Research Projects

Swirling flows, known as vortex breakdown, are characterized by spontaneous flow reversal and the formation of a recirculation zone. This phenomenon is crucial for improving combustor efficiency, especially in swirl-stabilized combustors. Two distinct types of vortex breakdown occur in swirling jets: bubble and conical forms of vortex breakdown (BVB and CVB). These forms have unique spatiotemporal characteristics, including differences in recirculation zone shape, size, and unstable spiral modes. Recent studies have demonstrated that BVB and CVB can exist as bistable flow states. However, CVB in turbulent swirling jets remains relatively unexplored. This project aims to perform large-eddy simulations (LES) of turbulent swirling jets at a moderate Reynolds number, document spatiotemporal features of BVB and CVB, examine their bistability characteristics using hysteresis studies, characterize the different unstable spiral modes using global linear stability and spectral proper orthogonal decomposition (SPOD), and develop reduced-order models based on the latter technique. The LES will be performed using the open-source, scalable, finite-difference, incompressible flow solver, Xcompact3d. The project will generate idealized equilibrium swirling inflow conditions by performing an independent LES of a flow through a rotating pipe and examining different inflow swirl strengths. The results are expected to shed light on a fundamental class of flows (swirling jets) and potentially improve combustor design and efficiency.