Large eddy simulations are performed to investigate the influence of combined axial and helical excitation on the structure and mixing characteristics of variable-density jets. The analysis includes various frequency ratios \(\mathcal{R}\) , two Reynolds numbers, and three density ratios between the jet and surrounding flow. Depending on \(\mathcal{R}\) , three distinct jet patterns are observed: five-armed, double-spiral and bifurcating. This parameter governs the azimuthal organization of coherent vortical structures, leading to fundamentally different jet shapes and mixing behaviour. The five-armed and double-spiral jets exhibit significantly enhanced entrainment and improved mixing compared to the bifurcating configuration. Entrainment analysis reveals strong suction of ambient fluid in the near field, followed by pronounced radial spreading further downstream. In particular, the double-spiral jet maintains elevated entrainment over a longer streamwise extent and proves especially effective for higher density ratio. A flow uniformity index demonstrates that excitation not only increases the amount of entrained fluid but also promotes its effective mixing into the jet core, leading to rapid homogenization of both mean temperature and its fluctuations. The results highlight the potential of excitation at a tuned \(\mathcal{R}\) for controlling jet dynamics and improving mixing.
