Effect of the viscosity of the internal fluid on fluid force acting on a spherical droplet near the plane wall

The drag and lift forces acting on a droplet moving near a plane wall were numerically investigated using a three-dimensional direct numerical simulation (DNS) based on the marker and cell (MAC) method. The numerical results showed that the presence of the wall causes an increase in the drag force. The less viscosity ratio of the internal fluid to the external fluid caused the decrease in the wall-induced drag coefficient. The direction of the wall-induced lift force acting on a droplet near the wall changed depending on the viscosity ratio in the high Reynolds number cases. At low Reynolds numbers, the wall-induced drag and lift coefficients of a droplet had the similarity for different viscosity ratios, respectively.