DEVELOPMENT OF ACTIVE SURGE CONTROL DEVICES FOR CENTRIFUGAL COMPRESSORS (Centrifugális kompresszorok aktív pompázs szabályozó eszközeinek fejlesztése) by KÁROLY BENEDA Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Supervisor Prof. József Rohács DEPARTMENT OF AERONAUTICS, NAVAL ARCHITECTURE AND RAILWAY VEHICLES Budapest University of Technology and Economics BUDAPEST, HUNGARY June 2013 NYILATKOZAT Alulírott Beneda Károly kijelentem, hogy ezt a doktori értekezést magam készítettem és abban csak a megadott forrásokat használtam fel. Minden olyan részt, amelyet szó szerint, vagy azonos tartalomban, de átfogalmazva más forrásból átvettem, egyértelműen, a forrás megadásával megjelöltem. Budapest, 2013. június ___________________________ Beneda Károly Az értekezésről készült bírálatok és a jegyzőkönyv a későbbiekben a Budapesti Műszaki és Gazdaságtudományi Egyetem Közlekedésmérnöki és Járműmérnöki Karának Dékáni Hivatalában elérhetőek. ACKNOWLEDGEMENTS As first my deepest grateful acknowledgements are due to my wife, Csilla, who has made me it possible to keep up with my work taking all the duties in the family, caring about our two sons unsparing her efforts. Her true love has helped me through all the hard periods. Then I have to thank my parents who have supported me to find my way in the life. I would like to express my gratitude to my present advisor, Professor József Rohács for the valuable support, guidance and suggestions throughout my work. I also wish to thank Professor Imre Sánta for his conscientious assistance even after his retirement. I am thankful to Árpád Veress, my roommate, for the useful remarks during our frequent discussions. I would like to express my special thanks for Vilmos Csomor and György Székely, the colleagues in the Department Laboratory, who have manufactured all required devices for my work. Hereby I wish to thank all other colleagues at the Department for their help as well. I would like to thank all my colleagues at AEROK Aviation Technical Training Centre for their endless support in improving my knowledge about aircraft engines and providing friendly atmosphere as well. I am very grateful to Budapest Aircraft Service Ltd. and to the deceased MALÉV – Hungarian Airlines, for their kind support on my work, providing an insight on the state-of- the-art aviation solutions. II ABSTRACT Centrifugal compressors are widely spread throughout the industry, with important applications in the transportation (aircraft engines, auxiliary power units), fuel cell systems, etc. All dynamic compressors are prone to instabilities at significantly lower mass flow rates than nominal, which restricts the useable operating range. In order to increase efficiency, stability and operational life, utilization requires finding solutions that are able to meet the requirements of the supplied downstream system while maintaining the compressor within the stable zone. Historically, the surge avoidance systems have been operated far from the surge margin, due to the lack of the possibilities for sensing the onset of surge and reacting on the conditions. As in electronics more sophisticated developments have been reached, the actively controlled surge suppression has been introduced in the late 1980’s. Over the past more than twenty years, most researches have focused on the improvement of existing systems, equipping them with more effective regulators, etc. The aim of the present dissertation is to find methods, which are not currently used as active surge suppression, but can meet the requirement of such application. The decision on the devices to be developed has to be based on a comprehensive analysis of the literature, in order to get familiarized with the up-to-date solutions in this field. With the selected methods, the investigation has to include a preliminary survey based on one-dimensional mathematical model, which is able to supply relevant information about the general behavior of the present devices. The software is written in MATLAB in order to extend the possibilities of calculations and visual interpretation. This has to be followed by detailed numerical simulations in three dimensions, in order to get information about the flow field in full particulars. For the CFD simulations, the ANSYS commercial software is selected, which is available at the Department. Another important step in the research is the design of a control system. Based on thorough survey of the related literature, a linear quadratic (LQ) optimal regulator has been chosen to develop and investigate. The simulation of compression system dynamic behavior with the investigated surge suppression device is realized in MATLAB Simulink environment as it offers extensive mathematical apparatus to solve similar problems in engineering. The previously mentioned parts of the work should also be supported by experimental research; hence a compressor test bench has been developed and equipped with a sophisticated data acquisition system. As a conclusion to the investigation, the achieved results are detailed and evaluated in order to ascertain the applicability of the chosen devices, draw consequences from the CFD simulations and find the possible ways of further improvement of the topic. III TABLE OF CONTENTS Introduction ................................................................................................................................ 1 Industrial background of the problem .................................................................................... 1 Aims of the thesis ................................................................................................................... 1 Method of the investigation .................................................................................................... 2 Organization of the thesis ....................................................................................................... 2 1. Phenomena and Possible Control of Centrifugal Compressor Surge ................................. 4 1.1. Centrifugal Compressors and Their Applications ....................................................... 4 1.1.1. General introduction ............................................................................................. 4 1.1.2. Operation principle of centrifugal compressors ................................................... 6 1.1.3. Determination of operational parameters of centrifugal compressors .................... 9 1.1.4. Major applications of centrifugal compressors .................................................. 15 1.2. Centrifugal Compressor Surge .................................................................................. 18 1.2.1. Introduction to Instabilities ................................................................................ 18 1.2.2. Classification of instabilities .............................................................................. 18 1.3. Effects of Surge on the Operation of the Centrifugal Compressor ............................ 22 1.3.1. Classifying species of surge ............................................................................... 22 1.3.2. Investigation of Effects of Deep Surge .............................................................. 26 1.3.3. Investigation of Effects of Mild and Classic Surge ............................................ 27 1.4. Possibilities of Active Surge Control on Centrifugal Compressors .......................... 28 1.4.1. Short Introduction into Passive Methods of Surge Avoidance .......................... 28 1.4.2. Active Surge Control Methods ........................................................................... 30 1.4.3. Concluding remarks ........................................................................................... 34 2. Active Control of Surge ................................................................................................... 35 2.1. Onset of Surge ........................................................................................................... 35 2.2. Mathematical Description of Surge Onset ................................................................. 37 2.2.1. Stability of a Compression System .................................................................... 37 2.3. Modeling of the Active Surge Control Methods ....................................................... 43 2.3.1. General Introduction to Surge Control Models .................................................. 43 2.3.2. Overview of the Developed Model .................................................................... 43 2.3.3. Governing Equations of the Model .................................................................... 44 2.4. Operational Concept of Investigated Methods .......................................................... 52 3. Developed Methods and Devices ..................................................................................... 54 3.1. Choosing the Methods for Development ................................................................... 54 3.2. CFD Simulation of Developed Surge Control Devices ............................................. 56 3.2.1. Introduction ........................................................................................................ 56 3.2.2. Variable Inducer Shroud Bleed .......................................................................... 56 3.2.3. Blade Load Distribution Control .......................................................................