The effects of spacing to diameter ratio on mixing characteristics of circular and elliptical twin jets

Twin jets are encountered in many engineering and industrial applications, such as aircraft propulsion systems and combustors. Twin jets create a flow field that is more complex than a single jet due to its interaction with the individual jets. This paper investigates the effects of spacing to diameter (S/D_e) ratio and orientation on the mixing properties of circular and elliptical twin jets at four different S/D_e ratios of 1.25, 1.50, 1.75, and 2.0, respectively. The numerical simulations of twin jets are carried out with a jet Mach number of 0.8 using the Shear Stress Transport (SST) K-ω turbulence model. The results show that near the orifice exit, the twin jets are issuing into ambient conditions separately and resemble a free jet, leading to a potential core length independent of S/D_e. The merging and combined point locations change linearly from the exit with an increasing S/D_e ratio. The decay rate is higher for Twin Ellipse Minor than those in Twin Circle and Twin Ellipse Major, verified by a shorter converging region. In addition, near the jet exit, the spread rate is higher for Twin Ellipse Minor, which is consistent with the closer merging point location. The jet mixing is superior for twin minor elliptical configuration compared to twin circle and twin major elliptical jets at all S/D_e ratios.