New single vortex generation method for flame/vortex interaction using flow behind a rotating cylinder

Abstract

This paper investigates a new experimental method to generate a single two-dimensional translated vortex for flame/vortex interaction studies. A rotating cylinder is immersed in a uniform flow and, its rotating speed is impulsively reduced. This sudden action triggers the generation of a single vortex when both the initial and the final rotation speeds are in the range of a steady-state regime. Flow visualization allows confirming the applicability of this method, while a complementary two-dimensional numerical simulation is conducted to understand the vortex formation process. A vorticity layer is detached from the cylinder, initiating a feeding process and gradual growth of a single leading vortex. The feeding process is saturated at a specific distance from the cylinder and, vortex separation from the vorticity layer is observed. At the final stage of the formation process, the generated vortex is advected away and, a steady-state regime is again established behind the cylinder. The vortex characteristics appear to be related to the normalized reduction in the rotation rate ∆α, defined as the initial and final rotation rates difference normalized by the initial rotation rate. Several combinations of initial and final rotation rates corresponding to different normalized reductions are investigated experimentally and numerically. The results allow understanding the effect of this parameter; a higher normalized reduction generates a stronger, more rapidly growing vortex. However, its trajectory is related to the wake deviation corresponding to the final rotation rate.