On Sun, 19 Nov 2006 00:15:00 +0200, SENECA wrote:

I thought about. Maybe the surface flow at the RCC underside is
unimportant for the BLT. In front of the RCC is the bow shock,
what deflects some of the incomming flow. The wing is inclined
by 40 degree. Therefore the wing below the RCC gets part of the
flow from the free space in front of the shuttle. In other words,
at the middle of the wing near the wheel bay only a fraction of
the BL mass flow there had passed the RCC underside. I`m not sure
on that but it may one explanation.

I posted this on the flow on the bottom side of the Orbiter some time ago.
http://groups.google.com/group/sci.s...054dc0607262a4
Basically, the airflow in the boundary layer, turbulent or laminar, has
passed through a bow shock, and then is expanded as it flows around the
wing. Compressed in the shock wave to 10000F, much of the energy is then
used to decompose the air into O and N and the temperature decreases to
3000F before coming into contact with the RCC. As the air flows around the
wing, it's actually going through an expansion. Decreasing the temperature
of the O2, N2, O, N, NO plasma. This is the environment the tiles find
themselves in, across the entire bottom of the Orbiter.

To me there must be a hysteresis effect to the chemical reaction. The
actual time in the bow shock and the extreme high temperatures cause the
decomposition of the air to occur rather quickly. But, as the air flows
around the wing and is expanded, the opposite reaction where the O and N
recombines into O2, N2 and NOx is much much slower. So, the temperature of
the air in the boundary layer, turbulent or not, is within the temperature
range that the tiles can handle.

Near the middle of the wing and at the wheel bay, all the air in the
boundary layer has passed through a bow shock, decomposed, then as
been expanded significantly. For the nose of the Orbiter and directly
behind it, the expansion was 50 degrees. At the nose, the air in the
boundary layer has gone from zero velocity, thru Mach 1, and continued
acceleration up to hypersonic velocity as it is expanded 50 degrees around
the curved surface of the RCC nose cap.

So, with Columbia, part of the bow shock entered the wing. But the flow
around the hole that didn't, still had some expansion to go through. I
imagine that might have kept the boundary layer somewhat well behaved.

--
Craig Fink
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