Effects of area-ratio on the near-field flow characteristics and deflection of circular inclined coaxial jets

An experimental study was carried out on 45° and 60° inclined coaxial jets, where secondary-to-primary jet area- and velocity-ratios were 4.0 and ranged from 0.5 to 2.0 respectively. Results reveal that the use of a relatively larger area-ratio here is able to suppress self-excited jet oscillations seen earlier in comparatively smaller area-ratio jets when velocity-ratio is 1.0. Flow visualization and PIV measurements demonstrate that this is due to the physically wider annular gap associated with a larger area-ratio. This reduces the extent to which primary and secondary ring-vortices can undergo vortex-pairing and merging seen in the previous study. Near-field centerline flow characteristics clarify the impact of area-ratio upon the flow fields, as well as its relationships with velocity-ratio and incline-angle. Unlike relatively smaller area-ratio jets, the effects of the velocity-ratio are found to be insignificant in the lower cases of 0.5 and 1 examined here. Correspondingly, primary jet deflections are found to be comparatively smaller for relatively larger area-ratio jets and significant only when velocity-ratio reaches 2.0. Lastly, jet velocity profile developments reveal that within the present measurement range, the two jet-streams in relatively larger area-ratio jets do not merge as rapidly as smaller area-ratio counterparts, particularly at a velocity-ratio of 2.0.