In this study, the influence of in-nozzle phenomena including flow separation, cavitation, turbulence and hydraulic flip on the morphology of the spray emerging from a convergent-divergent-convergent diesel injector is investigated numerically. Non-linear equations of state for the liquid diesel, diesel vapour and chamber gas are employed for the simulation of high pressure diesel injection and atomisation processes. A modified multiphase mixture energy equation which takes into account enthalpy of phase change due to cavitation is integrated into a previously developed compressible, multiphase Volume of Fluid Large Eddy Simulation. The mass transfer source terms are modelled using a modified Schnerr and Sauer cavitation model. The numerical method is validated by comparing simulated mass flow rates, momentum fluxes, effective injection velocities and discharge coefficients at different injection conditions against published experimental data obtained using the same injector. Favourable comparison between simulations and experimental measurements is achieved with minor discrepancies attributable to unknown experimental uncertainties and assumptions made in numerical modelling. Calculation of in-nozzle flow and primary spray breakup reveals that interfacial instabilities generated due to in-nozzle flow separation, cavitation and liquid-wall shear contribute greatly to the jet fragmentation. The increase in sensible enthalpy due to wall shear induced viscous heating together with enthalpy of condensation increase the surface temperature of the exiting jet. Comparison of the flow physics before and after the onset of hydraulic flip indicates that wall shear is one of the main mechanisms inducing most of the energy for jet breakup. This modelling shows that vapour production at nozzle entrance remains after the onset of hydraulic flip, limiting the extent of ambient air influx. In addition, the onset of hydraulic flip causes production of near nozzle shockwaves as a result of significantly increased injection velocity attributable to minimised wall shear. This aspect needs more experimental evidence and simulations to confirm and validate.

中文翻译：

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使用改进的可压缩多相方法模拟空化高压柴油喷雾的热效应

在这项研究中，包括流动分离、空化、湍流和液压翻转在内的喷嘴内现象对收敛-发散-收敛柴油喷射器喷出的喷雾形态的影响进行了数值研究。液态柴油、柴油蒸汽和室内气体的非线性状态方程用于模拟高压柴油喷射和雾化过程。考虑到空化引起的相变焓的修改后的多相混合能量方程被集成到先前开发的可压缩、多相流体体积大涡模拟中。质量传递源项使用修改后的 Schnerr 和 Sauer 空化模型进行建模。通过比较模拟的质量流量、动量通量、不同注入条件下的有效注入速度和流量系数与使用相同注入器获得的已发表实验数据的对比。由于未知的实验不确定性和数值建模中所做的假设，模拟和实验测量之间实现了有利的比较。喷嘴内流动和初级喷雾破碎的计算表明，由于喷嘴内流动分离、空化和液壁剪切而产生的界面不稳定性对射流破碎有很大贡献。由于壁面剪切引起的粘性加热以及冷凝焓引起的显热焓增加，从而增加了离开射流的表面温度。水力翻转开始前后的流动物理比较表明，壁面剪切是产生大部分射流破裂能量的主要机制之一。该模型表明，喷嘴入口处的蒸汽产生量在液压翻转开始后仍然存在，从而限制了环境空气流入的程度。此外，液压翻转的开始导致近喷嘴冲击波的产生，这是由于壁剪切最小化导致注射速度显着增加的结果。这方面需要更多的实验证据和模拟来证实和验证。液压翻转的开始导致近喷嘴冲击波的产生，这是由于壁剪切最小化导致注射速度显着增加的结果。这方面需要更多的实验证据和模拟来证实和验证。液压翻转的开始导致近喷嘴冲击波的产生，这是由于壁剪切最小化导致注射速度显着增加的结果。这方面需要更多的实验证据和模拟来证实和验证。