The Mixing of Free Axially-Symmetrical Jets of Mach Number 1.40

Abstract

Axially-symmetrical, supersonic, fully-expanded jets of diameter about 0.75 in. and of Mach number 1.40 issuing into an atmosphere at rest were investigated by schlieren and shadow photography and by pressure traversing. The development of the jets was found to depend critically on the strength of the shock waves in the core of the jet at the nozzle exit. With strong shock waves present the jet spread very rapidly and was very unsteady. The jet did in some cases break up into large eddies of the same size as the diameter of the jet. When no disturbances were present in the core of the jet the spreading was far more gradual and the jet showed only slight unsteadiness. The turbulent mixing region of the first part of the jet with strong shock waves was investigated in detail by pitot tubes. The first inch was found to correspond to a two-dimensional half-jet. The velocity profiles were similar and well represented by the error integral. The rate of spreading was only half the value for low-speed flow. By integrations across .the mixing region the entrainment and-the loss of kinetic energy were determined. These quantities were found to agree well with the values estimated by assuming an error-integral velocity profile.