The Different Types of Flow- Laminar, Turbulent & Vortex flow

 The Different Types of Flow-

Laminar, Turbulent & Vortex flow

We will first go through some of the prerequisites in short for a better understanding of our topic- The Types of Flow.

However, what precisely comes under the topic fluids?

Fluid could be defined as a substance that frequently deforms or said to flow below a certain amount of applied shear stress or external force. Fluids include different states of matter namely liquids, gases, and plasmas. These are the substances with properties like zero shear modulus to explain in less complicated terms, they are the substances that can’t resist any external shear force at all. Some of the examples of fluids around us are water, air, blood, etc.

Interesting Fact – Our ear contains a fluid called Endolymph which is responsible for maintaining the balance of our body. And if the position of it is disrupted one gets motion sickness. Isn’t that interesting? Just a tiny amount of liquid affecting us without us knowing.

Now that we have seen what precisely fluids are we are ready to move forward and look at types of fluids. It is important to know which type of fluid we are having before studying its flow type. We’ll look at it in short and in very simple terms.

Types of Fluids: -

Ideal fluid-

A fluid having properties like it can’t be compressed and the viscosity does not fall in the category of an ideal fluid. Of course, it is an imaginary fluid i.e. ideal fluid does not exist in real life. Just like ideal conductors with zero don’t exist.

Real fluid-

Fluids having viscosity all come under liquids. As the name suggests it exists in real life hence called real fluid.

Newtonian fluid-

The fluid obeying Newton’s law of viscosity is known as a Newtonian fluid. Examples of Newtonian fluids are honey, water, etc.

Non-Newtonian fluid-

The fluids that do not obey Newton’s law of viscosity are known as Non-Newtonian fluids. Corn starch solution is an excellent example of Non-Newtonian fluid.

Ideal plastic fluid-

The fluid satisfying the following conditions is designated as ideal plastic fluid: -

·        The shear stress should be proportional to the velocity gradient.

·        Shear stress should be more than the yield value.

If the above conditions are satisfied then they are knowns as ideal plastic fluid.

Incompressible fluid-

If the density of the fluid does not change even when an external force is applied then it is known as an incompressible fluid.

Compressible fluid-

If the density of the fluid changes when an external force is applied then it is known as compressible fluid.

Now, that we are clear with prerequisite concepts we are ready to know everything about types of flows finally.

Types of Flows: -

They are broadly classified into three types (classification is done based on Reynolds Number): -

1.    Laminar Flow

2.    Turbulent Flow

3.    Vortex Flow

Fig. 1

Fig. 1 demonstrates a real-life example depicting smoke of incense stick changing its flows from laminar to turbulent going through the transition phase.

This is still vague and arbitrary we need a more concrete way to distinguish between them. And what is more concrete than mathematical proof. We will look at the mathematical method now.

The differential equations for flow have 2 solutions: either time-independent or time-dependent. In the first condition, the fluid rate is constant in time at every purpose, and therefore the and therefore the is termed laminar. The flow is designated turbulent if the speed changes over time.

For a better understanding of flow, we use visual representation tools and shape is in the form of cylindrical water beam or easier terms one can imagine it as continuous flow through. The smooth part represents laminar flow while rough or random flow represents turbulent flow. The randomness increases with the increase of Reynold’s number.

Reynolds Number and Determination The Flow Types: -

Reynold’s Number is named after Irish scientist Osborne Reynolds. Reynolds number is a dimensionless quantity. It's just a number that is used to predict if the fluid flow is laminar or turbulent depending on several properties such as velocity, length, viscosity, etc. It is expressed as below:

Reynolds Number Calculation Formulae

If its value is less than 2300 the flow is considered laminar and if greater than 4000 the flow is considered turbulent. Between 2300 and 4000 it is considered a transition regime.

Flow type	Reynolds Number Range
Laminar regime	up to Re=2300
Transition regime	2300<Re<4000
Turbulent regime	Re>4000

Laminar, Turbulent And Vortex Flow: -

Laminar Flow:

In Laminar flow, the type of fluid is typically gas or liquid. In this kind of flow, the fluid travels in layers in regular paths in a straight line without cutting each other as shown in the diagram. The laminar flow is also typically called streamline flow because the velocity, pressure, and other flow properties remain constant in the fluid at every point. Laminar flow is often shown as a horizontal surface that may be thought of as of thin layer, or laminae stacked one over the other parallel to each other. Hence, the name Laminar Flow.

Laminar flow is also classified into two types namely:

• Uniform or Axis symmetric – Flow is a streamline as seen in the figure above.

• Non-Uniform Asymmetric – Flow curvature is parabolic as represented in the middle diagram in the picture above.

Laminar flow in a straight cylindrical pipe can be considered as the relative motion between concentric cylinders of fluid, the outside one fixed at the pipe wall and as the center of the pipe is approaches, speeds goes on increasing. Some of the common examples of laminar flow are:

Smoke rising in a straight line from an incense stick is having laminar flow. After rising to a small distance, the smoke usually starts changing to turbulent flow.

Turbulent flow:

In Turbulent flow, the type of fluid is typically gas or liquid. In this kind of flow, the fluid undergoes random fluctuations, or the pathways of individual elements intersect with each other, in contrast to laminar flow in which the fluid moves in layers parallel to each other. In turbulent flow, the velocity, pressure, and other flow properties are continuously changing in both magnitude and direction. 

Turbulent Flow of Water

Boat Wake

The classic examples of Turbulent flow are atmosphere and ocean currents. Besides that, the flow in boat wakes and around aircraft-wing tips are also common examples.

Vortex Flow:

A vortex can be defined as a region in a fluid where the flow revolves around a certain fixed axis line, which may be straight or curved shaped. Vortices form in stirred fluids and will be seen in smoke rings, whirlpools within the wake of a ship, and therefore the winds encompassing a tropical cyclone, tornado, or whirlwind.

Whirlpool

Tornado

In the absence of external forces, viscous friction inside the fluid tends to arrange the flow into a set of irrotational vortices, probably superimposed to larger-scale flows, together with larger-scale vortices. Once created, vortices will move, stretch, twist, and act in complicated ways and can turn horrific. With many software, one can predict the flow if predicted with the right input parameters.

The main advantage of using these softwares is that visual representation tends to better illustrate a subject. The descriptive images help to describe the crucial definition of fluid flowing very easy way. The importance of the principle of Reynolds Number, which aids in the determination of flow forms, is also highlighted.

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