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.     

EFFECT OF ENLARGED FREE JET ON ENERGY CONVERSION IN PELTON TURBINE

NOMENCLATURE Q —flow rate H— head Dref —diameter of pitch circle B —inner width of bucket ω —angular speed of runner QDH —unit discharge Sn —needle strokesn—relative needle stroke Dinj —diameter of injector inlet Dt —diameter of nozzle throat D     

岸边并联泄洪洞下游河道冲坑预测

挑流水舌对下游河道的冲刷关系到工程安全。根据动量方程推导了射流在下游水垫中的扩散规律,分析了下游水垫流速对射流扩散的影响,提出了动水垫下射流的临底流速计算方法。研究结果表明:动水流速增加了射流在水中的扩散距离,促进了射流扩散及射流流速衰减,降低了射流临底流速。将研究结果应用于白鹤滩岸边泄洪洞下游河道的冲坑深度预测。模型试验结果表明:在鼻坎水流参数相同的情况下,河道中水流为动水时的冲坑深度较静水时冲坑深度减小约10%,且位于河道下游侧的挑流水舌形成的冲坑深度小于上游侧挑流水舌形成的冲坑深度。与常规预测公式相比,该方法能准确预测不同位置挑流水舌的冲坑深度,研究结果可为泄洪设施下游河道消能防冲设计提供依据。     

Numerical analysis of cavitation cloud shedding in a submerged water jet

Focused on the unsteady behavior of high-speed water jets with intensive cavitation a numerical analysis is performed by applying a practical compressible mixture flow bubble cavitation model with a simplified estimation of bubble radius. The mean flow of two-phase mixture is calculated by unsteady Reynolds averaged Navier-Stokes(URANS) for compressible flow and the intensity of cavitation in a local field is evaluated by the volume fraction of gas bubbles whose radius is estimated with a simplified RayleighPlesset equation according to pressure variation of the mean flow field. High-speed submerged water jet issuing from a sheathed sharp-edge orifice nozzle is treated. The periodically shedding of cavitation clouds is captured in a certain reliability compared to experiment data of visualization observation and the capability to capture the unsteadily shedding of cavitation clouds is demonstrated. The results demonstrate that cavitation takes place near the entrance of nozzle throat and cavitation cloud expands consequentially while flowing downstream. Developed bubble clouds break up near the nozzle exit and shed downstream periodically along the shear layer. Under the effect of cavitation bubbles the decay of core velocity is delayed compared to the case of no-cavitation jet.     

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。     

NUMERICAL SIMULATION OF LAMINAR SQUARE IMPINGING JET FLOWS

A theoretical study has been undertaken to determine the flow characteristics associated with a three-dimensional laminar impinging jet issuing from a square pipe nozzle. Interesting flow structures around the jet are detected. The numerical result reveals the existence of four streamwise velocity off-center peaks near the impingement plate, which is different from the rectangular jet impingement. The mechanism of the formation of the off-center velocity peaks and the parameters affecting the flow-field characteristics are discussed by comparison of the computed results with different nozzle-to-plate spacings and Reynolds numbers.     

LARGE-EDDY SIMULATION OF THREE-DIMENSIONAL VORTICAL STRUCTURES FOR AN IMPINGING TRANSVERSE JET IN THE NEAR REGION

The three-dimensional vortical structures for an impinging transverse jet in the near region were numerically investigated by means of Large-Eddy Simulation (LES). The LES results reproduced the skewed jet shear layer vortices close to the jet nozzle and the scarf vortex in the near-wall zone, in good agreement with the experimental observations. Different vortical modes in the skewed jet shear layer close to the jet nozzle were identified depending upon the velocity ratio between jet and crossflow, namely changing from an approximately axisymmetric mode to a helical one with the velocity ratios varying from 20 to 8. Moreover, the scarf vortex wrapped around the impinging jet in the near-wall zone showed distinct asymmetry with regard to its bilateral spiral legs within the near region. And the entrainment of the ambient crossflow fluids by the scarf vortex in the near-wall zone was appreciably influenced by its asymmetry and in a large part occurred on the surface of the spiral roller structures in the course of spreading downstream.     

Flow field simulation of supercritical carbon dioxide jet: Comparison and sensitivity analysis

As a new jet technology developed in recent years, the supercritical carbon dioxide(SC-CO2) jet technology enjoys many advantages when applied in oil and gas explorations. In order to study the properties and parametric influences of the SC-CO2 jet, the flow fields of the SC-CO2 jet are simulated using the computational fluid dynamics method. The flow field of the SC-CO2 is compared with that of the water jet. The influences of several parameters on the flow field of the SC-CO2 jet are studied. It is indicated that like the water jet, the velocity and the pressure of the SC-CO2 jet could be converted to each other, and the SC-CO2 jet can generate a significant impact pressure on the wall, the SC-CO2 jet has a stronger impact pressure and a higher velocity than those of the water jet under the same conditions, the maximum velocity and the impact pressure of the SC-CO2 jet increase with the increase of the nozzle pressure drop, under the stimulation condition of this study, the influence of the SC-CO2 temperature on the impact pressure can be neglected in engineering applications, while the maximum velocity of the SC-CO2 jet increases with the increase of the fluid temperature. This paper theoretically explores the properties of the SC-CO2 jet flow field, and the results might provide a theoretical basis for the application of the SC-CO2 jet in oil and gas well drillings and fracturing stimulations.     

NUMERICAL INVESTIGATION OF FLOW OVER A WEIR

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THEORETICAL AND EXPERIMENTAL STUDY ON THE CONICAL SWIRLING WATER JET FLOW

This paper is concerned with theoretical and experimental study on theconical swirling water jet flow.Based upon the theoretical analysis,the experiment on thestructural characteristics of swirling water jet flow including the velocity and pressure dis-tribution laws,on which the parameters of the jet,nozzle and directional blades havemore or less influence,was carried out in CSSRC by using a 3-D LDV in order to optimizea new high-efficiency jet instead of swirling drilling bit for rock-breaking and continuouslydrilling,and to meet the demand of radial horizontal drilling technology.Meanwhile basedon the experimental results,the numerical simulation was conducted for the conicalswirling water jet in the immersed well-bottom flow by solving the RANS equations in the3-D body-fitted coordinate system with the k-ε turbulence model.The numerical resultsare consistent with the experimental data,and lead to some conclusions which are impor-tant for applying the conical swirling water jet to the petroleum drill     

溢洪道挑流鼻坎水气二相流数值模拟研究

针对某溢洪道挑流消能存在的问题,采用VOF方法、立方体网格和k-ε紊流模型对溢洪道整体水力特性进行了三维数值模拟,对挑射水流流态、水舌掺气、水垫塘底板压强、下游河道流速等方面进行了分析。将某溢洪道由原高低式挑流鼻坎修改为差动式后,增大了下泄水流入水范围,提高了挑流消能的消能效率,减小了水垫塘底板压强,降低了下游河道水流流速。优化方案数值模拟结果得到了模型试验结果的验证。     

水下高速喷气气水流场研究

水下喷气是一个复杂的过程，本文在一定假设的基础上，将复杂的流场分为三部分：喷管内流场、气泡流场及流体水流场。喷管内流场采用准一维模型，用差分格式求解，气泡模型采用滞止等压泡模型；液体流场采用MAC方法，通过步进法实现三个流场的耦合求解。给出了几种环境压力及速度下的数值计算结果，初步掌握了水下喷气的特征。     

EXPERIMENTAL STUDY ON VELOCITY PROFILE OF SUBMERGED ABRASIVE SUSPENSION JET FLOW

1. INTRODUCTIONAbrasive Water Jet (AWJ), has been developed the into a remarkable and extensively used cutting technology in last two decades. In recent years, the polymer PAM has generally been applied to jetting fluid to further increase the abrasive ve…     

Numerical simulation of the abrasive supercritical carbon dioxide jet: The flow field and the influencing factors

The supercritical carbon dioxide(SC-CO_2) jet can break rocks at higher penetration rates and lower threshold pressures than the water jet. The abrasive SC-CO_2 jet, formed by adding solid particles into the SC-CO_2 jet, is expected to achieve higher operation efficiency in eroding hard rocks and cutting metals. With the computational fluid dynamics numerical simulation method, the characteristics of the flow field of the abrasive SC-CO_2 jet are analyzed, as well as the main influencing factors. Results show that the two-phase axial velocities of the abrasive SC-CO_2 jet is much higher than those of the abrasive water jet, when the pressure difference across the jet nozzle is held constant at 20 MPa, the optimal standoff distance for the largest particle impact velocity is approximately 5 times of the jet nozzle diameter; the fluid temperature and the volume concentration of the abrasive particles have modest influences on the two-phase velocities, the ambient pressure has a negligible influence when the pressure difference is held constant. Therefore the abrasive SC-CO_2 jet is expected to assure more effective erosion and cutting performance. This work can provide guidance for subsequent lab experiments and promote practical applications.     

RESEARCH ON MOTION CHARACTERISTICS OF GAS-SOLID JET FLOW

l.INThoDUCT1ONTheresearchontwo-phasejetflowisbecomingahotspotofjetflowresearchinrecentyears.Therapiddevelopmentofcomputertechnologyhasmadeitpossibletosimulatetwo-phasejetflow,whichisofessentialimPortanceinvariousengineeringapplications.Forin-stanceitisausualproceduretospoutparticlesintoreactororcombustorinengineering.Theeffectofflowonparticlesdeterminestheparticledistributionandthepresenceofparticleshaveeffectonjetflowinturn.Therefore,theinvestigationontheparticledistributionandtheflowchar…     

垂直射流冲刷砂床的喷嘴间距试验研究

疏浚工程中常利用射流进行河道清淤和冲砂施工。为探究喷嘴间距对射流冲刷的影响,开展了一系列不同靶距、速度和间距的双喷嘴冲刷粗砂、中砂砂床试验,分析了冲刷坑形、冲坑深度和冲坑截面积的变化特性,得到了各工况下的最优喷嘴间距L_B和不利喷嘴间距L_N。结果表明,对于同一粒径砂床,改变靶距和速度冲刷时的L_B和L_N值变化较小,而与粗砂砂床相比,冲刷中砂砂床时的L_B和L_N值均有所增加。研究成果可供疏浚工程中射流系统设计作为参考。     

DETERMINATION OF ROCK-BREAKING PERFORMANCE OF HIGH-PRESSURE SUPERCRITICAL CARBON DIOXIDE JET

In this study, a well-designed experimental setup is used to determine the rock-breaking performance of a high-pressuresupercritical carbon dioxide (SC-CO2) jet. Its rock-breaking performance is first compared with that of a high-pressure water jetunder the same operation conditions. The effects of five major factors that affect the rock-breaking performance of the high-pressureSC-CO2jet, i.e., the nozzle diameter, the standoff distance, the jet pressure, the rock compressive strength and the jet temperature areexperimentally determined. The experimental results indicate that the rock-breaking performance of the SC-CO2jet is significantlyimproved over the high-pressure water jet. It is also found that the rock-breaking performance of the SC-CO2jet is improved with theincrease of the nozzle diameter or the standoff distance, until the nozzle diameter or the standoff distance reaches a certain criticalvalue and after that it begins to deteriorate. The rock-breaking performance of the SC-CO2jet improves monotonically with theincrease of the jet pressure, while it shows a monotonic deterioration with the increase of the rock compressive strength. In addition,it is found that, under the same working conditions, the SC-CO2jet can always provide a better rock-breaking performance than thesubcritical liquid CO2jet.     

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 …     

浅尾水深水平底板上表面射流水力特性的数值模拟研究

采用VOF(volume of fluid)方法追踪自由液面,辅以Realizable(可实现化)湍流模型封闭两相流时均方程,对浅尾水深水平底板上的表面射流水力特性进行了数值模拟。微分方程的离散采用有限体积法,速度与压力耦合求解使用了压力隐式算子分裂PISO(Pressure-Implicit with Splitting of Operators)算法。研究并分析了入射速度、尾水深和进口宽度等对流场流线分布、速度场及横断面最大流速沿程衰减规律等水力特性的影响。研究发现:流场内存在一个大的漩涡,入射流速越大,漩涡长度越长;横断面上水平流速和纵向流速在漩涡区和明渠流区分布规律不同;横断面最大流速沿程衰减主要受进口流速大小的影响。