Particle settling in a stratified fluid

Particles settling in a stratified fluid experience an increased drag caused by the vertical displacement of isopycnals. Using a combination of microscale Synthetic Schlieren experiments and numerical simulations, we have quantified the extra drag due to stratification at low and moderate Reynolds numbers for particles as small as 157 $\mu$m. Our results suggest that the extra drag depends on a combination of the Reynolds, Froude and Prandtl numbers through a single dimensionless parameter which we called the Stratification number.