Mach diamonds?

[Nootnam]

ive been noticing that people mention these alot and i dont know what they are. can someone help me?

 

[Chrisn]

They look so awesome!

From wikipedia:
Shock diamonds (also known as Mach diamonds, Mach disks or dancing diamonds) are a formation of shock waves in the exhaust plume of an aerospace propulsion system, such as a supersonic jet engine, rocket, ramjet, or scramjet. It is formed when the supersonic exhaust from a nozzle is slightly over or under-expanded, meaning that the pressure of the gases exiting the nozzle is different from the ambient pressure. A complex flow field results as the shock wave is reflected at the free jet boundary and a visible diamond-shaped pattern is formed which gives the shock diamond its name.
https://en.wikipedia.org/wiki/Shock_diamond

 

[BsSmith]

They mostly show up in larger HPR motors and ones with a low amount of smoke. I have seen some extremely small ones in MPR G's, but you'd need a very high reselution camera to see them.

 

[cjl]

They look pretty cool too, though as mentioned above, they are usually found in HPR more than MPR. Here's a shot of my recent flight of an Aerotech L2200 showing some mach diamonds:

 

[MarkII]

Somewhere I read that FSI claimed that you could see mach diamonds with some of their motors, like the E60 and F100. Is that even possible with BP motors?

Chrisn: That photo that you attached to your post is one of the clearest illustrations of the phenomenon that I have ever seen!

MarkII

 

[Chrisn]

13+ diamonds:

they also occur on jet engines:

and visible on the SSMEs:

 

[Nootnam]

thanks alot guys. those look really cool

 

[cjl]

Somewhere I read that FSI claimed that you could see mach diamonds with some of their motors, like the E60 and F100. Is that even possible with BP motors?

Chrisn: That photo that you attached to your post is one of the clearest illustrations of the phenomenon that I have ever seen!

MarkII

In theory, it's possible with any motor with a supersonic exhaust (which corresponds to an ISP greater than about 35). So yes, it should be possible, although they could be rather hard to spot on motors that small. As for pics, I still like this one:

 

[Chrisn]

Chris: you cant hot link from that site, by the looks of it

 

[n5wd]

...As for pics, I still like this one:

cjl, you might note that Aerospacenews.com doesn't like you hotlinking to one of their images. Please note the little bit of extra information that's directed to a forum's moderator.

 

[cjl]

That's weird, the image shows up fine for me. One moment...

EDIT: OK, it should all be working now...

 

[Nootnam]

ya now it works. that is the coolest pic of these ive seen yet

 

[Chrisn]

High speed video rocket mach diamond shock diamonds

[youtube]KeGidtk6t2Y[/youtube]

 

[Chrisn]

Found this 5 page thread about mach diamonds on the TRFarchive https://www.rocketryforumarchive.com/showthread.php?t=13453

Note: this should be moved to the propulsion forum, correct?

 

[4G's]

I have seen them a few times..I see them mainly in jets (rc jets sometimes). I like to look at them taken in jet photes since they are quite large and can be seen very clearly.

 

[shreadvector]

All those responses, and nobody posts this one?

https://www.spacemodeling.org/JimZ/enerjet/ejn02.pdf

 

[RoyAtl]

Somewhere I read that FSI claimed that you could see mach diamonds with some of their motors, like the E60 and F100. Is that even possible with BP motors?

Chrisn: That photo that you attached to your post is one of the clearest illustrations of the phenomenon that I have ever seen!

MarkII

Enerjet claimed that with their motors (though only in static test).

I don't remember FSI making that claim, unless it was for their composite motor (that few ever saw).

 

[MarkH]

The new G80T supposedly has mach diamonds but I barely caught a glimpse of my Initiator when I launched it on one, let alone see any mach diamonds.

 

[Reed Goodwin]

And anyone wanting to see what's going on...

Overexpanded flow

Underexpanded flow

Reed

 

[MarkII]

Enerjet claimed that with their motors (though only in static test).

I don't remember FSI making that claim, unless it was for their composite motor (that few ever saw).

Maybe that was where I saw it, in an Enerjet ad.

MarkII