Studies on Twin Non-Parallel Unventilated Axisymmetric Jets

Abstract

Twin non-parallel jet configurations occur in many practical devices like burners, combustion chambers, and also in the area of fluidics etc. Despite the importance of such configurations, studies on the interaction of twin non-parallel jets are very limited. The present work is an attempt to investigate the mixing of two axisymmetric jets obliquely oriented towards each other. Experimental studies were made on the interaction of twin intersecting axisymmetric jets issuing from two unventilated convergent nozzles. The nozzles of exit diameter (D) 10 mm were set on a common end wall with their axes intersecting each other at half angles (α3) of 0°, 5°, 10° and 15°. The centre-to-centre spacing (S) of the nozzles, non-dimensionalized, as S/D, was 3.1. The jet exit Mach number (Me) studied was 0.2. The results indicate that the near field characteristics are strongly influenced by α3. However, the potential core of the individual jets and the far field characteristics of the twin jet flow field, that is beyond downstream distances of 40 nozzle diameters, are not significantly influenced by α3. The cross-section of the jet just downstream of the combining point is approximately elliptic. The axis switching phenomenon normally associated with non-circular jets is observed in the jet flow field. The spread of the combined jet is more in the transverse direction than in the spanwise direction. Entrainment of the ambient fluid is found to be more in the case of twin parallel jets (α3 = 0°). The entrainment decreases with increasing α3. The self-preserving nature of the combined jet is almost independent of the initial geometric conditions. The combined jet is axisymmetric with regard to the normalized velocity and length scales.