液面监测辅助漏速测量误差分析

液面监测技术作为一种快捷、经济的作业手段在作业液吊灌,井筒压井液漏速测量领域得到了广泛应用,通过现场实践,取得了较好的安全、井控实践效果,但测量过程受到一些因素的影响,存在一定误差,本文从这些影响因素出发,结合现场实例分析误差产生原因,达到提高检测准确性的目的。

汽轮机速关油内漏故障分析与处理

对某厂重催装置汽压机组汽轮机控制油系统进行了阐述,分析速关油内漏故障引发原因,最后给出详细的故障排查和处理方法。

钻井液漏失位置确定方法综述

钻井液漏失是钻井施工中常见的复杂情况,压力一旦失衡极难调整,漏失防控是钻井工程的重大技术难题之一。漏层确定是漏失研究的首要任务,介绍了常见测、录、钻等漏失位置确定方法,简要分析各方法优、缺点,以及结合漏失机理、分类、地质特征等综合判定漏失位置方法。指出了区块漏失风险的综合研究和钻前风险预测,是提高漏层确定、支撑现场漏失对策制定的有效途径。未来,井漏防控除开展不同地层钻井压裂缝扩展特征等理论研究外,更需经济、高效的多参数漏层测量仪器和漏失监测软件的研发和应用,因其连续、实时优势,必将成为漏失防控基础装备,具有广阔的发展前景。

基于光电吸收截面指数的漏点识别及漏失参数评价

井漏会增加作业成本,延误工期,封堵漏液会影响测井资料对地层信息的响应。渤海地区第三系的砂泥岩地层井漏现象严重、漏失频次高,部分井漏失规模大,导致出现失返现象。准确定位漏失层段和预测漏失规模,进而对易漏地层开展针对性研究,可为后期钻探提供风险预警。通过光电吸收截面指数测井曲线准确定位漏失层段,利用其与瞬时漏速相关性较好预测漏速。提出采用多矿物模型分析方法计算地层中重晶石相对体积含量,将其与泥浆中重晶石实际含量结合计算漏失量。在渤海地区几大油田的现场应用表明,利用光电吸收截面指数计算的漏速和漏失量与现场实际提供的数据对比,误差较小。利用光电吸收截面指数定位漏失层段、计算漏速及漏失量的方法可用于漏点识别及漏失参数评价。

重温事故吸取教训提高井控技术水平

文章从有代表性的井喷事故井的发生及危险井的治理过程分析了从溢流到井喷发展的几个阶段,强调了防止井喷要分别重视的发现溢流、关井、压井三个环节及各环节要把握的技术要点,强调了要根据溢流的动因把握观察、发现溢流的关键时机,根据不同的动因重建井底压力平衡应采取的压井方法;还分析了国内外现用的几种关井方法的优缺点,提示了选择的关井方法应适应"快"的要求。

Research on Volume Identification with the Method of Discharging at the Velocity of Sound

The method of volume identification in pneumatics was studied through theoretical analysis and experimental investigation. Regarding discharging from a container as a thermodynamic process with invariable index the dependence of the container’s volume on the pressure in the container and the index, during discharging at the velocity of sound, is deduced. Then through a lot of experiments, the value of index n of the process is found with a given precision and a specified volume range. Furthermore, the feasibility and practicability of this method are verified by experiments.

Comparison of two methods for assessing leakage radiation dose around the head of the medical linear accelerators

Objective:The aim of this study was to measure the leakage by two methods with ion chamber and ready packs film,and to investigate the feasibility and the advantages of using two dosimetry methods for assessing leakage radiation around the head of the linear accelerators.Methods:Measurements were performed using a 30 cm3ion chamber;the gantry at 0°,the X-ray head at 0°,the field size at between the central axis and a plane surface at a FSD of 100 as a reference,a series of concentric circles having radii of 50,75,and 100 cm with their common centre at the reference point.The absorbed dose was measured at the reference point,and this would be used as the reference dose.With the diaphragm closed,the measurements were taken along the circumference of the three circles and at 45°intervals.Results:Leakage radiations while the treatment head was in the vertical position varied between 0.016%–0.04%.With the head lying horizontally,leakage radiation was the same order magnitude and varied between 0.02%–0.07%.In the second method,the verification was accomplished by closing the collimator jaws and covering the head of the treatment unit with the ready pack films.The films were marked to permit the determination of their positions on the machine after exposed and processed.With the diaphragm closed,and the ready packs films around the linear accelerator the beam turned on for 2500 cGy(2500 MU).The optical density of these films was measured and compared with this of the reference dose.Leakage radiation varied according to the film positions and the magnitude of leakage was between 0.005%–0.075%.Conclusion:The differences between the values of the leakage radiation levels observed at different measurement points do not only reflect differences in the effective shielding thickness of the head wall,but are also related to differences in the distances between the target and the measurement points.The experimental errors involved in dosimetric measurement also contribute to such differences.

Numerical Investigation of the Unsteady Tip Leakage Flow and Rotating Stall Inception in a Transonic Compressor

It is well known that tip leakage flow has a strong effect on the compressor performance and stability. This paper reports on a numerical investigation of detailed flow structures in an isolated transonic compressor rotor-NASA Rotor 37 at near stall and stalled conditions aimed at improving understanding of changes in 3D tip leakage flow structures with rotating stall inception.Steady and unsteady 3D Navier-Stokes analyses were conducted to investigate flow structures in the same rotor.For steady analysis,the predicted results agree well with the experimental data for the estimation of compressor rotor global performance.For unsteady flow analysis, the unsteady flow nature caused by the breakdown of the tip leakage vortex in blade tip region in the transonic compressor rotor at near stall condition has been captured with a single blade passage.On the other hand, the time-accurate unsteady computations of multi-blade passage at near stall condition indicate that the unsteady breakdown of the tip leakage vortex triggered the short length-scale-spike type rotating stall inception at blade tip region.It was the forward spillage of the tip leakage flow at blade leading edge resulting in the spike stall inception. As the mass flow ratio is decreased,the rotating stall cell was further developed in the blade passage.

Numerical Investigation of Influence of Tip Leakage Flow on Secondary Flow in Transonic Centrifugal Compressor at Design Condition

In a centrifugal compressor, the leakage flow through the tip clearance generates the tip leakage vortex by the in- teraction with the main flow, and consequently makes the flow in the impeller passage more complex by the inte- raction with the passage vortex. In addition, the tip leakage vortex interacts with the shock wave on the suction surface near the blade tip in the transonic centrifugal compressor impeller. Therefore, the detailed examination for the influence of the tip leakage vortex becomes seriously important to improve the aerodynamic performance cs- pccia｜ly for the transonic centrifugal compressor. In this study, the flows in the transonic centrifugal compressor with and without the tip clearance at the design condition were analyzed numerically by using the commercial CFD code. The computed results revealed that the tip leakage vortex induced by the high loading at the blade tip around the leading edge affected the loss generation by the reduction or the suppression of the shock wave on the suction surface of the blade.

Fundamental Analysis of Helium-Gas Coolant Leakage Rate Through First-Wall Cracks in Tokamak Fusion Reactors

A fundamental analysis of helium-gas coolant leakage rate through first-wall cracks in Tokamak fusion reactors was made. Criteria for ascertaining the correct flow models were thoroughly investigated. After testing the criteria, it was determined that the correct model is the compressible choked flow for the helium-gas coolant under the normal operating conditions in the Tokamak fusion reactors. The upper bound leakage rates through metallic wall for two crack sizes were calculated. The calculated maximum numbers of allowable cracks through metallic and silicon-carbon composite wall were also reported. The experimental data of specimen S-23 (the small crack size), checked with the predicted or calculated leakage rate. But the experimental data of specimen S-4 (the large crack size, which is only 4.4 times larger than the crack size of specimen S-23) were two orders of magnitude higher than the calculated value. This is probably due to the many through-cracks undetected and therefore, not reported in the experiment, and not due to the difference in crack sizes. It should be noted that since there are only two test data points, it is recommended that more testing or experimental data will be needed. The results of two previous investigations about the calculated leakage values, their equations used, and their flow models employed were also reviewed. It is concluded that the correct model for the analysis is the compressible choked flow, and that helium can be as an effective coolant for fusion power reactors. Several recommendations are also made. Specifically, more experiments for helium, and similar analysis and experiments for lithium and water coolant are needed; and should be encouraged.

Rotating Stall and Stall-Controlled Performance of a Single Stage Subsonic Axial Compressor

Activities by various authors on aerodynamics and control dynamics of rotating stall in axial compressor are first traced. Then, a process of stall cell evolution in a subsonic stage is discussed based on a 2-D CFD. A few numbers of vortices grow ahead of the rotor accumulating vorticity ejected from lightly stalled blades, and eventually organize a cell of circumferentially aligned huge vortices, which merge and recess repeatedly during the rotation. Such stall disturbance is intensified on trailing side of a circumferential inlet distortion and decays on the leading side. Considering these features, a new algorithm for stall warning is developed based on a correlation between pressure waveforms at each passing of a fixed blade. A remarkable change in the correlation level at near-stall provides a warning signal prior to the stall onset with sufficiently large time margin. This scheme is applied to achieve rotating stall prevention by actuating flaps installed on the hub. The last issue is on characteristics of forward swept blade which has much increased throttle margin with decreased tip loss. A 3-D computation shows that a secondary vortex generated in suction surface mid span interacts to reduce the tip leakage vortex that initiates the stall.

Leaky modes and the first arrivals in cased boreholes with poorly bonded conditions

The generation mechanism of the first arrivals in the cased boreholes for the poorly bonded conditions is investigated. Based on the analyses of the Riemann surface structure of the characteristic function, the dispersion features, excitation spectra and contributions of modes excited in the cased boreholes with different cementing types are studied. The phase velocity dispersion studies of leaky modes show that high-order modes form "plateau" regions with one approximate velocity denoted by v separated by their cutoff frequencies, in which the phase velocity changes little with a considerable frequency range, while the group velocity keeps a relatively constant high value. Usually, the operation frequency range of a specific cementing evaluation acoustic logging tool is covered by such a "plateau" region. Mode excitation and contribution analyses show that the first arrivals in the cased boreholes for the poorly bonded conditions are the contributions from leaky modes, where the traveling velocity of the first arrivals processed by slowness time coherence(STC) method is equal to the approximated velocity v. Analyses on generation of leaky modes in the cased boreholes supplement the understanding of the generation mechanism of the first arrivals.

Circumferential Propagation of Tip Leakage Flow Unsteadiness for a Low-Speed Axial Compressor

Full-annulus three-dimensional unsteady numerical simulations were conducted for a low-speed isolated axialcompressor rotor, intending to identify the behavior of self-induced unsteady tip leakage flow within multi-bladepassages. There is a critical mass flow rate near stall point, below it, the self-induced unsteadiness of tip leakageflow can propagate circumferentially and thus initiates two circumferential waves. Otherwise, the self-inducedunsteady tip leakage flow oscillates synchronously in each single blade passage. The major findings are: 1) whilethe self-induced unsteadiness of tip leakage flow is a single-passage phenomenon, there exist phase shifts amongblade passages in multi-passage environments then evolving into the first short length wave propagating at abouttwo times of rotor rotation speed after the transient period ends; and 2) the time traces of the pseudo sensors locatedon the rotor blade tips reveal another much longer length-scale wave modulated with the first wave due tophase shift propagating at about half of rotor rotation speed. Features of the short and long length-scale circumferentialwaves are similar to those of rotating instability and modal wave, respectively.

Experimental Investigation of Effects of Suction-Side Squealer Tip Geometry on the Flow Field in a Large-scale Axial Compressor using SPIV

It is well known that the non-uniform tip geometry is a promising passive flow control technique in turbomachinery.However,detailed investigation of its effects on the unsteady flow field of turbomachinery is rare in the existiug hteratures.This paper presents an experimental investigation of effects of suction side squealer tip configuration on both the steady and unsteady flow field of an isolated compressor rotor.The flow field at 10%chord downstream from the trailing edge was measured using a mini five-hole probe.Meanwhile,the unsteady flow field inside the passage was investigated using stereo particle image velocimetry(SPIV).The steady results show that the SSQ tip configuration exerts positive effect on the static pressure rise performance of this compressor,and the radial equilibrium at the rotor outlet is obviously rearranged.The SSQ tip configuration would create a stronger tip leakage vortex at the formation phase,and it experiences a faster dissipation process around the rear chord.Also,the splitting process of the tip leakage vortex is severer,which is the main cause of the relatively higher probability of the presence of the streamwise reverse flow.The quantitatively analysis of the tip leakage vortex indicates that the velocity loss inside the blockage region is direct response of the evolutionary procedure of the tip leakage vortex.It keeps increasing until the end of the splitting process.Although the blockage coefficient grows sustainably,the velocity loss will reduce once the turbulent mixing procedure is dominant.

Unsteady flow structures in the tip region for a centrifugal compressor impeller before rotating stall

To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RANS solver techniques. It is found that the flow unsteadiness on the pressure side is much stronger than that on the suction side. The periodical frequency of the unsteady flow is around half of the blade passing frequency. The originating mechanism of the flow unsteadiness is illustrated with the time-dependent tip leakage flow and blade loading at the tip region. Due to the blockage caused by the joint effects of broken-downed tip leakage vortex, separated fluids and tip leakage flow at downstream, a low pressure region is formed on the pressure side, consequently the blade loadings is altered. In turn, the changed blade loadings will alter the intensity of tip leakage flow. Such alternative behavior finally results in the periodic process. By comparing the calculated flow field in the cases of single-passage and four-passage models, it is confirmed that the investigated flow unsteadiness is confined in each single passage, as no phase differences are found in the model of four passages. This is different from the situation in axial compressor when the rotating instability is encountered. The flow unsteadiness only occurs at the working conditions with small mass flow rates, and the oscillation intensity will be enhanced with the decrease of mass flow rate. When the mass flow rate is too small, the flow unsteadiness in a single passage may trigger rotating stall, as the disturbance propagates in the circumferential direction.