A random-walk simulation of thermophoretic particle deposition in a turbulent boundary layer

Deposition of log-normally distributed particles in isothermal and heated turbulent boundary layers is studied via Lagrangian random-walk simulations. The velocity and temperature fields and the thermophoretic force are considered to be Gaussian random fields. Their mean values were obtained from law-of-the wall relations (velocity and temperature) and from a Knudsen number dependent expression for the thermophoretic force; their rms fluctuations were determined by polynomial fits to experimental data. The effect of aerodynamic (Saffman) lift and crossing trajectories on particle deposition is examined. We find that for particle sizes in the diffusion–impaction deposition regime the mean thermophoretic force gives the dominant contribution to total particle deposition, whereas the thermophoretic fluctuating force has only a limited contribution. The effect of lift and crossing trajectories on deposition is small with respect to the effect of the mean thermophoretic force, comparable to the effect of the fluctuating thermophoretic force, and dependent on the mean particle size. The effect of crossing trajectories (in the presence of lift) is small in isothermal flows. A limited number of particle runs was found sufficient to obtain steady-state total deposition velocities in simulations of log-normal particle-size distributions. Simulation results are compared to experimental data: we find reasonable agreement for total deposition velocity, deposited mass, and axial location of maximum deposition.