Canxu Liu , Xi Xi , Rong Xie, Hong Liu, Wenfei Li, Ming Jia, Han Gu
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引用次数: 0
摘要
本文提出了一种将喷嘴内流与外部喷雾和雾化耦合的方法。建立了一个混合 VOF-DPM 模型,以研究不同偏心率(0、0.5、0.62 和 0.81)对柴油发动机喷嘴雾化特性的影响。通过大涡模拟(LES)捕捉喷嘴内部流动和破裂形态。在高压喷射和非蒸发条件下,从喷雾形态、喷雾锥角、穿透距离和雾滴大小等方面对雾化性能进行了评估。使用发动机燃烧网络(ECN)中的 "Spray C "喷嘴对模型进行了验证,模拟结果与实验结果吻合良好。研究表明,椭圆形喷嘴在排放性能和雾化质量方面普遍优于圆形喷嘴。适当增加偏心率可促进液体破裂并缩短穿透距离,从而提高雾化效果。初级破裂受喷嘴内部湍流剪应力和近场空气动力的强烈影响。因此,偏心喷嘴的雾化促进机理是,偏心结构加剧了压力波动和湍流扰动,从而加剧了液芯的断裂和初级破裂时尖端薄片的拉伸和断裂,剥离出更多的夹带液滴。然后通过二次雾化产生更小、分布更均匀的微小液滴。
Numerical study on the effects of eccentric nozzles on spray evolution using a hybrid method
In this paper, a methodology is proposed to couple between the nozzle inner flow and external spray and atomization. A hybrid VOF-DPM model is developed to investigate the influence of different eccentricities (0, 0.5, 0.62, and 0.81) on the atomization characteristics of diesel engine nozzles. Large eddy simulations (LES) are performed to capture the nozzle inner flow and morphology of the breakup. The atomization performance is evaluated in terms of spray morphology, spray cone angle, penetration distance, and droplet size under high-pressure injection and non-evaporative conditions. The model is validated using the "Spray C" nozzle from the Engine Combustion Network (ECN), with simulation results showing good agreement with experimental findings. The research reveals that elliptical nozzles generally outperform circular ones in terms of discharge performance and atomization quality. The appropriate increase in eccentricity enhances atomization by promoting liquid breakup and reducing penetration distance. The primary breakup is strongly influenced by the turbulence shear stress inside the nozzle and the aerodynamic forces in the near field. Thus, the promoting atomization mechanism of the eccentric nozzle is that the eccentric structure intensifies pressure fluctuations and turbulent disturbances, thereby exacerbating the fracture of the liquid core and the stretching and breaking of the tip thin sheets during the primary breakup, peeling off more entrained droplets. The smaller and more uniformly distributed tiny droplets are then generated through secondary atomization.
期刊介绍:
The International Journal of Multiphase Flow publishes analytical, numerical and experimental articles of lasting interest. The scope of the journal includes all aspects of mass, momentum and energy exchange phenomena among different phases such as occur in disperse flows, gas–liquid and liquid–liquid flows, flows in porous media, boiling, granular flows and others.
The journal publishes full papers, brief communications and conference announcements.