Gas Turbine Heat Transfer Research Articles

Liquid Crystal Thermography in Gas Turbine Heat Transfer: A Review on Measurement Techniques and Recent Investigations

Liquid Crystal Thermography is a widely used experimental technique in the gas turbine heat transfer community. In turbine heat transfer, determination of the convective heat transfer coefficient (h) and adiabatic film cooling effectiveness (η) is imperative in order to design hot gas path components that can meet the modern-day engine performance and emission goals. LCT provides valuable information on the local surface temperature, which is used in different experimental methods to arrive at the local h and η. The detailed nature of h and η through LCT sets it apart from conventional thermocouple-based measurements and provides valuable insights into cooling designers for concept development and its further iterations. This article presents a comprehensive review of the state-of-the-art experimental methods employing LCT, where a critical analysis is presented for each, as well as some recent investigations (2016–present) where LCT was used. The goal of this article is to familiarize researchers with the evolving nature of LCT given the advancements in instrumentation and computing capabilities, and its relevance in turbine heat transfer problems in current times.

Advanced Cooling in Gas Turbines 2016 Max Jakob Memorial Award Paper

Gas turbines have been extensively used for aircraft engine propulsion, land-based power generation, and industrial applications. Power output and thermal efficiency of gas turbines increase with increasing turbine rotor inlet temperatures (RIT). Currently, advanced gas turbines operate at turbine RIT around 1700 °C far higher than the yielding point of the blade material temperature about 1200 °C. Therefore, turbine rotor blades need to be cooled by 3–5% of high-pressure compressor air around 700 °C. To design an efficient turbine blade cooling system, it is critical to have a thorough understanding of gas turbine heat transfer characteristics within complex three-dimensional (3D) unsteady high-turbulence flow conditions. Moreover, recent research trend focuses on aircraft gas turbines that operate at even higher RIT up to 2000 °C with a limited amount of cooling air, and land-based power generation gas turbines (including 300–400 MW combined cycles with 60% efficiency) burn alternative syngas fuels with higher heat load to turbine components. It is important to understand gas turbine heat transfer problems with efficient cooling strategies under new harsh working environments. Advanced cooling technology and durable thermal barrier coatings (TBCs) play most critical roles for development of new-generation high-efficiency gas turbines with near-zero emissions for safe and long-life operation. This paper reviews basic gas turbine heat transfer issues with advanced cooling technologies and documents important relevant papers for future research references.

천이 열전달 측정 실험에서 3차원 전도 효과의 보정

Accurate heat transfer coefficient measurement of gas turbine component is very important for heat transfer design of components exposed to high temperature. Transient heat transfer measurement method with one-dimensional semi-infinite solid model assumption has been widely applied to gas turbine heat transfer studies for the last decades because it dose not require complex boundary conditions. But there are several defect in the technique caused by the 1D heat transfer assumption. In this paper, various analysis were performed to investigate the 3D conduction effect in each technique and introduced better model which can minimize the 3D conduction effect.

Flow and Heat Transfer Analysis in a Single Row Narrow Impingement Channel: Comparison of Particle Image Velocimetry, Large Eddy Simulation, and RANS to Identify RANS Limitations

The present study aims to understand the flow, turbulence, and heat transfer in a single row narrow impingement channel for gas turbine heat transfer applications. Since the advent of several advanced manufacturing techniques, narrow wall cooling schemes have become more practical. In this study, the Reynolds number based on jet diameter was ≃15,000, with the jet plate having fixed jet hole diameters and hole spacing. The height of the channel is three times the impingement jet diameter. The channel width is four times the jet diameter of the impingement hole. The dynamics of flow and heat transfer in a single row narrow impingement channel are experimentally and numerically investigated. Particle image velocimetry (PIV) was used to reveal the detailed information of flow phenomena. PIV measurements were taken at a plane normal to the target wall along the jet centerline. The mean velocity field and the turbulent statistics generated from the mean flow field were analyzed. The experimental data from the PIV reveal that the flow is highly anisotropic in a narrow impingement channel. To support experimental data, wall-modeled large eddy simulation (LES) and Reynolds-averaged Navier–Stokes (RANS) simulations (shear stress transport k–ω, ν2−f, and Reynolds stress model (RSM)) were performed in the same channel geometry. Mean velocities calculated from the RANS and LES were compared with the PIV data. Turbulent kinetic energy budgets were calculated from the experiment, and were compared with the LES and RSM model, highlighting the major shortcomings of RANS models to predict correct heat transfer behavior for the impingement problem. Temperature-sensitive paint (TSP) was also used to experimentally obtain a local heat transfer distribution at the target and the side walls. An attempt was made to connect the complex aerodynamic flow behavior with the results obtained from heat transfer, indicating heat transfer is a manifestation of flow phenomena. The accuracy of LES in predicting the mean flow field, turbulent statistics, and heat transfer is shown in the current work as it is validated against the experimental data through PIV and TSP.

Stagnation Region Heat Transfer Augmentation at Very High Turbulence Levels

Current land-based gas turbines are growing in size producing higher approach flow Reynolds numbers at the leading edge of turbine nozzles. These vanes are subjected to high intensity large scale turbulence. This present paper reports on the research which significantly expands the parameter range for stagnation region heat transfer augmentation due to high intensity turbulence. Heat transfer measurements were acquired over two constant heat flux test surfaces with large diameter leading edges (10.16 cm and 40.64 cm). The test surfaces were placed downstream from a new high intensity (17.4%) mock combustor and tested over an eight to one range in approach flow Reynolds number for each test surface. Stagnation region heat transfer augmentation for the smaller (ReD = 15,625–125,000) and larger (ReD = 62,500–500,000) leading edge regions ranged from 45% to 81% and 80% to 136%, respectively. These data also include heat transfer distributions over the full test surface compared with the earlier data acquired at six additional inlet turbulence conditions. These surfaces exhibit continued but more moderate acceleration downstream from the stagnation regions and these data are expected to be useful in testing bypass transition predictive approaches. This database will be useful to gas turbine heat transfer design engineers.

Build Direction Effects on Additively Manufactured Channels

With the advance of direct metal laser sintering (DMLS), also generically referred to as additive manufacturing (AM), novel geometric features of internal channels for gas turbine cooling can be achieved beyond those features using traditional manufacturing techniques. There are many variables, however, in the DMLS process that affect the final quality of the part. Of most interest to gas turbine heat transfer designers are the roughness levels and tolerance levels that can be held for the internal channels. This study investigates the effect of DMLS build direction and channel shape on the pressure loss and heat transfer measurements of small-scale channels. Results indicate that differences in pressure loss occur between the test cases with differing channel shapes and build directions, while little change is measured in heat transfer performance.

Flow Visualization of Multi-Hole Film-Cooling Flow under Varying Freestream Turbulence Levels

A flat plate film cooling flow from a multi-exit hole configuration has been numerically simulated using both steady and unsteady Reynolds Averaged Navier Stokes (RANS and URANS) Computational Fluid Dynamics (CFD) formulations. This multi-exit hole concept, the Anti-Vortex Hole (AVH), has been developed and studied by previous research groups and shown to mitigate or counter the vorticity generated by conventional holes resulting in a more attached film cooling layer and higher film cooling effectiveness. The film cooling jets interaction with the free stream flow is a long studied area in gas turbine heat transfer. The present study numerically simulates the jet interaction with the multi-exit hole concept at a high blowing ratio (M = 2.0) and density ratio (DR = 2.0) in order to provide a more detailed, graphical explanation of the improvement in film cooling effectiveness. This paper presents a numerical study of the flow visualization of the interaction of film cooling jets with a subsonic crossflow. The contour plots of adiabatic cooling effectiveness were used to compare the multi-exit hole and conventional single hole configurations. The vortex structures in the flow were analyzed by URANS formulations and the effect of these vortices on the cooling effectiveness was investigated together with the coolant jet lift-off predictions. Quasi-Instantaneous Temperature Isosurface plots are used in the investigations of the effect of turbulence intensity on the cooling effectiveness and coolant jet coverage. The effect of varying turbulence intensity was investigated when analyzing the jets’ interaction with the cross flow and the corresponding temperatures at the wall. The results show that as the turbulence intensity is increased, the cooling flow will stay more attached to the wall and have more pronounced lateral spreading far downstream of the cooling holes.

History of Short-Duration Measurement Programs Related to Gas Turbine Heat Transfer, Aerodynamics, and Aeroperformance at Calspan and The Ohio State University

Short-duration facilities have been used for the past 35 years to obtain measurements of heat transfer, aerodynamic loading, vibratory response, film-cooling influence, purge flow migration, and aeroperformance for full-stage, high-pressure turbines operating at design-corrected conditions of flow function, corrected speed, and stage pressure ratio. This paper traces the development of experimental techniques now in use at The Ohio State University (OSU) Gas Turbine Laboratory (GTL) from initial work in this area at the Cornell Aeronautical Laboratory (CAL, later to become Calspan) from 1975 through to the present. It is intended to summarize the wide range of research that can be performed with a short-duration facility and highlight the types of measurements that are possible. Beginning with heat flux measurements for the vane and blade of a Garrett TFE 731-2 HP turbine stage with vane pressure-surface slot cooling, the challenge of each experimental program has been to provide data to aid turbine designers in understanding the relevant flow physics and help drive the advancement of predictive techniques. Through many different programs, this has involved collaborators at a variety of companies and experiments performed with turbine stages from Garrett, Allison, Teledyne, Pratt and Whitney (P/W), General Electric Aviation (GEA), Rocketdyne, Westinghouse, and Honeywell. The vane/blade interaction measurement and computational fluid dynamics (CFD) program, which ran from the early 1980s until 2000, provided a particularly good example of what can be achieved when experimentalists and computational specialists collaborate closely. Before conclusion of this program in 2000, the heat flux and pressure measurements made for this transonic turbine operated with and without vane trailing edge cooling flow were analyzed and compared to predictive codes in conjunction with engineers at Allison, United Technologies Research Center (UTRC), P/W, and GEA in jointly published papers. When the group moved to OSU in 1995 along with the facility used at Calspan, refined techniques were needed to meet new research challenges, such as investigating blade-damping and forced response, measuring aeroperformance for different configurations, and preparing for advanced cooling experiments that introduced complicating features of an actual engine to further challenge computational predictions. This required conversion of the test-gas heating method from a shock-tunnel approach to a blowdown approach using a combustor emulator to also create inlet temperature profiles, the development of instrumentation techniques to work with a thin-walled airfoil with backside cooling, and the adoption of experimental techniques that could be used to successfully operate fully cooled turbine stages (vane row-cooled, blade row-cooled, and proper cavity purge flow provided). Further, it was necessary to develop techniques for measuring the aeroperformance of these fully cooled machines.

Fundamental Gas Turbine Heat Transfer

Gas turbines are used for aircraft propulsion and land-based power generation or industrial applications. Thermal efficiency and power output of gas turbines increase with increasing turbine rotor inlet temperatures (RIT). Current advanced gas turbine engines operate at turbine RIT (1700 °C) far higher than the melting point of the blade material (1000 °C); therefore, turbine blades are cooled by compressor discharge air (700 °C). To design an efficient cooling system, it is a great need to increase the understanding of gas turbine heat transfer behaviors within complex 3D high-turbulence unsteady engine-flow environments. Moreover, recent research focuses on aircraft gas turbines operating at even higher RIT with limited cooling air and land-based gas turbines burn coal-gasified fuels with a higher heat load. It is important to understand and solve gas turbine heat transfer problems under new harsh working environments. The advanced cooling technology and durable thermal barrier coatings play critical roles for the development of advanced gas turbines with near zero emissions for safe and long-life operation. This paper reviews fundamental gas turbine heat transfer research topics and documents important relevant papers for future research.

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Preface: Gas Turbine Heat Transfer

Impulse Response Processing of Transient Heat Transfer Gauge Signals

A new, computationally efficient method is presented for processing transient thin-film heat transfer gauge signals. These gauges are widely used in gas turbine heat transfer research, where, historically, the desired experimental heat transfer flux signals, q, are derived from transient measured surface-temperature signals, T, using numerical approximations to the solutions of the linear differential equations relating the two. The new method uses known pairs of exact solutions, such as the T response due to a step in q, to derive a sampled approximation of the impulse response of the gauge system. This impulse response is then used as a finite impulse response digital filter to process the sampled T signal to derive the required sampled q signal. This is computationally efficient because the impulse response need only be derived once for each gauge for a given sample rate, but can be reused repeatedly, using optimized MATLAB filter routines and is highly accurate. The impulse response method can be used for most types of heat flux gauge. In fact, the method is universal for any linear measurement systems which can be described by linear differential equations where theoretical solution pairs exist between input and output. Examples using the new method to process turbomachinery heat flux signals are given.

Comparison of Heat Transfer Augmentation Techniques

Dr. Phil Ligrani is currently of Mechanical Engineering and Director of the Convective Heat Transfer Laboratory at the University of Utah and a Fellow of the American Society of Mechanical Engineers. He has beenworking on convection heat transfer and fluid mechanics research problems since he received his Ph.D. degree from the Department of Mechanical Engineering at Stanford University in 1980. From 1979 to 1982, he was an Assistant in the Turbomachinery Department of the von Karman Institute for Fluid Dynamics, Rhode-Saint-Genese, Belgium. From 1982 to 1984, he worked in the Department of Aeronautics of the Imperial College of Science and Technology, University of London. From 1984 to 1992, he was an Associate in the Department of Mechanical Engineering of the U.S. Naval Postgraduate School. In his research, he has investigated the ultra-small-scale motions that exist near walls in turbulent boundary layers, the effects of surface roughness on turbulent boundary layers, transitional phenomena in curved channels including the development and structure of Dean vortex pairs, and innovative schemes for internal cooling and surface heat transfer augmentation, such as dimpled surfaces and swirl chambers, as well as a variety of gas turbine heat transfer and blade cooling problems. He served as Guest Editor for the journal Measurement Science and Technology from 1998 to 2000, and he will serve as Associate Technical Editor for the Journal of Heat Transfer from 2003 to 2006. He has published approximately 150 journal papers, conference papers, and book chapters. In 1995, he was presented with the Professor of the Year award at the University of Utah for outstanding classroom teaching. Some of his other activities and recognitions include a Guest Professorship in 2000 at the Institut fur Thermische Stroemungs-maschinen-Universitaet Karlsruhe, a Visiting Senior Research Fellowship from 1982 to 1983 at the Imperial College of Science and Technology-University of London, a NASA Space Act Tech Brief Award in 1991 for Development of Subminiature Multi-Sensor Hot-Wire Probes, and the Carl E. and Jessie W. Menneken Faculty Award in 1990 for Excellence in Scientific Research. E-mail: ligrani@mech.utah.edu.

Studies on free stream turbulence as related to gas turbine heat transfer. A review of authors' past work and future implications.

A review of the past work done on free stream turbulence (FST) as applied to gas turbine heat transfer and its implications for future studies are presented. It is a comprehensive approach to the results of many individual studies in order to derive the general conclusions that could be inferred from all rather than discussing the results of each individual study. Three experimental and four modeling studies are reviewed. The first study was on prediction of heat transfer for film cooled gas turbine blades. An injection model was devised and used along with a 2-D low Reynolds number k-epsilon model of turbulence for the calculations. Reasonable predictions of heat transfer coefficients were obtained for turbulence intensity levels up to 7%. Following this modeling study a series of experimental studies were undertaken. The objective of these studies was to gain a fundamental understanding of mechanisms through which FST augments the surface heat transfer. Experiments were carried out in the boundary layer and in the free stream downstream of a gas turbine combustor simulator, which produced initial FST levels of 25.7% and large length scales (About 5-10 cm for a boundary layer 4-5 cm thick). This result showed that one possible mechanism through which FST caused an increase in heat transfer is by increasing the number of ejection events. In a number of modeling studies several well-known k-epsilon models were compared for their predictive capability of heat transfer and skin friction coefficients under moderate and high FST. Two data sets, one with moderate levels of FST (about 7%) and one with high levels of FST (about 25%) were used for this purpose. Although the models did fine in their predictions of cases with no FST (baseline cases) they failed one by one as FST levels were increased. Under high FST (25.7% initial intensity) predictions of Stanton number were between 35-100% in error compared to the measured values. Later a new additional production term indicating the interaction between the turbulent kinetic energy (TKE) and mean velocity gradients was introduced into the TKE equation. The predicted results of skin friction coefficient and Stanton number were excellent both in moderate and high FST cases. In fact these model also gave good predictions of TKE profiles whereas earlier unmodified models did not predict the correct TKE profiles even under moderate turbulence intensities. Although this new production term seems to achieve the purpose, it is the authors' belief that it is diffusion term of the TKE equation, which needs to be modified in order to fit the physical events in high FST boundary layer flows. The results of these studies are currently being used to come up with new diffusion model for the TKE equation.

Gas Turbine Heat Transfer: Past and Future Challenges

The demand for gas turbines with increasing power and efe ciency calls for extremely high temperatures in the hot-gas sections of the engines. These temperatures can only be realized by employing sophisticated cooling schemes. Inadequate cooling may result in excessive material temperatures with reduced reliability and a lifetime of those parts subjected to the hot gas. Based on a survey of the different cooling techniques employed in modern gasturbineenginesandtheirapplicationin gasturbinecombustors, aswellasturbinecomponents,modernaspects and future developments are discussed. Results from laboratory experiments that help to understand the physical phenomena arepresented, as well as theoretical analyses. Thepossibleuse of ceramicmaterialsisdemonstrated by means of tests carried out at the Institut f ¨ ur Thermische Str ¨ omungsmaschinen, University of Karlsruhe. Besides describing current techniques, new developments are assessed and goals for future research are discussed.

Prediction of Unsteady Rotor-Surface Pressure and Heat Transfer From Wake Passings

The research described in this paper is a numerical investigation of the effects of unsteady flow on gas turbine heat transfer, particularly on a rotor blade surface. The unsteady flow in a rotor blade passage and the unsteady heat transfer on the blade surface as a result of wake/blade interaction are modeled by the inviscid flow/boundary layer approach. The Euler equations that govern the inviscid flow are solved using a time-accurate marching scheme. The unsteady flow in the blade passage is induced by periodically moving a wake model across the passage inlet. Unsteady flow solutions in the passage provide pressure gradients and boundary conditions for the boundary-layer equations that govern the viscous flow adjacent to the blade surface. Numerical solutions of the unsteady turbulent boundary layer yield surface heat flux values that can then be compared to experimental data. Comparisons with experimental data show that unsteady heat flux on the blade suction surface is well predicted, but the predictions of unsteady heat flux on the blade pressure surface do not agree.