LXVIII. Experiments on separation of boundary layers on probes in front of blunt-nosed bodies in a supersonic air stream

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Abstract
If a blunt-nosed body of revolution is fitted with a slender probe at the nose and placed in a supersonic air stream, there is an interaction between the shock wave in front of the body and the boundary layer on the probe. Schlieren photographs of this type of flow were taken for bodies of revolution with hemispherical and flat noses and various lengths of probe, at a, Mach number of 1 ·96. Measurements of pressure distribution were also made on the hemispherical-nosed body for one length of probe. With a probe length of abotut 1 1/2 body diameters, the boundary layer separates near the nose of the probe and a nearly conical dead-air region is formed. With this type of flow, which occurs with both shapes of body, the drag is considerably less than it is without a probe. For greater probe lengths the boundary layer separates behind the nose of the probe, and the shape of the dead-air region and shock-wave pattern depend on whether the boundary layer is laminar or turbulent at the point of separation. For smaller probe lengths the conical flow is still found with the hemispherical-nosed body, but with the flat-nosed body there is a regular oscillation between widely different types of flow. In the present experiments the oscillation had a frequency of about 6 000 cycles per second, and the sequence of events during a cycle was traced by taking a number of flash photographs at random time intervals. A detailed discussion of the relations between different phases of the oscillation is given. This throws some light on the general problem of the interaction of shock waves and boundary layers.

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