Jet Characteristics and Optimization of a Cavitation Nozzle for Hydraulic Fracturing Applications

Hydraulic jetting is a form of fracturing that involves using a high-pressure jet of water to create fractures in the reservoir rock with a nozzle serving as the central component of the hydraulic sandblasting perforation tool.In this study,the flow behavior of the nozzle is simulated numerically in the framework of a SST k-ωturbulence model.The results show that the nozzle structure can significantly influence the jet performance and related cavitation effect.Through orthogonal experiments,the nozzle geometric parameters are optimized,and the following configuration is found accordingly:contraction angle 20°,contraction segment length 6 mm,cylindrical segment diameter 6 mm,cylindrical segment length 12 mm,spread segment length 10 mm,and spread angle 55°.

Experimental Investigation on Noise of Cavitation Nozzle and Its Chaotic Behaviour

The researches of cavitation noise mainly focus on the incipiency and developing of cavitation to prevent the cavititation erosion in the hydraulic machinery, while there is few report about the collapse strength of cavitation bubbles produced by water jet through the cavitation nozzle to utilize efficiently the collapse energy of cavitation bubbles. The cavitation noise signals are collected with hydrophones for the cavitation nozzle and general nozzle at the target position and the nozzle exit separately in the conditions of different standoff distance. The features of signal’s frequency spectrum and power spectrum are analyzed for various nozzles by way of classical methods. Meanwhile, based on chaotic theory, phase space reconstruction is processed and the maximum Lyapunov index is calculated separately for each cavitation signal’s time series. The results of chaotic analysis are compared with the one of conventional analysis. The analyzed data show that there are the marked differences at the spectrum between the cavitation nozzle and general nozzle at the target position while the standoff distance is 35 mm, which mainly displays at the high frequency segment (60-120 kHz). The maximum Lyapunov index calculated appear at standoff distance 35 mm, which is an optimum standoff distance for the most bubbles to collapse at the target. At the nozzle exit, the noise signal of cavitation nozzle is different from the general nozzle, which also displays at the high frequency segment. The results demonstrate that the water jet modulated by the cavitation nozzle can produce effectually cavitation, and at the target position the amplitude and energy of noise spectrum in high frequency segment for cavitation nozzle are higher than conventional nozzle and the Lyapunov index of cavitation nozzle is larger than conventional nozzle as the standoff distance is less than 55 mm. The proposed research reveals that the cavitation noise produced by collapse of cavitation bubbles attributes mainly to the high frequency segment of the spectrum, which provides references for the research on cavitation noise.

Effect of Geometrical Parameters on Submerged Cavitation Jet Discharged from Profiled Central-body Nozzle

The flow characteristics of cavitation jets are essential issues among relevant studies. The physical properties of the jet are largely determined by the geometrical parameters of the nozzle. The structure and cavitation jets characteristics of the angular-nozzle and the self-resonating cavitation nozzle have been extensively studied, but little research is conducted in the central-body cavitation nozzle mainly because of its hard processing and the cavitation jet effect not satisfactory. In this paper, a novel central-body nozzle (a non-plunger central-body nozzle with square outlet) is studied to solve above problems. Submerged jets discharged from the novel central-body nozzle are simulated, employing the full cavitation model. The impact of nozzle configuration on jet properties is analyzed. The analysis results indicate that when central-body relative diameter keeps constant, there is an optimal contraction degree of nozzle’s outlet, which can induce intense cavitation in the jet. The central-body relative diameter also affects jet profiles. In the case of large central-body relative diameter, most of the bubbles settle in the jet core. On the contrary, a smaller relative diameter makes bubbles concentrate in the interface between the jet and its surrounding fluid. Moreover, the shorter outlet part allows the cavitation zone further extend in both the axial and racial directions. The research results further consummate the study on the central-body nozzles and the correlation between cavitation jet and the structure, and elementarily reveal the mechanism of cavitation jet produced in a non-plunger novel central-body nozzle and the effect of the structure parameters on the cavitation jet, moreover, provide the theoretical basis for the optimal design of the nozzle.

Influence of Diesel Nozzle Geometry on Cavitation Using Eulerian Multi-Fluid Method

Dependent on automatically generated unstructured grids, a comprehensive computational fluid dynamics(CFD)numerical simulation is performed to analyze the influence of nozzle geometry on the internal flow characteristics of a multi-hole diesel injector with the multi-phase flow model based on Eulerian multi-fluid method.The diesel components in nozzle are considered as two continuous phases, diesel liquid and diesel vapor respectively.Considering that both of them are fully coupled and interpenetrated, sepa...

Investigation of the Flow Pattern inside a Diesel Engine Injection Nozzle to Determine the Relationship between Various Flow Parameters and the Occurrence of Cavitation

In diesel engines the fuel injection system produces the spray, which directly affects the combustion of the fuel, which in turn determines the production of pollutants. In spite of this, the details of this causal relationship remain unclear. There is, however, a lack of quantitative experimental data for determining and visualizing the cavitation inside real size diesel injector nozzle. The present work is devoted to analyze analytically the flow pattern inside the nozzle of a diesel engine working with hydrocarbon fuel (Diesel fuel) and to predict the relationship between the various flow parameters and occurrence of fuel cavitation in such nozzles. Basic physical parameters affecting this phenomenon are identified and quantified while the effect of nozzle geometry, fuel injection pressure, and engine cylinder temperature upon the flow pattern and occurrence of cavitation in such nozzles are assessed. In this study, a commercial computational fluid dynamics (CFD) package (FLUENT-T grid) is used while a computational grid is generated for the real geometry of diesel injector nozzle using (ANSYS). The suitability of the generated computational grid to give reliable results is examined using the suitable procedures and techniques. The results indicated that, cavitation modeling has reached a stage of maturity and it can usefully identify many of the cavitation structures present in internal nozzle flows and their dependence on nozzle design and flow conditions. The qualitative distributions and comparison of cavitation inception and distribution as well as flow parameters at the nozzle exit are also studied.

Flow-visualization and numerical investigation on the optimum design of cavitating jet nozzle

Cavitating jet is widely used in drilling,rock cutting and ocean re source exploitation because of its stro ng erosion ability.The analysis of the relationship between the flow characteristics and the structure of cavitating jet nozzle is critical.Here,we utilized 3 D printed technology and high-speed photography to design visualization experime nts to analyse the impact of the variation of resonator and throat size of the organ-pipe self-resonating cavitating nozzles on the cavitation characteristics through image processing.The velocity field,pressure field and vapor volume fraction injected by the nozzle were taken as the objective functions to study the influence of different structural parameters on the cavitation effect based on FLUENT 19.0 software,and the results were compared with the experimental results.The results show that increasing the length and diameter of the resonator contributes to the occurrence of cavitation and the structure stability of the flow field.However,excessive size affects self-resonant of the nozzle and makes it difficult to form resonance effect.In this study,the optimal values of nozzle throat length and divergent angle are twice the throat diameter and 40°,respectively.This research provides an integrated research method to study the optimization of self-resonating nozzle and cavitating jet characteristics.

Experimental and Numerical Evaluation of the Cavitation Performances of Self-Excited Oscillating Jets

Self-excited oscillating jets(SOJ)are used in several practical applications.Their performances are significantly affected by structural parameters and the target distance.In this study,a geometric model of the SOJ nozzle accounting for multiple structural parameters is introduced,then the related cavitation performances and the optimal target distance are investigated using a Large-Eddy Simulation(LES)approach.Results are also provided about an experiment,which was conducted to validate the simulation results.By analyzing the evolution of the vapor volume fraction at the nozzle outlet,a discussion is presented about the effect of the aforementioned structural parameters on the cavitation performances and the target distance.It is shown that the distribution of cavitation clouds at the outlet of the SOJ nozzle displays a non-monotonic trend(first increasing,then decreasing).Under working conditions with an inlet pressure of 4 MPa,a SOJ nozzle outlet/inlet diameter ratio(D_(1)/D_(2))of 1.2,and a chamber diameter ratio(D/L)close to 1.8,the nozzle outlet cavitation performance attains a maximum.The optimal structural parameters correspond to the optimal target distance,which is near 50 mm.The experiments have revealed that the SOJ nozzle with the above parameters displays a good cavitation erosion effect at the target distance of 50 mm,in satisfactory agreement with the numerical simulation results.

Effects of Area Discontinuity at Nozzle Inlet on the Characteristics of Self-resonating Cavitating Waterjet

The current research on self-resonating cavitating waterjet（SRCW） mainly focuses on the generation mechanism and structure optimization.Researches relating to the influences of disturbances at nozzle inlet on the characteristics of the jet are rarely available.In order to further improve the performance of SRCW,effects of area discontinuity（enlargement and contraction） are experimentally investigated using three organ-pipe nozzles.Axial pressure oscillation peak and amplitude as well as aggressive erosion intensity of the jet are used to evaluate the effects.The results reveal that area enlargement and contraction affect the peak differently,depending on the inlet pressure,nozzle geometry,and standoff distance;while area contraction always improves the amplitude regardless of these factors.At inlet pressures of 10 MPa and 20 MPa,area discontinuity improves the peak at almost all the testing standoff distances,while this only happens at smaller standoff distances with the inlet pressure increased to 30 MPa.The capability of area discontinuity for improving the amplitude is enhancing with increasing inlet pressure.Moreover,the cavitation erosion ability of the jet can be largely enhanced around the optimum standoff distance,depending on the type of area discontinuity and nozzle geometry.A preliminary analysis of the influence of area discontinuity on the disturbance waves in the flow is also performed.The proposed research provides a new method for effectively enhancing the performance of SRCW.

Sensitivity Analysis of Injection Characteristic to Structural Parameters of GDI Injector Nozzle Hole

The nozzle inner-flow characteristic of the“spray G”injector was studied by the computational fluid dynamics(CFD)simulation,and the sensitivity of cycle fuel mass to the conicity and entrance radius of the nozzle hole were analyzed.Results show that the inner conicity of nozzle hole inhibits the development of cavitation phenomena,and increases the injection rate.While the outer conicity of nozzle hole promotes the diffusion of cavita-tion,leading to reductions of the liquid volume fraction of the nozzle outlet and the local flow resistance of the nozzle hole.The sensitivity of cycle fuel mass to inner-cone nozzle hole is stronger than that of the outer-cone noz-zle,especially at the smaller hole conicity.The increase of injection pressure enhances the sensitivity of the injection characteristics to the nozzle hole structure,in which inner-cone nozzle has higher sensitivity coefficient than the outer-cone nozzle hole.However,the increase of injection pressure aggravates the offset of liquid jet to the nozzle axis of the outer-cone nozzle hole.With the increase of the inner conicity of nozzle,the sensitivity of the injection characteristics to the entrance radius of the hole decreases.With the increase of the outer conicity of nozzle hole,the sensitivity of the injection characteristics to the entrance radius of the hole increases.

Unsteady Behavior of Cavitating Waterjet in an Axisymmetric Convergent-Divergent Nozzle: High Speed Observation and Image Analysis Based on Frame Difference Method

Although it is well known that cloud cavitation shows unsteady behavior with the growing motion of an attached cavity, the shedding motion of a cloud, the collapsing motion of the cloud shed downstream and a reentrant motion in flow fields such as on a 2-D hydrofoil and in a convergent- divergent channel with a rectangular cross-section, observations for the periodic behavior of cloud cavitation in a cylindrical nozzle with a convergent-divergent part, which is mainly used in an industrial field, have hardly been conducted. From engineering viewpoints, it is important to elucidate the mechanism of periodic cavitation behavior in a cylindrical nozzle. In this study, a high-speed observation technique with an image analysis technique was applied to the cloud cavitation behavior in the nozzle to make clear the mechanism of unsteady behavior. As a result, it was observed in the nozzle that the periodic behavior occurs in the cloud cavitation and pressure waves form at the collapse of clouds shed downstream. Also, it was found through the image analysis based on the present technique that the pressure wave plays a role as a trigger mechanism to cause a reentrant motion at the downstream end of an attached cavity.

Numerical simulation on turbulent flow field in convergentdiveroent nozzle

Because of the complication of turbulence＇s mechanism and law as well as the jet pressure in nozzle is difficult to test by experiment, five turbulent models were applied to numerically simulate the turbulent flow field in convergent-divergent nozzle. Theory analysis and experiment results of mass flow rates conclude that the RNG k-ε model is the most suitable model. The pressure distribution in the convergent-divergent nozzle was revealed by computational fluid dynamic （CFD） simulating on the turbulent flow field under different pressure conditions. The growing conditions of cavitation bubbles were shown; meanwhile, the phenomena in the experiment could be explained. The differential pres- sure between the upstream and downstream in nozzle throat section can improve the cavitating effect of cavitation water jet.

Injector Nozzle Flow Model and Its Effects on the Calculations of High Pressure Sprays

This paper discusses the flowing process inside a nozzle, especially the formation mechanism of cavitations within the nozzle and puts forward a nozzle flow model, which takes account of the injection conditions and nozzle geometry. By the model being implemented to the KIVA codes, the spray characteristics (e. g., spray penetration and cone angle) of diesel and dimethyl ether (DME) are simulated. The comparisons between the computational and experimental results are performed, which show that the liquid spray characteristics could be more truly demonstrated by considering the existence of the cavitations. Key words nozzle model - spray characteristics - cavitation - atomization CLC number O 35 - TK 402 Foundation item: Supported by the National Natural Science Foundation of China (50376018) and the National 973 Basic Research Program of China (2001CB209207)Biography: WEI Ming-rui (1967-), male, Associate professor, Ph. D, research direction: computational combustion, computational fluid dynamics.

Effect of the structure of backward orifices on thejet performance of self-propelled nozzles

Self-propelled nozzle is a critical component of the radial jet drilling technology.Its backward orifice structure has a crucial influence on the propulsive force and the drilling performance.To improve the working performance of the nozzle,the numerical simulation model is built and verified by the experimental results of propulsive force.Then the theoretical model of the energy efficiency and energy coefficient of the nozzle is built to reveal the influence of the structural parameters on the jet performance of the nozzle.The results show that the energy efficiency and energy coefficient of the backward orifice increase first and then decrease with the angle increases.The energy coefficient of forward orifice is almost constant with the angle increases.With the increase in the number and diameter,energy efficiency and energy coefficient of the forward orifice gradually decrease,but the backward orifice energy coefficient first increases and then decreases.Finally,it is obtained that the nozzle has better jet performance when the angle of backward orifice is 30°,the number of backward orifice is 6,and the value range of diameter is 2-2.2 mm.This study provides a reference for the design of efficiently self-propelled nozzle for radial jet drilling technology.

Optimization of a Diesel Injector Nozzle

Multiphase simulations based on the VOF(Volume of Fluid)approach,used in synergy with the cavitation Schnerr-Sauer method and the K-Epsilon turbulence model,have been conducted to study the behavior of an injector nozzle as a function of relevant structural parameters(such as the spray hole diameter and length).The related performances have been optimized in the framework of orthogonal experimental design and range analysis methods.As made evident by the results,as the spray hole diameter increases from 0.10 to 0.20 mm,the outlet massflow rate grows by 243.23%.A small diameter of the spray hole,however,has a beneficial effect in terms of cavitation suppression.Moreover,rounding the spray hole can effectively increase the outlet massflow rate and improve theflow characteristics while mitigating the cavitation phenomenon inside the spray hole.In particular,with the optimized nozzle design,the outlet massflow rate can be increased by 13.33%,while the fuel vapor volume is reduced by 33.53%,thereby,leading to significant improvements in terms offlow characteristics and cavitation control.

Relationships and Mechanisms of Sand Grain Promotion on Nozzle Cavitation Flow Evolution: A Numerical Simulation Investigation

The objective of this study was to primarily investigate the effects of sand grains with different mean diameters and concentrations on cavitation flow development in a nozzle. One new solid-liquid-vapor three-phase coupling numerical method was presented and a cavitation model was changed to perform numerical simulations. Results indicated that sand grain-pure water-cavitation flow(SG-PW-CF) vapor contents were greater than in pure water-cavitation flow(PW-CF). Sand grains were found to promote cavitation flow development, with the concentration promotion range becoming smaller with increased mean diameter. The mechanisms for these effects were explored and revealed as well. In SG-PW-CF, cavitation nuclei number was greater and tensile stress was also greater than in PW-CF. The maximum and absolute minimum slip velocities and maximum and minimum turbulent kinetic energies of SG-PW-CF were greater than in PW-CF. These effects on SG-PW-CF evolution were large, involving primary factors. The calculated magnitude of the Saffman lift force in SG-PW-CF was small(10^(-2)), with its effects relatively weak and it was thus a secondary factor. Effects of variations of flow fields were more significant than force changes. In SG-PW-CF, variations of a single parameter with the concentration could not reflect the alternating relationships of vapor content with the concentration. Indeed, it was a combination of variations of all parameters.

Helmholtz型空化射流喷嘴结构优化数值模拟研究

目前Helmholtz型空化射流喷嘴结构尺寸偏大,不适用于空化射流洗井解堵作业,且与其相关研究缺乏对射流脉冲特性的评价。为此,利用CFD数值模拟方法探讨了结构参数对Helmholtz型空化射流喷嘴脉冲性能的影响规律,对该类型喷嘴的结构进行了优化。研究结果表明:在入口长度为5~15 mm时,空化射流脉冲特性和入口长度呈反比关系;在出口长度为5~10 mm时,空化射流的脉冲峰值和脉冲幅度与出口长度呈正比关系,脉冲频率基本不受影响;所得喷嘴最优结构尺寸为喷嘴入口直径2.5 mm,入口长度5.0 mm,谐振腔入口圆角1.0 mm,谐振腔直径10.0 mm,谐振腔长度2.0 mm,碰撞壁夹角60°,出口长度10.0 mm,出口直径3.0 mm。研究结果可为空化射流解堵技术中空化射流喷嘴结构优化设计提供理论参考。

燃油喷嘴雾化空化特性数值模拟分析

燃油喷嘴雾化质量对保障车辆尾气排放质量具有重要意义。利用气液多相流模型,研究燃油喷嘴雾化空化特性。通过数值模拟分析燃油喷嘴入口压力对气相体积分数、燃油流动速度、空化因数的影响。在相同燃油喷嘴入口压力下,随着入孔角因数的增大,燃油空化现象明显减弱。空化因数随燃油喷嘴入口压力的增大而增大,并且增大速率较快。增大燃油喷嘴入口压力能够起到较好的雾化效果,但是会带来空化因数的增大。选取合理的燃油喷嘴入口压力,是保证雾化质量的关键。

喷嘴结构内流场数值模拟研究

提升雾化喷嘴出口流量可以提高液体出口速度,从而获得更细小的雾滴,增强雾化效果.为了抑制空化效应,获得更大的出口流量,本文通过建立喷嘴内流场的数值模型,对内流场速度、液相体积分数以及湍动能分布等流场信息进行分析.针对空化的产生机理,提出多种改进喷嘴结构的方案:减小喷嘴长度、增加喷嘴倒角和降低壁面粗糙度,有效降低了空化效应,显著增大了喷嘴的出口流量,改善了雾化效果,为喷嘴结构的优化提供了参考.

船体清洗空化喷嘴设计与仿真

为提高空化射流技术在船舶清洗领域的应用范围,设计了一种适用于船体底部海洋附着物清洗的异形中心体空化喷嘴。通过FLUENT流场数值模拟方法,研究了中心体末端形状、中心体末端延伸长度、中心体末端直径、扩散段角度和扩散段长度等参数对空化效果的影响,得到相应参数下喷嘴流场的气相分布云图、中心轴线上的速度和压力分布曲线以及靶面压力曲线等结果。研究表明:空化现象主要产生于中心体末端和扩散段壁面;中心体直柱形末端相较于锥形末端有更好的空化效果;合适的直柱形中心体末端延伸距离会使气相分布范围更广;扩散段角度在60°~70°时空化效果较好,适当增加扩散段长度有利于扩大气相分布范围。

风琴管喷嘴空化水射流流场的大涡模拟

针对空化水射流流场空化云演化采用RANS方法模拟不准确的问题,采用大涡模拟(Large-eddy simulation,LES)对风琴管空化喷嘴流场进行数值模拟。基于Mixture多相流模型和Zwart-Gerber-Belamri(ZGB)空化模型,分别采用SM模型(Smagorinsky-Lilly model,SM)、壁面适应的局部涡黏模型(Wall-adapted local eddy-viscous,WALE)和代数壁面模型(Wall-modeled large eddy simulation,WMLES)3种不同的亚格子模型,对风琴管喷嘴空化水射流流场进行数值模拟,分析空化水射流特性、空化云演化规律及脱落频率。结果表明:WALE模型可以较为准确模拟空化云演化周期,与高速摄像拍摄结果吻合较好;在喷嘴内圆柱段以及扩散段壁面附近产生涡环,加快了空化泡析出,WALE模型较好的模拟了涡环结构;涡量分析表明涡流在喷嘴出口附近出现,射流的末端空化泡破碎产生扰动,大尺度涡演化为小尺度涡,WALE模型模拟出涡的破碎范围较SM模型更大,WMLES模型未捕捉到小尺度涡。