Controlling Helical Instability By Modifying The Shape Of Swirler Centerbody In An Isothermal Turbulent Swirl Combustor Flow

Abstract Swirling flows underpin engineering systems, yet their dominant instability—the precessing vortex-core (PVC) associated with vortex-breakdown—can cause detrimental flame wrinkling, pressure oscillations and increased pollutant formation. This work examines how swirler center-body (CB) geometry alters PVC dynamics in a non-reacting, isothermal swirl-combustor. Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations with shear-stress-transport k- ω model are performed for double-bullet and cylindrical CBs, with grid-independence and validation against reported measurements. PVC characteristics are extracted using two-point cross-spectral analysis of axial-velocity fluctuations near inner shear layer, time-domain signals for persistence and low-pressure isosurfaces for associated vortex-core (VC) visualization. Both configurations exhibit a dominant m=1 correlated oscillatory component. Double-bullet case shows a strong PVC at ≈122 Hz, whereas cylindrical CB shifts it to ≈25 Hz and substantially attenuates the oscillation. Low-pressure isosurfaces show a clear asymmetric single-helical VC in double-bullet case, while cylindrical-CB case possesses a more symmetric near-swirler core with a weakly-asymmetric downstream extension, i.e., deformed single-helical VC. The resolved fluctuations remain largely persistent in both cases. Further, the weak persistent response in cylindrical CB case is not fully explained by expected eigenmode-based suppression/intermittency. Accordingly, eigenmode-based interpretation here appears to be sensitive to mean-flow linearization and turbulence model used in URANS for predicting mean-flow topology; therefore, PVC behavior deduced from linear eigenmodes and mean-flow state should be interpreted here only qualitatively.