Well defined shockwave along A320 wing
Posted by NiklasAstro@reddit | aviation | View on Reddit | 87 comments
first time sitting by the emergency exit and was thrilled to see this
Posted by NiklasAstro@reddit | aviation | View on Reddit | 87 comments
first time sitting by the emergency exit and was thrilled to see this
deleted_by_reddit@reddit
[removed]
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Blazing_Lino@reddit
Can someone explain what I'm looking at š
VladAkimov@reddit
What you are seeing there is a shockwave created by the air moving at the speed of sound.
It is created because the particles don't have the time to "react" to the incoming movement, so instead a shock is created. You can usually see this of faster fighter jets, however commercial airplanes operate on what's called the transonic speed regime, meaning that while the airplane is under subsonic speed (below the speed of sound), some parts may be at or above the speed of sound (supersonic). This happens here over the wings here because those are designed in such a way so that the flow of air on the upper side speeds up and as a result creates a pressure loss, like a "suction", therefore creating lift. And it's because of this acceleration that the local flow there is faster than the one felt on the rest of the plane, and it's the reason why you see the small shock wave.
I tried to explain in a simple but somewhat detailed way, I hope you got the idea :)
Underradar0069@reddit
So this isnāt a scratch on the window, it is shockwave.
GlockAF@reddit
We sure? Likeā¦sure sure?
NiklasAstro@reddit (OP)
It is probably worth watching with a fast internet connection, compression kinda kills it. but I find it almost more striking further up the wing, with several of these happening side by side
VladAkimov@reddit
Yep
DeadFacesInMyPocket@reddit
Damn. Very excellent answer and a large reason if why follow this sub!
JasonIsFishing@reddit
Good explanation. This is a visualization of what happened when the USAF Thunderbird āwent supersonicā in Chicago. The aircraft itself was never supersonic or it would have been more than booms and a few broken windows!
LandscapePenguin@reddit
Now you've got me curious. What would there have been besides boom and broken windows?
JasonIsFishing@reddit
The jet was in very close proximity to downtown Chicago right over the water. There would have been thousands of ruptured eardrums and a good portion of the glass in the high rises would have broken.
Azurehue22@reddit
This is a very dumb question, but I was under the assumption a sonic boom was like very close thunder. Is it louder? Iāve never heard one.
kpfeifmobile@reddit
That happened to the north of you in Milwaukee two years ago - https://youtu.be/9AOwm4CoQ0M?si=2n1CcjJuezxC7Qtl
As far as I know, no windows were lost. Maybe too far away?
RatherGoodDog@reddit
I personally saw a pair of Eurofighter Typhoons fly directly overhead at supersonic speed, and fairly low altitude. Maybe 1000-3000ft maximum. It was loud as hell and rattled the windows but ruptured eardrums is a bit melodramatic.
JasonIsFishing@reddit
Nope. With the proximity that the Thunderbirds fly during an airshow, a couple of hundred feet AGL and right in front of the viewing area, ruptured eardrums from the aircraft itself (not just flight surfaces) flying supersonic is by no means melodrama.
53V3N@reddit
Well, maybe. The energy is there, but it turns out you have to be extremely close--200ft close.
https://www.aero-news.net/index.cfm?do=main.textpost&id=D3EFB603-F4F2-4120-BAFB-3DB867C52D90
Lawsoffire@reddit
The Mythbusters thing was on thick modern glass, however.
As someone that lives in an area that frequently saw interception of Russian aircraft pre-2022. I can assure you supersonic booms can destroy windows. Old farmhouses, greenhouses and such have all had windows destroyed by supersonic booms from F-16s.
TheBlacktom@reddit
Why can we see it? What is it exactly what we see? Air is transparent. This is not exactly transparent.
VladAkimov@reddit
Because it has a significant change in pressure and temperature that distorts the light that goes through it.
RobotMaster1@reddit
Is the āsuctionā aspect more of an influence on lift than the āblowingā aspect under the wing?
rsta223@reddit
Yes, the lift contribution of the suction side of the airfoil is much larger than the contribution of the pressure side, at least if you define that by looking at pressure difference compared to ambient and integrate that around the surface.
headphase@reddit
Your framing is setting up a bit of a red herring. The Newtonian component (equal and opposite reactions) has nothing to do with "pressure side" airflow contributing to pushing the wing up.
When we talk about Newtonian physics generating lift and the 3rd law in particular, it's all about angle of attack causing a downward redirection of air past the airfoil's trailing edge. Wings with a large camber exaggerate this effect.
This is a big deal because Bernoulli's principle (the low pressure 'suction' effect) does not explain how symmetrical wings (or inverted flight) are possible.
Both explanations are codependent of each other.
rsta223@reddit
Actually, you're the one falling down a bit of a trap here. Bernoulli and Newton aren't competing explanations at all, and both fully explain the lift (well, you need to use a modified Bernoulli above Mach 0.3 or so thanks to compressibility contributions to flow energy, but that's just a correction, not Bernoulli fundamentally being wrong or anything).
If you take a subsonic wing, look at the airflow around it, and use Bernoulli (or modified Bernoulli at speeds where compressibility becomes relevant), you can fully account for all the lift on the wing. Yes, even if it's upside down. Yes, when if it's symmetrical. Bernoulli doesn't tell you what the flow speed and countries are, it just tells you that if you know the flow speed relative to free stream at some point among a non-dissipative stream tube in the flow, you know the pressure as well. They are linked because all Bernoulli's relation is, fundamentally, is a statement of conservation of energy, and in a flow without significant shock waves and outside of a thin boundary layer, there's no mechanism for much energy loss, so conservation of energy holds.
The Newtonian approach is also true, of course. You'll also fully account for the lift if you look at the downwash behind the wing relative to the incoming flow. This is also based on a conservation law - this is just a restatement of conservation of momentum, while Bernoulli is conservation of energy.
Neither approach actually will tell you the shape and velocity of the flow field though. Newton lets you calculate lift if you know your downwash, and Bernoulli does if you know your flow speeds around the airfoil, but neither lets actually figure out those speeds and angles in the first place. For that, you need substantially more complex math and to start looking at things like flow circulation and the Kutta condition that occurs at a sharp trailing edge.
triggerfish1@reddit
Yeah I think your last paragraph makes it quite clear. The pressure gradient is the mechanism for turning the flow downward and thus will also create the downwash. It's two sides of the same coin. I also find it quite elegant to note, that the pressure's only job in an incompressible flow field is to prevent divergence.
YouToot@reddit
FOR GOD SAKES JUST GIVE ME THE DAMN NUMBER
rrredditor@reddit
Oh, god. What have you done...
dunderthrowaway3@reddit
Mega maid has gone from suck to blow!
Allaplgy@reddit
There's actually still a lot of debate on that very subject.
PowwowPuffer@reddit
No, there's not
Bernoulli's Principle and Newton's 3rd Law both explain lift forces for different reasons, and it's naive to assume a force can only be generated from one thing.
Bernoulli explains how the faster moving air over the top of a traditional wing design lowers pressure on the top side to "suck" the wing upward. Bernoulli's Principle further provides explanation for wingtip vortices and induced drag. See also, the Magnus Effect
Newton primarily helps explain how the angle of attack increases lift.
Bernoulli's better explains most normal flight, but is more difficult for people to visualize. Both forces would be enough to lift a plane provided they move forward fast enough.
LandscapePenguin@reddit
Yet somehow planes can fly inverted.
VladAkimov@reddit
Planes can fly inverted because that has to do with angle of attack. As long as you can have enough power to keep the speed up for the relative airflow and not exceed the critical angle of attack, it will fly. Much worse, but will fly. Also that's why not all airplanes can fly inverted continuously.
PowwowPuffer@reddit
Yet somehow you think that makes any of what I said false.
mig82au@reddit
There's zero debate about that specific question. The pressure distributions are well studied and the net force is more suction driven.
rsta223@reddit
No, for nearly any reasonably shaped subsonic airfoil, the suction side will contribute much more than the pressure side to overall lift.
VladAkimov@reddit
The "suction" is created by the air accelerating on the top side. It doesn't exactly blow, but a force is exerted. You can see this by holding a piece of A4 paper by it's tips on one side and blowing over it. The paper will lift up :)
monstherocket@reddit
Thanks for the explanation- loved reading this so hereās my poor manās award š„
VladAkimov@reddit
Cheers! :)
flightwatcher45@reddit
Isn't it tied into the low pressure right area too, not just the air speed. Its low pressure so the low pressure the mach speed is lower? I just woke up lol.
VladAkimov@reddit
In this case yes as the low pressure area is where the speed of the relative airflow is faster, thus "simplifying" the creation of the shockwave.
The low pressure is a side effect of the speed increase.
Mia_in_antigua@reddit
One of the best illustrations of Bernoullis Principle I've ever read. Kudos, my fellow redditor
VladAkimov@reddit
Thank you very much! Cheers! āļø
cruisin_urchin87@reddit
Explained it well. I love when Reddit opens my eyes to new (to me!) and interesting things.
Charlie3PO@reddit
The aircraft is flying in the transonic speed region where, although the aircraft is flying below the speed of sound, it's close enough that there are local areas of airflow of airframe where the air exceeds the speed of sound briefly before slowing back down below the speed of sound.
In this specific case, the aircraft is likely flying 70-80% the speed of sound, as air accelerates over the top of the wing, it's able to reach and exceed the speed of sound in certain areas. As the airflow moves further back over the wing, it then slows back down, a shock is formed at the point where the speed of the air falls from supersonic back to subsonic.
So that's what you're seeing, the shock, where the airflow is suddenly slowing back to subsonic speeds. It's visible because the temperature and density of the air rapidly changes when it goes through the shock.
rooood@reddit
Yeah I was thinking about that. Airlines today seem to fly as slow as they can get away with to save fuel, it feels just as rare to see an airliner flying this fast lol
gaylord9000@reddit
Can you explain how the wing shape accerates the air? I can't intuitively grasp how that works. I would think the air could only be accelerated to match the airspeed of the plane.
realborislegasov@reddit
Pretty sure itās a cobweb
sampathsris@reddit
A glitch in the matrix. That's what it feels like to look at a shockwave like this.
Darth19Vader77@reddit
Standing shock wave.
A wing generates lift by causing a pressure difference between its upper and lower surface and a decrease in pressure creates an increase in speed of the air flowing over the wing.
Since the upper surface of the wing increases the speed of the air flowing over it, as an aircraft approaches the speed of sound, the air above the wing reaches the speed of sound before the aircraft does. When this happens a shock wave forms on the upper surface of the wing and a shockwave is by definition a change in density.
The change in density changes the way light is refracted which is what allows you to see the wave.
ScienceMechEng_Lover@reddit
Lambda shock. To generate lift, you need a pressure difference between the upper and lower surface of the wing. The shape of an aerofoil makes it so that the flow above the wing has a higher velocity than the flow below the wing, and higher flow velocity means lower pressure.
When cruising, the flow above the wing can exceed the speed of sound, resulting in the shockwave seen in the video. This can be bad as it will lead to flow separation over the wing and a reduction in lift as a result.
Modern aircraft have supercritical wings which alleviate the issues caused by lambda shocks; they don't get rid of the shockwave but move it further rearwards, meaning flow separation occurs further downstream and less lift is lost as a result.
Loose-Cicada5473@reddit
If you could run your hand through it, I wonder what that would feel like
ILikeFlyingMachines@reddit
Cold
ShonOfDawn@reddit
Passing your hand through the shockwave is actually pretty complicated to describe. Your hand would form its own shockwave because it would need to stop the supersonic air over the wing, and those two shockwaves would interact in some counterintuitive way. Supposing low levels of chicanery such as a random supersonic jet forming at the interaction and hitting your hand, at Mach 0.85 and 0.3 bar, stagnation pressure is something like 0.5 bar (excluding pressure losses to the shockwave but those are low), so the differential is somewhat in the order of 0.2 bar or 2000 kg/m\^2. On the area of a human hand that is around 30 kg of force, which is not absurd but definitely not a fun experience. This unless I'm missing some crucial phenomena, please correct me if I'm wrong
arizonadeux@reddit
I would be much more concerned about my hand freezing solid. Right around Mach 1, the temperature increase across the normal shock is pretty low as the heat transfer coefficient is going to be just about maximum.
ShonOfDawn@reddit
That is definitely the worse effect, I was actually surprised that the dynamic effects are relatively manageable at that speed.
archer505@reddit
Probably like one of those Dyson air blade hand dryer things /s
boris_squanch@reddit
I think it would obliterate your fingies
cruisin_urchin87@reddit
Itās presumably where the aircraft is supersonic so, your hand would probably not be attached to your body for long (or maybe Iām wrong)
DogsAreMyFavPeople@reddit
Bad. It would feel bad.
Brennan_Schwartz@reddit
ChimkimNugger@reddit
I hope you ga e
Da
VladAkimov@reddit
Fantastic video! Allow me to save this to share with students!
NiklasAstro@reddit (OP)
Sure! I got another clip that shows the wave shaking together heavily from turbulance, I can upload it to streamable (and also this one if it makes saving easier)
VladAkimov@reddit
Thank you very much! āļø
NiklasAstro@reddit (OP)
https://streamable.com/g3wxjq
https://streamable.com/ey5o3h
CalmpBump49@reddit
can you provide which flight you are? I want to playback on FlightRadar24 and check for Ground Speeds =)
NiklasAstro@reddit (OP)
EW9592, happened shortly before/while crossing the alps
VladAkimov@reddit
Superb! Thank you!
729reddit@reddit
How are you certain that this is a shockwave and not a boundary layer?
mig82au@reddit
Boundary layer transition is far smaller in height and transonic shocks are expected on airliners.
AnohtosAmerikanos@reddit
And boundary layer transition doesnāt lead to notable density gradients, which is why we can see the shock
NiklasAstro@reddit (OP)
I am not, I have seen similair looking videos described as a shockwave but if it isnāt, please correct me
mr_dee_wingz@reddit
Bro was hauling ass!
readonlyred@reddit
Schlieren photography!
jarcaf@reddit
Yeah I'm wondering if the sun is reflecting off the winglet at just the right angle and with the right point/line source conditions that it's basically an accidental schlieren effect. Very cool if so.
ilovenacl@reddit
Thatās crazy. Iāve flown so much in my life, almost always seated at the wing, and I always thought those squiggly wiggly lines were coming from the window
jarcaf@reddit
Very lucky lighting conditions to see this so clearly! Awesome!!
start3ch@reddit
That is awesome! I always sit by the wings, and look for these when flying, but have never gotten lucky enough to actually see one.
ScuffedA7IVphotog@reddit
Sure that's not just a thing floating on someones eye
MutedFeeling75@reddit
Wow
Raphy8884@reddit
WINDOWSAIR
danit0ba94@reddit
Seems to be happening right at the top of the wing curvature.
The place I would expect it to happen 1st. Very nice.
NaahLand@reddit
Pilot is trying to break the soundbarrier. /s
StockholmParkk@reddit
Is this why on night flights the paint on the sharklet looks so weird and wavy?
Desutor@reddit
Thats the Window
PowwowPuffer@reddit
That's sick!
post-explainer@reddit
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