Simulation investigation on fluid characteristics of jet pipe water hydraulic servo valve based on CFD

Simulation investigation on fluid characteristics of the water hydraulic jet pipe servo valve （WHJPSV） is conducted through a commercial computational fluid dynamics （CFD） software package FLUENT. In particular, the factors to fluid characteristics of WHJPSV are addressed, which include diameter combination of jet pipe and receiver pipe, jet pipe nozzle clearance, angle between two jet receiver pipes and deflection angle of the jet pipe. It is concluded from the results that： （i） Structural parameters have great influences on fluid characteristics of WHJPSV, when d1 = d2 = 0.3 mm, α= 45 , b = 0.5 mm, and the simulation exhibits better fluid characteristics; （ii） The magnitude of the recovery pressure and flow velocity increase almost linearly with the deflection angle of jet pipe. The research work in this paper is important for determining and optimizing the structural parameters of the jet pipe and jet receiver. The relevant conclusions could be extended to the study of other water hydraulic servo control components.

Numerical Simulation of Jet Issuing Diagonally Upward into Density-Stratified Fluid in Cylindrical Tank

This study simulates the behavior of a jet issuing into a two-layer density-stratified fluid in a cylindrical tank and the resulting mixing phenomena. The upper and lower fluids are water and an aqueous solution of sodium chloride (NaCl), respectively, with the lower fluid issuing diagonally upward from a nozzle on the bottom of the tank. The angle between the centerline of the jet and the tank bottom is 60°. The phenomena when the Reynolds number Re of the jet is 475, 1426, and 2614 are simulated. The mass concentration of the aqueous solution of NaCl is 0.02. The simulation successfully grasps the jet behavior and the resulting mixing, which agree with the authors’ experimental results at the corresponding Re value. The secondary flows that appear in the horizontal cross-sections consist of a pair of vortices and flows along the tank wall. The secondary flow at the density interface represents the intrusion of an internal density current, which gives rise to mixing along the interface.

Investigation of the Behavior of a Jet Issued into Two-Layer Density-Stratified Fluid

This study experimentally investigates a jet flow issued into a two-layer density-stratified fluid in a tank and the resultant mixing phenomena. The upper and lower fluids are water and a NaCl- water solution, respectively, with the lower fluid issued vertically upward from a circular nozzle mounted on the tank bottom. Experimental highlights of the jet behavior and mixing phenomena are classified into three patterns according to the jet Reynolds number and mass concentration of the NaCl-water solution. The internal density current clearly occurs along the density interface, and the maximum jet height is predicted by the Froude number defined by the density difference between the upper and lower fluids. The effect of fluid thickness on the maximum jet height is also clarified.

Behavior of a Jet Issuing Diagonally Upward into Two-Layer Density-Stratified Fluid in a Cylindrical Tank

This study is concerned with the experimental investigation of a jet issuing diagonally upward into a two-layer density-stratified fluid in a cylindrical tank and the resulting mixing phenomena. The upper and lower fluids are water and an aqueous solution of sodium chloride (NaCl), respectively, and the lower fluid issues from a nozzle on the bottom of the tank. The angle between the centerline of the jet and the bottom of the tank is 60o, and the mass concentration of the NaCl solution is 0.02. The investigation reveals that secondary flow is caused by the jet in the horizontal cross-sections of the tank and that it is composed of a pair of vortices. It confirms that the secondary flow at the density interface corresponds to an internal density current. The investigation also clarifies the effect of the Reynolds number of the jet on mixing between the lower and upper fluids.

Spray Atomization and Structure of Supersonic Liquid Jet with Various Viscosities of Non-Newtonian Fluids

These experimental investigations are designed to study shock wave characteristics and spray structure. Supersonic liq- uid jets injected into ambient fields are empirically studied using projectile impacts in a two-stage light gas gun. This study looks primarily at the design of the nozzle assembly, the tip velocity of the high speed jet, the structure of the spray jet and the shock wave generation process. The supersonic liquid jets were visualized using an ultra high-speed camera and the schlieren system for visualization to quantitatively analyze the shock wave angle. The experimental re- sults with straight cone nozzle types and various non-Newtonian fluid viscosities are presented in this paper. The effects of nozzle geometry on the jet behavior are described. The characteristics of the shock wave generation and spray jet structure were found to be significantly related to the nozzle geometry. The expansion gases accelerated the projectile, which had a mass of 6 grams, from 250 m/s. As a result, it was found that the maximum jet velocity appeared in the liquid jet with high viscosity properties. Supersonic liquid jets, which occurred at the leading edge the shock waves and the compression waves in front of the jets, were observed. Also, the shock waves significantly affected the atomization process for each spray droplet.

Optimization of Surface Milling of Hardened AISI4340 Steel with Minimal Fluid Application Using a High Velocity Narrow Pulsing Jet of Cutting Fluid

Surface milling of hardened steel is carried out with copious supply of cutting fluid and is obviously associated with problems related to procurement and storage of cutting fluid. The disposal of cutting fluid has to comply with environmental legislation such as OSHA regulations. The present investigation proposes an environment friendly minimal pulsed jet cutting fluid application scheme for surface milling of AISI4340 steel with a hardness of 45 HRC using commercially available carbide tools. This scheme can be implemented as such on the shop floor with out the need for any major alternations on the existing facilities and it was observed that the new scheme is not only environment friendly but also provided better cutting performance when compared to conventional wet milling which requires copious supply of cutting fluid.

Observations on sand jets in viscoplastic fluids

Sand jet in non-Newtonian viscoplastic fluid is associated with a number of industrial and engineering applications, including sand capping for the reclamation of oilsands railings ponds and sediment deposition into soft mud. In this study, several experiments were carried out by depositing circular sand jets vertically into viscoplastic fluids, known as Laponite gel. The deformation regimes of sand jets in the gel were investigated. The yield-gravity parameter of the deformed sand drop in the gel was computed.

深海多金属结核集矿装置水力输送流场分析与试验

对深海多金属结核集矿装置水力输送流场进行了理论计算,得到了多金属结核粒径与输送通道最小输送速度的关系;仿真分析了喷嘴射流速度分别为15、20、25 m/s时输送通道内水流流态分布,给出了流道下表面30 mm处的流速。在实验室进行了输送喷嘴不同射流速度的采集试验,实验结果与理论计算及仿真分析结果相符。

Study on Collision Process of Opposing Unsteady Supersonic Jets and Shock Waves

Double pulsed-laser-ablation is a promising method to prepare nanoparticle composites. The backward movement of the plume after the collision with counter-propagating shock wave has been observed in experiments. In the present study, collision dynamics of the oppositely injected Si and Ge jets into a He background gas was numerically calculated as a simulation for double pulsed-laser-ablation. The experimentally observed backward movement was reproduced. The effect of distance between two jet exits on the distance of backward movement of the jet, BL, after the collision with the counter-propagating shock front was calculated to discuss the collision dynamics and to optimize the target distance for the experiment. We found that BL does not decrease monotonically with increasing distance between two jet exits, but has a maximum value at a certain distance. This behavior is discussed by calculating the expansion dynamics of an individual jet. Shock wave grows with time at the initial stage of the jet expansion and then attenuates;the density just behind the shock front for individual jet has a maximum value at a certain time and position. BL has a maximum value when the densities just behind the shock fronts for the individual jets have maximum values. This result is important for designing the appropriate distance between the two jet exits, i.e., the distance between the targets of double pulsed-laser-ablation.

喷水式超声检测的声−流耦合模型

为研究超声波在射流水柱中的传播特性,提出了喷水式超声检测的声−流耦合建模方法。使用计算流体动力学方法得到喷水探头内部流场的湍动能、速度和压力,并通过弱形式偏微分方程将其映射到声学网格作为声场分析的边界条件,用线性纳维−斯托克斯方程求解湍动能、流速等引起的声学变化,建立了喷水式超声检测的声−流耦合模型。仿真计算了不同流速时工件内部的声压分布,进水口流速的变化不会改变工件中声压的分布规律,但空间声压幅值随着流速的增大而减小。仿真计算了不同流速时的平底孔回波,回波幅值随着流速的增大而减小,通过与实验结果对比,验证了本文方法的准确性。

结构参数对气液下喷式喷射器性能的影响研究

喷射环流反应器是一种新型的气液或气液固接触反应装置,其中的喷射器结构会对反应器性能产生重要影响。文章采用计算流体力学方法,建立了文丘里型喷射器的数学模型,分析了吸气室、喉部和扩散段等结构对喷射器吸气量的影响规律。模拟结果表明:吸气室直径和气相入口方式对吸气量影响不大;喷嘴与喉部之间距离越小,喉部长度越短,吸气量越高;扩散段扩散角度在2~4°之间时吸气量存在最大值。

喷水推进器进水流道格栅流固耦合特性研究

为了研究格栅部件对喷水推进船舶效率的影响,本文拟采用流固耦合的数值计算方法系统地对格栅表面受力及其强度特性进行计算,结合有限元方法和流固耦合理论,以STARCCM+和ABAQUS软件为工具,根据目前已知的格栅剖面设计方法,对目前格栅的剖面形式进行改进,形成新型对称剖面形式的格栅。基于上述计算流体力学与流固耦合计算方法对其进行周围流场、结构静力强度、结构动力强度进行计算与分析。结果表明:对称形式的格栅剖面对于降低格栅的变形与应力水平有一定的帮助,采用新型对称形式的剖面结构使格栅总体变形模式发生了变化,但是最大变形位置与最大应力出现在格栅的位置未发生明显变化,新型对称剖面形式格栅具有比较好的静强度与动强度特性,各栅条均匀承受流体载荷。

带同轴引气激光制孔中的气动特性分析

针对锥形激光加工器在航空发动机热部件冷却孔加工过程中的吹渣效果,研究了射流冲击孔板附近的流场特性及其影响因素。针对同轴高压气体撞击带盲孔平板的射流结构,采用数值模拟方法,分析了不同进气压力p_(int)(0.2~1.5 MPa)、射流间距H/De(3.6,5.6,7.6)和冲击角度α(30°,45°,60°,90°)对盲孔附近气体动力学性能的综合影响。研究结果表明,当H/De为3.6时,随进气压力的增大,盲孔附近的气体动力学性能呈现先逐步提高后剧烈下降的趋势,较好工作压力为1 MPa;当射流间距H/De达到5.6及以上时,适当地增大喷嘴压力可以提高盲孔附近气流的气动水平,但提升有限。随着冲击角度α减小,盲孔内流出质量流量逐渐增大,α为30°时较垂直射流提升约11倍,但在冲击表面上气体的剪切流动随冲击角度减小逐渐变弱。

A Theoretical Study of Rock Drilling with a High Pressure Water Jet

Based on analyses of experimental results of water jet drilling, the fluid motion law in rock pores and the tendency of energy distribution, the rock-breaking process under high pressure water jet drilling has been studied systematically. The research indicates that the main interaction between the rock and water jet is interface coupling, that the impacting load and the static pressure of the water jet act together to make the rock break, and that the stress wave is the main factor. Water jet drilling can be divided into two stages: At the initial stage, the stress wave plays the main role and most of the rock breaking takes place; at the later stage, the existing rock defects, for instance, micro-holes and micro-cracks, are propagated and merged to make macroscopic damage, and then the diameter of the jet-drilled hole is expanded.

介质管介电常数对大气压Ar冷等离子体射流特性的影响

通过二维流体模型,研究介质管的介电常数对大气压氩气冷等离子体射流放电性质的影响.结果表明,射流在介质管内外具有不同的放电性质.当射流在介质管内时,电离波沿着介质管内表面向管口传播,因而呈现环状结构,其传播速度先增加后减小.介电常数越大,环形结构的半径越小,电子密度越低,射流传播的速度也越小.当射流喷出管口后,射流的传播速度迅速提升,然后减小,介电常数越大,提升越快.随着射流的传播,环状结构不断收缩,最终消失.研究结果对大气压冷等离子体源的设计和优化具有一定的理论指导意义.

基于LSDYNA的井下套管水力切割仿真与实验研究

为弥补传统井下开窗方法的不足,磨料水射流技术逐渐被应用到此领域,基于实际井下应用,若开出(30×50)mm的孔,则可继续喷射地层,实现一次性开窗及破岩。磨料水射流技术开窗具有效率高、无毛刺、喷嘴结构简单的特点。这里利用LSDYNA软件模拟磨料水射流对套管壁的冲蚀与仿真,并分析了割缝中工件压力分布。采用第一次实验确定模拟模型,利用第二次实验进行模型的验证,用确定好的模拟模型对不同结构的喷嘴进行仿真,为研制可切割(30×50)mm孔的喷嘴提供依据,节省实验成本。

脉冲型流体振荡器射流对叶栅角区分离的控制研究

通过流体振荡器特有结构产生双孔振荡射流,采用非定常数值模拟方法研究其抑制压气机叶栅大攻角下角区分离的控制机理。重点分析了射流位置、射流角度、射流流量和单个/阵列型射流对控制效果的影响。结果表明:在近端壁单个射流器方案下,最佳射流位置位于角区分离未充分发展处(54%叶片轴向弦长),最佳射流角度和射流流量比分别为10°和0.09%,并使总压损失系数降低6.48%,静压升系数增加2.39%。振荡射流通过向附面层内低能流体注入高流向动量,抑制了附面层的发展;其非定常激励将吸力面大尺度分离涡离散破碎成一系列小尺度涡,并且其锁频效应减小尾缘压力脉动幅值,最终减小损失。相比单个射流器方案,阵列型射流方案在全叶高范围内进行振荡射流,通过5倍流量的输入,使气动性能增益增加了约1倍。

反循环气动潜孔锤进气端分流引射接头设计及结构参数分析

为解决反循环气动潜孔锤在钻进过程中岩石重复破碎及排渣效率低下的问题,笔者基于NGQ-320反循环气动潜孔锤设计了进气端分流引射接头。该接头可实现潜孔锤供气量的动态调节,其引射结构可以将部分压缩气体引入中心通道,对井底流场产生泵吸作用的同时改善冲击机构的动力供给;同时采用CFD技术研究了分流引射接头局部流场,分析了喷射孔夹角、喷射孔开口深度、喷射孔直径和喷射孔偏转角度等参数对中心通道抽吸性能的影响,确定了各项结构参数的较优取值。结果表明,分流引射接头在喷射孔开口深度320~330 mm、喷射孔夹角30°~35°、喷射孔直径12 mm、喷射孔偏转角11°~13°的情况下具有较好的抽吸性能。

淹没水射流式贝肉清洗装置设计与试验

随着贝类预制菜产业的发展,基于贝肉的精加工预制食品逐渐在市场上推广,虽然市场上清洗装置品类较多,但是尚未有适合各类贝肉产品清洗的装备,存在清洗效率低、洗净率差和易破损等问题。本研究基于淹没水射流机理,设计了以淹没水射流为清洗动力的贝肉清洗装置,并对清洗装置进行Fluent-EDEM耦合数值模拟,确定清洗装置的关键结构参数范围。通过2个阶段试验论证了该清洗装置的合理性,第1阶段通过清洗正交试验得出,当射流口直径为10 mm,清洗量为14 kg,清洗时间为6 min,淹没水射流式清洗效果最佳;第2阶段进行了生产性对比试验,并以洗净率和破损率作为评价指标,对比3种清洗装置洗净率。结果显示:以扇贝裙边为清洗对象时,淹没水射流式清洗装置的平均洗净率为97.77%,且无破损现象,较螺旋桨式清洗装置洗净率提高了14.4%,较超声波式清洗装置洗净率提高了7.3%;以鸟蛤肉为清洗对象时,淹没水射流式清洗装置的平均洗净率为98.23%,较螺旋桨式清洗装置的洗净率提高了12.49%,较超声波式清洗装置洗净率提高了6.7%,且无破损情况。研究表明,淹没水射流式装置具有较好的清洗效果,具备产业化推广价值。

Wear behavior of copper material removal during fluid jet polishing:A comparative study between experiment and simulation

As a crucial part in micro-electromechanical manufacture,local ultra-precision processing of highly ductile copper is expected to be realized by fluid jet polishing(FJP),which widely utilized in optical elements.Since copper exhibits different wear behavior from stiff and brittle material,there is currently no abrasive wear prediction model applicable for copper to investigate the polishing mechanism.This research reveals that the copper material removal is dominated by deformation wear rather than cutting wear through abrasive jet impact experiments and localized wear scars analysis.A three-dimensional gas-liquid-particle triphasic wear model for copper in FJP is developed by considering impact energy and wear mechanism simultaneously.Ultimately,validation assessments at various working pressures and impingement angles achieve the goodness-of-fit up to 0.92–0.97 in quantitative comparison between simulations and experimental measurements,which demonstrate the wear prediction ability of the proposed model.This investigation facilitates a better understanding of copper wear mechanism and provides theoretical guidance for FJP process optimization.