Frequency response of liquid jet under nozzle velocity disturbance

Based on the VOF （volume of fluid） interface capture method and the dynamic adaptive grid technique，a direct numerical simulation of the breakup process of a circular jet was carried out.The surface morphology of the circular jet and the response characteristics of liquid ligaments and droplets under different disturbance frequencies were revealed.The results showed that Rayleigh linearized dispersion theory can well explain the instability process of jet surface wave.When the nozzle disturbance frequency （66.6 kHz） was less than the theoretical critical value of 95.5 kHz，the jet gradually lost stability with the evolution of time and space.When it was greater than the critical value，the amplitude of surface wave gradually weakened and the liquid core became smooth.When the surface wave was unstable，the falling droplets impacted the nodal structure and impact dents left on its surface；with the increase of nodal amplitude，the liquid film broke through，and then a large number of detached liquid ligaments and droplets were formed.Appropriate frequency disturbance can reduce the velocity fluctuation of the jet head and slow down the atomization process of the jet.The breakup of the jet surface wave and the breakup process of the liquid core head determined the size of the SMD （Sauter mean diameter） of spray field，and there existed mutual coupling between them.