Laminar, Turbulent and Vortex Flow

1.    INTRODUCTION

 

The flow past a two-dimensional cylinder is one of the most studied aerodynamics. It is relevant to many engineering applications. Flow over a cylinder is a classical problem for understanding the flow over an obstacle. The geometry of the cylinder is simple and allows us to understand all the complexities that occur and turbulence for different Reynolds Numbers. Reynolds Number helps us to understand the flow patterns of the different fluid flow situations.

The different range of Reynolds Numbers represents different flow patterns. At low Reynolds Numbers, the flow pattern is observed to be Laminar i.e., Smooth, Constant fluid motion. At higher Reynolds Numbers the flow pattern is observed to be Turbulent i.e., Chaotic eddies, Vortices, and Flow instabilities. In this project, we will try to understand the variation of velocity and pressure in certain flow directions for different Reynolds Numbers by simulating it with proper boundary conditions, Mesh sizing, and Convergence criteria using SolidWorks Flow Simulation.

 

 

2.     CONCEPT OF FLOW AND ITS TYPES

Flow refers to the motion of a fluid, either a liquid or a gas, from one location to another. In fluid mechanics, flow is analyzed in terms of its velocity, pressure, and temperature, as well as its effect on surrounding objects and the environment. The study of flow is important in a variety of applications, including aerodynamics, hydrodynamics, heat transfer, and many others, as it is crucial for understanding the behavior of fluids in different conditions and systems.

2.1  Types of flow as follows:-

a)     Laminar flow

b)    Turbulent Flow

c)     Vortex flow

 

3.     CONCEPT OF REYNOLDS NUMBER

Fluid-dynamics difficulties depend on the kind of flow that a fluid experiences in a channel, which in turn impacts how heat and mass are transferred in fluid systems. An essential factor in the equations determining whether fully developed flow conditions result in laminar or turbulent flow is the dimensionless Reynolds number. No of the size of the fluid system, the Reynolds number measures how fast the fluid is moving relative to how viscous it is. It is the ratio of the inertial force to the shearing force of the fluid. Laminar flow typically happens when a fluid is exceedingly viscous or moving slowly. The flow will change from laminar to turbulent when the Reynolds number rises, for example by raising the fluid's flow rate.

The geometry of the flow system and flow pattern will determine the precise calculation of the Reynolds number and the values at which laminar flow occurs. The Reynolds number is established using the usual example of flow through a pipe as

·     Mathematical Reynolds Number Equation:-

 

Where,

Re = Reynolds Number,

 = Density of the Fluid,

  = Dynamic Viscosity,

 v = Velocity of the Fluid,

 D = Diameter of the tube or the Cylinder,

V = Kinematic Viscosity.

 

 

4.     LAMINAR FLOW

 Laminar flow is a type of flow that occurs when fluid particles follow clean courses in layers, passing each other without much or any mixing between them. Adjacent layers tend to glide past one another like playing cards at low velocities where the fluid tends to flow without lateral mixing. There are no eddies, swirls, or cross-currents that run parallel to the flow direction. In laminar flow, fluid particles move in a very ordered manner, traveling in straight lines parallel to a solid surface when they are close to it. Low momentum convection and high momentum diffusion are the two characteristics of laminar flow.

·        The characteristics of laminar flow are:-

a)     Fluid particles move in parallel, smooth lines

b)    No turbulence or mixing of fluid particles

c)     Low speed and smooth flow

d)    Fluid velocity is constant across the flow direction

e)     Fluid pressure is constant along a streamline

f)      The fluid layer closest to the surface is stationary and the layers get progressively faster as they move away from the surface

g)    Laminar flow is typically observed at low Reynolds numbers, where fluid viscosity is dominant over fluid inertia.

 

·        Examples of the Laminar flow:-

a)     The flow of water in a straight, narrow channel or pipe

b)    The flow of syrup from a bottle

c)     The flow of oil through a fine mesh filter

d)    The flow of air in a wind tunnel

e)     The flow of blood in a healthy blood vessel with smooth walls.

 

 

 

5.     TURBULENT FLOW

Turbulence, also known as turbulent flow, is a fluid motion in fluid dynamics characterized by erratic fluctuations in flow velocity and pressure. In contrast, laminar flow takes place when a fluid moves in parallel layers without any interruptions between them. Turbulence is frequently seen in commonplace phenomena like surf, swiftly moving rivers, billowing storm clouds, and chimney smoke. The majority of fluid flows in nature and those produced by engineering are turbulent: 2 Excessive kinetic energy overcomes the dampening effect of the fluid's viscosity, causing turbulence in certain areas of a fluid flow. Turbulence is frequently observed in low-viscosity fluids as a result. Generally speaking, unstable vortices of various diameters interact in a turbulent flow. In turbulent flow, fluid particles move in a zig-zag and haphazard way. They do not follow any regular pattern while flowing. Individual fluid particles cross one another and exhibit irregular energy losses.

 

·        Turbulent flow is characterized by:-

a)     Irregular and chaotic motion of fluid particles.

b)    Mixing and rapid exchange of momentum, energy, and mass.

c)     Formation of eddies and vortices of varying size and shape.

d)    Increased Reynolds number and decreased laminar flow.

e)     Higher diffusion of substances, such as heat and mass.

f)      Increased frictional resistance and decreased velocity at a given cross-section.

g)    Higher turbulence intensity is defined as the ratio of turbulent kinetic energy to the mean flow kinetic energy.

h)    Non-uniform velocity and pressure distribution.

 

·        Examples of turbulent flow are:-

a)     The flow of water in a rapidly flowing river or stream

b)    The flow of air over a rough surface such as mountains or buildings

c)     The flow of fluid in a pipe with a high Reynolds number, where fluid inertia becomes dominant over fluid viscosity

d)    The flow of air in a room with an open window, where the air is mixing rapidly due to the presence of eddies and vortices

e)     The flow of fluid in a mixing tank, where the fluid is agitated and mixed rapidly due to the presence of turbulence.

 

6.     VORTEX FLOW

A vortex flow is a type of fluid flow characterized by the presence of rotating cylindrical fluid structures, called vortices. These vortices form due to the movement of fluid and the resulting conservation of angular momentum. In a vortex flow, fluid particles move in circular paths around a central axis, causing a swirling motion that can be seen in a smoke or fluid stream.

There are two main types of vortex flow: laminar and turbulent. Laminar vortex flow is characterized by a smooth, orderly flow pattern with no turbulence, while turbulent vortex flow is characterized by chaotic and irregular fluid motion, with the formation of eddies and vortices of varying sizes and shapes.

 

·        The vortex flow is of the following types:-

a)     Forced vortex flow

b)     Free vortex flow

 

(i) Forced Vortex Flow:-

Forced vortex flow is one in which the fluid mass is made to rotate employing some external agency. The external agency is generally mechanical power which imparts a constant torque on the fluid mass. Then, in such a flow there is always an expenditure of energy. The forced vortex motion is also called flywheel vortex or rotational vortex.

In this type of flow, the fluid mass rotates at constant angular velocity. The tangential velocity of any fluid particle is given by:-

V = rω

(Where r = radius of the fluid particle from the axis of rotation)

angular velocity,

ω = v/r = constant

Example;-

a) Rotation of water through the runner of the turbine.

b) Rotation of liquid inside the impeller of the centrifugal pump.

c) Rotation of liquid in a vertical cylinder.

 

(ii) Free Vortex Flow:-

Free vortex flow is one in which the fluid mass rotates without any external impressed contact force the whole fluid mass rotates either due to fluid pressure itself for the gravity or due to rotation previously imparted the free vortex motion is also called as potential vertex or irrotational vortex.

Example:-

a) Flow around the circular bend

b) A whirlpool in a river

c) Flow of liquid in centrifugal pump casing after it has left the impeller

d) Flow of water in turbine casing before it enters the guide vanes.

e) Flow of liquid through a hole or outlet provided at the bottom of a Shallow vessel (eg, wash basin, bathtub, etc)

 

  

7.    A practical Application has been taken for a better understanding of the flows.

 

Applying the simulation of the flow over the cylinder in the practical application will be more useful for conceptual understanding. Therefore, the Circular pillar of the Pune central bridge is taken for the study of the flow over the cylinder.

·     Required Inputs of the Pillar of Pune central bridge:-

a)     Diameter:- 252 cm = 2520 mm.

b)     Material of the Pillar:- Concrete.

c)     Flow type:- Water.

d)     For Flow of Water:- Gravitational Force towards the ‘Z-Axis.

(Image of the circular pillar of the Pune Central Bridge)

 

7.1           Results as Follows:-

(Image 01:- Scale of the velocity)

(Image 02:- Velocity results by simulation, Flow from left to right)

 

(Image 03:- The laminar flow is formed in the red box, the turbulent flow is in the blue circles, and the vortex flow is in the yellow circles.)

 

 

Institute and Group details are as follows:-

Bansilal Ramnath Agarwal Charitable Trust’s

Vishwakarma Institute of Technology

(An Autonomous Institute affiliated to Savitribai Phule Pune University formerly University of Pune)

 

Academic Year:-  2022 – 2023

Department:- Mechanical Engineering

Class:- SEDA

Batch:- 02

Group No.:- 04

Subject:- Fluid Engineering

GROUP DETAILS:-

SR. NO.	NAME OF THE STUDENT	ROLL NO.	PRN NO.
1	Pooja Rajendra Lahare	43	12220138
2	Lavkesh Jagadish salunke	44	12220211
3	Varad Anand Lomte	45	12220179
4	Yash Balasaheb Mali	46	12220205
5	Nishiraj Nitin Mane	47	12220010
6	Kaustubh Vinod Palande	54	12220132