Further results on the mixing of free axially-symmetrical jets of mach number 1.40

Abstract

An axially-symmetrical supersonic fully-expanded jet of diameter 0.75 in. was investigated by pitot- and static-tube traverses in the region from the exit to 100 diameters downstream. The investigation is supplementary to that reported by Johannesen. In the jet discussed in this report the initial internal disturbances were weak, as compared with those in the jet investigated previously. The structures of the mixing regions in the initial parts of the two jets showed substantial differences. Further downstream the jet with weak internal disturbances showed a very slow approach to self-preserving flow. This was clear from the curves of the jet width and of the reciprocal of the centreline velocity plotted against distance from the exit approaching straight lines only slowly, but was particularly clearly indicated by the static-pressure distributions. The ratio of static pressure to dynamic pressure showed no tendency to become constant on the axis, even at the last station of measurement. The relation between the static-pressure distributions and the jet turbulence is discussed and it is shown that if the classical corrections to the readings of pitot and static tubes are adequate the errors in the deduced structure of the jet, ignoring these corrections, may be very considerable.