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

Deposition of log-normally distributed particles in isothermal and heated t urbulent boundary layers is studied via Lagrangian random-walk simulations. The velocity and temperature fields and the thermophoretic force are consi dered to be Gaussian random fields, Their mean values were obtained from la w-of-the wall relations (velocity and temperature) and from a Knudsen numbe r dependent expression for the thermophoretic force; their rms fluctuations were determined by polynomial fits to experimental data. The effect of aer odynamic (Saffman) lift and crossing trajectories on particle deposition is examined. We find that for particle sizes in the diffusion-impaction depos ition 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 trajectori es on deposition is small with respect to the effect of the mean thermophor etic force, comparable to the effect of the fluctuating thermophoretic forc e, and dependent on the mean particle size. The effect of crossing trajecto ries (in the presence of lift) is small in isothermal flows. A limited numb er of particle runs was found sufficient to obtain steady-state total depos ition velocities in simulations of log-normal particle-size distributions. Simulation results are compared to experimental data: we find reasonable ag reement for total deposition velocity, deposited mass, and axial location o f maximum deposition. (C) 2000 Elsevier Science Ltd. All rights reserved.