Particle erosion of gas turbine thermal barrier coating

UNIVERSITY OF CINCINNATI Date: 28-Oct-2009 I, Rohan Swar , hereby submit this original work as part of the requirements for the degree of: Master of Science in Aerospace Engineering It is entitled: Particle Erosion of Gas Turbine Thermal Barrier Coating Student Signature: Rohan Swar This work and its defense approved by: Committee Chair: Awatef Hamed, PhD Awatef Hamed, PhD Widen Tabakoff, PhD Widen Tabakoff, PhD Robert A Miller, PhD Robert A Miller, PhD 11/23/2009 253 Particle Erosion of Gas Turbine Thermal Barrier Coating A thesis submitted to the University of Cincinnati In partial fulfillment of the requirements for the degree of Master of Science (M.S.) in the Department of Aerospace Engineering and Engineering Mechanics of College of Engineering 2009 By Rohan Swar B.Tech, IIT Madras, Chennai, India, 2006 Committee Chair: Dr Awatef Hamed Dr Widen Tabakoff Dr Robert A Miller Abstract The purpose of this research is to examine and understand the complex phenomenon associated with the particle impacts on turbine blades and the associated erosion of Thermal Barrier Coated (TBC) turbine vane and blade surfaces by ingested solid particle impacts Both experimental and computational techniques were used to find out the parameters relevant to rebound characteristics of particles and erosion rate of TBC coatings In the experimental study, tests were conducted in the erosion wind tunnel facility at University of Cincinnati for TBC coated and uncoated blade materials to determine the erosion rates and particle restitution characteristics under different impact conditions Particle Image Displacement Velocimetry (PIDV) technique was used to determine particle rebound characteristics for different impact conditions From the experimental results, empirical erosion rate models and restitution coefficient models for alumina particles impacting on TBC coated blade surface are developed using non-linear regression analysis technique to predict the erosion rate and restitution coefficients for various impact conditions In the computational analysis, numerical simulations were conducted for the three-dimensional flow field and particle trajectories through a high pressure single stage i axial gas turbine The solution to the Reynolds Averaged Navier Stokes (RANS) equations for turbulent compressible flow were obtained numerically using ANSYS CFX solver for unsteady N-S equations in their conservation form In gas turbine applications generally the particle loadings that are encountered are sufficiently low hence a one-way gas-particle interaction model was used to simulate the particle dynamics involved This does not take into consideration the effects of dispersed particles’ momentum exchange with the gas flow field The experimentally based particle surface restitution models were incorporated in the simulations to determine particle rebound conditions after each surface impact The computed particle surface impact statistics were combined with experimentally based erosion models to predict the stator vanes and rotor blades coated surface erosion pattern and intensity The experimental results reveal that the erosion rate increases with increase in impingement angle, impact velocity, and temperature The trajectories are determined for 26 μm and 500 μm alumina particles The simulation results show that the particle velocity in the stator is reduced by the surface impacts, which causes the particles to enter the rotor with negative incidence compared to the flow The rotor impacts reduce the particle velocities in the rotating frame, but could increase their absolute velocity It was observed that inertia dominates the 500 µm particle trajectories that reenter the stator row ii after rebounding from the rotor leading edge The simulation results predicted the intensity and pattern of TBC erosion over the stator and rotor blade surfaces and the variation in the overall blade surfaces erosion with ingestion velocity iii Acknowledgements I would like to express my gratitude to all those who helped me in completing this thesis This thesis would not have been possible without the help and support of a great number of people The individual to whom I am most indebted is my advisor and mentor, Dr Awatef Hamed, for her constant support, guidance and encouragement during the course of my MS In particular, I would like to express my most sincere gratitude to Dr Widen Tabakoff for his important contribution to this work I deeply appreciate his expertise, knowledge, valuable suggestions and support for the completion of my thesis I would also like to thank Dr Robert A Miller from NASA GRC for supporting my research and for obliging to serve in my thesis committee I wish to thank Rob Ogden and Russ DiMicco for their technical expertise and support in the lab I am grateful to all of my friends and fellow graduate students in Cincinnati for their help during my study Lastly, I would like to give my love and thanks to my parents and my sister for their sacrifice and encouragement during this journey I dedicate this work to them v To my family, iv Table of Contents List of Tables ………………………………………………………………………… viii List of Figures ………………………………………………………………………… ix Introduction 1.1 Literature Review ……………………………………………………….…… …1 1.2 Motivation for research ………………………………………………………… 1.3 Need for Experimental study…………………………………………………… 1.4 Need for Computational study…………………………………………………….6 1.5 Objective of the present work…………………………………………………… 1.6 Present Research………………………………………………………… Experimental Setup 2.1 Air Supply System………………………………………………………… 2.2 Particulate flow wind tunnel…………………………………………………… 10 2.3 Test Section………………………………………………………… 11 2.4 High Speed Photography……………………………………………………… 12 vi Measurement Methodology 3.1 TBC Erosion Rate Measurements……………………………………………… 14 3.2 Data reduction from High Speed photography ………………………………….15 3.3 Statistical Analysis of High Speed Photography Data………………………… 17 Computational Analysis 4.1 Turbine Geometry and modeling ………………………………… 21 4.2 Grid generation …………………………… ………………………………… 21 4.3 Governing Equations…………………… ………………………………… 22 4.4 Computational Details……………………… …………………………………24 4.5 Particle Trajectory Simulations…………… ………………………………… 25 Experimental Results and Discussion 5.1 Erosion test Results from TBC coated samples …………………………………26 5.2 Results from High Speed Photography ………………………………… 28 vii Fig High Speed Camera 49 Fig 5: High Speed Photography 50 V = 226 ft/s, Impact Angle = 25 o 0 10 15 20 25 Sample Impact Rebound -5 Y (mm) -10 -15 -20 -25 X (mm) Fig Schematic of Sample Particle Trajectory 51 Fig Solid Model of the Turbine blade Fig Computational Grid 52 30 Erosion Rate (mg/g) 25 20 15 10 Uncoated INCO-718 Coated-TBC 0 10 20 30 40 50 60 70 80 Impingement Angle (deg) Fig.9 Measured erosion rates of coated and uncoated samples (10 mils coating, T = 2,000o F, V= 1,200 ft/s, Qp = gm) Fig 10 Nominally 26 µm alumina particles 53 90 30 25 Erosion Rate (mg/g) 20 15 10 400 ft/s 800 ft/s 1200 ft/s 0 10 20 30 40 50 60 70 80 90 Impingement Angle(deg) Fig 11 TBC Erosion Test Results (10 mils coating, T = 1,800o F, Qp = gm) 25 Erosion Rate (mg/g) 20 15 10 1200 ft/s 800 ft/s 0 10 20 30 40 50 60 70 80 90 Impingement Angle (deg) Fig.12 TBC Erosion Test Results (10 mils coating, T = 1,600o F, Qp = 5gm) 54 30 25 Erosion Rate (mg/g) 20 15 10 mils Coating 10 mils coating 0 10 20 30 40 50 60 70 80 90 Impingement Angle (deg) Fig.13 Comparison of Erosion Test Results for & 10 mil coated samples (T = 2,000 oF, V = 1,200 ft/s, Qp = gm) 25 Erosion Rate (mg/g) 20 15 10 400 ft/s 800 ft/s 1200 ft/s 0 10 20 30 40 50 60 70 80 90 Im pingem ent Angle (degrees) Fig 14 mil TBC Erosion Life Test Results (T = 2,000 oF, Qp = gm) 55 β1 v 1.2 mean ev 0.8 ev = V2/V1 + dev - dev 0.6 0.4 0.2 0 10 20 30 40 50 60 70 80 β (deg.) Fig 15 Variation of Velocity coefficient of β restitution (ev) with impact angle β1 β1 1.4 1.2 eβ = β2/β1 0.8 0.6 Mean eb 0.4 + deb - deb 0.2 0 10 20 30 40 50 60 70 β (DEG) Fig 16 Variation of Direction coefficient (eβ) with Impact angle β1 56 80 Fig 17 Pressure Contours at blade mid-span Fig 18 Mach Contours at blade mid-span 57 Fig 19 Particle Trajectory for 26 μm Alumina Particles 58 Fig 20 Particle Trajectory for 500 μm alumina Particles 59 Fig 21 Schematic of particle size affect on entrance velocity relative to the rotor 60 Fig 22 Erosion pattern for 26 μm alumina particle impacts 61 Fig 23 Erosion pattern for 500 μm alumina particle impacts 62 Over All Erosion Rate Erosion Rate of Stator Erosion Rate of Rotor Erosion Rate (mg/g) 0 10 20 30 40 50 60 Injection velocity as percentage of flow velocity Fig 24 Erosion Rate variation with injection velocity 63 70 80