ASPIRATION EFFICIENCY OF A THIN-WALLED CYLINDRICAL AEROSOL SAMPLER AT YAW ORIENTATIONS WITH RESPECT TO THE WIND

A Computational Fluid Dynamics (CFD) technique has been developed to numerically predict the aspiration efficiency of a thin-walled, cylindrical aerosol sampler at orientations with respect to the wind direction from 0 to 90°. The three-dimensional turbulent air flow around and inside the sampler are simulated by employing the standard turbulent k-(epsilon) model and the control volume algorithm in the bodyfitted coordinate version. The numerical technique adopted in this paper allows an accurate description of the mean motion of the turbulent air flow in the vicinity of the cylindrical sampler under realistic operating conditions. The aspiration efficiency is determined by tracing the particle trajectories through the integration of the particle equations of motion. Numerical results have been obtained for orientations of 30, 45, 60 and 90° and the dependency of the aspiration efficiency on the orientation of the wind, the particle Stokes number and the ratio of the undisturbed to the sampling air velocities have been thoroughly investigated. The numerical predictions reveal some interesting phenomena for particle Stoke numbers which are close to unity. Further, the numerical results are in reasonable agreement with the existing experimental data.