Aero- and hydroacoustics of the impact for a droplet freely falling onto the water surface

Abstract

Studies of processes arising in the case of the impact of a droplet falling vertically onto a quiescent water surface, which began in the nineteenth century [1], nowadays, as previously, attract attention of scien� tists, both theoreticians and experimentalists [2]. This is associated with the importance of these processes for practical applications and the complexity of the mathematical description of relevant flows. Among the most interesting phenomena accompanying these processes, we can indicate the evolution of the shape of the arising cavern, as well as the splash and the cas� cade of vortices propagating into the bulk of the liquid. The objects of the studies are rapid processes (forma� tion of a cavern or of a splash and droplets ejected by basic liquid), which are illustrated well by the mono� graphs [3, 4]. However, slow process (e.g., droplet transformation to the vortex ring [1] and the cascade� vortex generation [5]) are also extremely interesting. The appearance in the beginning of the last century of sensitive microphones has complemented hydrody� namic studies by investigations of sound propagating from the region of the impact of a droplet with water in the perturbed medium [6]. The hydroacoustics of the droplet impact with water began to develop during World War II when problems of remote location and secrecy of submarines became urgent. The potentiali� ties of the equipment existing that time made it possi� ble to find only qualitative regularities, in particular, the power and the spectrum of sound as functions of rainfall intensity [7]. More recently, studies of sound emitted into the bulk of the liquid and associated with the impacts of individual droplets have begun [8].