UTSR Success Stories

UTSR Success Stories

SR100, Virginia Polytechnic Institute

Under a University Turbine Systems Research (UTSR) program, a Virginia Tech (VT) project (SR100) is evaluating various computer simulation algorithms to predict the complex flows and heat transfer for internal cooling channels of turbine airfoils. The project has established that the Large Eddy Simulation (LES) approach can be used for robust, repeatable, and accurate predictions of heat transfer in ribbed cooling channels, such as used in gas turbines. LES has been successfully applied for the first time to develop the detained flow and heat transfer at the entrance and within a 180 degree bend. Detached eddy simulations (DES) were for the first time applied to predict heat transfer in a ribbed channel and shows favorable comparisons with LES but at a much lower computation cost.

The computational advancements achieved in this project have been recognized in an article appearing in the Fall 2004 issue of ACCESS, the publication of the National Center for Supercomputer Applications.

Significance: The VT project is analyzing, developing, and verifying advanced computational techniques for use in improving the cooling design of turbine airfoils. The project has enabled new advances in prediction technology for internal cooling flows. This technology should result in more cost effective design of more efficient cooling of turbines, with corresponding benefits in turbine efficiency and power.

SR098, Louisiana State University

Under the University Turbine Systems Research (UTSR) program, a Louisiana State University (LSU) project (SR098) is evaluating the potential benefits of contouring the end walls of turbine airfoil passages and the using airfoil fillet shaping to control secondary flows and heat transfer to end walls. Experiments and analyses to date have defined an end wall contour that reduces airfoil passage total pressure losses and end wall heat transfer coefficients compared to a baseline case.

Significance: The LSU project is providing turbine engineers with data and analyses for improved strategies to improve aerodynamic efficiency of turbine airfoil passages and reducing the heat load to passage end walls. The resulting designs offer the potential for lower end wall cooling air requirements, with resulting improved fuel efficiency and improved reliability of gas turbines.

SR095, Georgia Institute of Technology

Under the University Turbine Systems Research (UTSR) program, a Georgia Tech (GT) project (SR095) is conducting experiments and analyses to evaluate pressure oscillations in turbine combustors. The project has characterized combustion process non-linearities that determine the amplitude of instabilities, developed and validated models of turbulent flame/acoustic wave interactions that occur during screeching instabilities, and has shown practical control approaches for preventing instabilities. Two promising instability control approaches have been demonstrated in the project. The first provides open loop control of combustion instabilities by fuel injection rate modulation at non-resonant frequencies. The second approach demonstrated inhibition of instabilities by adjusting the inner and outer swirler air flow ratio for a combustor fuel injector.

Significance: Results from the GT project are providing the gas turbine industry with improved understanding and methods of control of the processes that cause combustion instabilities that have resulted in removal of turbines from service due to excess noise and structural damage.

SR096, University of Minnesota

Under the University Turbine Systems Research (UTSR) program, a University of Minnesota (UM) project (SR096) is evaluating contouring of the end wall of transition passages between the turbine combustor and first stage stator vanes for improved end wall cooling and reduced aerodynamic losses in the passage. Cascade tests and computational codes are also being used to identify the aerodynamic and cooling effects of factors such as leakage flows, misalignments that produce steps in the flow boundary, and the slash face gap in the platforms between adjacent vanes.

The project evaluations showed that convex curvature of the end wall stabilizes the boundary layer and reduces the strength of secondary passage flows, thereby reducing aerodynamic losses. Flow leakage through the slash face produced the largest effect (up to 20%) on passage losses of the other passage features that were evaluated. Next in importance is a step in the transition section gap, where a step up on the contoured end wall resulted in a decrease in passage losses.

Significance: The UM project is evaluating effects on aerodynamic performance of transition passage features. The data and analyses will provide turbine engineers with information and data to improve transition passage designs for increased engine performance.

SR103, University of Central Florida

Under the University Turbine Systems Research (UTSR) program, a University of Central Florida (UCF) project (SR103) is evaluating and comparing two non-destructive evaluation (NDE) techniques (photostimulated luminescence spectroscopy and electrochemical impedance spectroscopy) for thermal barrier coatings (TBCs). A range of microstructural analytical techniques is also being developed and used to better understand failure mechanisms of TBCs and develop/refine NDE techniques. These evaluation approaches are being applied to five types of TBCs tested under high temperature thermal cycle conditions and analyzed at 10%, 50% and 70% lifetimes.

Significance: TBCs, originally developed for aircraft turbines with relatively frequent maintenance intervals, have needed durability improvements for the much longer life requirements of land-based turbines. The testing and analyses in this program of a range of TBC types with a wide variety of NDE and analyses techniques is developing a comprehensive set of data and knowledge concerning the fundamental science of thermo-kinetics and thermo-mechanics as a basis for improving TBC durability and reliability.

SR104, Brigham Young University (BYU)

Under the University Turbine Systems Research (UTSR) program, a Brigham Young University (BYU) project (SR104) is measuring surface roughness on airfoils that have operated in turbines, measuring surface roughness on specimens from deposition tests using ash from coal and other alternate fuels, and conducting experiments and computations to determine surface roughness effects on flow shear stress and heat transfer for cooled surfaces.

Significance: Surface roughness of turbine airfoils affects both aerodynamic performance and cooling effectiveness. The experimental and computational roughness characteristics determined in this project are correlated with roughness characteristics from turbine components that have experienced service. Consequently, the verified semi-empirical roughness evolution models to be incorporated into computational codes in the project should provide the gas turbine community with useful predictive capabilities for airfoil aerodynamic and cooling design for operation with conventional and alternate fuels such as coal syngas.

Significant Accomplishments Success Story

RAMGEN has rejoined the IRB as an Associate Member (non voting). RAMGEN is the sixth organization to join the IRB in 2005. This brings the number of IRB Associate Members to 13, in addition to the 5 Voting Members. SCIES has notified applicants to the Fellowship Program that the new companies are part of the IRB for possible assignment in 2005.

SR110, Virginia Polytechnic Institute

Under the University Turbine Systems Research (UTSR) program, a Virginia Tech (VT) project (SR110) is evaluating performance of film cooling for conditions of surface roughness and cooling hole blockage, such as due to deposition and repeated application of thermal barrier coatings. Another focus of the research is effects on film cooling of end wall gaps between adjacent vanes and at the intersection between the combustor sections and first stage vane segments. The research identified a specific gap design configuration between adjacent parts that provides more favorable cooling effects (compared to other designs) from flows passing through the gap between the parts. Experiments using obstructions representing deposits adjacent to cooling holes suggest that, in most cases, film-cooling effectiveness is more sensitive to downstream obstructions (deposits) than upstream obstructions (deposits). Small obstructions have little affect for a cooling hole blowing ratio of 0.4, but obstructions larger than 25% of the cooling hole diameter obliterate the cooling jet and significantly affect cooling performance.

Significance: The VT project is evaluating effects on film cooling performance for turbine passage end walls under roughness and deposit conditions representative of those in syngas turbines. The project has also identified a configuration for end wall gaps between adjacent hot section parts that provides more favorable cooling benefits from gap flows than other configurations, which could aid turbine engineers in the design of end wall gaps.

Significant Accomplishments Success Story

Ingersoll Rand Energy Systems and Capstone Turbines have agreed to join the IRB as Associate Members (non voting). These are the first microturbine manufacturers to participate on the IRB and were encouraged to join by the Energy Efficiency and Renewable Energy (EERE) part of DOE. SCIES provided input to the DOE for a possible Secretary of Energy's Weekly Report describing the benefits of this interagency participation in the UTSR Program. SCIES also notified potential applicants to the Fellowship Program that the two new companies are part of the IRB and will be hosting Fellows in 2005.

SR102, Georgia Institute of Technology

Under the University Turbine Systems Research (UTSR) program, a Georgia Tech (GT) project is developing turbine combustor monitoring techniques. Promise and progress have been demonstrated for two acoustic based techniques, one to monitor turbine combustor stability margin and the other to monitor combustor blowout margin. GT is also evaluating the feasibility of a novel ion sensing approach for blowout detection and is corroborating that approach with the acoustic approach. GT is working closely with Alta Solutions, a turbine monitoring company, to code and test acoustic techniques for monitoring combustion stability and blowout margins. Efforts have started to transition the progress to the field and turbine tests are being planned. Another effort with Woodward Industrial Controls is testing an ion-based technique to detect blow out precursors. This work, partially funded by Woodward, compares acoustic and ion signals from a combustor operating near blowout.

Significance: Low emission turbine combustors operate near their lean blowout limits to minimize NOx. Due to changes in tolerances and characteristics resulting from wear and other hardware degradations, low NOx combustors have needed removal from service caused by unstable oscillations or blowout. The GT technologies are designed to detect impending instabilities or blowout before damage to turbine combustors and are now moving from the laboratory to verification in the field.

SR107, University of Connecticut

Under the University Turbine Systems Research (UTSR) program, a University of Connecticut project (SR107) is developing air plasma sprayed (APS) processes to manufacture thermal barrier coatings (TBC) that are much thicker than TBC than have been produced in the past. Conventional APS coatings are limited to less than 1 mm thickness to prevent premature spontaneous spallation. Using the UCONN process, TBC that are over 3 mm thick have been produced. The coatings have microstructures needed for TBC such as an excellent topcoat-bond coat interface, a uniform and porous microstructure containing through-thickness vertical cracks, and no splat boundaries.

Significance: Thicker TBCs provide increased insulation to turbine parts and enable turbine operation at higher temperatures and performance without requiring additional cooling and associated power and efficiency losses. A goal of the DOE Turbine Program is increased turbine performance.

SR109, Pennsylvania State University

Under the University Turbine Systems Research (UTSR) program, Pennsylvania State University (PSU) is conducting experiments in a laboratory scale combustor to characterize and understand the effects of operating conditions (including fuel composition) on the static (blowout) and dynamic (combustion oscillations) stability of lean-premixed combustors. Experiments to date have explored the role of flame-vortex interactions on instabilities using a variable length combustor. A comprehensive set of data has been obtained at 40 different operating conditions and 28 different combustor lengths, for a total of more than 1000 test conditions. Unstable combustion only occurred for operating conditions where the ratio of vortex travel time to acoustic period (a function of combustor length) was in the range from about 0.2 to 0.4. There was also stable operation at some conditions within this range. Further analysis of the data is in progress to determine bounds that expand the prediction capabilities to identify design parameters for stable operation.

Significance: Gas turbine combustors are designed for lean-premixed operation, which results in relatively low flame temperatures that limit NOx emissions. However, the combustors operate near their lean limits for blowout where damaging oscillations can occur. Such oscillations have caused excessive noise and structural damage due to vibrations and resulting forced shut downs of turbines in the field. Although turbine manufacturers are developing combustor design approaches to alleviate blowout and instabilities, additional research is needed to improve design methods, especially for variability and different composition for syngas compared to conventional fuels. The PSU project is identifying stable/unstable boundaries for design parameters that should enable engineers to produce more stable, higher performance low emission turbine combustors.

SR106, Cleveland State University

Under the University Turbine Systems Research (UTSR) program, Cleveland State University (CSU) is evaluating methods for in-situ, real time monitoring of the deterioration of thermal barrier coatings (TBC) operating in gas turbines. The CSU approach is to dope the TBC with marker materials that are released as the TBC degrades and can be monitored optically in the combustion stream or turbine exhaust. Measurements of the gas stream concentrations of the marker materials are used to infer the mechanical condition and deterioration of the TBC. To date, the CSU project has identified lithium oxide as a promising marker material for TBCs. Lithium oxide was determined to be chemically compatible with primary TBC components. Experiments showed that the extent of cracking and spallation of a lithium oxide doped coating were correlated with lithium spectral density measurements.

Significance: Initial evaluations in the first year of the three year CSU project indicate the potential for doping TBC with a material that is released into the turbine stream and optically measured to detect and track TBC degradation without taking turbines out of service.

SR101, University of Pittsburgh

Under the University Turbine Systems Research (UTSR) program, the University of Pittsburgh (PITT) is evaluating process and compositional modifications for thermal barrier coatings (TBCs) for improved resistance to cyclic oxidation, hot corrosion, and impact/erosion. PITT is also shown progress for non-destructive evaluations (NDE) of TBCs involving improvement of a NASA life prediction model using acoustic emissions data as input.

Significance: The close collaboration between PITT, other universities, national laboratories, industrial coating manufacturers and users in this project is advancing the definition and development of more durable TBCs operating in harsh environments such as in syngas turbines. NDE tests lifetime prediction models are being defined to assess the condition of TBCs before failure.

SR102, Georgia Institute of Technology

Under the University Turbine Systems Research (UTSR) program, Georgia Tech (GT) University is developing sensing strategies to monitor turbine combustor health and performance. Based on project results, GT has filed a patent disclosure for a method to monitor pressure or heat release data to determine the stability margin of gas turbine combustors and thereby enable plant operators to avoid excessive noise, structural failures, and forced removal of turbines from service from instabilities such as have occurred in the past for low emissions combustors.

Significance: Low emissions combustors operate at conditions near their lean blowout limits to reduce combustion temperatures and consequently inhibit the formation of thermal NOx. However, combustion instabilities have occurred in low NOx turbine combustors due to changes in ambient conditions and systems degradation (e.g., wear). Currently, turbine operators have little idea how the stability of the combustors are changing during operation until the system actually becomes unstable which could result in flame blowout and complete system shutdown.

SR097, University of Connecticut

Under the University Turbine Systems Research (UTSR) program, a University of Connecticut project is investigating non-destructive methods to detect internal damage and predict remaining life of thermal barrier coatings (TBC) used to insulate turbine parts from high temperatures. The project is developing photo-stimulated luminescence piezo spectroscopy (PLPS) to measure stresses within TBC produced by the electron beam, physical vapor deposition process. Coated specimens are exposed to thermal cycling at turbine temperatures and remaining lifetimes of the coatings are correlated with the measured stress levels. The project has determined that remaining life of the coating correlates with stress level measured by PLPS and is nearly independent of the cycle temperature. The time duration of the thermal cycles only moderately affected the relationship between remaining coating life and measured stress levels. The data showed that measured stress level at failure was consistent to within 6.7% for all temperatures and thermal cycle times used in the experiments.

Significance: The development of non-destructive methods to determine remaining life of TBC during turbine inspections will reduce unplanned shutdowns due to coating failures or needlessly removing parts with acceptable coatings on a statistical basis to prevent failures. Research in the UCONN project shows that the PLPS method of measuring stresses within TBC offers promise for a relatively simple non-destructive approach to determine remaining life while requiring minimal or no knowledge or monitoring of the histories of part temperature or thermal cycling.

SR094, Texas A&M University

Under the University Turbine Systems Research (UTSR) program, a Texas A&M (TAM) project is investigating methods to improve cooling performance for turbine airfoil vanes and blades. Various rib configurations to increase turbulence within internal airfoil cooling channels and thereby improve cooling effectiveness for stationary and rotating airfoils are being explored both experimentally and computationally. An improved computational model has been shown to provide much better flow and heat transfer predictions than the standard turbulence model for rotating cooling channels with angled ribs to enhance turbulence. The project has also shown that (compared to W-shaped ribs, discrete W-shaped ribs and angled ribs), discrete V-shaped ribs provide the best overall thermal performance in both rotating and stationary cooling channels.

Significance: Improvements in the effectiveness of internal cooling enables use of less cooling air to sustain acceptable vane and blade materials temperatures and life with lower turbine power and efficiency penalties associated with cooling. The TAM project is providing turbine engineers with design data on the best internal cooling channel features to enhance turbulence and reduce the amount of cooling air needed to achieve specified surface temperatures for both stationary vanes and rotating blades. The numerical computer models being developed in this project will also provide computational tools for improved cooling design of vanes and blades.

SR105, University of Wisconsin

Under the University Turbine Systems Research (UTSR) program, a University of Wisconsin (UW) project has the goal of developing fiber-optic sensors for monitoring gas temperature profiles and blade surface temperatures in turbine engines. Significant progress in this project in less than one year since award includes interaction with several gas turbine companies to identify an acceptable means of fiber-optic access to turbine combustors and hot sections and development of a novel laser system that is well-suited to the challenging sensing task. The sensing system can produce >1mW of specialty wavelength agile laser light on each of 64 sensing optic fibers that penetrate into the engine and deliver and receive laser light. The project has also produced a computer algorithm for rapidly processing the optical data to determine the gas temperatures at each sensed location.

A strategy for blade temperature measurements with the optical sensor has also been advanced. Optic fibers will be embedded into micro-drilled holes in turbine blades for point measurements of local metal temperatures.

Significance: Turbine inlet gas temperature is a main determinant of performance (power and fuel efficiency). The gas temperature profile and airfoil surface temperatures are import factors affecting vane and blade lifetimes. Success in the UW project could provide instrumentation to diagnose performance and life for new engine designs and could later be integrated into production engines to enable active, real time control of temperature distributions to fine tune engine performance and improve lifetimes.

SR103, University of Central Florida

Under the University Turbine Systems Research (UTSR) program, a University of Central Florida (UCF) project has the goal of verifying two complementary techniques for non-destructive evaluation (NDE) and investigation of sources of failure for thermal barrier coatings (TBC). Experiments have included thermal cycling to failure at turbine temperatures of specimens representing all five TBC types and monitoring the specimen status with the two NDE techniques. Early results during the first year of the three-year UCF project have shown that one of the NDE techniques can monitor micro-structural changes leading to failure of one TBC type. The potential to monitor critical micro-structural changes (sintering of the TBC, growth of an interface oxide scale, and progressing internal damage leading to failure) has been shown for other TBC types using the second NDE technique. The data are also leading to a better understanding of sources of failure for TBCs.

Significance: Thermal barrier coatings, along with advanced cooling techniques, have been the two most important technologies that have enabled turbines to operate at increasing operating temperatures and resulting increased performance (greater power output and fuel efficiency) with time. However, the full potential of TBCs has not been realized because of their limited durability and inconsistency of life. Consequently, development of improved non-destructive evaluation (NDE) techniques has been needed to improve TBC production processes, evaluate TBC quality before placing coated parts into a turbine, monitor remaining coating lifetimes during turbine inspections, and to improve understanding of TBC degradation processes. The UCF project is advancing new NDE techniques for such TBC benefits.

SR112, University of California, Irvine

Lean premixed combustors have been widely used to control turbine NOx emissions from natural gas fuels. For these combustors, the fuel must be uniformly mixed under lean conditions in a pre-mixer upstream of the primary combustion zone to achieve relatively low primary combustion temperatures and consequently low emissions. The pre-mixer must be designed for the fuel residence time to be sufficiently long for thorough mixing (needed for low NOx) but not so long as to result in damaging autoignition within the pre-mixer. Autoignition depends on the fuel chemistry and pre-mixer operating conditions. Little quantitative autoignition data are available for compositions of syngas and hydrogen bearing (SGH) fuels at pre-mixer conditions.

Under the University Turbine Systems Research (UTSR) program, the University of California at Irvine (UCI) project has the goal of establishing design guidelines for avoiding premature autoignition and flashback from SGH fuels in lean premixed combustion systems. Chemical kinetic computer calculations and experiments are to be used to determine ignition delay times for compositions representative of SGH fuels. In the initial six months of the project, an existing experimental facility is being upgraded to simulate conditions (up to 18 atmospheres pressure and 1400 F temperature) of turbine combustor pre-mixers. Initial computer calculations of ignition delay times for SGH fuel compositions have shown that ignition delay is significantly shorter for the hydrogen in SGH fuels compared to natural gas. This indicates a challenge for the design of low emission SGH combustors.

Significance: Current syngas turbines rely on water or steam injection to reduce combustion temperatures to achieve low NOx emissions. The resulting higher mass flows and water vapor levels in the combustion products increase heat transfer to turbine vanes and blades so that the inlet temperatures of current syngas turbines are lowered to achieve adequate lifetimes. This results in decreased fuel efficiency for current syngas plants. Data obtained in the UCI project might facilitate lean premixed combustion that could reduce or eliminate water/steam injection to enable increased plant performance.

Thermal barrier coatings (TBC) insulate turbine metal surfaces to reduce cooling requirements and thereby improve turbine power and efficiency. Originally developed for aircraft turbines, TBC use in utility and industrial turbines with much longer life requirements has been impeded because of a lack in necessary service durability and reliability.

Under the University Turbine Systems Research (UTSR) program, the University of Connecticut (UCONN), working with the University of Pittsburgh and the University of Central Florida, have conducted experiments and analyses to determine TBC manufacturing process approaches to improve life. Six industrial partners have also participated in the project.

Significance: This university project has demonstrated that more than a factor of three times increase in TBC spallation life can be achieved by i) media finishing the TBC bond coat to make it as smooth as possible, ii) pre-oxidizing the smooth bond coat to form a thin, continuous alpha alumina layer prior to depositing the outer ceramic layer, and iii) by using bond coats containing silicon and hafnium for improved long term adherence of the bond coat.