Article
Mechanics
Benjamin W. Keeton, Jaime Carpio, Keiko K. Nomura, Antonio L. Sanchez, Forman A. Williams
Summary: The transition to bubble and conical vortex breakdown in low-Mach-number laminar axisymmetric variable-density swirling jets is studied using theoretical predictions and numerical simulations. The critical values of swirl number for the onset of bubble and cone are determined as the jet-to-ambient density ratio is varied. Numerical calculations and theoretical predictions show consistent results, and the critical swirl number for the cone is found to depend on viscous effects.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jianwei Zhu, Guoqing Zhang, Lei Gao, S. C. M. Yu
Summary: The formation process of the leading vortex ring in starting jets with uniform background co- and counter-flow has been studied numerically. For counter-flow, the normal formation process of the leading vortex ring would be destroyed at lower velocity ratios. An analytical model based on the kinematic criterion has been developed to describe the relationship between the formation number and velocity ratio. Different equations are proposed for the co-flow and counter-flow cases.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Jianwei Zhu, Guoqing Zhang, Lei Gao, S. C. M. Yu
Summary: The formation and evolution process of the outer vortex ring (OV0) in annular starting jets have been numerically studied. The initial formation process of OV0 is similar to that of the leading vortex ring in a circular starting jet, but with lower circulation strength that decreases with increasing beta. During the pinch-off process, OV0 is stretched and deformed by the strain field generated by the trailing jet's instability and vorticity is shed. Additionally, OV0 accelerates the irrotational fluids around it under viscous action to form an induced velocity field, which consumes energy and sheds vorticity further.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Raphael Limbourg, Jovan Nedic
Summary: This study examines vortex rings formed from orifices with different orifice-to-tube diameter ratios, calculating non-dimensional invariants and introducing a new time scale to unify the formation numbers of orifices and straight nozzles.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Eirik Aesoy, Jose G. Aguilar, Nicholas A. Worth, James R. Dawson
Summary: The study investigates the hydrodynamic response of an axisymmetric jet placed at various positions in a standing wave oriented normally to the jet. Different modes of fluctuations are excited at velocity and pressure nodes, causing asymmetric forcing and bifurcation of momentum streams between the nodes. The asymmetrical response can be approximated by superposition of boundary conditions at pressure and velocity nodes, with the jet symmetry and momentum spreading proportional to the transverse acoustic velocity magnitude.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Raphael Limbourg, Jovan Nedic
Summary: This study experimentally investigated the formation of orifice-generated vortex rings at a Reynolds number of 5300 and tube-to-orifice diameter ratio of 2.0. It was found that the circulation, impulse, and energy of the rings increase significantly with stroke ratio, and critical parameters and time scales in the formation process were defined. The study also measured non-dimensional vortex ring numbers alpha, beta, and gamma, which were consistent with previous work and suggested universality for all isolated vortex rings.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Thermodynamics
Hao Fu, Chuangxin He
Summary: This study investigates the dynamics of coherent vortex rings in a successively generated turbulent pulsed jet. The results demonstrate a close relationship between turbulence enhancement and the generation and structure of vortex rings. Furthermore, it is found that the compactness of the vortex rings is positively correlated with the pulsing frequency.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2022)
Article
Mechanics
Yunxing Su, Monica M. Wilhelmus, Roberto Zenit
Summary: Vortex rings are crucial for generating thrust underwater. This study investigates the evolution of isolated vortex rings crossing a stable two-layer system and examines how their translation direction relative to gravity affects their behavior. The production of baroclinic vorticity is found to significantly impact the propagation of vortex rings at the density interface. The results highlight the breakdown of symmetry between vortex rings traveling from dense to light fluids and from light to dense fluids, with the maximum penetration depth occurring when the vortex propagates against the density gradient.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Rigoberto Ortega-Chavez, Lian Gan, Philip H. H. Gaskell
Summary: The controlled discharge of fluid with swirl promotes the breakdown of the leading vortex ring structure, resulting in significant negative azimuthal vorticity generation. The interaction between vortex breakdown and swirl increases the radius of the primary vortex core, decreases the self-induced propagation velocity of the leading ring, and increases vortex stretching along the circular primary vortex core. These effects lead to an increased dimensionless kinetic energy for the primary ring and a decrease in the circulation based formation number, F.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
Hao Fu, Chuangxin He
Summary: This experimental study investigates the characteristics of coherent swirling vortex rings in a turbulent pulsed jet. The combination of vortex rings and swirling flows enhances turbulent fluctuation intensity, and this effect is related to the compactness of the vortex rings and central recirculation zone. The development and decay of the vortex rings depend on factors such as the swirl number and pulsing frequency.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2023)
Article
Mechanics
Christopher M. Douglas, Lutz Lesshafft
Summary: This paper explores the effect of axial and radial confinement on the flow topology of laminar swirling jets and finds that confinement significantly influences the flow behavior.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Christopher M. Douglas, Benjamin L. Emerson, Timothy C. Lieuwen
Summary: This paper characterizes the steady and time-periodic behavior of swirling jets using numerical bifurcation analysis. The study reveals a wide array of flow patterns within a certain range of Reynolds number and swirl ratio, showing both stable axisymmetric flows and unstable three-dimensional flow structures. The research highlights the role of unsteady nonlinear interactions on the overall behavior of swirling jets and discusses the similarities and differences between this type of unconfined jet and other classes of swirling flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Ben Steinfurth, Julien Weiss
Summary: The experimental study investigated the interaction between starting jets and a steady cross-flow, finding different flow structures when compressed air is injected into a rectangular outlet. The results can aid in the selection of appropriate actuation parameters in active mixing and separation control.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
E. Duran Venegas, P. Rieu, S. Le Dizes
Summary: In this work, Joukowski's rotor wake model is applied to a two-blade rotor, providing solutions using a free-vortex method. The analysis includes stability and performance evaluation of the solutions obtained.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Andrey I. Aleksyuk, Matthias Heil
Summary: We investigate the initial development of three-dimensional mode A instability in the wake behind a circular cylinder. We observe that long-wavelength perturbations organize in a time-shifting pattern, where the in-plane velocity of each streamwise slice corresponds to the base flow solution at shifted times. We analyze the mechanisms governing the growth or decay of these perturbations, emphasizing the crucial role of the tilting mechanism and its non-local interactions similar to Biot-Savart induction. We also discuss the generalization of our findings to other flow types.
JOURNAL OF FLUID MECHANICS
(2023)