Acoustic resonances in Francis turbines often define undesirable limitations to their operating ranges at high load. The knowledge of the mechanisms governing the onset and the sustenance of these instabilities in the swirling flow leaving the runner is essential for the development of a reliable hydroacoustic model for the prediction of system stability. The present work seeks to study experim...

We consider Eulerian two-point, two-time correlations of a turbulent velocity field and those of a passive scalar mixed by a turbulent velocity field. Integral expressions are derived for the modal time-correlation functions of the velocity and scalar fields using the stretched-spiral vortex model. These expressions are evaluated using asymptotic methods for high wavenumber and, alternatively, ...

Abstract We have carried out numerical simulation of the flow in jet mill ejector. The features ejector are an annular unit for supplying additional gas form a confuser section at inlet to accelerating tube, as well outlet tube. In course study, we varied length and angle supply. established optimal parameters ejector, which it has been most uniform distribution velocity use scheme under study ...

Kelvin’s Theorem on conservation of circulations is an essential ingredient of G. I. Taylor’s theory of turbulent energy dissipation by the process of vortex-line stretching. In previous work, we have proposed a nonlinear mechanism for the breakdown of Kelvin’s Theorem in ideal turbulence at infinite Reynolds number. We develop here a detailed physical theory of this “cascade of circulations”. ...

We consider the steady propagation of an air finger into a buckled elastic tube initially filled with viscous fluid. This study is motivated by the physiological problem of pulmonary airway reopening. The system is modelled using geometrically non-linear, Kirchhoff–Love shell theory coupled to the free-surface Stokes equations. The resulting three-dimensional fluid-structure-interaction problem...

Vortices are archetypal objects that recur in the universe across the scale of complexity, from subatomic particles to galaxies and black holes. Their appearance is connected with spontaneous symmetry breaking and phase transitions. In Bose-Einstein condensates and superfluids, vortices are both point-like and quantized quasiparticles. We use a two-dimensional (2D) fluid of polaritons, bosonic ...

The purpose of this paper is to study how the geometry and the spatial distribution of energy fluctuations of different length scales in a spiral vortex layer are related to each other in a time-dependent way. The numerical solution of Krasny [J. Comput. Phys. 65, 292 (1986)], corresponding to the development of the Kelvin-Helmholtz instability, is analyzed in order to determine some geometrica...