Effect of droplet characteristics on liquid-phase distribution in spray zone of internal mixing air-mist nozzle

In continuous casting production,droplet characteristics are important parameters for evaluating the nozzle atomization quality,and have a significant impact on the secondary cooling effect and the slab quality.In order to study the behavior of atomized droplets after reaching the slab surface and to optimize the spray cooling effect,the influence of droplet diameter and droplet velocity on the migration behavior of droplets in the secondary cooling zone was analyzed by FLUENT software.Results show that the droplets in the spray zone and on the slab surface are mainly concentrated in the center,thus,the liquid volume fraction in the center is higher than that of either side.As the droplet diameter increases,the region of high liquid volume fraction on the slab surface becomes wider,and the liquid phase distribution in the slab width direction becomes uneven.Although increasing the droplet velocity at the nozzle exit has little effect on droplet diffusion in the spray zone,the distribution becomes more uneven due to more liquid reaches the slab surface per unit time.A prediction formula of the maximum water flow rate on the slab surface for specific droplet characteristics was proposed based on dimensionless analysis and validated by simulated data.A nozzle spacing of 210 mm was recommended under the working conditions in this study,which ensures effective coverage of the spray water over the slab surface and enhances the distribution uniformity of water flow rate in the transverse direction.

Comparison of One-Dimensional Analysis with Experiment for CO₂Two-Phase Nozzle Flow

The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, it is measured that the temperature profile in the stream-wise direction of a divergent-convergent nozzle through which CO2 in the supercritical pressure condition is blown down into the atmosphere. In the analysis, a one-dimensional model which assumes steady, adiabatic, frictionless, and equilibrium is proposed. In the convergent part of the nozzle the flow is treated as single-phase flow of liquid, whereas in the divergent part the flow is treated as separated two-phase flow with saturated condition. The analytical results indicate that the temperature and the pressure decrease rapidly in the divergent part, and the void fraction increases immediately near the throat. Although this analysis is quite simple, the analytical results can follow the experimental results well within this study.

Numerical simulation of the gas-solid two-phase flow inside the multi-channel nozzle for the surface nanocrystallization induced by the ultrasonic particulate peening

Using a gas-solid two-phase model(a discrete phase model),the authors investigated the flow field inside the multi-channel nozzle for surface nanocrystallization(SNC)induced by the ultrasonic particulate peening(USPP).By computation,the velocity fields of both the gas and the solid phases were simulated and the track of the solid phase was analyzed in detail.It can be found that the velocities of the two phases are able to reach an ultrasonic level;meanwhile,the dispersion width of the solid phase at the nozzle exit is less than that of the gas phase.When particle diameters are less than 5 μm,there is a decreasing trend in the dispersion width of the solid phase with an increase in particle diameters.The trend becomes stable as the particle diameters are greater than 5 μm;in the meantime,the distribution of solid particles is near the axis of the jet flow.The optimal standoff distance between the nozzle and the substrate in the process of USPP is about 120 mm.Simulation results can help improve the design of mass-production-oriented multi-channel nozzles for SNC induced by USPP.

Study on Venturi nozzle for gas-liquid two-phase flow metering

Experiments were carried out to study gas-liquid two-phase flow through a horizontally mounted Venturi nozzle. The inner diameter of pipe is 25 mm and the throat diameter of Venturi nozzle is 5. 1 mm. The pressure difference and pressure loss across the nozzle were measured. It was found that the degree of pressure fluctuation strongly depends on the gas quality. However,the relationship between the standard deviation of pressure difference and the gas quality is not monotonous. Multiple solutions may occur when the relationship was used to determine gas quality. On the other hand,the standard deviation of pressure loss was found to be monotonously correlated to X. This phenomenon was applied to measured gas quality. Also a modified Lin's equation is proposed to calculate the two-phase flow rate. The experimental measurements agree well with the predicted values.

AN IMPLICIT ALGORITHM OF THIN LAYER EQUATIONS IN VISCOUS，TRANSONIC，TWO－PHASE NOZZLE FLOW

Omitting viscosity along flow direction, we have simplified the dimensionless N-Sequations in arbitrary curved coordinate system as the thin layer equations. Using theimplicit approximate-factorization algorithm to solve the gas-phase governing equ-ations and the characteristic method to follow the tracks of particles, we then obtainedthe full coupled numerical method of two-phase.transonic, turbulent flow. Here, par- ticle size may be grouped, the subsonic boundary condition at entry of nozzle is ireatedby quasi-characteristic method in reference plane and the algebraic model is used forturbulent flow. These methods are applied in viscous two-phase flow. calculation of ro-cket nozzle and in the prediciton of thrust and specific impulse for solid propellant ro-cket motor. The calculation results are in good agreement with the measurerment va-lues. Moreover, the influences of different particle radius, different particle mass frac-tion and particle size grouped on flow field have been discussed, and the influences of particle two-dimensional radial velosity component and viscosity on specific impulse ofrocket motor have been analysed.The method of this paper possesses the advantage of saving computer time. More important, the effect is more obvious for the calculation of particle size being grouped.

Experiment and Numerical Simulation of Free Water Jet by a Central-body Nozzle

The recent research about cavitation jet mainly focuses on the organ-pipe nozzle and triangular nozzle. The research content mainly includes the optimized design about the structure of nozzles, the observation and flow analysis about the cavitation jet in the water, and the theory of rock attacked by the cavitation jet, while the energy characteristic of the free jet is not studied yet. In China, the research about the central-body nozzle is almost empty. For the purpose of studying the energy characteristic and the structure of free water jet discharged from central-body nozzle, an experiment with phase Doppler particle anemometry（PDPA） technology is carried out to measure the free water jet flow, which is produced by a central-body nozzle under the jet pressure of 15 MPa. While five sections with different axial distances from the nozzle outlet are selected for data process and analysis, the axial and radial velocity and the droplets of the particle size are studied. Meanwhile, numerical calculation of corresponding flow field is conducted by using volume of fluid（VOF） multiphase model, and the jet flow feature is discussed. The experimental and calculating results show that the axial velocity of high speed jet flow dissipates slowly in the air, and the core area and diffused area are discovered. The diameter of droplet in the core area is small, and jet energy is concentrated, while in the diffusion area, water is mingled with ambient air and radial velocity is relatively large. Obvious low-pressure area exists behind the central body and potential cavitation may occur in that area. The proposed research reveals the energy characteristic of free jet discharged from central-body nozzle, provides the theoretical basis for preestimating erosion feature of the central-body nozzle and also the theoretical foundation for revealing the mechanism of erosion.

Influence of Self-excited Vibrating Cavity Structure on Droplet Diameter Characteristics of Twin-fluid Nozzle

It is a great challenge to find effective atomizing technology for reducing industrial pollution; the twin-fluid atomizing nozzle has drawn great attention in this field recently. Current studies on twin-fluid nozzles mainly focus on droplet breakup and single droplet characteristics. Research relating to the influences of structural parameters on the droplet diameter characteristics in the flow field is scarcely available. In this paper, the influence of a self-excited vibrating cavity structure on droplet diameter characteristics was investigated. Twin-fluid atomizing tests were performed by a self-built open atomizing test bench, which was based on a phase Doppler particle analyzer(PDPA). The atomizing flow field of the twin-fluid nozzle with a self-excited vibrating cavity and its absence were tested and analyzed. Then the atomizing flow field of the twin-fluid nozzle with different self-excited vibrating cavity structures was investigated.The experimental results show that the structural parameters of the self-excited vibrating cavity had a great effect on the breakup of large droplets. The Sauter mean diameter(SMD) increased with the increase of orifice diameter or orifice depth. Moreover, a smaller orifice diameter or orifice depth was beneficial to enhancing the turbulence around the outlet of nozzle and decreasing the SMD. The atomizing performance was better when the orifice diameter was2.0 mm or the orifice depth was 1.5 mm. Furthermore, the SMD increased first and then decreased with the increase of the distance between the nozzle outlet and self-excited vibrating cavity, and the SMD of more than half the atomizing flow field was under 35 μm when the distance was 5.0 mm. In addition, with the increase of axial and radial distance from the nozzle outlet, the SMD and arithmetic mean diameter(AMD) tend to increase. The research results provide some design parameters for the twin-fluid nozzle, and the experimental results could serve as a beneficial supplement to the twin-fluid nozzle study.

Impact Pressure Distribution in Flat Fan Nozzles for Descaling Oil Wells

The suitability of high pressure nozzles in terms of impact upon targeted surfaces has indicated its effectiveness for the cleaning of oil production tubing scale, which has recently attracted wider industrial applications considering its efficiency, ease of operation and cost benefit. In the oil and gas production, these nozzles are now used for cleaning the scale deposits along the production tubing resulted mainly from salt crystallization due to pressure and temperature drop. Detailed characterizations of flat-fan nozzle in terms of droplet sizes and mean velocities will benefit momentum computations for the axial and radial distribution along the spray width, with the view of finding the best stand-off distance between the target scale and the spray nozzle. While the droplet sizes and the velocities determine the momentum at impact, measuring droplet sizes has been known to be difficult especially in the high density spray region, still laboratory characterization of nozzles provides a reliable data especially avoiding uncontrollable parameters. While several researches consider break up insensitive to the cleaning performance, this research investigates the experimental data obtained using PDA （phase doppler anemometry） which led to established variation in momentum across the spray width thus, non-uniformity of impact distribution. Comparative model was then developed using Ansys Fluent code, which verifies the eroded surfaces of material using the flat-fan atomizer to have shown variability in the extent of impact actions due to kinetic energy difference between the center and edge droplets. The study＇s findings could be useful in establishing the effect of droplet kinetic energies based on the spray penetration, and will also add significant understanding to the effect of the ligaments and droplets, along the spray penetration in order to ascertain their momentum impact distribution along the targeted surface.

成对斜喷管气动力同步性与身管振动控制研究

为降低某30 mm航炮连续射击时的身管振动和对飞行器的冲击,提出对武器身管产生动力偶和反后坐力、不产生横向力的成对斜喷管振动控制方案。基于两相流理论,建立考虑身管侧向导气的武器内弹道模型,运用TVDMacCormack差分格式进行了数值求解,获得了武器膛内流场和两喷管气动力随时间的变化曲线。进一步对航炮连续射击过程进行动力学仿真,分析了成对斜喷管对炮口振动的影响。结果表明,两斜喷管气动力峰值发生时间相差0.07 ms,且瞬态最大气动力差0.5%,具有较好的同步性;控制装置能在弹丸初速度基本不降低的情况下,使炮口的横向振动线位移和线速度分别减小26.9%和44.3%,炮口振动响应降低较为明显;同时武器后坐冲量减小17.93%,且不对飞行器产生横向力作用,武器对机身的冲击明显降低。该研究可为航炮成对斜喷管身管振动控制装置的设计提供理论依据。

螺旋喷嘴内外流场特性的实验研究

通过实验的方式研究旋流室顶部具有螺旋形导流结构的空心喷嘴。搭建可容纳1~4个喷嘴工作的喷淋实验台,制作可视化螺旋喷嘴,进行喷淋特性实验。使用高速摄像机进行内部流场特性的可视化研究,并通过测量装置采集外部流场喷淋密度的分布情况。分析不同工况下内部流场空气柱、湍流流动的变化规律以及外部流场喷淋密度的特性。结果表明,在内外压差的作用下,喷嘴内部形成空气柱,由于单侧切向入口和螺旋导流结构的作用,空气柱中心线与旋流室中心线存在偏移。外部流场周向有效喷淋密度呈现双峰值分布,峰值区域分别位于120°和280°附近。

喷嘴位置对轴承腔内油气润滑两相流的影响

基于气液两相流理论,采用多重坐标系法构建角接触球轴承数值计算模型,分析不同喷嘴位置和转速下轴承腔内油相体积分数、保持架表面及轴承内外圈的油气分布特性。结果表明:在轴承低转速下,正面供油时轴承腔内油相体积分数及其周向分布的波动大于背面供油;正面供油时保持架下表面会产生润滑油的积聚,造成润滑油无法及时通过出口排出,而背面供油时润滑油在保持架表面的油相分布更均匀;正面供油时内圈左面油相体积分数较高,外圈油相分布变化较大,而背面供油时内圈右面、中间面及外圈中间面油相体积分数较高。不同转速下喷嘴位置对腔内油相分布的影响也不同,低转速下正面供油时腔内油相体积分数更高,高转速下喷嘴位置对轴承腔内油相分布的影响较小,润滑油在轴承腔内分布较为均匀,保持架下侧未见明显的润滑油积聚。

板坯宽度方向非均匀冷却条件下凝固模拟

利用多物理场仿真软件COMSOL模拟板坯连铸宽度方向非均匀冷却状态下的凝固过程的数值模拟。通过将各冷却区设定的铸坯表面目标温度作为约束条件代入傅里叶传热微分方程,反向推算板坯内弧表面中线上各冷却区的换热系数。在此基础上,根据二冷区喷嘴的布置及喷嘴喷雾分布试验数据将该换热边界条件沿铸坯宽度方向进行拓展,计算出板坯从MD弯月面开始到最末扇形段出口的整个铸流区间的3D温度场。通过该方法可模拟出相同冷却条件下不同铸坯宽度在厚度中性层剖面两相区区间范围的区别,并且也可以清晰地反映出喷嘴的布置对铸坯表面温度及凝固终点的影响,从而为生产中的凝固末端压下策略和喷嘴布置的设计提供有力的数据支撑。

基于RBF代理优化的固体火箭发动机喷管型面设计

针对固定扩张比与扩张段长度的二维轴对称固体火箭发动机喷管进行扩张段型面优化,优化目标为喷管推力最大化,优化参数为贝塞尔曲线控制点的径向位置,优化方法采用径向基函数(Radial Basis Function, RBF)代理优化算法。采用纯气相与两相流两种模型分别进行优化设计,纯气相的结果表明,对于10个控制点表达的贝塞尔曲线,优化后的推力提高了1.64%。以此优化型面为初始型面,增加控制点个数至16个,二次优化后的推力又提高了0.095%。增大优化参数范围,同时引入判断拐点的约束,对于10个控制点表达的贝塞尔曲线进行单轮优化,结果同上述经过两轮优化之后的结果相近,优化后的喷管推力提高了1.78%,说明算法具有较强的稳定性。通过对不同控制参数个数的贝塞尔曲线优化过程的对比,给出了合理选择控制点个数的方法与建议。两相流的优化结果表明,由于颗粒的滞后影响造成了两相流损失,两相流喷管的推力小于纯气相喷管,但两相流喷管优化后的推力较优化前初始型面的推力提高了1.87%,略高于纯气相喷管。RBF代理优化算法适用于由任意数量控制点组成的贝塞尔曲线表达的喷管扩张段型面优化,并有较高的效率与较强的稳定性。

有限元模拟仿真在压力容器对接接管焊缝相控阵超声检测工艺设计中的研究与验证

针对大壁厚压力容器接管焊缝多为窄间隙对接焊接头,超声检测中存在扫查路径复杂、定量定性精度差和检出率相对较低等难点,引入有限元模拟仿真技术。通过建立工件3D模型和不同类型的缺陷,模拟各缺陷在压力容器筒体外壁和接管内壁相控阵超声检测时的响应情况,优化相控阵超声探头、楔块设计和探头运动轨迹,最终实现检测工艺的理论设计。在带有自然缺陷的模拟试块上,验证检测工艺的准确性和可靠性。对比有限元模拟仿真和在模拟试块上的实际检测情况表明,经过仿真设计过的相控阵超声检测工艺可有效提高接管窄间隙焊缝中缺陷的检出率和检测精度。

取向硅钢常化冷却段空气雾化喷嘴内流场数值模拟

为改善取向硅钢常化过程带钢的冷却效果,对空气雾化喷嘴内气液两相流动过程进行三维数值模拟研究,分析空气压力和水流量对喷嘴内流场速度和液相体积分数的影响。数值计算值与实验测试值吻合良好且最大误差小于10%。结果表明:当水流量一定时,随着空气压力的逐渐增大,喷嘴内速度增大、液相体积分数减小,喷嘴出口处速度分布均匀性变差,液相体积分数分布更均匀;当空气压力一定时,随着水流量的逐渐增大,喷嘴内速度逐渐减小、液相体积分数增大,喷嘴出口处速度分布更均匀,液相体积分数分布均匀性变差;喷嘴气水压力比为1.1时冷却均匀性较好,冷却均匀性最佳的工况为空气压力0.2 MPa、水流量180 L/h。

喷管两相湍流数值模拟及湍流模型性能评估

研究固体火箭发动机喷管中颗粒质量流率对两相流的影响规律以及不同RANS模型对该问题的预测性能,可为喷管设计等工程应用提供重要参考。在欧拉-拉格朗日(Euler-Lagrange)框架下,通过3D大涡模拟(3D LES)研究了颗粒质量流率对喷管两相流场的影响规律,以3D LES结果作为参考依据,分析了不同RANS模型针对喷管两相流在2D轴对称和3D模拟中的性能。结果表明:由于扩张段内颗粒集中在中轴线附近区域,颗粒质量流率越大,该区域马赫数越低,温度越高;壁面附近存在无颗粒区,故边界层内流动几乎不受颗粒影响。另外,采用不同湍流模型计算得到的颗粒分布与LES基本相同。在2D轴对称RANS模拟中,发现RNG k-ε模型所预测的气相质量流率和喷管比冲与LES结果吻合最好;在高颗粒质量分数下(约30%),不同湍流模型预测的相对比冲损失差别可超过3%。在3D RANS模拟中,发现Realizable k-ε模型表现出最佳的综合性能,所预测的物理量沿中轴线分布的准确性均优于其他模型。当颗粒质量分数约为31.2%时,Realizable k-ε模型所预测的比冲为与LES结果相比误差仅1.56%。

矩形喷管出口宽高比对流场与声场的影响

为探究矩形喷管出口宽高比对喷流流场和声场的影响规律,采用DES/FW–H混合算法对出口宽高比为3和1.5的矩形喷管超声速完全膨胀喷流开展研究,分析出口宽高比对喷流流动与噪声的影响。针对多个流场变量进行对比分析,以验证数值模拟方法的可行性,发现喷管出口宽高比不同,靠近出口内壁面上的压力变化也有所不同:喷管出口宽高比越大,压力变化越快。结合已有噪声实验数据和计算数据,验证了噪声模拟的准确性。对不同出口宽高比下剪切层厚度的变化进行了分析,研究了这种变化对喷流噪声的影响,发现随着宽高比增大,剪切层厚度增大,且剪切层快速扩张位置和高频噪声源位置向上游方向移动。对比了不同宽高比下出口唇线上特定频率噪声的相速度,研究发现:喷管宽高比不同,同样频率的近场噪声有着不同的相速度,这决定了近场噪声向下游传播的最大角度;相速度对应的马赫角越大,近场噪声向下游传播的最大角度越大;宽高比增大,长轴唇线上的相速度显著降低,近场噪声向下游的辐射角度减小。

闪沸喷雾孔几何形状对孔内流动特性影响的数值模拟

研究了汽车直喷汽油机喷嘴的几何形状对于闪沸喷雾孔内流动以及相变过程的影响机理。基于热不平衡假设建立了一维的两相相变流动模型,对于具有不同喷孔流道长度、直径、入口处圆角以及流道锥角的结构,分析了闪沸喷雾孔内流动的特性。将该模型结果与作者团队先前的实验结果进行了精度比对,验证了模型的准确性。结果表明:喷孔流道长度越长,孔径越小,从而孔内相变越剧烈。流道入口处圆角会减少喷孔内部蒸汽的生成。收缩型喷孔压降较小,孔内蒸汽相的生成也相应减少,从而扩张型喷嘴增大蒸汽产生速率。不同的喷孔结构,改变了流道内的压力以及速度分布;压力分布影响了气泡的生长速率,速度分布影响了气泡的生长时间,而两者共同作用影响了孔内的相变特性。

环形自激振气举泵提升性能试验研究

为提高气举泵的提升效率,设计了一种带有振荡腔结构的新型气举泵,通过振荡腔对混合流的激励作用,增强气液混合物在提升管内的输运能力。计算了提升管内气液两相流流型随气相速度的变化规律,并通过试验对比分析振荡腔结构与无振荡腔结构在不同浸没率下,排水量、峰值点位置、提升效率随着进气量增加的变化规律。结果表明:受提升管内流型变化的影响,排水量随着进气量增大存在先升后降的趋势;进气量<75 m^(3)/h时,有振荡腔结构提升效率高于无振荡腔结构,进气量>75 m^(3)/h时,提升效率低于无振荡腔结构,最佳进气量范围在50~75 m^(3)/h之间;新型结构气举泵提升性能受进气量、浸没率影响,存在最佳工况,且在最佳工况范围内,相较于传统结构效率提高10%~20%。研究结果可为气举泵的优化设计提供参考。

密闭容器内旋流喷头除砂过程数值分析

为探究旋流喷头除砂过程容器内流场分布特性及流场对除砂能力的影响规律,采用RSM和DPM模型对密闭容器内部流场和颗粒运动轨迹进行了数值模拟。研究结果表明,压降从20 kPa增大到45 kPa时,容器内部旋流稳定性逐渐增强,容器中心颗粒质量分数不断增大,逃逸颗粒中大颗粒质量分数逐步增大;压降从45 kPa增大到100 kPa时,旋流稳定性减弱,逃逸颗粒中大颗粒质量分数小幅度下降,压降为45 kPa时旋流喷头能够以较低的能耗实现最佳的除砂效果。在旋流喷头中心管下端添加挡板可以有效减弱下游旋流切向速度,对旋流稳定性和轴向速度影响较小,有效提高了喷头对大颗粒的清除效率;挡板间隙h=15 mm时相比h=5 mm时整体旋流切向速度更小,对大颗粒的清除效果更高。喷头安装高度从100 mm下降到50 mm的过程中,喷头下方切向速度增大,喷头对大颗粒的清除能力减弱;安装高度为25 mm时喷头足够接近容器底部,中心轴向速度增大,喷头对大颗粒的清除能力激增。所得结论可为旋流喷头的操作参数、结构优化及安装位置确定提供数据参考。