General Question reentry flames on launch (screenshot)

[chevelle505]

Why am I getting reentry flames on launch all of the sudden? Ive tried turning reentry flames off as well as particles..no change..whats going on?

 

[ljetibo]

That look like the flames you get if you're in atmospheric flight and you exceed certain velocity. I don't know if those are handled differently than "re-entry" flames (I'd assume not, but if you can still see them with that option turned off then I guess they are).

If you give up more details, like the current TAS or height above sea level, or any additional description of when the flames appear maybe someone with more experience could help you.

 

[chevelle505]

Ok will do...id like to be able to just disable it all together

 

[Ripley]

If you see flames after launch, that means you are too fast in a (still) too dense atmosphere.
So why would you disable them? They are an indicator that you must follow a more precise (slower) launch profile. Just accelerate more gently.

 

[chevelle505]

Well i would but this is the "autopilot" with shuttle fleet 4.8 which i intent to continue using...not sure what changed but it didnt used to do this. Is there something i can edit in the scenario file to change this? I was wondering if the autopilot controls throttle down for max Q as well as throttle up or could this be the problem where they're just running wide open at 104% the entire time?

 

[kuddel]

What Orbiter Version are you using?
Since Orbiter 2016 did change the atmosphere modelling (I think) this might effect that.
If I remember correct, you can choose a "legacy" atmosphere model somewhere. Maybe that helps.

I think that Shuttle Fleet 4.8R2 was developed for Orbiter 2010, so if you are using Orbiter 2016, that might be some kind of incompatibility...

 

[chevelle505]

Using orbiter 2010 (30080 i think)

 

[boogabooga]

Re-entry effects in Obiter2010 are triggered when density times velocity cubed exceeds a preset threshold. This can be wrong on both sides, displaying the effects at relatively low Mach numbers at low altitude or not displaying effects at orbital velocity in the high atmosphere.

It's weird that it happens when you disable re-entry effects, though.
Please post screenshot of Surface MFD when this is happening.

 

[chevelle505]

just a little before SRB Sep it starts to form..by the time i get a solid separation the orbiter and ET are completely engulfed in "flames". this is driving me nuts. and like I said, this is all on the autopilot, I have not changes ANYTHING aside from hi res textures but it was fine well after the texture upgrade.
For what its worth.. immediately following srb sep it goes away

 

[ljetibo]

Yeah, that does seem too slow to cause the ionization at that altitude. I think kuddel is closest in his guess with:

I think that Shuttle Fleet 4.8R2 was developed for Orbiter 2010, so if you are using Orbiter 2016, that might be some kind of incompatibility...

if it worked for a long time and then suddenly stopped working recently something had to change. Did you update/upgrade any of the modules or orbiter itself?

 

[boogabooga]

Is there a payload?

 

[chevelle505]

No payload..empty bay with ODS..but payload doesnt seem to have an affect..ive launched different iss scenarios and had no change. As far as addons..the list isnt too long but yes ive made a few mods...id hate to have to start all over 1 by 1 to find the culprit

 

[Thorsten]

Re-entry effects in Obiter2010 are triggered when density times velocity cubed exceeds a preset threshold. This can be wrong on both sides, displaying the effects at relatively low Mach numbers at low altitude or not displaying effects at orbital velocity in the high atmosphere.

This is sort of the default physics assumption, and I've started out modeling with that as well. Then I compared to some data (the Concorde at Mach 2, the SR-71 at Mach 3.2, the X-15 around Mach 7 and some temperatures I got from the Columbia accident report - and it turns out the model plainly doesn't fit.

After tinkering some with the data set I had assembled, it turns out that the role of density is less important than the above expression in reality and the velocity is more important for plasma formation.

If a rho v^3 is used, it explains how this could happen during launch, because the density is fairly high - if the dependence on the density is weakened, you'll find it hard to get plasma-high temperatures till around Mach 14 or so.

(Fun fact - the aerodynamical stresses during a Shuttle launch are about two times higher than during entry - of course the thermal stresses are way more severe during entry...)

 

[boogabooga]

Not quite velocity, but Mach number. Density doesn't really matter so long as you are in the realm of continuum mechanics.

I would say that when one tries to decide whether to render re-entry flames, they should consider the heating of the air (via shock heating), and not on the vehicle. So basically what is happening is that a sufficiently blunt body moving through a compressible perfect gas at faster than the speed of sound generates a leading bow shock wave. Static absolute temperature and pressure increase across this shock. If you approximating the bow shock as a normal shock (i.e. assume that the fluid streamlines do not change their direction), you can see the relevant equations for example here:
https://www.grc.nasa.gov/www/k-12/airplane/normal.html

Notice that these are functions only of Mach number and "gamma," which is a parameter that has a value of about 1.4 on Earth and 1.33 on Mars. For example, at Mach 15, these equations predict an absolute temperature increase of 44.7 times across the shock. This is before "friction" has been considered at all and the effects can extend well away from the vehicle. But air isn't really a perfect gas and at high enough temperatures will undergo endothermic chemistry as the molecules dissociate and ionize (i.e. plasma). However, the air will still be heated to incandescence. Viola, "re-entry flames"

Rho V cubed is not only wrong, it is over-thought. A much more appropriate trigger criteria could only have to consider the Mach number being above a certain threshold (I believe Mach 12 or so) and the vehicle being within a detectable atmosphere.

 

[Thorsten]

Rho V cubed is not only wrong, it is over-thought. A much more appropriate trigger criteria could only have to consider the Mach number being above a certain threshold (I believe Mach 12 or so) and the vehicle being within a detectable atmosphere.

Actually this was pretty much my first attempt at a parametrization, but this completely hinges on the definition of 'detectable atmosphere' - if you have a threshold, plasma appears suddenly instead of slowly fading in. If you do not and fade in the effect, you just reproduce what you put in. Not very physics-like...

So the more sophisticated parametrization of the temperature I used of the data I have is ~ rho^0.3 * M^1.5

(with M the Mach number). This is missing the Concorde and SR-71 data points somewhat, but I assumed since they're in a dense and cold atmosphere, there'd be some additional cooling which I'm missing in my model.

I did check after the fact that the region this parametrization gives me temperatures in the plasma range coincides pretty nicely with the radio blackout region for a normal entry.

Anyway, it also states that usually during a launch or an Nz holding entry at Mach 10 you would not expect any plasma, but that a TAL (especially when MECO needs to be early) causes rather severe temperature peaks as compared to a regular entry.

I would say that when one tries to decide whether to render re-entry flames, they should consider the heating of the air (via shock heating), and not on the vehicle.

True - but the outcome of this seems to be that heating of the vehicle is a (shape-dependent) fraction of the shock heating. So with reasonable accuracy it seems to boil down to just select the right transfer coefficient for the vehicle.

 

[chevelle505]

OK guys I made a breakthough....I've narrowed it down to the fact that it does it when I run it with D3D9 client...when I just open orbiter through the normal .exe everything is the same with the exception that Atlantis is now pure white (I have Hi Res textures that requires D3D9) everything works fine, clear skies all the way up through SRB Sep...so its something that D3D9 is doing.

 

[chevelle505]

Any ideas as to why d3d9 would cause this???

 

[YODAFORCE]

Bumping this because I'm having the same problem. d3d9 client starts rendering the reentry flames too soon:

d3d9 client


Default orbiter Renderer

Panel screenshot for the above flight


On another flight, i was starting to pitch up to an angle of attack of 40º during reentry and the flames are already appearing. As you can see the altitude was 94km and dynamic pressure were only about 40Pa. All The temperatures on the XR5 was around -80ºC. This is too early to reentry flames to appear. This only occur with the d3d9 client.
Does anyone has any idea of why this is happening? And how to fix it? Edit:Forgot to say that i'm using orbiter 2010 (100830)

 

[Urwumpe]

Well, if you are fast enough, plasma will form around the spacecraft. Independent of the air density, that just increases how dense the plasma is. Generally, all visualizations are wrong though. If you look at shuttle launch videos, you can see how faint greenish plasma already dances around the ET before separation. It turns pink during reentry with changing atmospheric composition.

 

[YODAFORCE]

Well, if you are fast enough, plasma will form around the spacecraft. Independent of the air density, that just increases how dense the plasma is. Generally, all visualizations are wrong though. If you look at shuttle launch videos, you can see how faint greenish plasma already dances around the ET before separation. It turns pink during reentry with changing atmospheric composition.

Thanks for the reply. But do you have any idea of what the d3d9 client does differently to make the flames appear early?