Near-Field Characteristics of Elliptic Coaxial Jets

Abstract

Coaxial jets, in which an annular jet surrounds a central jet, arise in numerous combustion applications due to their vigorous mixing characteristics. To understand the effects of a elliptic coflow on a circular inner jet flow-field, the near-field flow characteristics of a turbulent elliptical coaxial jet with 0.55 and 1.45 velocity ratios (m = Uo/Ui) were numerically computed and experimentally measured. The flow characteristics were compared with a baseline condition (circular coflow). An annular exit velocity of approximately 22.0 m/s was used for the circular and elliptical coaxial nozzle. Elliptical coflow analyses reveal the jet approaching symmetry at x = 30.48 cm. The first half of axis switching is captured in the numeric simulations. A dependence on the outer structures with different velocity ratios is observed in the elliptical coflow jet. Radial u velocity plots show a wider jet produced on the major axis plane. Merging of the inner and outer flow occurs earlier with a velocity ratio of 0.55. The coflow analyses show a higher concentration of turbulent kinetic energy in the outer shear layer. The rms axial velocity is minimal, less than 0.5 m/s at the center of the jet up to x = 25.4 cm for both velocity ratios, and increases away from the centerline with the maximum value where the outer shear layer forms.