Effects of Pre-Diffuser on Performance of Dump Diffuser

研究了突扩扩压器中前置扩压器各参数与总压损失和静压恢复间的关系。采用实验与fluEnT计算结合的方法,通过水槽PIV实验得出扩压器内的流场信息,对照不同的湍流模型,得出最佳的计算方案。根据此计算方案计算不同的扩张角下前置扩压器性能的变化,得出各参数之间的规律。结果表明雷诺应力模型能够较好地预测扩压器内部流场;前置扩压器扩张角存在一个最佳值,大于最佳值前置扩压器会出现流动分离;结合理论分析和计算数据总结出计算前置扩压器总压损失系数和静压恢复系数的公式,利用此公式还可求出最佳的前置扩张角和前置扩压器长度,计算误差在5%左右。Diffuser is one key component of the gas turbine combustor following the compressor.Its primary function is to slow down the air flow delivered by the compressor in order to promote efficient combustion and avoid large total pressure losses.An experimental and computational study of cold flow in the dump diffusers was presented.The main aims were to evaluate the influence of pre-diffuser wall angle and pre-diffuser length on the performance of dump diffusers,and to identify the pressure loss mechanisms.PIV experiments were conducted in a simplified test model to help choose of congruent turbulence model.It was observed that apparent flow separation occurred on pre-diffuser wall when pre-diffuser wall angle amplified to certain degree.The pre-diffuser exit flow was distorted,indicating that the uniform exit conditions typically assumed in the diffuser design were violated.Skew distribution of the pre-diffuser outlet flow can result in strong transverse mixing for liquid,the total pressure loss of pre-diffuser increases significantly.The formula of the total pressure loss coefficient and the pressure recovery coefficient was developed.The optimal pre-diffuser length and pre-diffuser wall angle can be conveniently obtained by this equation,the calculation error was less than 5%.中央高校基本业务费(2013121019); 航空基金(20132268003

Numerical Simulation of the Break-up and Atomization Process of the Impinging Liquid Jets

本文以液体火箭发动机中常用的撞击雾化喷注器为研究对象，采用AdaptiveMeshRefinement(AMR)自适应网格技术及VolumeofFluid(VOF)模型对撞击射流破碎雾化过程进行了数值模拟。 计算得到了不同射流速度、撞击角、射流速度比，射流直径比工况下，两股射流从喷出、互相撞击、破碎的全过程，得到了射流形成液丝并最终破碎为液滴的各种形态特性。对比计算结果表明：总体上，射流决定了射流的撞击雾化模式，较小时液膜稳定，此时不稳定现象不明显，液膜保持封闭。随着的增大，液膜表面不稳定性增强，液膜表面出现明显撞击波，撞击波逐渐向下游发展、放大，并诱发液膜边缘液丝脱落，液丝在气动力作用下继...In this paper, Adaptive Mesh Refinement (AMR) adaptive mesh technology and Volume of Fluid (VOF) model are used to simulate the atomization process of the two impinging jets, which aims to analyze atomization characteristics of the impinging fuel injector applied in the liquid rocket engine. The effects of different jet velocity, impact angle, jet velocity ratio and jet diameter ratio on the char...学位：工程硕士院系专业：航空航天学院_工程硕士(机械工程)学号：3202014115285

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.国家自然科学基金(51406171);; 中央高校基本科研业务费(20720150180);; 福建省自然科学基金(2015J05111