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Supersonic/Hypersonic Kinetic-Heating / Blunt and Sharp Noses

KJ_Lesnick

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I have a number of questions here which pertain to supersonic and hypersonic kinetic heating, and the effects of blunt and sharp noses on temperature and drag


FIRST

From what I remember kinetic heating manifests at all speeds, although miniscule and generally insignificant at subsonic speeds, and becomes more pronounced, and undoubtedly significant at supersonic speeds. By the time hypersonic speeds are achieved, this heating effect becomes substantially more extreme.

I remember hearing somewhere that past a certain mach-number range (hypersonic) the rapid rise in kinetic-heating starts to even out (Around Mach 8 to 10 IIRC, but I could be wrong). Is this true, and if so, why does the very rapid rise in temperature start to even out past a given mach number (Mach 8 to Mach 10)?

I am also wondering is this mach-number range Mach 8 to 10 or is it some other figure (higher or lower)?


SECOND

I am aware that blunt-noses (at the expense of drag) produce significant reductions in nose temperatures at hypersonic speeds. However, I am not certain how much of a difference the degree of bluntness (or sharpness for that matter) make on temperature differences. My questions as a result pertain to this issue.

At hypersonic-speeds between Mach-5 and Mach-10
1.) How much of a reduction in kinetic-heating can an aircraft with a highly blunt-nose offer over an aircraft with a mildly blunt-nose?
2.) How much of a reduction in kinetic-heating can an aircraft with a mildly blunt-nose offer over an aircraft with a moderately sharp-nose?
3.) How much of a reduction in kinetic-heating can an aircraft with a moderately sharp-nose offer over an aircraft with a highly sharp-nose?

At hypersonic-speeds between Mach-10 and Mach-15
1.) How much of a reduction in kinetic-heating can an aircraft with a highly blunt-nose offer over an aircraft with a mildly blunt-nose?
2.) How much of a reduction in kinetic-heating can an aircraft with a mildly blunt-nose offer over an aircraft with a moderately sharp-nose?
3.) How much of a reduction in kinetic-heating can an aircraft with a moderately sharp-nose offer over an aircraft with a highly sharp-nose?

At hypersonic speeds between Mach-15 to Mach-25
1.) How much of a reduction in kinetic-heating can an aircraft with a highly blunt-nose offer over an aircraft with a mildly blunt-nose?
2.) How much of a reduction in kinetic-heating can an aircraft with a slightly blunt-nose offer over an aircraft with a moderately sharp-nose?
3.) How much of a reduction in kinetic-heating can an aircraft with a moderately sharp-nose offer over an aircraft with a highly-sharp nose?

To clarify,
When I say a highly blunt-nose I'm talking about the level of bluntness you'd see on a 9mm handgun-round, or the nose of the space-shuttle.
When I say a mildly blunt-object I'm talking about the level of bluntness you'd see on the nose of the X-15
When I say a moderately sharp-nose, I'm talking about the level of sharpness you'd see on an F-8 Crusader, an F-4 Phantom II, or F-14 Tomcat
When I say a highly sharp-nose, I'm talking about the level of sharpness you'd see at the bluntest an F-15 Eagle's nose, to the sharpness seen on the X-3, and X-43's nose (razor sharp)


THIRD

While blunt noses produce reductions in temperature by detatching the shockwave which then results the hottest of the air to be carried away. I am also aware that this unfortunately comes with a serious drag-penalty. I'm not exactly sure how much a difference various nose bluntness or sharpnesses make at those mach numbers. I know there are other factors at work (the airframe), but I'm particularly focused on nose bluntness and sharpness for the purpose of these questions...

At hypersonic-speeds between Mach-5 and Mach-10
1.) How much more drag does a moderately sharp-nose produce over a highly sharp-nose?
2.) How much more drag does a mildly blunt-nose produce over a moderately sharp-nose?
3.) How much more drag does a highly blunt-nose produce over a mildly blunt-nose?

At hypersonic-speeds between Mach-10 and Mach-15
1.) How much more drag does a moderately sharp-nose produce over a highly sharp-nose?
2.) How much more drag does a mildly blunt-nose produce over a moderately sharp-nose?
3.) How much more drag does a highly blunt-nose produce of a mildly blunt-nose?

At hypersonic-speeds between Mach-15 and Mach-25
1.) How much more drag does a moderately sharp-nose produce over a highly sharp-nose?
2.) How much more drag does a mildly blunt-nose produce over a moderately sharp-nose?
3.) How much more drag does a highly blunt-nose produce over a mildly blunt-nose?

To clarify,
When I say a highly blunt-nose I'm talking about the level of bluntness you'd see on a 9mm handgun-round, or the nose of the space-shuttle.
When I say a mildly blunt-object I'm talking about the level of bluntness you'd see on the nose of the X-15
When I say a moderately sharp-nose, I'm talking about the level of sharpness you'd see on an F-8 Crusader, an F-4 Phantom II, or F-14 Tomcat
When I say a highly sharp-nose, I'm talking about the level of sharpness you'd see at the bluntest an F-15 Eagle's nose, to the sharpness seen on the X-3, and X-43's nose (razor-sharp)


I am aware that I have asked questions in the past regarding kinetic heating and mach number, however I did not ask any questions pertaining to the rapid rise in temperatures between Mach-5 to Mach 8-10, followed by a relatively smaller rise from then on.

I also have also, to the best of my knowledge, not asked comprehensive questions regarding the precise degree of heating and drag-levels for various nose bluntnesses/sharpnesses. I have often learned that the more you find out, the more you find out how little you actually know.


KJ Lesnick
BTW: I am not trying to sponge and have done online searches, but I have received so many discrepancies in information I figure it would be best to ask this question on an aviation forum where you have large numbers of members who actually know a few things about aircraft and aerodynamics.
 

Just call me Ray

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These links might be useful:

http://www.aerospaceweb.org/question/aerodynamics/q0231.shtml

http://www.aerospaceweb.org/question/aerodynamics/q0151.shtml
 

Trident

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KJ_Lesnick said:
FIRST

From what I remember kinetic heating manifests at all speeds, although miniscule and generally insignificant at subsonic speeds, and becomes more pronounced, and undoubtedly significant at supersonic speeds. By the time hypersonic speeds are achieved, this heating effect becomes substantially more extreme.

I remember hearing somewhere that past a certain mach-number range (hypersonic) the rapid rise in kinetic-heating starts to even out (Around Mach 8 to 10 IIRC, but I could be wrong). Is this true, and if so, why does the very rapid rise in temperature start to even out past a given mach number (Mach 8 to Mach 10)?

I am also wondering is this mach-number range Mach 8 to 10 or is it some other figure (higher or lower)?

As temperatures get higher and higher, there comes a point where the flow medium will start to break down - first, diatomic molecules dissociate into individual atoms and later on these will start shedding electrons which results in ionisation. A lot of kinetic energy is spent on these processes rather than heating your hypersonic object, getting carried away in the slipstream as a result.
 

KJ_Lesnick

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That's why the temperature don't continue to rise higher and higher? Are you sure? (I'm not trying to be difficult, and I do not mean to offend -- I just want to be absolutely sure).

KJ Lesnick
 

zhuravlik

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Hi Kendra,
May I suggest you to read this book?
http://www.secretprojects.co.uk/forum/index.php/topic,4917.0.html

Best regards,

Francesco
 

KJ_Lesnick

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Just Call Me Ray,

I looked at both articles. It doesn't quite give me the data I'm looking for.

I was kind of looking for figures like... a very sharp nose produces a 50% drag reduction over a blunt nose, a very sharp nose produces a 200% increase in heat. Some actual figures and numbers, even if estimates.


KJ
 

AeroJadeXG

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I'm looking through my notes from a hypersonics course I finished a few months back, but I can give you some approximate answers as I search for the hard data:

Most of the hypersonic data you're going to find is skewed by what altitude it occurs at. The readily available data is for re-entry vehicles, which are traveling in the high hypersonic ranges (M=20+) at extremely high altitudes (i.e. nearly no atmosphere at about 60 km) and they slow down as they proceed, but the heat increases. This heat increase is due to an increase in atmospheric density.

I can tell you that the atmospheric heating seen on a bluntbody and sharp body are very similar. The heating values of the two aren't actually any different, in fact, the blunt body actually generates MORE heat. (There's a catch I'll explain) The blunt nose sees, in a fairly large area, essentially a normal shock, which brings the flow back to, for all intensive purposes, stagnation temperature T0/T=1+(gamma-1)/2 *M^2 where that simplifies, in most cases, to Temp=1+.2*M^2*Freestream Temp. This temperature applies to anywhere where the flow is essentially standing still. All T values are in K or R, to be clear.

At first glance it would seem a sharp shape minimizes the region exposed to this extreme heating, and as such, should be very effective. The problem is that there simply isn't enough material at that sharp edge to handle the heat transfer. The sharper the edge, the less material there is for that heat to dissipate into, and the higher the steady-state temperature of the object becomes. Cooling would be a solution, except that a thin edge doesn't allow coolant to get close enough to save the leading edge from heating too far (past the anneal point, in most cases). As you hollow out more material closer to the leading edge to fix this, you incrementally reduce the strength of the leading edge, which is exposed to extreme aerodynamic forces that follow the Isentropic pressure relation (The pressure version of the Temperature equation I stated above). The blunt body has much more mass near the leading edge, and as such can handle these extreme air temperatures.

The truth of the matter (and a little off topic) is that any chance we have of EVER realistically developing a hypersonic flight vehicle lies in the use of Waveriders. I, unfortunately, do not have very much knowledge in that section of hypersonics, and for that I apologize. I'm in the process of generating a report for a lab course at the moment, but once I find some more free time, I'll go grab my notes, and toss them your way.

edit: I should clarify that there are 2kinds of heating, which you seem to be combining into one. There is heating due to skin friction: a boundary layer problem, which is the sort of thing you hear about with the SR-71 and the Concorde, and then there's the heating I'm describing, which occurs when flow is slowed down to near stagnation, as it is behind shocks and at stagnation points.
 

KJ_Lesnick

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AeroJadeXG,

That's actually a very good point. I forgot to factor in altitude into the equation...
 

AeroJadeXG

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Everyone does. (well not everyone, but you get the idea) There are a few things to be wary of in hypersonics:
1 ALWAYS check altitude. Mach 20 isn't hard in very cold, very thin atmosphere, since a=SQRT(gamma*R*T)
2 Find out whether the model is accounting for CEA (chemical equilibrium analysis) i.e. deionization in the flow
3 Be skeptical of 'performance' figures, as many groups are looking for funding, and just like with electric vehicles nowadays, they start publishing ideal cases instead of real ones
 

KJ_Lesnick

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When you find the hard data for the figures I'm asking for, you'll be able to answer the questions if I give you specific altitudes to work with?

KJ Lesnick
 

AeroJadeXG

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update: 30 page final report out of the way. I'll find your documentation in the morning.

As for firm figures, I'll be able to give you the equations you need to calculate every parameter you can possibly desire. the heating equation is based on radius, so you can vary that as you like, and I can give you a run through of the relevant heat transfer equations if you aren't familiar. add all of that to some thermal structural modeling, and you have yourself a graduate level thesis.
 

KJ_Lesnick

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AeroJadeXG,

As for firm figures, I'll be able to give you the equations you need to calculate every parameter you can possibly desire. the heating equation is based on radius, so you can vary that as you like, and I can give you a run through of the relevant heat transfer equations if you aren't familiar. add all of that to some thermal structural modeling, and you have yourself a graduate level thesis.


Understood. Still, if you can, please explain it out thorougly -- it's actually been awhile since I've done really heavy duty math.


KJ Lesnick
 

AeroJadeXG

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ok, I found the blunt nose stagnation point heating equations (remember, everything is, eventually, blunt, just depends on the scale). This heat rate applies to an area around the stgnation point fairly well, too.

Ok, so looking at this there's a TON of technical crap here that really isn't important. The relation that matters to you is that qw(the heat transfer rate into the wall) goes like 1/SQRT(R) with R being the radius of the edge.

I can get you more, but I think the better solution here is me scanning all this stuff in (I've got some 200 pages of notes) both for my purposes, and for sharing. I'll keep loking for a full qw relation, but that looks to involve prandtl number, something that isn't accurately calculable at high mach numbers (there are tables of Pr up to about M=5)
 

flateric

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KJ, would be interesting reading for you
 

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quellish

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flateric said:
KJ, would be interesting reading for you

Oooo good one flateric!

This would also be of interest to KJ.
http://dtrs.dfrc.nasa.gov/archive/00001356/
 

mz

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This dissertation pdf has some nice work regarding heating too.
http://www.fedoa.unina.it/1475/1/De_Stefano_Fumo_Ingegneria_Aerospaziale_Navale_e_della_Qualita.pdf
 

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