微小口径涡街流量计设计与测量特性研究

涡街流量计是基于流体振荡原理对流量进行测量的流量计,但在低流速下输出的信号很微弱,在实际测量过程中会叠加各种现场产生的噪音。并且目前工业上使用小口径涡街流量计在小流量工况下存在测量局限性,一般最小口径仅到DN15。针对目前涡街流量计存在的问题对DN10及以下的微小口径涡街流量计结构及参数进行研究,以满足工业上的测量新需求。基于模拟仿真计算平台,建立不同尺寸参数的微小口径涡街流量计数值计算模型并进行仿真计算,提出优化的涡街流量计结构尺寸。通过对不同压力监测点的压力波动强度及频率的研究,分析传感器的最佳布置位置。最后以电磁流量计为标准表对所研制的微小口径涡街流量计在微量程段进行了测试,对该被检流量计的误差、精度等参数进行实验,同时对雷诺数与斯特劳哈尔数之间的关系及仪表系数进行分析,结果表明,仿真所获的测量特性与实验测得的特性具有较好的一致性,且该微小口径涡街流量计相对误差优于0.5%,重复性等指标能够满足微量程段内的测量标准。

涡街流量计取压方式对检定结果的影响分析

涡街流量计广泛应用于工业管道气体流量的计量。本文对比分析了涡街流量计表前取压和表后取压两种取压方法对检定结果的影响,根据得到的数据提出了减小因取压方式不同造成检定结果差异的措施。

A Climatology of the Southwest Vortex during 1979–2008

Using a new vortex detection and tracing method, a dataset of the Southwest Vortex(SWV) is established based on Japanese 25-year Reanalysis(JRA-25) reanalysis data during 1979–2008. The spatiotemporal features of the SWV are derived from the dataset. In comparison to other seasons, summer yields the least SWVs, but with the highest probability that they will migrate from their region of origin. SWVs mostly emerge in the southwest of the Sichuan Basin and the southeast of the Tibetan Plateau. Migratory SWVs mainly move along either an eastward or southeastward path. Detailed composite analysis of warm-season SWVs shows that the subtropical high is a key factor in determining the direction of migratory SWVs. Furthermore, the steering wind at 700 hPa dominates the moving direction of migratory SWVs. Potential stability diagnosed by pseudo-equivalent potential temperature ? se is of certain significance for the evolution and movement of SWVs. On the other hand, migratory SWVs possess relatively greater strength than stationary SWVs, due to a stronger low-level jet with enhanced baroclinicity and moisture transport providing more energy to support the growth of SWVs along their paths of movement.

Diagnostic Analysis of the Evolution Mechanism for a Vortex over the Tibetan Plateau in June 2008

Based on the final analyses data （FNL） of the Global Forecasting System of the NCEP and the obser- vational radiosonde data, the evolution mechanism of an eastward-moving low-level vortex over the Tibetan Plateau in June 2008 was analyzed. The results show that the formation of the vortex was related to the convergence between the northwesterly over the central Tibetan Plateau from the westerly zone and the southerly from the Bay of Bengal at 500 hPa, and also to the divergence associated with the entrance re- gion of the upper westerly jet at 200 hPa. Their dynamic effects were favorable for ascending motion and forming the vortex over the Tibetan Plateau. Furthermore, the effect of the atmospheric heat source （Q1） is discussed based on a transformed potential vorticity （PV） tendency equation. By calculating the PV budgets, we showed that Q1 had a great inffuence on the intensity and moving direction of the vortex. In the developing stage of the vortex, the heating of the vertically integrated Q1 was centered to the east of the vortex center at 500 hPa, increasing PV tendency to the east of the vortex. As a result, the vortex strengthened and moved eastward through the vertically uneven distribution of Q1. In the decaying stage, the horizontally uneven heating of Q1 at 500 hPa weakened the vortex through causing the vortex tubes around the vortex to slant and redistributing the vertical vorticity field.

A Study of Structure and Mechanism of a Meso-beta-scale Convective Vortex and Associated Heavy Rainfall in the Dabie Mountain Area Part I: Diagnostic Analysis of the Structure

An analysis was conducted on the evolutional process of a mesoscale convective vortex （MCV） and associated heavy rainfall in the Dabie Mountain area on 21-22 June 2008,as well as their structural characteristics in different stages,by using the mesoscale reanalysis data with 3 km and 1 h resolution generated by the Local Analysis and Prediction System （LAPS） in the Southern China Heavy Rainfall Experiment.The results showed that the latent heat released by convection in the midtroposphere was the main energy source for the development of a low-level vortex.There was a positive feedback interaction between the convection and the vortex,and the evolution of the MCV was closely related to the strength of the positive interaction.The most typical characteristics of the thermal structure in different stages were that,there was a relatively thin diabatic heating layer in the midtroposphere in the formative stage;the thickness of diabatic heating layer significantly increased in the mature stage;and it almost disappeared in the decay stage.The characteristics of the dynamic structure were that,in the formative stage,there was no anticyclonic circulation at the high level;in the mature stage,an anticyclonic circulation with strong divergence was formed at the high level;in the decay stage,the anticyclonic circulation was damaged and the high-level atmosphere was in a disordered state of turbulence.Finally,the structural schematics of the MCV in the formative and mature stage were established respectively.

A Study on the Dynamic Mechanism of the Formation of Mesoscale Vortex in Col Field

The mesoscale vortex associated with a mesoscale low-level jet （mLLJ） usually causes heavy rainfall in the col field. The col field is defined as a region between two highs and two lows, with the isobaric surface similar to a col. Using a two-dimensional shallow water model, the meso-β scale vortex couplets （MβVCs） induced by eight types of mesoscale wind perturbations in an ideal col field were numerically simulated. With the sizes of -100 km, the MβVCs induced by northerly perturbation （NP） and southerly perturbation （SP） moved toward the col point. The sizes of MβVCs induced by southwesterly perturbation （SWP）, southeasterly perturbation （SEP）, northwesterly perturbation （NWP）, and northeasterly perturbation （NEP） were relatively small for the perturbations moving toward dilatation axis. The MβVC induced by easterly perturbation （EP） and westerly perturbation （WP） could not develop because they quickly moved away from the col point, before the circulation could form. The size of the circulation was determined by the distance between the vortex and the col point. The closer to the col point the vortex was, the larger the size of vortex. The comparisons of maximum vorticity and vorticity root mean square error （RMSE） of the NP, the SWP, and the WP show that the maximum vorticity and the vorticity RMSE of the NP decreased slower than other perturbations. Therefore, the weak environment of the col field favors the maintenance of vorticity and the formation of vortex. When a mesoscale vortex forms near the col point or moves toward the col point, it may maintain a quasitationary state in the stable col field.

On the Key Dynamical Processes Supporting the 21.7 Zhengzhou Record-breaking Hourly Rainfall in China

An extremely heavy rainfall event occurred in Zhengzhou,China,on 20 July 2021 and produced an hourly rainfall rate of 201.9 mm,which broke the station record for China's Mainland.Based on radar observations and a convection-permitting simulation using the WRF-ARW model,this paper investigates the multiscale processes,especially those at the mesoscale,that support the extreme observed hourly rainfall.Results show that the extreme rainfall occurred in an environment characteristic of warm-sector heavy rainfall,with abundant warm moist air transported from the ocean by an abnormally northward-displaced western Pacific subtropical high and Typhoon In-Fa(2021).However,rather than through back building and echo training of convective cells often found in warm-sector heavy rainfall events,this extreme hourly rainfall event was caused by a single,quasi-stationary storm in Zhengzhou.Scale separation analysis reveals that the extreme-rainproducing storm was supported and maintained by the dynamic lifting of low-level converging flows from the north,south,and east of the storm.The low-level northerly flow originated from a mesoscale barrier jet on the eastern slope of the Taihang Mountain due to terrain blocking of large-scale easterly flows,which reached an overall balance with the southerly winds in association with a low-level meso-β-scale vortex located to the west of Zhengzhou.The large-scale easterly inflows that fed the deep convection via transport of thermodynamically unstable air into the storm prevented the eastward propagation of the weak,shallow cold pool.As a result,the convective storm was nearly stationary over Zhengzhou,resulting in record-breaking hourly precipitation.

四川盆地西部连续两次特大暴雨过程的西南涡特征分析

针对两次四川盆地西部特大暴雨过程中西南涡发展与演变特征,利用欧洲中心ERA5逐小时再分析资料和FY4A卫星云顶相当黑体温度资料进行诊断分析。结果表明:两次过程的西南涡均生成于低槽东移和副高西伸的有利环流背景下。过程一的西南涡在高能高湿的环境下生成和发展,低层的感热和潜热加热作用更为显著,正涡度随高度向西倾斜发展且高度达到400 hPa,涡度拉伸项和扭转项对西南涡的发展起主要作用。过程二的偏南气流更为强盛,对流层高层的辐散抽吸作用更强,热力条件弱于过程一,西南涡范围内为高湿状态,对流层高层强的感热和凝结潜热加热使得高层增温,从而增强西南涡的发展,其正涡度发展至对流层顶,正涡度柱随高度垂直延伸,动力作用强于过程一,涡度拉伸项、扭转项和垂直输送项对西南涡的发展起主要作用。

涡发生器安装位置对风力机翼型流场影响的数值研究

采用数值模拟的方式对带/不带涡发生器的翼型流场进行计算,并与相应的试验数据进行对比,验证数值计算方法的可靠性。在此基础上,对3种不同弦向位置涡发生器对翼型气动特性的影响进行计算与分析。结果表明,3种安装位置的涡发生器均可有效推迟失速攻角及提高最大升力系数,但由于位置不同,产生的诱导涡的强度有较大差别,并对速度型线产生较大影响,最终导致翼型气动特性上的差异。在3种弦向位置中,20%弦向位置可取得较好的流动控制效果。

基于FLUENT对涡街流量传感器流场仿真及特性研究

运用FLUENT数值仿真软件成功的模拟出流体流经涡街流量传感器时所产生的卡门涡街现象。通过将仿真得到的涡街脱落频率与实验结果比较,两者之间的最大误差不超过10%,表明了FLUENT用于涡街流量传感器流场仿真,进而对传感器进行改进和优化的可行性。基于仿真结果与实验的比较,利用FLUENT数值仿真得到了目前最常用的梯形旋涡发生体后的最佳取压位置为距发生体尾部2.8倍的截流面宽度处,并将梯形发生体与T形发生体进行了对比研究,研究表明T形发生体产生的旋涡信号要优于梯形发生体。

黄河中游一次中层低涡暴雨的中尺度数值模拟

本文采用改进的MM4巾尺度模式模拟系统对造成1982年7月29日—8月2日黄河中游特大暴雨过程后一阶段强降水的低涡系统进行了中尺度数值研究。结果表明:与强降水密切相关的该中尺度系统是在登陆台风外围东南风急流影响下发展起来的具有斜压性的中尺度低涡,其风场上最强的气旋性涡旋在对流层中层。它并非登陆台风变性而成,而是由新生低涡发展而成的一个对流层中高层涡旋。造成暴雨中尺度低涡发展的主要机制是非绝热湿过程。凝结潜热释放在非绝热湿强迫中占主导地位。低涡发展时垂直运动与对流凝结潜热释放之间的正反馈过程是低涡持续发展、强降水发生的主要能量基础。地面热通量并非是决定暴雨中尺度系统发展的主要因子,没有地面热通量的贡献,大气的热力结构会受到影响,进而影响系统发展的强度,但系统的发展仍能维持,演变趋势不受影响。

具有叶顶间隙的涡轮正弯叶栅流场的拓扑与旋涡结构

为进一步揭示在具有间隙的涡轮叶栅中叶片正弯降低泄漏损失的机理，采用微型束状与球头五孔测针详细测量了直叶栅和正弯叶栅间隙内和诸横截面流场中的气动参数，并对壁面（包括上、下端壁和叶片表面）进行了墨迹显示。根据测量与显示结果，应用拓扑学原理分析了壁面与横截面流动的拓扑结构，推测出叶栅内流场的旋涡结构。分析结果表明，在直叶栅中存在着七条分离线与七大集中涡系，它们分别为上端壁叶顶进口吸力边与压力边马蹄涡、泄漏涡、二次涡、下端壁进口边马蹄涡和上、下通道涡。与直叶栅比较，叶片正弯明显减少了壁面与横截面流场中奇点的数量，消除了上通道涡，并使叶顶吸力边的二次涡分离流动由闭式分离转变为开式分离。

带根部间隙的直、弯压气机静叶流场的实验

为了获得正弯静叶在动态压气机中的性能特点,分别对采用带根部间隙的直静叶和正弯静叶的重复级低速轴流压气机在不同流量工况下的静叶出口流场进行了实验测量,结果表明,正弯静叶对气流的扩压能力在设计工况和近喘工况下强于直静叶,在最大流量工况下弱于后者。设计工况下,流道内存在的两个主要旋涡结构,分别为上通道涡和刮削涡,且刮削涡在正弯静叶流道内的尺度要远小于直静叶流道中;最大流量工况下直静叶流道中的刮削涡明显增大而正弯静叶中则基本保持不变;近喘工况下分离严重,旋涡随之消失。考查出口气流角可以发现,正弯静叶对气流的折转能力在整个流量工况下都弱于直静叶,但沿叶高的分布更为均匀。

端壁附面层抽吸对大转角扩压叶栅旋涡影响的实验研究

为探明附面层抽吸技术对压气机叶栅气动性能的影响及其与栅内旋涡结构的关联,通过十个横截面的实验测量结果研究了高负荷压气机叶栅抽吸端壁附面层前后的主要旋涡结构以其对应损失的演变过程。研究对象为矩形低速扩压叶栅,来流马赫数约为0.23。研究结果表明,端壁附面层的变化对叶栅端区的主要旋涡发展过程影响显著。在原型方案中,壁面涡、尾缘脱落涡的演变过程对应着较高的流动损失,通道涡自身产生的损失较小,主要起到向远离端壁的方向输运低能流体的作用;在流向槽吸气方案中,壁面涡和尾缘脱落涡因端壁附面层径向迁移及角区分离受到抑制而被明显削弱;而来流附面层抽吸方案则最为有效地控制了通道涡的演变过程。

地气图预测全国月降水的实践总结

根据地热涡的移动规律和地热释放的持续性，我们设计了两种月降水的预测方法：（1）外推法，依据过去2～3个月地热涡和多雨区的移向、移速，外推下个月多雨区的位置；（2）“正多负少”规则，利用地热释放的持续性，对3．2m地温月际变温为正的地区，预测下月多雨，月际变温为负的地区预测下月少雨（“正多负少”规则）。此规则的历史拟合率约为65％。指出了5种不符合“正多负少”规则的情形及其可能原因。利用上述2种方法，从2005年9月开始进行全国降水预测试验，按全国统一评分方法，2年多来平均得分为67．5分，2007年12个月的平均得到70．5分。

高负荷弯曲扩压叶栅中旋涡流动的研究

在不同冲角下,采用五孔探针对三种大弯角压气机叶栅流场进行了详细测量,并利用数值模拟研究了流动分离和旋涡结构对弯叶栅气动性能影响。结果表明,叶栅流道内旋涡由多涡结构向单一涡结构转变的趋势明显,叶片正弯曲加强了近吸力面涡系径向掺混作用;高负荷压气机叶栅中采用正弯叶片,必须抑制中部流动恶化。

旋流泵变转速性能及无叶腔流场实验研究

为研究旋流泵变转速相似定律换算、内部流场变化和外特性与内部流动的关联,研制32WB8-12型旋流泵试验样机.通过型式及变转速外特性试验,得出泵扬程、功率、效率和临界汽蚀余量曲线变化规律;用5孔球形探针对无叶腔流场进行测量,得到变转速流场5个测点静压、绝对速度、圆周速度、径向速度和轴向速度变化规律,证明轴向旋涡运动为主流,存在回流运动;通过对实验数据进行分析,解释了外特性参数与内部流动参数之间的联系和变化规律,阐明旋流泵抽吸及扬程形成原理;验证流量、扬程和轴功率满足相似理论比例定律,汽蚀余量不满足汽蚀相似定律,且其曲线呈与离心泵等相反的趋势.

后驻体喷孔位置对驻涡腔流动冷态数值的影响

为使采用驻涡燃烧的旋转冲压发动机的燃烧组元获得燃烧的稳定性,研究后驻体喷孔位置对驻涡腔流动冷态数值的影响.应用Fluent软件模拟驻涡燃烧室中三维冷态流场的流动特性;湍流模型采用RNG k-ε模型,近壁面处采用标准壁面函数法;设置喷射物质为理想气体;控制方程离散采用基于控制体中心的有限体积方法,选用隐式二阶迎风格式;驻涡燃烧室三维几何模型采用结构化适体网格,网格节点单元数约为600 000;求解方程组采用动量方程和能量方程进行耦合的方法,控制残差<10-4.结果表明:后驻体喷孔位置对驻涡腔的总压损失、喷射质量流率影响较小;随着喷射位置向后驻体外侧偏移,驻涡腔内的流场平均流速有所降低,形成有利于稳定火焰的流动条件.计算预测的变化趋势与实验结果相同,表明可为实际设计提供一种有效的方法.

涡流发生器周向相对位置和高度对高负荷风扇性能的影响

为了研究涡流发生器周向相对位置和高度对高负荷风扇性能的影响,根据风扇的流动特点,设计了在第二级静子叶根入口前加涡流发生器的流动控制方案,并以此为基础提出了多种不同周向位置和高度的涡流发生器方案,通过计算对采取各种方案下的流场进行了分析。研究表明,涡流发生器对风扇第二级静子角区气流分离有较好的控制作用;涡流发生器的周向位置对第二级静子角区气流分离和损失的影响较大,采取方案C时可以更好地抑制角区气流分离,减少局部损失;涡流发生器高度过高会使静子压力面出现不同程度的低速区,同时也会引起静子通道内局部损失增加,在所研究的范围内,当涡流发生器高度降低1%叶高时,其对吸力面角区分离的控制效果更加明显。

尾流影响下的CSPRs配对进近侧向碰撞风险分析

为研究近距平行跑道(CSPRs)配对进近的侧向碰撞风险,首先,建立运动学方程,描述配对进近飞机的运动过程,确定配对进近飞机之间的时变间隔;然后,通过大涡模拟的方法仿真尾流强度,分析前机尾涡流场特性和后机遭遇前机尾流后的响应机制,构建后机受尾流扰动时的力矩平衡模型,确定尾流安全区域;最后,考虑侧向定位误差,应用概率论基本原理计算和分析侧向碰撞风险。结果表明:CSPRs配对进近过程中前后机之间碰撞风险不断增大并在最后时刻取到最大值,且随初始间隔、正侧风的增大而增大。