Supersonic and hypersonic shockwave mitigation

[avaneeshg]

TL;DR

A way to reduce the intensity of shockwaves during supersonic and hypersonic flight.

The main reason supersonic flight is inefficient is because of the shockwave. The shockwave is caused by the inability of air to escape the path of the aircraft in time. As a result, the air builds up in front of the aircraft and a shockwave is formed. To try to reduce this effect, can't we add a small hole in the nose of the aircraft? It'll be connected to a tube that spans the length of the aircraft's fuselage. In this configuration, the severity of the shockwave could be reduced. What are your thoughts?

 

[berkeman]

Welcome to PF.

Have you looked at the design efforts currently underway to produce a new supersonic commercial passenger jet that has a much lower sonic boom issue? I'll have to look for some links, but it's an active area of research...

 

[berkeman]

I think this is the one I'm thinking of. Still searching for a good link on the technologies involved...

https://boomsupersonic.com/

 

[berkeman]

Hmm, it may be that they still generate sonic booms when supersonic, but are aiming to fly just under mach 1 over land and accelerate to supersonic over water...

https://boomsupersonic.com/faq

 

[russ_watters]

The main reason supersonic flight is inefficient is because of the shockwave. The shockwave is caused by the inability of air to escape the path of the aircraft in time. As a result, the air builds up in front of the aircraft and a shockwave is formed. To try to reduce this effect, can't we add a small hole in the nose of the aircraft? It'll be connected to a tube that spans the length of the aircraft's fuselage. In this configuration, the severity of the shockwave could be reduced. What are your thoughts?

That's not really true as stated, but be aware that anything that redirects flow just adds more shock waves and more drag. It's not like there's something being inflated in front of the plane that can be deflated to reduce drag.

 

[Baluncore]

As a result, the air builds up in front of the aircraft and a shockwave is formed. To try to reduce this effect, can't we add a small hole in the nose of the aircraft?

Subsonic aircraft are most efficient with a rounded front and a pointed rear, while supersonic aircraft need to open a passage through the still air, without the air needing to become supersonic. That requires a sharply pointed front, in order to give the air more time to be pushed subsonically aside. Unfortunately, it is an impossible task, as the air that becomes part of the attached boundary layer, will become supersonic in the direction of flight, which will generate noise and requires engine power.

Your hypothetical length-ways internal duct would need a large diameter in order not to choke completely on its internal boundary layer, so it would come close to doubling the wetted surface area of the vehicle. That would be particularly inefficient, as the duct would rapidly fill with hot air and noise.

At supersonic speeds, the engine air intake is one way of passing the still air through an internal duct, but for a turbojet there must be a cowl that follows the surface of the aircraft, to prevent an attached boundary layer from entering and choking the internal engine airflow.

There are too many things required in supersonic flight and propulsion for there to be a simple solution. Everything will need to be a compromise, engineered specifically for each application.

 

[boneh3ad]

Great googly moogly...

The reason supersonic aircraft are usually inefficient because the design criteria for efficient flight is dramatically different for subsonic and supersonic craft, so you have to pick one for your design even though the plane has to do both. It's not because of "shockwaves."

A mass relieving hole through the middle would do nothing. You  could do it without choking and to avoid a shock forming at the hole (though you'd still get one on the outside surfaces) but it would really only work at one angle of attack and one speed, so it's still useless, plus it would take up space you'd want for avionic, propulsion, a pilot, etc.

 

[russ_watters]

It did occur to me that the OP's idea has been used before; there have been a few supersonic planes with a giant hole where the nose should be:
https://en.m.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-21

https://en.m.wikipedia.org/wiki/North_American_F-100_Super_Sabre

 

[cjl]

That's not really a hole for drag purposes though, that's just where they decided to put the engine inlet. You need to intake air somewhere, and for a single engine supersonic jet, the nose is as good a place as any other*. Also, as boneh3ad said, it wouldn't really help you with drag or noise anyways. There are some interesting shaping things you can do to reduce the boom, and there are well known ways to reduce wave drag through shaping, but those can only do so much (and particularly in the case of the drag reducing ones, we've known about them and implemented them for more than half a century at this point).*caveat: the nose is actually not as good a place as any other for a few reasons, which is why modern single engine fighters don't do that, but that's getting way into the weeds compared to what is relevant here