The effects of near wall corrections to hydrodynamic forces on particle deposition and transport in vertical turbulent boundary layers

• We study effects of near wall forces on particles in a turbulent boundary layer.
• Drag effects reduce small particle deposition, increases large particle deposition.
• Inclusion of lift has a small effect on particle deposition.
• Corrected drag gives big differences between particle and flow streamwise velocities.

In a previous paper we presented a model for the transport and deposition of particles in a turbulent boundary layer which involved tracking individual particles via their interactions with a succession of random eddies found in each quadrant of the fluid Reynolds shear stress domain. Using drag forces based on unbounded flow, the model in common with other stochastic models significantly underestimated the deposition rates for small particles with particle relaxation times (in wall units) St < 5. Here, using the same model we consider the influence on the transport and deposition of corrections to the drag and lift force in the near wall region utilizing the composite correlations proposed by Zeng et al. for a rigid spherical particle. As far as deposition rates are concerned, the inclusion of near wall effects and lift forces are unable to explain the underestimate in deposition for low inertial particles compared to the benchmark experimental measurements of Liu et al. More specifically, the overall effect of near-wall corrections to the drag is found to decrease deposition rates for small particles and to increase them for large particles. The inclusion of a Saffman lift force into the particle equation of motion (for a uniform bounded shear flow) reduced the deposition rates of the particles considered but the change was not significant (unlike previous predictions). The inclusion of a lift force based on Zeng et al.’s formula (Zeng et al., 2009) which accounts for both wall and Reynolds number effects was little different to that based on Saffman’s formula. In contrast, the corrected drag does yield significant differences between the particle and carrier flow streamwise velocities for large particles (St ∼ 20) in the near wall region. Given all the results obtained, whether the wall effects on the hydrodynamic forces should be included or not depends on specific applications.