Considerations for Modeling Particle Entrainment into the Wake of a Circular Cylinder

The objective of this work is to evaluate the performance of the steady state Reynolds Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) models for estimating concentration of low Stokes number aerosols (Stk = O(10⁻⁴)) in the wake of a bluff body. These simulations are compared with experimental data. In the simulations and experiments, particles are released upstream of the body and convected downstream, where some are entrained into the wake. The air velocity is computed using a steady state renormalized group k ∼ ϵ model. Lagrangian particle trajectory simulations are performed in conjunction with each airflow model to calculate concentrations. The experiments are performed in an aerosol wind tunnel in which phase Doppler velocimetry measurements are obtained for the velocity field and aerosol concentration.

The RANS model yields a wake concentration deficit that extends downstream past x/D = 10, while the experiments produce elevated concentrations immediately downstream of the near wake. It is postulated that the concentration peak is at least in part attributed to particle interaction with the boundary layer by the following mechanism. Particles are transported into the boundary layer by turbulent diffusion, turbophoresis, and/or inertial forces. Particles then separate from the cylinder with the airflow and travel in a sheath around the periphery of the near wake to converge at the downstream edge of the near wake. Underestimation of the wake concentration by the RANS model is potentially due to inadequacy in the boundary layer approximation used in the model.

Acknowledgments

The research presented in this article was supported in part by grants #1 R01 OH07363 and #1 R03 OH09302-01 from the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control (CDC). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of NIOSH. Computational resources were made available by the North Carolina Supercomputing Center, project 11059.