圆环旋转黏性液体射流空间不稳定性研究

利用线性稳定性理论, 进行了液体黏性对不同旋转强度下圆环旋转液体射流 空间不稳定性影响的研究. 在推导出的三维扰动下具有固体涡核型旋转速度分布的圆环旋转 黏性液体射流色散方程的基础上, 针对中低速射流, 进行了类反对称模式与类对称模式下圆 环旋转黏性液体射流的空间不稳定性分析. 研究结果表明, 对于旋转强度较大的圆环旋转液 体射流, 液体黏性的增加, 不利于射流的破碎; 随着液体黏性的增加, 射流的特征频率和最 不稳定波数减小. 然而, 对于旋转强度较小的圆环旋转液体射流, 液体黏性的增加, 有利于 射流的破碎; 随着液体黏性的增加, 类反对称模式下射流特征频率先减小后增大, 类对称模 式下射流特征频率增大; 随着液体黏性的增加, 类反对称模式下射流最不稳定波数先减小后 增大, 类对称模式下射流最不稳定波数增大.     

分级进风对旋流燃烧室内湍流燃烧的影响

本文在分级进风旋流燃烧室的实验台上,测量了在不同的分级进风比率或二次直流风率条件下,湍流旋流燃烧的时均温度场、O_2、CO_2、CO和NO浓度场的分布。通过实验测量结果分析了分级进风对旋流燃烧室内湍流燃烧过程及NOx生成的影响。     

A remark on the Lipschitz estimates of solutions to Navier–Stokes equations

In this paper, we establish a constant‐type growth estimate in the Lipschitz norm of solutions to the 2D Navier–Stokes equations with fractional diffusion and a polynomial‐type growth estimate of solutions to the 3D axisymmetric Navier–Stokes equations. Copyright © 2010 John Wiley & Sons, Ltd.     

A novel combustion system for liquid fuel evaporating and burning

To utilize sustainable biofuel, the current study proposes a novel combustion technique that directly burns liquid ethanol without a spray system. Two swirling air flows are induced by tangentially injected the gas from two concentric tubes at different stages. The liquid ethanol is fed by a liquid tank at the center. At the beginning methane flame assists in preheating the system to vaporize liquid ethanol and ignite the vapor. Thereafter methane is switched off, and liquid ethanol can be continuously vaporized through self-burning released heat. The heat and mass transfer processes are examined to illustrate such self-sustained burning–heating–evaporating system. The ethanol flow rate is gradually increased to provide different heat output. The flame structures, temperature distributions and pollutant emissions are carefully examined. The results show that the ethanol can be steadily burned to provide heat output between 0.7 and 2.5?kW. Generally a blue flame is obtained, and the NO_x and CO concentrations are ultralow. By increasing ethanol flow rate to exceed 8?mL/min, an unsteady, sooting flame is observed owing to incomplete evaporation and poor mixing. A parametric study is conducted to evaluate the influences of liquid tank position, flow rate and tip structure on the combustion characteristics. Additionally, an optimal operation condition is proposed. The current study provides a promising method to burn low-boiling liquid fuel in a clean, efficient and compact way.     

旋流排气管的一维非定常流动计算

动力机械装置中广泛存在着非定常旋流流动现象．本文根据质量、动量、能量和旋流动量矩守恒方程，建立了管内非定常旋流流动的一维计算模型，并应用特征线方法推导出了其数值计算格式，是管内非定常一维流动计算的扩展．应用于一台四缸涡轮增压柴油机旋流排气管的计算，通过与实测压力波的比较，表明计算模型有较好的计算精度．     

Determination of principal characteristics of turbulent swirling flow along annuli: part 4: an asymptotic solution

An asymptotic solution of the momentum equation is given that describes the decay of swirling flow passing along the annulus formed between two concentric, straight, circular-section pipes having a common starting point. The flow is considered turbulent and approximations are made consistent with the notion of fully developed flow conditions. Applications of this approach are reviewed and shortcomings highlighted. A series of calculations are presented and compared with experimental and theoretical data previously obtained by the authors. It is shown that acceptable predictions of the overall flow behavior can be obtained over a wide range of initial conditions provided the calculations procedure is applied in regions of validity, which has not been the case in some published work. Substantial errors are found if, for example, the procedure is allowed to commence at inlet to the annulus owing to the inconsistency of the assumptions in the initially developing-flow region, which for this work extends at least five outer-pipe diameters downstream from inlet. The authors' previous numerical integration scheme may be used to predict flows satisfactorily in the developing-flow region and the present asymptotic solution used subsequently to reduce computation time and cost.     

旋流燃烧室内湍流燃烧速度场的实验研究

建立了采用分级进风方式的同轴射流旋流燃烧室实验装置，选用耐高温的氧化铝细粉作为示踪粒子，实现了用三维激光粒子动态分析仪(PDA)测量湍流旋流燃烧的热态瞬时速度场．在分级进风比率和旋流致不同的3组实验工况条件下，得到了气体时均轴向与切向速度、轴向与切向脉动速度均方根值和轴向—切向脉动速度二阶关联量的分布．     

Effect of swirl intensity on the flow and combustion of a turbulent non-premixed flat flame

An experiment in a turbulent non-premixed flat flame was carried out in order to investigate the effect of swirl intensity on the flow and combustion characteristics. First, stream lines and velocity distribution in the flow field were obtained using PIV (Particle Image Velocimetry) method in a model burner. In contrast with the axial flow without swirl, highly swirled air induced streamlines going along the burner tile, and its backward flow was generated by recirculation in the center zone of the flow field. In the combustion, the flame shape with swirled air also became flat and stable along the burner tile with increment of the swirl number. Flame structure was examined by measuring OH and CH radicals intensity and by calculating Damkohler number (Da) and turbulence Reynolds number (Re _T ). It appeared that luminescence intensity decreased at higher swirl number due to the recirculated flue gas, and the flat flames were comprised in the wrinkled laminar-flame regime. Backward flow by recirculation of the flue gas widely contacted on the flame front, and decreased the flame temperature and emissions concentration as thermal NO. The homogeneous temperature field due to the widely flat flame was obtained, and the RMS in the high temperature region was rather lower at higher swirl number. Consequently, the stable flat flame with low NO concentration was achieved.     

Experimental investigations into vortex flow in a straight,annular section channel

Results of experimental velocity measurements in air at several cross-sections along a straight annular section channel comparable to a hydraulic machine admission duct are presented. The flow analysis focuses on the axial and tangential velocity components and their modification with changes in the intensity of swirl along the channel. Particular prominence is given to an anomalous flow, the ‘dead water core’, occurring at the greatest swirl intensities. An earlier method of evaluating the core size of this anomalous flow on the basis of a vortex-type schematization is tested; Strscheletzky's method is also analysed. Finally a definition of the dead water core dimensions based on the axial velocity component distribution is proposed     

垂直管内气液螺旋流的衰减特性研究

气液两相旋流在工业中应用广泛,为了研究螺旋流的维持距离,从而提高气井的携液能力,本文通过数值模拟研究了叶片式起旋器引发的气液两相螺旋流衰减特性,获得了预测螺旋流维持距离的关系式.研究发现:起旋器下游气液相分布变化,环状液膜沿管周向分布逐渐变均匀,气相切向速度相对于轴向和径向速度,衰减最明显;然后基于模拟结果,通过气液两...