Transonic small disturbances equation applied to the solution of two-dimensional nonsteady flows

Transonic nonsteady flows are of large practical interest. Aeroelastic instability prediction, control figured vehicle techniques or rotary wings in forward flight are some examples justifying the effort undertaken to improve knowledge of these problems is described. The numerical solution of these problems under the potential flow hypothesis is described. The use of an alternating direction implicit scheme allows the efficient resolution of the two dimensional transonic small perturbations equation

Rapport I.6 Fonctionnement des turbines Francis aux charges partielles

Francis turbine, being a single regulated machine through the wicket gates, presents often non satisfactory behaviour at part load. The problem is of highest importance for equipments involving a single unit : the partial discharge for the equipment could not be obtained by the shut down of several machines. The profitability of the investment is then directly linked to the possibility of part load operation. We present here the various phenomenon affecting part load operation and some of the palliatives used to achieve reasonably smooth working.Les turbines Francis n'utilisant qu'un simple réglage au niveau du distributeur n'ont pas toujours un comportement satisfaisant aux charges partielles. Le problème est tout particulièrement important pour les aménagements équipés d'un groupe : le débit partiel de l'équipement ne peut être obtenu par l'arrêt de certaines machines. La rentabilité de l'investissement passe alors souvent par une nécessaire exploitation à charge partielle. Nous présentons ici les divers phénomènes et problèmes rencontrés à débit partiel ainsi que certains palliatifs susceptibles de rendre de tels fonctionnements acceptables.Couston M. Rapport I.6 Fonctionnement des turbines Francis aux charges partielles. In: Machines hydrauliques. Conception et exploitation. Développements récents et Applications aux différents secteurs industriels. Vingtièmes journées de l'hydraulique. Lyon, 4-6 avril 1989. Tome 1, 1989

La législation des forces hydrauliques en Angleterre

Couston M. La législation des forces hydrauliques en Angleterre. In: Deuxième congrès de la Houille blanche, Lyon, septembre 1914. Rapports qui devaient être présentés au congrès. Tome 1, 1914

Dynamics of mixed convective-stably-stratified fluids

International audienceWe study the dynamical regimes of a density-stratified fluid confined between isothermal no-slip top and bottom boundaries (at temperatures T-t and T-b) via direct numerical simulation. The thermal expansion coefficient of the fluid is temperature dependent and chosen such that the fluid density is maximum at the inversion temperature T-b > T-i > T-t. Thus, the lower layer of the fluid is convectively unstable while the upper layer is stably stratified. We show that the characteristics of the convection change significantly depending on the degree of stratification of the stable layer. For strong stable stratification, the convection zone coincides with the fraction of the fluid that is convectively unstable (i.e., whereT > T-i), and convective motions consist of rising and sinking plumes of large density anomaly, as is the case in canonical Rayleigh-Benard convection; internal gravity waves are generated by turbulent fluctuations in the convective layer and propagate in the upper layer. For weak stable stratification, we demonstrate that a large fraction of the stable fluid (i.e., with temperature T < T-i) is instead destabilized and entrained by buoyant plumes emitted from the bottom boundary. The convection thus mixes cold patches of low density-anomaly fluid with hot upward plumes and the end result is that the T-i isotherm sinks within the bottom boundary layer and that the convection is entrainment dominated. We provide a phenomenological description of the transition between the regimes of plume-dominated and entrainment-dominated convection through analysis of the differences in the heat transfer mechanisms, kinetic energy density spectra, and probability density functions for different stratification strengths. Importantly, we find that the effect of the stable layer on the convection decreases only weakly with increasing stratification strength, meaning that the dynamics of the stable layer and convection should be studied self-consistently in a wide range of applications