Modeling particle deposition onto rough walls in ventilation duct

An improved Eulerian model is proposed to predict particle deposition velocity onto rough walls in fully developed turbulent duct flow. The model treats the turbulent flow over rough walls as three different regimes of turbulent boundary layer (hydraulically smooth, transition and completely rough) according to the value of roughness Reynolds number (or called dimensionless roughness), k+. For each regime, the velocity and concentration boundary layer has a different thickness compared to that of the separated free shear layer, as flow separation behind the roughness is different, and this results in different shifted distance of virtual origin of velocity boundary layer. Thus a fitted equation is proposed based on measured data to estimate the shifted distance of velocity boundary layer for different values of k+, when calculating particle deposition velocity onto rough walls. Besides, as a successive study of previous one by the authors, the model also accounts for turbophoresis as well as Brownian diffusion, turbulent diffusion and gravitational settling. Turbophoretic velocity is calculated by employing a function of dimensionless normal distances in boundary layer to the duct walls. It only needs the friction velocity as the input. The predicted results agree well with published measured data for rough walls in most cases, and also agree better with measurement in ventilation ducts than those using the existing model.