Heat-fluid-solid coupling mechanism of supercritical carbon dioxide jet in rock-breaking

Aiming at the synergistic rock-breaking mechanism of supercritical carbon dioxide(SC-CO_(2))jet pressure and tem-perature difference,a heat-fluid-solid calculation model of rock-breaking stress was established and verified to be effective,and the variations of jet flow field and rock stress with jet standoff distance of SC-CO_(2),water and nitrogen were studied.With the increase of jet standoff distance,the jet pressure of SC-CO_(2) decreases and the jet temperature difference increases.The SC-CO_(2) jet is higher in pressure than the nitrogen jet and differs little from the water jet.Temperature difference of SC-CO_(2) jet is 5 times that of water jet and more than 2.5 ti mes that of nitrogen jet when the jet standoff distance is larger than 10.The tem-perature stress is the main reason why SC-CO_(2) jet is superior to water and nitrogen jets in rock-breaking.The rock under the SC-CO_(2) jet has greater rock stress,effective rock-breaking jet standoff distance and rock-breaking area.The jet pressure plays a major role in rock-breaking when the jet standoff distance is small,while the jet temperature difference plays a major role in rock-breaking when the jet standoff distance is large.The SC-CO_(2) jet is an efficient volume rock-breaking method,which results in tensile and shear failure on the rock surface under short time jet and large area tensile failure inside the rock simultaneously under long time jet.

Simulation study of supercritical carbon dioxide jet fracturing for carbonate geothermal reservoir based on fluid-thermo-mechanical coupling model

Geothermal energy is a kind of renewable,sustainable and clean energy resource.Geothermal energy is abundant in carbonate reservoirs.However,low matrix permeability limits its exploitation.The super-critical carbon dioxide(SC-CO_(2))jet fracturing is expected to efficiently stimulate the carbonate geothermal reservoirs and achieve the storage of CO_(2) simultaneously.In this paper,we established a transient seepage and fluid-thermo-mechanical coupled model to analyze the impact performance of sc-CO_(2) jet fracturing.The mesh-based parallel code coupling interface was employed to couple the fluid and solid domains by exchanging the data through the mesh interface.The physical properties change of sC-CO_(2) with temperature were considered in the numerical model.Results showed that SC-CO_(2) jet frac-turing is superior to water-jet fracturing with respect to jetting velocity,particle trajectory and pene-trability.Besides,stress distribution on the carbonate rock showed that the tensile and shear failure would more easily occur by SC-CO_(2) jet than that by water jet.Moreover,pressure and temperature control the jet field and seepage field of sC-CO_(2) simultaneously.Increasing the jet temperature can effectively enhance the impingement effect and seepage process by decreasing the viscosity and density of SC-CO_(2).The key findings are expected to provide a theoretical basis and design reference for applying SC-CO_(2) jet fracturing in carbonate geothermal reservoirs.

Predictability of the Summer East Asian Upper-Tropospheric Westerly Jet in ENSEMBLES Multi-Model Forecasts

The interannual variation of the East Asian upper-tropospheric westerly jet （EAJ） significantly affects East Asian climate in summer. Identifying its performance in model prediction may provide us another viewpoint, from the perspective of uppertropospheric circulation, to understand the predictability of summer climate anomalies in East Asia. This study presents a comprehensive assessment of year-to-year variability of the EAJ based on retrospective seasonal forecasts, initiated from 1 May, in the five state-of-the-art coupled models from ENSEMBLES during 1960-2005. It is found that the coupled models show certain capability in describing the interannual meridional displacement of the EAJ, which reflects the models＇ performance in the first leading empirical orthogonal function （EOF） mode. This capability is mainly shown over the region south of the EAJ axis. Additionally, the models generally capture well the main features of atmospheric circulation and SST anomalies related to the interannual meridional displacement of the EAJ. Further analysis suggests that the predicted warm SST anomalies in the concurrent summer over the tropical eastern Pacific and northern Indian Ocean are the two main sources of the potential prediction skill of the southward shift of the EAJ. In contrast, the models are powerless in describing the variation over the region north of the EAJ axis, associated with the meridional displacement, and interannual intensity change of the EAJ, the second leading EOF mode, meaning it still remains a challenge to better predict the EAJ and, subsequently, summer climate in East Asia, using current coupled models.

Numerical analysis on coal-breaking process under high pressure water jet

Based on the theory of nonlinear dynamic finite element,the control equation ofcoal and water jet was acquired in the coal breaking process under a water jet.The calculationmodel of coal breaking under a water jet was established;the fluid-structure couplingof water jet and coal was implemented by penalty function and convection calculation.The dynamic process of coal breaking under a water jet was simulated and analyzed bycombining the united fracture criteria of the maximum tensile strain and the maximal shearstrain in the two cases of damage to coal and damage failure to coal.

Impact of the Preceding Boreal Winter Southern Annular Mode on the Summertime Somali Jet

One of the major high-latitude circulation systems in the Southern Hemisphere is the Southern Annular Mode(SAM). Its effect on the Somali Jet(SMJ), which connects the Southern and Northern hemispheres, cannot be ignored. The present reported results show that time series of both the Southern Annular Mode Index(SAMI) during the preceding winter and the summertime Somali Jet intensity Index(SMJI) display a significant increasing trend and have similar interdecadal variation. The latter was rather strong around 1960, then became weaker up to the mid-1980 s, before starting to strengthen again. The lead-lag correlations of monthly mean SAMI with the following summertime SMJI showed significant positive correlations in November, December, and January. There are thus connections across two seasons between the SAM and the SMJ. The influence of the winter SAM on the summer SMJ was explored via analyses of SST anomalies in the Southern Indian Ocean. During strong(weak) SAM/SMJ years, the SST east of Madagascar is colder(warmer) while the SST west of Australia is warmer(colder), corresponding to the positive(negative) Southern Indian Ocean Dipole-like(SIODL) event. Subsequently, the SIODL excites an anticyclone located over the Arabian Sea in summer through air-sea coupling from winter to summer, which causes an increase in the summer SMJ intensity. The anticyclone/high branch of the SAM over the Southern Hemisphere subtropics and the cyclone/low over the east coast of Madagascar play an important role in the formation of Southern Indian Ocean "bridge" from winter to summer.

RESEARCH ON STABILITY OF MOVING JET CONTAINING DENSE SUSPENDED SOLID PARTICLES

The spatial stability equation of moving jet containing dense suspended solid particles was derived out by means of the continuum phase-coupled model. The stability curves of moving jet far different downstream distances, Reynolds number of flow-field, particle properties and velocities of jetting device are got by the finite difference method based on the asymptotic method and the Eulerian conservative difference scheme. Founded on the analysis of the obtained stability curves it is found that the positive velocity of jetting device widens the unstable frequency range of flow-field hut the effect of the negative one is contrary. In addition, particles existing in the flow-field curb the instability of flow-field and the effect enhances with the decrease of Reynolds number of flow-field. These conclusions benefit learning the development of moving two-phase jet.

Investigate the effects of magnetic fields on the penetration ability of a shaped charge jet at different standoffs

The influence of a magnetic field on the stability of a shaped charge jet is experimentally investigated at standoffs of 490,650 and 800 mm.The experimental results without and with the magnetic field are compared in terms of the shaped charge jet form,stability and penetration ability.A theoretical model based on one-dimension fluid dynamics is then developed to assess the depth of penetration of the shaped charge at those three standoffs and magnetic conditions.The results show that the penetration capability can be enhanced in more than 70%by the magnetic field.The theoretical calculations are compared with the experimental results with reasonably good correlation.In addition,the parameters introduced in the theory are discussed together with the experiments at three standoffs studied.

表面活性剂流体的空化-冲蚀耦合射流试验研究

为了研究赫姆霍兹空化喷嘴的射流机理,依据空化射流理论,以低黏度黏弹性表面活性剂(VES)溶液为介质,基于Schnerr-Sauer空化模型与DPM模型对赫姆霍兹自激振荡空化喷嘴进行流场仿真,对添加颗粒后的VES空化-冲蚀耦合射流近壁面流场特性与颗粒撞击壁面的运动特性进行了数值模拟,并通过淹没射流试验台开展空化-冲蚀耦合射流试验,探讨了VES溶液空化-冲蚀耦合射流对靶材的冲击特性。结果表明:相比于清水,VES射流能够提供更高的冲蚀速率,为清水冲蚀速率的1.37倍,达到3.29×10^(-3)kg/kg;同等条件下,空化喷嘴的冲蚀速率为7.47×10^(-4) kg/kg,略小于流线型喷嘴,但空化喷嘴对靶材的冲蚀凹坑直径为10.5 mm,大于流线型喷嘴的7.5 mm,并且空化喷嘴对靶材的的冲击形貌为V形,相比于流线型喷嘴的W形,更有利于钻井破岩。通过分析空化作用及流体性质对靶材冲蚀特性的差异,阐述了VES溶液空化-冲蚀耦合的射流机理,研究成果为基于VES的空化-冲蚀耦合射流辅助钻井以及提高井下破岩效率提供了新的思路。

RESEARCH ON STABILITY OF INTERFACE OF JET CONTAINING SUSPENDED SOLID PARTICLES

The stability equation of interface of two-phase jet and the corresponding particle-gas disturbance velocity ratio equation are derived by means of the phase-coupled model. The stability nares of interface of two-phase jet for different particle properties and the corresponding particle-gas disturbance velocity ratio curves are given out through numerical computation. Further, several important conclusions on effect of particle property on growth and propagation of disturbance of interface of two-phase jet and particle disturbance property me presented on the basis of analyses of the obtained stability curves and particle-gas disturbance velocity ratio curves. These important conclusions can play a guiding role in studying development of two-phase jet and executing artificial controls over it in project practice.

综掘工作面风流调控装置与射流风幕综合调控粉尘场优化分析

为解决目前综掘工作面传统混合式通风下粉尘聚集污染严重的问题,提出了利用出风口风流调控装置与抽风口射流风幕综合调控优化粉尘场的思路。以陕北某矿综掘工作面为研究对象,建立了风流-粉尘气固耦合场有限元模型,分析了调控装置口径、调控装置右偏角、风幕出口宽度、风幕出口速度及风幕出口张角等参数对粉尘场的影响;设计了正交试验以确定最佳综合调控方案,设计搭建了实验平台进行综合调控方案准确性和降尘效果验证。结果表明:在该综掘工作面通风系统布局下,当调控装置口径1.2 m,调控装置右偏角9°,风幕出口宽度0.14 m,风幕出口速度7 m/s,风幕出口张角60°时,司机位置粉尘质量浓度和行人呼吸带高度平均粉尘质量浓度分别降低91.7%和74.9%,测试误差均在10%以下,有效改善了通风环境。

水下聚能金属射流载荷特性及毁伤效应研究

为研究水下接触爆炸产生的金属射流载荷及其对双层水间隔板的损伤特性。使用耦合欧拉-拉格朗日方法,通过改变圆锥型金属罩的锥角,研究锥角对聚能射流速度的影响。改变金属罩的形状,得到不同类型的聚能侵彻体,在水下模拟其对双层靶板的毁伤作用。不同的锥角影响聚能射流的作用强度,锥角为90°的金属盖能形成最佳射流形状和最大射流速度,穿透效果最好;而不同的聚能侵彻体对靶板造成的损伤各不相同,聚能射流有更强的穿透力,而爆炸成型弹丸造成更大的毁伤面积。通过改变金属罩的形状,可获得不同类型的穿透体,能够适应复杂多变的海洋和损伤要求。该研究可为水下武器的研制和潜艇的防爆、抗冲击和防护提供参考。

基于爆压耦合约束原理的双锥复合药型罩成型及侵彻特性

为有效应对大容积中、轻型装甲目标,提升破甲战斗部综合毁伤能力,本文设计了一种基于爆压耦合约束原理的双锥药型罩,通过小锥角上锥与大锥角下锥的配合,兼顾侵彻深度与扩孔直径。设计了双锥药型罩的射流模拟方案,通过靶场实验结果与数值模拟结果对比,得出了穿深和孔径数值仿真结果误差分别为4.8%、8.1%,验证了数值模拟方案的可靠性。通过正交试验,探究了药型罩罩高比、装药高度与装药直径比和壁厚对射流成型参数的影响规律,并进行了侵彻分析,结果表明:基于爆压耦合约束原理的双锥药型罩可以保持射流的侵彻深度,提升射流的扩孔能力;探究了罩高比、装药高径比、壁厚3个因素对射流头部速度与断裂时间的影响趋势。其中药型罩壁厚、罩高比不会对射流头部速度与断裂时间产生明显影响关系,装药高径比增加使得射流断裂时间提前,射流头部速度增加。最后,通过大量数值模拟确定了装药高径比对射流头部速度、断裂时间的影响曲线,并根据曲线结果,优化了双锥药型罩的结构和炸高,使得药型罩侵彻深度增加23%,穿孔孔径增加了35%。

基于VOF-DPM耦合的Y型喷嘴雾化研究

采用VOF-DPM(流体体积-离散相模型)耦合方法的数值模拟,研究液体黏度对Y型喷嘴内流动和喷嘴雾化性能的影响。首先对Y型喷嘴内部和外部区域进行多面体网格划分,并借助基于气液体积分数值的自适应网格加密技术有效提高气液界面识别精度。分析喷嘴内流动与喷嘴外雾化的关联,研究液体黏度对雾化性能的影响。结果表明:重油黏度较高,流速较小,喷嘴内重油不易被气体吹散和掺混,液体雾化较难。柴油密度低于重油,易被加速,导致喷雾贯穿距离大于重油,雾化更容易,柴油的喷雾锥角与重油差距不大。重油的喷雾索特平均直径d s为137.14,略高于柴油d s约0.8%。研究对评估燃烧器燃烧性能及其适应多种燃料的改造设计具有重要的应用价值。

基于SPH-FEM的油菜茎秆磨粒气体射流切割仿真与试验

针对传统油菜收获切割刀具振动大、茎秆缠绕磨损及效率低等问题,该研究提出一种油菜茎秆磨粒气体射流切割技术,以实现作业机具与油菜无接触式切割和高效低耗收获。采用光滑粒子流体力学与有限元(smooth particle hydrodynamic-finite element method,SPH-FEM)耦合仿真对油菜茎秆射流动态切割过程进行分析,揭示气-固间能量传递规律,获取射流切割动态特性,并搭建试验系统进行射流切割试验验证。研究结果表明,采用4 mm孔径高速喷嘴,射流压力为20 MPa时气流及磨粒最高速度分别为741和411 m/s,约95%加速过程发生在喉管段与扩张段;喷嘴外流场流速呈现先下降后上升的变化规律,射流压力越大速度变化越剧烈;射流束主要通过气体膨胀-收缩-膨胀的加速过程将压力能转化为射流束动能;入口压力从3 MPa增加至10 MPa时,磨粒最大速度提升率从31%下降至11%。当压力超过3 MPa后,随射流压力提高,射流束压力能-动能转换效率显著减小;在相同条件下0.1 mm粒径磨粒的最大速度比0.3 mm粒径磨粒大19%;粒径越大磨粒获得的切割动能越大,0.3 mm粒径磨粒切割动能最大,其次为0.2与0.1 mm粒径磨粒;磨粒速度在120 m/s时可以实现茎杆有效切割,对应射流压力约为0.4 MPa;横移速度为5 mm/s、靶距在10 mm以内可一次切断茎秆,横移速度超过5 mm/s时无法一次切断茎秆;靶距5 mm、横移速度5 mm/s时,可获得最小切割侵蚀体积,切口宽度在1~6 mm之间;射流切割能力主要受横移切割速度影响,切割靶距影响相对较小;茎秆切割效果主要受靶距影响,横移速度影响相对较小。研究成果还可用于其他类似作物茎秆的切割,可为农业非接触式高效切割技术装备的开发提供理论与技术支撑。

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。

惰性气体射流协同控制火焰振荡和NO_(x)排放性能研究

预混火焰燃烧通常会出现热声振荡等问题,严重制约了燃气轮机或油气锅炉的安全运行和洁净排放。为此,提出通过惰性气体射流来调控预混燃烧过程,从而实现火焰振荡和NO_(x)排放的协同控制。惰性气体射流将导致预混火焰振荡模态迁移,既可降低火焰振荡幅值,还可使火焰振荡频率发生改变。相对原子质量大的氩气比相对原子质量小的氦气的控制效果好。惰性气体射流能够显著改变火焰结构,使预混火焰长度变短。

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。

纤维束与异形筘内合成气流的相互耦合作用

为提高喷气织机辅助喷嘴的引纬效率,设计了3类多孔阵列式辅助喷嘴,揭示了多孔形状与阵列方式对合成气流速度分布和弹性纤维束运动位移的影响规律。建立了纤维束-气流耦合的动力学模型,基于任意拉格朗日-欧拉法数值模拟了三维瞬态流场分布及纤维束运动位移,并采用高速摄像机拍摄纤维束运动位移,验证了数值模拟结果的正确性。通过数值模拟得到了异形筘道内合成气流速度分布、速度梯度及纤维束头端运动位移。结果表明:异形筘道内合成气流速度梯度变化与纤维束头端位移具有相关性,合成气流速度梯度越小,纤维束运动位移也越小;三圆孔中心阵列辅助喷嘴形成的合成气流速度梯度最小,纤维束运动位移最小,适合用于弹力较大织物的引纬。

有机硅改性聚丙烯酸酯预处理对涤棉织物喷墨印花性能的影响

为提升涤棉织物涂料喷墨印花工艺的印花性能,采用半连续种子乳液聚合法,以醋酸乙烯酯(VA)、丙烯酸丁酯(BA)和丙烯酸异辛酯(EHA)为共聚单体,丙烯酸羟乙酯(HEA)为功能单体,引入硅烷偶联剂(KH-1706),制备得到有机硅改性聚丙烯酸酯乳液(KH-1706/PVAc),并将其作为预处理液应用于涤棉织物;探究引入不同质量分数的KH-1706对乳液烘干后所得乳胶膜性能的影响,并分析以KH-1706/PVAc为预处理液对涤棉织物涂料喷墨印花性能的影响。结果表明:当引入KH-1706的质量分数为2%时,乳胶膜具有较好的热稳定性和耐水性,吸水率为16.8%;乳液运用于涤棉织物预处理后,有效抑制了墨滴在织物上的渗化,墨滴渗化面积为20.8 mm2;预处理后印花织物耐湿摩擦牢度提高半级,印花精细度提升约13%,并且复杂图案打印后仍具有较好的印花效果,表现出良好的综合印花性能。该研究可为提升涤棉织物涂料喷墨印花的印花性能提供理论参考。

2020年7月一场梅雨暴雨的异常空间分布及形成机制

利用GPCP逐日降水资料、NCEP/NCAR和ERA5再分析资料,研究了2020年7月17—19日长江梅雨大暴雨异常空间分布及成因。结果表明,强降水主雨带在长江下游呈纬向分布,与长江干流位置重合、走向一致、长江中游雨带为西南—东北走向。中高层大气环流出现“两脊一槽”的异常大气环流型,南亚高压主体强盛东伸,副高西北侧水汽通道持续维持,为暴雨的形成和维持提供了有利环流背景。17—18日高空西风急流呈纬向分布、副高控制华南、低空西南急流持续加强并东移;19日高空西风急流转为“V”型分布,江淮气旋形成,长江中下游位于高空急流入口区南侧、副高的西北侧和低空西南急流出口区北侧。“两脊一槽”和“V”型大气环流配置结构使得上层的“抽吸”作用和下层的抬升活动相重叠,伴有江淮气旋的辐合作用,导致强烈的上升运动,易产生大暴雨。过程内高低空急流和副高位置和形态的变化是暴雨空间分布出现变化的主要原因。诊断结果显示,热力因子对抬升活动起主要作用,位涡垂直输送和非绝热加热随气压变化项均有利于位涡增强,假相当位温在500 hPa与850 hPa之差的峰值、强上升运动和位涡高值区与强降水中心重合为本次大暴雨形成提供了有利的热力与动力条件。假相当位温在500 hPa与850 hPa之差的谷值具有较好前期预报指示意义。