气液段塞流在网管式分离器中的流动分离特性数值模拟研究

网管式分离器占地面积小,能够满足在线、低能耗及连续分离的要求,适用于深水、荒漠和山区等特殊环境下的多相分离。该文对气液段塞流在网管式分离器中的流动分离与流场演变过程进行了三维数值模拟,分析发现,支管间距为16倍直径的五根支管双层网管式分离器可以达到良好的分离效果,气液两相在前两根支管内存在激烈的流动竞争现象,对气液分离贡献最大。沿程支管的液柱高度逐渐下降,气液交界面愈加趋于稳定。随着气相体积分数的减小,段塞流在分离器主管中逐渐演变为气泡流。表明在该模拟的工况条件下,调整支管间距及个数可以达到较理想的分离效果。

Simulation of the erosion of casing and perforation under staged sand fracturing conditions in horizontal sections

The new fracturing technology of intensive stages and high-intensity proppant injection shows significant advantages of cost reduction and high efficiency in the volume fracturing of unconventional reservoirs,but it also intensifies the erosion of the casing and the perforations,with a perforation diameter expansion and the casing wall thinning.To solve this problem,in view of the applications of the perforation fracturing technology under the construction conditions in Mahu Area in Xinjiang,China,the structure parameters of the downhole strings are measured and a calculation model of the perforation casing erosion is established for the large-displacement sand fracturing process in horizontal sections.The software ANSYS-FLUENT is used to simulate the casing and perforation erosion under different conditions of the displacement,the sand content,the proppant particle size,and the fracturing fluid viscosity in the sand fracturing process.The particle size of the proppant and the viscosity of the fracturing fluid mainly affect the erosion area,but they have little influence on the erosion rate.The sand content and the displacement significantly affect the erosion rate.Among these factors,the sand content has a more significant effect on the erosion rate and the displacement has a more significant effect on the erosion area.Due to the influence of gravity,the perforation erosion rate is larger when the phase angle ranges from 120°to 240°.

Experimental investigation of the effect of the wall proximity on the mode transition of a vortex-induced vibrating flexible pipe and the evolution of wall-impact

The present work experimentally investigates the vortex-induced vibration(VIV)and the pipe-wall impact of a flexible pipe in an oblique flow.The flexible pipe with an aspect ratio of 86.67 and an oblique angle of 30°is immersed in the water flow with the initial gap ratio in the range of 0.2–0.8 and 49.5.The space-time varying oscillation responses in both the in-line and cross-flow directions are recorded using the non-intrusive optical measurement with high-speed cameras in the normal reduced velocity range of 3.40–14.43.The oblique flow induces the spatial variations of the inclination angle to the flexible pipe as a result of the bending deformation during the oscillation.Consequently,the flexible pipe experiences an asymmetrical response along the span and an out-of-sync mode transition in the in-line and cross-flow directions.As the gap ratio decreases,the VIV response is suppressed,and the vibration regions of lower modes are prolonged with the result of the delay of higher excited modes.Additionally,the wall proximity results in an upward deflection of the equilibrium position,and this offset is enlarged with the decrease of the gap ratio.The occurrence of the pipe-wall impact depends on the amplitude of the spatial-temporal varying oscillation and the dominant response mode.Five pipe-wall impact patterns are proposed in terms of the number and the length of the contact pipe segments.The evolution of the pipe-wall impact pattern with the increase of the normal reduced velocity is closely related to the variations of the dominant response mode and the amplitude and the alteration of its spatial distribution.

A highly efficient and selective probe for F^-detection based on 1H-imidazo[4,5-b]phenazine derivative

A new colorimetric and fluorimetric chemosensor for F detection based on 1H-imidazo[4,5-b]phenazine derivative has been designed and synthesized.It shows excellent fluorescent specific selectivity and sensitivity for F^- in DMSO solution.Upon addition of F^- to the solution of probe 1,a remarkable color change from yellow to red could be observed easily by the naked-eye.The detection limit of this probe toward F^- is 6.2× 10 ^-6mol/L.Analysis by^1 H NMR proved that the imidazolyl N–H could be hydrogen-bonded with added fluoride anions,and results in the difference of colors.

倾斜布置柔性管的涡激振动特性实验研究

该文采用高速摄像非介入测试方法,在循环实验水槽中开展了倾斜布置柔性管的涡激振动响应与IP(独立性)准则的适用性研究,通过分析振动频率、位移、斯特劳哈数及振动模态过渡特征,综合判断IP准则的适用范围。实验结果表明:倾角的增加引入了多频参与振动,且高频的权重不断增加,存在时间上的频率切换和空间上的频率竞争现象,流向模态过渡在较低的约化速度时出现;倾角的存在造成了平衡位置、振幅、频率及斯特劳哈数的变化,偏离了IP准则,因而对于柔性管而言,不能简单运用IP准则来预测其振动响应。

柔性立管涡激振动响应的模态转移及时空竞争特性

该文基于Van Der Pol尾流振子模型,研究了两端铰接的柔性立管在不同约化速度下横向和流向的振动响应特性。采用二阶中心差分法对时域和空间域的耦合方程组进行了迭代求解,并与现有文献的实验数据和模型预测结果进行了对比。结果表明:随约化速度的增大,高阶模态在两个方向逐渐被激发出来,主导模态转移时,出现均方根振幅跃升的现象。两个方向主导振动模态比在一定的约化速度范围内保持不变,将其定义为模态组。在同一个模态组中,横向和流向的均方根振幅均随着约化速度单调增加,但在主导模态转移时,两个方向的频率比均发生跳跃。在模态过渡组次,立管的振动响应呈多模态共同参与,且在振动过程中,振动模态具有在空间上竞争和时间上切换的特征,主导频率能量较为集中,在模态切换的过程中出现的频次也更大。

附加开式平板叶片的圆柱流致旋摆响应数值研究

该文对Re=150时,附加开式平板叶片的圆柱流致旋摆响应进行了数值模拟,分析了叶片数量(n=1-5)对旋转模式、流场特性和水动力系数的影响。结果表明,结构调稳后,将围绕新的旋摆平衡位置往复摆动,该平衡位置和初始位置之间的夹角与叶片的数量有关。模拟发现了三种响应模式:(1)类静止模式(n=2和4),摆幅几乎为零,相较于单圆柱升力减小接近100%。但n=2和n=4的原因不同,n=2时,涡量带呈对称分布,圆柱后方存在更长的回流区;而n=4时,尾涡泄放的位置位于圆柱下游五倍直径处,对近尾迹区的影响小,后端上侧叶片后方出现了较长的回流区。(2)小幅摆动模式(n=1和3),n=1时,叶片旋转到圆柱后方,摆幅为3.723°,尾涡与裸柱没有明显差异;n=3时,前端叶片分割来流,后端两叶片对称分布,结构稳定性增强,摆幅减小为1.498°。圆柱表面的旋涡脱落被抑制,叶片上泄放的旋涡以双排涡的形式向下游迁移。(3)大幅摆动模式,n=5时结构摆幅达到15.575°,前端叶片上分离的边界层再次附着于后端叶片或圆柱,并与后端叶片及圆柱的剪切层共同作用,使得圆柱后方近尾流场更为复杂,旋涡的耗散及合并行为频发。从机械能的捕获角度出发,推荐附加叶片数量为1,此时系统获得较大的摆幅、较高的摆动频率且摆动周期性更强。此外,还以n=2为例,探究了初始位置(α=0-90°)对旋摆平衡位置与摆幅的影响,模拟发现旋摆平衡位置与初始攻角无关。当初始位置与平衡位置重合时,摆幅最小;当二者不重合时,转动引起旋涡不规则脱落,旋涡的融合位置提前,导致了摆幅的增大。