基于Hartmann谐振腔的雾化喷嘴声场流场特性

Aeroacoustic and flow field features of ultrasonic atomizer based on Hartmann resonance tube

采用试验与数值模拟相结合的方法研究了谐振腔孔径、谐振腔深度、谐振腔与射流喷孔距离以及喷嘴压比(NPR)对基于Hartmann谐振腔(HRT)的气动式超声波雾化喷嘴外部流场及声场的影响.结果表明:当喷嘴压比大于2时,喷嘴压比增大对声场频率影响较小;当喷嘴压比小于2时,谐振腔依然能够产生高频声场,但其频率较高喷嘴压比时产生的小.当谐振腔深度小于1倍射流喷孔孔径时,此时高频声场主要由射流的不稳定性引发,声场频率与谐振腔深度经验关系式此时并不适用;当谐振腔孔径大于1.75倍射流喷孔孔径时,声场频率大小有降低趋势.谐振腔与射流喷孔距离与声场频率关系紧密,当谐振腔放置在自由射流压力增大区域时,才可获得理想高频声场.

Experimental and numerical studies were carried out to investigate the effects of operation parameters, such as diameter of resonance tube, resonance tube depth, jet nozzle hole to resonance tube spacing and nozzle pressure ratio （NPR）, on the flow and acoustic field characteristics of a ultrasonic atomizer based on the Hartmann resonance tube （HRT）. The modifications of the geometry of HRT in spectral and flow field characteristics were studied in detail. Result shows that that, when NPR is higher than 2, the increase of NPR has little effect on the frequency, however, when NPR is lower than 2, the lower frequencies of the acoustic field are obtained. The simulation results of flow field suggest that when the length of the resonance tube is smaller than diameter of jet nozzle hole, the reciprocating phenomenon of flow in the cavity is dampened, leading to a decrease of acoustic field frequency compared with cases having longer resonance tube length, and the classical relation between acoustic field frequency and tube resonance length is not appropriate for these situations. Also, the oversized diameter of resonance tube （typically, the diameter of resonance tube more than 1.75 times the diameter of jet nozzle hole） results in a lower oscillation acoustic field frequency for the interaction of the reciprocating and the shock is weakened. Furthermore, resonance occurs when the cavity is put in the regions where pressure arises for free jet.