Video: The Effect of Surfactants on a Plunging Breaker

Surfactants on troubled waters

“…This implies that for surfactants in abundance the effect is expected to cease, as then the plunging breaker surface is fully covered with surfactant even in the stretched state so that no Marangoni forces emerge any longer. This is exactly what Erinin et al (2023) observe: for large enough Triton X-100 concentration the dynamics is quite similar to the clean case. This again shows that it is not the surface tension itself which mainly matters but the surface tension gradient.…”

“…Though the ocean surface conditions Franklin will have experienced on his journey across the Atlantic from America to England will have been anything else but exclusively smooth, surprisingly, the focus of the studies on the effect of surfactants on waves until recently has been on relatively smooth gravity and capillary waves. After Liu & Duncan (2006) had studied the effect of surfactants on gentle spilling breakers, Erinin et al (2023) have now studied their effect on plunging breakers -exactly the rough flow situation Franklin will have met on his passage. But Erinin et al (2023) did not do so in the ocean, but under very controlled conditions, namely in a laboratory wave tank which allows for the creation of plunging breakers with a dispersively focused wave packet.…”

“…After Liu & Duncan (2006) had studied the effect of surfactants on gentle spilling breakers, Erinin et al (2023) have now studied their effect on plunging breakers -exactly the rough flow situation Franklin will have met on his passage. But Erinin et al (2023) did not do so in the ocean, but under very controlled conditions, namely in a laboratory wave tank which allows for the creation of plunging breakers with a dispersively focused wave packet. They performed the experiments with two sets of surfactants: first, with different concentrations of the soluble surfactant Triton X-100 dissolved in clean water; second, less controlled, with originally clean water exposed to the environment for increasing times up to 21 hr, before the plunging breaker experiments were done.…”

“…This again shows that it is not the surface tension itself which mainly matters but the surface tension gradient. Erinin et al (2023) went a step further and measured the concentration-dependent surface tension with a Langmuir trough, building on the ideas and design of Agnes Pockels. This information was then combined with their (two-dimensional) direct numerical volume-of-fluid simulations of a plunging breaker, which employed Popinet's open-source Basilisk software (Popinet 2018), in order to quantitatively reveal the degree of compression and dilation on the surface and the resulting Marangoni forces.…”

“…After Liu & Duncan (2006) had studied the effect of surfactants on gentle spilling breakers, Erinin et al. (2023) have now studied their effect on plunging breakers – exactly the rough flow situation Franklin will have met on his passage. But Erinin et al.…”