基于LES-VOF方法的花瓣孔喷嘴内空化流动和近场雾化的数值研究

A Numerical Study on the In-nozzle Cavitating Flow and Near-field Atomization of a Spiral Hole Nozzle Using LES-VOF Method

为改善柴油机的油气混合性能,借鉴航空发动机离心喷嘴中的设计,在锥形喷嘴孔壁上设置若干螺旋弧槽,形成花形截面的螺旋花瓣喷嘴。本文采用多相流耦合大涡模拟(VOF-LES)方法对柴研究了螺旋花孔喷嘴结构对柴油机喷嘴空化流动和一次雾化特性的影响。数值计算结果表明,螺旋花喷嘴的速度系数较小。并且,由于螺旋花瓣结构的存在,在螺旋花喷嘴的近场区域可以观察到强旋转射流。最后,螺旋花喷嘴喷出的射流具有更大的扩散角和更小的液滴尺寸,在螺旋花喷嘴出口处也有一些液丝和液滴与主射流分离。

Referring to the design that the tangential groove is used to guide the fuel to rotate and enhance atomization in the centrifugal nozzle of aero-engines, a spiral hole nozzle, in which several spiral arc grooves are set on the hole wall of tapered nozzles to form a flower-shaped cross section,had been designed. In this paper, the multi-phase flow inside and outside the nozzle was calculated using a volume-of-fluid, large eddy simulation(VOF-LES) method to clarify the effects of spiral hole nozzle structure on the cavitating flow and primary atomization characteristics for diesel nozzles.Numerical results showed that the discharge coefficient and velocity coefficient of the flow over the spiral hole nozzle were considerably lower than those of the non-spiral hole nozzle. Additionally, a jet with strong rotation can be observed in the near-field region of spiral hole nozzles due to the centrifugal effect resulted from spiral arc grooves structures. Moreover, the jets emerged from the spiral hole nozzle showed wider spreading angles and smaller droplet sizes. Finally, some liquid ligaments and droplets to separate from the main jet at the outlet of spiral hole nozzles.