NUMERICAL STUDY OF FLOW AND DILUTION BEHAVIOR OF RADIAL WALL JET

The radial wall jet is a flow configuration that combines the radial jet and the wall jet. This article presents a simulation of the radial wall jet by applying the transition Shear-Stress Transport (SST) model. Tanaka's experimental data are used for validation. The computed velocity profiles agree well with the experimental ones. The distributions of the velocity on cross-sections show a similarity in the main region and the profiles are different with those of the free radial jet or the wall jet, because the presence of the wall limits the expansion of the jet. By introducing the equivalent nozzle width, the maximum velocity decays and the half-width distributions are normalized, respectively. In addition to compare the flow field with experiments, this paper also analyzes the dilution effect of radial wall jets in terms of the concentration distributions. The concentrations on the wall keep constant within a certain distance from the nozzle. And the concentration distributions also show a similarity in the main region. Both the decays of the maximum concentration and the distributions of the concentration half-width fall into a single curve, respectively. The dilution effect of radial wall jets is thus verified.     

Velocity and concentration measurements in initial region of submerged round jets in stagnant environment and in coflow

Velocity and concentration fields are measured in submerged round jets in a stagnant environment and in coflow using laser Doppler anemometry and laser-induced fluorescence. Measurements are made in the initial region within distances of 40 jet exit diameter at jet Reynolds number between 1000 and 5000 and coflow-to-jet velocity ratio from 0 to 0.43. Different behaviors of jet spreading and dilution are found in jets at three different ranges of Reynolds number in which the jets are classified as initially laminar, transitional or turbulent. In the zone of established flow, the jet centerline velocity and concentration decay with downstream distance at different rates in the three groups of jets. For jets in coflow, axial development of normalized forms of centerline mean excess velocity and mean concentration at different velocity ratios can be reasonably well collapsed onto universal trends through the use of momentum length scale. Turbulence properties inside a jet are increased by the presence of a strong coflow. Inside the zone of flow establishment, some strange features are observed on jet turbulence properties. The length of zone of flow establishment increases from the turbulent jets, to the transition jets and to the laminar jets. The zone lengths for concentration are shorter than those for velocity by one to two jet exit diameters. Both lengths are shortened further in the presence of a coflow. For jets a stagnant environment and in the strong jet flow region of jets in coflow, jet widths increase linearly with downstream distance in transitional and turbulent jets. Self-similarity of radial profiles of mean velocity or excess velocity, mean concentration, turbulence intensities and concentration fluctuation level is explored in the zone of established flow.     

动水环境中有限宽窄缝湍射流的水力特性研究

本文采用粒子图像测速(PIV)系统，在分析了水中粒子跟随性的基础上，对动水环境中多种喷口长度和流速比情况下的有限宽窄缝湍射流近区流场进行测试，并结合数值模拟结果分析讨论了动水环境中有限宽窄缝湍射流的近场三维流动特性。在实验观测的流速比范围内，射流势流核长度随着流速比的增加而增大并逐渐趋近于平面自由湍射流的势流核长度，雷诺数对射流的发展轨迹影响很小，射流发展主要由流速比控制。同时，给出了射流背流面逆流区长度与流速比、喷口形状因子之间的关系。     

射流冲刷试验研究

为研究影响射流冲刷的因素，作者进行了７０组试验，分别研究了单管和多管，水平和有入射角，贴底和离开床面，静水和动水等情况。对试验结果的分析表明，在床沙一定、河流流速与射流流速相比不大的情况下，冲刷坑的几何尺寸与Ｖ＾２／３Ｄ＾５／６有较好的关系。     

不同动力环境下孔间距对双孔射流特性的影响

为研究孔间距对双孔射流运动和稀释特性的影响,采用粒子图像测速技术(PIV)和激光诱导荧光技术(PLIF)分别对静水、横流和波浪环境下双孔射流的速度场和浓度场进行测量,对比分析了孔间距为5倍、10倍和15倍射流孔直径时双孔射流的轴向速度、横断面垂向速度、轨迹线及浓度场分布情况。结果表明:在静水环境下,孔间距较小时双孔射流的轴向速度衰减较单孔射流慢,随着孔间距的增大双孔射流轴向速度衰减的程度逐渐趋近于单孔射流。在横流环境下,随着孔间距的增大,前方射流对后方射流的遮掩作用不断减小,而后方对前方射流的卷吸作用也有所减弱,导致前方射流弯曲程度的增大和后方射流上升高度的降低。在波浪环境下,孔间距较小时,两孔中间存在一个独立的高浓度区;孔间距增大后,浓度等值线逐渐呈"凸"形分布。为降低双孔射流相互作用对射流初始稀释的影响,建议在波浪和横流环境下双孔射流的孔间距不宜小于射流孔直径的10倍。     

圆形喷嘴平行射流组流体动力学特性

本文在簿剪切层理论基础上，建立了平行射流组的理论模型，并依据Ｐｒａｎｄｔｌ混合长度理论，求出了该模型的分析解。通过该模型的计算分析，得出：（１）沿流动方向轴向速度逐渐衰减，其轴心最大速度衰减与单射流相同；（２）沿ｙ方向，轴向速度按余弦规律分布，并且随着向射流组上游发展，其速度振幅逐渐减少，直到趋于平坦。在离喷嘴足够远的流动相似区，计算结果与实验结果是一致的。     

EVALUATION OF THE CUMULATIVE FORMATION OF HIGH-SPEED LIQUID JETS

1 .　INTRODUCTIONHigh speedliquidjetsareoftenseeninrainerosionsimulationofaircraftandmissiles ,JilbertandField[1] and jetcuttingofmaterials ,Kob ayashi[2 ] .Inthegenerationofjets ,itistechnicallyinterestingtoknowhowtooperatetheexperimen talfacilityattheoptimumconditiontoobtainthejetvelocitymostefficiently .ThisisdescribedbyShiandTakayama[3] ,ShiandItoh[4 ] ,ShiandIt oh[5] .Intheearlieststudyofa pulsedhigh speedliquidjet ,BowdenandBrunton[6 ] puttheliquidinanozzleandthenusedaslugimpact…     

淹没紊动射流三维流场特性的数值模拟

采用RNGk-ε紊流模型对有限空间的单孔、双孔紊动射流的流场进行了三维数值模拟研究。研究结果表明:无论入流条件如何变化,经无量纲处理后的轴线流速分布曲线几乎都落在同一条无量纲速度分布曲线上,说明流动存在相似性。双孔射流时,流场存在分区结构,在不同的喷嘴间距下,射流的卷吸程度不同,S/D越大,射流之间的卷吸掺混作用越弱。     

湍浮力射流形成区内特性的预报

应用作者所提出的数学模型和计算方法,对浮力射流形成区内的特性进行了预报。得出了形成区内中线流速、温度和湍动能的沿程变化,以及射流核的长度和掺入速度。也得出了流速、温度和湍动能在断面上的分布。并分析和讨论了出口条件及环境分层对这些特性的影响。     

双股射流壁面脉动压强与近壁紊动流速相关与频谱特性

本文用多通道动态压力检测系统和二维激光测速仪对在单股和双股射流作用下,水垫塘底板脉动压强与近壁脉动流速的相关,功率谱和紊动比尺进行了测试研究。实测表明,双股射流形成的动水扩建在塘底水平方向的脉动使得双股射流在第二冲击点下游的脉动量特性与单股射流不同：前者的水平脉动速度与脉动压强的互相关系数较后者明显增大,且水平脉动速度和脉动压强的功率谱具有大致相同的优势频率。单股和双股射流塘底脉动压强系数与近壁紊     

THE MERGING OF TWO UNEQUAL AXISYMMETRIC PARALLEL TURBULENT JETS

Results of an experimental study of the merging of unequal parallel round turbulent jets are presented.Experiments were conducted for a jet axial separation to nozzle diameter ratio of 3.0 and the Reynolds numbers ranging from 8 000 to 15 000.The distance to the point where the jets are merged was measured for a range of jet source momentum flux ratios.Three different merger criteria were used based on the mean velocity profile,mean passive tracer concentration profile,and Reynolds stress profile.The results show that the concentration profile merges closest to the jet sources followed by the velocity profile with the Reynolds stress profile merging furthest from the nozzles.For all three profiles the merge distance is relatively insensitive to the momentum flux ratio,consistent with previous findings for slot jets and buoyant round jets.The measured merge distances are consistent with previously published results for equal round jets,though the poor spatial resolution of data in the literature means that limited comparison is possible.There are no studies of unequal jet merger currently in the literature that could be used for comparison.     

水垫塘三元复杂紊流场试验测试研究

本文采用了五孔毕托球结合压力传感器，通过微机自动的采样和处理，设计了一套可施测三元流场的测试系统，并测试了一大比尺模型的多股水舌入射水垫塘塘内的三元流态，首次得到水垫塘水流流态的概化图，揭示了多股水看入射水垫塘形成的塘内复杂的流态特征，并将其流态特征归类为三个区：水舌入射区，螺旋流区和扩散区，并对每个流区作了分析。     

STUDY ON FLUID MECHANICS OF HYPERVELOCITY LIQUID JETS

The fluid mechanics in the generation of hypervelocity water jets, light oil jets and glycerin jets was studied. Framing high-speed photography and single-shot photography were used to observe the jets directly. The purposes of this study is to investigate the disintegration and atomization processes at the velocity of 2km/s-3km/s as well as the auto-ignition and self-combustion of the light oil jets. Therefore, in the jet velocity measurement in addition to the high-speed photography, the results by other methods such as the laser beams cutting method and the shock wave detection using pressure transducers were also given. In the observation of the jets events, the illumination phenomenon was found, which may be regarded as the result of the auto-ignition and combustion of the light oil jets. Finally, the Munroe jet was studied.     

横流中射流及其温度标量输运大涡模拟

将动力拟序涡黏性亚格子应力模型拓展到温度标量亚格子模型中,数值模拟了横流条件下有、无温度标量场作用的射流,得到的横流条件下浮力射流的温度和速度分布与Anwar的试验值吻合一致。在此基础上,分析了有、无温度标量场作用下射流回流区域大小和射流轨迹线特性,对比分析了回流区域内涡心和分离点处湍动能和耗散率、拟涡能以及边界层处拟序结构等湍流特性。计算结果表明:温度场的作用使射流的回流区域增大,射流速度轨迹线高度增加,回流区域内湍流的湍动能增加,边界处拟序结构的周期性不如无温度场时明显。     

流动环境中高浓度射流的三维数值模拟

应用流动环境中高浓度圆孔射流的三维RNG湍流模型,模拟计算不同水深和环境来流下的流态和浓度场分布,结果表明在已有射流区、冲击区以及异重流区的基础上,还存在1个上游入侵区。该上游入侵区的长度随环境流速的增大而减小,水深对其的影响相对较小。射流触底点位置随环境流速以及水深的增大而下移,触底点浓度则随环境流速以及水深的增大而减小。流态分析显示,壁面反射流形成动量较强的附壁射流时,会在较短距离内收缩和膨胀,紊动掺混剧烈,水深较浅时容易形成全水深掺混。比较而言,附壁射流较弱时无上游入侵,在射流孔口下游附近横断面上会形成较为特别的水滴状浓度等值线分布,在水体底部形成更为稳定的异重流。最后探讨了水体底面横向最大浓度沿流向的分布特征。     

NUMERICAL SIMULATION OF TURBULENT JETS WITH LATERAL INJECTION INTO A CROSSFLOW

1. INTRODUCTION The interaction of jets with crossflow generates complex flow fields which exist in a variety of industrial applications, e.g. internal film cooling of turbine blades, dilution air jets in combustion chambers, jet from V/STOL aircraft in transition flight. Systematic experimental, theoretical and numerical investigations of the flow fields began several decades ago, where the parameters studied include the jet injection angel, the jet-to-crossflow velocity ratio, the jet …     

Two-phase velocity measurement in a particle-laden jet

A horizontally discharging jet laden with solid sediment particles is investigated experimentally. The submerged jet discharges water with an initially horizontal direction into stagnant water of the same density but the presence of sediment particles produces jet effluent having a combined density greater than that of the ambient water. A modified particle-imaging velocimetry (PIV) technique is applied to estimate the velocity fields of the solid particle phase and the jet fluid liquid phase. Phase separation is achieved optically between the scattered light signals from the particles and the laser-induced fluorescence signal from the jet fluid dozed with a fluorescent dye. It is found that initial sediment concentrations below 0.1% volume fraction do not cause significant changes to the global properties of the jet flow. In jets of higher initial sediment concentrations, settling of sand particles are observed to drag the jet to spread with a downward-bending mean trajectory. Intensive particle–flow interaction is also observed in jets of high sediment concentrations.     

双射流流动结构实验研究

应用PIV实验方法对由直射流和同心的环状旋转射流组成的双射流流场进行了测量，并分析研究了流场的速度和旋度变化规律。分析表明，双射流等速核长度较小，仪约为5倍喷距；随喷距的增加其多股射流特性逐渐减弱，其主要原因为直射流和旋转射流在交界面上很强的剪切作用；旋转射流的径向发展因受直射流吸附作用的影响而减小，相应直射流速度在喷嘴轴线上的衰减则增加。在4-6倍喷距间的旋转射流速度突然下降和相应位置处旋度场的涡环都显示该处可能存在较强的空化现象，而大大提升双射流的能力。     

Progress in numerical simulation of cavitating water jets

This paper reviews recent progress made toward modeling of cavitation and numerical simulation of cavitating water jets. Properties of existing cavitation models are discussed and a compressible mixture flow method for the numerical simulation of highspeed water jets accompanied by intensive cavitation is introduced. Two-phase fluids media of cavitating flow are treated as a homogeneous bubbly mixture and the mean flow is computed by solving Reynolds-Averaged Navier-Stokes (RANS) equations for compressible fluid. The intensity of cavitation is evaluated by the gas volume fraction, which is governed by the compressibility of bubble-liquid mixture corresponding to the status of mean flow field. Numerical results of cavitating water jet issuing from an orifice nozzle are presented and its applicability to intensively cavitating jets is demonstrated. However, the effect of impact pressure caused by collapsing of bubbles is neglected, and effectively coupling of the present compressible mixture flow method with the dynamics of bubbles remains to be a challenge.     

An Investigation of Turbulent Rectangular Jet Discharged Into A Narrow Channel Weak Crossflow

A computational investigation of the mean flow field of turbulent rectangular jets issuing into a narrow channel crossflow is presented. The length of the jet slot spans more than 55% of the crossflow channel bed, leaving a small clearance between the jet edge and sidewalls. A finite volume code employing the standard k-εmodel is used to predict the mean, three-dimensional flow field. The mean flow field is investigated for two velocity ratios （6 and 9）. Important flow features, such as the formation of different vortical structures and their characteristics owing to different values of the velocity ratio, are discussed. Some predicted results are compared with the experimental data reported in the literature. The predicted mean and turbulent flow properties are shown to be in good agreement with the experimental data.