The document discusses the basics of airfoil design and development. It provides a brief history of airfoil research from the late 1800s through modern times. Key topics covered include [END SUMMARY]
Aircraft Finite Element Modelling for structure analysis using Altair ProductsAltair
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The Airbus airframe design process has considerably evolved since 20 years with the constant improvement of numerical simulation capability and the computational means capacity. Today the size of Finite Element Models for aircraft structural behaviour study is exceeding the boundary of airframe components (fuselage section, wing); for the A350, a very large scale non-linear model of more than 60 million degrees of freedom has been developed to secure the static test campaign. This communication will illustrate the partnership with Altair and the use of Altair products for the creation and verification of very large models at Airbus. It will deal with: - Geometry preparation - Meshing - Property assignment - Assembly - Checking More generally, numerical simulation will play more and more a major role in the aircraft process, from the development of new concepts / derivatives to the support of the in-service fleet. Then, this presentation will also state the coming needs regarding model creation tools to cope with Airbus strategy.
Speakers
Marion Touboul, IngĂŠnieur en Simulation NumĂŠrique - Calcul Structure, Airbus OpĂŠrations SAS
Aircraft Finite Element Modelling for structure analysis using Altair ProductsAltair
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The Airbus airframe design process has considerably evolved since 20 years with the constant improvement of numerical simulation capability and the computational means capacity. Today the size of Finite Element Models for aircraft structural behaviour study is exceeding the boundary of airframe components (fuselage section, wing); for the A350, a very large scale non-linear model of more than 60 million degrees of freedom has been developed to secure the static test campaign. This communication will illustrate the partnership with Altair and the use of Altair products for the creation and verification of very large models at Airbus. It will deal with: - Geometry preparation - Meshing - Property assignment - Assembly - Checking More generally, numerical simulation will play more and more a major role in the aircraft process, from the development of new concepts / derivatives to the support of the in-service fleet. Then, this presentation will also state the coming needs regarding model creation tools to cope with Airbus strategy.
Speakers
Marion Touboul, IngĂŠnieur en Simulation NumĂŠrique - Calcul Structure, Airbus OpĂŠrations SAS
For Video Lecture of this presentation: https://youtu.be/u7bp9IJqRVM
The topics covered in this session are, Slip: Types of slip, Sideslip angle, Sideslip angle sign conventions, restoring yaw moments, physical significance, Calculation of sideslip angle, Measurement of sideslip.
Attention! "Gate Aerospace Engineering aspirants", A virtual guide for gate aerospace engineering is provided in "Age of Aerospace" blog for helping you meticulously prepare for gate examination. Respective notes of individual subjects are provided as 'Embedded Google Docs' which are frequently updated. This comprehensive guide is intended to efficiently serve as an extensive collection of online resources for "GATE Aerospace Engineering" which can be accessed free of cost. Use the following link to access the study material
https://ageofaerospace.blogspot.com/p/gate-aerospace.html
For Video Lecture of this presentation: https://youtu.be/u7bp9IJqRVM
The topics covered in this session are, Slip: Types of slip, Sideslip angle, Sideslip angle sign conventions, restoring yaw moments, physical significance, Calculation of sideslip angle, Measurement of sideslip.
Attention! "Gate Aerospace Engineering aspirants", A virtual guide for gate aerospace engineering is provided in "Age of Aerospace" blog for helping you meticulously prepare for gate examination. Respective notes of individual subjects are provided as 'Embedded Google Docs' which are frequently updated. This comprehensive guide is intended to efficiently serve as an extensive collection of online resources for "GATE Aerospace Engineering" which can be accessed free of cost. Use the following link to access the study material
https://ageofaerospace.blogspot.com/p/gate-aerospace.html
Aerofoil Shapes plays a major role in understanding the principles of flight. This ppt gives basic knowledge about the aerofoil shapes and the variation of aerodynamic forces.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
The flow velocity over airfoils increases over the convex surface resulting in lower average pressure on the 'suction' side of the airfoil compared with the concave or 'pressure' side of the airfoil.
Meanwhile, viscous friction between the air and the airfoil surface slows the airflow to some extent next to the surface.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
The flow velocity over airfoils increases over the convex surface resulting in lower average pressure on the 'suction' side of the airfoil compared with the concave or 'pressure' side of the airfoil.
Meanwhile, viscous friction between the air and the airfoil surface slows the airflow to some extent next to the surface.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
The flow velocity over airfoils increases over the convex surface resulting in lower average pressure on the 'suction' side of the airfoil compared with the concave or 'pressure' side of the airfoil.
Meanwhile, viscous friction between the air and the airfoil surface slows the airflow to some extent next to the surface.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
The flow velocity over airfoils increases over the convex surface resulting in lower average pressure on the 'suction' side of the airfoil compared with the concave or 'pressure' side of the airfoil.
Meanwhile, viscous friction between the air and the airfoil surface slows the airflow to some extent next to the surface.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
The flow velocity over airfoils increases over the convex surface resulting in lower average pressure on the 'suction' side of the airfoil compared with the concave or 'pressure' side of the airfoil.
Meanwhile, viscous friction between the air and the airfoil surface slows the airflow to some extent next to the surface.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
The flow velocity over airfoils increases over the convex surface resulting in lower average pressure on the 'suction' side of the airfoil compared with the concave or 'pressure' side of the airfoil.
Meanwhile, viscous friction between the air and the airfoil surface slows the airflow to some extent next to the surface.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
The flow velocity over airfoils increases over the convex surface resulting in lower average pressure on the 'suction' side of the airfoil compared with the concave or 'pressure' side of the airfoil.
Meanwhile, viscous friction between the air and the airfoil surface slows the airflow to some extent next to the surface.
Airflow over an airfoil produces a distribution of forces over the airfoil surface.
A Good Effect of Airfoil Design While Keeping Angle of Attack by 6 Degreepaperpublications3
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Abstract: Airfoil is a shape of wing or blade of (a propeller, rotor or turbine) by which a fluid generates an aerodynamic force. The component of this force perpendicular to the direction of its speed is called lift force and the component parallel to its speed is called drag forces. Here we see that if we set the angle of attack by 6 degree in fluid NACA0012 we found the aerodynamic forces with suitable positive result our research is totally based on iterations method and based on the help of cfd software.
SAP Sapphire 2024 - ASUG301 building better apps with SAP Fiori.pdfPeter Spielvogel
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Building better applications for business users with SAP Fiori.
⢠What is SAP Fiori and why it matters to you
⢠How a better user experience drives measurable business benefits
⢠How to get started with SAP Fiori today
⢠How SAP Fiori elements accelerates application development
⢠How SAP Build Code includes SAP Fiori tools and other generative artificial intelligence capabilities
⢠How SAP Fiori paves the way for using AI in SAP apps
Communications Mining Series - Zero to Hero - Session 1DianaGray10
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This session provides introduction to UiPath Communication Mining, importance and platform overview. You will acquire a good understand of the phases in Communication Mining as we go over the platform with you. Topics covered:
⢠Communication Mining Overview
⢠Why is it important?
⢠How can it help todayâs business and the benefits
⢠Phases in Communication Mining
⢠Demo on Platform overview
⢠Q/A
Dr. Sean Tan, Head of Data Science, Changi Airport Group
Discover how Changi Airport Group (CAG) leverages graph technologies and generative AI to revolutionize their search capabilities. This session delves into the unique search needs of CAGâs diverse passengers and customers, showcasing how graph data structures enhance the accuracy and relevance of AI-generated search results, mitigating the risk of âhallucinationsâ and improving the overall customer journey.
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
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Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
Removing Uninteresting Bytes in Software FuzzingAftab Hussain
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Imagine a world where software fuzzing, the process of mutating bytes in test seeds to uncover hidden and erroneous program behaviors, becomes faster and more effective. A lot depends on the initial seeds, which can significantly dictate the trajectory of a fuzzing campaign, particularly in terms of how long it takes to uncover interesting behaviour in your code. We introduce DIAR, a technique designed to speedup fuzzing campaigns by pinpointing and eliminating those uninteresting bytes in the seeds. Picture this: instead of wasting valuable resources on meaningless mutations in large, bloated seeds, DIAR removes the unnecessary bytes, streamlining the entire process.
In this work, we equipped AFL, a popular fuzzer, with DIAR and examined two critical Linux libraries -- Libxml's xmllint, a tool for parsing xml documents, and Binutil's readelf, an essential debugging and security analysis command-line tool used to display detailed information about ELF (Executable and Linkable Format). Our preliminary results show that AFL+DIAR does not only discover new paths more quickly but also achieves higher coverage overall. This work thus showcases how starting with lean and optimized seeds can lead to faster, more comprehensive fuzzing campaigns -- and DIAR helps you find such seeds.
- These are slides of the talk given at IEEE International Conference on Software Testing Verification and Validation Workshop, ICSTW 2022.
Unlocking Productivity: Leveraging the Potential of Copilot in Microsoft 365, a presentation by Christoforos Vlachos, Senior Solutions Manager â Modern Workplace, Uni Systems
UiPath Test Automation using UiPath Test Suite series, part 5DianaGray10
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Welcome to UiPath Test Automation using UiPath Test Suite series part 5. In this session, we will cover CI/CD with devops.
Topics covered:
CI/CD with in UiPath
End-to-end overview of CI/CD pipeline with Azure devops
Speaker:
Lyndsey Byblow, Test Suite Sales Engineer @ UiPath, Inc.
Climate Impact of Software Testing at Nordic Testing DaysKari Kakkonen
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My slides at Nordic Testing Days 6.6.2024
Climate impact / sustainability of software testing discussed on the talk. ICT and testing must carry their part of global responsibility to help with the climat warming. We can minimize the carbon footprint but we can also have a carbon handprint, a positive impact on the climate. Quality characteristics can be added with sustainability, and then measured continuously. Test environments can be used less, and in smaller scale and on demand. Test techniques can be used in optimizing or minimizing number of tests. Test automation can be used to speed up testing.
Alt. GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using ...James Anderson
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Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Elevating Tactical DDD Patterns Through Object CalisthenicsDorra BARTAGUIZ
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After immersing yourself in the blue book and its red counterpart, attending DDD-focused conferences, and applying tactical patterns, you're left with a crucial question: How do I ensure my design is effective? Tactical patterns within Domain-Driven Design (DDD) serve as guiding principles for creating clear and manageable domain models. However, achieving success with these patterns requires additional guidance. Interestingly, we've observed that a set of constraints initially designed for training purposes remarkably aligns with effective pattern implementation, offering a more âmechanicalâ approach. Let's explore together how Object Calisthenics can elevate the design of your tactical DDD patterns, offering concrete help for those venturing into DDD for the first time!
GridMate - End to end testing is a critical piece to ensure quality and avoid...ThomasParaiso2
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End to end testing is a critical piece to ensure quality and avoid regressions. In this session, we share our journey building an E2E testing pipeline for GridMate components (LWC and Aura) using Cypress, JSForce, FakerJSâŚ
Essentials of Automations: The Art of Triggers and Actions in FMESafe Software
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In this second installment of our Essentials of Automations webinar series, weâll explore the landscape of triggers and actions, guiding you through the nuances of authoring and adapting workspaces for seamless automations. Gain an understanding of the full spectrum of triggers and actions available in FME, empowering you to enhance your workspaces for efficient automation.
Weâll kick things off by showcasing the most commonly used event-based triggers, introducing you to various automation workflows like manual triggers, schedules, directory watchers, and more. Plus, see how these elements play out in real scenarios.
Whether youâre tweaking your current setup or building from the ground up, this session will arm you with the tools and insights needed to transform your FME usage into a powerhouse of productivity. Join us to discover effective strategies that simplify complex processes, enhancing your productivity and transforming your data management practices with FME. Letâs turn complexity into clarity and make your workspaces work wonders!
DevOps and Testing slides at DASA ConnectKari Kakkonen
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My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
2. History:
ďźThe serious work on the development of airfoil sections began in the late 1800's.
ďźIt was known that flat plates would produce lift when set at an angle of incidence, some suspected that shapes
with curvature, that more closely resembled bird wings would produce more lift or do so more efficiently.
ďźH.F. Phillips patented a series of airfoil shapes in 1884 after testing them in wind tunnels (artificial currents of
air produced from induction by a steam jet in a wooden conduit)
ďźOctave Chanute writes in 1893, "...it seems very desirable that further scientific experiments be made on
concavo-convex surfaces of varying shapes, for it is not impossible that the difference between success and failure of
a proposed flying machine will depend upon the sustaining effect between a plane surface and one properly curved
to get a maximum of 'lift'.â
ďźOtto Lilienthal, in 1894, after measuring the shapes of bird wings, tested the airfoils on a 7m diameter
"whirling machine". He believed that the key to successful flight was wing curvature or camber. He also
experimented with different nose radii and thickness distributions .
ďźWright Brothers aerofoil closely resembled Lilienthal's sections: thin and highly cambered. (This was possible
because early tests of airfoil sections were done at extremely low Reynolds number, where thin and cambered
sections behave better than thicker ones.)
ďźSome of the first airplanes (Wright Brothers Flyer) were biplanes reason being erroneous belief that efficient
airfoils must be thin and highly cambered. A biplane is a fixed-wing aircraft with two main wings. A biplane wing
structure has a structural advantage, but produces more drag than a similar monoplane wing. It become obsolete
by the late 1930s.
2
3. ďąA wide range of airfoils developed
ďąA family of sections used and tested by the NACA in the early 1920's
ďąEastman Jacobs, in 1939, at the NACA in Langley, designed and tested the first laminar flow airfoil section
having extremely low drag and a high lift to drag ratio of about 300.
ďąThe reasons airfoils looks quite different from one another is that the flow conditions and design goals changes
from one application to the next.
3
4. The Reynolds number Re is a dimensionless number which gives a measure of the ratio of inertial forces to
viscous forces and quantifies the relative importance of these two types of forces for given flow conditions.
It is used to characterize different flow regimes, as laminar or turbulent flow:
laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by
smooth, constant fluid motion while turbulent flow occurs at high Reynolds numbers and is dominated by
inertial forces, which tend to produce random, erratic, chaotic eddies, vortices and other flow .
At very low Reynolds numbers (<10,000 based on chord length) efficient airfoil sections looks peculiar as the
sketch of a dragonfly wing.
The Eppler 193 is a good section for model airplanes.
The Lissaman 7769 was designed for human-powered aircraft.
4
5. The various terms related to airfoils are defined below:
1. The mean camber line is the locus of points midway between the upper and lower surfaces.
2. The chord line is a straight line connecting the leading and trailing edges of the airfoil, at the ends of the
mean camber line.
3. The chord is the length of the chord line and is the characteristic dimension of the airfoil section.
4. The maximum thickness and the location of maximum thickness are expressed as a percentage of the chord.
5. For symmetrical airfoils both mean camber line and chord line pass from centre of gravity of the airfoil and
they touch at leading and trailing edge of the airfoil.
6. The aerodynamic centre is the chord wise length about which the pitching moment is independent of the lift
coefficient and the angle of attack.
7. The centre of pressure is the chord wise location about which the pitching moment is zero.
8. The aspect ratio is defined as the span-to-mean-chord ratio of an airfoil. The aspect ratio of a wing is the
length of the wing compared with the breadth (chord) of the wing. A high aspect ratio indicates long,
narrow wings, whereas a low aspect ratio indicates short, stubby wings. For most wings, the length of the
chord varies along the wing so the aspect ratio (AR) is defined as the square of the wingspan divided by the
area of the wing platform i.e. AR=b2/S; where, b is the wingspan, and S is the area of the wing platform.
9. The solidity ratio is defined as the sum of tip widths divided by the fan circumference. Solidity is Measure of
a fanâs pressure capability.
10. The stall point is the fan operating condition where the boundary layer of air separates from the airfoil and
causes turbulence.
5
6. Airfoil Geometry
ďąAirfoil geometry can be characterized by the coordinates of the upper and lower surface.
ďąOne can generate a reasonable airfoil section given these parameters:
ďChord length,
ďmaximum thickness,
ďmaximum camber,
ďposition of max thickness,
ďposition of max camber,
ďand nose radius
6
7. NACA aerofoil (Eastman Jacobs)
The NACA 4 digit and 5 digit airfoils were created by superimposing a simple mean line shape with a thickness
distribution that was obtained by fitting a couple of popular airfoils of the time:
y = (t/0.2) * (.2969*x0.5 - .126*x - .3537*x2 + .2843*x3 - .1015*x4)
The camber line of 4-digit sections was defined as a parabola from the leading edge to the position of maximum
camber, then another parabola back to the trailing edge.
4 4 12
Max camber in % chord Position of maximum Maximum thickness in % of chord
camber in 1/10 of chord
NACA 4412
2 30 12
Approx Max camber in Position of maximum Maximum thickness in % of
% chord camber in 2/100 of chord chord
NACA 23012
NACA 5 â digit sections had the same thickness distribution, but used a camber line with more curvature near
the nose.
7
8. The 6-series of NACA airfoil sections were generated
1. from a more or less prescribed pressure distribution and
2. were meant to achieve some laminar flow.
6 3 2 2 12
Six series Location of minimum Half width of low drag Ideal CL in Max thickness in
Cp in 1/10 of chord bucket in 1/10 of CL tenths % of chord
After the six-series sections,
1. airfoil design became much more specialized
2. particular application specific
3. these sections form basis of several airfoil sections and then the entire geometry is modified based on
its 3-D characteristics.
8
9. Airfoil Pressure Distributions and Performance
The aerodynamic performance depends on the distribution of pressure over the airfoil.
This distribution is expressed in terms of the pressure coefficient which is the difference between local static
pressure and free stream static pressure, non-dimensionalized by the free stream dynamic pressure.
Cp = (P-Pâ)/(1/2 ĎU2â)
Plot Cp vs. x/c:
x/c varies from 0 at the leading edge to 1.0 at the trailing edge.
1. Stagnation Point : The stagnation point occurs near the leading edge.
It is the place at which V = 0,
In incompressible flow Cp = 1.0,
In compressible flow it may be somewhat larger.
2. The upper surface pressure is lower than the lower surface in this case. But it doesn't have to be always.
3. The lower surface sometimes carries a positive pressure, and pulls the wing downward (near the mid-chord).
9
10. 4. The region of the pressure distribution is called the pressure recovery region or region of adverse pressure
gradient. The pressure increases from its minimum value to the value at the trailing edge.
5. Adverse pressure gradient is associated with boundary layer transition and separation, if the gradient is too
severe.
6. The pressure at the trailing edge is related to the airfoil thickness and shape near the trailing edge. For
infinitely thin sections Cp = 0 at the trailing edge.
7. Large positive values of Cp at the trailing edge imply more severe adverse pressure gradients.
severity of the adverse pressure gradient.
10
11. Effect of pressure on flow:
⢠For equilibrium we must have a pressure gradient when the flow is curved
⢠The pressure must increase as we move further from the surface (negative Cp)
⢠Depends on angle of attack and aerofoil shape
11
12. Effects of changes in camber, leading edge radius, trailing edge angle, and local distortions in the airfoil surface.
Cp vs. x/c plots 2
1
4
3
5 1. Reduced camber at aft/rear section pushing the
surface downward
2. Sharp nose leads to favourable gradients over 50% of
the section
3. A thicker section will have a less prominent peak
(pressure peak near the nose)
4. Only one line because at zero lift (symmetric upper
6 and lower section with 00 attack), the upper and lower
surface pressure coincide.
5. A conventional cambered section.
6. An aft-loaded section, the opposite of a reflexed
airfoil carries more lift over the aft part of the airfoil.
Supercritical airfoil sections look like this.
12
13. Airfoil Design
Airfoils may be designed to produce
1. low drag without generating any lift
2. low drag while producing a given amount of lift
3. very high lift to drag ratio
4. maximum lift and drag doesn't really matter
To achieve any of these, constraints may apply on
1. thickness, or
2. stagger angle, or
3. pitching moment, or
4. off-design performance, or
5. stall characteristics, etc.
1. pitch chord ratio/ solidity, or
2. blade spacing, or
Design Approach
1. Design by authority
2. Use of an already designed airfoil
3. Works well if the goals of a particular design problem matches with the goals of the original airfoil design
4. The availability of the test data ensures, with the available tools now airfoil section can be designed with
accurate predictability without testing
13
14. Methods for airfoil design
Direct design
Inverse design
Direct Methods involve
ďA specified section geometry (such as a NACA airfoil)
ďReady calculation methods for pressures and performance
ďEvaluation based on given shape
ďIdentifying the problems in the performance characteristics
ďModification of the shape to improve the performance
The two main problems of direct methods are
1. The identification of the problems in performance
2. Shape optimization for improved performance
Inverse Design Methods involve
ďThe objective function as the target pressure distribution or the least squares difference between the
actual and target Cp
ďChanging the airfoil shape to improve the performance.
This may be done in several ways:
1. By hand, using knowledge of the effects of geometry changes on Cp and Cp changes on
performance.
2. By numerical optimization, using shape functions to represent the airfoil geometry and letting
the computer decide on the sequence of modifications needed to improve the design. 14
15. Typical Problems
1. Thick Airfoil Design
The minimum pressure decreases due to thickness
A more severe adverse pressure gradient and the need to start recovery sooner
The section with maximum thickness must recover pressure with almost steepest possible gradient
This problem addressed by Liebeck in connection with maximum lift
The thickest possible section has a boundary layer just on the verge of separation throughout the recovery
2. High Lift Airfoil Design
Requires large negative pressures on the upper surface of the airfoil. The limit to this suction is associated with
i. compressibility effects, and
ii. the boundary layer to be capable enough of negotiating the resulting adverse pressure recovery.
For maximum lift, it is best to keep the boundary layer on the verge of separation
For maximum airfoil lift, the best recovery location is chosen and the airfoil is made very thin so that the lower
surface produces maximum lift as well. (Since the upper surface Cp is specified, increasing thickness only reduces
the lower surface pressures.)
3. Laminar Airfoil
Useful for reducing skin friction drag, increasing maximum lift, or reducing heat transfer.
At low Reynolds numbers it is achieved by maintaining a smooth surface and using an airfoil with a favourable
pressure gradient.
15
16. Typical Problems
4. Transonic Airfoil Design
Severe instability can occur at transonic speeds. Shock waves move through the air at the speed of sound. When
an object also moves at the speed of sound, these shock waves build up in front of it to form a single, very
large shock wave. During transonic flight, the body must pass through this large shock wave, as well as cope
up with the instability caused by air moving faster than sound over parts of the wing and slower in other
parts.
Objective is to limit shock drag losses at a given transonic speed.
Since both lift and thickness reduce (increase in magnitude) the minimum Cp, the transonic design problem is to
create an airfoil section with high lift and/or thickness without causing strong shock wave.
Supercritical airfoil are designed to operate efficiently with substantial regions of supersonic flow. But the
maximum local Mach numbers should not exceed about 1.2 to 1.3 on a well-designed supercritical airfoil.
16
17. Mach number, Ma
It is the speed of an object moving through air, or any other fluid media, divided by the speed of sound in that
medium at that particular condition of temperature and pressure.
Ma=V/Vs
where, Ma is the Mach number
V is the relative velocity of the source to the medium and
Vs is the speed of sound in the medium
At Standard Sea Level conditions (150C temperature), the speed of sound is 340.3 m/s in the Earth's atmosphere.
High-speed flow around objects
High-
Regime Subsonic Transonic Sonic Supersonic Hypersonic
hypersonic
Mach No, Ma <1.0 0.8â1.2 1.0 1.2â5.0 5.0â10.0 >10.0
When an aircraft exceeds Mach 1 (i.e. the sound barrier) a large pressure difference is created just in front of the
aircraft, called a shock wave. This spreads backward and outward from the aircraft in a cone shape (called as a
Mach cone). It causes the sonic boom as heard when fast moving aircraft travels overhead.
17
18. Mach number, Ma
High-
Regime Subsonic Transonic Sonic Supersonic Hypersonic
hypersonic
Mach No, Ma <1.0 0.8â1.2 1.0 1.2â5.0 5.0â10.0 >10.0
in a subsonic compressible flow
in a supersonic compressible flow
where, M is Mach number
is impact pressure and
P is static pressure and
Îł is the ratio of specific heat of a gas at a constant pressure to that at constant volume (1.4 for air)
18
19. Typical Problems
5. Low Reynolds Number Airfoil Design
Too much laminar flow
Restricted severe pressure gradients and maximum lift capability
The boundary layer is much less capable of handling an adverse pressure gradient without separation
Laminar separation bubbles are common can lead to excessive drag and low maximum lift
6. Multiple Design Point Airfoils
ďąOne of the difficulties in designing a good airfoil is the requirement for acceptable off-design performance.
ďąLow drag section must perform well without separation at an angle of attack slightly away from its design
point.
ďąAirfoils with high lift capability may perform poorly at lower angles of attack.
ďąTo overcome these one can design the upper and lower surface of the section to satisfy separate design point
operation. Often it is clear that the upper surface will be critical at one of the points and we can design the upper
surface at this condition. The lower surface can then be designed to make the section behave properly at the
second point.
ďąVariable geometry can be employed (at some expense) as in the case of high lift systems.
19
Editor's Notes
In a biplane aircraft, two wings are placed one above the other. Both provide a portion of the lift, although they are not able to produce twice as much lift as a single wing of similar size and shape because the upper and the lower are working on nearly the same portion of the atmosphere. For example, in a wing of aspect ratio 6, and a wing separation distance of one chord length, the biplane configuration can produce about 20 percent more lift than a single wing of the same planform.[1]In the biplane configuration, the lower wing is often attached to the fuselage, while the upper wing is raised above the fuselage with an arrangement of cabane struts, although other combinations have been used. Almost all biplanes also have a third horizontal surface, the tailplane, to control the pitch, or angle of attack of the aircraft (although there have been a few exceptions). Either or both of the main wings can support flaps or ailerons to assist lateral rotation and speed control; usually the ailerons are mounted on the upper wing, and flaps (if used) on the lower wing. Often there is bracing between the upper and lower wings, in the form of wires (tension members) and slender interplane struts (compression members) positioned symmetrically on either side of the fuselage.Aerodynamic research by NASA found that it was necessary for the two wings to be different in either chord or span otherwise longitudinal oscillation would occur.
At very low Reynolds numbers (<10,000 based on chord length) efficient airfoil sections can look rather peculiar as suggested by the sketch of a dragonfly wing. The thin, highly cambered pigeon wing is similar to Lilienthal's designs. The Eppler 193 is a good section for model airplanes. The Lissaman 7769 was designed for human-powered aircraft.
The Reynolds number Re is a dimensionless numberthat gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions. Named after Osborne Reynolds (1842â1912), who popularized its use in 1883. Reynolds numbers frequently arise when performing dimensional analysis of fluid dynamics problems, and as such can be used to determine dynamic similitude between different experimental cases.They are used to characterize different flow regimes, such as laminar or turbulent flow:laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion;while turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow These definition of Reinclude the fluid properties of density and viscosity, plus a velocity and a characteristic length or characteristic dimension. characteristic dimensionThis dimension is a matter of convention â for example a radius or diameter are equally valid for spheres or circles, but one is chosen by convention. For aircraft or ships, the length or width can be used. For flow in a pipe or a sphere moving in a fluid the internal diameter is generally used today. Other shapes (such as rectangular pipes or non-spherical objects) have an equivalent diameter defined. For fluids of variable density (e.g. compressible gases) or variable viscosity (non-Newtonian fluids) special rules apply.Re= (Ď)(L)(V)/(Îź) = (V)(L)/(v)V is the mean velocity of the object relative to the fluid (SI units: m/s)L is a characteristic linear dimension, (travelled length of the fluid; hydraulic diameter when dealing with river systems) (m)Îź is the dynamic viscosity of the fluid (Pa¡s or N¡s/m² or kg/(m¡s))ν is the kinematic viscosity (ν = Îź / Ď) (m²/s)Ď is the density of the fluid (kg/mÂł)Transition Reynolds numberIn boundary layer flow over a flat plate, experiments can confirm that, after a certain length of flow, a laminar boundary layer will become unstable and become turbulent. This instability occurs across different scales and with different fluids, usually when Rex= 5x105, where x is the distance from the leading edge of the flat plate, and the flow velocity is the freestream velocity of the fluid outside the boundary layer.For flow in a pipe of diameter D, experimental observations show that for 'fully developed' flow (Note:[13]), laminar flow occurs when ReD < 2300 and turbulent flow occurs when ReD > 4000.[14] In the interval between 2300 and 4000, laminar and turbulent flows are possible ('transition' flows), depending on other factors, such as pipe roughness and flow uniformity). This result is generalised to non-circular channels using the hydraulic diameter, allowing a transition Reynolds number to be calculated for other shapes of channel.
NACA:National Advisory Committee for AeronauticsOne can generate a reasonable airfoil section given these parameters. This was done by Eastman Jacobs in the early 1930's to create a family of airfoils known as the NACA Sections.
x/c varies from 0 at the leading edge to 1.0 at the trailing edge. Cpis plotted "upside-down" with negative values (suction), higher on the plot. (This is done so that the upper surface of a conventional lifting airfoil corresponds to the upper curve.) The Cpstarts from about 1.0 at the stagnation point near the leading edge... It rises rapidly (pressure decreases) on both the upper and lower surfaces... ...and finally recovers to a small positive value of near the trailing edge.Upper Surface The upper surface pressure is lower (plotted higher on the usual scale) than the lower surface Cp in this case. But it doesn't have to be. ⢠Lower Surface The lower surface sometimes carries a positive pressure, but at many design conditions is actually pulling the wing downward. In this case, some suction (negative Cp -> downward force on lower surface) is present near the mid-chord. Pressure Recovery This region of the pressure distribution is called the pressure recovery region. The pressure increases from its minimum value to the value at the trailing edge. This area is also known as the region of adverse pressure gradient. As discussed in other sections, the adverse pressure gradient is associated with boundary layer transition and possibly separation, if the gradient is too severe.
The relationship between airfoil geometry and airfoil pressure distributions effect of changes in surface curvature For equilibrium we must have a pressure gradient when the flow is curved. In the case shown here, the pressure must increase as we move further from the surface. This means that the surface pressure is lower than the pressures farther away. This is why the Cp is more negative in regions with curvature in this direction. The curvature of the streamlines determines the pressures and hence the net lift.
Reduced camber at aft/rear section pushing the surface downwardSharp nose leads to favourable gradients over 50% of the sectionA thicker section will have a less prominent peak (pressure peak near the nose)Only one line because at zero lift (symmetric upper and lower section with 00 attack), the upper and lower surface pressure coincide. A conventional cambered section. An aft-loaded section, the opposite of a reflexed airfoil carries more lift over the aft part of the airfoil. Supercritical airfoil sections look a bit like this.
Transonic speed is an aeronautics term referring to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.8 to 1.2, i.e. 600-900 mph. This condition depends not only on the travel speed of the craft, but also on the pressure and temperature of the airflow of the vehicle's local environment. It is formally defined as the range of speeds between the critical Mach number, when some parts of the airflow over an air vehicle or air foil are supersonic, and a higher speed, typically near Mach 1.2, when all of the airflow is supersonic. Between these speeds some of the airflow is supersonic, and some is not.Severe instability can occur at transonic speeds. Shock waves move through the air at the speed of sound. When an object such as an aircraft also moves at the speed of sound, these shock waves build up in front of it to form a single, very large shock wave. During transonic flight, the plane must pass through this large shock wave, as well as contending with the instability caused by air moving faster than sound over parts of the wing and slower in other parts.Transonic speeds can also occur at the tips of rotor blades of helicopters and aircraft. However, as this puts severe, unequal stresses on the rotor blade, it is avoided and may lead to dangerous accidents if it occurs. It is one of the limiting factors to the size of rotors, and also to the forward speeds of helicopters (as this speed is added to the forward-sweeping (leading) side of the rotor, thus possibly causing localized transonics).
When an aircraft exceeds Mach 1 (i.e. the sound barrier) a large pressure difference is created just in front of the aircraft. This abrupt pressure difference, called a shock wave, spreads backward and outward from the aircraft in a cone shape (a so-called Mach cone). It is this shock wave that causes the sonic boom heard as a fast moving aircraft travels overhead. A person inside the aircraft will not hear this. The higher the speed, the more narrow the cone; at just over M=1 it is hardly a cone at all, but closer to a slightly concave plane.At fully supersonic speed, the shock wave starts to take its cone shape and flow is either completely supersonic, or (in case of a blunt object), only a very small subsonic flow area remains between the object's nose and the shock wave it creates ahead of itself. (In the case of a sharp object, there is no air between the nose and the shock wave: the shock wave starts from the nose.)As the Mach number increases, so does the strength of the shock wave and the Mach cone becomes increasingly narrow. As the fluid flow crosses the shock wave, its speed is reduced and temperature, pressure, and density increase. The stronger the shock, the greater the changes. At high enough Mach numbers the temperature increases so much over the shock that ionization and dissociation of gas molecules behind the shock wave begin. Such flows are called hypersonic.It is clear that any object traveling at hypersonic speeds will likewise be exposed to the same extreme temperatures as the gas behind the nose shock wave, and hence choice of heat-resistant materials becomes important.