Experimental study of the influence of piston oscillations on double-diffusion dynamics in a Hele–Shaw cell

Artificial upwelling is a promising technology for bringing nutrient-rich deep waters to the sur-face, enhancing the productivity of marine ecosystems and restoring so-called «oceanic de-serts». One of the mechanisms capable of driving such upward transport is double-diffusive con-vection, which arises in stratified fluids. This study examines the potential for enhancing double-diffusive convection through vertical piston oscillations, which could ultimately improve the effi-ciency of artificial upwelling. We present the results of an experimental investigation into the effect of vertical piston oscillations on the structure and intensity of double-diffusive convection in a two-layer system of aqueous NaCl and sucrose solutions in a Hele–Shaw cell. Oscillations with frequencies of 2-4 Hz and amplitudes of up to b = 0,66 cm were generated using a hydraulic circuit, producing oscillatory motion of the two-layer liquid system along the inner walls of the stationary cell. The evolution of double-diffusive finger structures was analyzed using space – time methods. In the absence of oscillations, the system exhibits classical finger devel-opment propagating upward and downward from the initial interface between the layers. Under vibrational forcing, however, the finger structures become more regular and adopt a pronounced vertical alignment. This effect intensifies with increasing oscillation amplitude. We also present the results of a quantitative analysis of the mixing between the initial layers and calculations of an effective diffusion coefficient Deff. At an amplitude of b = 0,66 cm, Deff increases fourfold com-pared to the non-oscillatory case. This enhancement is attributed to intensified longitudinal transport due to vibration-induced dispersion, analogous to Taylor dispersion. The results confirm the potential of piston oscillations as a means of intensifying mass transfer in stratified fluids, including artificial upwelling systems.