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National Advisory Committee for Aeronautics, Technical Notes - Heat Transfer and Pressure Measurements on Flat Faces Cylinders at Mach Number of 2

Flat-faced.cylinders of 12-inch diameter and h-inch diameter were
tested at a Mach number of 2 and sea-level conditions in the preflight
jet of the Langley Pilotless Aircraft Research Station at Wallops Island,
vs. Both pressure distributions and heat-transfer rates were measured.

The pressure data from the h-inch-diameter model agreed well with
the results of several other investigations. The stagnation-point pres-
sure gradient was indicated to be about 50 percent of the gradient on an
equivalent-size hemisphere. The heat-transfer data agreed reasonably well
with the theoretical results when the flow was laminar. The stagnation-
point heating rates were approximately 55 percent as great as the stag-
nation heating rates on a hemisphere of equal diameter.

On a reentry ballistic missile, the area most seriously affected by
aerodynamic heating usually is the nose. A pointed nose may be desirable
because of its low drag characteristics but is undesirable because the
heat-transfer coefficient is extremely large at the tip in relation to
the mass available to absorb the incoming heat. One method of allevi-
ating this heating problem is to blunt the nose. The blunting reduces
the heat-absorption problem by two means. First, the heat-transfer
coefficient is an inverse function of the square root of the nose radius
of curvature and thus is reduced by blunting, and second, much greater
amounts of material are available for heat absorption.

The flat-faced cylinder is the simplest of all blunt—nose shapes.
Theoretically the flat nose has the lowest stagnation—point heating rates
(with the p0ssible exception of concave shapes). For these reasons a
series of tests on flat-faced cylinders was made to obtain the heat-
transfer and pressure distributions_on this shape, and the results are
presented in this report. Four models were tested, two 12-inch-diameter
models and two h-inch-diameter models.