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.

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.

自激振荡脉冲喷嘴空化效应及其射流形态的数值分析

基于自激振荡脉冲喷嘴空化效应和多相流模型,建立了自激振荡脉冲射流空化模型。依据自激振荡腔室结构及其几何参数建立了腔室轴对称物理模型,计算得到了振荡周期100ms内自激振荡脉冲射流的空化泡破碎、腔室内两相分布、湍动能分布和速度分布等结果。研究表明:在1.02~2.37ms时,空化泡半径减小,气泡开始径向运动形成泡面加速射流;在2.69~4.67ms时,空化泡面压力达到极限破碎值时气泡开始破碎;在自激振荡周期前25ms,主射流与空气接触边界面形成较强湍动能,自激振荡腔室中心漩涡区逐渐变大,外流场连续射流被割断成多股状射流,射流在喷射轴线附近速度达到并稳定在30~40m/s;在振荡周期的40~90ms,腔室内中心空化气囊形成并开始阻挡主射流运动,喷嘴出口流道出现大面积空化区域,湍动能最大区域集中在下喷嘴出口下游;在振荡后期,随着主射流与空气相互作用及射流贯穿距离增加,主射流速度逐渐趋于稳定且扩散作用减弱。

埙型结构喷嘴自激振荡脉冲空化射流的数值模拟

为研究自激振荡脉冲空化喷嘴空化性能,采用流体仿真分析平台Fluent,以Helmholtz喷嘴原型构建一种具有埙型结构的喷嘴模型,同时基于自激振荡脉冲空化喷嘴的空化效应与多相流模型,数值模拟其在100ms振荡时间内的空化情况,并与Helmholtz喷嘴空化效果进行对比。并分别改变埙型结构喷嘴上下流道的直径比和弧线角度,通过数值模拟考察直径比和弧线角度对喷嘴空化效果的影响。结果表明:上、下流道直径比在0.5～0.6空化效果最好;弧线角度θ=50°时的埙型结构喷嘴,出口处速度呈现均匀性,同时出口更易形成均匀负压区域,喷嘴腔室内空化呈对称分布,空化效果最佳。

自激振荡脉冲射流喷嘴的修正空化模型

根据自激振荡脉冲射流喷嘴中的空化发生机理,一种考虑剪切力(包括雷诺剪切力和粘性剪切力)和由湍动能产生的压力脉动对空化影响的修正空化模型被提出来提高喷嘴内流场的模拟精度。修正空化模型通过用户自定义函数UDF挂入到Fluent中定义空化压力属性。采用该修正空化模型模拟计算所得到的不同入口压力和腔径条件下的喷嘴出口压力峰值与以往的实验结果吻合得很好,验证了该修正空化模型的正确性。进一步对剪切力和由湍动能产生的压力脉动对空化的影响进行了分析,并且研究了不同入口压力条件下这两个因素对空化发生的影响的强弱程度以及空化初生的能力。

自激振荡式旋转冲击钻井工具在胜利油田的应用

自激振荡式旋转冲击钻井工具安装于钻头上部,钻井液高速流经自激振荡器,形成水力脉冲作用于冲击传递杆,产生低幅高频机械冲击力传递至钻头,提高钻头破岩效果;所产生的水力脉冲再向下传递,经钻头水眼喷出形成脉冲射流,改善井底流场,提高井底净化和清岩效率,同时井底瞬时负压脉冲产生局部瞬时欠平衡,改变井底岩面破岩应力状态,可明显提高机械钻速。在胜利油田沙三和沙四段地层进行了钻井试验,无论是牙轮钻头还是PDC钻头都有明显的提速效果,试验井段的机械钻速都提高了30%以上,可成为钻井提速的新途径。

基于声发射的自振脉冲空化射流实验研究

为增加低渗透性能煤层气的采前预抽取量,提高深部煤层的开采效率,采用信号分析法从射流振荡状态研究自振脉冲空化射流特性。基于水声传感技术获取淹没环境中声发射信号,利用频谱分析法研究围压下自振脉冲空化射流冲击砂砖块产生的空化噪声,分析不同压力下随时间变化时主要破坏频率,通过声功率谱(PSD)及空化噪声能量变化探讨冲蚀效果。结果表明,钻孔率随钻孔时间增加而降低且孔深存在临界深度。水中射流脉动的频率范围为11. 44～17. 14 k Hz,砂砖主要破碎频谱范围为38. 74～46. 05 k Hz。随冲蚀时间增大,声发射信号能量强度先增加后降低。此外,射流频谱分析和PSD方法对射流性质的研究提供新的思路及方法。

自激振荡脉冲空化射流喷嘴谐振机理及协同优化研究

自激振荡脉冲空化射流喷嘴的打击力峰值和打击力脉动幅值是衡量其射流性能的重要指标,对其进行准确预测具有重要的理论和工程实践意义。为探究自激振荡脉冲空化射流喷嘴内外流场的演化机理,建立该喷嘴射流过程仿真模型。以入口圆角、腔径、腔长、下喷嘴直径为设计变量,以打击力峰值和打击力脉动幅值为目标变量,将正交试验法、反向传播神经网络与非支配排序遗传算法相结合,确定自激振荡脉冲空化射流喷嘴协同优化设计方法。计算结果表明,在入口压力为1 MPa时,各因素对喷嘴综合射流性能影响的主次顺序依次为入口圆角、下喷嘴直径、腔径、腔长;协同优化结果比正交试验最优结果的打击力脉动幅值提升62.68%,打击力峰值提升1.13%;喷嘴最优结构能产生明显的脉冲空化射流,喷嘴内腔空化区域随时间做周期性缩张;入口压力越大,谐振腔内空化强度越高,射流中空泡含量越高。基于协同优化结果,采用3D打印技术加工自激振荡脉冲空化射流喷嘴流场可视化试验模型,通过试验验证仿真模型的正确性。所得结论为自激振荡脉冲空化射流喷嘴设计理论的发展提供支持。