Instabilities and routes to turbulence in rotating disc boundary layers and cavities.

Studied for more than a century, first in the field of geophysics, flows over rotating discs present a great diversity of complex instability behaviours that are not yet fully understood. While the primary instabilities are now well characterized experimentally, theoretically and numerically, their role in the transition mechanisms to turbulence remains an open question that still challenges the scientific community. This article brings together the main results of the literature related to the instabilities over rotating discs, but also in the connected problem of rotating cavities, and reviews the main scenarios currently assumed to describe the flow breakdown to turbulence. A particular focus is on more recent studies of generic flows in rotating cavities bounded by two coaxial rotating discs, that occur in many industrial systems, the performances of which and their improvement are linked to a better understanding of these mechanisms. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.

[Prognostic significance of groin lymph node ratio in vulvar squamous cell carcinoma]. / Signification pronostique du ratio d'atteinte ganglionnaire inguinale dans le carcinome épidermoide vulvaire.

OBJECTIVES: The aim was to review the clinical impact of lymph node ratio (LNR) of groin metastatic nodal disease in women with vulvar squamous cell carcinoma. MATERIAL AND METHODS: Cohort study of women with vulvar squamous cell carcinoma, managed between January 2005 and December 2015, in five institutions in France with prospectively maintained databases (French multicenter tertiary care centers). POPULATION: In total, 636 women managed for VSCC of whom 508 (79.9%) underwent surgical groin nodal staging. MAIN OUTCOME MEASURES: Comparison of overall and recurrence free survival between women according to LNR. RESULTS: In total, 176 women (34.6%) had at least one positive lymph node (LN). There was a significant differences for the 5-year overall survival and recurrence free survival rates between women with LNR>0.2 and women with LNR<0.2. CONCLUSION: LNR seems to be a significant prognostic factor in women with vulvar squamous cell carcinoma.

Geometry effects on Rayleigh-Bénard convection in rotating annular layers.

Rayleigh-Bénard convection is investigated in rotating annular cavities at a moderate dimensionless rotation rate Ω=60. The onset of convection is in the form of azimuthal traveling waves that set in at the sidewalls and at values of the Rayleigh number significantly below the value of the onset of convection in an infinitely extended layer. The present study addresses the effects of curvature and confinement on the onset of sidewall convection by using three-dimensional spectral solutions of the Oberbeck-Boussinesq equations. Such solutions demonstrate that the curvature of the outer boundary promotes the onset of the wall mode, while the opposite curvature of the inner boundary tends to delay the onset of the wall mode. An inner sidewall with a radius as low as one tenth of its height is sufficient, however, to support the onset of a sidewall mode. When radial confinement is increased the two independent traveling waves interact and eventually merge to form a nearly steady pattern of convection.

Square patterns in rotating Rayleigh-Bénard convection.

The Küppers-Lortz instability occurs in rotating Rayleigh-Bénard convection and is a paradigmatic example of spatiotemporal chaos. Since the steady state of convection rolls is unstable to disturbance rolls oriented with an angle of about 60 degrees with respect to the given rolls in the prograde direction [G. Küppers and D. Lortz, J. Fluid Mech. 35, 609 (1969)], a spatiotemporally chaotic pattern is realized with patches of rolls continuously replaced by other patches in which the roll axis is switched by about 60 degrees. Surprisingly and contrary to this established scenario, Bajaj [Phys. Rev. Lett. 81 (1998)] observed experimentally square patterns in a cylindrical layer in the range of parameters where Küppers-Lortz instability was expected. In this paper we present square patterns which we have obtained in a numerical study by taking into account realistic boundary conditions. The Navier-Stokes and heat transport equations have been solved in the Oberbeck-Boussinesq approximation. The numerical method is pseudospectral and second order accurate in time. The rotation velocity of the square pattern increases linearly with the control parameter epsilon=Ra/R a(c) -1 , as in the experiment of Bajaj Furthermore, it was observed that this velocity decreases when the aspect ratio of the cylinder increases. These results indicate that the square pattern appears when the flow is laterally confined. The range of epsilon for which this pattern is stable tends to vanish for more extended layers.

Identification of complex flows in Taylor-Couette counter-rotating cavities.

The transition in confined rotating flows is a topical problem with many industrial and fundamental applications. The purpose of this study is to investigate the Taylor-Couette flow in a finite-length cavity with counter-rotating walls, for two aspect ratios L=5 or L=6. Two complex regimes of wavy vortex and spirals are emphasized for the first time via direct numerical simulation, by using a three-dimensional spectral method. The spatio-temporal behavior of the solutions is analyzed and compared to the few data actually available.