Experimental Investigation of Inter-Blade Vortices in a Model Francis Turbine

The inter-blade vortex in a Francis turbine becomes one of the main hydraulic factors that are likely to cause blade erosion at deep part load operating con- ditions. However, the causes and the mechanism of inter- blade vortex are still under investigation according to present researches. Thus the causes of inter-blade vortex and the effect of different hydraulic parameters on the inter-blade vortex are investigated experimentally. The whole life cycle of the inter-blade vortex is observed by a high speed camera. The test results illustrate the whole life cycle of the inter-blade vortex from generation to separation and even to fading. It is observed that the inter- blade vortex becomes stronger with the decreasing of flow and head, which leads to pressure fluctuation. Meanwhile, the pressure fluctuations in the vane-less area and the draft tube section become stronger when inter-blade vortices exist in the blade channel. The turbine will be damaged if operating in the inter-blade vortex zone, so its operating range must be far away from that zone. This paper reveals the main cause of the inter-blade vortex which is the larger incidence angle between the inflow angle and theblade angle on the leading edge of the runner at deep part load operating conditions.

Numerical simulation of cavitation turbulence in Francis turbine runner with splitter blades

Cavitation will reduce the turbine performance and even damage the turbine components.To verify the effects of splitter blades on improving the cavitation performance,the cavitation flow inside a Francis turbine runner with splitter blades was numerically simulated by using the Singhal cavitation model and the standard k-ε turbulence model.The distributions of static pressure and gas volume fractions on the surface of the runner blades were predicated under different conditions,and the cavitation in the flow field of the runner was analyzed.The results show that the static pressure and gas volume fractions are more uniformly distributed on the short blades than those on the long blades in Francis turbines with splitter blades,and there is almost no cavitation on the short blades;their distributions are more uniform under small flow conditions than those under large flow conditions;and large gas volume fractions are concentrated at the outlet tip near the band on the suction side of the long blade.The installation of splitter blades can improve the cavitation performance of conventional Francis turbines.

On Hemingway's Iceberg Theory——From The Short Happy Life of Francis Macomber

Ernest Hemingway's world-wide influence and distinctive writing style-the Iceberg Style-caused a stylistic revolution in the field of literature all over the world.Hemingway always tries his best to avoid depicting things by piling gorgeously big words;on the contrary,he adopts direct description and short sentences which are precise,laconic,bright and vivid.For instance,the novel titled The Short and Happy Life of Francis Macomber is universally acknowledged as his masterpiece,in which "Iceberg Theory"is skillfully presented.With a full analysis of the story,the uniqueness of "Iceberg Theory"will be emphasized in this paper.

Numerical Study on the Blade Channel Vorticity in a Francis Turbine

A relevant way to promote the sustainable development of energy is to use hydropower.Related systems heavily rely on the use of turbines,which require careful analysis and optimization.In the present study a mixed experimental-numerical approach is implemented to investigate the related mixed water flow.In particular,particle image velocimetry(PIV)is initially used to verify the effectiveness of the numerical model.Then numerical results are produced for various conditions.It is shown that an increase in the guide vane opening can reduce the extension of the region where the fluid velocity is 0 at the inlet of the runner blade,i.e.,it can counteract the generation of the channel vortex;an increase in the guide vane opening also contributes to mitigate the pressure acting on the runner blade;no matter what the working conditions are,the surface pressure is usually higher than that on the suction surface,and there is a cliff-like drop of pressure at the tail of the blade,which indicates that the runner blade tail is more prone to develop backflow.

A Fatigue Analysis of a Hydraulic Francis Turbine Runner

In this work, the estimation of crack initiation life of a hydraulic Francis turbine runner is presented. The life prediction is based on the local strain approach to predict the initiation life. First, the analysis is carried out in air and in water condition and the runner’s natural frequencies were calculated using the finite element (FE) method. The analysis in air is compared with experimental analysis in order to have a representative model of real runner and subsequently the numerical analysis was perform in water. In the case of the runner immersed in water, the added mass effect due to the fluid structure interaction (FSI) is considered. Second, the static and dynamic stresses were calculated according to life estimation. For the calculation of static stresses, the pressure distribution of water and the centrifugal forces were applied to the runner. The dynamic stresses were estimated for interactions between the guide vane and the runner. Lastly, the estimation of the crack initiation life of the runner was obtained.

On the Unequal Relationship in “The Short Happy Life of Francis Macomber” from the Perspective of Discourse Framework

"The Short Happy Life of Francis Macomber",is a representative short story of Hemingway since it clearly embodies hisprinciple of creation.To illustrate the unequal relationship between the hero Macomber and the heroine Margot,this paper employsBurton’s(1980)Discourse Framework theory to analyze the distribution,classification and pattern of these two characters’chal-lenging moves.On the basis of the dialogue analysis,the author attempts to analyze the patterns of their challenging moves,whichcan reflect Macomber is in a more inferior position in marriage than his wife.And the reasons for this are Margot not only holdsmany challenging moves but also seizes the speaking rights in communication.

FRANCIS QL ALGORITHM FOR FINDING THE EIGENVALUES OF ANTI-SYMMETRIC MATRICES

In this paper,we demonstrate that the double-shift QL algorithm for an irreducible anti-symmetric iridiagonal matrix with the shifts being two eigenvalues of the 2×2 matrix in the left upper corner of this matrix is convergent and the convergence rale of Ms kind of algorithm is generally cubic.

Prediction of Hydraulic Stability of Francis Turbines of Three Gorges Hydropower Station

The Francis turbine of Three Gorges hydropower station is one of the large turbines with great head variation in the world. The operational stability of the turbine has been the top subject for departments of design, research, manufacture and operation to be concerned about. During the course of preparing bid invitation documents and executing the contract for the Three Gorges left power plants turbogenerator units, the hydraulic stability of the turbine was regarded as the most important problem and specific stability indexes of the model turbine and the prototype turbine were respectively specified in the contract. In the model tests for turbine model acceptance, pressure fluctuation phenomena in the case of partial load were found to be different from the usual ones as people had known. Within the range of operating water head, there existed a peak value zone of pressure fluctuations with higher frequencies, and large amplitude pressure fluctuations simultaneously occurred in several localities from the spiral case entrance to the draft tube. On the basis of test results from the model, the influence of cavitation coefficient and aeration on pressure fluctuations is analyzed, and some measures to improve the hydraulic stability of turbines of Three Gorges hydropower station are expounded.

Francis Turbine and Governor Improved Models Considering Step Closing Law of Guide Vanes for Power System Stability Analysis

The Francis turbine governing system models in PSD-BPA can’t precisely reflect the actual characteristics. Endeavor was done in this paper to solve the problem. An improved model of actuating mechanism was developed, which could reflect the step closing characteristic of hydro guide vanes. The effect of the inflection point value of actuating mechanism on load rejection was analyzed based on simulation. The non-linear Francis turbine model with power versus gate position module was researched in this paper. Based on field test, comparisons of simulation results with measured data were presented. The analysis demonstrates that the improved models of Francis turbine and governor proposed in this paper are more realistic than the models of BPA, and can be applied in power system simulation analysis better.

The Pact of the Catacombs: An Early Harbinger of Pope Francis’ Vision of the Church

Fifty-four years ago, the Pact of the Catacombs was signed by a small group of churchmen, determined to make a difference. It was the time of the Second Vatican Council. It was the closing phase of that momentous experience in the Church’s life―a transforming event about which many still talk about, half a century later. A handful of bishops―40 out of an impressive 2,000-plus contingent meeting in St Peter’s Basilica―decided to assemble at the dead of night in the Catacombs of Domitilla, outside Rome. During that eventful night of 16 November 1965, they dreamt of a poor servant church. In that holy place, beneath the earth’s surface, where many generations of early Christians met to pray and to bury their loved ones, those 40 modern-day bishops met in heartfelt prayer to celebrate the Eucharist. They also signed the Pact of the Catacombs as they committed themselves to the ideals of Vatican II. The group of like-minded courageous shepherds was led by Archbishop Helder Camara of Recife, Brazil, the revered champion of the downtrodden poor and marginalized. Those gathered made a common pledge to live according to the daily manner of ordinary people, with regard to housing, food, means of transport, and such routine needs. In the Pact, they renounced the appearance and trappings of wealth, especially the use of gaudy vestments, resembling those of earthly monarchs, and symbols of precious metals, insisting that such signs should rather be according to the spirit of the Gospel. They promised to divest themselves of earthly riches and properties, and if they had to possess anything they placed it in the name of the diocese or some charitable foundation. In the humble consoling light of flickering candles, the group renounced all those aspects which appeared to be associated with privilege, prominence, and the wealthy echelons of society. In line with this, they expressed their desire not to be addressed verbally or in writing with titles expressing power, but rather with the more scriptural and homely title of “Father”. Their evangelical intention was focused on avoiding any sort of vanity. The signatories that night at the Domitilla Catacombs affirmed that “we will give whatever is needed in terms of our time, our reflection, our heart, our means, etc., to the apostolic and pastoral service of workers and labour groups and to those who are economically weak and disadvantaged, without allowing that to detract from the welfare of other persons or groups of the diocese. We will support lay people, religious, deacons and priests whom the Lord calls to evangelize the poor and the workers, by sharing their lives and their labours”. This paper shows how the Pact of the Catacombs was to be an early harbinger of Pope Francis’ vision of the church.

Giorgio Vasari＇s Saint Francis： An Aretine Fervor

Giorgio Vasari （1511-1574）, painter, architect, and writer, was fascinated with the image of Saint Francis because of the association of La Verna with Arezzo, his native town, where the miraculous event of Saint Francis＇s stigmatization occurred in 1224. Also in Arezzo, in the church of San Francesco, the beautiful frescoes of Piero della Francesca＇s Legend of the True Cross were commissioned by his wife＇s ancestors, the Bacci family. This study discusses Vasari＇s two types of religious representation of Saint Francis. One type is devotional, as in the paintings of Holy Families, e.g., The Holy Family with Saint Francis of 1541, at the County Museum of Art of Los Angeles, CA. The other is historical, focusing on the miraculous moment of the stigmatization, e.g., Saint Francis Receiving the Stigmata, 1548, in the church of San Francesco in Rimini. Employing mannerist colors to express the spirituality of the event, Vasari created a new conception of piety, where sobriety and humbleness are honored. These paintings reveal the humanness and sanctity of the protagonist, Saint Francis, devoid of any heroic glamour.

The San Francisco Peace Treaty and the Problems Regarding Japan’s Exemption from Blame for the Colonization of Korea

The 1951 San Francisco Peace Treaty was the one and only international opportunity that would have allowed demanding for Japan’s responsibility of the colonization of Korea.However,the United States did not demand of such to be done.Soon,Korea and Japan resumed their diplomatic relationship and had their first summit in 1952.After numerous negotiations,finally in 1965,the“Korea-Japan Treaty”was agreed upon.Even in this treaty,the interpretation of the colonization was different for both countries and ultimately resulted as an unresolved issue.This is because of the Japanese dependence to the San Francisco Peace Treaty.On the other hand,the League of Nations,founded in 1920,believed that the systematization of international law was vital to keeping international peace.Therefore,they put much effort in and successfully carried out the codification of international law.The“Report on the law of Treaties”which was completed in 1935,noted that the“1905 Protectorate Treaty”,which was the ultimate treaty that led to Korea being annexed by the Japanese,was one of the three treaties that had no effective standing.This decision was carried out to the International Law Commission of the United Nations in 1963 and became a Resolution after being submitted to the General Assembly in the end of the same year.Using the decisions of the League of Nations and the United Nations as evidence,this paper critically reviews the San Francisco Peace Treaty’s lack of reviewing the Japanese responsibility of the colonization of Korea.

Interpretations of St. Francis of Assisi in the 20th Century： Philosophical-Anthropological Perspective

The article deals with investigating and comparing key modern and postmodern interpretations of St. Francis of Assisi from a philosophical-anthropological perspective. We determine these interpretations to be as follows： a man of wonder and lover of wisdom, in other words, a true philosopher; hero of all times; defender of the poverty and poor; “champion of liberty”; peace-maker and pacifist; God＇s troubadour; patron of nature and animals. All of these manifestations of St. Francis＇ personality have been enriched by his Christocentrism and joyful vision. Moreover, this can be traced in primary sources and also echoes in the late modern period. Postmodernity not only incorporated similar motives into the cultural space with new focus and accent, but it also put forward some new visions. St. Francis was postulated as God＇s Fool, not so much in the medieval as in the postmodern sense of foolishness and madness as a way of interaction with the absurd and puzzle-like world in which we live. It also reconciles traditional opposition between joy and laughter as inner feelings and outward emotions within the frame of the postmodern Divine Comedy.

Francis Tchiegue

Francis Tchiegue,a Cameroonian,is something of a legend in China.He came to the country in 2003 for doctoral studies,but is now known to Chinese television audiences as Jie Gai,a crosstalk performer. The art of crosstalk[A stand-up comedy routine],or xiangsheng,is difficult even for native Chinese speakers to do,let alone foreigners. Tchiegue’s success has kept him performing across China.He recently spoke with ChinAfrica about his story.

Dynamic Stresses in a Francis Turbine Runner Based on Fluid-Structure Interaction Analysis

Fatigue and cracks have occurred in many large hydraulic turbines after they were put into production. The cracks are thought to be due to dynamic stresses in the runner caused by hydraulic forces. Computational fluid dynamics （CFD） simulations that included the spiral case, stay vane, guide vane, runner vane, and draft tube were run at various operating points to analyze the pressure distribution on the runner surface and the stress characteristics in the runner due to the fluid-structure interactions （FSI）. The dynamic stresses in the Francis turbine runner at the most dangerous operating point were then analyzed. The results show that the dynamic stresses caused by the hydraulic forces during off-design operating points are one of the main reasons for the fatigue and cracks in the runner blade. The results can be used to optimize the runner and to analyze other critical components in the hydraulic turbine.

Numerical analyses of pressure fluctuations induced by interblade vortices in a model Francis turbine

Interblade vortices can greatly influence the stable operations of Francis turbines. As visible interblade vortices are essentially cavitating flows, i.e., the ones to cause interblade vortex cavitations, an unsteady simulation with a method using the RNG k- ？ turbulence model and the Zwart-Gerber-Belamri（ZGB） cavitation model is carried out to predict the pressure fluctuations induced. Modifications of the turbulence viscosity are made to improve the resolutions. The interblade vortices of two different appearances are observed from the numerical results, namely, the columnar and streamwise vortices, as is consistent with the experimental results. The pressure fluctuations of different frequencies are found to be induced by the interblade vortices on incipient and developed interblade vortex lines, respectively, on the Hill diagram of the model runner＇s parameters. From the centrifugal Rayleigh instability criterion, it follows that the columnar interblade vortices are stable and the streamwise interblade vortices are unstable in the model Francis turbine.

NUMERICAL SIMULATION AND ANALYSIS OF PRESSURE PULSATION IN FRANCIS HYDRAULIC TURBINE WITH AIR ADMISSION

In this article, the three-dimensional unsteady multiphase flow is simulated in the whole passage of Francis hydraulic turbine. The pressure pulsation is predicted and compared with experimental data at positions in the draft tube, in front of runner, guide vanes and at the inlet of the spiral case. The relationship between pressure pulsation in the whole passage and air admission is analyzed. The computational results show： air admission from spindle hole decreases the pressure difference in the horizontal section of draft tube, which in turn decreases the amplitude of low-frequency pressure pulsation in the draft tube; the rotor-stator interaction between the air inlet and the runner increases the blade-frequency pressure pulsation in front of the runner.

ANALYSIS AND ESTIMATION OF HYDRAULIC STABILITY OF FRANCIS HYDRO TURBINE

With the development of large-capacity hydro turbines, the hydraulicinstability of hydro turbines has become one of the most important problems that affect the stableoperation of the hydro-electric units. The hydraulic vibration and unstable operation of Francishydro turbines are primarily caused by the unsteady pressure pulsations inside draft tubes. Theforced rotating vortex core at the runner exit and the channel vortices inside Francis turbinerunners are origins of the unsteady pressure pulsations when operating at partial load. This paperbriefly analyzes the hydraulic instability of operation caused by the vortex core and channelvortices at partial load, then, presents a way to estimate the hydraulic stability by calculation ofthe flow behavior at the runner exit. The validity of estimation is examined by comparison withexperimental data. This will be helpful to evaluate the alternative design and predict the hydraulicstability for both the prototype and model hydro turbines.