DESIGN AND CONTROL OF A VARIABLE GEOMETRY TURBOFAN WITH AN INDEPENDENTLY MODULATED THIRD STREAM DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Ronald J. Simmons, M.S. * * * * * The Ohio State University 2009 Dissertation Committee: Professor Meyer Benzakein, Adviser Professor Richard Bodonyi Approved by Professor Jeffrey Bons Professor Jen-Ping Chen Adviser Professor Nicholas J. Kuprowicz Aerospace Engineering Graduate Program Distribution Statement A: Unlimited Distribution. Cleared for Public Release by AFRL/WS Public Affairs Case Number 88ABW-2009-1697 The views expressed in this article are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government. ABSTRACT Abstract Emerging 21st century military missions task engines to deliver the fuel efficiency of a high bypass turbofan while retaining the ability to produce the high specific thrust of a low bypass turbofan. This study explores the possibility of satisfying such competing demands by adding a second independently modulated bypass stream to the basic turbofan architecture. This third stream can be used for a variety of purposes including: providing a cool heat sink for dissipating aircraft heat loads, cooling turbine cooling air, and providing a readily available stream of constant pressure ratio air for lift augmentation. Furthermore, by modulating airflow to the second and third streams, it is possible to continuously match the engine‟s airflow demand to the inlet‟s airflow supply thereby reducing spillage and increasing propulsive efficiency. This research begins with a historical perspective of variable cycle engines and shows a logical progression to proposed architectures. Then a novel method for investigating optimal performance is presented which determines most favorable on design variable geometry settings, most beneficial moment to terminate flow holding, and an optimal scheduling of variable features for fuel efficient off design operation. Mission analysis conducted across the three candidate missions verifies that these three stream variable cycles can deliver fuel savings in excess of 30% relative to a year 2000 reference turbofan. This research concludes by evaluating the relative impact of each variable technology on the performance of adaptive engine architectures. The most promising technologies include modulated turbine cooling air, variable high pressure turbine inlet area and variable third stream nozzle throat area. With just these few features it is possible to obtain nearly optimal performance, including 90% or more of the potential fuel savings, with far fewer variable features than are available in the study engine. It is abundantly clear that three stream variable architectures can significantly outperform existing two stream turbofans in both fuel efficiency and at the vehicle system level with only a modest increase in complexity and weight. Such engine architectures should be strongly considered for future military applications. ii Dedication Dedicated to my beloved bride Bonnie. iii ACKNOWLEDGMENTS Acknowledgments I wish to express thanks to my adviser, Professor Meyer Benzakein, and the entire dissertation committee for creating plentiful intellectual challenges, providing emotional support, and offering an almost inexhaustible supply of patience. You recognized potential in this aging student long before I did and cultivated a desire to live up to your expectations. Furthermore, I would like to acknowledge a number of consummate professionals at the Air Force Research Laboratory (AFRL). Mr. Jeffrey Stricker, Mr. Tim Lewis, Mr. Chris Norden, Mr. Jed Cox, and Mr. Greg Bruening for their insight into variable cycle engine operation and research guidance. It is likely that this research would have been helplessly adrift without your steadfast direction. Additionally, I would like to recognize Dr. Tom Curran of Universal Technology Corporation for his research into the history of variable cycle engines. To Mr. Jim Felder, Mr. Scott Jones, Mr. Tom Lavelle, and Mr. Scott Townsend of the NPSS support group at NASA Glenn research center, you have my most sincere thanks; without your tireless efforts this research would not have been possible. Finally, I would like to express my most sincere gratitude to my family for their support throughout this process. To my wife Bonnie, may God richly bless you for cups of late night coffee and inspirational words after a demoralizing test. To my children who have been a continuous motivation to me, I pray that God fill your heart with dreams and the faith to achieve each of them. Most of all, I wish to thank the Lord for seeing me through this course of study and working every hindrance for good (Romans 8:28); to God be all praise, honor and glory forever. This work was supported by the Air Force Research Laboratory, Propulsion Directorate, Turbine Engine Division, Engine Integration and Assessment Branch, Wright-Patterson AFB, OH. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. iv VITA August 16, 1965 ............................ Born – Harvey, Illinois 1988 ............................................... B.S. Aeronautical Engineering, US Air Force Academy B.S. Astronautical Engineering, US Air Force Academy 1990 ............................................... M.S. Aeronautical and Astronautical Engineering, MIT 1991-1994 ..................................... Assistant Professor of Astronautics, US Air Force Academy 2006-Present .................................. Doctoral Student, The Ohio State University PUBLICATIONS Research Publication 1. R. J. Simmons, J.E. Cox, N.J. Kuprowicz “System level benefits of a turbofan propulsion system equipped with an independently modulated auxiliary stream.” 56th JANNAF Propulsion Meeting, Boston MA, (2008). FIELD OF STUDY Major Field: Aerospace Engineering v TABLE OF CONTENTS Page Abstract .......................................................................................................................................................... ii Dedication ..................................................................................................................................................... iii Acknowledgments ..........................................................................................................................................iv VITA ............................................................................................................................................................... v List of tables ................................................................................................................................................. vii List of figures .............................................................................................................................................. viii Nomenclature .................................................................................................................................................. x Chapters: ......................................................................................................................................................... 1 1.0 Introduction .............................................................................................................................................. 1 1.1 Theoretical framework .......................................................................................................................................... 2 1.2 History of variable cycle engines .......................................................................................................................... 9 1.3 Vision missions................................................................................................................................................... 11 2.0 Computational framework ...................................................................................................................... 15 2.1 Numerical simulations ........................................................................................................................................ 15 2.2 Study engines ...................................................................................................................................................... 17 2.3 Controlling the double bypass engine ................................................................................................................. 21 2.4 Spillage drag ....................................................................................................................................................... 23 2.5 Aft body drag ...................................................................................................................................................... 26 2.6 Fuel use calculations ........................................................................................................................................... 27 2.7 Objective function and nested optimization ........................................................................................................ 30 2.8 Searching a discontinuous design space with numerous local minima ............................................................... 32 3.0 Results ...................................................................................................................................................