Flow characteristics of multiple round jets with square arrangement

The present paper describes the flow characteristics of multiple round air jets with square arrangement at a relatively low-Reynolds number (Re = 4.1×103). The diameter of a round nozzle was d = 6 mm. To investigate the influence of number of nozzles on the flow characteristics, the number of nozzles was varied 4×4, 6×6 and 8×8 with the nozzle spacing ratio of l/d = 3 where l was the nozzle spacing. To investigate the influence of nozzle spacing, the nozzle spacing ratio l/d was varied from 1.5 to 5 for the multiple round jets with the number of nozzles of 6×6. The mean and fluctuating velocities were measured using constant-temperature anemometer with the normal and reflected image layout cross-wire probes. In case of 6×6 and 8×8 square matrix nozzles, the shape of round jets which were located at the side of the ambient fluid were stretched into elliptical shape by the secondary flow caused by entrainment of the multiple round jets. The combined point of the multiple round jets issuing from square nozzle arrangement was x/d ≈ 16 without relation to the number of nozzles. At the downstream, the flow field of multiple round jets with square matrix arrangement has similarity for the dimensionless parameters of y/De, u /Ub, and u'rms /Ub, without relation to the nozzle number. The multiple round jets with 6×6 matrix arrangement merged easily when the nozzle spacing ratio became small. Thus, the centreline velocity of the combined flow formed by the confluence of the multiple round jets increased with decreasing the spacing ratio. At x/l ≥ 12, the multiple round jets developed as a single jet, and the flow field has similarity for the dimensionless parameters of y/l, u /Ub, and u'rms /Ub without relation to the nozzle spacing ratio.