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Effects of cavitation on high-pressure atomization.

机译：空化对高压雾化的影响。

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Although disintegration and breakup of a liquid jet emerging from a nozzle has been studied for a long time, the effects of nozzle internal flow and specifically cavitation on the breakup of liquid jets have not been well understood. In the orifice of liquid injectors at high pressure, cavitation occurs behind the sharp corners, where a strong pressure drop is present due to quick change in the flow direction. In addition, a high level of shear stress is present inside the boundary layer. Therefore, it is important to understand the influence of the shear on the cavitation. There are two main questions to be answered: What is the effect of the shear stress on the cavitation inception? And, how does the shear stress influence the cavitation bubble dynamics?;In order to answer the above questions, the laminar flow of a liquid through the orifice of an atomizer is studied by means of numerical solution of Navier-Stokes equations. The total-stress criterion for cavitation is applied to find the regions where cavitation is likely to occur and compared with those of the traditional pressure criterion. Results show that the viscous stress has significant effects on cavitation inception.;Cavitation bubble dynamics is also affected by the presence of shear strain or normal strain in the flow. Interaction between a single cavitation bubble and strained flow is considered in the next part. As a result of interaction between the shear flow and the bubble, two re-entrant jets are observed on two sides of the bubble during the collapse phase. Re-entrant jets with enough strength could breakup the bubble into smaller bubbles.;Finally, four sources of disturbances are proposed that could be responsible for the improvement of atomization due to cavitation. Three of these sources are monopoles, quadrupoles and the vorticity generated during the bubble growth and collapse. It is shown that the monopole sources have the strongest contribution to the disturbances at the orifice exit. The other mechanism is the roll-up of the separated vortex sheet inside the orifice due to the disturbances caused by cavitation bubbles.
机译：尽管已经长时间研究了从喷嘴出来的液体射流的分解和破裂，但是还没有很好地理解喷嘴内部流动以及特别是气蚀对液体射流破裂的影响。在高压液体喷射器的孔口中，在尖角后面会发生气穴现象，在尖角处由于流动方向的快速变化而出现了很大的压降。另外，边界层内部存在高水平的剪应力。因此，重要的是要了解剪切对空化的影响。有两个主要问题要回答：切应力对空化开始的影响是什么？并且，剪切应力如何影响空化气泡动力学？；为了回答上述问题，通过Navier-Stokes方程的数值解研究了液体通过雾化器孔的层流。应用空化的总应力准则来查找可能发生空化的区域，并将其与传统压力准则进行比较。结果表明，粘性应力对空化开始有显着影响。空化气泡动力学也受到流动中剪切应变或法向应变的影响。下一部分将考虑单个空化气泡和应变流之间的相互作用。由于剪切流和气泡之间的相互作用，在坍塌阶段在气泡的两侧观察到两个凹入的射流。折返射流具有足够的强度，可以将气泡分解为较小的气泡。最后，提出了四种扰动源，它们可以改善空化导致的雾化。这些源中的三个是单极，四极以及气泡生长和破裂过程中产生的涡度。结果表明，单极子源对节流孔出口的扰动影响最大。另一个机理是由于空化气泡引起的扰动，使分离的涡流片在孔内卷起。

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