Experimental investigation on turbulent mixing enhancement in confined, co-axial jets using chute mixer configuration

Abstract

The present work is an experimental investigation of turbulent mixing of two co-axial jets with low annular to core area ratio in a non-separating confinement. Experiments were conducted in a newly designed set-up having a duct to nozzle diameter ratio of 1.19. Two centrifugal blowers driven by motors of 30 kW power each generated the air flow. Influence of chute geometry on the turbulent mixing of two co-axial streams is studied by using two chute mixer configurations having 10° and 20° angles of penetration of the annular stream towards the core region at a velocity ratio of 1.8. Contours of mean velocity and streamwise and transverse turbulence intensities were obtained by making measurements close to the point of injection with a very fine grid. The results show an improved mixing due to chutes. A stronger transverse turbulence component (w′) is observed close to the injection points, which seems to enhance mixing. Profiles at the downstream locations show a faster approach towards uniform mean velocity and homogeneous turbulence intensity. With the chute model having 20° angle of penetration, nearly complete mixing is achieved at a distance of 2.2 duct radii itself, suggesting feasibility of shortening of the duct by about 50%. However, a higher total pressure loss of about 1.7% is the penalty to be paid for enhanced mixing of the jets.