The effect of surfactants on droplet generation in a plunging breaker

An experimental study is conducted to compare droplet generation in a deep-water plunging breaker in filtered tap water and in the presence of low and high bulk concentrations of the soluble surfactant Triton X-100. The breakers are generated by a programmable wave maker that is set with a single motion profile that produces a highly repeatable dispersively focused two-dimensional (2-D) wave packet with a central wavelength of $\lambda _0=1.18\,\rm m$ . The droplets are measured with an in-line cinematic holographic system. It is found that the presence of surfactants significantly modifies the overall droplet number and the distributions of droplet diameter and velocity components produced by the four main droplet producing mechanisms of the breaker as identified by Erinin et al. ( J. Fluid Mech., vol. 967, 2023, p. A36). These modifications are due to both surfactant-induced changes in the flow structures that generate droplets and changes in the details of droplet production mechanisms in each flow structure.