THE CÆSAR CODE FOR AEROSOL RESUSPENSION IN TURBULENT PIPE FLOWS. ASSESSMENT AGAINST THE STORM EXPERIMENTS

Abstract

The aim of this work is the development of a new model of aerosol resuspension in turbulent pipe flows, which is based on the force balance concept. The model considers both types of aerodynamic forces, drag and lift forces, and properly balances these forces with the frictional and adhesive forces. Original aspects of the new model are that it takes into account the reduction of the adhesive force due to the surface roughness and the random increase of the lift force above its mean value due to the fluctuations of the turbulent flow. The resuspension model has been implemented in a computer code, CÆSAR, and its performance has been verified against several experiments of the STORM programme. In the experiments, the velocity of the flow passing over the deposits was increased stepwise. Significant particle entrainment was observed at the beginning of each velocity stage. Then, resuspension decreased sharply and became practically zero after a few tens of seconds. This behaviour was correctly reproduced with CÆSAR, although the duration of the period of strong resuspension predicted with the code was shorter than the one measured in the experiments. The faster resuspension predicted with CÆSAR is due in part to the fact that the code models the resuspension of monolayer deposits in which all particles are exposed to the flow, which is not the case of the STORM experiments.