The Effect of Thin-Layer Swirl on Turbulent Jet Mixing and Noise

The effect of thin-layer swirl on the evolution of subsonic turbulent jet is investigated. The linear spatial stability analysis is used to estimate spatial amplitudes and phases of instability waves in an inviscid jet for different azimuthal modes, m=±1,±2,and ±3, and swirl number, S. For low and moderate swirl strength, negative helical modes are more unstable as compared to the positive counterparts, and the trend is reversed for higher swirl strength jets. High-order Implicit LES was used to verify the effect of thin-layer swirl on mixing and on noise mitigation. The thin-layer swirl is introduced at the nozzle exit by twelve vanes that impart angular momentum to the shear layer. Three additional nozzle configurations with azimuthally varying exit swirl were designed to study the effect of swirl modulation on mixing. The simulation results show that the thin-layer swirl promotes jet mixing in the near-field with uniform swirl performing higher mixing than swirl modulated jets.