HIGH-TECH LAB COURSES


Objectives


In order to illustrate our multiphysics and multiscale approach and give students the opportunity to manipulate the most advanced techniques that we use in our research, all our lab-courses are suitable for students from L3 to Master levels having a background in mechanics and wishing to reinforce their skills in their field of competences. Higher grade students in mechanics (PhD) sould prefer modules out of their field of expertise for introductory purposes.

Initiation to fluid turbulence


Turbulence is a canonical example of multi scale phenomenon. This multi scale character is actually at the very center of the phenomenological theory of turbulence by Kolmogorov. During this lab course, the trainees will be initiated to the PIV (Particle Image Velocimetry) measurement technique that provides 2D spatial maps of a flow. We will focus on the wake behind a NACA foil in pitching motion. This introduction to major experimental techniques in fluid mechanics (and to their limitations) will be augmented by an initiation to numerical techniques (and the issues associated to them) such as direct numerical simulations, RANS method, or Large Eddy Simulations.

Granular MEDIA: Experimental and numerical analysis of the behaviour


In this practical session, we will perform shear tests on a 2D granular media with the help of the device called 1γ2ε. This unique apparatus allows to apply various loading paths on granular assemblies made of rods. By means of a 80 MPixels camera, discrete kinematics fields will be assessed and analyzed. Comparisons between experimental and numerical simulations by means of Discrete Element Modeling will also be performed. The multiscale kinematic behavior will then be discussed.

Red blood cells distribution in a model network


One of the functions of the vascular system is to bring oxygen to the body via the red blood cells. The vascular system consists of a large number of vessels subdividing themselves in increasingly small vessels, where the distribution in cells is highly heterogeneous. The purpose of this practical work is to measure these heterogeneities in a simplified artificial network, where real blood samples will be injected. The results will then allow comparison with existing models from the literature.

Dense gravitational flows


The aim of this lab-course is to tackle the problem of the modeling of dense gravitational flows dynamics and the mitigation of avalanches. Dense flows of granular materials will be produced and analyzed with the help of two laboratory devices: a large inclined plane equipped with advanced instrumentation (granular PIV, fringe projection, etc.) and a reduced model with similar yet simplified instrumentation. Emphasis will be placed on the problem of abrupt variations of flow depths, velocity and density, namely granular jumps, that occur when granular flows impact walls. The laboratory tests will be backed up with theory and numerical simulations, with the objective of inferring the relevant rheological parameters of the studied granular fluid.

Investigation of fibrous materials behaviour using X-ray tomography


The aim of this module is to emphasize the interest of coupling 3D imaging and fine scale fluid flow simulation to estimate the both the microstructures and the permeability of fibrous reinforcements commonly used in fiber reinforced composites or geotextiles. A woven fabric will be subjected to a tensile loading with a mechanical testing machine placed inside a X-ray microtomograph, allowing the 3D in situ observations of the fibrous microstructure of the textile during its deformation. The microstructure will be then finely characterized using 3D image analysis subroutines provided by the freeware ImageJ (Fiji). Therefrom, the permeability of the initial and deformed fibrous reinforcements will be estimated from fluid flow simulation inside the imaged fibrous microstructures using a finite volume CFD software (GeoDict).

Wave turbulence


Wave turbulence is a statistical state that aims at describing the nonlinear random ensemble of waves as commonly observed at the surface of the ocean. Here we will experiment on a physical model for wave turbulence: the vibrating elastic plate in which a state of wave turbulence is obtained by shaking a thin steel plate at low frequency. In this lab-course, turbulence will be observed and measured using imaging tools, and a numerical simulation of the vibrating plate will be carried out to further investigate the behaviour of wave turbulence.

Rheology of suspensions


The purpose of this lab course is to discover the mechanisms involved in membrane ultrafiltration processes in relation with the rheological behavior of the aqueous filtered suspensions. During the filtration process under shear flow and pressure forces, the filtered particles accumulate near the membrane surface forming a concentrated layer of a few hundred micrometers. The changes from a dilute phase to a concentrated phase induce a change in the rheological behavior of the suspensions which control the performance of the process. The proposed approach is to combine the characterization of the filtration properties of the suspensions, the in-situ visualization of the accumulated layers and the rheometric behavior of the suspensions.

Propagation of viscoplastic surges over complex topography


Viscoplastic, or yield-stress, fluids are involved in numerous geophysical and industrial applications. These materials have the property to behave either as fluids or solids, depending on the applied loading. Due to the coexistence in the flows of fluid and solid zones, whose respective boundaries are a priori unknown, simulating the propagation and deposition of free-surface viscoplastic surges remains challenging, in particular when the basal topography is complex. The objectives of this lab-course are (1) to perform well-controlled laboratory experiments in which viscoplastic, gravity-driven surges are generated over a complex topography; and (2) to compare experimental results to the predictions of a hydraulic numerical model.

Bubble columns and diphasic flows


The objective of this lab-course is to study experimentally a bubble column. A bubble column is a vertical cylindrical vessel containing a liquid phase where a gaseous phase is injected into the bottom by a gas distributor. This gaseous phase rises through the liquid, and finally escapes through the upper free surface.

Despite their widespread use in industry, the modelling of such devices remains unsatisfactory due to the lack of reliable physical model describing the interactions between phases. As the void fraction of bubbles is high (up to 50%), these are opaque flows, and the standard techniques used in fluid mechanics are no longer useful. We will therefore use an alternative state-of-the-art technique, the optical probe, which allows to obtain time resolved 1D time signals and to measure the void fraction, the bubbles size and velocity distributions. We will therefore be able to check the different models available in the literature and to explore the complexity of two-phase flows.