Talk:Shock diamond

Does This Mean

Does this "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." mean that you could "slightly" adjust the pressure rate to greatly increase the thrust?Tidyforbabar (talk) 05:57, 8 June 2009 (UTC)

Mechanism of shock diamonds

Article states that diamonds form when unburned propellant burns. This is false, the diamonds are purely from the interaction between supersonic flow and ambient air, [you can simulate](https://www.comsol.com/blogs/analyzing-a-supersonic-ejector-with-cfd-simulation/) diamond formation without modeling combustion. — Preceding unsigned comment added by 2A01:CB18:992:E400:D128:C3F3:E200:62E8 (talk) 16:57, 1 May 2020 (UTC)

I don't have independent knowledge of the phenomenon, but the Comsol link you gave includes the statement "These shock diamonds can also be observed experimentally in the case of reacting flow; for example, when combustion takes place in the flow" which seems to indicate that combustion or other reaction is necessary for the diamonds to become visible. Retswerb (talk) 00:00, 27 June 2020 (UTC)

No, it says "can also be observed"; therefore, post-combustion is not necessary for visible diamonds to occur; the visibility is due to refraction of light through differing density gas, not due to combustion. Have you ever heard of Schlieren photography? JustinTime55 (talk) 14:58, 29 June 2020 (UTC)

My read of that sentence is that simulator results show the diamonds, but they can also be observed experimentally *in the case of reacting flow*. In other words, you can simulate them fine but if you want to see them visually you need combustion or other reaction. Perhaps not the clearest sentence. Retswerb (talk) 04:18, 5 July 2020 (UTC)

Visibility of shock diamonds

The article states: As the exhaust passes through the normal shock wave, its temperature increases, igniting excess fuel and causing the glow that makes the shock diamonds visible. I'm not sure if this is really true for all cases. Afterburners are run lean such that there should not be much excess fuel left. For fuel-rich rockets, I doubt that there is enough ambient air mixed into the jet core, at least by the first Mach disk. I believe that the radiation originates from the temperature and density jumps over the shock. This simply causes excited radicals to glow. --Thomasphi (talk) 08:09, 5 August 2014 (UTC)

Isothermal temperature increase

It says "This pressure increase in the exhaust gas stream is isothermal, and therefore, by the second law of thermodynamics, its static temperature is substantially increased". Well, _isothermal_ means: The temperature does not change. Thus there can be no increase. But if it is adiabatic (what I consider it to be), it makes more sense. However, I read this paragraph several times, and I'm still not sure what is meant. 2003:65:EA44:7A00:298B:E93F:7682:E01B (talk) 19:37, 15 September 2016 (UTC)

It looks contradictory to me too. Isothermal processes are very slow too. It probably means adiabatic. Pulu (talk) 16:47, 28 September 2016 (UTC)

Radio Jets With Shock Diamonds

In the "Radio jets" section, it is stated that some radio jets have regular knots, which have been hypothesised to be an example of shock diamonds. This has a "citation needed" tag, with the reason given being: "the source cites simply discuss the phenomena; they do not support that these are in any way shock diamonds". This seems irrelevant; the point of the statement is that is has been hypothesised to be an example of shock diamonds, not that they are. Asking for a citation to show something which is not the statement seems to be missing the point, and simply having an article which says that it has been hypothesised would be sufficient given the statement.

Singularities421 (talk) 22:49, 19 September 2018 (UTC)

From or by ?

"The diamonds are formed from a complex flow field ..."

Should that not better be "formed by a complex flow field" ? JB. --92.193.208.41 (talk) 22:57, 15 July 2019 (UTC)

That is a kind of clumsy, arm-wavy sentence as it stands. I would say the diamonds actally are the "complex flow field", so neither preposition is actually accurate. JustinTime55 (talk) 23:05, 15 July 2019 (UTC)

Do you think that 'as' could possibly be better? Dwightol102 (talk) 18:36, 10 February 2022 (UTC)

Mach disks in volcanic eruptions

I encourage you to review and include new information on mach disks in other contexts.

See

• https://eos.org/articles/sparks-may-reveal-the-nature-of-ash-plumes
• http://meetings.aps.org/Meeting/DPP19/Session/UO4.13 — Preceding unsigned comment added by FriendlyBrewer (talk • contribs) 15:47, 8 January 2020 (UTC)

That doesn't seem appropriate here. The source you cite makes no mention at all of repeating diamond patterns; it only talks about a Mach disk, which is the interface between subsonic and supersonic flow. These disks are what form at the nozzle exit and at each repeating node of a diamond; this article is about such repeating patterns. The lead sentence actually errs slightly when it implies "Mach disk" is a synonym for shock diamond, which it isn't exactly. The geometry of expanding flow from a volcanic eruption doesn't look like it is conducive to the pattern of expansion and compression shock which forms a repeating pattern. Also, the "Mach disk" here isn't really shaped like a disk, but appears to wrap around the flow field like a balloon. One might intuitively expect an eruption vent (of gas, not liquid lava) to generate a flow field similar to the nozzle, but apparently that's not what is shown to happen here.

The info from this article might better apply to the volcanic lightning page. JustinTime55 (talk) 16:19, 8 January 2020 (UTC)