Understanding the role of grid turbulence in enhancing PM10 deposition: Scaling the Stokes number with Rλ

Abstract

Isotropic turbulence in wind tunnel experiments enhances PM10 particle deposition on surfaces used to simulate vegetation. The effect of isotropic turbulence on inertial impaction dominated particle deposition to surfaces in an unconfined flow was studied. The contribution of turbulence on deposition is shown to scale with a dimensionless parameter formed from a combination of the classical Stokes number (Stk) and the Taylor-microscale Reynolds number (Rλ). This scaling helps explain the role that the intermediate sized eddies (λ) and turbulent fluctuations (u′) have on deposition fraction (DFλ). A modified Stokes number (Stk⋆ = Stk·Rλ0.3) parameterization (DFλ=100 − 100/(440.5(Stk⋆)3.88+1)) was devised to utilize this new scaling and incorporate physically significant turbulent deposition parameters (i.e., λ and u′). The experiments covered a practically relevant Stk range of ∼0.005–0.065 and Rλ range of ∼40–280. These experimental results suggest that current impaction correlations substantially underestimate deposition to surfaces in turbulent unconfined flows, for example, in modeling deposition to windbreaks downwind of unpaved roads.