Benoît Semin

Influence of flow confinement on the drag force on a static cylinder

The influence of confinement on the drag force F on a static cylinder in a viscous flow inside a rectangular slit of aperture h0 has been investigated from experimental measurements and numerical simulations. At low enough Reynolds numbers, F varies linearly with the mean velocity and the viscosity, allowing for the precise determination of drag coefficients λ∥ and λ⊥ corresponding, respectively, to a mean flow parallel and perpendicular to the cylinder length L. In the parallel configuration, the variation in λ∥ with the normalized diameter β=d/h0 of the cylinder is close to that for a two-dimensional (2D) flow invariant in the direction of the cylinder axis and does not diverge when β=1. The variation in λ∥ with the distance from the midplane of the model reflects the parabolic Poiseuille profile between the plates for β⪡1 while it remains almost constant for β∼1. In the perpendicular configuration, the value of λ⊥ is close to that corresponding to a 2D system only if β⪡1 and/or if the clearance between...

Viscometer using drag force measurements

A robust and precise viscometer using the forces exerted by a laminar flow inside a small duct is presented: the force is measured on a long cylindrical sensor dipped into the flow. Two devices of respective volumes 1.4 and 0.031 ml have been realized, demonstrating that the technique is usable with small fluid volumes. Several Newtonian and non-Newtonian fluids have been tested at shear rates ranging from 0.3 to 10 s(-1) for the first device and from 85 to 2550 s(-1) for the second one. For Newtonian fluids, of viscosities ranging from 10(-3) to 0.1 Pa s, the linear response of the device has been verified and a 90% agreement with the values provided by commercial rheometers is obtained. For non-Newtonian polymer solutions, the variation of the force with the flow velocity allows one to determine the dependence of the viscosity on the shear rate. Two shear thinning polymer solutions with a power law behavior at intermediate shear rates have been investigated and their rheological parameters have been determined.

Identification of the shape of curvilinear beams and fibers

This work concerns the shape identification of curvilinear objects, for example bent beams or wires in mechanics. The beam’s digital picture is analyzed with the introduced Virtual Image Correlation method. This one consists in finding the optimal correlation between the beam’s image and a virtual beam, whose curvature field is described by a truncated series. The gray level and amplitude of the virtual beam does not need to reproduce exactly the ones of the physical beam image. The analytical form of the optimal shape allows one to derive mechanical properties: the identification of the Young’s modulus of a bar is given as an example. We will also show the robustness of the method with regards to the quality of the image.