宽范围面积比下液气射流泵性能试验

结合液气射流泵的工作特点,介绍了其不同的应用场合时对泵具有不同的性能要求。以喉管/喷嘴面积比m为主要研究参数,在喉管长度固定情况下,对15种面积比(1.1025～110.25)单级液气射流泵工作性能进行了试验研究,结果显示面积比大小具有一定范围使泵正常工作,小面积比的液气射流泵可以得到较大的压力比,大面积比情况下可以得到较大的液气比。对于本文试验中给定的供水离心泵扬程大小和液气射流泵模型,以液气射流泵效率最高为衡量,存在最优面积比使泵效率最高,且该值与Cunningham经验公式变换后的计算值一致,同时试验得到小面积比情况下(m<4.41)合适的工作水压力值。试验结果为液气射流泵的工业应用提供依据。     

液气射流泵喉嘴距数值模拟及其最优范围确定

基于Fluent软件在不同流量比及不同喉嘴距下对液气射流泵进行了三维数值模拟,获得了液气射流泵的压力比和效率的仿真结果,并对不同工况下液气射流泵的性能曲线和效率曲线进行分析比较。结果表明:当喉嘴距不变时,随着流量比的增加,压力比逐渐减小;当流量比不变时,随着喉嘴距的增加,液气射流泵的效率先增加然后迅速减小,当喉嘴距为1.5倍喷嘴直径时,液气射流泵的效率最高;以效率最高点下降5%为标准,确定了液气射流泵最优喉嘴距范围为1.0～1.7倍喷嘴直径。     

超大面积比射流泵性能的数值模拟与流动分析

对超大面积比射流泵进行了三维数值模拟研究。采用Realizable k-epsilon湍流模型和标准壁面函数法,对面积比分别为57.4和60.05的单喷嘴射流泵进行了数值模拟和结构优化。基于数值模拟结果,对泵内压力和速度分布进行了分析。试验研究表明:对于超大面积比射流泵,随着流量比的增加,被吸流体阻力增加较快,导致压力比下降趋势不同于常规面积比射流泵的线性下降,从而呈现抛物线形式;随着面积比的增加,最高效率点右移,所需最优喉管长度也增大;对于超大面积比射流泵,工作流体进入喉管后仍有足够的空间进行径向扩展,其内部流场更近似于无限空间伴随射流。     

出口形状对中心体喷嘴射流性能的影响

提出将中心体喷嘴与异形喷嘴组合以产生更好的空化射流效果的思路。采用Mixture多相流模型,在15MPa的射流压力下,对正方形出口、三角形出口和圆形出口3种中心体喷嘴产生的淹没射流流场进行数值计算,重点对轴向速度、径向速度、湍动能和空泡相体积份额进行了对比分析。研究表明:圆形出口的中心体喷嘴比另两种异形出口的中心体喷嘴产生更高的射流速度和湍动能;正方形出口比三角形出口的中心体喷嘴的射流稳定性能更强,圆形出口的中心体喷嘴产生的集束性能较强;异形出口的中心体喷嘴产生的流场中,空泡相延伸距离更长,异形出口的中心体喷嘴产生的空化射流效果更好。     

带气环旋喷射流流场特征及喷嘴结构正交优化研究

为提高二/三重管法旋喷射流切割土体效率,采用Mixture多相流模型和RNG κ-ε湍流模型,开展了淹没环境下带气环旋喷射流流动模拟研究,获得了射流速度、气液两相体积分布、靶体作用压力等流场特征,并基于L₁₆(4⁵)正交试验设计及误差分析方法,获得了旋喷射流喷嘴关键结构参数对射流速度及其作用靶体压力的影响敏感程度与影响规律。结果表明：带气环旋喷射流能量衰减慢且集中在轴心区域,射流等速核心段长,冲击破坏土体性能好;喷嘴结构参数对射流冲击性能的影响敏感次序为：射流喷嘴出口直径>收敛角>气体喷嘴直径>气液喷嘴间距>射流喷嘴长径比;射流轴心速度及其作用靶体压力随出口直径和气体喷嘴直径的增大呈先快速增加后缓慢增加趋势,随收敛角、长径比、气液喷嘴间距的增大呈先增加后降低趋势。基于此,考虑旋喷射流设备性能,给出了最优结构参数为：射流喷嘴出口直径2.0 mm,收敛角12°或18°,长径比1,气体喷嘴直径0.9 mm,气液喷嘴间距5 mm。     

基于射流与两相流的射流曝气器研究

采用数值模拟的方法研究了射流器的射流及气液两相流动，并改变射流曝气器的长径比和喷嘴面积比，计算射流曝气器的两相流的气液流量比，分析了长径比和喷嘴面积比对射流曝气器流场和空气与液体流量比的影响以及喷嘴与混合管的相对位置对气蚀的影响，最后提出了新型射流曝气器主要结构的合适参数。     

射流泵内流动的数值模拟及喉管优化

采用κ-ε双方程紊流模型，运用混合有限分析法，贴体变换技术，研究射流泵的喉管入口段，喉管段，扩散段，出口段流态，对射流泵内部流动进行数值模拟，分别计算了具有不同喉管长度的射流泵内部流场，并通过分析，确定出射流泵的最优喉管尺寸，避免了喉管长度确定的任意性。     

管道气体助送的加气装置试验研究

针对绞吸式挖泥船排泥输送距离往往不能满足有关于工程需要的情况,采用了管道加气减阻以延长排距的方法,其中的加气方式和装置是影响减阻及排距的重要因素.研究了管道输送加气减阻的机理,对比分析了小孔多孔加气、双级喉管喷射加气、微孔材料渗气加气和旋转射流水气混合喷射加气的试验结果,得到了旋转射流水气混合喷射加气效果最好的结论,并设计了旋转射流水气混合喷射喷嘴.     

高压头比下射流泵的设计方法研究

从射流泵的基本方程入手,推导出了射流泵的性能包络线方程,并采用雅克比迭代的方法,利用Matlab绘制出了射流泵的性能包络曲线;联立性能包络线方程,推导并简化了射流泵在高压头比工况下最优参数的计算方法。利用有限元软件ANSYS模拟对比了常规设计方法和新方法设计出的射流泵的性能,发现在高压头比的工况下,常规方法设计出的射流泵面积比过小且喉管过短,不利于工作流体与被吸流体在喉管处充分混合,导致能量损失较大;而新设计方法设计出的射流泵各参数都比较合理,其性能相比于常规方法设计出的射流泵有很大的改善。     

吸入室直径对液气射流泵流场特性影响的数值模拟

为了全面分析液气射流泵内部结构对液气射流泵吸气性能的影响,以提高液气射流泵整体吸气性能。利用Fluent软件对不同吸入室直径下液气射流泵内部流场进行了三维数值模拟,获得了液气射流泵内部压力场和速度场分布以及轴心静压曲线,并拟合出压力比、流量比、效率与不同吸入室直径的关系曲线。对比分析表明,吸入室直径的大小会对液气射流泵内部压力、速度及吸气效率产生很大影响。射流泵其他结构一定时,吸入室直径大小存在最优值或者最优范围,使得液气射流泵的吸气性能最佳。     

An experimental study of the nozzle lip thickness effect on supersonic jet screech tones

It is well known that screech tones of supersonic jet are generated by a feedback loop driven by the instability waves. Near the nozzle lip where the supersonic jet mixing layer is receptive to external excitation, acoustic disturbances impinging on this area excite the instability waves. This fact implies that the nozzle lip thickness can influence the screech tones of supersonic jet. The objective of the present study is to experimentally investigate the effect of nozzle-lip thickness on screech tones of supersonic jets issuing from a convergent-divergent nozzle. A baffle plate was installed at the nozzle exit to change the nozzle-lip thickness. Detailed acoustic measurement and flow visualization were made to specify the screech tones. The results obtained obviously show that nozzle-lip thickness significantly affects the screech tones of supersonic jet, strongly depending on whether the jet at the nozzle exit is over-expanded or under-expanded.     

水气射流通风器参数对吸风性能影响的实验研究

分析了水气射流通风器的工作原理,介绍了理论确定水气射流通风器结构参数可应用的资料及实验用水气射流通风器的制作,建立了水气射流通风器实验系统,进行了不同吸风管结构、喉嘴距、喷嘴型式及水压对吸风量影响的正交试验,同时对实验结果进行了分析.实验结果表明,与射流泵对照,水气射流通风器最佳优参数既有其共同之处,也有其不同点.     

基于离散相模型的水力喷砂射孔器优化设计

针对常用水力喷砂射孔器冲蚀磨损严重、使用寿命短的问题,运用数值模拟软件的离散相模型,分析了常用水力喷砂射孔器的冲蚀磨损规律,提出了工具结构和喷嘴结构的优化设计方案;并对新型水力喷砂射孔器的射流性能和耐冲蚀性能进行验证。研究结果表明：常用水力喷砂射孔器的冲蚀磨损主要集中在工具内腔喷嘴入口处、喷嘴内流道和工具外壁喷嘴出口处,且射孔器结构、射孔液运动特性、管柱振动和工作环境是造成冲蚀磨损的4个主要原因;相同条件下,相比于常用水力喷砂射孔器,所提出的新型水力喷砂射孔器的射流速度更大,上下层喷嘴间的速度差更小,耐冲蚀性能更佳。     

Stereoscopic-PIV measurement of turbulent jets issuing from a sharp-edged circular nozzle with multiple triangular tabs

Three-dimensional (3D) flow structures of a turbulent jet issuing from a sharp-edged circular nozzle having multiple triangular tabs are experimentally studied by employing a stereoscopic-PIV (SPIV) system. Two different sharp-edged jet nozzles having 4 and 8 tabs are investigated at a jet Reynolds number of Re = 10,000. The SPIV measurements are carried out at 5 different cross-sectional planes along the jet direction. Spatial distributions of turbulent statistics including mean velocity, mean vorticity, and turbulent kinetic energy are obtained at each cross-sectional plane. The jet entrainment rate showing the mixing of the jet and ambient fluids is also estimated using the measured 3D velocity field information. As a result, the jet issuing from the nozzle with 4 tabs shows better turbulent mixing effect at further downstream position than the 8 tabs case because of the reduced reciprocal interactions of the streamwise vortices that promote the turbulent dissipation.     

定向喷嘴布置对PDC钻头井底流场影响研究

定向喷嘴布置的方式对PDC钻头的井底流场将有很大的影响,尤其是能改变PDC钻头的水力性能,因而研究定向喷嘴布置具有重要的意义.本文分析了喷嘴的不同布置方法,并通过数值方法模拟其对PDC钻头井底流场的影响.结果表明:在不完全对称布置方案的冲击区,在射流刚开始从喷嘴处流出去,但还未接触井底,各喷嘴射流处于衰减地带之内,这样的话将对钻头的清洗和携带岩屑离开井底非常有效果;在漩涡区,喷射角大、距钻头中心远的喷嘴射流则对清洗和携带井壁附近的岩屑起主要作用,喷射角小、距钻头中心近的喷嘴射流则对清洗和携带井底中心的岩屑起主要作用;在刀翼上的附面层由于周围喷嘴的影响,刀翼切削面低速区明显减少,剪应力增大,更好地预防、清除PDC钻头的泥包.最终达到提高机械钻速的效果.     

An investigation on effect of geometrical parameters on spray cone angle and droplet size distribution of a two-fluid atomizer

A visual study is conducted to determine the effect of geometrical parameters of a two-fluid atomizer on its spray cone angle. The liquid (water) jets exit from six peripheral inclined orifices and are introduced to a high speed gas (air) stream in the gravitational direction. Using a high speed imaging system, the spray cone angle has been determined in constant operational conditions, i.e., Reynolds and Weber numbers for different nozzle geometries. Also, the droplet sizes (Sauter mean diameter) and their distributions have been determined using Malvern Master Sizer x. The investigated geometrical parameters are the liquid jet diameter, liquid port angle and the length of the gas-liquid mixing chamber. The results show that among these parameters, the liquid jet diameter has a significant effect on spray cone angle. In addition, an empirical correlation has been obtained to predict the spray cone angle of the present two-fluid atomizer in terms of nozzle geometries.     

An experimental study of supersonic dual coaxial free jet

A supersonic dual coaxial jet has been employed popularly for various industrial purposes, such as gasdynamic laser, supersonic ejector, noise control and enhancement of mixing. Detailed characteristics of supersonic dual coaxial jets issuing from an inner supersonic nozzle and outer sonic nozzles with various ejection angles are experimentally investigated. Three important parameters, such as pressure ratios of the inner and outer nozzles, and outer nozzle ejection angle, are chosen for a better understanding of jet structures in the present study. The results obtained from the present experimental study show that the Mach disk diameter becomes smaller, and the Mach disk moves toward the nozzle exit, and the length of the first shock cell decreases with the pressure ratio of the outer nozzle. It was also found that the highly underexpanded outer jet produces a new oblique shock wave, which makes jet structure much more complicated. On the other hand the outer jet ejection angle affects the structure of the inner jet structure less than the pressure ratio of the outer nozzle, relatively.     

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.     

Supersonic jet noise control via trailing edge modifications

Various experimental data, including mixing areas, cross correlation factors, surface flow patterns on nozzle walls, and far field noise spectra, was used to draw a noise control mechanism in a supersonic jet. In the underexpanded case, mixing of the jet air with ambient air was significantly enhanced as presented before, and mixing noise was also dramatically reduced. Screech tones, in the overexpanded case, were effectively suppressed by trailing edge modifications, although mixing enhancement was not noticeable. From mixing and noise performance of nozzles with modified trailing edges, enhancing mixing through streamwise vortices seems an effective way to reduce mixing noise in the underexpanded flow regime. However, screech tones in the overexpanded flow regime is well controlled or suppressed by making shock cells and/or spanwise large scale structures irregular and/or less organized by a proper selection of trailing edges. The noise field in the overexpanded flow regime was greatly affected by the symmetricity of the nozzle exit geometry. In the underexpanded flow regime, the effects of the symmetricity of the nozzle exit on mixing were negligible.     

收缩喷嘴内部流道型线对射流流场的影响

为研究收缩喷嘴内部流道形成对射流流场的气体动特性参数的影响，根据可压缩流体轴对称N-S方程，采用非结构网格和二阶精度的有限体积法，对不同内部流道形线的喷嘴自由射流进行数值模拟。亚声速射流采用RNGk-ε湍流模型，超声速射流采用S-A湍流模型，计算结果与实验较吻合。在亚声速流动中，收缩喷嘴的收缩角大小会影响其对射流的阻滞效果，内部流道形线设计为维多辛斯基曲线可以获得更好的流场动特性参数，有利于提高喷嘴的工作效率。在超声速流动中，喷嘴流道型线对出口膨胀波的角度与强弱影响较大，要根据射流的有效作用区域选择合适的喷嘴，才能使能量的损失最小。若要获得较佳的外部流场参数，优化喷嘴内部流道设计十分重要。