Characteristics of self-oscillating twin jets

Abstract

This study is focused on the behavior of self-oscillating twin jets emanating from round and square cross section nozzles into a narrow cavity. Computational fluid dynamics simulations are carried out in a confined rectangular cavity using the Reynolds stress turbulence model. Flow field characteristics are evaluated at nozzle spacing-to-diameter ratios (S/d) of 2, 3, 4, 5, at a jet Reynolds number of 27 000 based on nozzle exit velocity and diameter (d). Effects of nozzle spacing on the frequency of oscillation, mean velocity, vortex structure, and turbulence features are examined. For S/d up to four, the two jets merge downstream and oscillate as an equivalent single jet. At larger spacing, the two jets do not merge but oscillate separately between the sidewalls and cavity centerline. Comparison of round and square twin jets demonstrates that the nozzle shape does not significantly affect the jet decay. The turbulence intensity of twin jets shows higher values at the center of the cavity for S/d < 5 and around the centerline of each jet for S/d = 5. With increasing nozzle spacing, the Reynolds shear stress demonstrates that mixing increases in the inner shear layer region and the Reynolds shear stress values for S/d < 5 are lower than for S/d = 5. Twin oscillating jets produce higher spread and turbulence intensity over a wider area which may be beneficial for cooling of hot devices in industrial applications.