 Hello and welcome to this lecture series on turbo machinery aerodynamics. Today's lecture is the first lecture of this 40 odd lecture series on turbo machinery aerodynamics, where we are going to cover various aspects of the aerodynamics associated with the different types of turbo machines like axial compressors, axial turbines and centrifugal compressors and radial turbines. So, we will of course, be discussing the details of the syllabus and the course contents in this particular lecture series. My name is Pradeep and along with me Professor Bhaskar Roy, both of us are from the department of aerospace engineering IIT Bombay. We shall be taking up this course which we shall be covering in about 40 lectures or so. So, in today's lecture which is basically an introductory lecture, I shall take you through the syllabus, the course contents of this course as well as the text books or reference and additional reading material that we feel would be appropriate for this course. And subsequently we will also quickly go through the lecture wise schedule of this particular course, where I shall explain what are the course contents that we shall be covering in each of the next several lectures. So, this course on turbo machinery aerodynamics is a course which will basically be looking at the aerodynamics of the flows associated with turbo machines, the various types of turbo machines and the theory behind working of these different types of turbo machines. So, as I mentioned there are two of us who will be handling this course, Professor Bhaskar Roy and me Pradeep, both of us from the aerospace engineering department IIT Bombay. And this course is basically a video course where we shall be taking up all the lecture contents through video lectures. And also of course the transcript of the lecture material also would be available on the NPTEL website. So, in this particular course on turbo machinery aerodynamics, as I mentioned we shall be covering different aspects associated with the aerodynamics of many of the components, which constitute let us say an aircraft engine for example, there are different components which constitute an aircraft engine. Two of the most important components are the compressors and the turbines, these are the basic turbo machine which constitute a gas turbine engine. Similarly, of course turbo machines can be found in various other applications. And the main intent of this particular course is to introduce the various concepts, the working principle and the theory behind many of these turbo machinery components. And so, let us take a very quick look at what are the different topics that we going to cover in this lecture series. So, the course outline is what I will be discussing in the next few slides. We will of course begin the lecture series with an introduction to turbo machines, which we will start in this second half of this lecture which professor Roy will be covering. He will begin the introduction to various aspects of turbo machine in this lecture itself. So, subsequently we will start our course with discussion, detailed discussion on axial flow compressors and fans. We will be discussing the aerothermodynamics of flow through axial flow compressors. We will also be discussing in detail the losses associated with axial flow compressor stage. And once we have looked at the different losses and which constitute an axial flow compressor, we will also look at how we can estimate these losses and how these losses affect the performance of axial flow compressor stage. And then the different aspects of the three dimensional flow, which constitute an axial flow compressor stage like secondary flows, the tip leakage flow and the flow scrubbing, which are basically some of the loss generating mechanisms which are constituents of which are inherent part of an axial flow compressor machine. We will also be carrying out certain amount of 3D flow analysis, the radial equilibrium and the associated equation which constitute the 3D flow analysis of an axial flow compressor stage. We will be spending quite some time in understanding the compressor characteristic. We will be looking at the axial flow compressor, the single stage as well as the multi stage characteristics of an axial flow compressor. This is very important because the way in which the compressor performance is expressed is basically through the compressor characteristics. And it is a very important ingredient which is required by an aircraft engine designer to understand the compressor characteristic carefully. We shall be also looking at the certain fundamental aspects of compressor blade design. We will begin with 2D blade designs and airfoil data. We will subsequently take up the axial flow track design and also the characteristics as I just mentioned. Now, most of the modern day compressors, in fact many of the modern day compressors are not necessarily low speed, they are essentially transonic compressors. So, it is also important that we understand the working principle behind transonic, the high speed compressors or the transonic compressor stages. So, we will spend some time in understanding aerodynamics of the transonic compressor stages. We will also look at the shock structure associated with a transonic compressor blade and also the characteristics of a transonic compressor. We will then move on to the 3D blade design of rotors and stators because the aspect of related to the airfoil data and all those things are basically limited to 2 dimensional blades, but most of the modern blades are 3 dimensional in nature. So, we will also look at the 3D blade design of both rotors as well as stators. We will then spend a substantial amount of time in discussing about the instabilities of axial compressors. There are different instability mechanisms of axial flow compressors and it is necessary that we understand these instabilities in detail. So, as to enable us to design an axial compressor which is more efficient. So, we will look at the instabilities and the loss of stability margin and the associated problems with loss of stability margin in axial compressors. We will also spend some time in understanding the noise problems associated with axial flow compressors and fans because modern day engines are required to have or to limit noise to certain levels which are very stringent and getting stricter every year or so and it is necessary and most of this major chunk of this noise is originating from the axial fan and the compressor. So, it is necessary that we understand the noise generating mechanism of these axial flow compressors. Now, once we have understood and covered the axial flow compressors in detail, we shall then look at another component which is also an axial flow component, but it is a turbine. So, we will also look at the design and the performance characteristics of axial flow turbines. So, that would be the second module of this particular course of axial flow turbines. We shall understand what constitutes a turbine stage and turbine 2D analysis. We will look at work done and degree of reaction in detail and then we will understand the loss mechanism losses and the efficiencies of an axial flow turbine. We look at the flow passage and flow track in multi stage turbines the same way as we had done for axial compressors. We will then look at the 3 different types of or classes of turbines the subsonic, the transonic and the supersonic turbines and in terms of characteristics how we can understand and analyze the performance of axial turbines in a very similar manner as we carried out for axial compressors. So, we will look at multi staging of axial turbines, the axial flow conditions and very important aspect of turbine flow is the turbine blade cooling. So, we will spend some time in understanding the various mechanisms which are used for cooling of turbine blades, because as we know that a higher turbine inlet temperature is always desired for better efficiency and thrust of an aircraft engine for example, but it is the material that limits very high temperatures from being used in axial in turbines in general. So, one of the ways or methods of extending or enabling higher turbine inlet temperatures is to use certain cooling mechanisms and. So, it is necessary that we understand the various types of turbine blade cooling mechanisms which are used. We will then spend some time on understanding turbine blade design and we will start with airfoil design and its profile construction and so on. And then we will extend that theory to 3D blade design the same way which we carried out for the axial flow compressors. So, this would complete the second module of this course which is on axial turbines. So, once we have covered the axial compressor and the axial turbines, we will then move on move towards the other components the other counterpart of these the centrifugal compressors and the radial turbines. So, the third module that we are going to cover in this course is on centrifugal compressors. So, in centrifugal compressors we will start with some fundamentals of centrifugal compressors and we will basically be talking about the different components of centrifugal compressor, the inlet duct, the impeller and of course, the inducer and related components. We will then understand what is meant by slip factor and its effect on the performance. We will be discussing about the concept of rothalpy and the ideal and real work done. We will also spend some time discussing about the incidence and the lag angles and the different types of diffusers which are used in centrifugal compressors. And subsequently we will spend time discussing about the centrifugal compressor characteristics and we will be talking about the surge margin which is an important performance characteristics characteristic associated with centrifugal compressors. We will then be discussing about surge and rotating stall in detail which we also covered in terms of the instability mechanisms in axial compressors. We will also be discussing about the similar instability mechanisms which affect a centrifugal compressor. And then we will also discuss about the different variants of centrifugal compressors of modern day centrifugal compressors. So, this would complete the third module of this course which was on centrifugal compressor and the fourth module is on radial turbine. So, we will begin with some introduction to radial turbine. Then we will also talk about the thermodynamics and aerodynamics of radial turbines and of course, the radial turbine characteristics, losses and efficiency and design of radial turbine. So, radial turbine as you can see will also complete some elementary aspects of radial turbine. But, we would probably not be spending too much time on radial turbine as compared to let us say axial turbine primarily because of the fact that we would be dealing with axial turbines more commonly than radial turbines. And towards the end of this course we will also spend may be a lecture or two on discussion of on the use of computational fluid dynamics in turbo machinery design and analysis. So, this is computational fluid dynamics or CFD is increasingly being popularly used in design as well as in analysis of turbo machines. And the computational tools are getting better day by day in terms of their accuracy and ability to accurately predict the complex three dimensional flow in turbo machine. So, we will discuss some of the aspects associated with the use of CFD in modern day turbo machine design and analysis. So, these are some of the topics or the modules that we shall be covering in this course on turbo machinery aerodynamics. As you can see the discussion is purely on aerodynamics of these components we shall not really be discussing the mechanical design aspects of turbo machines. So, that is purely out of scope of this particular course which is also evident from the title of the course which is turbo machinery aerodynamics. So, we will only be discussing about the aerodynamic aspects of design as well as analysis of these components and the mechanical aspects of design will not really be covered in this course. So, before we move further it is necessary that I also mentioned that there is a certain prerequisite required for those of you who plan to take the take up this course because it is dealing with aerodynamics of turbo machines. It is necessary that one should have undergone a full course in aerodynamics before attempting to take up this course. So, the prerequisite for this course is essentially a full course in aerodynamics and therefore, it is expected that students would be conversant with the various fundamental aerodynamic theories many of which obviously are directly used in this course and it is also desirable that you have undergone some course in the fundamentals of thermodynamics because that also would be part of many of the discussions that we are going to take up in this particular course. So, we will assume that you have already undergone a course in aerodynamics and you also have some fundamental understanding of thermodynamics because these are going to be used very frequently throughout this course. Now, let us now take a look at what are the textbooks that we recommend that you read while taking up this course. We will also suggest some additional reading material which you can take up as and when you require the need for that. So, textbook and references because we will begin with compressor the different types of compressors one of the very fundamental textbooks which deal with compressor aerodynamics in great detail is by Nicholas Cumsty on compressor aerodynamics published in the year 2004 by Krieger publications USA. There is another book on axial flow compressor which is basically kind of a report published by NASA and it is by Johnson and Bullock the report number is NASA SP 36 on axial flow compressors this was released in the year 2002 and similarly for turbines we have a NASA report NASA SP 290 on axial flow turbines this was also released in the year 2002. There are two classical textbooks if I may call this on turbo machines axial flow compressors by J. H. Horlock this was published as you can see way back in 1958, but it is still considered as a very good book dealing with the fundamental aerodynamics of compressors. Another book which was published by the same author by J. H. Horlock is on axial flow turbines published in the years 1965. A textbook which deals with both the aspects of fluid mechanics as well as the heat transfer in turbo machineries was published in the year 1995 by Budhugur Lakshmi Narayana and this is also considered as a very good textbook which can give you great in depth analysis of many of the fundamentals of turbo machines in terms of both the aerodynamics as well as the heat transfer and also this book will also give you some idea about how to use computational fluid dynamics or numerical techniques how they can be used in analysis design and analysis of turbo machines. So, Lakshmi Narayana's book is also highly recommended in terms of not only as a textbook for covering fundamental aspects of aerodynamics of flow as well as heat transfer, but also for understanding of the use of numerical techniques in design and analysis of turbo machines. So, these are some of the fundamental textbooks that we would recommend that you should try and read as you undergo this course. Besides this there are a few additional textbooks that we might suggest two of them are listed here. One of the books is by Gordon Ords it is on Aerothermodynamics of Aircraft Engine Components and it is an AIAA series publication which was published in the year 1985. Another series of another textbook I would say or on Aerodynamics of Gas Turbine Engines was published by the International Gas Turbine Institute which is affiliated to the American Society of Mechanical Engineers ASME. The design of Gas Turbine Engine Thermodynamics and Aerodynamics basically chapters 8 and 10 which are of interest to us this was published in the year 2005 by ASME and of it also comes with few video lectures on covering various aspects of these courses. So, we recommend and suggest that some of these textbooks obviously are would be of great interest to you can also go through some of the advanced textbooks especially by Lakshmi Narayana or some of these additional textbooks that we have suggested would be of interest to you as you undergo this course. So, you might want to go through these courses these textbooks as you undergo this course and various chapters of this particular course. So, what I am going to do now is to take you through the lecture wise schedule of this course and what is it that we shall be covering in each of these lectures during this entire lecture series. So, let me go through the lecture schedule we will start with lecture number 1 which is basically today's lecture primarily to do with introduction syllabus references and schedule. So, as I mentioned professor Roy is going to take up some of the fundamentals and introduction to turbo machineries. The second lecture is on is where we will start with the axial flow compressors and fans the first of that lecture would be on introduction to compressor aerothermodynamics which will be covered by me. The third lecture would be on the two dimensional analysis of axial flow compressors and fan basically the cascade aerodynamics which will also be covered by me. Next lecture would be on the loss estimation 2 D losses in axial flow compressors stage the primary losses and what are the loss mechanisms which will again be covered by me. So, the next lecture we shall be taking up a tutorial we will solve certain examples and also I shall give you some tutorial problems which you can solve later on. The next lecture would be to do with the three dimensional flows we will deal with 3 D flow in blade passages secondary flows and triplicages blade scrubbing and so on. So, professor Roy is going to take up this course of this particular lecture. The next lecture lecture number 7 would be 3 D flow analysis the radial equilibrium concept which will be covered by professor Roy and then we will take up the classical blade design loss the free vortex and other loss which are used in design of axial flow machines. Professor Roy is going to again take up this particular lecture. So, at the end of this the next lecture lecture number 9 would be devoted to a tutorial the second tutorial of this course solved examples and tutorial problems and we will also have a quiz during this particular lecture that would be lecture number 9. And then on lecture 10 we have the radial equilibrium equation the full radial equilibrium equation and the streamline curvature theory which will be covered by professor Roy. Lecture 11 which I shall be handling would be on axial compressor characteristics single stage as well as multi stage and multi spool characteristics. So, basically lecture 11 is on compressor characteristics of both single as well as multi stage types. Lecture 12 will be on instability in axial compressors and what are the different types of distortions which can affect a compressor performance. Lecture 13 would be the discussion on inlet distortion and rotating stall and what is the effect of distortion on rotating stall. Lecture 14 which will be covered by professor Roy would be on compressor instability and control mechanisms. Lecture 15 would be design of compressor blades starting with airfoil design and then we will also be covering subsonic, transonic and supersonic profiles because the blades as you will see would be quite different as it goes from subsonic to supersonic. Lecture number 16 is on transonic compressors and shock structure models and also characteristics of transonic compressors. Lecture 17 would be axial flow track design inter spool duct 3D blade shapes of routers as well as status. Lecture 18 will devote to noise problem in axial compressors and fan the origin of noise and what is it that probably could be done to prevent or control the levels of noise. And then after we have covered the axial compressors in detail we will move on to the axial flow turbines as we have discussed during the syllabus. The second module is the turbine axial flow turbine. Axial flow turbine the introduction to turbine aero thermodynamics will be covered by professor Roy and the 2D analysis of turbine blades the casket and analysis of axial flow turbines to be covered by me. And then lecture number 21 would be axial turbines the work done degree of reaction losses and efficiency. Subsequently we will take up axial flow turbine in terms of the blade and axial flow passages and the exit flow matching with the nozzle. Lecture 23 would be a quiz well a tutorial on axial flow turbines which again will be covered by me. Lecture number 24 would be multi staging and multi spooling of axial turbines to be covered by professor Roy. Lecture 25 is 3D flow in axial turbines the 3D flow theories the free vortex theories etcetera. And lecture 26 would be the fourth tutorial which would cover the 3D flows in axial flow turbines. And then we will spend some time in understanding the cooling effects or the effect of blade cooling on performance we will understand what are the different types of blade cooling techniques. The fundamentals of heat transfer and blade cooling and which will continue on the next lecture that is lecture 28 we will continue with blade cooling technologies. Lecture number 29 is turbine blade design turbine profiles air file data profile construction etcetera which will be covered by professor Roy. Lecture 30 is turbine blade design 3D blade shapes. And then from lecture 31 to 32 we shall be taking up centrifugal compressors in detail. Lecture number 33 is the fifth tutorial which will be on centrifugal compressors which again I shall be covering. We shall also have some lectures devoted towards design of centrifugal compressors the impeller design. And lecture 35 we will take up the other components of centrifugal compressors the subsonic and supersonic vane diffusers vane less volutes etcetera. Radial turbine we shall start on lecture number 36 thermodynamics and aerodynamics of radial turbines followed by radial turbine characteristics in lecture 37. Lecture 38 is the sixth tutorial on radial turbines as well as a quiz. Lecture 39 is on design of radial turbines. And the next few lectures as I mentioned we shall also spend some time to look at the use of computational tools numerical techniques in the design and analysis of axial flow well turbo machines. So, we will spend a few lectures on understanding the basics of the numerical tools. So, we will start with use of CFT for turbo machinery based basically computer aided blade profiles and cascade analysis. We will then look at in lecture 41 grid generation periodicity and boundary conditions as well as the flow analysis. Lecture 42 would be 3 D blade generation and analysis using CFD. And the last lecture of this lecture series would be the flow track and inter spool duct analysis and design using CFD. So, as you see the last few lectures we have specifically set aside to introduce the concept of the use of numerical techniques in turbo machinery design and analysis because this is becoming increasingly important in modern day design of turbo machines. So, as you have seen there are about 43 or lectures in this lecture series during which we shall be covering the fundamental aspects of the aerodynamics and of turbo machines the different types of turbo machines starting with axial flow compressors and fans, axial flow turbines, the centrifugal compressors and the radial turbines. So, this the lecture wise schedule is what I had discussed in the last few minutes. And in the next part of this today's lecture which is going to be taken up by professor Roy he shall give an introduction a brief introduction to the different concepts of the types of compressors and turbine basically an interaction to this whole course itself. So, this second half of this lecture is going to be taken up by professor Roy. You have just been given a full details by professor Pradeep about the course content and the course coverage and all the details about how the course is going to be taken through the various lectures over this lecture series. He has also given you details about some of the books very good books that you may have to acquire or you may have to ask your college library to acquire because most of these books are published abroad and hence you may have to take a little trouble to acquire those books, but those books are indeed very useful for this course. So, if you or your college library can acquire this books it will be really useful addition to this course coverage. What I will do is I will look at the basic elements that we are going to cover over this lecture series and try to give you a very brief sketch of what these elements are. As professor Pradeep has mentioned we will be looking at compressors and turbines as essentially the term machinery elements in this course. One may think of other term machineries like wind turbines, but those are not part of this course. We are looking at the elements that he has talked about essentially the elements that are part of aircraft propulsion system or aircraft engines. So, those are the elements that we would be looking at more closely and in great detail in this lecture series. So, I will very quickly look at these elements the compressors and the turbines to give you a very quick idea about what we are really up to in this course. The first question is why do you need compressors and turbines in an aircraft engine or in an engine that produces thrust for aircraft to fly. Now, this is a question that actually is answered a little more precisely with a little help from thermodynamics. So, we will have a very quick peek at what the thermodynamics indeed gave us to begin with from which we have taken off to create this complex machineries called compressors and turbines. So, if you look at where the engine has come from understanding that an aircraft engine is fundamentally a heat engine and this heat engine finally helps us produce thrust. So, let us take a look at the basis of this heat engine very quickly. If you look at this diagram it is basically a temperature entropy diagram or a T s diagram as it is popularly known and this T s diagram essentially encapsulates or captures what is happening in an engine. So, typically in an engine the flow goes through a process of compression from 1 to 2 and then it goes through a process of combustion in which energy is put inside the engine by burning of the fuel and having put in this energy this energy highly energized flow is then used in an expansion process partly to run a turbine which in turn essentially runs the compressor and then partly to take out the flow through the nozzle or a jet nozzle to create jet thrust. Now, the question is what are these compressors and then the turbines indeed doing here. If you look at this diagram you will see that if you have a compression the thermodynamic diagram indeed goes from 1 to 2 and then it goes in the combustion from 2 to 3. The question is if you do not have compression what will happen is to reach that temperature 3 for example, you would have to start your combustion process at 1 and then go all the way along this and reach that temperature 3 along that path. Now, that path as you can very well imagine now is going to be a very long path of burning of fuel and the burning of fuel would then be done at a low pressure and not at a high pressure. So, the path of combustion would then be extremely large to reach that same temperature level from which you can hopefully do some amount of expansion. The point is for good combustion you need to have a good compression without a good compression the combustion process often end up being a very inefficient process. So, for combustion or a for good combustion you do need a certain amount of compression to be accomplished before the flow is taken through the combustion chamber. Now, once the flow is taken through the combustion chamber you have high energy gas you have compressed gas and you have high temperature gas which is then fed into the expansion system. Now, the first expansion system as we see here is actually the turbine. Now, this turbine essentially is an expander indeed and we will be covering turbine in great detail in this course. This produces work or as it is written here the compressed burned gas essentially facilitates turbine work production. Turbine is the work producer or work extractor from the high energy gas and this work is essentially extracted or produced to run the compressor. So, the entire work produced here in typical aircraft engine is transferred to the compressor which then does the compression job to take the flow to high pressure. So, turbine and compressor essentially are coupled and they work in a loop also certain amount of energy then actually is fed into the gas or into the air through the compressor and it is taken out through the turbine. So, that amount of energy is essentially going into this energy loop which is between the turbine and the compressor it goes through the combustion chamber again comes back through the turbine into the compressor and then the remainder of the energy is fed into the jet nozzle to create the jet thrust. So, you do need compressor to take the flow to high pressure which facilitates the work of the turbine and then it secondly facilitates the work of the jet nozzle for creation of thrust. So, compressor is a very important part of an aircraft engine for most of the aircraft engines that we know of and as a result of which it has become an integral part of aircraft propulsion system right from the beginning of flying. Now, let us take a quick look at what an aircraft engine a modern aircraft engine typically would look like consisting of compressors combustion chambers and turbines. Now, if you look at this engine you would see there are so many parts we would be dealing essentially with fans compressors. So, the flow goes through these fans and then goes through these ducting system then into the compressors and then through large amount of compression through let us say various compressor stages and those various stages would be introduced to you and then fed into the combustion chamber and finally, the flow goes from the combustion chamber into the turbine which extracts the work and through the shaft system runs the compressor. We will be talking about the multi shaft system or multi spool system by which various groups of turbines run various groups of compressors or fans. So, those things would be introduced to you in the process of this lecture series. What we have here is very complex machinery of compressors fans on one hand and turbines on the other hand. I am calling these machineries because these are fundamentally aerodynamic machines. These aerodynamic machines are essentially used inside the aircraft engine for creation of thrust. So, these are essentially aerodynamic machines. Make no mistake about it they are indeed machines that work that produce work that absorb work and finally, that helps in creation of thrust. Let us take a closer look at some of these components which make up an aircraft engine. If you look at this components you will see here compressors. The first picture on the left that you see here is indeed a multi stage compressor. You can see here so many rows of blades and one row of blade here rotor here is shown here in a little more detail. It consists of so many blades. These blades as we go along we shall see are indeed made up of aerofoil sections and these aerofoil sections are at the basis of which these blades are made and then these blades are lined up. First they are arranged circumferentially in a certain manner and then rows of these circumferentially arranged rotors are lined up to make what is called a multi stage compressor. Now in between these rotors we shall see later on as we go along. We would have compressor stators that means another row of blades which are stationary and hence they are called stators. These stator blades again row are shown here in some detail and these are the blades that come in between two rows of rotors. So we have one row of rotor and then another row of stator and here the final assembly is shown where rotors and stators surrounded and covered by a casing which is the final assembly is shown here. So we have a compressor which consists of a large number of blades which are arranged in a certain manner and those manners are what we are going to talk about in great detail and when you arrange them correctly and when you arrange them in an appropriate manner you have a compressor that produces compression and feeds the compressed air into the combustion chamber. So this is what a compressor is all about. We will take a look at a turbine. A turbine is typically made up of high temperature materials. So as you can see here in this picture it shows that it is of a different color because it is made up of very high temperature material, high temperature gas from the combustion chamber is going into the turbine but these turbines are also made up of aerofoils slightly different kind of aerofoils but indeed they are aerofoils and those aerofoil kinds are shown over here on the right hand side. These kind of aerofoils are used in turbine blades in rotors and in stators. The one you see on the right hand side is indeed a rotor and one on the left hand side is indeed a stator. You can see here some very small row of holes drilled along the surface of this stator blade and these rows of small holes essentially or micro holes essentially are the cooling mechanism that cools this blade internally and gives it sufficient life to work for few thousands of hours. We will be talking about the mechanism of the cooling, the aerodynamics of the cooling and how the cooling essentially enhances the working life of a turbine in a useful manner. We will be talking about those things as a part of our lecture series. So, this is what a turbine essentially would be looking like. Again it is made up of aerofoils and we will have to understand how these aerofoils are arranged to make up turbine blades. The other kind of compressors that we would be indeed talking about other centrifugal compressors which Professor Pradeep mentioned and these centrifugal compressors indeed the other kind of turbines is the radial turbines and we will see later on that the radial turbines and centrifugal compressors outwardly they are not really similar. They work very differently but looks wise they may look somewhat similar to each other. So, I am showing you here a typical centrifugal compressor which also does the job of compression and this flow here it enters over here it goes out from this side and then it is surrounded by a row of diffusers which is indeed equivalent to the stators that we talked about for axial compressors and when you put them together the diffuser and the impeller together you have a compressor. In addition to these two units you also have this compressor manifold which essentially then take up the compressed air and supply to the combustion chamber. As you can see here there are number of supply manifolds which are essentially supplying to various combustion chambers. So, a centrifugal compressor essentially consists of an impeller or diffuser and then of course, a set of manifold which supply the compressed air to various combustion chambers. So, these are the components with which we shall be dealing with in great detail. We shall see how these components are indeed made out, how they are analyzed exactly what shapes they are, how do they work and finally, we use CFD in the modern compressor analysis and design and we shall see how these shapes are essentially created with an analyzed with the help of CFD. So, that would be the course coverage in this particular course. I will round up today's introduction with the comments that you would do need to have a good grinding in the basics of aerodynamics. We shall be using those basic aerodynamic knowledge all the time and we will not have time to go back and essentially detail out those fundamental concepts all over again. We will be assuming that you are familiar with those fundamental concepts. So, you really need to get yourself familiarized with those fundamental concepts and as I mentioned that we will be using certain concepts of CFD. It may be useful if you have a passing knowledge of CFD. So, that when we come to towards the end of this lecture series and we get into using CFD for computational analysis of compressors turbines, it is necessary that you have some passing knowledge of CFD. We will mention that when these blades and impeller shapes are created, it may be useful for you to have some knowledge of geometric modeling. The CAD models which are often used to finally, give shapes to this complex shapes which as I mentioned are essentially aerodynamic machines. You need to give them aerodynamic shapes for these machines to work in an efficient manner. So, this is what we would be doing in this lecture series over a period of little more than 40 lectures and in the process we hope that we will be able to introduce to you the fundamental aerodynamic details of compressors turbines, how they are analyzed, how they are designed and how they are finally, created to go inside aircraft engines in modern aircraft engine for creation of thrust.