Shear induced diffusion and mixing in sheared particulate suspensions
| Quand ? |
Le 14/06/2016, de 10:45 à 12:00 |
|---|---|
| Où ? | Centre Blaise Pascal |
| Participants |
Bloen Metzger |
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Shear induced diffusion characterizes the random motion observed by particles in a sheared suspension. I will first discuss the origin of this phenomenon in a periodic flow configuration. By changing the particle roughness, we find that smoother particles lead to a larger critical strain amplitude beyond which the system loses its reversibility. A geometrical model, which considers quasi-particles having a strain- and roughness-dependent effective volume, successfully reproduces the measured critical strain amplitude.
I will then address the question of how the presence of particles in a shear flow contribute to enhance mixing. High-resolution PIV measurements in the fluid phase were performed to reconstruct the stretching histories of the interstitial fluid material lines. We found that the nature of the stretching law changes drastically from linear, in absence of particles, to exponential in the
presence of particles: the mean and the standard-deviation of the material line elongations are
found to grow exponentially in time and the distribution of elongations converges to a log-normal.
A multiplicative stretching model, based on the distribution of local shear-rates and on their persistence time, is derived. This model quantitatively captures the experimental stretching laws. The presence of particles is shown to accelerate mixing at large Peclet numbers. However, the wide distribution of stretching rates results in heterogeneous mixing and hence, broadly distributed mixing times, in qualitative agreement with experimental observations.