocity of flowing fluid. If the velocity of a fluid is constant over a period of time, then flow is uniform, if velocity is not constant over period, then flow is non-uniform.

### Laminar and turbulent flow:

In case of “laminar flow”, a particular flow is having a length of all the particles in flowing fluid moves in a straight line. It follows a straight path that does not cross over another. In this case, flow is having layers that do not interchange or overlap over another. For “laminar flow”:

### Flowing fluid >> All particles are in a straight line

In case of “turbulent flow” fluid particles overlap over another and cross each other’s path. Due to that, turbulence occurs in fluid. In this case, particular fluid particles form voltages or they cross each other’s boundaries, this is an irregular type of fluid flow.

## Compressible flow

As the name indicates, such sorts of fluid can be compressed. It means density of fluid particles or density of flowing fluid changes with respect to time. Density of flowing fluid can be altered over a period and it becomes compressible. Dentistry plays a crucial role here in determining compressibility of a particular fluid.

## Incompressible flow

In case of “incompressible fluid”, density of flowing fluid does not change with respect to time. Most of the fluids or all the fluids are “perfectly incompressible” in nature. In the case of “Pascal’s Law”, “incompressible fluid” is taken into consideration. Compressibility is related to flow of gases through the duct. The gases can be compressed but fluid cannot be compressed. Therefore, fluid or liquid is perfectly incompressible.

### Conclusion

Imagine a world where flow does not take place and it would be so different. Flows of fluids are very essential for natural phenomena. Flow of fluids can take place in liquids as well as in gases. The flow of fluid takes place due to the movement of particles and unbalanced forces. Unbalanced forces create motion in fluids until it is applied to them. Fluids have certain types of characteristics and based on that; fluids are classified into different types. These characteristics differ in each classification of fluids. Density changing over time is different from “compressible and incompressible fluid”. All fluids are “incompressible fluids” in nature.

Get answers to the most common queries related to the GATE Examination Preparation.

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