Particle Image Velocimetry (PIV) measurements in a water film, application to a tire rolling through a puddle

International audienceA measurement method based on Particle Image Velocimetry with refraction of the laser sheet at a win-dow/water interface is proposed for the measurement of the velocity field of a water flow formed by a tire moving inside a water puddle. This study focuses of the feasibility and repeatability of this optical measurement method. The characterization of the optical properties of the measurement technique defines the integration effect in height of the measurement method. The analysis of the overall features of the flow is focused on two main zones in front and around the tire. The flow inside the first zone is defined by a characteristic velocity of the water displaced in an area located in front of the tire ; in the second zone a characteristic velocity representative of the flow in the vicinity of the shoulder of the tire is also defined. Correlations of both characteristic velocities with the car speed and water film height are established. New and worn tires were tested in this work

A penalization method for the simulation of bubbly flows

This work is devoted to the development of a penalization method for the simulation of bubbly flows. Spherical bubbles are considered as moving penalized obstacles interacting with the fluid and a numerical method for ensuring the shear free condition at the liquid– bubble interface is proposed. Three test-cases (curved channel, inclined channel and 3D translating bubble) are used to validate the accuracy of the discretization ensuring the slip condition at the interface. Numerical simulations of a rising bubble in a quiescent liquid are performed for moderate Reynolds numbers. Considering bubble terminal velocities, initial accelerations and wake decay, the effect of the penalization viscosity used to ensure a uniform velocity in the penalized object is discussed. Finally, simulations of bubble swarms have been carried out in a fully periodic box with a large range of void fractions from 1% to 15%. The statistics provided by the simulations characterizing the bubble-induced agitation are found in remarkable agreement with the experiments