Self-induced sloshing excited by a horizontally injected plane jet

A self-induced free-surface oscillation termed "self-induced sloshing" was observed in a rectangular tank with a submerged and horizontally injected w ater jet. Self-induced sloshing is excited by the flow itself without any e xternal force. Its behaviour was examined by experiment. The dominant frequ ency was found to be close to the first or second eigenvalue of fluid in a tank. The conditions of sloshing excitation were obtained for four tank geo metries. They were called the 'sloshing condition, and defined in terms of inlet velocity and water level. Sloshing conditions were found to be strong ly dependent on inlet velocity and tank geometry. A two-dimensional numeric al simulation code was developed to simulate self-induced sloshing. The cod e was based on the boundary-fitted coordinate (BFC) method with height func tion. The numerical results were qualitatively verified by the experimental results, and were found to correlate well in terms of flow pattern, free-s urface shape and sloshing conditions. In this study, sloshing growth was ev aluated quantitatively using the simulation results. Oscillation energy sup plied for the sloshing motion during a sloshing period (E-con) was calculat ed from simulation results. Sloshing growth was found to be strongly relate d to the sign and magnitude of E-con. The distribution of E-con showed that jet flow had a strong correlation with the sloshing growth. It was clarifi ed that sloshing growth was primarily dependent on the spatial phase state of jet fluctuation. A governing parameter of self-induced sloshing, the mod ified Strouhal number St,, was proposed on the basis of numerical evaluatio ns of oscillation energy. The value of St, suggests that one or two large v ortices generated by jet fluctuations exist between the inlet and outlet du ring a sloshing period. When St, is approximately either 1 (first stage) or 2 (second stage), self-induced sloshing occurs consistently in all experim ental cases. The dependence of sloshing on inlet velocity, water level and tank geometry was revealed using St, For several tank geometries, a sloshin g mode shift or jet mode (stage) transition was found to occur due to chang es in inlet jet velocity. The combination of sloshing mode and jet stage ca n determine the state of the self-induced sloshing. As a result of this stu dy, we propose a new excitation mechanism of self-induced sloshing, represe nted by a simple feedback loop closed by sloshing motion and jet fluctuatio n. The overall physical oscillation mechanism of self-induced sloshing was clarified using this feedback loop.