PSU Mark
Eberly College of Science Mathematics Department

Meeting Details

For more information about this meeting, contact Yuxi Zheng, Kris Jenssen, Xiantao Li.

Title:Effective Viscosity of Bacterial Suspensions
Seminar:CCMA Luncheon Seminar
Speaker:Brian Haines, Penn State University
Abstract:
We present a PDE model for dilute suspensions of bacteria in a three-dimensional Stokesian fluid. This model is used to calculate the statistically-stationary bulk deviatoric stress and effective viscosity of the suspension from the microscopic disturbance flow and the details of the interaction of an elongated body with a prescribed generic background flow. A bacterium is modeled as a prolate spheroid with self-propulsion provided by a point force, which appears in the model as an inhomogeneous delta function in the PDE. The bacterium is also subject to a stochastic torque in order to model tumbling (random reorientation). Due to a bacterium's asymmetric shape, interactions with the background flow cause the bacterium to preferentially align in certain directions. Due to the noise provided by the stochastic torque, the steady-state distribution of orientations is unique for a given background flow. Under this distribution of orientations, self-propulsion produces a reduction in the effective viscosity. For sufficiently weak background flows, the effect of self-propulsion on the effective viscosity dominates all other contributions, leading to an effective viscosity of the suspension that is lower than the viscosity of the ambient fluid. This is in agreement with recent experiments on suspensions of Bacillus subtilis. We also present recent numerical work that helps to elucidate the role played by hydrodynamic interactions between bacteria in the reduction of the effective viscosity.

Room Reservation Information

Room Number:MB114
Date:11 / 12 / 2010
Time:12:15pm - 01:30pm