Beschreibung:
<jats:p>Nano- and micrometer particles tend to stick together to form agglomerates in the presence of attractions. An accurate calculation of the drag and lift forces on an agglomerate is a key step for predicting the sedimentation rate, the coagulation rate, the diffusion coefficient, and the mobility of the agglomerate. In this work, particle-resolved direct numerical simulation is used to calculate the drag and lift forces acting on linear and irregular agglomerates formed by spherical particles. For linear agglomerates, the drag coefficient CD follows the sine squared function of the incident angle. The ratio between CD of a linear agglomerate and that for a sphere increases with the agglomerate size, and the increasing rate is a function of the Reynolds number and the incident angle. Based on this observation, explicit expressions are proposed for CD of linear agglomerates at two reference incident angles, 60° and 90°, from which CD at any incident angle can be predicted. A new correlation is also proposed to predict the lift coefficient CL for linear agglomerates. The relative errors for the drag and lift correlations are ∼2.3% and ∼4.3%, respectively. The drag coefficient for irregular agglomerates of arbitrary shape is then formulated based on the sphericity and the crosswise sphericity of agglomerates with a relative error of ∼4.0%. Finally, the distribution of the lift coefficient for irregular agglomerates is presented, which is non-Gaussian and strongly depends on the structure. The mean values and the standard deviations of CL can be well correlated with the Reynolds number.</jats:p>