Article
Mechanics
Fabian Burmann, Jerome Noir
Summary: Experimental results on flows in a precessing triaxial ellipsoid show two branches of solutions for the uniform vorticity component as a function of the Poincare number. The first branch is characterized by large total fluid rotation amplitude and moderate tilt angle of the fluid rotation axis, while the second branch tends to align with the precession axis. Early occurrences of parametric instabilities saturate in the second branch, where the kinetic energy in the base flow and instabilities are of the same order.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Francesco Romano, Antoine Charles, Francois Dottori, S. Amir Bahrani
Summary: A simplified one-dimensional model is proposed to investigate the transition to turbulence in nonisothermal and non-Newtonian pipe flows. The study reveals that uniformly heating the pipe wall results in earlier transition to turbulence, while differential heating produces a stabilizing effect. Additionally, it is demonstrated that an increase in the power-law index leads to stabilization of the system for power-law fluids.
Article
Mechanics
Byung-Hee Choi, N. K. Anand, Yassin A. Hassan, Piyush Sabharwall
Summary: This study investigated the inlet flow conditions of flow through an axisymmetric sudden expansion with an expansion ratio of 2.0 using large eddy simulations. It was found that turbulence intensity affects the critical Reynolds number, reattachment length, and a correlation expression was proposed. Proper orthogonal decomposition analysis was conducted to enhance the understanding of complex flow structures downstream of the expansion, leading to an overall correlation expression for the reattachment length for specific ranges of Reynolds number and turbulence intensity.
Article
Mechanics
Luca De Vincentiis, Dan S. Henningson, Ardeshir Hanifi
Summary: The instability of incompressible boundary-layer flow over an infinite swept wing with disc-type roughness elements and free-stream turbulence was investigated through direct numerical simulations. The study aimed to analyze the sensitivity of transition to free-stream turbulence intensity and confirmed experimental observations regarding the laminar-turbulent transition mechanisms.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Elena Marensi, Shuisheng He, Ashley P. Willis
Summary: Buoyancy forces can suppress turbulence in fluid flow through a pipe, leading to severe heat transfer deterioration, which is undesirable in both heating and cooling applications. In vertical flow, axial buoyancy forces help drive the flow. Our research shows that buoyancy can suppress the convection driven state, transitioning the flow from turbulence to a relatively quiescent state.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
K. Kato, A. Segalini, P. H. Alfredsson, R. J. Lingwood
Summary: The study investigates the instability and transition in the boundary layer on a slender cone rotating in still fluid. Results show that transition starts at a well-defined Görtler number, rather than the Reynolds number, in contrast to broad cones. Experimental data indicate that locally measured disturbances in the boundary layer have specific frequencies, possibly associated with centrifugal instability.
JOURNAL OF FLUID MECHANICS
(2021)
Review
Environmental Sciences
Peter A. Davidson
Summary: In this article, we review the recent progress made in understanding large scales in homogeneous but anisotropic turbulence. We specifically focus on turbulence that arises from Saffman-like initial conditions, where vortices possess finite linear impulse. These turbulent flows support long-range velocity correlations and we discuss the evolution of energy, integral scales, and passive scalar variance using real space methods.
Article
Mechanics
Lin Fu, Michael Karp, Sanjeeb T. Bose, Parviz Moin, Javier Urzay
Summary: The study investigates the interaction between a hypersonic laminar boundary layer and an incident shock wave over a cold wall, finding that at high incidence angles, the boundary layer transitions to turbulence shortly downstream of the shock impingement. Higher incidence angles lead to increased thermomechanical loads, and WMLES can accurately predict DNS results with lower computational cost.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Milad Samie, Vlad Aparece-Scutariu, Philippe Lavoie, Dong-hyuk Shin, Andrew Pollard
Summary: This study uses direct numerical simulation to investigate three-dimensional vortical and very-large-scale coherent structures in a turbulent round jet at a Reynolds number of 7300. The results show the importance of horseshoe vortices in the jet and the existence of symmetric and asymmetric horseshoe vortices that affect the high and low momentum regions in the flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Chemical
Pooja Kumari, Arnab Atta
Summary: In this study, we demonstrate the influence of downstream geometric constraints on droplet breakup and subsequent distribution dynamics in a microdevice. Two distinct breakup regimes were observed, and the degree of breakup asymmetry increased with the continuous phase Reynolds number and dispersed phase capillary number. Our results highlight the significance of downstream feedback in the constricted and parallel microchannel network.
CHEMICAL ENGINEERING RESEARCH & DESIGN
(2022)
Article
Thermodynamics
Najib Laraqi
Summary: This article tackles the complex problem of thermal constriction caused by mixed boundary conditions and proposes new analytical solutions. It extends the study from semi-infinite axisymmetric media to finite thickness media and provides simple and accurate correlations for calculating thermal constriction resistance.
INTERNATIONAL JOURNAL OF THERMAL SCIENCES
(2022)
Article
Mechanics
Zecong Qin, Aurore Naso, Wouter J. T. Bos
Summary: The study found that in axisymmetric turbulence sustained by a linear forcing mechanism, a stable, entirely poloidal flow can be observed when the toroidal forcing component is below a threshold, with the pressure-strain correlation allowing energy to be redistributed towards the toroidal component. A simple statistical model can capture the main physical effects on the level of global energy balance.
JOURNAL OF TURBULENCE
(2021)
Article
Multidisciplinary Sciences
Yin Wang, Erik P. Gilson, Fatima Ebrahimi, Jeremy Goodman, Kyle J. Caspary, Himawan W. Winarto, Hantao Ji
Summary: The authors conducted an experiment and simulation to study a global non-axisymmetric magnetohydrodynamic instability. They discovered the standard magnetorotational instability and confirmed its existence through numerical simulations.
NATURE COMMUNICATIONS
(2022)
Article
Thermodynamics
Najib Laraqi, Taissir Kasraoui, Jean-Gabriel Bauzin
Summary: This study investigates the thermal constriction resistance developed in a semi-infinite medium subjected to a circular heat source with mixed boundary conditions. The thermal constriction resistance is determined analytically and takes a simple form, applicable to various problems. The proposed solutions are verified through comparison with analytical results in the literature, and an analysis based on different boundary conditions and the curvature of the axisymmetric source is also conducted.
INTERNATIONAL JOURNAL OF THERMAL SCIENCES
(2021)
Article
Physics, Multidisciplinary
Yin Wang, Erik P. Gilson, Fatima Ebrahimi, Jeremy Goodman, Hantao Ji
Summary: This study presents the first direct evidence for the axisymmetric standard magnetorotational instability (SMRI) through a combined experimental and numerical approach. The study demonstrates that the radial magnetic field on the inner cylinder increases linearly with the magnetic Reynolds number when a vertical magnetic field is applied along the rotation axis. The onset of the axisymmetric SMRI is identified as a nonlinear increase of the radial magnetic field beyond a critical magnetic Reynolds number. This study also reveals that the axisymmetric SMRI exists only under specific conditions of the magnetic Reynolds number and the vertical magnetic field.
PHYSICAL REVIEW LETTERS
(2022)