Tornado air intakes
Discussion
Why are Tornado engine intakes shaped the way they are? First of all at an angle rather than the front of the intake being at 90deg to the airflow. Secondly the angle is such that the base of the opening is further back when having them the other way up would appear better from a FOD point of view
The intakes are shaped in such a way that the shock wave produced by the forward part of the intake intersects with the other side, air passing through a shock wave slows down and in doing so increases in pressure slightly. The intake is designed so that a number of shock waves will occur, raising the pressure before finally passing though a 'normal' shock wave which occurs at Mach 1 slowing the flow to subsonic speeds, the duct then expands and slows down the air some more so that by the time it reaches the compressor the pressure of the air flowing into it has been substantially raised.
The amount of compression you can achieve in a supersonic intake means that the J58 engines used on the SR71 would actually dump air from the intake into the afterburner and the engine would operate more like a ramjet.
The amount of compression you can achieve in a supersonic intake means that the J58 engines used on the SR71 would actually dump air from the intake into the afterburner and the engine would operate more like a ramjet.
Dr Jekyll said:
alangla said:
Same shape as Concorde and pretty much every other fast jet of the late 70s, early 80s surely (thinking F14/15, MiG29, SU27 etc here)
Most but not all, (EG Phantom, Jaguar) hence my question. I could just have easily asked about F15 intakes but we are British, so there.
The rectangular shape and sloped lips are to do with controlling the airflow at transonic and supersonic speeds. Jet engines don't like supersonic airflow, so, if the aircraft is travelling at or above the speed of sound, the intakes are designed to slow the speed of the airflow down so that it is subsonic as it enters the engine itself.
I think it's also worth pointing out some of the effects between supersonic flow and subsonic flow.
If air is subsonic and travels through a duct the gets progressively narrower, the flow will speed up, and conversely it it travels though an expanding duct, it will slow down. However the reverse is true for supersonic flow. This is why rocket nozzles have that characteristic hourglass shape. In a converging duct, if the pressure difference between either side is high enough, the flow will increase in speed so that it reaches Mach 1, the flow travelling through this shock wave will then slow down again back to subsonic speeds. However, the point at with it reaches the local speed of sound inside the flow, you start to expand the duct, the flow will continue to accelerate and reach even higher speeds. In the case of rocket engines this exit velocity can be on the order of km/s. For an intake you simply run this in reverse, contacting duct to slow the flow down to subsonic speeds, then an expanding duct to further slow the subsonic air.
It's also worth noting that the local speed of sound is only dependant on the temperature of the fluid, so when you design an intake, each time the flow passes through a shock wave and increases in pressure, there is also a corresponding increase in density and temperature, which changes the Mach number slightly, which changes the angle at which the sock wave is produced. So these intake designs can be extremely complex and modern intakes tend to be variable geometry affairs, that can be optimised for the flight conditions.
If air is subsonic and travels through a duct the gets progressively narrower, the flow will speed up, and conversely it it travels though an expanding duct, it will slow down. However the reverse is true for supersonic flow. This is why rocket nozzles have that characteristic hourglass shape. In a converging duct, if the pressure difference between either side is high enough, the flow will increase in speed so that it reaches Mach 1, the flow travelling through this shock wave will then slow down again back to subsonic speeds. However, the point at with it reaches the local speed of sound inside the flow, you start to expand the duct, the flow will continue to accelerate and reach even higher speeds. In the case of rocket engines this exit velocity can be on the order of km/s. For an intake you simply run this in reverse, contacting duct to slow the flow down to subsonic speeds, then an expanding duct to further slow the subsonic air.
It's also worth noting that the local speed of sound is only dependant on the temperature of the fluid, so when you design an intake, each time the flow passes through a shock wave and increases in pressure, there is also a corresponding increase in density and temperature, which changes the Mach number slightly, which changes the angle at which the sock wave is produced. So these intake designs can be extremely complex and modern intakes tend to be variable geometry affairs, that can be optimised for the flight conditions.
LimaDelta said:
So not an issue for fast-subsonic aircraft with 'straight' intakes then (Harrier, Hawk, Skyhawk etc.) I guess?
In those cases you tend to have what is known as a Pitot Intake, which have more rounded intake lips, whereas supersonic intakes have edges that are sharp. These sharp lips means you have what is called an 'attached' shock', which has a lower drag than a 'bow shock' that you get on blunter objects. But sharp intakes are rubbish at subsonic speeds as the flow will separate from the sharp edge and create turbulence particularly at high throttle settings at low speeds, or during manoeuvring, causing issues with the engine's compressor aerodynamics leading to things like compressor stall. Pitot intakes still work at modest supersonic speeds, but you have far less pressure recovery than a well designed mutli-shock intake.Edited by Fugazi on Friday 1st December 13:30
karma mechanic said:
That carrier aircraft (Vigilante?) above is even more impressive looking back - a supersonic carrier-launched nuclear delivery aircraft designed in the fifties without anything we'd recognise as a computer.
I've said it before but I think it bears repeating. I have always maintained that North American Aviation in the 1940s, 50s, 60 and early 70s were the most adventurous and advanced airframe manufacturers in the world.Some of their products in the period 1940 to 1975 -
P-51 Mustang
P-82 Twin Mustang
F-86 Sabre
F-100 Super Sabre
F-107
A-5 Vigilante
XB-70 Valkyrie
X-15
SII stage (the middle stage)of the Saturn V - and the hardest one to develop
Apollo Command and Service Modules
Space Shuttle Orbiter
A lot of the same people worked on all these projects. It's an amazing list.
karma mechanic said:
That carrier aircraft (Vigilante?) above is even more impressive looking back - a supersonic carrier-launched nuclear delivery aircraft designed in the fifties without anything we'd recognise as a computer.
Concorde's variable ramp system and associated Air Intake Control Units were impressive for their day and were key to Concorde's performance, especially around Mach 2 (The USSR was keen to get access to tthe AICUs)Nice explanation of the ramp system and how they work here:
http://www.concordesst.com/powerplant.html
Also some interesting stuff about AICUs here:
https://www.tapatalk.com/groups/concordesst/concor...
(ChristianJ was on the original development team IIRC)
I've got four AICUs in my shed ....;)
StephenP said:
Concorde's variable ramp system and associated Air Intake Control Units were impressive for their day and were key to Concorde's performance, especially around Mach 2 (The USSR was keen to get access to tthe AICUs)
Nice explanation of the ramp system and how they work here:
http://www.concordesst.com/powerplant.html
Also some interesting stuff about AICUs here:
https://www.tapatalk.com/groups/concordesst/concor...
(ChristianJ was on the original development team IIRC)
I've got four AICUs in my shed ....;)
A first for PH - a supersonic shed Nice explanation of the ramp system and how they work here:
http://www.concordesst.com/powerplant.html
Also some interesting stuff about AICUs here:
https://www.tapatalk.com/groups/concordesst/concor...
(ChristianJ was on the original development team IIRC)
I've got four AICUs in my shed ....;)
StephenP said:
Concorde's variable ramp system and associated Air Intake Control Units were impressive for their day and were key to Concorde's performance, especially around Mach 2 (The USSR was keen to get access to tthe AICUs)
Not just the USSR.Rockwell wanted to buy the information for the B1 but Rolls Royce demanded too high a price.
One of the Concorde engineers was in the US at the time and Rockwell proudly showed off their new 'Mach 2 bomber'. At the time they couldn't get past Mach 1.7 because of problems with intake airflow but this was a closely guarded secret..
The Concorde engineer looked at the B1 engine intakes and said "I'm impressed you got to Mach 2 in this, in fact, I can't see how you managed to get past Mach 1.7."
This caused consternation, but he then explained that there had been similar issue with Concorde and from experience with that he reckoned the B1 would probably suffer more because the intakes were so close to the leading edge of the wing. He also spotted some probes fitted to the intake that appeared to be there to measure the airflow and put 2 and 2 together.
Krikkit said:
The Valkyrie was a completely different design though...
That said, isn't the B1 stuck at about 1.3?
The B1 that entered service was a lesser aircraft compared to the original prototypes. The B1A version was cancelled by Carter but the less capable B1B was re-instated by Reagan.That said, isn't the B1 stuck at about 1.3?
Also, aircraft designed for the low level supersonic strike role usually operate in that speed regime so it goes as fast as it was designed to go for the mission it was designed to do.
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