Influence of nozzle aspect ratio and orientation on flow characteristics of multiple elliptic jets

Abstract

An experimental study is conducted to investigate the flow characteristics of multiple elliptic jets issuing from a 6×6 nozzle array at a relatively low-Reynolds number (Re (= U_b·d_e/ν) = 4.3×10³). Two aspect ratios of the multiple elliptic nozzles (equivalent diameter, d_e, of a nozzle was 6 mm), namely a/b = 2.25 and 6.25, where a and b are the radii of the major and minor axes of an elliptic nozzle, respectively, and two nozzle azimuthal orientations, namely the same and alternate azimuthal orientation arrangements, were used. The mean and fluctuating velocities were measured using a constant-temperature hot-wire anemometer. The multiple jets located at the side of the ambient fluid were stretched due to interactions between the self-induced flow of an elliptic vortex ring and the secondary flow caused by the entrainment of the ambient fluid. For a/b = 2.25, axis switching occurred only once in the range of 1 < x/d_e ≤ 3 for both nozzle azimuthal orientations. For a/b = 6.25 and the same azimuthal orientation arrangement, axis switching occurred only once at 3 < x/d_e ≤ 5; axis switching did not occur for the alternate azimuthal orientation arrangement. Thus, the flow characteristics of multiple elliptic jets are influenced by the azimuthal orientation of adjoining nozzles.