关于矽钢片涡流问题的讨论

通过定量分析，表明矽钢片的涡流及其单位体积的涡损都和其厚度的平方成正比．

The lift-off effect analysis of flexible differential pick-up koch fractal eddy current probe

This study utilized finite element simulation and experimental methods to investigate the evolution of crack detection performanceof a flexible differential fractal Koch eddy current probe at different excitation frequencies as the lift-off distance increases.As the lift-off distanceincreased,the distribution shape of induced eddy currents changed,leading to reduced similarity in the shape of the excitation coil and an expandeddistribution range of induced eddy currents,ultimately resulting in weakened output signal strength.The experimental results showed that forexcitation frequencies of 10 kHz,20 kHz,50 kHz,100 kHz,200 kHz,500 kHz,and1000 kHz,the maximum lift distances of the real partof the output signal when cracks were detected were 5.0 mm,7.0 mm,8.0 mm,8.0 mm,8.0 mm,6.5 mm,and 4.0 mm,respectively.Theimaginary parts were 6.5 mm,6.5 mm,7.5 mm,5.5 mm,8.0 mm,6.5 mm,and 6.5 mm,respectively.

石油化工装置磁力泵磁力联轴器的设计与传动特性分析

磁力联轴器是磁力泵的核心部件,通过外转子的转动带动内转子的转动,实现转动动力的传递。通过对磁力联轴器工作时传动性能作的影响因素进行探索,可提高磁力泵的工作效率。在分析磁力泵工作原理的基础上,我们设计了一款磁力联轴器,并分析了磁极对数、工作转速,工作温度磁钢间隙磁钢倾斜度以及磁钢分级对磁转矩与磁涡损的影响,分析结果可作为磁转子结构参数设计的重要参考。

Modeling of ocean mesoscale eddy and its application in the underwater acoustic propagation

Aiming at the influence of ocean mesoscale eddy on underwater acoustic propagation, a theoretical computation model of ocean mesoscale eddy was established based on the in-situ hydrographic data in the sea area of ocean mesoscale eddy. An underwater acoustic modeI-MMPE was used to simulate the acoustic propagation under the influence of different types, different intensities and positions of eddies, and different frequencies and depths of sources. It is found that warm-core eddy can make the convergence zone ＂move back＂ and the width of it increases, while cold-core eddy can make the convergence zone ＂move forward＂ and the width of it decreases. The bigger the intensity of eddy, the more notable the ＂forward ＂or ＂back ＂effect. Sound source located depths and source frequencies can change the acoustic propagation characteristics in the eddy area.

Performance Analysis of RF Spiral Inductor with Gradually Changed Metal Width and Space

To decrease the metal losses of RF spiral inductor,a novel layout structure with gradually reduced metal line width and space from outside to inside is presented. This gradual changed inductor has less eddy-current effect than the conventional inductor of fixed metal width and space. So the series resistance can be reduced and the quality （Q） factor of the inductor relating to metal losses is increased. The obtained experimental results corroborate the validity of the proposed method. For a 6nH inductor on high-resistivity silicon at 2.46GHz,Q factor of 14.25 is 11.3% higher than the conventional inductor with the same layout size. This inductor can be integrated with radio frequency integrated circuits to gain better performance in RF front end of a wireless communication system.

Patterned Dual pn Junctions Restraining Substrate Loss of an On-Chip Inductor

Dual pn junctions in lateral and vertical directions are formed by diffusing the p^＋ on the patterned n-well in standard CMOS technology, which are inserted under the inductor in order to reduce the currents in the substrate induced by the electromagnetic field from the inductor. The thickness of high resistance is not equivalent to the width of the depletion region of the vertical pn junctions,but the depth of the bottom pn junction in the substrate are both proposed and validated. For the first time, through the grounded p^＋-diffusion layer shielding the suhstrate from the electric field of the inductor, the width of the depletion regions of the lateral and vertical pn junctions are changed by increasing the voltage applied to the n wells. The quality factor is improved or reduced with the thickness of high resistance by 19%. This phenomenon validates the theory that the pn junction substrate isolation can reduce the loss caused by the currents in the substrate induced by the electromagnetic field from the inductor.

Effects of stator bending on pressure field and loss of transonic turbine stage

To study effects of the upstream flow field changing on the downstream flow field of transonic turbine, different three-dimensional bowed blades, which are the stator blades of transonic turbine stage, were designed in this paper. And then numerical calculations were carried out. The effects on downstream flow field were studied and analyzed in detail. Results show that, at the middle of stator blades, although the increasing Maeh number causes the increase of shock-wave strength and friction, the middle flow field of downstream rotors is improved obviously. It is an important change in transonic condition. This causes the loss of the rotor＇ s middle part decreased greatly. Correspondingly, efficiency of the whole transonic stage can be increased.

Vortex Dissipation Due to Airfoil-Vortex Interaction

The influences due to several AVIs （airfoil-vortex interactions） are studied by using a two-dimensional CFD （computational fluid dynamics） method. The primary goal of this effort is to assess the variation of vortex center location and vortex circulation associated with sequential AVI toward an improvement of the hybrid method of CFD and prescribed wake model, which closely relates to predicting the BVI （blade-vortex interaction） noise radiated from a helicopter rotor. The representative of sequential AVI is performed by single vortex and two airfoils. Investigations with respect to vortex center location and vortex circulation after AVIs have been made by varying the miss-distance, which is the vertical distance between the airfoil leading edge and the vortex center. Correlations between miss-distance and vorticity field show that there exists complicated vortex wake flow with several vortices newly induced in 1st AVI. The pressure fluctuation amplitude clarifies that the intensity in 2nd AV1 is significantly low compared to the intensity in 1st AVI due to the influence of vortex dissipation. Simulations turned out to modify the vortex center location represented by the hybrid method using an offset value for a streamwise direction and to dissipate the vortex circulation for improving the accuracy of BVI noise prediction.

High Frequency Transformers for DC/DC Converter Used in Solar PV System

This paper presents and investigates planar and coaxial high frequency power transformers used for DC/DC converters in a three phase photo voltaic （PV） power systems. The winding structure including a Faraday shield between the primary and secondary windings is designed to minimize eddy current losses, skin and proximity effects, and to reduce the leakage inductance, and the inter winding coupling capacitance. Finite Element Method is employed to analyze the magnetic flux and eddy current distributions. The two different kinds of prototype high frequency transformers are designed and tested. The simulation and experiment results are demonstrated and compared with non-shielded transformers. The shielded transformers have achieved the expected results with a relatively small coupling capacitance, compared with the conventional high frequency transformer. This shield decreases the inter-winding coupling capacitance Cps. The topology of this shield has to be such that it acts as a Faraday screen while avoiding eddy current generation.

Modeling Abrasion Forces in a Pneumatically Powered Grinding Tool Using Compressible Large Eddy Simulation

This paper describes the design of a new kind of miniature abrading sphere, which is magnetically mounted inside a spherical gap and set in rotation pneumatically with air. Large eddy simulation is performed in conjunction with the compressible Smagorinsky model. Minimal temperature variation allows for the assumption of adiabatic walls. Fluid-solid interaction is modeled using the law of the wall for compressible turbulent flow. A parametric study is done to determine optimal geometric layout while taking physical restrictions into account. The resulting optimal configuration is then examined in detail in order to determine demands to be met by the computerized control of the magnetic bearing as well as to quantify the force available to the abrasion process. Finally, a mathematical relation is given that determines available abrasion force depending on standard volumetric flow rate and rotation frequency. The findings presented here provide a basis for further development of smaller versions of the tool.

An Automated Ultrasonic NDT System for In-Situ Inspection of Wind Turbine Blades

It is crucial to maintain wind turbine blades regularly, due to the high stress leading to defects or damage. Conventional methods require shipping the blades to a workshop for off-site inspection, which is extremely time-consuming and very costly. This work investigates the use of pulse-echo ultrasound to detect internal damages in wind turbine blades without the necessity to ship the blades off-site. A prototype 2D ultrasonic NDT （non-destructive testing） system has been developed and optimised for in-situ wind turbine blade inspection. The system is designed to be light weight so it can be easily carried by an inspector onto the wind turbine blade for in-situ inspection. It can be operated in 1D A-scan, 2D C-scan or 3D volume scan. A software system has been developed to control the automated scanning and show the damage areas in a 2D/3D map with different colours so that the inspector can easily identify the defective areas. Experiments on GFRP （glass fibre reinforced plastics） and wind turbine blades （made of GFRP） samples showed that internal defects can be detected. The main advantages of this system are fully automated 2D spatial scanning and the ability to alert the user to the damage of the inspected sample. It is intended to be used for in-situ inspection to save maintenance time and hence considered to be economically beneficial for the wind energy industry.

Contribution to the Study and Analysis of the Lightning Aggression on the Wind Turbine

Generally, lightning damage has mainly been to home appliances and telephones, towers and power transmission and generation equipment mal functions and damage due to strikes on power lines. With the adoption of wind power generation equipment, however, lightning damage is also increasing in this area. Through his dimensional characteristics, the wind power system is more exposed in the nature compared to all others systems. Lightning damage is the single largest cause of unplanned downtime in wind turbines, and that downtime is responsible for the loss of countless megawatts of power generation. The wind turbines are important structures, since they can easily attract the wrath of storms hits heights close, they can also capture the most distant. The rotation of the blades may also trigger lightning and result in considerable increase in the number of strikes to a wind turbine unit. Since wind turbines are tall structures, the lightning currents that are injected by return strokes into the turbines will be affected by reflections at the top, at the bottom, and at the junction of the blades with the static base of the turbine. We present our contribution in this paper to study lightning strokes and their effects on the wind turbines with the aim to enrich the work and to suggest more effective means of protection against lightning.

Performance Analysis of Mini Centrifugal Pump with Splitter Blades

Design method for a mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Then, a semi-open impeller for the mini centrifugal pump with 55mm impeller diameter is adopted in this research to take simplicity and maintenance into consideration. Splitter blades are adopted in this research to improve the performance and internal flow condition of mini centrifugal pump having large blade outlet angle. The performance tests are conducted with these rotors in order to investigate the effect of the splitter blades on the performance and internal flow condition of the mini centrifugal pump. A three dimensional steady numerical flow analysis is conducted to analyze rotor, volute efficiency and loss caused by a vortex. It is clarified from the experimental results that the performance of the mini centrifugal pump is improved by the effect of the splitter blades. Flow condition at outlet of the rotor becomes uniform and back flow regions are suppressed in the case with the splitter blades.Further, the volute efficiency increases and the vortex loss decreases. In the present paper, the performance of the mini centrifugal pump is shown and the flow condition is clarified with the results of the experiment and the numerical flow analysis. Furthermore, the performance analyses of the mini centrifugal pumps with and without the splitter blades are conducted.

Numerical Investigation of Loss Generation Mechanisms of Flow in Turbomachinery by Using Curved Square Duct

The secondary flow within a passage of turbomachinery exhibits a complex flow pattern by the effect of the centrifugal and the Coriolis forces. The passage vortex in this secondary flow generates a major part of the losses. However, the mechanism of the loss generation has not been fully clarified yet. In this point of view, the passage vortex is closely examined by the computational method using the two-dimensional curved square ducts as fundamental models. The inlet boundary layer thickness and the inlet velocity distortion are considered to be the major parameters affecting the generation of passage vortex in the present study. The computed results revealed that the passage vortex gave the predominant effects for the generation of loss not only in the breakdown process but also in the development process.

Profile and Secondary Flow Losses in a High-Lift LPT Blade Cascade at Different Reynolds Numbers under Steady and Unsteady Inflow Conditions

The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the cascade performance under real engine operating conditions.The Reynolds number has been varied in the range 100000<Re<300000,where lower and upper limits are typical of cruise and take-off/landing conditions,respectively.The effects induced by the incoming wakes at the reduced frequency f+=0.62 on both profile and secondary flow losses have been investigated.Total pressure,velocity and secondary kinetic energy distributions at the downstream tangential plane have been measured by means of a miniaturized 5-hole probe.These quantities provide information on both blade wake and secondary flow structures(passage and horse-shoe vortices).The analysis of the results allows the evaluation of the aerodynamic performance of the HL front-loaded blade in terms of both profile and secondary losses.

Flow Development through HP&LP Turbines,PartⅠ:Inward Rotating Cavity Flow with Superimposed Throughflow

With the aid of numerical method, both flow field and its accompanied loss mechanism within the rotating cavity are investigated in detail in the 1^(st) part of the two parts paper. For ease of comparison, rotating cavity is further classified as the rotor-stator cavity case and the rotor-rotor cavity case. Results indicate that flow within both kinds of the cavity act as the inviscid flow except that the flow near walls, neighboring the lower G region and in the vicinity of the rotating orifices. In the regions except such inviscid-flow-dominate domains, the theoretical core rotation factor can be safely used to predict the swirl ratio within the cavity. When detailed flow pattern is considered, Ekman-type flow exists near periphery of the surface's boundary layer where viscous effect is non-negligible. However, due to the complex profile of the simulated cavity case, vortices structure is varied within the cavity. By comparison, swirl ratio can be used to predict the magnitude of loss. Due to the relatively evident rotating effects of the rotor-rotor cavity, swirl ratio even increases to 1.4 in the current model, which means that flow is moving faster than the surrounding disc. Further investigation finds that this kind of highly rotating flow is accompanied with serious undesirable pressure loss. Parenthetically, unlike its counterpart, swirl ratio above 1.0 doesn't happen when fluid passes through the rotor-stator cavity. So it is suggested that rotor-rotor flow cavity with the superimposed inward throughflow should be avoided in the engine design or certain measurements should be provided when such structure design is unavoidable. Simulation done in the current paper is meaningful since these dimensional parameters are typical in the design of state-of-art. Relatively lower range of Re_φ and C_w is not considered in the current two parts paper.

Pneumatic Measurements Downstream of a Radial Turbine Nozzle Cascade

This paper deals mainly with pneumatic measurements on a radial turbine nozzle cascade. The fill radial cascade guarantees the exit flow field periodicity downstream of it. A special traversing mechanism with a five - hole conical probe moving along a circular path behind the cascade was used for flow field investigation in this type of cascade with very low aspect ratio. The analyses of results of 2D and 3D pneumatic measurements including loss coefficient values are presented.

Flow Development Through HP&LP Turbines,PartⅡ:Effects of the Hub Endwall Secondary Sealing Air Flow on the Turbine's Mainstream Flow

Although many literatures have been focused on the underneath flow and loss mechanism, very few experiments and simulations have been done under the engines' representative working conditions or considering the real cavity structure as a whole. This paper aims at realizing the goal of design of efficient turbine and scrutinizing the velocity distribution in the vicinity of the rim seal. With the aid of numerical method, a numerical model describing the flow pattern both in the purge flow spot and within the mainstream flow path is established, fluid migration and its accompanied flow mechanism within the realistic cavity structure(with rim seal structure and considering mainstream & secondary air flow's interaction) is used to evaluate both the flow pattern and the underneath flow mechanism within the inward rotating cavity. Meanwhile, the underneath flow and loss mechanism are also studied in the current paper. The computational results show that the sealing air flow's ingestion and ejection are highly interwound with each other in both upstream and downstream flow of the rim seal. Both the downstream blades' potential effects as well as the upstream blades' wake trajectory can bring about the ingestion of the hot gas flow within the cavity, abrupt increase of the static pressure is believed to be the main reason. Also, the results indicate that sealing air flow ejected through the rear cavity will cause unexpected loss near the outlet section of the blades in the downstream of the HP rotor passages.

High mixing effectiveness lobed nozzles and mixing mechanisms

For a circular lobed nozzle with the exit plane displaced from the center body,adding a central plug at exit or replacing the nozzle with an alternating-lobe nozzle can improve the mixing effectiveness.In this study,numerical investigations of jet mixing in the lobed nozzles with a central plug and alternating-lobe nozzles in pumping operation were conducted.The effects of the central plugs with the wake ranging from attached to separated flow on the mixing were analyzed,along with the mechanism of improving the mixing performance in a"sword"alternating-lobe nozzle.The simulation results reveal that the large-scale mixing rate,which is dominated by streamwise vortices,is related to the intensity of the attainable heat and mass transfer in the streamwise vortices.The effects of the streamwise vortices on the normal vortex ring are virtually a manifestation of the heat and mass transfer/mixing process of the streamwise vortices.The simulation results also show that the central plug with the attached rear-flow performs better in improving the mixing effectiveness and pumping performance;on the contrary,if the rear-flow is separated,more pressure loss will be induced.In particular,a completely separated flow over the rear of the central plug will severely degrade the attainable heat and mass transfer in the streamwise vortices.For the sword alternating-lobe nozzle,wider sword deep troughs help to increase the flux of the secondary stream around the core region and delay the confluence of the primary stream in the region between the deep and shallow troughs.Thus,the mixing is improved in the middle and posterior segments.Compared to the lobed nozzle with a central plug,the improved sword alternating-lobe nozzle can achieve a higher mixing effectiveness with much less pressure loss,which is preferred in situations when the power loss of the engine is restricted.

Influences of Incidence Angle on 2D-Flow and Secondary Flow Structure in Ultra-Highly Loaded Turbine Cascade

An increase of turbine blade loading can reduce the numbers of blade and stage of gas turbines. However, an increase of blade loading makes the secondary flow much stronger because of the steep pitch-wise pressure gradient in the cascade passage, and consequently deteriorates the turbine efficiency. In this study, the computations were performed for the flow in an ultra-highly loaded turbine cascade with high turning angle in order to clarify the effects of the incidence angle on the two dimensional flow and the secondary flow in the cascade passage, which cause the profile loss and the secondary loss, respectively. The computed results showed good agreement with the experimental surface oil flow visualizations and the blade surface static pressure at mid-span of the blade. The profile loss was strongly increased by the increase of incidence angle especially in the positive range. Moreover, the positive incidences not only strengthened the horseshoe vortex and the passage vortex but also induced a new vortex on the end-wall. Moreover, the newly formed vortex influenced the formation of the pressure side leg of horseshoe vortex.