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Heat Transfer Effects of Surface Protuberances on the X-15 Airplane

The heat—transfer effects of flow separation forced by two types of surface protu—
berances on the fuselage of the X—15 airplane were measured in flight at Mach numbers
near 5 and local Reynolds numbers of approximately 5 x 107. The two protuberance
configurations were a 0. 20—inch (0° 51—centimeter) forward—and—aft—facing step and a
sine wave of O. 20-inch— (0. 5l-centimeter—) amplitude at a right angle to the stream
direction. Heat—transfer coefficients were calculated from measured skin temperatures
across the protuberances and normalized to measured smooth—panel data. The variation
of the heat—transfer coefficient across the protuberances ranged from 0.09 to 2. 23 times
the smooth—surface value. Flight data were compared with wind—tunnel data measured
in turbulent flow.

The adverse heating effects of surface protuberances such as panel—edge
discontinuities, skin buckles, cavities, and corrugations can be of great importance in
the design of hypersonic vehicles. Consequently, the local aerodynamic—heating effects
of separated flow forced by surface protuberances have been the subject of many wind—
tunnel investigations in recent years. A wide variety of surface—protuberance
configurations has been investigated but most of the data has been obtained in laminar
flow at low stagnation temperatures and low Reynolds numbers.

One of the primary purposes of flight tests on the X—15 airplane was to extend the
data beyond the conditions in wind—tunnel tests such as those discussed in references 1
and 2. This paper presents the results of flight heat—transfer measurements on two
protuberance configurations: a forward—and—aft—facing step at a Mach number of 4. 6
and a Reynolds number of 6 x 107, and a sine -wave corrugation at a right angle to the
stream direction at a Mach number of 5. 2 and a Reynolds number of 4 x 107. The ratio
of boundary—layer thickness to protuberance height :37 was 14 on the step test and 18 on
the wave test, in contrast to most wind-tunnel data, which are in the 3— range of 0. 25
to 2. 00.