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AERODYNAMICS BEHAVIOUR OF PERSONA CAR USING COMPUTATIONAL FLUID DYNAMICS (CFD)

MOHD SHAIFULLAH BIN SHAHRUDDIN

Report submitted in fulfilment of the requirements for the award of the degree of

Bachelor of Mechanical Engineering with Automotive Engineering

Faculty of Mechanical Engineering UNIVERSITI MALAYSIA PAHANG

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i

SUPERVISOR’S DECLARATION

I hereby declare that I have checked this project and in my opinion, this project is adequate in terms of scope and quality for the award of the degree of Bachelor of Mechanical Engineering with Automotive Engineering.

Signature :

Name of Supervisor : MUHAMAD ZUHAIRI SULAIMAN Position : Lecturer

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ii

STUDENT’S DECLARATION

I hereby declare that the work in this project is my own except for quotations and summaries which have been duly acknowledged. The project has not been accepted for any degree and is not concurrently submitted for award of other degree.

Signature :

Name : MOHD SHAIFULLAH BIN SHAHRUDDIN ID Number : MH06041

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iii

To my beloved father mother Shahruddin bin Ahmad

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iv

ACKNOWLEDGEMENTS

First of all, I want to thank The Almighty Allah SWT for the beautiful life that has been given to me in the past 22 years and the present. I am very thankful to be given the time and chances to finally complete this research. I am grateful and would like to express my sincere gratitude to my supervisor Mr. Muhamad Zuhairi Sulaiman for his brilliant ideas, invaluable guidance, continuous encouragement and constant support in making this research possible. He has always impressed me with his outstanding professional conduct, his strong conviction for science, and his belief that a Bachelor program is only a start of a life-long learning experience. I appreciate his consistent support from the first day I applied to PSM course to these concluding moments. I am truly grateful for his progressive vision about my work progressing, his tolerance of my naive mistakes, and his commitment to my future career. I also would like to express very special thanks again to my supervisor for his suggestions and co-operation throughout the study. I also sincerely thanks for the time spent proofreading and correcting my many mistakes.

I also would like to express my gratitude to the Faculty of Mechanical Engineering and Universiti Malaysia Pahang, for their assistance in supplying the relevant literatures.

I am also obliged to express my appreciation towards my beloved mom and dad and also my family members for their enduring patience, moral and financial supports. My fellow friends should also be recognised for their support. My sincere appreciation also extends to all my colleagues and others who have provided assistance at various occasions. Their views and tips are useful indeed. Unfortunately, it is not possible to list all of them in this limited space. Thank you to all. Thank you for everything. May God bless all of you.

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v

ABSTRACT

An aerodynamic characteristic of a car is of significant interest in reducing car accidents due to wind loading and in reducing the fuel consumption. On the limitations of conventional wind tunnel experiment and rapid developments in computer hardware, considerable efforts have been invested in the last decade to study vehicle aerodynamics computationally. This report presents a numerical simulation of flow around Proton Persona car using commercial fluid dynamics software FLUENT for 2D simulation and COSMOSFloWorks for 3D simulation. The study focuses on CFD-based lift and drag coefficient prediction on the car body and the air flow pattern around the car body using Computational Fluid Dynamics (CFD) software. A three dimensional computer model of a Proton Persona was used as the base model in this study. The wind speed selected in this study ranges from 80 km/hr to 140 km/hr with increment of 20 km/hr. After numerical iterations are completed, the aerodynamic data and detailed complicated flow behaviour are visualized clearly. The drag and lift coefficient of Proton Persona have been estimated by using a mathematical equations. The pressure and velocity distributions along the surface of the car also have been analyzed. From the results obtained, it was found that highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest. Therefore it satisfies the Bernoulli's principle. In addition, the flow pattern around the model showed very similar with the previous works, emphasizing in findings.

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vi

ABSTRAK

Ciri aerodinamik sesebuah kereta adalah sangat penting dalam pengurangan kadar kemalangan kereta yang disebabkan oleh beban angin dan dalam mengurangkan penggunaan minyak. Oleh sebab terdapat had-had bagi eksperimen terowong angin konvensional dan pembangunan pantas dalam perkakasan komputer, ikhtiar yang banyak telah dilaburkan dalam dekad yang lalu untuk mengkaji aerodinamik kenderaan secara pengkomputeran. Laporan ini membentangkan satu penyerupaan berangka aliran sekitar kereta Proton Persona menggunakan perisian komersial dinamik bendalir FLUENT untuk simulasi 2D dan COSMOSFloWorks untuk simulasi 3D. Kajian itu menumpukan pada ramalan pekali daya angkat dan seretan pada badan kereta dan corak aliran udara sekitar badan kereta itu menggunakan perisian Computational Fluid Dynamics (CFD). Satu model komputer tiga dimensi, Proton Persona telah digunakan sebagai model asas dalam kajian ini. Kelajuan angin yang pilih dalam julat kajian ini adalah daripada 80 km/jam hingga 140 km/jam dengan tambahan setiap 20 km/jam. Selepas iterasi berangka siap, data aerodinamik dan sifat aliran rumit yang terperinci dipaparkan dengan jelas. Pekali seretan dan daya angkat Proton Persona telah dianggarkan dengan menggunakan persamaan matematik. Pengagihan tekanan dan halaju sepanjang permukaan kereta itu juga telah dianalisis. Daripada keputusan yang diperolehi, didapati kelajuan tertinggi itu berlaku di mana tekanan terendah, dan kelajuan terendah berlaku di mana tekanan tertinggi. Oleh itu ia memuaskan prinsip Bernoulli. Seperkara lagi, corak aliran sekitar model itu menyerupai dengan kajian terdahulu, mengukuhkan lagi penemuan.

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vii TABLE OF CONTENTS Page SUPERVISOR’S DECLARATION i STUDENT’S DECLARATION DEDICATION ii iii ACKNOWLEDGEMENTS iv ABSTRACT v ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xiii

LIST OF ABBREVIATIONS xiv

CHAPTER 1 INTRODUCTION

1.1 Project Background 1

1.3 Problem Statement 2

1.3 Objectives 2

1.4 Scopes of Study 2

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction 3

2.2 History Of Automotive Aerodynamics Technology 3

2.3 Aerodynamics Theory 2.3.1 Bernoulli’s Theorem

5 5

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viii 2.4 2.3.2 Aerodynamics Drag 2.3.3 Aerodynamics Lift 2.3.4 External Flow 2.3.5 Pressure Distributions 2.3.6 Separation Flow

2.3.7 Formation of Vortex Shedding Turbulent Models

2.4.1 Classification of Turbulent Models

2.4.2 Reynolds-Averaged Navier-Stokes (RANS) Models 2.4.3 Computation of Fluctuating Quantities

2.4.4 Governing Equations 7 8 9 10 12 13 14 14 14 15 15 2.5 Computational Fluid Dynamics (CFD)

2.5.1 Definition

2.5.2 Advantages and Disadvantages 2.5.3 Elements 2.5.4 CFD in Automotive Industry 17 17 18 19 19 CHAPTER 3 METHODOLOGY 3.1 Introduction 20 3.2 3.3

Flow Chart Methodology Modelling Geometry 21 22 3.4 3.5 2D Simulation Setup 3.4.1 Mesh Generation 3.4.2 Fluent Setup

3.4.3 Defining the Models 3.4.4 Solver

3.4.5 Viscous

3.4.6 Defining the Material Properties 3.4.7 Boundary Conditions

3.4.8 Executing the Fluent Code 3D Simulation Setup

3.5.1 COSMOS FloWorks setup 3.5.2 Frontal Area 23 23 24 24 25 25 25 26 26 27 27 29

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ix

CHAPTER 4 RESULTS AND DISCUSSION

4.1 Introduction 30

4.2 Calculation of Reynolds Number 31

4.3 2D Analysis Result

4.3.1 Drag and Lift Analysis

4.3.2 Sample Calculation for Drag and Lift Coefficient 4.3.3 Pressure, Velocity and Flow Pattern Analysis 4.3.4 Pressure Distribution Analysis

33 33 36 37 41 4.4 3D Analysis Result

4.4.1 Important Parameter of flow analysis 4.4.2 Data Collection and Analysis

4.4.3 Sample Calculation for Drag and Lift Coefficient 4.4.4 Contour Plot of Velocity and Pressure

4.4.5 Flow Trajectories of Velocity Analysis

42 42 42 46 47 49 CHAPTER 5 CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion 53

5.2 Further Study Recommendations 54

REFERENCES 55

APPENDICES 56

A1 Gantt Chart for FYP 1 56

A2 Gantt Chart for FYP 2 56

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x

LIST OF TABLES

Table No. Title Page

3.1 Variables and convergence criteria for FLUENT simulation of free layers apparatus.

27

4.1 Table of various velocities, drag and lift data 33

4.2 Table of various velocities and percentages of CDand CL

changes (2D)

35 4.3 Data collection for analysis with various velocities 42 4.4 Table of various velocities and percentages of CDand CL

changes (3D)

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xi

LIST OF FIGURES

Figure No.

Title

Page

2.1 History of vehicle dynamic in passenger car 4

2.2 Venturi Effect 6

2.3 Flow around a vehicle (schematic) 10

2.4 Flow field and pressure distribution for a vehicle-shaped body in two-dimensional flow (schematic)

10

2.5 Separation of the boundary layer flow at a wall (schematic) 12

2.6 Major locations of flow separation on a car 13

2.7 Regimes of flow around circular cylinder 14

2.8 Car Aerodynamic Simulation 19

3.1 Flow Chart Methodology 21

3.2 Drawing of Proton Persona 22

3.3 Computational grid for FLUENT CFD modeling 24

3.4 Computational domain and boundary condition 28

3.5 Grid refinement around the Proton Persona model 28

3.6 The frontal area of Proton Persona 29

4.1 Variation of CDover speed range of Persona car 33

4.2 Variation of CLover speed range of Persona car 34

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xii 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19

The pressure contour with several of velocities inlet The velocity contour with several of velocities inlet Separation flow at the front end of Persona car

Reattachment flow at the front edge hood of Persona car Reverse flow and vortex generation at rear end of the Persona car

The pressure distribution along the Persona car at velocity 80 km/h

Graph of drag coefficient, CDagainst various velocities

Graph of lift coefficient, CLagainst various velocities

Graph of the CDand CLpercentage changes against velocity

The velocity contour with several of velocities inlet The pressure contour with several of velocities inlet

The isometric view of trajectories velocity flow of 140 km/h The side view of trajectories velocity flow of 140 km/h Separation flow at the front end of the car

Reattachment flow at the roof of the car

Reverse flow and vortex generation at the rear end of the car

37 38 39 39 40 41 43 44 45 47 48 49 50 50 51 52

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xiii LIST OF SYMBOLS A Area CD Drag Coefficient CL Lift Coefficient p Pressure ρ Density v Velocity FD Drag Force FL Lift Force μ Dynamic Viscosity CP Pressure Coefficient p∞ Initial Pressure v∞ Initial Velocity

k Turbulence kinetic energy ε Kinetic energy dissipation rate τij Shear-stress tensor

Sij Shearing-rate tensor

σk Prandtl number of the turbulence kinetic energy

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xiv

LIST OF ABBREVIATIONS

2-D Two Dimensional

3-D Three Dimensional

CAD Computational Aided Design CFD Computational Fluid Dynamics DNS Direct numerical simulation DSM Differential stress models EVM Eddy-viscosity models FYP Final year project LES Large-eddy simulation

NLEVM Non-linear eddy-viscosity models RANS Reynolds-Averaged Navier-Stokes Re Reynold Number

RNG Renormalization Group

RSTM Reynolds-stress transport models SOC Second-order closure models

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CHAPTER 1

INTRODUCTION

1.1 PROJECT BACKGROUND

This project is about to study and analysis aerodynamics behaviour of Persona Car using Computational Fluid Dynamics (CFD). This project involves drawing and simulating a geometrical model of Proton Persona by using aerodynamic simulation software. By the end of the project, we should be able to determine aerodynamic lift, drag and flow characteristics of the car. Actually, there are other methods to analysis aerodynamic behavior of a car such as wind tunnel but for this project the analysis is based on aerodynamic simulation software.

Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Understanding the motion of air (often called a flow field) around an object enables the calculation of forces and moments acting on the object. Typical properties calculated for a flow field include velocity, pressure, density and temperature as a function of position and time. In automotive field, the study of the aerodynamics of road vehicles is very important. The main concerns of automotive aerodynamics are reducing drag (though drag by wide wheels is dominating most cars), reducing wind noise, minimizing noise emission and preventing undesired lift forces at high speeds. For some classes of racing vehicles, it may also be important to produce desirable downwards aerodynamic forces to improve traction and thus cornering abilities.

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1.2 PROBLEM STATEMENT

The study of aerodynamics in the automotive industry is important to improve fuel economy as well as vehicle comfort and safety. Instead of wind tunnel testing which is high in cost, the alternative method to study aerodynamics by using Computational Fluid Dynamics (CFD). CFD is widely use by researchers to apply in various type of field. This technology provide enormous amount of information as well as high economical efficiency. It is also very useful for initial prediction of new design of a vehicle. The problem about this project is to analysis aerodynamic characteristic such as aerodynamic drag, lift and flow behavior of Proton Persona car by using CFD software.

1.3 OBJECTIVES

1. To estimate the drag coefficient, CD and lift coefficient, CL of the Persona car. 2. To study the air flow behavior around the body of Proton Persona car using

Computational Fluid Dynamics (CFD) software. 1.4 SCOPES OF STUDY

The scopes of this project covered study and analyses the drag and lift coefficient and also the flow behaviour of Proton Persona using CFD software. The model geometry will be created using CAD software, SolidWorks. The analysis of this model geometry will be based on 2-D and 3-D simulations which will be developed using two different softwares which are FLUENT 6 and COSMOSFloWorks respectively. The simulations only involve the external flow of the car.

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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

In this chapter, the explanations and some history of aerodynamics, theories, the previous research and findings are included. With reference from various sources such as journal, thesis, reference books, literature review has been carried out to collect all information related to this project. CFD software and performing analysis by this software also described.

2.2 HISTORY OF AUTOMOTIVE AERODYNAMICS TECHNOLOGY

Aerodynamics and vehicle technology have merged only very slowly. A synthesis of the two has been successful only after several tries. This is surprising since in the neighboring disciplines of traffic technology, naval architecture, and aeronautics the cooperation with fluid mechanics turned out to be very fruitful. Of course, the designers of ships and airplanes were in a better position. They found their originals in nature from fish and birds. From these natural shapes they took many essential features. The automobile had no such originals. Hence its designers tried to borrow shapes from ships and airplanes, which must have appeared progressive to them. Very soon this turned out to be the wrong approach. Only when it broke away from these improper originals did aerodynamics make a breakthrough in the automobile.

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Another reason for the early repeated failures of aerodynamics with vehicles is that it started far too early. The first automobiles were pretty slow. On the bad roads of those days streamlined bodies would have looked ridiculous. Protecting driver and passengers from wind, mud and rain could be accomplished very well with the traditional design of horse-drawn carriages. Later the prejudice that streamlined bodies were something for odd persons overrode the need for making use of the benefits of aerodynamics for economical reasons.

A brief overview of the history of vehicle aerodynamics is summarized in Figure 2.1. During the first two of the total four periods, aerodynamic development was done by individuals, most of them coming from outside the car industry. They tried to carry over basic principles from aircraft aerodynamics to cars. Later, during the remaining two periods, the discipline of vehicle aerodynamics was taken over by the car companies and was integrated into product development. Since then, teams, not individual inventors, have been (and are) responsible for aerodynamics.

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The first automobile to be developed according to the aerodynamic principles was a torpedo-shaped vehicle that had given it a low drag coefficient but the exposed driver and out of body wheels must have certainly disturbed its good flow properties. However they ignored the fact that the body was close to the ground in comparison to aircrafts and underwater ships flown in a medium that encloses the body. In a car like this, the ground along with the free-standing wheels and the exposed undercarriage causes disturbed flow.

As the years pass the studies on aerodynamic effects on cars increase and the designs are being developed to accommodate for the increasing needs and for economic reasons. The wheels developed to be designed within the body, lowering as a result the aerodynamic drag and produce a more gentle flow. The tail was for many years long and oddly shaped to maintain attached the streamline. The automobiles became developed even more with smooth bodies, integrated fenders and headlamps enclosed in the body. The designers had achieved a shape of a car that differed from the traditional horsedrawn carriages. They had certainly succeeded in building cars with low drag coefficient [1]. 2.3 AERODYNAMICS THEORY

2.3.1 Bernoulli’s Theorem

Bernoulli’s theorem implies that if the fluid flows horizontally so that no change in gravitational potential energy occurs, then a decrease in fluid pressure is associated with an increase in fluid velocity. If the fluid is flowing through a horizontal pipe of varying cross-sectional area, for example, the fluid speeds up in constricted areas so that the pressure the fluid exerts is least where the cross section is smallest. This phenomenon is sometimes called the Venturi Effect (Figure 2.2), after the Italian scientist G.B. Venturi (1746–1822), who first noted the effects of constricted channels on fluid flow [1].

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Figure 2.2: Venturi Effect [1].

Bernoulli's principle can be applied to various types of fluid flow, resulting in what is loosely denoted as Bernoulli's equation (Eq. 2.1). In fact, there are different forms of the Bernoulli’s equation for different types of flow. The simple form of Bernoulli's principle is valid for incompressible flows (most liquid flows) and also for compressible flows (gases) moving at low Mach numbers. More advanced forms may in some cases be applied to compressible flows at higher Mach numbers.

p + 1

2ρv

2 = constant (2.1)

Where the p, ρ, v are pressure, density and velocity, respectively.

Bernoulli's principle is equivalent to the principle of conservation of energy. This states that in a steady flow the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remain constant. If the fluid is flowing out of a reservoir the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit mass (the sum of pressure and gravitational potential ρgh) is the same everywhere.

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Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.

2.3.2 Aerodynamics Drag

The force on an object that resists its motion through a fluid is called drag. When the fluid is a gas like air, it is called aerodynamic drag (or air resistance). When the fluid is a liquid like water it is called hydrodynamic drag. Drag is a complicated phenomena and explaining it from a theory based entirely on fundamental principles is exceptionally difficult.

Fluids are characterized by their ability to flow. In semi-technical language, a fluid is any material that can't resist a shear force for any appreciable length of time. This makes them hard to hold but easy to pour, stir, mix, and spread. As a result, fluids have no definite shape but take on the shape of their container. Fluids are unusual in that they yield their space relatively easy to other material things at least when compared to solids.

Fluids may not be solid, but they are most certainly material. The essential property of being material is to have both mass and volume. Material things resist changes in their velocity and no two material things may occupy the same space at the same time. The portion of the drag force that is due to the inertia of the fluid is the resistance to change that the fluid has to being pushed aside so that something else can occupy its space is called the pressure drag [1].

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8 Cd= Fd 1 2ρv2A (2.2) Where Fd = Drag force Cd = Drag coefficient

ρ = fluid density A = frontal area v = Velocity

2.3.3 Aerodynamics Lift

Lift is normally of little importance in passenger cars as their speed is usually too low to produce much lift. It was noticed early on that something strange happened at high speeds: the car seemed to be lifting off the ground. Lift can be serious, particularly in racing cars. It has a serious effect on the control and handling of the car [1].

Lift occurs because the airflow over the top of a car is faster than across the bottom. This occurs to some degree in all cars. As the speed increases, the pressure decreases, according to Bernoulli’s theorem. The top of the car therefore has a lower pressure than the bottom, and the result is a lifting force.

The amount of lift generated by an object depends on a number of factors, including the density of the air, the velocity between the object and the air, the viscosity and compressibility of the air, the surface area over which the air flows, the shape of the body, and the body's inclination to the flow, also called the angle of attack.

CL= FL 1 2ρV 2 A (2.3) Where FL = lift force CL = Lift coefficient

ρ = fluid density A = frontal area v = Velocity

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2.3.4 External Flow

The external flow around a vehicle is shown in Figure 2.3. In still air, the undisturbed velocity v∞ is the road speed of the car. Provided no flow separation takes

place, the viscous effects in the fluid are restricted to a thin layer of a few millimeters thickness, called the boundary layer. Beyond this layer the flow can be regarded as inviscid, and its pressure is imposed on the boundary layer. Within the boundary layer the velocity decreases from the value of the inviscid external flow at the outer edge of the boundary layer to zero at the wall, where the fluid fulfills a no-slip condition. When the flow separates (Figure 2.3 shows separation at the rear only) the boundary layer is “dispersed” and the flow is entirely governed by viscous effects. Such regions are quite significant as compared to the characteristic length of the vehicle. At some distance from the vehicle there exists no velocity difference between the free stream and the ground. Therefore, in vehicle-fixed coordinates, the ground plane is a stream surface with constant velocity V∞,

and at this surface no boundary layer is present. This fact is very important for the simulation of flows around ground vehicles in wind tunnels. The boundary layer concept is valid only for large values of

Rel= ρvL µ >10 4 (2.4) This dimensionless parameter is called the Reynolds number. It is a function of the

speed of the vehicle v, the viscosity µ and density ρ of the fluid, and a characteristic length as defined in Figure 2.3. The character of the viscous flow around a body depends only on the body shape and the Reynolds number. For different Reynolds numbers entirely different flows may occur for one and the same body geometry. Thus the Reynolds number is the dimensionless parameter which characterizes a viscous flow.

References

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