<DOC>
<DOCNO>
536
</DOCNO>
<TITLE>
transition in the viscous wakes of blunt bodies at
hypersonic speeds .
</TITLE>
<AUTHOR>
hidalgo,h., taylor,r.l. and keck,j.c.
</AUTHOR>
<BIBLIO>
j. ae. scs. 29, 1962.
</BIBLIO>
<TEXT>
  transition from laminar to turbulent flow in the hypersonic
wakes of spheres was detected in laboratory measurements of the
radiation from the flow field .  a hypervelocity gun facility was
used to fire models, 0.22-in. in diameter, into a range at velocities
from 10,000 to 17,000 ft sec .  experiments were performed by
changing ..  (a) the material of the projectile ,. (b) the ambient
gas in the range ,. and (c) the pressure in the range .  three
optical techniques were used to observe the wake radiation ..
which show a turbulent viscous wake as the pressure in the
range is decreased from one atmosphere to about 20 cm hg .
which show the luminous flow field at pressures between 30 and
ence of short luminous streaks, which disappear suddenly as the
pressure is decreased below 3 cm hg for air, and below 0.8 cm
hg for argon .
both air and argon, which show the main features of the flow
field .  above the transition pressure, the intensity of radiation
from the wake is always associated with fluctuations that appear
to be the same phenomenon as the drum-camera streaks .
  the appearance of the streaks in the drum camera and photomultiplier
data is interpreted as transition from laminar to turbulent
flow in the viscous wake, because experimental evidence
shows that their appearance is not controlled by chemical,
radiative, or ablative processes, but depends on aerodynamic
effects .  this conclusion is supported by other experiments based
on optical and schlieren techniques .  the transition in the wake
at positions very close to the body is given by a local reynolds
number of 10 for air, and 3 x 10 for argon .  the results indicate
a possible local-mach-number effect .
</TEXT>
</DOC>
