Numerical investigation of atomization of swirling liquid sheets using transforming algorithm

Abstract

The atomization of swirling liquid sheets is investigated with numerical simulations. An algorithm that transforms the small Eulerian droplets into the Lagrangian particles is developed to reduce the computational errors in describing the interfaces. Different transforming criteria are evaluated and the grid scale criterion is shown applicable for atomization simulations of swirling sheets. Due to the complexity in the flow field, the inverse transformation is implemented when the Lagrangian particles move close to the resolved Eulerian liquid structures. First, the transforming algorithm is verified through a series of test cases. Then the algorithm is applied to investigate the atomization of a single swirling sheet. Characteristic vortical structures are identified near the interfaces. It is found that the sheet disturbances coincide with the recirculation regions. The mechanisms to break up hole structures are found to be related to surface tension and aerodynamic forces. The diameter distribution of droplets and number of liquid structures are consistent with realistic conditions. Finally the atomization of coaxial swirling liquid sheets, which is rarely investigated in detail in previous studies due to difficulties in experiments and numerical methods, is simulated with the presented algorithm. The atomization process is captured in detail. The inner and outer sheets collide and merge with each other to form a single sheet due to the pressure difference. A high pressure region at the impinging positions is generated by the strong momentum exchange between the sheets and it promotes the rapid breakup of the merged sheet. The spray characteristics and diameter distributions of droplets are obtained and compared under different injection conditions.