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.

The effects of spacing to diameter ratio on mixing characteristics of circular and elliptical twin jets

“…The domain length of the present flow field is comparable to previous studies. 9,15,17 An unstructured mesh with triangular elements has been used in the computational domain generated by using different mesh methods available in the grid generation tool AN-SYS workbench. When a turbulent free jet is issued into a quiescent ambient atmosphere, it experiences strong velocity gradients in the streamwise, transverse, and span wise directions.…”

“…It was observed that the turbulent intensities of the combined jet increase progressively by increasing the S / D e ratio. Mosavati et al 15 investigated the round and square twin jets issuing into a narrow cavity using the Reynolds stress turbulence model at four different S / D e ratios and reported that the nozzle shape of the square and round twin jets does not significantly affect the jet decay. The effects of nozzle orientation on mixing and turbulent properties of elliptical twin jets were studied experimentally by Morris et al 16 It was found that the mean velocity does not vary significantly with orientation.…”

Numerical Study of Twin Jets Interactions using Realizable Model

“…The main finding results was that the width of the twin jets spreads linearly downstream and grows with nozzles spacing and the merging length of the two jets can be increased either by reducing nozzles spacing or increasing Mach number. More recently, a numerical study focused on the characteristics of self-oscillating twin jets using the Reynolds Stress Turbulence Model [14]. Many nozzles spacing are used with a fixed Reynolds number (Re = 27000).…”