Blunt-Nosed Bodies in a High-Temperature Gas Jet

Abstract

RECENTLY, the heating of nose cones on re-entry vehicles has become a challenging technical problem. To provide thermal protection of an object in the core of the nose cone for short duration, two major kinds of shielding materials may be used, namely, metals and plastics. The former is favourable for a heat sink while the latter is favourable for ablation cooling. To demonstrate these features, some simple experiments were performed using a variety of those common materials. The materials were machined into ½-in. diameter hemispheres. A thermocouple (Fig. 1A) was attached to the centre of the base of the hemispheric sample (B) next to a boron nitride insulator (C). The whole assembly was mounted on an arm (D) and swung into a jet of argon 3/16 in. in diameter emitted from a plasma generator (E). The velocity of the jet impinging on the testing sample was subsonic. The temperature of the jet, T _f, as estimated from ref. 1, was approximately 15,500° R. The measured temperature of the thermocouple, T ₀, increased with time, t, and was recorded on a Sanborn strip-chart recorder. Figs. 2 and 3 show these results respectively for metal and plastic samples. For convenience, both T ₀ and the non-dimensional temperature, θ₀ = T _f − T ₀/T _f − T _i, are used for the ordinate and t is chosen for the abscissa in the figures (here T _i is the room temperature).