Recovery Temperature Question 2

[acamarg]

Hello,

would it be possible to help me understand why, for an aircraft in flight, is the recovery temperature used instead of the ambient air temperature (Tinfinity) to determine the heat exchange between the skin of the aircraft with the ambient air?

 

[rb1957]

this is for a supersonic a/c ?

 

[acamarg]

The aircraft is flying at Mach 0.82 (subsonic aircraft).

 

[rb1957]

McGraw-Hill Science & Technology Dictionary:
adiabatic recovery temperature
(¦ad·ē·ə¦bad·ik ri′kəv·ə·rē ′tem·prə·chər)

(fluid mechanics) The temperature reached by a moving fluid when brought to rest through an adiabatic process. Also known as recovery temperature; stagnation temperature. The final and initial temperature in an adiabatic, Carnot cycle.

i had to look it up for myself. sort of explains it all ...

 

[rb1957]

researching i found this ...

The stagnation temperature is found using the freestream temperature as shown in equation 11.
Ts = Tf*(1+.2*r*M^2)

Ts: stagnation temperature
Tf: freestream temperature
r: recovery factor
M: Mach number

for subsonic a/c i'd've thought that Ts = Tf ?

 

[IRstuff]

You can calculate it with this online calculator:

http://www.grc.nasa.gov/

http://WWW/BGH/stagtmp.html

The mere motion of the plane through the air must increase the kinetic energy of the air that was moved through. And increased kinetic energy is one way of describing increased heat content.

TTFN
faq731-376

 

[WKTaylor]

acamarg ...

I work on a jet that cruises about M0.85. Extreme arctic studies have shown that, at M0.85, the skin temperature rises about 25F due to friction heating. So, -80F ambient will translate to a -55F skin temp.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[btrueblood]

"I work on a jet that cruises about M0.85."

Wow, I just work in an office

Wil, is your number an average value of the wing/skin surface? I'd think that at the nose/wing leading edges, the skin temp. might be a bit higher than, say, at the mid-chord.