CFD-CH01-Rao-2021-1.pdf

Computational Fluid Dynamics
(研-PE6123-021-M01)
School of Mechanical Engineering, Shanghai Jiao Tong University
Prof. Dr. RAO Yu (饶宇)

Lecture Instructor: Prof. Dr. RAO Yu (饶宇)
Institute of Turbomachinery,
Dept. Mechanical Engineering,
Shanghai Jiao Tong University
Office Address: Room 531, Building A
Email: yurao@sjtu.edu.cn
Tel: 021-34205986
助教TA: Mr. LUAN Yong (栾勇) & Ms. LYU Yuexuan (吕玥萱)，
Email: yuexuan.lv@sjtu.edu.cn;
Text book: Computational Fluid Dynamics A Practical Approach, 2nd
Edition (ISBN号: 0750685638)
Fluid Mechanics
Author: Jiyuan Tu, Guan Heng Yeoh, Chaoqun Liu
CANVAS: https://oc.sjtu.edu.cn/courses/25652

Text book: COMPUTATIONAL FLUID DYNAMICS A Practical Approach,
2nd Edition (ISBN号: 0750685638)
Fluid Mechanics
Author: Jiyuan Tu, Guan Heng Yeoh, Chaoqun Liu

Assessment:
Attendance 10%,
Group work 40%,
Final Project Report 50%
There will be no midterm exam and final exam.
The Project work is very important for the lecture.
If you have any questions about the exams, please send me e-mail or ask me
about it in the class.
Students are expected to turn in their own project assignments that are
substantially the result of their own work.
Any kind of cheating on project work will result in a zero grade in this class.

Some introduction
 CFD (Computational Fluid Dynamics (CFD)
--CFD applies numerical methods (called discretization) to develop
approximations of the governing equations of fluid mechanics and the fluid
region to be studied.
Governing differential equations-------algebraic,
The collection of cells is called the grid or mesh.
 The set of approximating equations are solved numerically (on a computer) for
the flow field variables at each node or cell.
System of equations are solved simultaneously to provide solutions.
 The solution is post-processed to extract quantities of interest (e.g. lift, drag,
heat transfer, separation points, pressure loss, etc.).

Page . 6
Page . 6
Computational domain: two cold channels +one hot channel;
Individual modelling and assemble, and export parasolid file.
计算模型（UG建模）

Page . 7
Page . 7
壁面网格的处理 Meshing at the wall
计算模型（ICEM-CFD网格划分）
采用BiGeometric方式进行壁面网格加密。
近壁面网格厚度0.05mm，增长率1.5

Page . 8
Page . 8
改变入口形状（No.2）Inlet Shapes on Velocity Contour
调整通道形状对换热性能的影响

 Today’s engineers are geared more towards the use of commercial CFD softwares (ANSYS, CFX,
Fluent or STAR-CD).
-- A sound knowledge and application in CFD is still required.
 Purpose of this book
-- provide samples to understand descriptions of fundamental CFD theories, basic CFD techniques,
and practical guidelines.
The dominant feature of the present book is to maintain practicality in understanding CFD.
 Now becoming more accessible to graduate engineers for research and development Mastery of
CFD in handling complex flow and heat transfer industrial problems is becoming ever more important.
Steep learning curve for practicing engineers,
-- extreme challenges to come up with solutions to fluid flow and heat transfer problems without a
priori knowledge of the basic concepts and fundamental understanding of fluid mechanics and heat
transfer.

Outlines of the Lecture
 Chapter 1 An introduction to CFD, an overview.
 Chapter 2 CFD Solution Procedure; how a CFD problem is currently handled
and solved.
 Chapter 3 Presents the basic thoughts and philosophy associated with CFD.
 Chapter 4 Deals with the computational solutions, numerical discretization,
SIMPLE algorithm…..
 Chapter 5 Deals with the numerical concepts of stability, convergence,
consistency, and accuracy….
 Chapter 6 Turbulence modeling, ….
 Chapter 7 Illustrate the power of CFD through a set of industrially applications
to a range of engineering disciplines.
 Chapter 8 Advanced CFD techniques.

 1.1 What actually is CFD(Computational Fluid Dynamics)?
it has certainly become a new branch, integrating not only the
disciplines of fluid mechanics with mathematics, but also with computer
science as illustrated in Fig. 1.1.
-- Fluid mechanics, ….
The fluid motion can usually be
described through fundamental
mathematical equations, usually in partial
differential form, which govern a process
of interest.
---- governing equations in CFD.

What Is Computational Fluid Dynamics
Fig 1.1 The different disciplines
contained within computational
fluid dynamics
 In order to solve these mathematical equations,
they are converted by computer scientists using high-
level computer programming languages into computer
programs or software packages.
 The computational part simply means the study of
the fluid flow through numerical simulations.
 And now it is expected that CFD field requires a
person who will proficiently obtain some subsets of
the knowledge from each discipline.
Presenting a step-by-step procedure of initially understanding of physics of fluid
dynamics, developing new mathematical models to represent flow physics, …..

Fig 1.2 The three basic approaches to solve
problems in fluid dynamics and heat transfer
CFD has also become one of the three basic
methods or approaches that can be employed to
solve problems in fluid dynamics and heat transfer.
each approach is strongly interlinked and does not
work in isolation.
 The trend is clearly toward greater reliance on
the computational approach for industrial designs,
particularly when the fluid flows are very complex.

• Theoretical
 Most important branch of fluid dynamics. Crucial in
understanding concepts (Example: L = ρUΓ), Usually good in
predicting trends (Example: δ ~ Re-1/2)
 Can obtain a lot of information using simplifying assumptions,
sometimes enough for detailed design (Example: the SR-71
Blackbird was designed completely using theoretical ideas)
 However, doesn’t always provide sufficient information
• Experimental
 Only way to obtain reliable data in many situations. However,
costly, difficult to achieve exact conditions, difficult to isolate effects,
sometimes difficult to assess error, sometimes not repeatable
• Computational (CFD)
 Becoming important as computers are getting faster and
cheaper. Potential to provide tremendous amount of data at a
fraction of the cost of experiments. But sometimes unreliable
because of numerical/modeling/human errors. Sometimes more
expensive than experiments
 Very important to validate with theory/experiments.

15
Where is CFD used?
Where is CFD used?
― Aerospace
― Appliances
― Automotive
― Biomedical
― Chemical Processing
― HVAC&R
― Hydraulics
― Marine
― Oil & Gas
― Power Generation
― Sports
F18 Store Separation
Wing-Body Interaction Hypersonic Launch
Vehicle
CFD has indeed become a powerful tool to be employed
either for pure or applied research or industrial applications.

Example of CFD results for applications in aerospace and defense industries

17
Marine
Where is CFD used?
― Aerospace
― Appliances
― Automotive
― Biomedical
― HVAC&R
― Hydraulics
― Marine
― Oil & Gas
― Sports
Model 5415 Steady Flow RANS Simulation
Velocity contours & vectors in propeller plane
and velocity contours on free surface
Fr=0.28, Re=1.38x107
CFDSHIP-IOWA v3.0
Velocity=0.1

1.2 ADVANTAGES OF COMPUTATIONAL FLUID DYNAMICS
 With the rapid advancement of computers, CFD remains at the forefront
of cutting edge research in sciences of fluid dynamics and heat transfer.
 Many advantages in considering computational fluid dynamics:
1. The theoretical development of the computational sciences focuses on the construction
and solution of the governing equation, and the study of various approximations to these
equation.
2. CFD complements experimental and analytical approaches by providing an alternative
cost-effective means of simulating real fluid flows.
3. CFD has the capacity of simulating flow conditions that are not reproducible in
experimental tests found in geophysical and biological fluid dynamics.
4. CFD can provide rather detailed, visualized, and comprehensive information when
compared to analytical and experimental fluid dynamics.

 CFD permits alternative designs to be evaluated over a range of
dimensionless parameters that may include Re, Ma, Rayleigh number,…..
 CFD will not soon replace experimental testing as a means to gather
information for design purposes.
-- it is a viable alternative.
-- Wind tunnel testing,……
 In other applications where CFD still remains a relatively primitive state of
development, experiment-based approach remains the primary source of
information.
multiphase flows, boiling, ……..
.

 Readers must also be fully aware of some inherent limitations of applying
CFD.
Numerical errors exist in computations, therefore there will be differences
between the computed results and reality.
 Visualization of numerical solutions using vectors, contours, or animated
movies of unsteady flows are by far the most effective ways of interpreting
the huge data from numerical computation.
-- There is danger that an erroneous solution, which may look good, may
not correspond to the expected flow behavior!!!

PIV Measurements and DES results of dimple flow

Optimization of Blower

1.3 APPLAICATION OF COMPUTATIONAL FLUID DYNAMICS
AS A RESEARCH TOOL
CFD can be employed to better understand the physical events or processes that occur in
the flow of fluids around and within the designated objects.
CFD, analogous to wind-tunnel tests, can be employed as a research tool to perform
numerical experiments. As illustrated in Fig1.3, Fig 1.4
Fig 1.3 Example of a CFD numerical experiment for a flow past two side-by-side cylinders.
(a) Experimental observation (b) Numerical simulation
a b

1.4 Example of another CFD numerical experiment for a flow past three side-by-side cylinders.
(a) Experimental observation, (b) Numerical simulation on a two-dimensional cross-sectional plane
and (c) Three-dimensional representation of the fluid flow through numerical simulation
a b
c
Numerical computation can provide
more comprehensive information
and details of the flow as visualized
in three-dimensions.

1.3.2 As An Education Tool To Basic Thermal-fluid Science
While CFD is typically studied at the graduate-level, the ease of use and broad
capability of commercial CFD software packages can enabled this tool to be brought
down into the undergraduate classroom.
-- The mission is to expose students to essential CFD concepts and expand the
learning experience with real-world applications. This is becoming an increasingly
important skill in today’s job market.
1.3.3 As A Design Tool
CFD , likewise as research and educational tools, is also becoming
an integral part of engineering design and analysis environment in
prominent industries.

1.3.4 Aerospace
CFD modelling has its roots in the aerospace industry and is an integral tool
for the design of aircraft. Alongside experimental testing, CFD is used to test and
optimise geometrical shapes, to improve the aerodynamic efficiency of an
aircraft and to study its performance envelope. .
To maintain an edge in a very competitive environment, CFD is playing a crucial role in
overcoming many challenges faced by these industries in improving flight and in solving
a diverse array of designs.
The simulation of fluid path lines in the vicinity of an F18 jet (left),
prediction of pressure coefficient contours at a 10 ~ angle of attack around a supersonic
missile system with grid fins (right).

26/09/2021 Intro to CFD 29
The rapid progress and implementation of Computational Fluid Dynamics (CFD) has contributed to substantial
improvements in the performance and efficiency of Gas Turbine engine components through enhanced
understanding of the complex viscous flow and heat transfer phenomena involved. For this reason, CFD is one of
the key computational tool used in Design & development of gas turbine engines.
Simulation of a whole gas turbine using RANS/LES coupling (van der Weide, 2008).

1.3.5 Automative Engineering
CFD modelling is a key tool in the transport industry and is widely used for a
variety of applications, from external aerodynamics to passenger comfort,
thermal management and engine development.
--This technology has delivered the ability to
shorten cycles, optimize existing engineering components and systems to
improve energy efficiency and meet strict standards and specifications,
improve in-car environment, and study the important external aerodynamics.

Fig 1.6 Examples of automotive aerodynamics (Both courtesy of ANSYS Inc., Fluent)

37
Automotive
Where is CFD used?
― Aerospace
― Appliances
― Automotive
― Biomedical
― HVAC&R
― Hydraulics
― Marine
― Oil & Gas
― Sports
External Aerodynamics Undercarriage
Aerodynamics
Interior Ventilation Engine Cooling

Biomedical Science and Engineering
Medical researchers are nowadays relying on simulation tools to assist in
predicting the behavior of circulatory blood flow inside human body.
Figure 1.7 illustrates just one of the
many sample applications of CFD in the
biomedical area where the blood flow
through an abnormal artery has been
predicted. With the breadth of physical
models and advances in areas of fluid-
structure interaction, particle tracking,
turbulence modeling and better meshing
facilities, rigorous CFD analysis is
increasingly performed to study the fluid
phenomena inside the human vascular
system.
Fig 1.7 CFD prediction of time-dependent wall shear
stress (WSS) fluctuation at the narrowest point

39
Biomedical
Where is CFD used?
― Aerospace
― Appliances
― Automotive
― Biomedical
― HVAC&R
― Hydraulics
― Marine
― Oil & Gas
― Sports
Temperature and natural
convection currents in the eye
following laser heating.
Spinal Catheter
Medtronic Blood Pump

1.3.6 CHEMICAL AND MINERAL PROCESSING
CFD also has close relation with the chemical and mineral processing
industries.
For examples, improving the performance of gas-sparged stirred tank reactors is
considered to be of paramount importance in the chemical industry. Figure 1.7
presents contours of different bubble size distribution within the stirred tank
accompanied by the local flow behavior, indicated by velocity vectors, around one
of the rotating blades.

Figure 1.8 illustrates a separation process in minerals processing
that involves the use of gas cyclones and hydro-cyclones.
FIGURE 1.8 Example of CFD application in the simulation of gas cyclone and hydro-cyclone
(Courtesy of ANSYS Inc., Fluent and ESSS and Petrobras, ANSYS Inc., CFX|

42
Chemical Processing
Where is CFD used?
― Aerospace
― Appliances
― Automotive
― Biomedical
― HVAC&R
― Hydraulics
― Marine
― Oil & Gas
― Sports
Polymerization reactor vessel - prediction
of flow separation and residence time
effects.
Shear rate distribution in twin-
screw extruder simulation
Twin-screw extruder
modeling

1.3.7 CIVIL AND ENVIRONMENTAL ENGINEERING
CFD also helps governments, research institutes, and corporations are actively
seeking ways to meet environmental legislations and guarantees by decreasing waste
while maintaining acceptable production levels fueled by increasing market demands.
In many cases, CFD simulations have been at
the heart of resolving many environmental issues.
For instance, CFD has been used to predict the
pollutant plume being dispersed from a cooling
tower subject to wind conditions as shown in Fig.
1.9
Fig 1.9 Example of CFD application to plume dispersion
from a cooling tower (Courtesy of ANSYS Inc., Fluent)

FIGURE 1.10 Example of CFD application to the construction of a new tank at a water treatment
plant. The top right-hand corner figure describes the CFD simulation of the water tank that will be
installed within the excavated construction site (Courtesy of MMI Engineering)

1.3.8 POWER GENERATION
CFD provide a better technological understanding of the equipment and
processes in an increasingly competitive energy market, utilities, and equipment
manufacturers industries.
CFD is being employed to optimize the turbine
blades for generating constant power under varying
wind conditions as demonstrated by a typical three
dimensional simulation.
CFD is also the only technology that has proven to
accurately model wind farm resource distribution
especially for highly complex terrain with steep
inclines as shown in the figure.
Fig 1.11 Example of CFD application to predicting
the velocity field of a wind turbine

For clean power technologies, gasification offers the promise of increased
generation efficiency and reduced emissions. Simulations can be performed to
meet the modeling needs of this important technology as typified by the
combusting fluidized coal bed in addition to other relevant unit operations as
demonstrated in Fig. 1.12.
Fig 1.12 Example of CFD simulation of bubbles in fluidized coal bed
(Courtesy of ANSYS Inc.,Fluent, Coal Gasification)

47
Power Generation
Where is CFD used?
― Aerospace
― Appliances
― Automotive
― Biomedical
― HVAC&R
― Hydraulics
― Marine
― Oil & Gas
― Sports
Flow pattern through a water turbine.
Flow in a
burner
Flow around cooling towers
Pathlines from the inlet
colored by temperature
during standard operating
conditions

1.3.9 SPORTS
Very recently, one of the most innovative uses of CFD in the sports arena is to "design“
the optimum stroke to achieve peak propulsive performance for elite swimmers as
demonstrated by the example in Fig. 1.13. And another sports area where CFD has played
a major role in is sport equipment design, as inFig1.14.
Fig 1.13 Example of CFD application for designing the
optimum stroke (Courtesy of USA Swimming, Honeywell
Engines and Systems and ANSYS Inc., Fluent)
Fig 1.14 Example of CFD simulation on designing
the ultimate aerodynamic helmet. (Courtesy of
Sports Engineering at CSES, Sheffield Hallam
University and ANSYS Inc., Fluent)

49
Sports
Where is CFD used?
― Aerospace
― Appliances
― Automotive
― Biomedical
― HVAC&R
― Hydraulics
― Marine
― Oil & Gas
― Sports

1.4 The Future of Computational Fluid Dynamics
We are witnessing a renaissance of computer simulation technology in many industrial
applications. This changing landscape is partly attributed by the rapid evolution of CFD
techniques and models.
jet flames, buoyant fires, multiphase / multicomponent flows,….
 With decreasing hardware costs and rapid computing times, engineers are increasingly relying
on this reliable yet easy-to-use CFD tool for delivering accurate results as already described by
the examples in the previous sections.
 In industry, CFD will eventually be so entrenched in the design process.
“Zero prototype engineering.”
Full vehicle CFD models…….
Time-dependent simulations…….

1.4 Future of Computational Fluid Dynamics
 In the area of research, the advances in computational resources are establishing large eddy
simulation (LES) or detached eddy simulation (DES) as the preferred methodology for many
turbulence investigations of fundamental fluid dynamics problems.
-- LES gradually replacing traditional two-equation models in academic research.
Single phase flow, complex flame characteristics,…
-- Two-equation turbulence models are still very prevalent in order to account the turbulence
within such flows.
 LES will eventually become a household methodology for investigating many physical
aspects of practical industrial flows.
-- DNS…..
 Deep machine learning will be used to improve the speed, accuracy and, the user-
friendliness of CFD software. The applications of CFD will expand beyond the usual
aerospace and mechanical/thermal areas.

52
Important factors influencing CFD
 Rapid growth in computing power;
 Greatly improved numerical models;
 More efficient numerical techniques;
 Advanced visualisation tools.

53
Advantages of CFD
Low Cost
― Using physical experiments and tests to get essential engineering data
for design can be expensive.
― Computational simulations are relatively inexpensive, and costs are likely
to decrease as computers become more powerful.
Speed
― CFD simulations can be executed in a short period of time.
― Quick turnaround means engineering data can be introduced early in the
design process
Ability to Simulate Real Conditions
― Many flow and heat transfer processes can not be (easily) tested - e.g.
hypersonic flow at Mach 20, nuclear accident analysis.
― CFD provides the ability to theoretically simulate any physical condition

54
Advantages of CFD (2)
Ability to Simulate Ideal Conditions
― CFD allows great control over the physical process, and provides the ability
to isolate specific phenomena for study.
― Example: a heat transfer process can be idealized with adiabatic, constant
heat flux, or constant temperature boundaries.
Comprehensive Information
 Experiments only permit data to be
extracted at a limited number of locations
in the system (e.g. pressure and
temperature probes, heat flux gauges,
LDV, etc.)
 CFD allows the analyst to examine a
large number of locations in the region of
interest, and yields a comprehensive set
of flow parameters for examination.

55
Limitations of CFD
Physical Models
― CFD solutions rely upon physical models of real world processes (e.g.
turbulence, compressibility, chemistry, multiphase flow, etc.).
― The solutions that are obtained through CFD can only be as accurate as the
physical models on which they are based.
Numerical Errors
― Solving equations on a computer always introduces numerical errors.
• Round-off error - errors due to finite number of digits available for variables on
the computer
• Truncation error - error due to approximations in the numerical models
― Round-off errors will always exist (though they should be small in most cases)
― Truncation errors will go to zero as the grid is refined - so mesh refinement is
one way to deal with truncation error.

56
Limitations of CFD (2)
Boundary Conditions
As with physical models, the accuracy of the CFD solution is only as good as the
initial/boundary conditions provided to the numerical model.
Example: Flow in a duct with sudden expansion.
If flow is supplied to domain by a pipe, you should use a fully-developed profile for
velocity rather than assume uniform conditions.
poor better
Fully Developed
Inlet Profile
Computational
Domain
Computational
Domain
Uniform
Inlet Profile
 Computer Resources
Even with the advent of ever faster computers and larger storage media,
simulation of complex engineering systems could still require more computer
resources.

1.5 SUMMARY
 Computational fluid dynamics has evolved through decades of rigorous
development of numerical techniques.
 Escalating computational power has permitted the ability to incorporate more
sophisticated models to better resolve increasingly complex flow transport
phenomena.
 CFD computation involves the generation of a number of cells, which will
hopefully provide a realistic approximation of a real fluid system. The main
outcome of any CFD work is that the reader acquires an improved
understanding of the flow behavior for the system in question.

In the next chapter, we begin by
discovering how a CFD code works through
the various elements that constitute a
complete CFD analysis.

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