Flow characteristics of orifice and tapered jets

Two types of small-aspect-ratio slot jets were investigated. An orifice slot jet with a 3:1 aspect ratio was shown to have features similar to an elliptic jet with a well-designed contraction. A larger spreading rate and enhanced turbulent mixing, relative to a circular jet, can be obtained using this orifice nozzle, which is advantageous for many practical applications. By adding a conical contraction to the slot jet (tapered slot jet) the characteristics were totally altered. The axes switching, typical to an elliptic jet, did not occur and the spreading rate at the major axis plane was larger than at the minor axis plane. The turbulence amplification in the initial core region was higher than both in the circular and elliptic jets. The transition from the conical contraction of the nozzle to the slot shape of the outlet section produced three-dimensional vortical structures. These structures interacted with the asymmetric vortices shed from this noncircular configuration to enhance the small scale turbulence in the core region as well as in the jet circumference. The large spreading rate of the two configurations of slot jets is beneficial to increase the bulk mixing with the surrounding fluid through entrainment. The augmented turbulence level of the tapered slot jet is important for reacting flows where small scale mixing is required.