Vortex Generators
A detailed explanation on this awesome tiny device-vortex generators!
Image courtesy:http://axoplasmic.com/Cardinal/index2.html
INTRODUCTION
Vortex generators are small fins on the surface of the wing near the leading edge which improves the plane’s aerodynamics by delaying the boundary layer separation over the wing. They are used to generate vortices just like the wing tips. when the vortices are created over the wing surface, the effectiveness of the wing increases. The vortex generators are also placed on the control surfaces such as ailerons, elevators, rudders, flaps to increase their effectiveness (effectiveness can be increased by delaying flow separation). These are also used in wind turbine blades.
How does a vortex generator work?
Before getting into the working mechanism, let’s look at what is a Boundary layer and why it is important to delay its separation?
When a solid object through the air, a small layer of air called boundary layer surrounds the object. Air is viscous, it slows down due to friction. As the fluid moves past the airfoil, the molecules right next to the surface stick to the surface. The molecules just above the surface are slowed down in their collisions with the molecules sticking to the surface.in Fact, the air right above the surface is not at all moving. This region of air where the friction slows down the air is called the boundary layer. Refer the image below,
Since the boundary layer is somewhat viscous, or sticky, and slow-moving compared to the moving aeroplane, it falls behind and separates from the object, creating a wake. This wake creates drag(wake drag) on the object and slows it down, resulting in higher energy requirements (This Boundary layer is the source of skin friction drag), as well as the potential for loss of lift, for aeroplanes.
Formation of the boundary layer with high energy keeps air flow in contact with wing surface. But at slow speed and higher angle of attack this airflow separates from the wing surface and sometimes aircraft stalls. Also, sometimes airflow separates from the wing before reaching to control unit such as ailerons. And pilot loses controls!
So to overcome such problems, Vortex Generators are used.
Consider an airfoil with no vortex generator installed and it moves in the air, at higher angles even at low speed, the flow over the airfoil gets separated and forms wake drag, which in turn reduces the speed of the aircraft. At the same time, when a vortex generator is installed, the separation is delayed by the vortex generated, now this Vortex generator when placed close to the leading edge generates a vortex and mix up the lower energy boundary layer with high energy air to delay the flow separation and as a result, stalling is delayed. At slow speed and higher angle of attack, airflow cannot remain attached with wing due to its low energy. So here come vortex generators. Vortex generators form vortices. Vortices are just small tornados. It brings high energy air above boundary layer near the surface of the wing by forming vortices and energize boundary layer. This keeps airflow attached with wing and reduce the possibilities of aircraft stalling.
How does a vortex generator look like?
Vortex Generators can be designed in various shapes, some known shapes as of now are
1.Gothic Vortex generators
2.Rectangular Vortex generators
3.Triangular vortex generators
4.Parabolic Vortex generators.
5.Ogive vortex generators.
Steps to design a Vortex generator:
From the above-mentioned shapes, choose the on that best fits your design purpose.
Determine the Reynolds number of the flow.
Determine the length of VGs and their location along the chord of your wing. (The VG’s should be placed just in front of laminar to turbulent transition, this takes place usually around 16% of chord)
Determine the height of the Vortex generators.
Calculate spanwise spacing of Vortex generators.
Uses:
- Changing Stall characteristics.
- It delays the stall by delaying the flow separation.
- Lowering takeoff and landing distances
- For example, to reduce the runway length you must have the required lift coefficient, this can be achieved with the help of VGs.
- Increasing maximum takeoff weight can be achieved.
- Reducing drag on large transonic aircraft
- Noise reduction (Airbus family incorporate vortex generators under the wing of A320 aircraft to reduce the noise generated by the airflow over circular pressure equalization vents for the fuel tanks. A maximum 2 dB noise reduction is reported.
10 Popular Websites to Find Jobs in India:
“Success will never be a big step in future, success is a small step taken just now”.When you have completed your engineering degree, the very first step is to create a resume and post on these 10 Popular Websites to Find Jobs in India.There are a lot of ways to get your resume in front of the right people, One of the easiest actions you can take is to distribute your resume on several sites and increase your chances of finding your dream job.
Let’s look at some of the best, based on the field you’re in or job you’re looking for
Naukri:
Naukri.com is an online platform for employers to hire quality talent and for job seekers to land their dream job. It is a forum built to bridge the gap between employers and job seekers.they provide information regarding the walk-ins, offering from companies, resume writing tips, interview tips and much more
Website: https://www.naukri.com/?othersrcp=2633&wExp=N&r=in&othersrcp=11457&wExp=N
MonsterIndia:
Monster India, India’s leading online career and recruitment resource with its cutting-edge technology provides relevant profiles to employers and relevant jobs to job seekers. Headquartered in Hyderabad, the company has the presence in 11 other cities of India viz., Mumbai, Delhi, Bangalore, Chennai, Pune, Kolkata, Ahmadabad, Baroda, Chandigarh and Cochin.
Website: http://www.monsterindia.com/
Times Jobs:
TimesJobs.com, the fastest growing and most innovative Indian online recruitment portal, was born with a mission to reach out to all Indians in the country and abroad and provide them with the best career opportunities available.
Website: http://www.timesjobs.com/
CareerBuilder India:
CareerBuilder is the global leader in human capital solutions. Through constant innovation, unparalleled technology, and customer care delivered at every touch point, CareerBuilder helps match the right talent with the right opportunity more often than any other site.
Website:https://www.careerbuilder.co.in/
Careersma:
Careesma.in is a brand new career website for the job market in India that specifically caters to the needs of employers and aspiring job seekers.Careesma.in is here to make the hiring process easier than ever before. its cutting-edge, proven and interactive application tool forms the basis of a professional, easy and transparent process for the recruiters and candidates.
Website: https://www.careesma.in/
Shine.com:
Shine.com is India’s most innovative and fastest growing Online Job Portal.
Today, Shine.com is changing the landscape of hiring, by integrating personal and social networks of candidates for enhancing the recruitment process – making it the world’s first job Portal site to do so. Shine.com now enables a recruiter to reach out to the personal network of employees and their connections, thus, giving them access to a vast network of good quality candidates.
Website:https://www.shine.com/
Indeed:
As the world’s #1 job site, with over 200 million unique visitors every month from over 60 different countries, Indeed has become the catalyst for putting the world to work.They even provide the reviews of the companies.
Website: https://www.indeed.co.in/
Simply Hired
You can post your resumes and find jobs relevant to your industries at simply hired
Website:https://www.simplyhired.co.in/job-search
Career jet:
Careerjet is a job search engine designed to make the process of finding a job on the internet easier for the user. It maps the huge selection of job offerings available on the internet in one extensive database by referencing job listings originating from job boards, recruitment agency websites and large specialist recruitment sites.
Website: https://www.careerjet.co.in/
Freshers world:
If you are interested in looking for a job after your degree, here is the chance to find yourself a job… Here you can find government as well as private jobs in the field. Be it mechanical engineering jobs, civil engineering jobs, electrical engineering jobs, biotechnology jobs, B.Tech jobs, MCA Jobs etc. Get the top Jobs for Graduates, with an extensive list of all graduate jobs online. Freshersworld is one of the Top Fresher job sites in India, with over 1000 companies listing jobs online.
Website: https://www.freshersworld.com/
Apart from these sites, you could develop a better Linkedin profile.its the place where the recruiters search for the talented people.
What to do after B.Tech Aeronautical/Aerospace:
Are you an aeronautical student? Studying final year and thinking about what next?
You have ‘n’ number of opportunities that lie in front of you. You could either study postgraduate, go for a job, take an internship, become an entrepreneur and so on…
You appeared for GATE, in a dilemma whether you will clear or not. You signed with these top 10 websites to find jobs. Still, you are not getting any notifications from these companies regarding the openings.
You are asking your seniors for a referral or your faculty for a referral in core companies, still, there are no boards that open for you.
Finally, you don’t know what you need to proceed with. Don’t worry this was the mindset even when I was in the final year, the same might be the mindset in 2020, and you are not the only one in this confusion.
Here is a list of top 10 companies every aeronautical final year students must check.
You must have a deeper understanding of what these companies do, who are their clients (if provided. Because most companies will not show up these details), what are the technical things that you must get upgraded with. These will be helpful in case you get a job notification from these companies. Personally, I feel, an aeronautical engineer must know his core companies(at least 10)
Here you go………
10 Core Companies:
| S.No | Companies | Website |
|---|---|---|
| 1. | ANSYS | Click here |
| 2. | BaeHAL | Click here |
| 3. | Safran group of companies | Click here |
| 4. | Axis cades | Click here |
| 5. | Quest global | Click here |
| 6. | Airbus | Click here |
| 7. | Rolls Royce | Click here |
| 8. | UTC aerospace | Click here |
| 9. | Boeing | Click here |
| 10. | P3 group of companies | Click here |
Ansys:
If you’ve ever seen a rocket launch, flown on an airplane, driven a car, used a computer, touched a mobile device, crossed a bridge, or put on wearable technology, chances are that, ANSYS software played a critical role in its creation. ANSYS is the global leader in engineering simulation. They help the world’s most innovative companies deliver radically better products to their customers. By offering the best and broadest portfolio of engineering simulation software, they help them solve the most complex design challenges and engineer products limited only by imagination.
Location: Pune,India
Link that you must check: https://www.ansys.com/en-in/solutions/solutions-by-industry/aerospace-and-defense
BaeHAL:
BAeHAL is a joint venture of BAE Systems,UK and Hindustan Aeronautics Limited,India. BAeHAL is built on the strength of its parentage to deliver world-class IT solutions for clients across the world.
Location: Bangalore
Link that you must check: http://www.baehal.com/expertise/engineering%20_services.php
Safran group of companies:
Safran is an international high-technology group and tier-1 supplier of systems and equipment in the Aerospace and Defense markets
Location: Bangalore
Link that you must check: https://www.safran-group.com/aviation
AXISCADES:
AXISCADES offers solution that range from concept generation phase to manufacturing support and certification, making them the preferred choice of engineering partner for Aerospace OEMs and Tier 1 suppliers.
Location: Bangalore
Link that you must check: http://www.axiscades.com/aerospace.php
QuEST Global:
QuEST provides integrated engineering services, product design, software testing in various industries around the globe like aerospace engineering etc.
Location: Bangalore
Link that you must check: https://www.quest-global.com/industries/aerospace-defence/
Airbus:
Hope you may not need more introduction about Airbus. Airbus is a leading aircraft manufacturer whose customer focus, commercial know-how, technological leadership and manufacturing efficiency have propelled it to the forefront of the aviation and air transport industries.
Location: Bangalore
Link that you must check: http://www.airbus.com/
Rollys Royce:
They design, develop, manufacture and service integrated power systems for use in the air, on land and at sea. They are providing Internships, check out the link provided below
Location: Bangalore
Link that you must check: http://careers.rolls-royce.com/rest-of-the-world/interns-and-graduates?country=india
UTC Aerospace:
UTC Aerospace Systems is one of the world’s leading providers of aerospace systems and services for large commercial aircraft.
Location: Bangalore
Link that you must check: https://jobs.utcaerospacesystems.com/
Boeing:
Boeing has been the mainstay of India’s commercial aviation sector with airlines such as Air India, Jet Airways and SpiceJet.
Headquartered in Delhi, Boeing’s India operations include an office and a Boeing Research & Technology Center in Bangalore, field service offices in Mumbai, Hindan, Rajali and New Delhi. Boeing subsidiary, Jeppesen—a provider of flight navigation solutions—is well established in Hyderabad. Another subsidiary, Continental Data Graphics (CDG) in Chennai, is also expanding its footprint in the country.They provide internship , check out the link below
Location:Delhi,Hyderabad,Bangalore
Link that you must check: http://www.boeing.com/careers/college/
P3 group of companies:
India is one of the world’s fastest growing economy and is expected to be a large consumer of products and services to meet its own demands as well as serve global demands from India. They have an academy called P3 Academy, where they train freshers to meet the industry requirements.
Those who are willing to do internships/attend training programs can check out the below-mentioned website.
Location: Bangalore
Link that you must check: http://p3academy.in/course/design/
Introduction:
AFCAT (Air Force Common Admission Test) is a recruitment examination organized by the Indian Air Force (IAF). The examination is held twice a year in the months of February and August, applications to which are made available in December and June respectively.
What’s New in AFCAT 2018?
- NCC Special Entry (Flying) & Meteorology Branch: This year’s AFCAT examination will also be used to recruit NCC Special Entry into flying branch and Meteorology branch under the Ground Duty section.
- Aadhar Card: From 2018 onwards, Aadhar card has been made mandatory for AFCAT application.
- Mode of Answering: From this year onwards, the written test will be a computer-based test (CBT) i.e. candidates will have to use the mouse to report answers on a computer screen.
- Application Fee: AFCAT 2018 will not be free of cost, rather an application fee ofRs. 250 shall be taken as application fee.
AFCAT 2018 Important Dates:
| Events | Dates |
|---|---|
| Release of Notification for AFCAT 2018 (I) | 16th December 2017 |
| Submission of Online Applications | 20th Dec 2017 (6:00 PM IST) – 23rd Jan 2018 (extended) |
| AFCAT 01 2018 Admit Cards | 7th Feb 2018 (Postponed) |
| AFCAT 2018 (1) Exam Date | 25th February 2018 |
| AFCAT 01 2018 Result Declaration | 1st week of April 2018 |
AFCAT 2018 Details:
| Questions | Answers |
|---|---|
| How many vacancies are there? | Not mentioned yet, will be updated soon |
| What is the Language of examination? | AFCAT 2018 exam will be conducted in both English and Hindi languages. |
| what is the Mode of Answering ? | a computer-based test will be used as mode of answering. |
| What is the eligibility? | Only Indian citizens can apply for the examination. |
How to apply?
| Things to do | Need |
|---|---|
| Application Fees. | 250 rupees |
| Photograph Specification | Colored passport sized scanned photograph – 10KB-50KB – JPEG/JPG format. |
| Signature specification | Scanned Signature – 10KB-50KB – JPEG/JPG format. |
| Thumb Impression | Thumb Impression (left thumb for male candidates and right thumb for female candidates) – 10KB-50KB – JPEG/JPG format |
AFCAT Selection Procedure:
Candidates who are short-listed based on AFCAT/ EKT will be called for further testing at one of the Air Force Selection Boards (AFSBs). AFSB or Air Force Selection Board is the board responsible for selecting officers of Indian Airforce. Thus if you want to join the IAF as an officer you have to appear before the board for an interview. There are four AFSB boards in India. These are in Dehradun, Mysore, Gandhinagar and Varanasi.
The AFSB’s are numbered for convenience.
- AFSB Dehradun – 1AFSB
- AFSB Mysore-2AFSB
- AFSB Gandhinagar – 3AFSB and
- AFSB Varanasi -4AFSB.
after clearing the interview you will be called for the airforce training institutes.
List of useful links that you need to check:
| Website | Links |
|---|---|
| Official page | Click here |
| Selection process details will be available @ | Click here |
| AFCAT 2018 Application portal | Click here |
| Useful materials and details will be available at | Click here |
DRAG REDUCTION METHODS
Four main types of drag are encountered in aerodynamics-Namely
- skin-friction drag,
- form drag,
- wave drag,
- induced drag.
The methods in use for reduction for the reduction of each type of drag are discussed in turn
REDUCTION OF SKIN- FRICTION DRAG
In broad terms, skin-friction drag can be reduced in one of the two ways. Either laminar flow is maintained by postponing transition, this is so called laminar- flow technology, or ways to found to reduce the surface shear stress generated by the turbulent boundary layer.The laminar-flow can be maintained passively by prolonging the favourable constant-pressure region over the wing surface. Active control of transition requires the use of suction, either distributed or through discrete spanwise slots. Often the suction is used in conjunction with the favourable pressure distributions. The basic principle of maintaining laminar flow by means of suction has been known for at least thirty-five to forty years. However, the problems with the practical implementation on aircraft, either real or perceptual, have prevented the widespread of the technology. It seems increasingly likely, however, that the considerable gains in efficiency which would result from the use of laminar -flow technology, will ensure that it will be much more widely exploited on commercial aircraft in the near future.Other methods for maintaining laminar-flow have been developed, but as yet, have not been seriously considered seriously for practical application in aviation.
A moderately effective method for reducing turbulent flow friction which has been developed in the recent years involves minute modification of the surfaces so that they are covered with riblets.Riblets can take many forms but essentially consist of streamwise ridges and valleys, as shown. These triangularly shaped riblets are available in the form of the film.
This corresponds to the actual spacing of 0.025 to 0.075 mm for flight conditions. This 3M riblet film has been tested on an in-service Airbus a 300-600 and in other aircrafts. The skin friction drag reduction observed as of the order of 5 to 8 percent and the skin-friction drag 30 to 40% of the total aircraft drag.Thus the overall drag reduction is modest but, nevertheless, represents a very considerable economic benefit with little in the way of a penalty.It is very likely, therefore, that riblets will be widely used on commercial aircraft In the future.The basic concept behind riblets had many origins, but it is probably the work at NASA Langley in the USA, which led to the present developments .he concept, was also discovered independently in Germany through a study of hydrodynamics of riblet –like formations on shark scales. A plausible explanation for the effect of riblets is that they interfere with the rear wall structure of the turbulent boundary layer in the region where the turbulence is mainly generated.The flow field in the turbulent boundary layer is highly complex, but the form of near wall structures has been elucidated in the seminal study of Kline et al at Stanford university.It appeared from this work that ‘hairpin’ vortices form near wall as shown these vortices then continue to grow until a point is reached when the head is violently ejected away from the wall and, simultaneously, the contra-rotating streamwise oriented branches of the vortices come together, inducing a powerful downwash of high-momentum fluid between the vortices towards the wall. This sequence of events constitutes what is termed a ‘near =wall burst’. The riblets act as barriers which prevent the free spanwise movement of the hairpin vortices.It is thought that owing to this the vortices cannot approach each other closely thereby weakening the near wall bursting process. It should be noted, however, that this explanation is not universally accepted
2. REDUCTION OF FORM DRAG
Form drag is kept to the minimum by preventing boundary-layer separation. Streamlining is vitally important for reducing form drag. It is worth noting that at high Reynolds’s numbers a circular cylinder has roughly the same overall drag as a streamlined aerofoil with a chord length equal to 100 cylinder radii. Form drag is overwhelmingly the main contribution to the overall drag for bluff bodies like the cylinder, whereas the predominant contribution in the case of the streamlined body is skin-friction drag, form drag being less than ten percent of the overall drag.For bluff bodies even minimal streamlining can be very effective.
3.REDUCTION OF INDUCED DRAG
Induced drag falls as the aspect ratio of the wing is increased.It was also shown that for a given aspect ratio elliptic-shaped wings have the lowest induced drag. Over the past fifteen years, the winglet has been developed as a device for reducing induced drag without increasing aspect ratio.Typical example is illustrated in the figure .winglets of this type have now been fitted too much type of commercial aircraft.The physical principle behind the winglet is illustrated in the figure. On all sub-sonic wings, there is a tendency for a secondary flow to develop from the high-pressure region below the wing around the wing tip to the relatively low-pressure region on the upper surface. This is the part of the process of forming the trailing vortices if a winglet of the appropriate design and orientation is fitted to the wing-tip, the secondary flow causes the winglet to be at an effective angle of incidence, giving rise to lift and drag components Lw and Dw relative to the winglet, as shown in the figure. Both Lw and Dw have components in the direction of the drag of the aircraft as a whole.Lw provides a component counter to the aircraft drag, while Dw provides a component which augments the aircraft drag.for a well-designed winglet, the contribution of Lw predominates, resulting in a net eduction in overall drag, or thrust, equal to delta T.
4.REDUCTION OF WAVE DRAG
To some extent in the discussion of a supercritical aerofoil, it was found that keeping the pressure uniform over the upper wing surface minimized the shock strength, thereby reducing the wave drag. A somewhat similar principle holds for the wing-body combination of transonic aircraft. This was encapsulated in the area rule formulated by Whitcomb. It was known that as a wing-body combination passed through the speed of sound of sound, the conventional straight fuselage, shown in the figure., experienced a sharp rise in wave drag. Whitcomb showed that this rise in drag could be considered reduced if the fuselage was Waisted as shown in the figure, in such a way as to keep the total cross-sectional area of the wing-body combination constant. Waisted fuselages of this type are now a common feature of aircraft designed for transonic operation.
Fundamentals of turbomachines -The Euler’s equation:
Rotating machines are called as turbomachines.
Turbomachines are a device, in which the rotating fluid interacts with the rotor which rotates about an axis.
When a fluid interacts with a rotor, two things take place
-
The energy transfer and
-
The energy transformation
The energy transfer takes place in the rotating parts( i.e) it may be transferred from the fluid to rotor or vice versa
In case if the energy is transferred from fluid to rotor it is called as a turbine
If the energy is transferred from rotor to fluid it is called as a compressor.
Energy transfer takes place only in the rotating parts
Whereas the energy transformation takes place both in the rotating and stationary parts.
Energy transformation means the change of kinetic energy to the pressure energy.
The forces developed in the turbomachines is because of Newton’s second law of motion or the combined action of both newtons second and third law.
Newton’s second law states that the rate of change of momentum is directly proportional to the force applied.
In case of turbomachines, the angular momentum takes place,
Therefore the rate of change of angular momentum is directly proportional to the applied torque.
Consider a fluid of mass m and interacts with the rotor with a tangential velocity C1 at a distance r1 from the axis of the rotor and leaves the rotor with a tangential velocity c2 at a distance r2 from the rotor. as this fluid (gas) interacts with the rotor which rotates about the axis A-A, there comes an angular momentum which is directly proportional to the torque applied.
The angular momentum at the inlet is mc1r1
The angular momentum at the exit is mc2r2
Applying Newton’s second law,
The applied torque = mc2r2 -mc1r1
The energy transfer E = T×ω(energy = torque * angular momentum)
E=(mc2r2 -mc1r1)×ω
E=m(c2r2 -c1r1)×ω
E=m(c2r2ω -c1r1ω)
E=m(c2u2 -c1u1) (u=rω )
If m=1
E=(c2u2 -c1u1)
this is the Euler’s energy equation.
where u2 and u1 is the tangential velocity of the rotoe and c2 and c1 is the tangential velocity of the gas.
c2u2 >c1u1 the energy transfer is positive and is a Turbine
If c2u2 < c1u1 the energy transfer is negative and is a compressor
Energy transfer equation of a Turbine is ET=(c2u2 -c1u1)
Energy transfer equation of a compressor is Ec=(c1u1 -c2u2)
Energy transfer equation of a compressor is Ec=(c1u1 -c2u2)
Get the video lesson here,
4 basics every engineer must know:
What pressure is and how it works is so fundamental to the understanding of aerodynamics.
There are two ways to look at pressure:
The action of a large number of molecules
By definition, Pressure is defined as the normal force per unit area.
Unit of pressure is N/m2 , Bar, Pascal.
Pressure is a Scalar quantity (i.e. it has only magnitude, not the direction)
A gas is composed of a large number of molecules that are very small relative to the distance between molecules.The molecules of a gas are in constant, random motion and frequently collide with each other and with the walls of any container.The molecules possess the physical properties of mass, momentum, and energy.
The momentum of a single molecule is the product of its mass and velocity,
Momentum P=m×v
As the gas molecules collide with the walls of a container, the molecules impart momentum to the walls, producing a force perpendicular to the wall.
The sum of the forces of all the molecules striking the wall divided by the area of the wall is defined to be the pressure.
The pressure of a gas is then a measure of the average linear momentum of the moving molecules of a gas. The pressure acts perpendicular (normal) to the wall.
The tangential (shear) component of the force is the shear stress.
If the gas as a whole is moving, the measured pressure is different in the direction of the motion. The ordered motion of the gas produces an ordered component of the momentum in the direction of the motion. We associate an additional pressure component, called dynamic pressure, with this fluid momentum.
Dynamic pressure
The pressure measured in the direction of the motion is called the total pressure and is equal to the sum of the static and dynamic pressures described by Bernoulli’s equation.
An important property of any gas is its density. Understanding density and how it works is fundamental to the understanding of rocket aerodynamics.
Density is defined as the mass of an object per unit volume. We know that some objects are heavier than other objects, even though they are the same size.
Density is a scalar quantity. Its unit is kg/m3
Different materials have different density. For example aluminum is less dense than iron. That is why airplanes, rockets, and some automobile parts are made from aluminum. For the same volume of material, one metal weighs less than another does if it has a lower density.
For solids, the density remains constant because the molecules are tightly bound. For example, a pure silver coin on the earth weighs same as in the moon.
However, for gases, the density can vary over a wide range because the molecules are free to move. Air at the sea level is different from the air at the stratosphere.
A gas is composed of a large number of molecules that are very small relative to the distance between molecules. The molecules are in constant, random motion and frequently collide with each other and with the walls of a container. Because the molecules are in motion, a gas will expand to fill the container. Density depends directly on the size of the container in which a fixed mass of gas is confined.
As a simple example, consider the figure. We have 10 molecules of a mythical gas. Each molecule has a mass of 50 grams (.05 kilograms), so the mass of this gas is .05 kg. We have confined this gas in a rectangular tube that is 1 meter on each side and 3 meters high. We are viewing the tube from the front, so the dimension into the slide is 1 meter for all the cases considered. The volume of the tube is 3 cubic meters, so the density is .16 kg/cubic meter.
An important property of any gas is temperature. An entire branch of physics, called thermodynamics, is devoted to studying the temperature of objects and the transfer of heat between objects of different temperatures.
The molecules are in constant, random motion and frequently collide with each other and with the walls of any container. The molecules possess the physical properties of mass, momentum, and energy. The momentum of a single molecule is the product of its mass and velocity, while the kinetic energy is one half the mass times the square of the velocity.
Unit is K, degree Celsius and degree farenheit.
The speed of “sound” is actually the speed of transmission of a small disturbance through a medium. The sound itself is a sensation created in the human brain in response to sensory inputs from the inner ear.
Disturbances are transmitted through a gas as a result of collisions between the randomly moving molecules in the gas.
The conditions in the gas are the same before and after the disturbance passes through. Because the speed of transmission depends on molecular collisions, the speed of sound depends on the state of the gas.
The speed of sound is a constant within a given gas and the value of the constant depends on the type of gas (air, pure oxygen, carbon dioxide, etc.) and the temperature of the gas.
Speed of sound =
These 4 basic definitions play a strong role in every sort of science. there is no need of memorising these definitions, but understanding provides good foundation for learning. These values vary from region to region in the atmosphere.
What is mean by Cabin Pressurisation in aircraft?
A Brief History of Cabin Pressurization:
Ever since the Wright Brother’s first powered flight, humans have strived to fly higher. Beyond the thrill of looking out your cockpit and seeing the world pass by like a distant fairy tale, flying high provides many benefits.
- Flying above the turbulent lower atmosphere means a more comfortable flight, while also providing an economic advantage due to the reduced air density.
- It allows military pilots to escape pursuit from less capable aircraft and avoid anti-aircraft fire from the ground
As we climb higher, air molecules are spread farther apart. When we breathe, our lungs take in less air, and less oxygen. At 18,000 feet, the atmospheric pressure is down to 7.3 psi, about half the sea-level pressure. There just isn’t enough oxygen in a breath of air to adequately supply the brain. At this pressure, a healthy adult has only 20-30 minutes of useful consciousness. Altitude sickness, hypoxia and decompression sickness create a triple threat that can ultimately kill the occupants of a high flying aircraft. Early pilots wore flight suits and oxygen masks to counter-act these effects. To survive high altitudes, occupants of an aircraft need help breathing. The solution is to pump air into the airplane so the interior pressure is high enough to keep the humans happy. But full cabin pressurization offered superior comfort, which was essential for commercial aircraft.
Why bother with pressurization? Why not fly down low?
Airplanes can certainly fly below 10,000 feet where the atmospheric pressure is a comfy 10 psi or higher, but it has some drawbacks:
- It’s tough to cross a 14,000-foot mountain range at 10,000 ft.
- Most bad weather is at lower altitudes.
- Turbofan engines are very inefficient down low.
- Aircraft ground speeds are slower at lower altitudes.
If you want a fast, smooth ride in a fuel-efficient airplane that can fly over a mountain range, we need to pressurize
How to achieve cabin pressurization:
Consider the airplane body, fuselage as a long tube which is capable of withstanding a fair amount of air pressure. It is hard to perfectly seal it. Even if it is sealed, the passengers could use all the available oxygen. To solve this problem, the pressurization systems constantly pump in the fresh outside air into the fuselage. To control the interior pressure and allow old stinky air to exit. There is a motorized door called as outflow valve located near the tail of the aircraft .it’s about the size of a briefcase and located on the side or bottom of the fuselage. Larger aircraft often have two outflow valves. The valves are automatically controlled by the aircraft’s pressurization system. If higher pressure is needed inside the cabin, the door closes. To reduce cabin pressure, the door slowly opens, allowing more air to escape. It’s one of the simplest systems on an aircraft cabin pressurisation.
Benefits of cabin pressurization:
- The constant flow of clean, fresh air moving through the aircraft.
- The environment becomes more comfortable for the passengers and making the transport fuel efficient.
Where does pressurized air come from?
- Electric Compressors
- Turbocompressors
- Engine Bleed Air
How do pilots control the pressurization?
It is very easy During preflight checks, pilots turn one knob to display the altitude of the landing airport.
3 Basic concepts every aeronautical engineer must know.
Every object persists in its state of uniform rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.
Applied on the airplane:
There are four major forces acting on an aircraft.
- Lift
- Drag
- Thrust
- weight
When flying at a constant altitude (cruising condition). There is no net force on the airplane and it travels at a constant velocity in a straight line. (i.e)Lift=weight and thrust=drag.When the pilot changes the thrust of the engine, the thrust and drag will become unbalanced. The aircraft will move in the direction of a greater force.
Force is equal to change in momentum per change in time. For a constant mass force equals mass times acceleration.
F = m * a
Applied on the airplane:
The motion of an aircraft resulting from aerodynamic forces, aircraft weight, and can be computed by using the second law of motion.
For every action, there is an equal and opposite reaction.
Applied to the airplane:
It helps to explain the generation of lift from an airfoil. Air, when deflected downwards by the action of an airfoil and in return, the wing pushed upwards.
A jet engine also works on the same principle. The engine produces hot exhaust gases, which flow out the back of the engine. In reaction, a thrusting force produced in the opposite direction.
How to study effectively for GATE AEROSPACE 2018?
As the big day is nearing, all those GATE aspirants are Working hard to step into a great future.All your dreams come true when you work smart rather than hard for your GATE AEROSPACE 2018. There are few effective strategies, I teach my students, When you follow with this method, you can increase your success rate.
Here is my complete guide for GATE AEROSPACE 2018 preparation. these are my best-known ways to prepare for an exam.
I have got 100% success rate with this methodology, even I use to teach using this methodology.
Planning your study time effectively for GATE AEROSPACE 2018:
So, when you come to the point of “time management “.You frequently hear the boring proverb “time and tide waits for none “.However, I believe “time is just an illusion” all you need to do is concentrate. Even if you read for half an hour, just try to understand the context. A deeper understanding of the context helps you learn the application techniques.
Therefore, it is not that how many hours you read; it is how well you read that matters.
I call this technique as “O-BAD”.
Yup, it’s really bad, because it gives you big bang results when you follow it seriously.
O-BAD Technique:
- Outline the” big Chunks”
- Break down and list the subtasks
- Analyze the tasks and subtasks
- Decide when each subtask has to be completed.
Outline the” big Chunks”:
Start with analysing in which subject you are strong. The subject that you choose will be your Big Chunk.Check for the major topics in that subject, these will be TASKS now.
For example, Big chunks in GATE AEROSPACE are Aerodynamics, Aircraft Propulsion, Aircraft Structures, Mathematics.
If you are good at Aerodynamics, it will be your Big chunk now. you have to sort down the topics in that, to find out your tasks.
In Aerodynamics, tasks will be
- Task No:1 -Fundamentals
- Task No:2-Inviscid Incompressible Flow,
- Task No:3-Inviscid Compressible Flow,
- Task No:4-Viscous flow.
now you are done with the first step of this technique. Let’s move to the next step.
Breakdown and list the subtasks :
Identify and list the steps that need to be taken in order to completely Cover each task.
Example: if aerodynamics is the Big chunk, and choosing task 2 -Inviscid Incompressible Flow as your task, now you have to list down the subtasks in that particular chapter and analyse the importance of each subtask with the previous year questions asked in that topic.and list down all the subtopics.
so for the task 2 Inviscid Incompressible flow, Sub tasks are
- Introduction to Bernoulli’s equation
- Introduction to Pitot tube
- Introduction to Laplace equation
- Types of Flows
- Kutta-Joukowski theorem
- d’Alembert’s Paradox
- Kutta condition
- Kelvin’s circulation theorem
- Classical Thin Airfoil theory
- Induced drag and Downwash
- The vortex filament
- The biot savart law
- Helmholtz theorem
- Prandtl’s lifting line theory
- Three-dimensional flows.
Hope you have understood.
Analyze the tasks and subtasks:
Take out and dust the previous year questions for it is much needed to analyze and Segregate the important topics.
Ask: which section-or concept has got more problems?
And which section you struggle the most?
(highlight and remember these topics. Since you need more attention )
Example: when you analyze the previous year question papers, on the Subject of aerodynamics, boundary layer problems have got a subsequent place.
If you are weak in this you need to have deeper learning in this boundary layer topic.
Decide when each subtask has to be completed :
Follow the seven-day rule for GATE AEROSPACE 2018 Preparation:
Day 1: organize your study material, that is you have to allow for a particular subject.Aerodynamics what are the materials you Have. Textbook or class lecture notes or some other, Downloaded from the web.
Day 2: Study with lecture notes
Day 3: Prepare with textbook
Day 4: Solve if you have got problems in class
Day 5: Try solving problems in book
Day 6: Go with previous year questions on the subtask chosen
Day 7: Review everything. If it is a highlighted topic all you have to do is to allot extra time on it.
Example: if you have chosen Classical thin airfoil theory as a subtask in Aerodynamics
You have to follow the seven-day rule allotting half an hour each day. If it is a Highlighted topic ( your weaker area) you have to allot one hour each day.
Make your own study timetable with this technique and follow it.This method will give you 100% success in GATE AEROSPACE
The books that I recommend for aerodynamics are
The method I have followed to prepare the study materials for GATE AEROSPACE 2018 propulsion.
