The Diffuser - Turbine Engines: A Closer Look

[@JulianJonesMusic]

I am currently a 2nd year engineering physics student in Canada and I just wanted to say thank you for making these videos they have really helped me grasp the ideas behind these engines

[@batuyilmaz1464]

I used to watch your videos with awe, now I am actually designing jet engines in one of the best companies. Thank you so much for your motivational "booster"s. :D Dont forget that you are inspiring people. Keep the amazing videos coming!!! Best regards...

[@jordanflorance4419]

I am currently building a jet engine at 14 this video and many others like it have helped me a great deal in understanding how it all works

[@glitchhacker300]

Yo I’ve been wanting to do that for so long! I’m 15 and I just don’t know where to even start…

[@N324F]

Beginning at 3:55, the view of the width of the narrowing stators finally clicked in my head how the physics of the compression really happens. I always understood WHAT happened in compression, now the HOW makes sense.

[@hhhhhhh6427]

This is a great video to learn!! I couldn't understand in writing but I totally understand through your video. Thank you so much.!!

[@joshuamwesigwa256]

Iam an aspiring engineer and these videos teach me more about what am studying and they make me even like the field more. Thank you so much and may God bless you.

[@AgentJayZ]

Thanks! I like it when learning is fun. ...You remember that kid that sat at the back of physics class, but was always asking the teacher questions ? That was me!

[@AeroWrench84]

You should be an A&P/AME instructor. I learn a lot more watching your videos that I did in my turbine theory and overhaul classes.

[@richwaight]

That concept bent my brain around a corner for a while. My brain tell me that by increasing the volume of the gas you would naturally decrease the pressure... But when you described what's happening with the speed I do actually think I get it. :)

[@modernpanther]

I wrote a comment earlier about the diffuser's role, but realized it is positioned BEFORE the combustor. In this context (before the combustor), the design advantages are (assuming subsonic flow): increases in fluid density, temperature. A temp increase would serve as preheating the fluid, so you don't have to use "too much" fuel in combustion, and save fuel costs; inc fluid density would give you more mass per unit of volume of air for combustion, which is always desirable. (CONT.)

[@CRyPTr023]

Was about to go to sleep 3 hours ago... Thanks for all your vids they really are very interesting! The more I find out about this engine the more I am astounded by how logically impressive it actually is. That & the awesome sound of it :D

[@Work-Horse]

Sir, you are more than a book ! Thank You so much for your videos, i use to watch them.

[@mytmousemalibu]

Jay is spot on. Think of it as a venturi in reverse. Bernouli's principal states that an increase in velocity is a decrease in pressure. Here in the diffuser the velocity is decreased and psi increases. Pressure and velocity are inversely proportional.

[@ilovegoatsecks]

you really know your stuff! i can loosely follow you on the theories and ideals and mechanics of this stuff, but it is really fun to watch you break it down.

[@ShubhamArya-zb7tl]

sir ,u have explained it much better than my teacher . thanks a lot..

[@robusto93]

Excellent explanation! I am truly jealous of your job, working around jet turbines is a childhood dream of mine!

[@Daluke61]

Pressure increases as it enters an area of greater volume (the diffuser in this case) while the air velocity decreases. The latter part of that I would have assumed. The first part however, that's a tough one to wrap my mind around. I'm vaguely familiar with Bernoulli's principle and how it applies to an airfoil (private pilot here) but beyond that, I'm somewhat clueless. Looks like I've got an exciting homework assignment. Yet another piece of the pie... thanks again, Jay!

[@bynunenkim603]

wow! ! ! i was quite confusing about learning the difuser's principle and and function of it but thanks to you i am able to get what exactly it is.

[@JCaSs1001]

great video mate, currently building a tin can gas turbine and this helped me work out what the inside of it should look like to increase pressure for ignition and then to increase velocity :) thanks

[@b.o8144]

Smooth and great explanation. Can't thank enough but thank you. Really appreciated!

[@TheCommanderMAD]

"So if you want to learn more about how to design a gas turbine engine, you need to become an engineer!" hahaha love it! Great video!

[@Bobkse]

@deSloleye One reason for having a diffuser is to slow down the air. When air exits the compressor, its velocity is about 500 ft/sec. The speed of burning kerosine at normal mixture ratios is only a few feet per second. So when the air enters the combustion chamber with a velocity of 500 ft/sec, the kerosine would just be blown away.

[@AgentJayZ]

We all need to remember that our opinions on what is happening don't matter. The way this works was all worked out over 250 years ago. No debate necessary... No need to scratch your head and come up with an explanation... just look up Bernoulli in your favorite search engine... or library !

[@Taste3339]

Bernoulli's principle can only be used on incompressible fluids, it does not apply to compressible fluids. You've got to relate the continuity equation and idealise the movement of the gas (isentropic).. Then you'll find a relationship that relates the speed to the gas to the size of the nozzle to the pressure of the gas. dA/A = (M^2-1)dV/dA. That equation explains the phenomenon.

[@AgentJayZ]

You are confusing the compressor with the diffuser. The diffuser is a passive aerodynamic device that, through its shape, converts some of the velocity contained in the gas stream into pressure. The compressor is an active aerodynamic device that adds velocity to the gas stream via the moving rotor blades, and then converts that velocity into pressure in the divergent passage created by the stator vanes. this is accomplished at each stage, and there are 17 of them.

[@oisiaa]

@deSloleye The highest temperature (pre-combustor) should be at the diffuser exit/combustor entrance.

[@modernpanther]

(CONT) Lastly, Inc pressure is your last gain, which serves a purpose related to the preheating effect of inc t. Steam cycles use the same objective of increasing temp and pressure before the heat addition stage to inc fuel efficiency. There are 2 differential equations found in any thermodynamics book under compressible flow that dictate diffuser shape, and fluid property changes.

[@manuelangulo871]

Awesome job! Helped me understand better for my interview! Thank youuuuu

[@74HC138]

@deSloleye If you go to the end of the video, you can pause it when you see the graphs in the book, these show the velocity, temperature and pressure of the air at the various stages of the engine

[@marsphoenix6445]

Very nice, that was wonderful explanation. Thanks a lot.

[@thatonemothafacko]

Magnificent video. Thank you!

[@williamyamm8803]

So interesting for me, a guy who didn't study science but love science (I was not good enough in math, too bad...) Thanks a lot from France.

[@mathewjoseph7493]

AgentJayZ, u r an excellent teacher. Thanks a lot.

[@AgentJayZ]

@343jonny You are indeed the first ! It's a story... basically I had to clean up a nickname that I was given - one that actually was fairly close to that really famous guy who does the music thing and is married to that really hot chick who used to be in that group...

[@TheRick2130]

@deSloleye they add the diffuser(velocity decrease and pressure increases ) because there will be too much air in the combustion section, because if you let pass that higher air velocity into the combustion chamber, you can have flame out or no flame at all! yes, diffuser has the highest pressure & temp. at the cold section

[@belchnasty]

As always a very good video. Informative & very interesting to see how the physics translates into engineering practice

[@AgentJayZ]

@343jonny Maybe the first one. Not the others.

[@jairus61]

Gracias a usted , estamos aprendiendo mas. Saludos desde Perú

[@RodricKing]

You did a great job, bro. (Student Helicopter Pilot)

[@cruisemissle87]

Thank you for another great video. Just a thought: I guess it is okay to say "that is out of my league", sometimes, when you have got a thorough grasp (like you do) of implicit hurdles, required efforts and capabilities, and need to choose between options or professional pathways, and when you are not afraid but content with building upon a certain choice. An engineer might just as well wish to be more hands on and practical like you can be now. On the other hand, you can just *choose* to learn more about the theory than is required as you like, where an engineering student might just rush it over to pass the exam/module.

[@phathomie27]

I'm tempted to say that its the static pressure that increases. The dynamic pressure (or ram pressure as agentjayz calls it) decreases because the velocity decreases. Its possible that the total pressure does indeed increase but it would mean that the static pressure increase would far outweigh the dynamic pressure decrease to cause that to occur, since Ps + Pd = Pt

[@343jonny]

First view and first comment, Jay. Great video! Whenever you get the time, here are some suggestions for future videos: 1. What kind of sensors are on turbine engines and where they are 2. How overspeed control works if the turbines you work on have it 3. TAC Generators: I've looked everywhere, but all I can find is that they convert heat to electricity and some hard-to-understand descriptions 4. Exciter boxes, and 5. My personal favorite: debunking the chemtrail myth :P

[@ZebaWood]

Great video's, many thanks for practical explanations.

[@crustaccione]

depends, sometimes it's to reduce the possibility of shock waves occurring, or to increase pressure in the system.

[@priyanarayan8755]

Ohhh finally my doubt cleared...! thank you

[@drkjk]

It can be a hard concept to accept that increased velocity = decreased pressure. Consider the hose end attachment for spraying weed killer or fertilizer for the lawn. The velocity of the water passing through the attachment "sucks" the fertilizer from the small tank. But it doesn't suck the fertilizer, the velocity of the water passing through the attachment creates a zone of low pressure such that the relatively higher pressure in the tank pushes the fertilizer up into the water stream.

[@modernpanther]

To the second question, while the diffuser increases T, the hottest part of the engine is probably combustion or right after it, which is why the temp. at which the turbine blade melts is an extremely important design factor.

[@AgentJayZ]

The compressor narrows down towards the rear not to compress the gas stream, but to maintain its overall velocity through the engine. It is already compressed, and therefore takes up less space. In order to keep moving a smaller volume at the same speed through a passage, the passage needs to get smaller as well. This video was made to discuss the diffuser section, not the compressor, which you have incorrectly called the inlet.

[@FrontSideBus]

Very well explained! Great video.

[@ToothyGus]

There will be a small decrease in pressure due to loss. The main idea is total pressure is sum of dynamic and static pressure. In a divergent duct, the air slows down so the dynamic pressure is converted to static pressure and vice versa in a convergent duct.

[@ididafewthings]

Hey... I always thought that the diffuser would take the high pressure and slow moving air from the combustion chamber and speed it up while decreasing the pressure. That sped up air on the other hand can then be used to power the turbine fans... So now I'm slightly confused... what is high pressure and slow moving air good for

[@deSloleye]

@343jonny Totally interested in the sensors that go towards controlling these things. That'd be a great video.

[@ytugtbk]

Who could not like this?

[@AgentJayZ]

Lets remember that air has a dual personality. Subsonic airflow is treated as incompressible, so Bernoulli's rules apply. Airflow is subsonic in the compressor. Before you jump all over me... remember that mach number rises with density, density is roughly proportional to pressure... and we're talking about a compressor...

[@vermash]

True, but then again, subsonic airflow is also treated incompressible up until 0.3 Mach only. Just wanted to add to your point...

[@deSloleye]

Ok, so why do you have diffusion? A lot of energy is added to the air in the previous combustion stages, and the air, I take it, gets very fast. What are the desired properties of the air coming from the diffuser that make the engine work? Second question, does this air get hotter in the diffuser or is it hottest at the point of the final compressor? I would think that heat is found where there's high pressure, but I think that idea assumes energy is added.

[@AgentJayZ]

Oh, the irony! we apply rules of incompressible gas flow to explain the way a compressor compresses air.... yes, that is what we are doing. It's almost as if the air is being tricked, no? Well, remember the compressor is an active device. The air is not flowing through it... it is being stuffed through it - the compressor adds energy to the airflow at every stage. The simplified Bernoulli equation deals with an airstream of a given energy being affected by various passive devices.

[@gnypp45]

I believe marek0086 refers to the illustration appearing in at 6:30, between letters D-D. There is a misunderstanding: Indeed the cross section of the white, central part decreases with distance. However, the air doesn't enter the white section. It goes outside of it, in the yellow section.

[@pjvenda]

nice one! anyone who knows a little bit of aerodynamics (not my field either) will have spotted your 'subsonic v' on the diagram :)

[@thakurbps6251]

VERY COOL EXPLANATION. THANK YOU.

[@hwknowshu1]

dose that meen thet once in the combuster the presure rises?more than it is

[@4fifty8]

Why do turbine engines need a diffuser? Is it to slow down the velocity of the compressed air so as not to blow out the flame?

[@traviscapehart7590]

i really not sure how pressure is increased. i am automotive master mechanic and in ic engines the term diffusion means to distribute a substance, either fuel or exhaust gases evenly throughout a larger mass, usually air. i can see how the drop in velocity would occur in the diffuser wich would also create lateral turbulence greatly improving the dispersal of fuel as it is introduced into the airflow. my question is how does the drop in velocity increase pressure?

[@AgentJayZ]

Diffusion has a different meaning in aerodynamics.

[@faustinoeldelbarrio]

The density of the fluid doesn't change dramatically (subsonic flow) then to mantain a steady mass flow the velocity at the exit od the diffuser MUST be lower than in the entrance because you have a larger cross-Area. This means that the fluid has decreased significantly it's kinetic energy (it depends on the square of V). As AgentJayZ said you can't dissapear energy, and taking into account there are no height changes and no significant heat exchange then the "Pressure energy" wil rise,

[@vasilikosolov]

Thanks mate.... got my answers for my assignment

[@nehakalani8654]

What is the advantage of having a static pressure rise both ahead of a compressor and after the combustion chamber?

[@AgentJayZ]

The first makes the compressor more efficient, and the second does not exist.

[@AsadRehmanism]

Wish I could remember all of it after graduation from university the past year.

[@fwp0406]

From the diffuser, the higher pressure, lower velocity air goes to the combustor am I wrong here? Why is higher pressure desired over the higher velocity going into the combustion stage? BTW cheers for the videos too, im going to watch all of them and see if i can understand them fully.

[@AgentJayZ]

The air needs to be moving slowly enough that it does not blow the flame out of the combustor.

[@fwp0406]

Thanks. Makes sense now

[@andrewzaborowski9685]

The whole point of jet engine construction is to compress air, burn fuel, then decompress, so the diffuser to me is just another part of the compressor, it improves on its result. I suck at thermodynamics but just burning fuel inside a moving mass of air doesn't propulse you into any direction, it is the fact that the air is being compressed on one end and decompressed on the other is what make is work. In a ramjet, as far as I understand, the sorta-kina-diffuser part is the whole compressor.

[@Vgk36]

3:25 he says high velocity in and at the divergent side high pressure… I’m confused I thought high velocity goes to low pressure.

[@AgentJayZ]

Here, we are discussing aerodynamic diffusion. In a divergent pathway velocity decreases and static pressure increases.

[@lukeflyby2430]

Does someone know what textbook is displayed at 1:43 ?

[@AgentJayZ]

It's featured in my vid called Jet Questions 96: Books! It's the thumbnail, actually.

[@mersenimers8545]

thanks mr AgentJayZ... a big heard...

[@ashishtiwari1912]

What will happen to the flame in the combustion chamber if there was no diffuser?

[@Taste3339]

True but that equation can only account for subsonic flow where the one I stated(even though I made a slight error in it *dV/V not dV/dA) describes the flow even with supersonic flow. You are right though the basic principles for sub sonic flow are governed by that equation. You are talking about flow through a nozzle here and not compression aren't you? Didn't mean to attack though. I appreciate all of your videos. It's nice to see a hands on approach.

[@izzybuker1947]

Thanks for your videos!

[@gleborlov3045]

From your experience working on engines; has there ever been a need to account for the compressibility of air within a diffuser? Or do engineers usually design it so that the air is always subsonic/incompressible within the diffuser?

[@AgentJayZ]

Air is not incompressible. It behaves that way only if unconstrained. All piston engines, and all gas turbine engines exploit the compressibility of air for their basic function. The process of aerodynamic diffusion is trading kinetic energy for pressure... the increased pressure makes a given mass of air smaller.

[@asemsardy158]

where is the turbo engine is in the asphalt plant....or what does it do in that plant ...?

[@zapfanzapfan]

On the image in the book at the end the velocity is almost constant (slight decrease) through the fan, compressor, diffuser and most of the combustion section. The pressure increases through the compressor but the diffuser doesn´t seem to contribute much. Did the author make a mistake?

[@AgentJayZ]

zapfanzapfan Velocity line looks right. The pressure line could have a small bump up in the diffuser area, but otherwise it looks good.

[@zapfanzapfan]

Ok, I thought the effect would be bigger or maybe that the difference was that the engine in the picture was flying and the numbers therefor were a bit different. The nozzle after the combustion and the turbine section, are they a convergent-divergent nozzle? Looks like the classic trading of temperature and pressure for speed in the diagram.

[@haddenindustries2922]

I think it's a regular convergent nozzle used in jet engines.convergent-divergent nozzle are mostly applied on rockets I think.but i'm not sure, i'm not an engineer just a plane enthousiast :-)

[@SebastianLopez-nh1rr]

Mickey DeVe he’s right, I do study engineering

[@danieldelgadosan]

my question is: when the air reaches the end of the diffuser, the space is bigger, so there's more volume, if you have more volume, and the same air, why doesen't the pressure decrease?

[@jstylin89]

makes alot more sense. i've already watched a few of your videos while studying for my a&p license exam. i just wanted to say thanks for taking your time making videos to help students like me. much appreciated and respect! do you still read these comments?

[@syed_taha_ahmed]

How does exhaust diffuser at exhaust of gas turbine increases pressure ratio

[@AgentJayZ]

The diffuser is not on the exhaust, but at the discharge of the compressor. Diffusion is an aerodynamic term describing a phenomenon which results in increased pressure in a flowing stream of gas. I suggest doing a search for that term.

[@dannyporter7746]

can you tell me if these are welded brazed on or what holds them on--old man thanks you---

[@AgentJayZ]

"these" is a word that leaves great uncertainty about just what part you are asking about. A bit of a description, or at least a time stamp would help me out.

[@AgentJayZ]

Yes, it does seem confusing. All the rules for subsonic airflow seem counterintuitive. Gotta do some reading, googling, what have you... about subsonic aerodynamics. A good source of info is "the Jet Engine" by Rolls Royce. Library, Ebay, Amazon... they all got it.

[@GiorgiBranquinho]

Nice Jay!! the stator of axial compressor compress the air like a diffuser or the stator just direct the air to next rotor stage?

[@AgentJayZ]

+Giorgi Lucas Stators form a diffusion passage. They also feed the next stage blades at the appropriate angle

[@GiorgiBranquinho]

Tanks Jay you are the best in jet city!!

[@URMECHANDUP]

is the inlet pressure of Diffuser is the outlet pressure of compressor ?? is the total pressure at the inlet and outlet of the diffuser same ??

[@AgentJayZ]

Yeah

[@URMECHANDUP]

sir , if the total pressure at inlet and outlet is same then the cross sectional area of duct should be constant through out its length right ?? please correct me if I am wrong ..

[@AgentJayZ]

+UR14ME067 CHANDU P If you don't understand the relationships between the components of total pressure, that is something you need to study, as it can't be cleared up in a video comment box.

[@URMECHANDUP]

sorry sir , I ll not trouble you anymore with these kind of doubts .Thanks for uploading the videos .It really help us a lott..

[@nehakalani8654]

Total pressure has two components. Like, force can be divided into two components. But, don't get confused again, pressure is not a vector. What I am talking about is its static and dynamic components. Well, if you are standing in a room with no fan or any other means of forced convection, and use a barometer or something to measure the pressure in the room, that pressure you measured will be the static pressure, as the air was not moving at all. And the other component is called the dynamic pressure. The dynamic pressure of air is when the air is moving, as you must have guessed by the word 'dynamic'. It is due to the velocity of air and is given by 1/2 * density * velocity ^2. Difficulty understanding yet? No problem. Think of this, the total pressure is the static pressure + dynamic pressure. If a fluid, say air, is moving at very high velocities, it has dynamic pressure due to the velocity and the static pressure, just because of its presence. Now put a huge obstruction in between so the air comes to rest. This brings the velocity of the air to ZERO. That means it stagnates and then the total energy of the air is only the static pressure energy or the total pressure is only due to the static pressure. But it still remains same. Why? Because the dynamic pressure converts itself into static pressure. Conservation of energy due to pressure, you see? This causes the total pressure to remain same, at both ends of the diffuser. However, the change in velocity, the decrease in velocity due to the area of cross-section change, causes the dynamic pressure at the outlet to convert into static pressure, giving higher static pressure at that end, as compared to the inlet. I hope I cleared your doubt. :)

[@j007pace]

Hi AgentJayZ. On a J79/LM1500, what is the approximate pressure difference from the higher velocity low pressure entrance side of the diffuser vs the lower velocity higher pressure exit to the combustion chamber? I'm very grateful for all the time you have taken to share so much about the inner workings of turbine engines. Thanks for all of your videos, I enjoy watching them immensely

[@AgentJayZ]

The pressure change through the diffuser is not something we measure, so I don't know. We measure CDP, but the exact position of the sensing port along the diffusion path is not something I'm aware of.

[@j007pace]

Thanks AgentJayz. Always learning with your videos!!

[@prathameshpatil2549]

Thanx for video it is so much helpful... But sir I have one doubt... The textbook diagram you have shown in that diagram the space is getting narrow after diffuser in combustion chamber and as you said in diffuser velocity of air get convert into pressure because of increase in volume so what happens after diffuser does it's pressure again decrease because of small volume....

[@maxhugen]

"the space is getting narrow after diffuser "... no, it's the area coloured yellow, and it's diverging (getting wider) in the diagram.

[@michahermann7869]

That diffusor looks like a rocket engine nozzle! How does it work that the same shape transforms a fast, low pressure airflow into a slow, high pressure one and at the same time transforms a slow, high pressure airflow into a fast, low pressure one? Isn't that contradicting?

[@AgentJayZ]

+Micha Hermann The rocket nozzle is a supersonic device. The axial compressor diffuser is a subsonic device. You have quite a bit of reading to do.

[@michahermann7869]

AgentJayZ Thanks for your quick answer! I didn't realize that air behaves in such different ways just because it's supersonic! Well I guess I'll learn the difference when I'm studying aerospace engineering

[@BlackVille2000]

Could you please share the title, author, etc. of the book used? Thanks

[@AgentJayZ]

+Lahfyn No. I've got bad news for you: if you can't find a book on the subject you are interested in, you're not going to make it.

[@wiggles8x0]

+Lahfyn The book doesn't matter much as much as the topic. For you to understand what is happening all you need to look up is Bernoulli's equation regarding static and dynamic pressure along with knowing what continuity is. Both of these topics should be in any Fluid Dynamic book as they are the fundamentals. If you are more interested about specifics of turbines, Mechanics and thermodynamics of Propulsion by Hill and Peterson is an excellent choice but it is condensed specifically with just the mechanics and thermodynamics, it is assumed that if you are reading the book, you understand fluid dynamics. Have fun learning!

[@BlackVille2000]

+Sophrosyne Thanks a lot for your reply. Excellent explanation. Regards....

[@kerrickakinola7398]

What's the name of the "introductory textbook" that you reference at the beginning of the video? You pointed to a diagram in this book. Thanks.

[@AgentJayZ]

From a while back: It's featured in my vid called Jet Questions 96: Books! It's the thumbnail, actually.

[@michaelmooney3369]

so the diffuser exchanges speed for pressure if I am understanding you.

[@michaelmooney3369]

***** in the water nozzle the water velocity goes up so the same amount of water can go through the constriction? "Bernoulli effect"

[@4fifty8]

Shockwaves are taken care of by the inlet. The air has to be slowed to subsonic speed before entering the engine.

[@GijsdeRue]

Nice video as always, though I like the nuts-and-bolts videos a little better. Incidentally, the "one-in-one-out-theory-system-idea" is more commonly known as the conservation of mass. ;)

[@mirzaahad6779]

I'm currently confused about the difuser and combustion chamber

[@AgentJayZ]

@deSloleye You need to do some research into the whys. There's no way I could give a lecture on physics, especially on KZbin.

[@i-travel8270]

What will happen if the aircraft has no diffuser ?

[@AgentJayZ]

Don't know. The diffuser section is part of the engine. Also between every pair of compressor stators is a diffuser. Without that shape, the engine will not work.

[@danieldelgadosan]

Thanks, I'll try to find it

[@zahiddd100]

sir . does the defuser provide resistance to the air flow.. ? i am confused

[@AgentJayZ]

Yes, and no. It depends what you mean by resistance. But in practical terms no. The diffuser converts kinetic energy to pressure. The diffuser slows down the air flowing through it, and raises its pressure. If you are going to google search aerodynamic diffuser, make sure you filter out all the race car or car related stuff.

[@zahiddd100]

sir.. for example there is a smoke chimney, whose diameter increases gradually. in this case as the velocity of the moving smoke is being converte pressure, will this increase in pressure provide resistance to the smoke entering the chimney and travelling upward in the chimney. thank you.:)

[@AgentJayZ]

No. That's not a diffuser.

[@zahiddd100]

AgentJayZ thanks for your time.

[@Gamefan232949]

agentJayZ, i know this must've been asked before but i haven't come across it yet: Are you an engineer or a mechanic with a serious amount of knowledge? thanks for making these videos. after watching just a few i've learned quite a lot about jet engines.

[@DanFrederiksen]

Isn't the exhaust folds also called a diffuser?

[@AgentJayZ]

Very vague, but if you are talking about the divergent pathway created by the variable exhaust nozzle when an afterburner is engaged... no, that is not a diffuser. Aerodynamics are very different in the supersonic speed regime.

[@DanFrederiksen]

@@AgentJayZ no I mean the transversely wavy outlet on some jet engines meant to mix airstreams

[@AgentJayZ]

Oh. Not a diffuser, although you could use that word conversationally instead of technically. The waves make the confluence of the two airstreams, which are at different speeds, more gradual. Instead of an abrupt edge, the moving air meets the transition at an angle, and this helps reduce noise.

[@Volans2000]

Another very good video... ;)

[@Stig007]

I searched this video cuz I fear that one of my study manuals is wrong does this differ for supersonic air or is it the exact same thing

[@AgentJayZ]

+Stig Cruise A lot of aerodynamics is the exact opposite once you get supersonic.

[@RedDaLord]

Speaking of supersonic speeds, does any air go supersonic in the engine? Does the aircraft's forward velocity affect engine airflow velocity?

[@AgentJayZ]

I think the compressor avoids supersonic airflow, and the only place in the eengine that does experience supersonic air is right at the exit of the exhaust accelerating nozzle.

[@andrewzaborowski9685]

Can be seen quite clearly in the graph he shows at 6:22. I wonder though, if the air was supersonic at the exhaust in theory you could use a rocket type diverging nozzle instead of a converging (subsonic) nozzle...

[@AgentJayZ]

Wonder no more. The variable exhaust nozzle used on afterburning engines takes the shape of a converging nozzle at non-AB settings, and then becomes what is known as a con-di nozzle when the AB is in operation. You can see it in operation in some of my afterburning J79 test run videos.