REPORTAJE FOTOGRÁFICO DEL TABOR DE AGÜIMES [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201

Dynamics of rolling bluff bodies

The fluid-structure interaction of bluff bodies rolling through a fluid along a flat surface is explored both numerically and experimentally. This thesis identifies relevant studies from the literature, describes the different methods of investigation and presents the outcomes of the research program. A major focus is on the initial transitions of two- (in the cylinder case) and three-dimensional flows, consistent with (mostly) restricting the Reynolds number to Re<300. The numerical code is based on the spectral-element method using a full coupled approach to include the fluid-structure interaction. Experiments are conducted in a water channel under quiescent conditions

Two- and three-dimensional wake transitions of an impulsively started uniformly rolling circular cylinder

International audienceThis paper presents the characteristics of the different stages in the evolution of the wake of a circular cylinder rolling without slipping along a wall at constant speed, acquired through numerical stability analysis and two-and three-dimensional numerical simulations. Reynolds numbers between 30 and 300 are considered. Of importance in this study is the transition to three-dimensionality from the underlying two-dimensional periodic flow and, in particular, the way that the associated transitions influence the fluid forces exerted on the cylinder, and the development and the structure of the wake. It is found that the steady two-dimensional flow becomes unstable to three-dimensional perturbations at Re c,3D = 37, and that the transition to unsteady two-dimensional flow – or periodic vortex shedding – occurs at Re c,2D = 88, thus validating and refining the results of Stewart et al. (2010). The main focus here is for Reynolds numbers beyond the transition to unsteady flow at Re c,2D = 88. From impulsive start up, the wake almost immediately undergoes transition to a periodic two-dimensional wake state, which, in turn, is three-dimensionally unstable. Thus, the previous three-dimensional stability analysis based on the two-dimensional steady flow provides only an element of the full story. Floquet analysis based on the periodic two-dimensional flow was undertaken and new three-dimensional instability modes were revealed. The results suggest that an impulsively started cylinder rolling along a surface at constant velocity for Re 90 will result in the rapid development of a periodic two-dimensional wake that will be maintained for a considerable time prior to the wake undergoing three-dimensional transition. Of interest, the mean lift and drag coefficients obtained from full three-dimensional simulations match predictions from two-dimensional simulations to within a few percent

Wake dynamics and flow-induced vibration of a freely rolling cylinder

International audienceThis article examines numerically the two-dimensional fluid-structure interaction problem of a circular cylinder rolling under gravity along an inclined surface under the assumption of a fixed but small gap. The motion of the cylinder is governed by the ratio of cylinder and fluid densities and the Reynolds number based on a velocity scale derived from the momentum balance in the asymptotic regime. For increasing Reynolds number, the cylinder wake undergoes a transition from steady to periodic flow, causing oscillations of the cylinder motion. The critical Reynolds number increases for light cylinders. Whereas the time-averaged characteristics of the asymptotic rolling states depend only on the Reynolds number, the density ratio has an additional influence on the vibration amplitude and on the cylinder motion during a start-up transient from rest. Light cylinders reach their final state quickly after the initial acceleration; heavier cylinders traverse a series of quasi-steady states, including a temporary velocity overshoot, before settling in the asymptotic regime. The amplitudes of the flow-induced vibrations remain small over the entire parameter range, which can be attributed to the value of the added-mass force associated with a rolling cylinder. Special attention is paid to the influence of the small but finite gap between cylinder and wall, since lubrication theory predicts a diverging pressure drag for a vanishing gap. The variations with gap size of the forces, torque and added mass are explored. The gap also influences the characteristics of the cylinder vibrations in the unsteady wake regime, in particular their amplitude

Fluid-structure interaction of a rolling cylinder with offset centre-of-mass

International audienc

Fluid-structure interaction of a rolling cylinder with offset centre-of-mass

International audienc

Fluid-structure interactions of a cylinder rolling down an incline under gravity

International audienc

Wake dynamics of freely rolling spheres and cylinders

International audienc

Fluid-structure interactions of unconstrained spheres rolling down an incline

International audienc

Fluid-structure interactions associated with a cylinder rolling down an incline under gravity

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