This sequence was Broadcast on the History Channel UK Documentary Whittle the Jet Pioneer by UK Based based CGI Animation Studio Rendermedia www.rendermedia.co.uk
The air sucked into the turbine by the fan to the multi-stage compressors already bears a huge momentum in its initial flow direction and with the addition of entropy or heat it will therefore accelerate while being compressed alongside. Hence there is no flow reversal in the path adapted by the air stream. Hope it helped :)
This is a jet engine that uses a Centrifugal flow compressor similar to the compressors you find in car turbo and superchargers, the system you're talking about is the Axial flow compressor spool which is the norm nowadays.
This is the first generation of british jet engines during WWII with radial (not axial) compression and separated combustion chambers like Rolls-Royce_Nene. The german Junkers Jumo 004 at this time had still separated chambers, but the more sophisticated axial compression, which lead to a much leaner silhouette with aerodynamic advantages.
This is an example of a centrifugal compressor. When I worked on C-130's we had axial compressors in the main engines which, like you say, had multiple compressor fans (14 stages of them, to be exact). Our APU (small engine used to start other engines) used a centrifugal compressor, much like this one right here. It's basically an impeller, much like the one used on a jetski, though they require very high rpm to compress the air sufficiently. C-130 main engines=13,820 rpm. APU ~ 35,000 rpm.
The exhaust gases are driving the turbine which directly drives the compressor to compress air into the combustion chamber. As long as there is combustion driving the turbine there will be compressed air from the compressor forcing airflow through the combustor section from front to back. If the airflow through the engine is disrupted/stalled (ex: engine inlet at too steep of an angle) the flow can stagnate and you can get a "cough" of flame out the front. This is called compressor stall.
This is a centrifugal compressor, which works by accelerating the air to move in a circle and pushes it outwards. It's used in small jet engines because they are simple to build and more compact. Downside is that the air effectively hits a wall. The compressor blades you mean work by pushing air through a narrowing tunnel. These are used in the jet engines of commercial airliners, because they're more efficient (the general air direction doesn't need to be changed) but is no good on small scale.
Thanks for all the comments, It really is just a simple animation sequence; it has to be simple to allow those who are not familiar with the process to look at it and to see how it works, If you are exhibiting to a general audience then you need to strip back the science to a degree and allow the process be clearly illustrated in a way that isnt distracted by all the other gubbings surrounding the model, The Software used is 3DS Max8 rendered with the Brazil renderer,
The pressure in a jet engine is highest right after it exits the compressor. as it enters the combustion section and is burned, the pressure decreases and the velocity increases according to Bernoulli's law. the higher pressure after the compressor acts as a sort of wall only allowing the gases to flow out the exhaust.
The compressor (front rotor) is a centrifugal compressor which throws air outwards, not thrown backwards like you're thinking. And just because the air goes upwards into the combustion chamber doesn't mean it loses pressure. You don't need multiple stages for compression either, this is a perfect example of a small gas turbine engine, which isn't a typical jet engine. They're mainly used for their shaft power, not thrust. Also a "turbo fan" is a type of engine, you're thinking of a turbine.
Simple. The hot gases escaping from the rear force the rear fan to turn. The rear fan is connected to the front fan, so the front fan is forced to turn and it blows air into the combustion chamber to be mixed with the fuel and support combustion. Of course the engine must already be turning before it's started. That's done either with compressed air or an electric motor connected to the fan shaft (depends on what the engine is used for).
very reliable due to its simplicity. You dnot see many aircraft with jets sitting around getting maintenance done on them, however, their maintenance is involving when the reach their major service intervals. I'm still in awe!
this is a very simple single spool engine with a centrifugal compressor. modern jets usually have multiple spool engines with axial compressors which are generally more efficient
Love the mixing of nomenclature here. This engine uses an IMPELLER rather than a compressor which consists of multiple arrays of static and moving fan blades at the front. This is the original design of the jet engine as built by Sir Frank Whittle. A turbofan jet engine has a primary fan at the front that is larger in diameter than those used in the compressor and directs air around the outside of the actual engine. This is not one of those either.
Thanks all for the comments, the software used is 3DS Max, its rendered using a renderer called Brazil by Splutterfish. I really enjoy creating these types of shots, its a great way of explaining with simple visuals how a process works without over complicating. If anyone would like to get in touch regards bespoke shots or projects for educational or broadcast please get in touch. Many Thanks Rendermedia
The hot air does not escape out the front of the engine because of pressure differences through out the engine. The area following the combustion chamber, the turbine, has an average pressure lower than the combustion chamber therefore the air goes into the turbine because it will always go to the area of lower pressure.
Because the pressure on the front side of the burner's is much higher than the pressure at the turbine, so the flow wants to go from high to low pressure thus going backwards through the turbine.
@mestizo23 You are correct on this. This is because turboprops and turboshafts (helicopters) are small engines that require little airflow since they produce less power. Impellers take very little space axially. When you try to increase the airflow through the engine, the impeller has to be increased in size radially. This means it must get wider. Thus you have a very wide, heavy engine. At some point it makes more sense switch to axial compressors. (about regional jet size like the ERJ147)
Whittle's jet engine was the first one and it had a centrifugal compressor because they hadn't invented the type with stages yet, which is called an axial compressor. As you can see in the illustration, the air radiates outward from the center of the compressor toward the edges, also taking advantage of centrifugal force. Some new engines use one of these compressors. Pratt &Whitney's PT6 turboprop has multi-stage axial and a single-stage centrifugal compressor. Google the term and enjoy!
because of the shape of the combustion chamber the flow is accelerated rearwards. Some pressure drop is required, as it is the reason why the expanding gases travel out the rear of the engine rather than out the front. Less than 25% of the air is involved in combustion, in some engines as little as 12%, the rest acting as a reservoir to absorb the heating effects of the burning fuel.
At the front of the engine, the compressor sucks the air in, and compresses it, the air coming in is fast enough to stop the flame going back out. Also the combuster cans keep the fire contained and out of direct flow, much of the air goes around the the can, so its difficult for the flame to go through the compressor.
Thank you all for your comments the animation is a very simplistic approach to how a jet engine works based on Sir Frank Whittles design, the animation ties in with audio commentary and because of this we slowed down the truespeed of the variouis stages, in real life what happens would be so quick that we decided to slow down each section to allow the viewer to take in what is happening.
This engine doesn't need a diffuser for the combustion chamber. The tubes take the place of the diffuser, this chamber type is a can-type combustion chamber. The combustion happens inside the "cans". The tubes compress air because the centrifugal compressor, which throws air outwards, not backwards forces lots of air into the tubes. Also, what second stage are you talking about? The rotor in the rear is a turbine, which catches the air and produces thrust and turns the compressor up front.
On a jet engine, the concept is that the pressure in the compressor section is higher than that of the combustion (fire) and turbine section. The compressor section can often produce compression ratios > 9.5:1 (Think: the same as your car). From front to back, the compressor section has the highest pressures, the combustion section is essentially a divergent duct where the pressure drops off, and the turbine section is where the pressure makes its final drop through another divergent duct.
If you had a jet engine without the compressor (fans) spinning and you introduced fuel into the combustion chamber and lit it, that's exactly what would happen. You have to get the fan spinning fast enough before you start burning fuel. Then the air is moving so fast that it can not escape out the front. The burning and expanding air rushes out the back and drives the rear fan which is connected to the front, which continues to suck in more air and oxygen to continue the fuel burning.
You're right. The first thing I noticed was that this uses centrifugal (radial) compressors and turbines. These are never used in propulsion engines, but they are used for power generation and APU's.
@willwoodhouse You are correct. The fan (we call it bypass flow in the industry) provides about 80% of the thrust in modern jet engines. The more we can pull into the bypass flow, the more efficient (generally) the engine is. Note for terminology: the part that does compression - ignition - expansion is called the CORE and the air that goes around it (through the fan) is called the BYPASS.
The heated gas cannot escape from the front because the last stage of the compressor blades is smaller than the first stage of the turbine blades. The turbine section will always have enough power to drive the compressor.
The impeller at the front is the compressor stage here - it compresses air by pushing it outwards towards the combustion chambers (centrifugal compression). That's the same method of compression that model gas turbines use, it saves on space and cost of manufacture.
The "front of the jet" is actually a compressor. It raises the air pressure quite alot. However, at the back of the engine, the air pressure tends to be the same as the outside atmosphere. So the heated gas, when having to "chose" between facing a high pressure at the front and a low pressure at the back, "choses" the easiest way out: through the back. That's Nature in action, basically.
Because the gas follows the path of least resistance when escaping the chamber. The front of the chamber is pushing high pressure gas inward while the back of the jet is free to allow gases to exit.
@GameSupervision 6) exhaust gasses are pushed through a secondary fan, which is connected to the first fan, causing the first fan to spin, repeating the cycle :)
@juredddd Yes, this is a much simpler design than the large turbofan engines we see on aircraft - the main difference is the method used to compress the air before combustion - in this case the front fan acts as a radial (centrifugal) compressor, pushing the air outwards from the centre, and into the combustion chambers. More complex turbofan engines use fixed turbine stages (stators) between multiple rotating fans, reducing in diameter and pushing the air backwards into the combustion chambers.
@orika001 thrust is what does most of the work. The engine itself is being pushed by thrust. There is a small vacuum created ahead of the engine,but the thrust is where the work is.There is more thrust than vacuum because of expansion from heat. So I guess the answer is....It depends on where the engine is mounted but the engine is being pushed.
@pengy44 It's "empty" space. In reality, we use this space to route cooling and pressurization air to be used elsewhere in the engine. The electronics and hydraulics are all mounted to the case of the engine, outside of where all the action is happening.
The gases will not leave out the inlet because of the high pressure forward of the combustion chamber. It is easier for the gases to escape out the rear end of the engine due to its construction. The gases will however escape out the inlet if the compressor fails to compress enough.
@willwoodhouse Yh your absolutely right mate Ive been doing research for my interview at rolls royce, the air that is being sucked in and used as thrust is known as bypass thrust, the air the is compressed and combusted is known as core thrust The type of engine is a turbofan, then there is either a high bypass engine which gains 80% of its thrust from bypass and the other is a low bypass engine which gains most of its thrust from the core etc
Not stupid at all. The pressure of the air as it enters the combustor is greater than the pressure blowing out the rear as thrust. The volume of the air as it enters the combustor is far less, however, If there is not enough pressure at the combustor you can have what is known as a hot start, which can quickly damage the engine, as the fuel burns in place.
1) the inflow has a very high velocity so it exerts a pressure on the inlet of the jet. there is no such pressure on the back side. therefore "stuff" tends to exit from the back side of the jet. 2) if the heated gas can escape out from the front of the jet, then inflow will be zero or minimal. this would inhibit the burning because the oxygen required for the burning of the fuel is supplied from the atmosphere.
the same is true for all air propulsion systems to some extent; the way a prop is driven forward is that the pressure behind it is greater than the pressure in front of it. you have to redefine your understanding of pressure somewhat; if the pressure masses were static, then yes, there would be back flow. however, the working fluid is moving, so the rules change somewhat. in addition, the pressure is being created and maintained by the compressor, which is inputting energy into the gas.
@orika001 pushing it. they use batteries to run up and get the compression started before they start injecting fuel and then the explosion pushes it forward. prop planes are the opposite, they pull
@mestizo23 You are right to an extent. Small engines tend to use impellers or centrifugal compressors. Impellers are very good at compressing in a small space, but as the engine gets bigger, the impeller has to get big enough to handle the mass flow. After a certain point, it's too big to be practical so you end up getting into axial compressors.
well the principle is the same. but in modern ones u find huge compressors in front of the combustion chamber(s) and in the commercial ones today (turbofan) there is an outer airstream that actually provides most of the thrust while the inner airstream is mainly used to power the fan.
good question i know several reasons one because of the way the stator vanes and rotor vanes are pitched to push and compress the air reward (like tiny propellors0 they both creat a low pressure behind itself and air always flows from high pressure to low pressure... also the air around the air that doesn't flow through the compressor known as secondary air helps keep the flame where they desire..not too mention the ducts are shaped as convergent and divergat angles to also manipulate the flame
Air pressure is lower out of the turbine section than coming in via the compressors, the air just naturally is propelled out of the rear and through the turbine.
That is a centrifugal compressor. It doesn't need several stages to get a sufficient compression. It forses the air upward because of centrifugal forse. It is the axial compressor that needs several stages. However, centrifugal compressors are not so common any longer. They are most used on APU's and older aircraft engines.
@thrax777 I think that some new engines still use an impeller, the PT6 from Pratt and Whitney does. But in general youre right, that's quite old technology.
actually there´s a wall between the fuel injecter and the combuster^^ so it only can choose one direction, by the way this animation is pretty simple, actually such a jet engine has up to 14 or more combustion chambers
Cool animation, just one flaw, the fire is ideally only in the combuster can, not flying through the turbine as shown. I guess this is done this way in orange to show that it is hot gas, but if the fire extended out of the can and was blowing through the turbine, the turbine would soon fail.
@thrax777 Impeller are still used for some models today as high pressure compressor (last stage), specially for turboprops. lol I just say that because I'm actually studying this =P
@willwoodhouse It's true that about 80% of thrust comes from the fan in modern engines, but only during take off at sea level. At altitude, the large area and high inlet speeds cause a lot of losses in the fan. There's a vector addition going on between the rotational speed of the fan and the inlet speed which causes the fan to "see" supersonic speeds. That creates a lot of losses and makes it difficult to extract work from the bypass stream at cruise, so thrust only comes from the inner stream
There are times, however, when the heated gas does escape out of the front of the jet. Google: Compressor Stall. When a compressor stalls due to external factors or a damaged blade, the pressure immediately drops to near ambient where the heated gas "realizes" that the path of least resistance is out of the front of the jet engine. This generally happens in short bursts, like a backfire, but due to the scale of the engines it often sounds like a cannon going off.
@orika001 interesting question, in my opinion it depends on the location of the engine relative to the wings mean aerodynamic chord. In propeller lingo if a prop. is behind the wings MAC it is a "pusher type" and in front of the wings MAC is a "tractor" type. So typically I would say that turbines are tractor type and pull the aircraft. This changes when you think of tail mounted turbines though, those would be pusher type.
@rapaceable The red bull x2011(concept) has one, but to utilize the turbine engine because they only like to stay at a relatively constant RPM, you would need to use a CVT transmission (that is currently no where strong enough) to handle the 1500 horsepower that this turbine would produce.
Lol, your very observative but the compressor configuration used on this engine is the centrifugal type, it was developed by the Britsh during WW2 while the Germans where developing the Axial flow compressor which does infact compress the air in stages using a series of rotors and stators while the centrifugal type uses an impeller to take the air in and push it up. Centrifugal types are not used often because it is not aerodynamic but it still produces more power without adding more weight.
Love this, when fuel explode in each chamber, how to make sure the heated air go to the back not the front. unless you have a valve at the air inlet, it will close in every blow.
Beautiful job. Top notch, pro!. The lighting and reflections are great on their own, but the other fuel effects are equally impressive. What kind of light set up did you use? Does 3D Max have a cut tool to create cross-sections or do you have to do that manually?
