Pelton Turbines ThiS is a FM Blank Page Zh. Zhang Pelton Turbines Zh. Zhang Swiss Federal Institute of Technology in Zurich Zurich Switzerland ISBN 978-3-319-31908-7 ISBN 978-3-319-31909-4 (eBook) DOI 10.1007/978-3-319-31909-4 Library of Congress Control Number: 2016943114 Translation from the German language edition “Freistrahlturbinen.Hydromechanik und Auslegung” by Zhengji Zhang, © Springer-Verlag Berlin Heidelberg 2009. All Rights Reserved © Springer International Publishing Switzerland 2016 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Printed on acid-free paper This Springer imprint is published by Springer Nature The registered company is Springer International Publishing AG Switzerland Foreword Pelton turbines are classical hydraulic machines to convert stream flow energy into electricity for medium to high heads. Although invented already in the 1870s by the American Lester Allan Pelton, his runner design is still largely used today in the hydroelectric power industry. Compared to Francis turbines, Pelton wheels offer particularly favourable partial load efficiency degrees and are preferred for low flow rates. They are unrivalled for very high heads above some 700 m, so that their application is mainly in the high mountain regions all over the world. Pelton runners exist in all size classes, from very small Pico hydro applications, e.g. to use tap water from water delivery systems, to the largest units with capacities of more than 400 MW like in the Swiss Bieudron hydropower scheme with a current world- record head of 1883 m. Despite the importance of these hydraulic impulse turbines in the hydropower domain, there is only marginal fundamental literature on their theory and design. This textbook of Dr. Zh. Zhang fills this gap, containing a broad analytical treat- ment of flow processes in real-world Pelton turbines, which renders it so unique and valuable for both the scientific and professional communities. Dr. Zhang not only has a sound scientific background in this topic, stemming from laser-based instru- mentation to small and large-scale experimental investigations, but also success- fully integrates his professional experience originating from decades of work in the hydraulic machinery or related industry into this textbook. While the design of turbines is traditionally part of mechanical engineering, Dr. Zhang also demonstrates that it cannot stand alone without considering the solids contained in the power water in many Pelton turbine applications. Because often run-off from mountain streams is used, the fluid at Pelton wheels is a water– sediment mixture rather than a monophase liquid, despite significant efforts on the civil engineering side to exclude the solids from the water using desilting schemes and new types of flushing systems. At relative velocities of up to some hundreds of kilometres per hour between jet and runner, depending on the head, the impact energy of the flow is so enormous that even the most sophisticated coatings using tungsten carbide, for instance, cannot resist these loads on the long term. An v vi Foreword optimized turbine design is thus also needed to counter hydroabrasive wear phe- nomena, which grow in extent due to increased sediment production as a result of climate change. I am convinced that this up-to-date textbook will have a great success among researchers and engineering professionals in the fields of hydroelectricity and hydromechanics, not least against the background of the growing worldwide need for sustainable energy production from hydropower. Zurich, Switzerland Robert M. Boes January 2016 Preface Pelton turbines have been used for over 100 years to convert hydraulic energy into mechanical work, as well as to generate electricity. The experiences achieved during this long period have enabled Pelton turbines nowadays to be designed and built with high hydraulic and mechanical performances. Nevertheless, there had been until the end of the last century a noticeable lack of fundamental explanations to the hydromechanics of this type of turbines. To extend the general knowledge of Pelton turbines, the author started his experimental research on jet flows in Pelton turbines at the beginning of the twenty-first century within an R&D project of the company Andritz Hydro (former VA TECH Hydro) in Switzerland. Extended studies with the entire hydromechanics of Pelton turbines as a part of research and development activities were carried out at the Oberhasli Hydroelectric Power Company (KWO AG) from 2004 to 2007. The results achieved through these research works have already been published in both journals and conference proceedings and later summarized in German in the textbook “Freistrahlturbinen”, Springer-Verlag, 2009. The current book originates from that German version and is extended with new knowledge, partly obtained at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich. In this textbook, the foundations of hydromechanics of Pelton turbines are presented from an engineering viewpoint of hydraulic designs and optimizations. In terms of reference, the content thus concentrates on the detailed flow processes and their quantitative descriptions regarding all relevant hydro-mechanical aspects. This includes the computational methods for determining the interaction between the jet and the rotating buckets, quantifying diverse flow losses in the system and specifying flow phenomena like the frictional effect and load shedding, which leads to the acceleration of the Pelton wheel rotation towards its runaway speed. The book also reveals the possible potential for further enhancing the system efficiency by indicating the most significant sources causing the greatest efficiency drops. It, thus, provides a useful reference with design and operational criteria for practical applications. vii viii Preface For all these reasons, this textbook is suitable for development and design engineers of Pelton turbines, as well as for those working in the field of fluid machinery. The examples presented in this book generally apply to students in advanced “fluid mechanics”. The author would especially welcome a lot of mechanical laws and rules presented in the textbook to be implemented in the context of Computational Fluid Dynamics (CFD). This should greatly contribute to the simplification of the CFD simulations without having always to start from the basic foundations, i.e. the Navier–Stokes equations. The author wishes to thank the company Andritz Hydro for initiating the project with the experimental investigation of jet flows. He again thanks the company KWO for generously supporting the entire research works during that time. The text was proofread for the correctness of English by Prof. K. Hutter, Ph.D. I thank him a lot for his help. Finally, the author highly esteems and particularly thanks his lovely wife Nan for her great spiritual support in the author’s research activities since decades and especially for the great patience she has shown in the last difficult year. Zurich, Switzerland Zhengji Zhang January 2016 Contents 1 Introduction .......................................... 1 1.1 Hydromechanics of the Pelton Turbine .................. 2 1.1.1 General Developments ........................ 2 1.1.2 Development of Experimental Methods . 3 1.1.3 Development by Numerical CFD Methods . 5 1.1.4 Developments of the Analysis Methods . ........... 6 1.1.5 Further Hydraulic Aspects . 7 1.2 Structural Mechanics of Pelton Turbines . ............... 7 1.3 Objectives of This Reference Book . 8 References ............................................ 9 2 Working Principle of Pelton Turbines ...................... 13 2.1 Conversion of Hydraulic Energy into Mechanical Energy ..... 13 2.2 Pelton Turbines and Specifications . ..................... 17 2.2.1 Geometric Specification of the Pelton Wheel . 17 2.2.2 Characteristic Hydromechanical Parameters . 20 2.2.3 Hydromechanical Specification of the Pelton Turbine . 24 2.2.4 Installation Form of Pelton Turbines .............. 27 2.2.5 Parameter Notations . 28 References ............................................ 28 3 Injector Characteristics ................................. 29 3.1 Flow Acceleration in the Injector Nozzle ................. 30 3.2 Discharge Coefficient φD0 and the Injector Characteristics . 32 3.3 Discharge Coefficient φD Referred to the Effective Nozzle Opening Area . 35 3.4 Reynolds Number Effect . 37 3.5 Flow Dynamic Forces and the Force Balance in the Injector . 37 3.5.1 Injectors