Flow and aeroacoustic characteristics evaluation of microjet noise reduction concept in the nozzle design for minimum quantity lubrication

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.