EFFECT OF UPSTREAM UNSTEADY FLOW CONDITIONS ON ROTOR TIP LEAKAGE FLOW by BORISLAV TODOROV SIRAKOV B.Sc. Aeronautical Engineering United States Air Force Academy, Colorado Springs, Colorado, 1999 Submitted to the Department of Aeronautics and Astronautics in partial fulfillment of the requirements for the degree of Master Of Science In Aeronautics and Astronautics AERO at the MASSACHUSETTS I STITUTE Massachusetts Institute Of Technology OF TECHNOLOGY AUG 13 2002 September 2001 LIBRAR IES © 2001 Massachusetts Institute of Technology. All rights reserved. Author: 71 Borislav T. Sirakov Department ofAeronautics and Astronautics August 23, 2001 (-7 A Certified by: 11F 1 01 1 Choon S. Tan, Ph.D. Senior Research Engineer Thesis Supervisor I I I j / AA- Ai/A Accepted by: Professor N#allace E. VanderVelde Professor of Aeronautics and Astronautics Chair, Committee on Graduate Students Effect of Upstream Unsteady Flow Conditions on Rotor Tip Leakage Flow By Borislav T. Sirakov Submitted to the Department of Aeronautics and Astronautics on Aug 20, 2001 in Partial Fulfillment of the Requirement for the Degree of Master of Science Abstract A study has been conducted, using unsteady three-dimensional Reynolds-averaged Navier- Stokes simulations to determine the impact on rotor performance of the interaction between the upstream stator wakes and rotor tip clearance flow. The key effects of this interaction are: (1) a decrease in loss and blockage associated with tip clearance flow; and (2) an increase in passage static pressure rise. Performance benefit is seen in the whole operability range of interest, from near design to high loading. The benefit is modest near design and increases with loading. The highest calculated benefit is a 5 % increase in the passage static pressure rise coefficient, a 27 % decrease in tip region blockage and, a 40 % decrease in tip region loss coefficient in the time-average unsteady case relative to the steady case. These significant beneficial changes occur when the phenomenon of tip clearance flow double-leakage is present. Double-leakage occurs when the tip clearance flow passes through the tip gap of the neighboring blade. Double- leakage typically takes place at high loading but can be present at design condition, as well. A benefit due to unsteady interaction is also observed in the operability range of the rotor and is estimated to be a 2.8 % decrease in the corrected mass flow coefficient from that of the steady flow situation. A new generic causal mechanism is proposed to explain the observed changes in performance. It identifies the interaction between the tip clearance flow and the pressure pulses, induced on the rotor blade pressure surface by the upstream wakes, as the cause for the observed effects. The direct effect of the interaction is a decrease in the time-average double-leakage flow through the tip clearance gap. The reduction of double-leakage flow means that a smaller amount of low relative stagnation pressure fluid exits the tip clearance gap. Thus, the stream- wise defect of the exiting tip flow is lower with respect to the main flow. A lower defect leads to a decrease in loss and blockage generation and hence an enhanced performance compared to that in the steady situation. The performance benefits increase monotonically with loading and scale linearly with upstream wake velocity defect. Thesis Supervisor: Choon S. Tan, Ph.D. Title: Senior Research Engineer, Gas Turbine Lab, Massachusetts Institute of Technology 2 ACKNOWLEDGEMENTS I would like to express my deep gratitude to the people who made it possible for me to attend MIT and accomplish this research degree. First, I would like to thank my thesis supervisor, Dr. Choon Tan for his technical advice and guidance, support, and many useful discussions on both technical and every-day issues. I owe special thanks to my Air Force Academy mentor, Dr. Bill Heiser, and to Dr. David Quick, Manager at Rolls Royce, for their continuous help and encouragement. I am proud to acknowledge the honor and generous financial support that I received from Rolls Royce and MIT through the Sir Frank Whittle Graduate Fellowship. My research was also made possible through the financial support from Mitsubishi Heavy Industries. The help and support received from Dr. Eng. Sunao Aoki, General Manager at MHI, and Mr. Hikaro Tashiro, Manager at MHI, is gratefully acknowledged. MHI also provided geometry and data from their low-speed research compressor for which I am indebted. This research was also funded by the Advanced Gas Turbine System Research (AGTSR), subcontract # 96-01-SR-045, DOE Morgantown, contract # DE-FC21-92MC24061. This support is gratefully acknowledged. I would like to thank Prof. Edward Greitzer, Prof. Frank Marble, and Prof. Bill Dawes for meeting with me and providing me with very useful advises. I thank Prof. John Denton for allowing me to use his CFD code and for the helpful discussions. I owe thanks to Dr. Choon Tan, Prof. Edward Greitzer, Prof. Alan Epstein, Prof. Ian Waitz, and Prof. Jack Kerrebrock for teaching me so many things about turbomachinery and engineering. I would also like to thank the Aero faculty at the Air Force Academy, especially Gen. Smith, Col. Haven, Col. Chen, Col. Pluntze, and Dr. Bertin for their great teaching, help, and encouragement. I am very grateful to my friends at Rolls Royce, Dr. Hernando Munevar, Dr. Bob Delaney, Dr. Ed Hall, Dr. Steve Gegg, Dr. Kurt Webber, Dr. Steve Wellborn, Dr. Shyam Neerarambam and Mr. David Hinko, for their help and advise. I thank the AFOSR for allowing me to use the computational resources at GTL acquired with their support. I also would like to thank Lori Martinez, Holly Anderson, Paul Warren, Marie Stupard, and Diana Park for their assistance and help in GTL and the department. Of course, this research would have been much harder without the every-day help from my GTL friends. Especially, I would like to thank Duc, Taek, and Yifang for providing research guidance on daily basis, and for being my best friends here, in GTL. I thank Tony, Patrick, Jeremy, Hyung-Soo, Dongwon, Sumita, Steve, Geoff, Luis, Jinwoo, Jin-Wook, Keith, Brenda, Niall, Aurelie and all GTL students for their friendship and help. Zdrasti ! - to my best friends in Bulgaria - Javor, Plamen, and Rossen who always remind me that there are other dimensions to life besides school, labs, and textbooks, and always cheer me up. I would like to express my gratitude to my girlfriend, Anastassia, for being my loving and caring best friend. I also need to thank her for the understanding when I had to spend many nights and weekends in the lab. Finally, I would like to acknowledge my parents, Todor and Jivka, and my sister, Diana. Their unconditional love and faith in me have always been giving me strength and encouragement. 3 CONTENTS L ist of Fi gures ............................................................................................... 6 List of Tables.......................................................... 9 N om enclature ................................................................................................ 10 A cron y m s..................................................................................................... 12 C hapter 1 Introduction ................................................................................ 13 1.1 B ackground ...................................................................................... .. 13 1.2 P revious W ork ................................................................................... 15 1.3 Technical O bjectives ............................................................................ 17 1.4 Approach and Numerical Tools................................................................ 18 1.4 .1 A pproach ................................................................................... 18 1.4.2 N um erical T ools.......................................................................... 19 1.5 C ontribution of T hesis............................................................................ 20 1.6 Organization of Thesis.......................................................................... 23 Chapter 2 Methodology for Comparing Steady and Unsteady Flow........................... 24 2.1 Definition of Upstream Unsteadiness and Description of U pstream W akes.............................................................................. 24 2.2 Method for Designing a Steady Calculation.................................................. 25 2.2.1 Introduction ................................................................................ 25 2.2.2 M ethodology............................................................................... 26 2.3 Method Assessment and Validation............................................................. 29 2.4 Sum m ary ........................................................................................... 30 4 Chapter 3 Effect of Upstream Unsteadiness on Rotor Tip Clearance Flow Time-Average Performance....................................32 3 .1 Intro du ction ........................................................... ........................... 32 3.2 Performance Results............................................... 32 3.3 Com parison to Previous W ork.................................................................. 41 3.4 Effect of Unsteady Interaction on Tip Clearance Flow Interface Angle.................. 42 3.5 Sum m ary ................................................................................ 43 Chapter 4 Discussion of Results and Establishment of Cause and Effect Relation..........................................45 4 .1 Introduction ....................................................................................... 4 5 4.2 Explanation of Cause and Effect Relation ................................ 45 4.3 Relevance of Proposed Mechanism to Observed Performance Changes................. 52 4.4 Summary....................................................... 55 Chapter 5 Conclusions and Recommendations.................................................. 56 5.1 Summary of Results and Conclusions....................................56 5.2 Recommendations for Future Work.............. ....................... 57 5.2.1 Effect of Upstream Wakes on Rotor Operability Range.............................. 57 5.2.2 Effect of Tip Clearance Vortex Resonance........................................... 58 References........................................................... 60 5 LIST OF FIGURES Figure 1.1 Schematic Representation of Tip Clearance Flow in a Com pressor Rotor (Graf [5])..................................................... 14 Figure 1.2 Stator Wake Appears as a Normal Jet Directed Away from the Rotor Suction Side in the Rotor Relative Frame.....................................15 Figure 1.3 Computational Grid Plane at 50 % Pitch Showing the Rotor Blade and Locations of Planes used for Performance and Boundary Conditions Calculations..................................................... 21 Figure 1.4 Computational Grid Plane at 25 % Span Showing the Rotor Blade and Locations of Planes used for Performance and Boundary Conditions Calculations..................................................... 22 Figure 1.5 Axial Computational Grid Plane at 30% Chord from LE Showing the Rotor Blade and Locations of Planes used for Performance and Boundary Conditions Calculations.................................................... 22 Figure 2.1 Strong and Typical Wakes ( Rotor Inlet Plane ).................................... 25 Figure 2.2 Inlet Absolute Total Temperature for Time Averaged Unsteady Solution (stars) and for Steady Solution (circles)........................28 Figure 2.3 Inlet Absolute Angle for Time Averaged Unsteady Solution (stars) and for Steady Solution (circles).................................... 28 Figure 2.4 Inlet Absolute Total Pressure and Exit Static Pressure for Time Averaged Unsteady Solution (stars) and for Steady Solution (circles).................................................................29 Figure 2.5 The Linear Dependence Between Loss and Wake Velocity Defect Calculated by Valkov for a 2-D E3 Stator is Confirmed for a 2-D Mid-span Section of the Present Rotor ( Valkov [1] )................. 30 Figure 3.1 Effect of Strong Upstream Wake on Rotor Total to Static Pressure Rise Coefficient Showing the Benefit of Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Time-Averaged Performance...........................................................33 6 Figure 3.2 Effect of Typical Upstream Wake on Rotor Total to Static Pressure Rise Coefficient Showing the Benefit of Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Tim e-A veraged Perform ance......................................................... 33 Figure 3.3 Beneficial Effect of Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Rotor Static Pressure Rise..................................... 34 Figure 3.4 Beneficial Effect of Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Tip Region Blockage Generation............................ 35 Figure 3.5 Beneficial Effect of Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Tip Region Loss Generation................................... 36 Figure 3.6 The Beneficial Effect of Upstream Unsteadiness Increases Monotonically with Upstream Wake Defect........................................ 36 Figure 3.7 Beneficial Effect from Strong Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Rotor Static Pressure Rise C oe fficien t................................................................................ 37 Figure 3.8 Beneficial Effect from Typical Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Rotor Static Pressure Rise C oefficient............................................................................... 38 Figure 3.9 Beneficial Effect from Strong Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Tip Region Blockage G eneratio n ................................................................................ 39 Figure 3.10 Beneficial Effect from Typical Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Tip Region Blockage Ge n eratio n ................................................................................ 39 Figure 3.11 Beneficial Effect from Strong Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Tip Region Loss G en eration ............................................................................... 40 Figure 3.12 Beneficial Effect from Typical Upstream Stator Wake-Rotor Tip Clearance Flow Interaction on Tip Region Loss G en eratio n ............................................................................... 40 Figure 3.13 Angle Between Tip Clearance Flow Exit Direction and Ax ial Di rection.................................................................... 43 Figure 4.1 Tip Clearance Mass Flow and Stream-wise Velocity for Steady and U nsteady C ases.................................................................... 46 7 Figure 4.2 Rotary Stagnation Pressure of Tip Clearance Fluid Exiting the T ip G ap ............................................................................ 47 Figure 4.3 Tip Clearance Flow Behavior in Steady and Unsteady Environment ( 98 % Span C ut)................................................................... 48 Figure 4.4 Tip Clearance Flow Behavior in Steady and Unsteady Environment ( 70 % Chord Cut from LE )...................................... 48 Figure 4.5 Upstream Wakes Appear as Normal Jets Directed Away from the Rotor Suction Side in the Rotor Relative Frame..................... 49 Figure 4.6 Instantaneous Disturbance Velocity Field in the Rotor.......................... 49 Figure 4.7 Instantaneous Position of Pressure Pulses in the Rotor Passage ( 50 % Span C ut)..................................................................... 50 Figure 4.8 Location of Isolated Pressure Pulse and Its Turning Effect on Tip Clearance Flow .............................................................. 50 Figure 4.9 Fluid Scenario to Explain the Reduction of Tip Clearance Fluid Double-Leakage and Enhancement of P erform ance........................................................................... 5 1 Figure 4.10 Wake Pressure Pulses Change the Tip Fluid Direction Close to the Blade Pressure Surface and Decrease Time-Average D ouble-L eakage....................................................................... 52 Figure 4.11 Control Volume Mixing Analysis for Prediction of Tip Clearance Lo ss.................................................................................. .. 5 3 Figure 5.1 Estimation of Last Stable Point for Strong Interaction Case Speed Li ne........................................................................ .... 58 Figure 5.2 Vortex Pair Instability (Bae [18] )................................................ 59 8 LIST OF TABLES Table 2.1 Upstream Wake Description....................................................... 25 Table 3.1 Rotor Geometry for the LAR Rotor as Described by Smith [13], GE E3 Blade Geometry as Described by Wisler [26] and Present Study Rotor Blade Geometry............................................. 41 Table 3.2 Benefit From Increasing Upstream Unsteadiness................................. 40 Table 4.1 Loss Results from CFD calculation and Fluid Model Estimation for a Strong Interaction Case........................................... 54 Table 4.2 Loss Results from CFD calculation and Fluid Model Estimation for a Typical Interaction Case........................................ 54 9 NOMENCLATURE SYMBOLS Ab Blocked Area Ap Total Pressure peak defect Atot Total Area Av Velocity peak defect b Distance between tip vortex and image across the casing B Blockage Cp Static Pressure Rise Coefficient e Energy _e Referring to rotor trailing edge exit plane _in Referring to rotor domain inlet plane m dot Mass flow p Pressure Pt Total Pressure Rc Radius of vortex core S Entropy t Time T Time Period Tip Rotor Tip Region Tp Total Pressure 99 % defect thickness Tt Total Temperature Tv Velocity 99 % defect thickness 10