AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Applying Extended Kirkwood-Riseman Theory to Rotating Fractal Aggregates in the Transition Regime
JAMES CORSON, George Mulholland, Michael Zachariah, University of Maryland
Abstract Number: 121 Working Group: Aerosol Physics
Abstract There is comparatively little focus on the rotational friction or diffusion coefficients, which affects particle alignment in an external field or from the flow field and relaxation time from an aligned state to a fully random state. Inclusion of rotational dynamics is also important when considering particle coagulation rates in Brownian motion simulations. We apply our extended Kirkwood-Riseman method to calculate the torque and rotational friction coefficient for fractal aggregates in the transition flow regime. For these calculations, we neglect hydrodynamic interactions due to rotation and translation-rotation coupling and consider only translational interactions between spheres due to their linear velocities. EKR results for DLCA aggregates are in good agreement with rotational friction coefficients computed using more rigorous Kirkwood-Riseman-based methods in the continuum regime – where the friction coefficient is proportional to the number of primary spheres to the power of approximately 1.6 – and a Monte Carlo method in the free molecule regime – where the friction coefficient is proportional to the number of spheres squared. This suggests that our EKR method is well-suited for studying the rotational behavior of DLCA aggregates in the transition regime. Our results also suggest that there is a universal relationship between the aggregate slip correction factor, defined as the ratio of the continuum rotational friction coefficient to the Knudsen-number-dependent friction coefficient, and an aggregate Knudsen number, defined as the ratio of continuum to free molecule friction coefficients. This result is analogous to the adjusted sphere method of Dahneke (1973) and Zhang et al. (2012) for the translational friction coefficient.