# Questions tagged [shock-waves]

A shock wave is a type of propagating disturbance. When a wave moves faster than the speed of sound in a liquid, gas or plasma (a "fluid", in physics terminology) it is a shock wave. Like an ordinary wave, a shock wave carries energy, and can propagate through a medium. It is characterized by an abrupt, nearly discontinuous change in pressure, temperature and density of the medium. In supersonic flows, expansion is achieved through an expansion fan.

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### What happens in order to make a shock when the flow first turns?

Imagine you have a really zoomed in view of a 2d ramp, which is at 20 degrees. Zoom in on the exact point the ramp turns from horizontal to 20 degrees. When the first supersonic air molecules reach ...
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### Why are shockwaves allowed different angles at different distances from a body?

It's been (well) established that a shockwave can only be at the angle of the Mach cone. (I now understand this part). However, in this picture: you can see that the shock is at 2 angles. I also ...
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### Why will the flow turning angle be 0 (or close to) inside of the Mach cone?

(Disclaimer : This probably seems like my 56th question on the same topic, but this will be my last relating to Mach cone angle and shock angles, as I think I understand most of the topic) So the ...
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### Can a shock in certain circumstances be at a lesser angle than the Mach cone?

(Excuse the drawing quality) What will happen if a shockwave has an angle less than that of the Mach cone? In this picture, the black line represents the Mach cone. The orange line represents the ...
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### Does the flow turning amount change as you get further away from an object?

Will the flow turning amount change as you get further away from an object? This answer explains why shockwaves will extend past the body that made them (good starting point). This question is asking ...
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### Why does the angle of a shock change when the flow leaves the influence area of an object?

In this (great) answer, it says: "far enough" from the Concorde's nose, the path followed by the airflow is not affected by its presence and it's just a straight line. Close to the nose we ...
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### Why does the shock angle always seem to equal the "sound cone" angle?

(I'm going to use the term "sound cone" for the area you can hear an aircraft when it's at Mach ≥ 1, illustrated by this picture. Not considering the shockwave.) So as explained in this ...
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### Can a sound wave travel through a shockwave?

Say you have a scenario where there is a shockwave, and you sent a normal sound wave towards it. Could the sound wave travel through that shockwave? If so/not, why? Would it depend on the strength of ...
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### Why doesn’t the air expanding behind a shockwave reverse the effects of wave drag?

Wave drag is (from my understanding) the difference in pressure between the front and rear of an object due to shockwaves, making an opposing force. This needs higher pressure in front of said object ...
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### Why do the shocks in supersonic jet exhaust end at the boundary?

As explained in this answer, the shocks in supersonic jet exhaust are created from the ambient air pressure compressing the exhaust stream. This eventually makes a shockwave, which reflects and then ...
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### Why do shocks travel further down the wing as the Mach number increases?

Inspired by this question, why do shocks move further back on a wing as the Mach number increases? Normal shocks on the surfaces of wings form when the air molecules of the pressure recovery area on ...
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### What happens to a shockwave when it goes through different temp/density air?

Specifically I am asking what happens to a shock as it travels through different density air. This answer's comments has some good information about it. As said in the linked answer, a shock will bend ...
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### Why does more lift make a stronger shock?

Why does more lift make an aircraft shock stronger? In this answer, it says more lift will make a stronger shock. The aircraft's lift contributes to the strength of the boom. What part of making ...
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### Why can you only hear an aircraft after the shockwave passes?

Why do you only hear engines and other noise from a jet going supersonic after the plane has passed? A lot of resources use this picture to illustrate : This is cool and all, but say you changed the ...
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### Why don’t shocks refract through other shocks?

The picture in this answer shows a shock traveling into the ground. When it does so it refracts. For this example pretend that if a lower strength shock went through a higher strength shock, there ...
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### How are shockwaves able to refract?

How are shockwaves able to refract? As said in this, When two shock waves collide, they interact with each other and produce complex patterns of compression, rarefaction, and reflection. The ...
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### What happens when shockwaves interact?

As seen here, there are two T-38's going supersonic. What happens when those shockwaves interact? They seem to dissipate in some places on this photo when they interact. Any source online says that ...
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### Why does a slip line form in between these 2 shocks?

As seen here, the trailing edge shock creates what looks like a slip line between the two shocks. I thought a slip line only formed when air that went through different shock systems interacted, so ...
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### What causes the vapor cone when an aircraft is traveling at M ≤ 1? [duplicate]

What causes the vapor cone of an aircraft going M ≤ 1? I know that the vapor is from the air expanding, but why is it in the cone shape? What shock system forms it into that shape?
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### Will air in a shockwave flow outwards?

It's well known that shockwaves extend outward from a plane, as seen in this picture. My question is, does the high-pressure air in the shockwave extend outward? This is hard to explain so I'll let ...
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### Why do shockwaves extend past the body that created them?

Why do shockwaves extend past the body that created them? As seen in this photo, the shock doesn’t stop in the air the plane is effecting, but continues on. I always assumed it was high pressure air ...
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### Why don't shockwaves expand rearwards when they expand out?

Why don't shockwaves expand rearward when they expand out? In this for some reason really big picture, you can see the shocks expanding out past the actual plane. Why don't they also expand rearward? ...
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### Why is the upper surface shock further forward than the bottom shock on this airfoil?

If you look at this picture, you’ll see the shock on the upper surface is further forward on the wing, compared to the lower shock. Why is that? (This is at Mach 0.9, as shown at the bottom of the ...
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### What causes this vortex pattern on the slip line of a shockwave?

What are these little vortex patterns from on the slip line of these shocks? At first I thought it was vortex shedding, but it looks a tiny bit different to me (than vortex shedding). You can see the ...
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### Will supersonic flow return to subsonic through shocks over a flat surface?

Will supersonic flow return to subsonic through shocks over a flat surface? Imagine supersonic flow over a plate. Will it always try to return to subsonic through a series of normal shocks? (Pretend ...
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### Are oblique shocks formed at the leading edge-top surface of a wing?

Do oblique shocks form on the leading upper surface of a wing? I know bow shocks are formed there, but is that the same thing as I’m talking about? Oblique shocks would have to form there because the ...
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### Are control surfaces less effective at supersonic speeds?

I am unsure if this is correct but this is my current explanation: Once past supersonic speeds, the larger the speed the larger the divot of air pressure around the plane. Because these divots can get ...
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### When an oblique shock forms, what happens to the normal shock that helped it form?

What happens to the normal shock that helped the oblique shock form, in the first shock of a lambda shock? Oblique shock waves form because : "An oblique shock wave is a shock wave that, unlike a ...
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### What determines the angle at which a shock will form?

What determines the angle that a shock will form? If you look at a lambda shock, you’ll see it isn’t straight up, but with an angle (both the front and rear part of the lambda shock). The second ...
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### Do the oblique shocks at the trailing edge cause as much resistance as the ones on the surface of a wing?

Shockwaves formed on a wing will move backward until they reach the trailing edge, when they turn into oblique shocks and stop. When they're on the surface of the wing, it makes sense why they would ...
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### Why are pressures equal across the slip line of a lambda shock, but density is not?

Why are pressures equal across the slip line of a lambda shock, but density is not? In this answer, it says this : The surface Σ is a slip line between zones 3 and 4. Velocities will be parallel ...
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### How do boundary layers and shocks interact?

How do boundary layers and shocks interact? What difference is made with thinner and thicker BL's? I've recently been researching this topic, but at least for me there are no good search results on ...
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### What causes the lambda shape in a shockwave?

What causes the λ (or lambda shape) in a shockwave? I heard it had something to do with the interaction between the shock and the boundary layer. If so, how do they interact and why does it make the ...
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### Why are bow shocks angled slightly downward at the leading edges of wings?

Why are bow shocks angled slightly downward on airfoils? In this picture if you look closely at the very bottom airfoil diagram, you'll see the "subsonic airflow" part is more below the ...
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### pressure wave propagation of shockwaves? [duplicate]

I can’t find a simple explanation of how the pressure waves propagate that leads to a shock over an aerofoil online. How does this happen with upstream flow that is high speed but subsonic?
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### How does a shockwave form from a subsonic upstream?

How does a shockwave form over say an aerofoil from a subsonic upstream? Wouldn’t the flow have to be supersonic before it ‘shocks’? Also, does the flow in a shockwave jump from let’s say it is at M=1....
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### What is a shockwave, and how does it form?

so I came across this picture on this website: https://howthingsfly.si.edu/aerodynamics/shock-waves I’m curious about why/how this shockwaves occurred after the supersonic speed and, would like to ...
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### Obtaining a special formula for the Theta-Beta-M diagram

I'm currently studying shockwaves, particularly their effects on drag. I've stumbled upon an odd formula in "Elements of Gasdynamics" (Liepman and Roshko, pages 52-53), in there I saw an ...
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### Can supersonic booms intensify as you fly longer?

If someone is flying just above Mach 1 for 10 minutes, I would think the sound/shock waves would just pile up and gain more energy, resulting in a very intense and loud boom when the pilot slows down. ...
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### How do swept back wings delay shock wave

Swept back wings can delay the formation of shock wave and increase the aircraft critical mach number of the aircraft, right? But how
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### Why do expansion fans cause oblique shock waves to curve?

When there is an expansion fan aft of an oblique shock such that its bounding mach waves intersect with the oblique shock, the oblique shock is curved in that region. What is the physical phenomenon ...
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### Would shockwave over a Supercritical aerofoil move downstream with Angle of attack? [duplicate]

over a supercritical aerofoil, would a shockwave move downstream with increase in angle of attack? I thought yes as the top surface is flat?
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### Can someone recommend a good book/paper on understanding shockwaves over aerofoil? [closed]

I’ve been trying to understand shockwaves around an aerofoil from some contour plots I saw here and on the internet, but I’m struggling to understand them Can someone please recommend a good book on ...
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### How are shock waves formed at fighter jet inlets when the shock wave is already formed at the nose cone?

If the main shock wave is formed at the nosecone of a jet aircraft at supersonic speeds, how is the airflow still supersonic at the inlet of the jet intake? Shouldn't the inlets experience subsonic ...
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### Why have supercritical airfoils not been used in designing the propeller blades?

In terms of specific fuel consumption, propellers are more economic than jet engines at low speeds (<0.5 Mach) but at high speeds, the propeller blade tip reaches locally to supersonic speeds which ...
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### How high could modern transonic commercial transport designers reasonably push L/D ratios?

One facet of the evolution of commercial transonic transport design since 1970 years is that L/D ratios (alternatively, the M * L/D) have increased only mildly over time. For example, see the ...
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### How does forward sweep of a wing affect the formation of shock waves?

I understand that sweeping a wing back reduces the component of velocity perpendicular to the wing and can allow it to travel at subsonic conditions, and reduce the formation of shock waves, even if ...
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### Could ramjets be implemented on sub/super-sonic aircraft wings due to the shockwaves generated by them?

Well, I'm a ignorant on aerodynamics and such, but let me explain first: In this video (it could be just a video, but) it is said that wings are angled backwards to avoid supersonic shock waves ...
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