Talk:Hypersonic speed

Article scope
should the history and recent progress be moved to hypersonic flight or hypersonic aircraft really this page should just be a definition of the term with links to hypersonic vehicles and proposals.Theon 20:35, Jun 18, 2004 (UTC)
 * I moved history and recent progress to Scramjet — Preceding unsigned comment added by 129.247.79.163 (talk) 15:39, 23 September 2004 (UTC)

Needs an expert
This article lacks any real detailed information on the subject. I have tagged it for an expert. Ifnord 14:15, 11 January 2006 (UTC)

Hypersonic fows dont obay the navier-stokes Equations
Surly all fluid flows obay the navier stokes equations, unless the dencity becomes too low to assume bulk flow charicteristics, ect. can some one expand on this? — Preceding unsigned comment added by 132.244.246.25 (talk) 12:49, 31 July 2006 (UTC)
 * Howard Brenner has a few ideas. Look him up, he's over at MIT. Reese has a paper in arxiv that you might find useful. However, NASA uses OVERFLOW for their Space Shuttle launches, and I do not think this uses any modified Navier-Stokes. Now, perhaps SRGULL uses modified Navier-Stokes (and indeed, it probably it does - it was used to simulate the X43-A to within 2% accuracy). -- kanzure (talk) 16:03, 9 March 2008 (UTC)

And that's exactly what it says in the article. AKAF 07:31, 8 August 2006 (UTC)

can we get a plain english version for this page? Hard to understand for us layfolks. — Preceding unsigned comment added by 71.195.33.69 (talk) 00:37, 7 January 2007 (UTC)

Space Shuttle and hypersonic speeds?
To get into earth orbit, people are telling me that you need to do Mach 25, and that the NASA Space Shuttle does in fact kick up to that speed. That's hypersonic. But what about the hypersonic shockwaves? NASA simulates their launches with OVERFLOW, a computer program for computational fluid dynamics, and as far as I can tell -- from reading Peter G. Buning's website -- there are no modified Navier-Stokes used in the program. The NS equations are known to fail beyond Mach 2 (or so) except in the case of the modifications by Howard Brenner and Reese et al., telling me that NASA is probably not accounting for hypersonic shockwaves since they can generate so much thrust with their truly awesome supply of LOX. Alternatively, maybe Max Q lets us know when we can kick up to hypersonic speeds, where shockwaves cannot be generated due to air density? Can anybody help me resolve this problem? Once again, it's just that it seems that NASA does not take into account hypersonic shockwaves, and I don't know why or how that's possible without them blowing up. Launch only, re-entry doesn't matter much to me at the moment. -- kanzure (talk) 16:10, 9 March 2008 (UTC)


 * From watching some of the launch sequences, you can see that the Shuttle reduces thrust before it passes the point of maximum dynamic pressure. This Max Q point and the trajectory are obviously carefully planned out, so hypersonic speeds at higher altitudes will not damage the shuttle.  The shuttle is capable of generating shock waves at very high altitudes (see the Knudsen number for the calculation procedure; continuum must exist for shock waves), but the control surfaces are smaller and therefore ineffective at lower altitudes.  I believe this loss of aerodynamic control happens when the shuttle is still at supersonic to low hypersonic speeds, so most of the control just becomes an issue of counteracting the dynamic pressure and not the shock wave structure.  I'm sure NASA has all of the shock wave information from launch to hypersonic speeds.  However, the shock waves generated during flight at transonic speeds is the more important issue.  There, the shock waves can be unsteady, and the tip geometry and location of the main tank and booster rockets has been carefully engineered to reduce detrimental shock wave interaction.  The Russian Buran program's fix for this issue was to merge the three tips together.  EMBaero (talk) 19:28, 9 March 2008 (UTC)EMBaero


 * Hi Kanzure. I think that there are two problems in what you are thinking. Firstly the Navier-Stokes equations are "valid" for all flow regimes, and there is no speed limit in which they become invalid. Therefore I can't support your statement that they are "known to fail", but perhaps you could provide a reference? Certainly there are problems using a central flux discretisation scheme in supersonic flows, and there are several stability problems which can be helped by particular limiters, but in general you can use a perfect gas RANS solver with an upwind scheme up to at least Mach 8 for most cases of general external aerodynamics. Mach 8 will be about the limit on the launch leg in the atmosphere of the shuttle anyway. Secondly, the hypersonic additions to a RANS solver mostly involve modifications to a multiple-temperature model or reacting-gas model together with boundary conditions for surface catalycity and supersonic inflow/outflow, none of which are strictly regarded as modifications to the Navier-Stokes equations. I'm wondering if you are referring to a case where you are expanding from a reservoir? Because in this case high Mach numbers will be associated with low pressure gases, which eventually no longer behave as NS predicts.AKAF (talk) 09:52, 10 March 2008 (UTC)

Vehicles used for controlled flight at hypersonic speeds
The article should include coverage of vehicles that fly at these speeds. Are there currently only two vehicle designs which are used for non-experimental controlled flight at hypersonic speeds (Shuttle and Soyuz re-entry)? Except when the Soyuz capsule reverts to ballistic reentry (as has happened recently), it is in controlled flight, as is (obviously) the shuttle. After shuttle's retirement (2010-ish), will there be only one, and an unreliable one at that? Or on ascent is any orbit-bound rocket "flying" at hypersonic speed? Is there a way to distinguish the kinds of aerodynamics involved in rocket ascent and capsule or orbiter reentry? (sdsds - talk) 17:37, 14 June 2008 (UTC)


 * I hope that there is only one. The only other example I can think of is nuclear warheads ;-)- (User) WolfKeeper (Talk) 18:08, 14 June 2008 (UTC)

Should be marked as too technical
I marked the article as too technical because of a number of technical terms it uses, and a huge number of assumptions it makes about the reader's knowledge. The article is entirely inaccessible to a person who does not already know the material in the article, which makes it useless. Since my tag was removed, here's a list of the problems in the article: a) "The hypersonic regime is a subset of the supersonic regime." - The word "regime" as used here does not match any common English definition of the word, so I assume it's jargon. b) "Flow" is never defined, but it is implied that it means "airflow". c) The section "Thin shock layer" has no link or explanation of the definition of "shock", and a very poor explanation of "shock layer". d) "Entropy" should be linked or defined. e) "a strong entropy gradient and highly vortical flow that mixes with the boundary layer" - Incomprehensible without definitions of "entropy gradient", "vortical flow", and "boundary layer". f) "large kinetic energy associated with flow at high Mach numbers transforms into internal energy in the fluid due to viscous effects" - "internal energy" is not linked. The whole thing is poorly explained... what viscous effects? What fluid? Why is large kinetic energy associated with flow at "high Mach numbers"? g) "High temperatures discussed previously as a manifestation of viscous dissipation cause non-equilibrium chemical flow properties such as dissociation and ionization of molecules resulting in convective and radiative heating." - First use of "dissipation" in the article (even though is says it was discussed previously), failure to define "non-equilibrium chemical flow", dissociation and ionization not linked. h) "The hypersonic flow regime is characterized by a number of effects which are not found in typical aircraft operating at low subsonic Mach numbers. The effects depend strongly on the speed and type of vehicle under investigation." Contains no useful information.

"Similarity parameters" is well-written and well-linked. Woo.

i) "Regime" is still undefined, even in its own section. j) References are made, again, to "the gas" without explanation of what gas. k) "Adiabatic" is hardly common English. l) "This is a subset of the perfect gas regime, where the gas can be considered chemically perfect, but the rotational and vibrational temperatures of the gas must be considered separately, leading to two temperature models. See particularly the modeling of supersonic nozzles, where vibrational freezing becomes important." - The section claims to "separate" hypersonic flow into a number of regimes, then says that one regime is a subset of another, so they're not, in fact, separate. This part also refers to a "chemically perfect" gas, "rotational and vibrational temperature", "supersonic nozzles", and "vibrational freezing", none of which are defined. m) "The type of gas selected begins to have an effect on the flow." - No selection was mentioned up until this point, so how can the reader understand what that word means? n) "the ionized electron population of the stagnated flow becomes significant" - What ionized electron population? Where did it come from? What is a stagnated flow? o) "freestream" is undefined. p) The link for "plasmas" does not explain "non-radiating plasmas", and neither does this section. q) "the heat transfer to a vehicle changes from being conductively dominated to radiatively dominated" - Barely understandable phrasing for a very simple concept.

Is it really necessary to have an entire alphabet of problems with an article for it to be deemed unacceptable? Someone needs to clean this article up, and since I don't know anything about hypersonic aircraft, I cannot be the person to do it. So I mark it for someone else to fix.Timaster735 (talk) 21:39, 17 February 2009 (UTC)


 * Well, this article isn't really meant for you, this is an article on a quite technical topic in the discipline of aerodynamics which is a pretty complex subject. And I will disagree with one thing in particular that you say. You say that regime is being used in an unusual way, but the article at regime does indeed cover the usage used in this article, under its science section.- (User) Wolfkeeper (Talk) 22:10, 17 February 2009 (UTC)


 * I mean, I'm seriously not being condescending when I state that not all articles are suitable for all people. If I look at Holonomic for example I've got little clue what the article is about, but I'm not about to slap a tag on it. Really, the idea that people should be able to read an article and get an immediate understanding of it is not going to fly. Atleast though you should have a good idea what part of knowledge it is in, and some sense of what it means. You should be able to read the first few sentences, but everything else is not guaranteed.- (User) Wolfkeeper (Talk) 22:21, 17 February 2009 (UTC)


 * http://en.wikipedia.org/wiki/Wikipedia:Make_technical_articles_accessible - The article for Holonomic properly links and defines all of the technical details. It makes every reasonable effort to help readers make sense of what is in the article. You say regime covers the usage, I ask why it's not linked? It's a sign that the person writing the article did not care to or know to make the article accessible. And it certainly shows. Every reasonable attempt was not made to make the article accessible, and it simply falls short of a number of guidelines. Timaster735 (talk) 10:54, 27 February 2009 (UTC)


 * Actually the reason why I didn't link all of the terms is that I didn't want to create a sea of redlinks. As far as accessible is concerned, if you want to write a thousand word article explaining each of the terms, be my guest. I didn't feel like it at the time since it was a quick and dirty rewrite and there haven't really been any updates since then. You should really understand though that in my opinion tagging something as technical indicates that you are willing to fix it yourself. Expecting others to rewrite an article until you can understand it is extremely optimistic. AKAF (talk) 11:47, 27 February 2009 (UTC)


 * FWIW red links aren't considered harmful in the wikipedia; they're considered a good thing.- (User) Wolfkeeper (Talk) 15:08, 27 February 2009 (UTC)


 * That's why they call it "rocket science." This raises the question, "Do we dumb-down Wikipedia when some people cannot understand the article?"  If so, to what level?  High school?  Grade school?  I think articles naturally become as technical as they need to be in order to convey the subject.  I would submit that the preface of a well-written article contains all the information required at a grade-school level, and that the first paragraph in each section contains more in-depth info suitable for the high-schooler.  The rest, well, if you don't understand it, then it's probably not meant for you.02:24, 24 October 2009 (UTC)  —Preceding unsigned comment added by 75.70.245.140 (talk)

High temperature flow.
Can someone with knowledge on this topic please complete the 'High temperature flow' section, as it ends in the middle of a sentence (after the word radiative)1812ahill (talk) 01:23, 4 January 2010 (UTC)

The definition of subsonic/transonic/supersonic
In the second line it is stated that: "The hypersonic regime is a subset of the supersonic regime." Also, in the "Supersonic" article, the first sentence reads: "The term supersonic is used to define a speed that is over the speed of sound (Mach 1)."

However, in the "Classification" section the supersonic range is defined as "1.0 - 5.0 Mach".

Wouldn't it be more correct to change the line in the "Classification" section to "> 1.0 Mach"?

Rasmuskold (talk) 11:35, 20 August 2010 (UTC)

I have changed the "subsonic" definition in the table, as well as the supersonic definition. If you're GOING to talk about a class of flows (and aircraft) called "transonic" then subsonic should be below the generally acknowledged limit of the validity of the Prandtl-Glauert compressibility correction.

Yes, of course I understand the "technicality" that below M=1 is "subsonic" but by the exact same token Mach 12 is then also "Supersonic".

With the general agreement that Supersonic-Regime only goes up to Mach 5 or so, comes the condition that Transonic gets to be it's own class, without overlapping with the others.

An aircraft designed to fly at M=0.9 for example would only rarely be described as "Subsonic". Modern airliners for example, often cruising at between M=0.8 and M=0.85 get referred to as "transonic aircraft".

Princeofdelft 18:39, 16 September 2010 (CEST)

That table is partially useless. Hypersonics/supersonics etc. is all well and good but doesn't only apply to air. 768 mph is only sonic velocity (i.e. mach = 1) at Sea Level in AIR at a certain temperature. That table should be removed if it isn't clarified that those are sea level values in air at 0 celsius (I believe). Speed of sound is dependent on temperature and gas characteristics. You can achieve hypersonic speed in the atmosphere of different planets and it won't be at the same speeds as on earth. 66.102.16.20 (talk) 01:58, 16 November 2010 (UTC)

Plasma
The table list "high hypersonic" (> Mach 10). The technical term for this is "plasmasonic". This should be mentioned in the article, perhaps even that entry in the table retitled "plasmasonic".--Solomonfromfinland (talk) 07:56, 4 December 2018 (UTC)


 * Plasmasonic is so called because the extreme speed ionizes the air, causing a "plasma blackout", blocking radio communication. (Happens during spacecraft reentry.)

Equivalency chart
The chart showing mach speeds, mph, km/h, and m/s needs going over with some math. The m/s and mph equivalencies are dodgy as shit. I would fix it, but I don't know which figures to go with (whether the mph or m/s figures are more accurate to the mach figures). Deltopia (talk) 23:17, 25 April 2011 (UTC)

Grammatical issues
The topic is challenging on its own, yet I found some of the paragraphs in this article to be formulated in a rather convoluted manner, which only adds to the difficulty. If someone with sufficient knowledge on the topic could look into that, I'd much appreciate it.

Examples:

"The density behind the shock that a body generates increases with its Mach number because conservation of mass demands a corresponding to a decrease in volume behind the shock wave and its distance to the body."

This sentence seems malformed. ("...demands a corresponding to a decrease...")

"Viscosity causes some of the great kinetic energy associated highly supersonic flow to become internal energy in the fluid, thereby increasing its temperature."

Does "great" carry meaning here? Could the "A associated B C" sentence structure be rephrased? If it means to say "supersonic flow associated with kinetic energy", then phrase it that way.

"The pressure gradient normal to the flow within a boundary layer is almost zero for low to moderate hypersonic Mach numbers, increasing the boundary layer's temperature and decreasing the layer's density and thus so expanding the layer's bottom that the boundary layer thickens and often merges with the leading edge's shock wave."

Sentences like this need to be split; it's almost incomprehensible. If you shorten it while maintaining its general structure, it too looks malformed: ("The pressure gradient is almost zero, increasing the layer's temperature, and thus expanding the bottom that the layer thickens and often merges with the leading edge's shock wave.")

I hope you see my point. I lack the required knowledge on this topic to fix these issues myself. MSUGRA (talk) 16:18, 6 May 2014 (UTC)

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