Talk:Hypersonic

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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

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

[edit] 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?

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.

[edit] 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)