ASPIRATION EFFICIENCY OF A THIN-WALLED CYLINDRICAL PROBE REAR-FACING THE WIND

The sampling mechanism of a thin-walled, cylindrical aerosol sampling probe which faces directly away from the wind (180 degrees orientation ) is numerically investigated. The turbulent fluid flow is predicted b y employing the control volume, finite-difference method and the k-eps ilon turbulence model. The particle trajectories are calculated by int egrating the particle equations of motion and thus the aspiration effi ciency of the sampler is determined. The numerical results have been o btained for two very long thin-walled cylindrical samplers of diameter s D = 2 and 5 cm which have zero thickness and the operating condition s as used in the experimental investigations of Vincent et al. (1986, J. Aerosol Sci. 17, 211-224) have been considered. The dependence of t he characteristics of the fluid flow and the aspiration efficiency on the freestream air speed, the diameter of the sampler and the ratio of the freestream speed to the sampling speed, have been thoroughly inve stigated. It is concluded that the numerical results for the aspiratio n efficiency are in reasonable agreement with all the existing experim ental data for thin-walled samplers which are placed at 180 degrees to the direction of the wind.