The onset of Taylor-Görtler vortices in impulsively decelerating swirl flow

The onset of hydrodynamical instability induced by impulsive spin-down to rest in a cylinder containing a Newtonian fluid is analyzed by using propagation theory. It is well-known that the primary transient swirl flow is laminar, but with initial high velocities secondary motion sets in at a certain time. The dimensionless critical time Τ_c to mark the onset of instability is presented here as a function of the Reynolds number Re. Available experimental data indicate that for large Re deviation of the velocity profiles from their momentum diffusion occurs starting from a certain time Τ≈4Τ_c. This means that secondary motion is detected at this characteristic time. It seems evident that during Τ_c⪯Τ⪯4Τ_c, secondary motion is relatively very weak and the primary diffusive momentum transfer is dominant.     

Effect of high hydrogen enrichment on the outer-shear-layer flame of confined lean premixed CH4/H2/air swirl flames

In this study, we investigated the H₂-induced transition of confined swirl flames from the “V” to “M” shape. H₂-enriched lean premixed CH₄/H₂/air flames with H₂ fractions up to 80% were conducted. The flame structure was obtained with Planar Laser-Induced Fluorescence (PLIF) of the OH radical. Flow fields were measured with Particle Image Velocimetry (PIV). It was observed that the flame tip in the outer shear layer gradually propagated upstream and finally anchored to the injector with the hydrogen fractions increase, yielding the transition from the “V” to “M” flame. We examined the flame structures and the flame flow dynamics during the transition. The shape transition was directly related to the evolution of the corner flame along the outer shear layer. With H₂ addition, the outer recirculation zone first appeared downstream where the corner flame started to propagate upstream; then, the recirculation zone expanded upward to form a stable “M” flame gradually. The flow straining was observed to influence the stabilization of the outer shear layer flame significantly. This study can be useful for the understanding of recirculation-stabilized swirling flames with strong confinement. The flame structure and the flow characteristics of flames with a high H₂ content are also valuable for model validation.     

Multiphase flow measurements using coupled slotted orifice plate and swirl flow meter

Multiphase flow metering is a major focus for oil and gas industries. The performance of a modified version of a close coupled slotted orifice plate and swirl flow meter for multiphase flow was evaluated to provide further development of a new type of multiphase flow meter. The slotted orifice provides well homogenized flow for several pipe diameters downstream of the plate. This characteristic provides a homogeneous mixture at the inlet of the swirl meter for a wide range of gas volume fractions (GVF) and flow rates. In order to evaluate the performance of the designed flow-meter, its response was investigated for varying pressures and water flow rates. The proper correlations were established to provide high accurate two-phase flow measurements. The new proposed approach provides the GVF measurement with less than ±0.63% uncertainty for GVF range from 60% to 95%.     

Co-firing hydrogen and dimethyl ether in a gas turbine model combustor: Influence of hydrogen content and comparison with methane

To promote the utilization of hydrogen (H₂) in existing gas turbines, dimethyl ether (DME) was used to co-fire with H₂ in a model combustor. The swirl combustion characteristics of DME/H₂ mixtures were measured under the varying H₂ content up to 0.7. The results show that the flow velocity elevates as the H₂ content increases, which is associated with the increased flame temperature. The OH level firstly increases and subsequently keeps nearly unchanged as the H₂ content increases. Meanwhile, the OH area nonlinearly increases with the increasing H₂ content. Moreover, the increasing H₂ content induces almost linearly decreased lean blowout limit (LBO), increased NO emission, and intensified combustion acoustics. Furthermore, the combustion characteristics of the 0.46DME/0.54H₂ mixture and CH₄ with the same volumetric heat value were compared. The 0.46DME/0.54H₂ flame displays lower LBO and higher NO emission than the CH₄ flame, which mainly results from the higher reactivity of 0.46DME/0.54H₂ mixture.     

某型航空发动机燃油喷嘴旋流室的微细电解加工研究

针对某型航空发动机燃油喷嘴结构尺寸微小、材料硬度较高、切削加工困难等问题,介绍了微细电解加工的原理和实验装置,制备了微细棒状工具电极和三角形钩状成形电极,利用分层电解铣削进行粗加工快速去除工件多余材料,再利用环形扫描电解铣削进行旋流室全锥面的精加工,实现了发动机喷嘴微小尺寸旋流室的微细电解加工成形,达到加工精度和表面质量要求。研究表明,微细电解铣削加工是加工金属材料微小结构的有效可行的方法。     

涡流室式柴油机性能的改进和排放的降低

本文系统全面地分析了国内涡流室式柴油机的性能和排放方面的发展现状,并介绍了进一步的研究成果和提高其性能,减少排放的一系列行之有效的方法和措施。     

电控燃油喷射稀燃五气门CA1102Q汽油机试验

介绍一例汽油机多气门化改造的结果。由普通二气门ＣＡ１１０２Ｑ汽油机改造为电控、进气道喷射的五气门汽油机,在未提高压缩比的情况下,采用可变进气技术。实验结果表明：小负荷工况降低比油耗２４％ ,怠速排放降低到仅为国标限定值的１０％ ,低速及高速动力性提高１０％ ,并将稀燃工况拓宽到了９０％ 负荷范围,显示了汽油机多气门化改造的潜力。     

Droplet size distribution and evaporation characteristics of fuel spray by a swirl type atomizer

Spray atomization and evaporation play extremely important roles in mixture formation and combustion processes of direct injection (DI) gasoline engines. In this study, the fundamental characteristics of a swirl spray injected into a constant volume vessel are investigated by means of several laser diagnostic techniques including the laser diffraction-based method for droplet size distribution, the laser induced fluorescence-particle image velocimetry for velocity distributions of droplets and spray-induced ambient air flow, and the two-wavelength laser absorption-scattering technique for concentration distributions of liquid and vapor phases in the spray. The results show that the droplets at outer zone of the spray exhibit larger diameter than those at inner zone under both ambient pressures 0.1 and 0.4 MPa. While this can be partially attributed to the effect of spray-induced ambient air flow, the strength of ambient air flow become small when increasing the ambient pressure from 0.1 to 0.4 MPa, indicating the strong influence of spray dynamics on the droplet size distribution. In the evaporating spray, there are higher vapor concentrations near the spray axis than at peripheral zones. At 4.0 ms after start of injection, spray droplets almost completely evaporate under ambient temperature 500 K and pressure 1.0 MPa, but there are significantly amount of fuels with equivalence ratio below 0.5 in the spray. Reduction in ambient pressure promotes the air entrainment and droplet evaporation, but lowered ambient pressure results in more fuel vapor of equivalence ratio above 1.3 along the spray axis.     

低速二冲程船用柴油机耦合涡流影响的现象学喷雾模型研究

为了更深入地研究低速机缸内涡流对喷雾的影响,开发新的现象学模型并进行了优化计算.该模型在传统的广安博之多区现象学模型之上加入了涡流效应.在模型中,涡流与喷雾的相互作用被分成两个阶段:一是喷雾破碎前空气与喷雾的互相撞击,二是喷雾破碎后的空气的混合与卷吸.根据这两个阶段不同的物理作用,结合动量守恒定理的推导,可以计算出这两...     

LIMITATIONS AND EMPIRICAL EXTENSIONS OF THE k-ε MODEL AS APPLIED TO TURBULENT CONFINED SWIRLING FLOWS

Shortcomings and recommended corrections to the standard two-equation k-ε turbulence model suggested by previous investigators are presented. They are assessed regarding their applicability to turbulent swirling recirculating flow. Recent experimental data on swirling confined flows, obtained with a five-hole pilot probe and a six-orientation hot-wire probe, are used to obtain optimum values of the turbulence parameters C_μ, C₂, and σ_ε, for swirling flows. General predictions of moderately and strongly swirling flows with these values are more accurate than predictions with the standard or previous simple extensions of the k-ε turbulence model.