THEORY AND EXPERIMENTAL STUDY OF THE SELF-EXCITED OSCILLATION PULSED JET NOZZLE

Comparing with usual continuous jet nozzle, the self-excited oscillationpulsed jet nozzle SEOPJN) can make jet generate a higher peak of pressure and larger scouringvolume. And it can make jet increase the effective standoff distance, too. The basic theories of theSEOPJN are introduced. Some experimental results are shown. According to the results, using tricornbits assembled the SEOPJN to drill oil well, the ROP increases by 8 percent approx 77 percent, andthe rates of the footage for tricorn bit increases by 6.7 percent approx 44.0 percent.

The Theory and Experimental Study of the Self-Excited Oscillation Pulsed Jet Nozzle (Pipeline Pulsed Flow Generator)

In this paper, the basic theories of the Self-excited Oscillation Pulsed Jet Nozzle (SEOPJN) invented by the authors are introduced. Then, some experimental results are shown. According to the results, using tricorn bits assembled the SEOPJN to drill oil well, the rate of penetration (ROP) increases by 8% - 77%, and the rate of the footage for tricorn bit increases by 6.7% - 44%. Although the test was conducted in the water, good result was got in nature gas transportation. The volume of gas transportation could be increased by the Self-excited Oscillation Pulsed generator while the gas pressure drop could be decreased, since it significantly reduced the pressure loss during gas transportation.

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.

NONLINEAR ANALYSIS OF EQUATORIAL EASTERN PACIFIC AIR-SEA COUPLING OSCILLATION AND A LIMIT-CYCLE THEORY FOR ENSO CYCLE

The troposphere and ocean mixed layer were considered as two components of a dynamic system operated by solar radiation as the constant source of energy, where upon an air-sea coupling self-exited coupling oscillation model was based with the aid of a locally averaged thermodynamic climate model, resulting mathematically in a closed self-governed dynamic system, a so-called El Nino-Southern Oscillation(ENSO) system. With the limit cycle solution of the system. It is shown that the essential physics of the coupled system can be described by the ENSO system. Compared with the observations, the theoretical limit cycle orbit matches the observed phase loop qualitatively. The ENSO system provides a useful theoretical framework for study of interannual variation of the tropical climate system.

Optical Measurements of Shock Waves in Critical Nozzles at Low Reynolds Numbers

Two-dimensional critical nozzle flows at low Reynolds numbers are visualized by the rainbow schlieren deflectometry. Experiments have been performed in a region of overexpanded nozzle flow. The variation of the shock structure against the back pressure ratio can be clearly visible with color gradation. Static pressure rises due to the shock-induced flow separation are compared with the previous theories. The unsteady characteristics of overexpanded critical nozzle flows at low Reynolds numbers are quantitatively and qualitatively visualized using laser schlieren and Mach-Zehnder interferometer systems combined with a high-speed digital camera. It was found that an oscillating normal shock wave appears inside the nozzle, and that the shock wave has a specified dominant frequency. Also the time-history of the oscillating shock wave is obtained from both the systems and compared with each other.

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.

Experiments on Deflecting & Oscillating Waterjet

A new type jet, the oscillating & deflecting jet, is put forward and its oscillating and deflecting characteristics are investigated. The nozzle of the self-oscillating & deflecting water jet consists of an upstream nozzle, a downstream nozzle, an oscillating chamber and two switches. It is experimentally shown that the deflective angle may reach 9.53 degree. The generated pressure fluctuation is very regular and the jet can efficiently increase the ability for breaking and cutting by eliminating the water cushion effect associated with a continuous jet.

自激振荡脉冲SC-CO_(2)射流冲击频率调制

SC-CO_(2)射流钻完井技术能保证煤层气井稳定性、提高钻井速度和破岩效率,具有广泛的应用前景。但较高的破煤能耗和复杂的系统限制了其工程推广,自激振荡脉冲SC-CO_(2)射流冲击频率和煤岩体的固有频率相同或满足相位关系,能充分发挥谐振效应,达到更好的破煤效果。喷嘴结构是影响射流冲击频率的关键,现有的自振脉冲水射流频率调制方法并不适用于SC-CO_(2)射流。为实现对SC-CO_(2)射流冲击频率的调制,采用大涡模拟研究不同喷嘴结构对自激振荡脉冲SCCO_(2)射流冲击频率的影响规律,通过权重分析得到不同喷嘴结构参数对射流冲击频率的影响程度。采用射流冲击频率测定实验及破煤实验验证喷嘴结构对射流冲击频率的影响规律以及射流冲击频率调制方法的可靠性。结果表明:振荡腔直径、振荡腔长度、碰撞壁角度是影响射流冲击频率的关键因素,可通过调节振荡腔结构实现对射流冲击频率的大幅调制,从而达到谐振效应。调节振荡腔结构使射流冲击频率与煤的固有频率形成谐振时破煤效果显著提升,且谐振倍数越小,射流破煤效果越好,能够有效提高破煤效率。当煤的固有频率是25 Hz时,设置上游和下游喷嘴出口直径为2.5、3.0 mm,调节振荡腔直径、长度、角度分别为10 mm、3 mm、120°,射流冲击频率达到25051.83 Hz,是煤体固有频率的1002.0倍,与煤的固有频率形成谐振效应,有效提高了破煤效率。

气举用脉冲进气自激振荡空气喷嘴数值模拟与试验研究

气举(气力泵)广泛应用在海洋采矿、钻孔水力开采、深水清淤等场合,越来越引起用户的重视。国内外学者对提升气举效率做了不少探索性研究,提出了脉冲进气是有效提升气举效率的途径之一,据此,提出一种亥姆霍兹式空气喷嘴,通过此喷嘴产生脉冲射流作为气举的进气方式,达到改善气举性能的目的。依据波涡理论,分析了自激振荡脉冲射流的产生机理;运用Fluent软件,对自激振荡空气喷嘴内流场进行了数值模拟,基于仿真结果进行试验研究。研究表明:结构参数和运行参数对射流特性影响显著。在入口压力为3 bar(1 bar=1×10^(5)Pa),腔长L=64 mm,频率为8 Hz情况下,压力脉动波动差值和幅值最大,产生的空气脉冲射流最显著;幅值随腔长的增大先上升后下降。数值模拟与试验结果一致。研究成果可为空气脉冲射流与气举一体化的工程应用提供参考,具有较高的工程应用价值。

环形自激振气举泵提升性能试验研究

为提高气举泵的提升效率,设计了一种带有振荡腔结构的新型气举泵,通过振荡腔对混合流的激励作用,增强气液混合物在提升管内的输运能力。计算了提升管内气液两相流流型随气相速度的变化规律,并通过试验对比分析振荡腔结构与无振荡腔结构在不同浸没率下,排水量、峰值点位置、提升效率随着进气量增加的变化规律。结果表明:受提升管内流型变化的影响,排水量随着进气量增大存在先升后降的趋势;进气量<75 m^(3)/h时,有振荡腔结构提升效率高于无振荡腔结构,进气量>75 m^(3)/h时,提升效率低于无振荡腔结构,最佳进气量范围在50~75 m^(3)/h之间;新型结构气举泵提升性能受进气量、浸没率影响,存在最佳工况,且在最佳工况范围内,相较于传统结构效率提高10%~20%。研究结果可为气举泵的优化设计提供参考。

无反馈通道自激扫掠喷嘴工作特性

无反馈通道自激扫掠喷嘴仅在压力驱动下,通过两股射流在耦合腔内部的相互作用,就能在出口实现液柱喷射方向的自激发高频变化。为了探索此新型喷嘴在航空发动机内燃油喷射的应用潜力,本研究综合采用高速阴影成像法和二维数值模拟方法,研究了不同工作介质、不同缩比尺寸下,无反馈通道自激扫掠喷嘴的特征流速、工作频率、扫掠张角等参数随工作压降的响应变化情况。结果表明,无反馈通道自激扫掠喷嘴在较宽的工作压力范围(0.1~6 MPa)和特征尺寸范围(0.2~7 mm)内均能够实现稳定的自激发扫掠振荡喷射,产生30°以上的扫掠张角和5 kHz以上的振荡频率。无反馈通道自激扫掠喷嘴的扫掠张角基本不随压力和等比缩放特征尺寸而变化,但是其工作频率与其喉道处的特征流速成正比,与喉道宽度成反比,且其频率响应存在双模态现象。

自激振荡脉冲射流喷嘴的试验研究

由作者发明和研制成功的自激振荡脉冲喷嘴所形成的脉冲射流 ,在相同条件下与常规的连续射流相比 ,射流的峰值压力 ,冲蚀体积和有效靶距均得到明显的提高 ,作者将多年来所进行的实验室实验 (振荡腔内流体压力的测定 ;非淹没射流条件下的实验分析 ;淹没条件下自激振荡脉冲射流的性能实验及其分析 ;在淹没和非淹没条件下自激振荡脉冲射流的冲蚀效果 ;碰撞壁碰撞区域的磨损对自激振荡脉冲射流的影响等 )

自激脉冲喷嘴发生机理数值模拟

本文揭示了自激脉冲喷嘴产生自激振荡的根本原因。由于腔内产生了低于汽化压力的负压,引起低压区液体的汽化,加上射流不稳定剪切层的作用,最终形成大小周期性变化的轴对称空化气囊;对脉冲喷嘴腔内流场进行了二维非定常数值模拟,通过对腔内压力和流场的分析,验证了上述结论;试验研究通过对腔内压力的数据采集及对脉冲现象的同步观察,进一步说明了本文结论的正确性。

低压大直径喷嘴自激脉冲射流空化模型

为解释低压大直径喷嘴自激脉冲发生机理,本文对空化初生条件进行了讨论,提出一种可适用于高速剪切流的非定常空化模型。认为自激振荡腔内空化或凝结的发生,不仅与当地压力有关,而且与当地速度有关,并根据能量平衡条件,给出了新的空化判别标准。在一定程度上改善了非定常空化模型的收敛性,解决了非定常状态下,由于压力的变化,流体发生周期性相变,即空化和凝结交替发生的数值模拟问题。最后,对低压大直径喷嘴自激脉冲射流进行了数值模拟,并对振荡腔内的压力场、速度场以及相图之间的关系进行了分析。

潜入式喷管对燃烧室中压力振荡的影响

燃烧室中压力振荡可能会造成发动机及飞行器的不稳定工作。喷管作为发动机主要部件之一,对压力振荡存在着重要影响。文中主要研究了潜入式喷管所引入的空腔体积及其入口形状对燃烧室中压力振荡的影响,发现空腔对压力振荡的振幅和频率均具有调节作用,也验证了潜入式喷管的空腔体积与压力振荡幅值之间的近似线性关系。与潜入式喷管空腔的入口形状相比,空腔体积对压力振幅的影响较大。结论可为大型固体火箭发动机潜入式喷管的设计提供参考。

自激振荡脉冲射流喷嘴频率特性实验研究

基于水声学和流体动力学原理,建立了振荡腔内脉冲射流频率模型,研究结果表明,模态数、流体密度及密度变化率是影响射流频率的关键因素。采用SD150测试系统,分析了自激振荡脉冲射流动态特性中各参数对其频率的影响程度,泵压和自激振荡腔长对射流频率影响的实验结果表明,脉冲射流幅值比连续射流提高了约20%;泵压升高,射流频率增加;腔长增大,射流频率降低,且存在一个使脉冲射流压力峰值达到最大的最佳腔长。实验结果与理论分析一致。

自激振荡脉冲射流喷嘴的理论分析

由作者发明和研制成功的自激振荡脉冲喷嘴在相同条件下与常规的连续射流相比 ,射流的峰值压力 ,冲蚀体积和射流的有效靶距均得到明显的提高 ,文中简要地对作者发明和研制的自激振荡脉冲喷嘴的基本理论 (剪切流动的稳定性、扰动波的有效反馈条件、振荡腔内剪切层的漩涡结构及在变换平面λP 中点涡的复速度势的计算等 )

自激振荡脉冲喷嘴结构参数配比试验研究

结构参数对自激振荡脉冲射流冲击效果存在着很大的影响,本文通过理论推导得出了自激喷嘴固有频率定性分析公式,并通过对上喷嘴直径为8-12.5 mm的低压大流量自激振荡脉冲射流喷嘴的系统试验研究,得到了其结构参数的最佳配比关系,并与以往文献介绍的高压小流量自激振荡脉冲喷嘴优化的结构参数配比相比较,根据定性公式分析引发差异的原因,结果对自激振荡脉冲射流喷嘴结构的设计具有借鉴价值。

自激振荡磨料射流的基本理论与初步试验

自激振荡磨料射流是在自激振荡脉冲射流和前混合磨料射流基础上，提出的新型射流。为此，重点讨论了自激振荡磨料射流喷嘴的结构和工作原理，分析了脉冲频率和幅值等参数对磨粒加速效果的影响。根据初步研究表明，磨粒速度受脉冲频率和幅度影响很大，磨粒速度可超过前混合磨料射流中磨粒的速度，最大钻孔速度比前混合磨料射流提高４１％ 。这一成果有望用于坚硬物料的切割和特种加工、石油钻井、大洋采矿、难采矿体的开采、坚硬岩石巷道（遂道）掘进、表面清洗等领域。

围压下自振空化射流冲蚀性能实验研究

自振空化射流是利用瞬态流和水声学原理调制而成的一种新型射流,为研究围压下自激振荡空化射流的冲蚀破碎规律,利用高压釜装置测量了1.0mm出口直径的风琴管自振空化喷嘴在各种射流参数情况下冲蚀铝试样的冲蚀质量,并与同等条件下锥形喷嘴冲蚀效率进行了对比。测量结果表明,冲蚀质量基本与射流压力成正比;存在最优喷距和围压,使得冲蚀效果最佳,在本实验条件,分别为喷嘴出口直径的5～7倍和2MPa左右;相同条件下,自振空化喷嘴冲蚀质量约为同等条件下锥形喷嘴冲蚀的1～2倍,这为自振空化射流提高钻井速度等实际应用提供了实验依据。