涡旋燃烧炉流动、传热和燃烧特性的研究

本文应用强旋湍流气一固两相流动和煤粉燃烧的数学模型，对新型涡旋燃烧炉内的流动、传热和燃烧过程进行了系统的模拟和分析，得到了与实验相符合的结果。结果表明，涡旋燃烧炉内的湍流空气动力场分布具有强旋、回流和正在发展流的特点。水冷壁总吸热量随燃烧热负荷的增大成比例地增加。煤粉颗粒在炉内的平均停留时间随初始粒径的增大而加长。炉内可实现煤粉的低温、强旋、高效率和高强度燃烧。     

MODIFICATION OF THE κ-ε TURBULENCE MODEL FOR SWIRLING RECIRCULATING FLOW IN A PIPE EXPANSION

SUMMARY

A modified turbulence model, incorporating anisotropic effects into the standard κ-ε model, is proposed for the numerical simulation of swirling recirculating flow in a pipe expansion. The new modification follows the concept that the correction to the standard κ-ε model is made only in the flow regions where the anisotropic effects are appreciable. The performance of the present hybrid κ-ε model for two swirling flows with moderate and high swirl levels is better than that of the standard κ-ε model and the modified κ-ε model proposed by Abujelala and Lilley and is also competitive with our previously developed hybrid κ-ε model. Moreover, the present hybrid modification provides a relatively simpler form compared to our previously developed model; this also helps alleviate the numerical instability in the calculation procedure. Encouraging improvement in the prediction of the size of the central toroidal recirculation zone using the present hybrid modification is also exhibited     

Inviscid evolution of incompressible swirling flows in pipes: The dependence of the flow structure upon the inlet velocity field

This paper analyses the influence of the inlet swirl on the structure of incompressible inviscid flows in pipes. To that end, the inviscid evolution along a pipe of varying radius with a central body situated inside the pipe is studied for three different inlet swirling flows by solving the Bragg–Hawthorne equation both asymptotically and numerically. The downstream structure of the flow changes abruptly above certain threshold values of the swirl parameter (L). In particular, there exist a value L_r above which a near-wall region of flow reversal is formed downstream, and a critical value L_f above which the axial vortex flow breaks down. It is shown that the dependence upon the pipe geometry of these critical values of the swirl parameter varies strongly with the inlet azimuthal velocity profile considered. An excellent agreement between asymptotic and numerical results is found.     

圆环旋转粘性液膜射流三维不稳定性研究

利用线性稳定性理论进行了射流液体粘性对圆环旋转液膜射流稳定性影响的研究,推导出了三维扰动下具有固体旋涡型速度分布的圆环旋转粘性液膜射流的色散方程;在此基础上进行了类反对称模式与类对称模式下的圆环旋转粘性液膜射流的三维不稳定性分析。研究结果表明,在类反对称模式下,液体粘性超过一定值后,射流最大扰动增长率随液体粘性的增加而迅速减小;轴对称模态的射流特征频率产生一个突降变化;随液体粘性增加,轴对称模态不稳定波数范围减小,非轴对称模态不稳定波数范围呈现出先减小后增大趋势。在类对称模式下,液体粘性对射流最大扰动增长率的影响主要体现在对非轴对称模态的影响上;液体粘性只在粘性较大时才会对非轴对称模态射流特征频率产生一定影响;液体粘性超过一定值后,轴对称模态与非轴对称模态的不稳定波数范围都会快速下降。     

Particle statistics in a gas–solid coaxial strongly swirling flow: A direct numerical simulation

A direct numerical simulation of a strongly coaxial swirling particle-laden flow is conducted with reference to a previous experiment. The carrier phase is simulated as a coaxial swirling flow through a short nozzle injecting into a large container. The particle phase is carried by the primary jet, and simulated in the Lagrangian approach. The drag force, slip-shear force and slip-rotation force experienced by particles are calculated. A partial validation of the results is followed. The results are analyzed in Eulerian approach focusing on the statistical behavior of particle motion. The relative importance of the drag, slip-shear and slip-rotation forces under different Stokes numbers is indicated quantitatively. The particle velocity profiles, fluctuations, Reynolds stress, and turbulence intensity are demonstrated and analyzed respectively. An important “choke” behavior for large particles within the mainstream is found and interpreted. Additionally, the patterns of particle distribution and the helical structures of particle motion under different Stokes numbers are demonstrated qualitatively and analyzed quantitatively.     

不同参数下环形通道内湍流旋流流动的模拟

应用一种合理考虑湍流一旋流相互作用及湍流脉动各向异性的新的代数ＲｅｙｎｏｌｄＳ应力模型,对环形通道内的湍流旋流流动进行了数值模拟．研究了旋流数、进口轴向速度和内外半径比等参数对环形通道内湍流旋流流动的影响,以及由此产生的流场变化对强化环形通道内传热的作用．     

旋流燃烧室内湍流燃烧的PDA实验研究

本文建立了采用分级进风的旋流燃烧室实验台，实现了用三维激光粒子动态分析仪（ＰＤＡ）测最湍流旋流燃烧的热态瞬时速度场。在一次风旋流数为０．６９的工况下，衍到了燃烧室内气体时均轴向与切向速度和轴向与切向脉动速度均方根值的分布。     

旋流数对湍流燃烧中NO生成影响的研究

通过实验和用湍流燃烧二阶矩概率密度模型对不同旋流数下甲烷-空气湍流燃烧和NO生成进行了研究。在燃料中加入少量氨模拟燃料氮。研究结果表明,随旋流数的增大（由0到1）,热NO排放先上升后下降,而总NO和燃料NO排放则先下降后上升。旋流数增大使湍流强度先下降然后稍有上升,使进口附近温度先上升然后稍有下降。热NO的生成受温度的影响更大而燃料NO的生成受湍流的影响更大。     

旋转射流冲击换热液晶显示实验研究

采用热色液晶测温技术对以二氧化碳为工质的稳态射流冲击换热和管内插入扭转带方式的旋转射流冲击换热进行了实验研究。与普通射流相比,旋转射流导致驻点附近区域的换热趋于均匀化。其换热系数在大于某一半径之后高于普通射流,但在驻点附近相对较低。旋转射流对换热的此种影响随雷诺数的增大而减弱。     

旋流燃烧室内同向和反向旋转射流湍流流动的数值模拟

针对发展高效低污染旋流燃烧技术的需要,对旋流燃烧室内两股同轴旋转射流相互作用的湍流旋流流动进行了数值模拟.计算中采用了一种新的代数Reynolds应力模型和QUICK离散格式.在两股射流同向旋转和反向旋转两种条件下,将模拟得到的燃烧室内湍流旋流流动的时均气体轴向速度场、切向速度场和静压场与实验数据进行了比较.