Vortex Breakdown in a Swirl-Stabilized Combustor

Umeh, Chukwueloka O. U.; Rusak, Zvi; Gutmark, Ephraim

doi:10.2514/1.b34377

Cited by 19 publications

(2 citation statements)

References 28 publications

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“…For example, vortex breakdown observed in model tornadoes plays a crucial role in inferring the internal structure and evolution of real tornadoes [9,10]. In combustion systems, recirculation zones due to bubble-type breakdown can help fuels burn more effectively and create a compact, stable flame [11][12][13]. In aerodynamics systems, such as flow over a delta wing, depending on the angle of attack, breakdown can occur in the leading-edge vortices, which can drastically alter stability of the aircraft [14,15].…”

Section: Introductionmentioning

confidence: 99%

Coupling of vortex breakdown and stability in a swirling flow

et al. 2019

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Swirling flows are ubiquitous over a large range of length scales and applications including micron-scale microfluidic devices up to geophysical flows such as tornadoes. As the viscous dissipation, shear, and centrifugal stresses interact, such flows can often exhibit unexpected fluid dynamics. Here, we use microfluidic experiments and numerical simulations to study the flow in a vortex T-mixer: a T-shaped channel with staggered, offset inlets. The vortex T-mixer flow is characterized by a single dominant vortex, the stability of which is closely coupled to the appearance of vortex breakdown. Specifically, at a Reynolds number of Re ≈ 90, a first vortex breakdown region appears in the steady-state solution, rendering the vortex pulsatively unstable. A second vortex breakdown region appears at Re ≈ 120, which restabilizes the vortex. Finally, a third vortex breakdown region appears at Re ≈ 180, which renders the vortex helically unstable. Thus, a counterintuitive flow regime exists for the vortex T-mixer in which increasing the Reynolds number has a stabilizing effect on the steady-state flow. The pulsatively unstable vortex evolves into a periodically pulsating state with a Strouhal number of St ≈ 0.5, and the helically unstable vortex evolves into a helically oscillating state with St ≈ 1.75. These transitions can be explained within the framework of linear hydrodynamic stability. In addition, the vortex T-mixer flow exhibits multistability; multiple flow states are stable over various ranges of Re, including a narrow range of tristability for 160 Re 170, in which the steady state, the pulsatile oscillation, and the helical oscillation are all stable. This study provides experimental and numerical evidence of the close coupling between vortex breakdown and flow stability, including the restabilization of the flow with increasing Reynolds number due to the appearance of a vortex breakdown region, which will provide new insights into how vortex breakdown can affect the stability of a swirling flow.

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Section: Introductionmentioning

confidence: 99%

Coupling of vortex breakdown and stability in a swirling flow

et al. 2019

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“…With a numerical methodology, the effects of compressibility in light gases to form vortex breakdown at high Reynolds numbers have also been described recently. 27 Umeh and his collaborators 28,29 also reported PIV measurements of the distribution of axial, radial, and circumferential components of the velocity field from which the position and size of the vortex breakdown region are determined for a certain swirler configuration with non-reacting cold and pre-heated flows together with reacting flows. Besides, there is lot of research work dealing with precessing vortex core (PVC) in swirl combustion systems.…”

Section: Introductionmentioning

confidence: 95%

Experimental study of rotating Hagen-Poiseuille flow discharging into a 1:8 sudden expansion

et al. 2015

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In this paper, we present experimental evidence for the five different states that result from rotating Hagen-Poiseuille flow when it discharges into a 1:8 sudden expansion, namely: stable, convectively unstable, unstable shear layer, stable and unstable vortex breakdowns. Sanmiguel-Rojas et al. [“Three-dimensional structure of confined swirling jets at moderately large Reynolds numbers,” Phys. Fluids 20, 044104 (2008)] numerically predicted four of these five states and mapped the transition from one state to another. Our main objective is to study the onset of instabilities and vortex breakdown in these states experimentally. For this purpose, we visualize the flow at the inlet of the expansion for several values of moderately large Reynolds numbers, Re, and of swirl parameters, S. We analyze the inner region of the state that corresponds to the unstable shear layer in the sudden expansion and find two different states that share the same character, although they have different non-dimensional frequencies. The first relates to an oscillating structure near the axis, which arises at a small value of the swirl parameter, as well as to a generation of vortices that move downstream. The second shows, for greater values of the swirl parameter, vortices interacting with the boundary layer located on the wall of the static container that is perpendicular to the flow direction. In addition, we find a transition from stable to unstable vortex breakdown when perturbations become absolutely unstable inside the rotating pipe flow. Therefore, the most remarkable experimental finding is a new state, namely, unstable or transient vortex breakdown that takes place for the same pair of values (Rea, Sa) at which the onset of the absolute instability curve appears and intersects the region of stable vortex breakdown.

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Effects of single- and dual-blockage disks on swirling coaxial jets at high annulus Reynolds numbers

Đức

2019

Heat Mass Transfer

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Vortex Breakdown in a Swirl-Stabilized Combustor

Cited by 19 publications

References 28 publications

Coupling of vortex breakdown and stability in a swirling flow

Coupling of vortex breakdown and stability in a swirling flow

Experimental study of rotating Hagen-Poiseuille flow discharging into a 1:8 sudden expansion

Effects of single- and dual-blockage disks on swirling coaxial jets at high annulus Reynolds numbers

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