Abstract Minimum quantity lubrication (MQL) is an efficient and sustainable technology, which has been considered to be an option of conventional flood cutting process. Even though MQL provides green solution for the cooling and lubrication function during machining, it brings about unendurable aeroacoustic jet noise from the high velocity spray. The acoustic pollution has seriously affected the operator's health and efficiency so that it should be paid much attention to. In this paper, with the utilization of microjets noise reduction concept, a noise cancellation accessory for MQL nozzle has been developed. The flow field and aeroacoustic characteristics of the original nozzle and microjets have been investigated numerically to help understand the noise reduction mechanism. Variables including the main jet flow rates, the air flow rate ratios of the microjets to the main jet and the measuring azimuths on noise directivities and sound pressure level (SPL) have been analysed. It has found the flow ratio is a critical parameter, which has an optimal value in regard to the main jet flux. The simulation results have been partially verified through OASPL measurement. The overall aeroacoustic noise reduction varied from 0.70 to 4.88 dB has been observed experimentally. Finally, the noise cancellation mechanism has been discussed from the flow field and the frequency characteristics points of view. The shrinking effect of microjet injection at appropriate air flow ratios has significantly narrowed the distribution of the turbulent intensity and reduced the SPL of low and medium frequency while increased that of the high frequency in specific directions. The overall amplitude of OASPL has been reduced. However, inappropriate air flow ratios will generate additional jet noise.

中文翻译：

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微喷降噪概念在微量润滑喷嘴设计中的流动和气动声学特性评估

摘要 微量润滑（MQL）是一种高效且可持续的技术，被认为是传统洪水切割工艺的一种选择。尽管 MQL 为加工过程中的冷却和润滑功能提供了绿色解决方案，但它带来了难以忍受的高速喷射的气动声学喷射噪声。声污染已严重影响操作人员的健康和工作效率，应引起高度重视。在本文中，利用微射流降噪概念，开发了 MQL 喷嘴的降噪附件。对原始喷嘴和微射流的流场和气动声学特性进行了数值研究，以帮助理解降噪机制。变量包括主射流流速，分析了微射流与主射流的空气流量比以及噪声方向性和声压级 (SPL) 的测量方位角。已经发现流量比是一个关键参数，它对于主射流通量具有最佳值。仿真结果已通过 OASPL 测量得到部分验证。已通过实验观察到整体气动噪声降低范围为 0.70 至 4.88 dB。最后，从流场和频率特性的角度讨论了噪声消除机制。在适当的空气流量比下，微射流喷射的收缩效应显着缩小了湍流强度的分布，降低了中低频的声压级，同时增加了特定方向的高频声压级。OASPL 的整体振幅已降低。然而，不适当的空气流量比会产生额外的喷射噪音。