title: Vortex breakdown control by adding near-axis swirl and temperature gradients.
abstract: Vortex breakdown (VB) is an intriguing effect of practical and fundamental interest, occurring, e.g., in tornadoes, above delta-wing aircraft, and in vortex devices. Depending on application, VB is either beneficiary or harmful and therefore requires a proper control. This study shows that VB can be efficiently controlled by a combination of additional near-axis swirl and heat. To explore the underlying mechanism, we address a flow in a cylindrical container driven by a rotating bottom disk. This model flow has been extensively studied being well suited for understanding both the VB mechanism and its control. Our numerical analysis explains experimentally observed effects of control corotation and counter-rotation (with no temperature gradient) and reveals some flaws of dye visualization. An important feature found is that a moderate negative (positive) axial gradient of temperature can significantly enforce (diminish) the VB enhancement by the counter-rotation. A strong positive temperature gradient stimulates the centrifugal instability and time oscillations in the flow with counter-rotation. An efficient time-evolution code for axisymmetric compressible flows has facilitated the numerical study.
authors.affiliation: Escuela Superior de Ingenieros, Universidad de Sevilla, 41092 Sevilla, Spain. herrada@eurus2.us.es
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Herrada
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shtern