Control of shear perturbation in coaxial swirling turbulent jets

The present study explores the swirl jet characteristics and the possibility of using artificial means for control of shear layers with the application as swirl jet mixing. A subsonic open jet facility and a mechanical perturbation device with straight-lobes are uniquely designed and fabricated. Furthermore, the numerical analysis is performed to investigate the helical-lobed perturbation effects for relatively high speed jets. It is shown that the overall response of the swirling jet to excitation is strongly dependent on the number of lobes. The excitation from both straight- and helical-lobes affects the flow structures in the vortex core and the shear layer around the jet periphery simultaneously. Especially, the preferred helicity shows the maximum dispersion and the wake reduction at the vortex core. In addition, from the particle trace results, the injected flow spreads out in radial direction with wide angle than any other cases, and a relatively small amount of flow stays along the jet centerline at the preferred helicity. These reveal the mixing phenomena between the inner and outer jets as well as between the jet and the surrounding media, which are not presented in their counterparts. Also, the perturbed swirl jet experiences the fast thermal decay along the jet centerline and the wide diffusion in radial direction at the same time.