轴对称湍流冲击射流场的数值预测

应用标准k-ε模型和一种重正化群（RNG）k-ε模型，对半封闭轴对称湍流冲击射流场进行了数值模拟。通过两种模型计算结果的比较以及与参考文献中LDV测量结果的比较，评价了RNGk-ε模型对冲击射流场的数值预测能力。最后，根据数值模拟的结果，从流体动力学角度分析了冲击射流场的结构特性。     

中心射流对旋流燃烧器热声振动的影响

在CH4与空气的化学当量比为0.7、空气量为25 m/s时进行了旋流燃烧器热声振动试验.分析了不同中心风量下旋流燃烧的热声不稳定特性.结果表明:在中心风量为10%时,旋流核心区明显受到中心射流的影响,热声振动振幅明显下降,最大峰值脉动压力下降216 Pa;中心射流对热声振动的影响存在一个阈值,提高射流速度可使中心射流作用于旋流核心区,从而影响燃烧与声波的耦合,以实现对热声振动的被动控制.     

基于横向射流的旋流燃烧器热声不稳定控制

为研究横向射流控制旋流燃烧器内自激热声不稳定的机理,搭建了旋流燃烧器热声不稳定控制试验台架,分别采用了横向射流(JICF)和横向火焰射流(JFCF)研究了空气流率为1.333.3 mL/s、化学当量比为0.9、旋流强度为0.77时旋流燃烧器的热声不稳定控制作用.试验发现横向射流能够大幅度降低旋流燃烧器的热声不稳定强度,而且横向射流所占用的空气流率比例小.当横向射流空气流率比例XJICF为6%时,热声不稳定的有效压力振幅从1.712.Pa降到185.Pa,降低了89.2%.另外,横向射流的控制作用远远优于横向火焰射流,横向火焰射流需要在燃料流率比例XJFCF50%,时才能获得大于32.5%的控制效果.     

Annular Impinging Jet Controlled by Radial Synthetic Jets

This experimental study focuses on generation and control of annular impinging jets. The annular nozzle used in the investigations was designed with an active flow control system using 12 synthetic jets issuing radially from the central nozzle body. Measurements of the control effects were made on the impingement wall. The data acquisition involved wall pressure and wall mass transfer (by the naphthalene sublimation technique) using air as the working fluid. Also measured was time-mean flow velocity (by a Pitot probe) in the jet flow field. Moreover, flow visualization was carried out. Two main flow-field patterns (A and B) were identified. The patterns differ in the size of the separated-flow recirculation regions that develop attached to the nozzle central body: While pattern A is characterized by a quite small recirculation region (bubble) extending not far from the nozzle exit, pattern B exhibits a large recirculation region, reaching up to the impingement wall, on which it forms a stagnation circle. The control action modifies the flow field, resulting in changes of the corresponding heat/mass transfer distributions. The convective transfer rate on the stagnation circle can be demonstrably enhanced by 20% at a moderate nozzle-to-wall distance, equal to 0.6 of the nozzle outer diameter.     

小喷嘴间距撞击流的径向射流速度分布

采用热线风速仪对小喷嘴间距撞击流产生的径向射流的速度分布进行了实验研究.研究结果表明,径向射流在各个r.2D的径向断面上的速度分布具有相似性,呈高斯分布.在撞击面上无因次径向射流速度随着无因次径向距离的增大先增大后减小,而与喷嘴直径(D)、喷嘴间距(L)和出口气速无关.无因次径向速度在达到最大值前,与无因次径向距离成正比,在达到最大值后,无因次径向速度与无因次径向距离的1.33次方成反比.在撞击面上径向射流速度的最大值与出口气速成正比,与无因次喷嘴间距的0.551次方成反比.当L/D1时,无因次最大径向速度的位置随无因次喷嘴间距的增加而增加,当L/D1时,无因次最大径向速度的位置保持不变.     

Influence of the Acoustic Liner in Large Eddy Simulation of Longitudinal Thermoacoustic Instability in a Model Annular Combustor

Although extensive efforts have been made to dampen the thermoacoustic instability,successfully controlling the pressure oscillations in modem gas turbines or aeroengines remains challenging.The influence of the acoustic liner on the longitudinal thermoacoustic mode in a model annular combustor is investigated by Large Eddy Simulation(LES)in this work.The result of the self-excited longitudinal thermoacoustic instability without the liner agrees well with the frequency and acoustic analysis of the pressure mode based on experimental data.Three different bias flow velocities of the liner located downstream of the combustor are then simulated.The results reveal that the existence of the liner influences not only the acoustic field but also the flow field.When the bias velocity is large,it leads to intense turbulence-induced fluctuations,and the pressure oscillation is modulated intermittently.It shows that the weak coupling between flow and pressure oscillations plays a significant role in the onset of the intermittency of a thermoacoustic system.Based on the dynamic analysis of the thermoacoustic system with the acoustic liner,this intermittency is caused by the influence of the flow field on the flame-acoustic coupling.Finally,a low-order modeling method based on Van der Pol(VdP)oscillator with additive stochastic forcing is conducted to reproduce the evolving dynamics of the thermoacoustic system.Although the numerical cases demonstrated in this work are relatively simpler than those in a practical combustion system,the results are helpful for us to understand the effect of the acoustic liner and show the attractive potential to apply this device to suppress thermoacoustic instability.     

The Mechanisms of Flame Stabilization and Low NO_x Emission in an Eccentric Jet Pulverized Coal Combustor

The mechanisms of flame stabilization and low NO_x emission features of an eccentric jet pulverized coal com-bustor were studied through numerical modelling and experimental investigation.The results show that theformation of the unique flowfield structure is closely related to the interaction among combustor configuration,the primary jet and the control jet;and that certain rules should be followed in order to obtain the optimumcondition for flame stabilization.The distributions of temperature and concentrations of NO,O_2,CO and CO_2inside the combustor were experimentally measured.The effects of structural and operational parameters oncombustion and NO formation were studied.It was found that reduction of primary air,suitable use of controljet and reasonable uptilt angle of the primary jet all contributed to the reduction of NO_x at the combustor exit.A new hypothesis,that reasonable separation of oxygen and fuel within the fuel-rich zone is beneficial to furtherreduction of NO_x emission,is given.The study showed that good compatibility existed between the capabilityof flame stabilization and low NO_x emission for this type of combustor.     

分级着火油燃烧器的冷态实验研究

为了得到油燃烧分级着火的有效配置,解决将少量油和空气混合物送入回流区中心的问题．设置了带喷孔的中心套筒,并进行了一系列冷态试验。试验测定了燃烧器出口流场和喷雾密度分布．证明了上述方法的有效性,得到了主要参数的最佳值。     

喷嘴结构对多孔喷油器喷射特性影响的研究

利用EFS8246单次喷射测量系统和高速闪光摄影系统对不同结构参数的非轴对称喷嘴的喷油规律和油束形态进行了试验研究.利用CFD软件Fire的两相流模型对各喷嘴内部流动和气蚀现象进行了仿真模拟.喷嘴结构参数包括喷孔数、喷孔直径、喷孔夹角和喷孔长径比.研究结果表明:各结构参数对喷嘴流量系数、雾束形态、各孔间流量差异、各次喷射的一致性均有不同程度的影响,而具体的影响程度由压力室和喷孔内的气穴强度决定.     

燃烧室内自激励振荡燃烧的数值研究

采用数值方法研究了Langhorne型燃烧室内自激励燃烧驱动振荡的不稳定现象．应用非稳态雷诺平均法、雷诺应力紊流模型和涡团耗散燃烧模型,捕获了该类型燃烧室内两种当量比条件下的不稳定燃烧特性．数值模拟结果给出振荡燃烧发生时燃烧室内的压力振荡频率和幅值,并同实验结果进行了比较．证明了在两种当量比下分别存在着“强振荡”和“弱振荡”,并给出了两种当量比条件下不稳定燃烧时火焰的周期影像,详细分析了振荡发生时燃烧室内的火焰发展情况．