Michel Lance

Turbulence in the liquid phase of a uniform bubbly air-water flow

The paper describes studies of the turbulence of the liquid in a bubbly, grid-generated turbulent flow field. Laser-Doppler and hot-film anemometry are used for the experimental investigation. It is found that the turbulent kinetic energy increases strongly with the void fraction α. Roughly speaking, there exist two distinct regimes: the first one corresponds to low value of α, where hydrodynamic interactions between bubbles are negligible, and the second one to higher values, for which, owing to their mutual interactions, the bubbles transfer a greater amount of kinetic energy to the liquid. The Reynolds stress tensor shows that the quasi-isotropy is not altered. At low enough values of α, the difference between the turbulent kinetic energy in the liquid phase and the energy associated with the grid-generated turbulence proves to be approximately equal to the intensity of the pseudo-turbulence, defined as the fluctuating energy that would be induced by the motion of the bubbles under non-turbulent conditions. The one-dimensional spectra exhibit a large range of high frequencies associated with the wakes of the bubbles and the classical

Bouncing motion of spherical particles in fluids

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Experiments on the motion of a solid sphere toward a wall: From viscous dissipation to elastohydrodynamic bouncing

power law is progressively replaced by a

Drag and lift forces on interface-contaminated bubbles spinning in a rotating flow

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Investigation of the Cavitation in High Pressure Diesel Injection Nozzles

dependence.

Drag measurements in laterally confined 2D canopies: reconfiguration and sheltering effect

We investigate experimentally the bouncing motion of solid spheres onto a solid plate in an ambient fluid which is either a gas or a liquid. In particular, we measure the coefficient of restitution e as a function of the Stokes number, St, ratio of the particle inertia to the viscous forces. The coefficient e is zero at small St, increases monotonically with St above the critical value Stc and reaches an asymptotic value at high St corresponding to the classical “dry” value emax measured in air or vacuum. This behavior is observed for a large range of materials and a master curve e/emax=f(St) is obtained. If gravity is sufficient to describe the rebound trajectory (after the collision) in a gas, this is not the case in a liquid where drag and added-mass effect are important but not sufficient: History forces are shown to be non-negligible even at large Reynolds number.

Particle resolved simulations of liquid/solid and gas/solid fluidized beds

In the present study, we investigate experimentally the motion of a macroscopic (non-Brownian and noncolloidal) solid sphere falling under gravity into a viscous liquid toward a solid wall. We observe the transition from a nonbouncing to a bouncing regime when increasing the Stokes number St which characterizes the particle inertia. In the bouncing regime, the recording of the particle trajectories allows us to determine the coefficient of “elastic” restitution e above the transition. We observe that e first increases with St as predicted by Davis, Serayssol, and Hinch (1986) and seems to reach a plateau at high St.

Development of a model for thin films and numerical sensitivity tests

The equilibrium position of a spherical air bubble in a solid body rotating flow around a horizontal axis is investigated experimentally. The flow without bubbles is checked to be solid body rotating. The area of influence of the bubble is characterized to determine for each bubble whether the incoming flow is perturbed or not. The demineralized water used is shown to Tbe contaminated, and spinning of the bubbles interface is observed and measured. From the measurement of the bubbles equilibrium position, drag and lift coefficients are determined. They appear to be dependent on two dimensionless numbers. Eo the E tv s number and Rω the rotational Reynolds o o number (or Taylor number Ta) can be varied independently by changing the control parameters, and for that reason are the convenient choice for experiments. (Re, Ro) with Ro the Rossby number is an equivalent choice generally adopted in the literature for numerical simulations, and Re denotes the Reynolds number. When using this second representation, the Ro number appears to be an indicator of the influence on the force coefficients of the shear, of the curvature of the streamlines of the flow and of the bubbles spinning. The bubbles spinning effect on the lift force is far from trivial. Its contribution explains the important gap between lift values for a bubble (not spinning) in a clean fluid and for a bubble (spinning) in a contaminated fluid as present.

A Model for Liquid Films in Steam Turbines and Preliminary Validations

Laser light sheet and shadowgraphy techniques have been applied to investigate cavitation phenomena in the spray hole of Diesel injection nozzles. The nozzles were operated on a test-bench based on a Common Rail injection system. Rail pressures up to 50 MPa were used. The diesel test oil was injected into a chamber which could be pressurized up to 8 MPa. The local position and range of cavitation films, lying between the flow and the nozzle wall, as well as single bubbles could be observed at different instants of the injection process. The pictures of the light sheet experiment were compared with photographs taken by the shadowgraphy technique under the same injection conditions. Cavitation number estimates were obtained by direct measurements of nozzle sac pressures.Copyright

Developments for Modeling of Droplets Deposition and Liquid Film Flow in a Throughflow Code for Steam Turbines

Plants in aquatic canopies deform when subjected to a water flow and so, unlike a rigid bluff body, the resulting drag force FD grows sub-quadratically with the flow velocity U. In this article, the effect of density on the canopy reconfiguration and the corresponding drag reduction is experimentally investigated for simple 2D synthetic canopies in an inclinable, narrow water channel. The drag acting on the canopy, and also on individual sheets, is systematically measured via two independent techniques. Simultaneous drag and reconfiguration measurements demonstrate that data for different Reynolds numbers (400–2200), irrespective of sheet width (w) and canopy spacing (l), collapse on a unique curve given by a bending beam model which relates the reconfiguration number and a properly rescaled Cauchy number. Strikingly, the measured Vogel exponent V and hence the drag reduction via reconfiguration is found to be independent of the spacing between sheets and the lateral confinement; only the drag coefficien...