bluuebunny/crossref_metadata_2025 huggingface dataset:
A Fractional-Factorial Investigation of the Design Parameters Affecting the Performance of a Pyrometer Purge Air System
Authors: Kerr Clive I. , Ivey Paul C.
Published: February 2009

One of the most strategically important devices within the field of gas turbine instrumentation is the optical pyrometer for turbine blade temperature measurement. With this instrument, the greatest operational problem is the optical fouling of its lens and the associated design problem is to fit the device within a given size envelope without adversely comprising the effectiveness of the purge air system. Consequently, a statistical-numerical investigation using the design of experiments approach was conducted by utilizing computational fluid dynamics (CFD) techniques to study the trade-offs in purge system design. This paper reports on the study carried out to determine the relative effects of the main geometrical design parameters on the performance of a purge air system using a two-level fractional factorial experiment.
Fast Response Probes Measuring Unsteady Flows in High-Speed Research Compressors
Authors: Georgakis C. , Bennett I. , Ivey P. C.
Published: February 2009

It is well recognised that multi-sensor fast response probes are widely used on several applications concerning unsteady flow measurements. Often the size of these probes is larger than ideal. It is probably this reason that the single sensor probes are sometimes preferred in the survey of the unsteady flows in the turbomachinery applications. This in turn can be of benefit due to the limited space often found in compressors. The advent of these miniature probes has been made possible due to the availability of small sensors capable of withstanding relatively high temperatures. There is no doubt that as the technology improves, the size of the probes is likely to be reduced. This will make it possible to use these probes in lower cost, smaller scale facilities. The behavior of a fast response probe is examined in detail prior to the presentation of a set of unsteady measurements acquired near the impeller tip region. The data obtained from the calibration routine is then compared with the actual measurements. Errors that could possibly be arising due to temperature drift of the sensor are taken into account and reduced to a minimum. The fast response probe is largely sensitive to pressure fluctuations that, after correction with temperature, result in an actual pressure reading. The sensitivity of the probe has proved to be adequate for measurement of flow direction and total pressure over a broad angular range. The simple geometry and small size of the probe contributes to a reduction in the blockage effects, the enhancement of the near wall measurements, the reduction of the run-time costs, and raise the confidence in the experiment. This fast response probe was extensively used to traverse the blade passage width. Detailed measurements clearly showed that strong pulsations dominate the distorted impeller exit flow.
A Multi-Component and Multi-Disciplinary Student Design Project Within an International Academic and Industrial Collaboration
Authors: Mund Friederike C. , Kalfas Anestis I. , Abhari Reza S. , Turcan Yasemin , Hourmouziadis Jean , Tre´binjac Isabelle , Vouillarmet Andre´
Published: February 2009

The design of modern aircraft engines increasingly involves highly sophisticated methodologies to match the current development pace. International company relations affect the collaboration between design offices all around the world. An important part of academic mission of modern engineering education is to produce graduates with skills compatible with industrial needs. Education may readjust accordingly to meet the higher requirements. However, a realistic scenario of the design process of an aircraft engine cannot possibly be transferred one-to-one into the student education process. A unique attempt to overcome this discrepancy was the International Gas Turbine Project. Within this project, undergraduate students have designed the cooling system of the HPT blades for a 30,000 lb thrust two-spool turbofan aeroengine. This project was collaboration between the Jet Propulsion Laboratory of TU Berlin, the Turbomachinery Group of EC Lyon and the Turbomachinery Laboratory of ETH Zurich. It also involved mentoring industry professionals from Rolls-Royce Deutschland, MTU, SNECMA and Alstom Power. Similar to modern aeroengine company structures, the design tasks included multi-component, multi-disciplinary and international interfaces of different educational systems. The student teams considered various aerothermodynamic and mechanical integrity aspects of the design. Particular attention was paid to design of the compressor, the secondary air system and the HP turbine including blade cooling. The three Universities integrated the project differently into their education curriculum and approached the tasks with different levels of software involvement. In this paper, the technical details of the design process, and the different approaches adopted are presented. Besides the application of turbomachinery-related knowledge, the impact of student interactions on the technical aspects of the project is discussed. The interfaces, including information management and the involvement of industrial partners are also addressed. Team spirit developed between the students from an initial competitive behavior to a final feeling of sitting in the same boat. It was observed that increased effort was required from academic staff in comparison to the conventional academic instruction. Nevertheless, students greatly benefited from the social interaction and an early training-on-the-job tuned to current industrial needs.
Gas Turbine Simulations in the Computerized Educational Program CompEduHPT: Educational Aspects
Authors: Salomo´n Marianne , Fridh Jens , Kessar Alexandros , Fransson Torsten
Published: February 2009

In the winter 1813–1814 I attended a mathematical school kept in Boston ... on entering his room, we were struck at the appearance of an ample Blackboard suspended on the wall, with lumps of chalk on a the ledge below, and cloths hanging at either side. I never heard such a thing before. The introduction of computerized presentation techniques and overheads has also changed the teaching process as the blackboard did it on the 19th century. Computerized techniques have made possible showing the students more material related with the specific subject. Special videos, simulations and other multimedia tools represent one of the most relevant changes in the traditional learning. Simulations enable the students to familiarize themselves with the topic and highlight the key parameters as well as their influence. Several simulations have been included in the Computerized Educational Platform (CompEduHPT) together with theory and other educational features. These simulations constitute an alternative way to learn, based on discovery and experience. It is important to realize that the simulations are only a part of the package of learning. All the simulations are preceded with theory chapters, quizzes and preparatory tasks to enable fruitful exercises to be designed, including the simulations. Furthermore, the majority of these simulations are supported by a “guide” that provides help advising the student on how to perform the simulation and inviting him/her to analyze the changes every time that the student clicks on it based on the theory given in the chapters. This creates a completely integrated educational tool designed to enhance the learning of students involved in gas turbine technology courses either at the campus or as distant learners. A variety of simulations exist, stretching from simulated basic physical phenomena to complete cycle simulations. The Gas Turbine related simulations comprise for example a number of ideal and real gas turbine cycles, basic two-dimensional velocity triangle simulations as well as aerodynamic design of turbomachines and aeroelasticity simulations. One of the objectives of this paper is to show the potential of integrating the simulations in the learning process and the possible ways to overcome some of the obstacles by using tools already available and designed to enhance the learning process such as CompEduHPT. Evaluations show that simulations are appreciated among the students as an aid to grasp the general physical understanding of formulas and theory enhancing the learning process. The learning method and learning pace are highly valued among the students, which indicates that a computerized program including multiple ways of learning may be of considerable support to the more conventional and personal student-teacher way of learning.
A New Concept of Impingement Cooling for Gas Turbine Hot Parts and Its Influence on Plant Performance
Authors: Facchini B. , Surace M. , Zecchi S.
Published: February 2009

Significant improvements in gas turbine cooling technology are becoming harder as progress goes over and over. Several impingement cooling solutions have been extensively studied in past literature. An accurate and extensive numerical 1D simulation on a new concept of sequential impingement was performed, showing good results. Instead of having a single impingement plate, we used several perforated plates, connecting the inlet of each one with the outlet of the previous one. Main advantages are: absence of the negative interaction between transverse flow and last rows impinging jets (reduced deflection); better distribution of pressure losses and heat transfer coefficients among the different plates, especially when pressure drops are significant and available coolant mass flow rate is low (lean premixed combustion chamber and LP turbine stages). Practical applications can have a positive influence on both cooled nozzles and combustion chambers, in terms of increased cooling efficiency and coolant mass flow rate reduction. Calculated effects are used to analyze main influences of such a cooling system on global performances of power plants.
Modelling of Circumferential Modal Coupling Due to Helmholtz Resonators
Authors: Stow Simon R. , Dowling Ann P.
Published: February 2009

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. Acoustic waves produce fluctuations in heat release, for instance by perturbing the fuel-air ratio or flame shape. These heat fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. A linear model for thermoacoustic oscillations in LPP combustors is described. A thin annular geometry is assumed and so circumferential modes are included but radial dependence is ignored. The formulation is in terms of a network of modules such as straight ducts and area changes. At certain operating conditions, the flow is predicted to be unstable, with linear waves growing in amplitude. Helmholtz resonators can be used to absorb acoustic energy and, when carefully designed and installed at appropriate locations, can stabilise the flow. Helmholtz resonators are included in the model. Connecting a Helmholtz resonator to an annular duct destroys the axisymmetry of the geometry. This results in coupling of the circumferential modes which must be calculated. The model is used to investigate the best arrangement of resonators around the circumference of an annular duct to achieve maximum damping of a circumferential oscillation.
Suppression of Instabilities in Liquid Fueled Combustors by Variation of Fuel Spray Properties
Authors: Lee J.-Y. , Lubarsky E. , Zinn B. T.
Published: February 2009

This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach is to break up the feedback between the combustion process heat release oscillations and the combustor oscillations that drives the instability by changing the characteristics of the combustion process (i.e., characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (Nanomiser™), which can independently vary its fuel spray properties, and investigated the dependence of acoustics-combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. The results of this study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using Abel’s deconvolution, this study showed that the instabilities were mostly driven in regions where the mean axial flow velocity was approximately zero, in the near field of the vortices that were generated in the combustor. The results of this study strongly suggest that a “slow” active control system that employs controllable injectors could be used to prevent the onset and/or damp detrimental combustion instabilities.
Validation of Multi-Frequency Eddy Current MWM Sensors and MWM-Arrays for Coating Production Quality and Refurbishment Assessment
Authors: Zilberstein Vladimir , Shay Ian , Lyons Robert , Goldfine Neil , Malow Thomas , Reiche Ralph
Published: February 2009

Coatings for oxidation, corrosion, and thermal protection provide the required materials performance for gas turbine blades and vanes in state-of-the-art industrial gas turbines. These turbines must withstand severe operating conditions for well over ten thousand hours. Variations in the coating thickness, and increased porosity, can influence the lifetime of such coatings significantly. For components that have been removed from service, effective assessment of the aged coating and substrate condition is critical for refurbish/replace/continue-to-run decisions. A suitable device for coating thickness measurement and detection of unacceptable porosity is needed for ensuring the quality of such coatings. In this paper, we present new results on coating thickness measurements for metallic MCrAlY overlay coatings on gas turbine parts. These measurements were performed with a Meandering Winding Magnetometer (MWM®) eddy-current sensor using grid methods. This technique allows proper coating measurements even after a diffusion heat treatment for a better coating adhesive strength. The MWM technology enables measurement of the coating thickness, the absolute electrical conductivity (which may in turn be related to porosity or other properties of interest), and lift-off, which is related to surface roughness. Single-channel MWM sensors and multi-channel imaging MWM-Arrays permit capture of features of interest for a population of components. New capabilities for inspecting gas turbine components are, thus, provided. Inspection applications include metallic and non-metallic coating thickness measurements, porosity measurements, and detection of cracks on complex surfaces. Results of coating assessment for a production line of gas turbine vanes by means of a multifrequency MWM technique are presented for various combinations of coatings and base metals. A description of improved multiple frequency quantitative inversion methods is provided for simultaneous and independent measurement of multiple unknowns such as metallic bond coat thickness, metallic bond coat porosity, and top coat thickness. Ongoing research focuses on characterization of aged components using MWM sensors and imaging MWM-Arrays as well as on development of enhanced algorithms for four and five unknown coating / substrate properties. In a recent study of hot corrosion, uncoated nickel alloy specimens were characterized using an MWM sensor with grid methods. Preliminary results indicated that, within the limitations of the three-unknown single-layer model used, the method could readily identify specimens with no apparent corrosion damage, specimens with moderate corrosion damage, and specimens with severe corrosion damage.
Two Financial Reasons Why Repowering Is Compelling Compared to Other Power Supply Options
Authors: Schretter James , Williams Steven , Brandett Jo¨rgen
Published: February 2009

The past two years has been a period characterized by an emphasis on cost cutting, improving the operation of existing assets and a constrained financial market. In such an environment, repowering offers the potential to significantly improve existing power plant assets. A repowering of an existing steam power plant can result in a more than 50% improvement in the heat rate, leading to enormous operating cost savings. However, despite the potential operational and financial benefits of repowering, the experience we have found from first-hand research, is that there are a number of misconceptions regarding repowering economics. It appears that such misconceptions are limiting the extent to which repowering is being considered as a power supply resource option. The two most common misperceptions regarding repowering economics relate to 1) the relative installed cost compared to greenfield construction and 2) the comparative financial returns on a life-cycle basis. In this paper we analyze and discuss these two issues and try and make the case that repowering should be routinely included in power supply planning, along with options such as greenfield construction, power purchase agreements and spot purchasing.
Effect of Blade Tip Geometry on Tip Flow and Heat Transfer for a Blade in a Low Speed Cascade
Authors: Saxena Vikrant , Nasir Hasan , Ekkad Srinath V.
Published: February 2009

A comprehensive investigation of the effect of various tip sealing geometries is presented on the blade tip leakage flow and associated heat transfer of a scaled up HPT turbine blade in a low-speed wind tunnel facility. The linear cascade is made of four blades with the two corner blades acting as guides. The tip section of a HPT first stage rotor blade is used to fabricate the 2-D blade. The wind tunnel accommodates an 116° turn for the blade cascade. The mainstream Reynolds number based on the axial chord length at cascade exit is 4.83 × 105. The upstream wake effect is simulated with a spoked wheel wake generator placed upstream of the cascade. A turbulence grid placed even farther upstream generates the required free-stream turbulence of 4.8%. The center blade has a tip clearance gap of 1.5625% with respect to the blade span. Static pressure measurements are obtained on the blade surface and the shroud. The effect of crosswise trip strips to reduce leakage flow and associated heat transfer is investigated with strips placed along the leakage flow direction, against the leakage flow and along the chord. Cylindrical pin fins and pitch variation of strips over the tip surface are also investigated. Detailed heat transfer measurements are obtained using a steady state HSI-based liquid crystal technique. The effect of periodic unsteady wake effect is also investigated by varying the wake Strouhal number from 0. to 0.2, and to 0.4. Results show that the trip strips placed against the leakage flow produce the lowest heat transfer on the tips compared to all the other cases with a reduction between 10–15% compared to the plain tip. Results also show that the pitch of the strips has a small effect on the overall reduction. Cylindrical pins fins and strips along the leakage flow direction do not decrease the heat transfer coefficients and in some cases enhance the heat transfer coefficients by as much as 20%.
Impingement Heat Transfer Under Linearly Stretched Arrays of Holes
Authors: Gao Lujia , Ekkad Srinath V. , Bunker Ronald S.
Published: February 2009

Impingement heat transfer for linearly stretched arrays of holes is investigated. In real engine configurations, impingement arrays are not always square with evenly spaced holes both in streamwise and spanwise direction. They are primarily directed to hot spot locations thus producing nonsquare arrays. In this study, the spacing between the holes increases in both the streamwise and spanwise direction simulating the stretching of the hole arrays downstream. Two different arrays are investigated with the first array having uniform diameter holes through the array placed in a stretched format. The second array has holes placed in the same locations with increasing diameter along the streamwise direction. The measured heat transfer coefficients for these arrays are then predicted using existing impingement heat transfer correlations based on regular evenly spaced arrays. Results show that the published correlations over-predict the effect of cross-flow. Also, the correlation was extrapolated for this study due to lack of information for extremely strong cross-flow effects. All measurements were obtained using the transient liquid crystal technique.
Parallel Thermoelasticity Optimization of 3-D Serpentine Cooling Passages in Turbine Blades
Authors: Dennis Brian H. , Egorov Igor N. , Sobieczky Helmut , Dulikravich George S. , Yoshimura Shinobu
Published: February 2009

An automatic design algorithm for parametric shape optimization of three-dimensional cooling passages inside axial gas turbine blades has been developed. Smooth serpentine passage configurations were considered. The geometry of the blade and the internal serpentine cooling passages were parameterized using surface patch analytic formulation, which provides very high degree of flexibility, second order smoothness and a minimum number of parameters. The design variable set defines the geometry of the turbine blade coolant passage including blade wall thickness distribution and blade internal strut configurations. A parallel three-dimensional thermoelasticity finite element analysis (FEA) code from the ADVENTURE project at the University of Tokyo was used to perform automatic thermal and stress analysis of different blade configurations. The same code can also analyze nonlinear (large/plastic deformation) thermoelasticity problems for complex 3-D configurations. Convective boundary conditions were used for the heat conduction analysis to approximate the presence of internal and external fluid flow. The objective of the optimization was to make stresses throughout the blade as uniform as possible. Constraints were that the maximum temperature and stress at any point in the blade were less than the maximum allowable values. A robust semi-stochastic constrained optimizer and a parallel genetic algorithm were used to solve this problem while running on an inexpensive distributed memory parallel computer.
Performance Benefits Using Siemens Advanced Compressor Cleaning System
Authors: Leusden Christoph Pels , Sorgenfrey Christoph , Du¨mmel Lutz
Published: February 2009

Extensive operational performance data from the Siemens Power Generation V64.3 unit in Obernburg, Germany (operated by Kraftwerk Obernburg GmbH) is evaluated. The unit was commissioned in 1996 and has been running continuously in base load operation with fuel gas to supply heat and power to a nearby chemical plant. In rare cases, fuel oil is used as a backup fuel. During the first major outage after approx. 25000 equivalent operating hours (EOH), the Siemens PG Advanced Compressor Cleaning System (ACCS) was implemented at Obernburg. ACCS features separate nozzle systems for online and offline compressor cleaning accounting for different operating conditions. For online cleaning, the droplet size is optimised for the droplets to remain in the main air flow in order to minimize erosion effects while providing a homogeneous field over the whole air intake. With reduced rotational speed during offline compressor cleaning, erosion is less critical. Offline nozzles, therefore, provide higher mass flow and larger droplets in order to maximize cleaning performance for all compressor stages. ACCS, in its maximum automated version, features operation from the control room, online-washing at low ambient temperatures (officially released down to −15°C without GT Anti-Icing) and minimum use of manpower. The ACCS system in Obernburg was operated according to the recommended online washing procedure. By June 2002, the V64.3-unit in Obernburg reached 50000 EOH and the second major inspection was carried out. For this paper, operational data from the second inspection intervals (24350–49658 EOH) and from three performance tests with calibrated equipment are compared in order to evaluate the effectiveness of the Advanced Compressor Cleaning System. Statistical evaluation of single-wash performance recovery and the evolution of long-term performance are presented. The effects of degradation and fouling are differentiated. It is shown that ACCS has a significant benefit for long-term engine performance.
Interactions of Film Cooling Rows: Effects of Hole Geometry and Row Spacing on the Cooling Performance Downstream of the Second Row of Holes
Authors: Saumweber Christian , Schulz Achmed
Published: February 2009

A comprehensive set of generic experiments is conducted to investigate the interaction of film cooling rows. Five different film cooling configurations are considered on a large scale basis each consisting of two rows of film cooling holes in staggered arrangement. The hole pitch to diameter ratio within each row is kept constant at P/D = 4. The spacing between the rows is either x/D = 10, 20, or 30. Fanshaped holes or simple cylindrical holes with an inclination angle of 30 deg. and a hole length of 6 hole diameters are used. With a hot gas Mach number of Mam = 0.3, an engine like density ratio of ρc/ρm = 1.75, and a freestream turbulence intensity of Tu = 5.1% are established. Operating conditions are varied in terms of blowing ratio for the upstream and, independently, the downstream row in the range 0.5<M<2.0. The results illustrate the importance of considering ejection into an already film cooled boundary layer. Adiabatic film cooling effectiveness and heat transfer coefficients are significantly increased. The decay of effectiveness with streamwise distance is much less pronounced downstream of the second row primarily due to pre-cooling of the boundary layer by the first row of holes. Additionally, a comparison of measured effectiveness data with predictions according to the widely used superposition model of Sellers [11] is given for two rows of fanshaped holes.
Detailed Investigation of Heat Flux Measurements Made in a Standard Propane-Air Fire-Certification Burner Compared to Levels Derived From a Low-Temperature Analogue Burner
Authors: Abu Talib Abd. Rahim , Neely Andrew J. , Ireland Peter T. , Mullender Andrew J.
Published: February 2009

This paper presents detailed heat flux measurements to a flat plate from an ISO2685 [1] standard, large propane fuelled burner used throughout the industry in aero-engine fire-certification. The authors have developed a custom-built heat transfer gauge to measure the heat flux from the burner under isothermal wall conditions. The heat flux from the standard burner is normally calibrated using either a watercooled copper tube or a Gardon gauge, each positioned at a single location. There are no reports in the literature of a detailed survey of heat flux distribution for the burner and the results are therefore of great interest to thermal engineers. These measurements provide benchmark data to allow the heat flux distribution from the ISO burner to be compared to levels derived from the low-temperature analogue burner developed by the authors. The analogue burner uses liquid crystals to measure heat transfer coefficient and adiabatic wall temperature on scale models of engine components and provides key data to facilitate the successful design of components used in fire zones. The objective of this paper is to further validate the low-temperature analogue burner technique developed by the authors which simulates the standard large propane-air burner for fire-certification in aero engine.
A Novel Liquid Crystal Image Processing Technique Using Multiple Gas Temperature Steps to Determine Heat Transfer Coefficient Distribution and Adiabatic Wall Temperature
Authors: Abu Talib Abd. Rahim , Neely Andrew J. , Ireland Peter T. , Mullender Andrew J.
Published: February 2009

This paper presents a novel experimental technique, which combines thermochromic liquid crystals with multiple steps in gas temperature, to determine heat transfer coefficient and adiabatic wall temperature distributions. The transient heat transfer experiments have been conducted on a flat plate using the low-temperature analogue of an ISO standard propane-air burner commonly used in aero-engine fire certification. The technique involves the measurement of the surface temperature response of an insulating model to a change in gas temperature. A coating comprising more than one thermochromic liquid crystal material is used to increase the range of the surface measurement and this is combined with multiple step changes in gas temperature. These measures induce several peaks in liquid crystal intensity throughout the transient experiment and these are shown to improve the accuracy. The current technique employs useful data from both the heating and cooling phases in the heat transfer test. To the authors’ knowledge, this has not been investigated before and it is likely to be very useful for other applications of the liquid crystal transient heat transfer experiment. The uncertainties in all measurements have been quantified and are presented in this paper.
Blade Aerodynamic Damping Variation With Rotor-Stator Gap: A Computational Study Using Single-Passage Approach
Authors: Li H. D. , He L.
Published: February 2009

One of the outstanding issues in turbomachinery aeromechanic analysis is the intra-row interaction effects. The present work is aimed at a systematic examination of rotorstator gap effects on blade aerodynamic damping by using a 3D time-domain single-passage Navier-Stokes solver. The method is based on the upwind finite volume discretization (AUSMD/V) and the single-passage Shape-Correction approach with enhanced accuracy and efficiency for unsteady transonic flows prediction. A significant speed up (by a factor of 20) over to a conventional whole annulus solution has been achieved. A parametric study with different rotor-stator gaps (56%–216% chord) for a 3D transonic compressor stage illustrates that the reflection from an adjacent stator row can change rotor aerodynamic damping by up to 100%. It is shown that this intra-row interference effect on the rotor aero-damping can be qualitatively altered by changing the number of stator blades. Thus, the stator blade count could be considered as a useful aeromechanical control/design parameter. Furthermore, the predicted non-monotonic relationship between the rotor blade aerodynamic damping and the gap distance suggests the existence of an optimum gap regarding rotor flutter stability and/or forced response stress levels.
LES Prediction of Combustor Emissions From a Practical Industrial Fuel Injector
Authors: Cannon Steven M. , Zuo Baifang , Smith Clifford E.
Published: February 2009

An axial-swirl, lean premixed fuel injector typical of stationary gas turbine combustors has been analyzed using Large Eddy Simulation (LES). The objective of the study was to evaluate the LES modeling approach for predicting emissions of CO and NOx at practical engine conditions (P = 13.6 atm, Tin = 734 K = 861°F) and over a range of natural gas-air equivalence ratios (0.42 to 0.58). Experimental data from a recent UTRC/DOE-NETL program was used to evaluate the model. The experimental tests found NOx emissions decreased significantly with a decrease in equivalence ratio while CO emissions decreased initially, but then increased at the leanest conditions. LES calculations were performed using a parallel (domain decomposition), pressure-based, unstructured-grid flow solver within the CFD-ACE+ commercial software. The LES software solves the general transport equations for mass, momentum, energy, and chemical species without assumption at the grid- and time-resolved scales of the flow, and models the turbulent mixing and chemistry below the locally resolved grid/time-scales. The Localized Dynamic subgrid Kinetic energy Model (LDKM) was used to model the unresolved turbulence and a 2-step assumed PDF method, with decoupled NOx, was used to model the unresolved turbulence-chemistry interactions. Parallel calculations on a cluster of 22 Linux-based PCs were carried out. It was shown that LES was able to accurately predict the CO and NOx at an equivalence ratio of 0.58, and at leaner equivalence ratios the model was able to give qualitative agreement with the measurements. Some inadequacies in the NOx chemistry at ultra lean conditions and the near-wall flow boundaries were observed.
New Airfoil Design to Extend Gas Turbine Compressor Surge Margin
Authors: Sahai Vivek , Cheng Dah-Yu
Published: February 2009

In many industrial gas turbine compressor designs, the compressors later stage blade angles are reduced in a constant flow area section as a means to even out the per stage workload. Most compressors use NACA 65 series type airfoils, which are good for high subsonic and supersonic flow, but are poor for middle or low subsonic flows. The temperature increases as the compression ratio increases; which cause the Mach number to drop. With reduced blade cascade overlaps, a reduction in axial blade solidity results. The compounding effect of low solidity and a low Mach number can cut the stalling angle by several degrees. This recent study found that compressor stall more or less is linked to the change of moment coefficient Cm, rather than lift coefficient Cl. Designing the airfoil, by extending the constant moment coefficient to a higher angle of attack region can delay the trailing edge upper surface separation to a higher angle of attack, the main source of rotating stall. This separated flow exhibits itself more clearly on the moment coefficient, but is obscured by an increase in lift coefficient before “aerodynamic” stall. This new design is based on the second order derivative of the camber line, with a low drag symmetrical airfoil thickness. Numerical simulation of a single airfoil and cascade of the new airfoil is compared with other shapes. The results show that the trailing edge flow separation begins at a 9.5-degree angle of attack for the NACA 65 series airfoils. The NACA 0012 separation (i.e. change in Cm) starts at 5 degrees (total stall occurs at 11 degrees). The new airfoil CFS18-0010 exhibits no separation for a single airfoil of up to 12 degrees. The cascade results showed no flow separation up to an angle of 15 degrees, which is enough to eliminate most of the rotating stall.
Investigation of a Nonlinear Numerical Mathematical Model of a Multi-Shaft Gas Turbine Unit
Authors: Kim Soo Yong , Kovalevsky Valeri P.
Published: February 2009

The development of numerical mathematical model to calculate both the static and dynamic characteristics of a multishaft gas turbine consisting of a single combustion chamber, including advanced cycle components such as intercooler and regenerator is presented in the paper. The mathematical model is based on the simplified assumptions that quasi-static characteristic of a turbo-machine and injector is used, total pressure loss and heat transfer relation for static calculation neglecting fuel transport time delay can be employed. The supercharger power has a cubical relation to its rotating velocity. The accuracy of each calculation is confirmed by monitoring mass and energy balances, and comparative calculations with different time steps of integration. The features of the studied gas turbine scheme are the starting device with compressed air bottles and injector supercharging air directly ahead of the combustion chamber. The start-up algorithms are reviewed at different geometrical characteristics of the injector and temperatures of ambient air.
Cooling Performance of an Integrated Impingement and Pin Fin Cooling Configuration
Authors: Yamawaki Shigemichi , Nakamata Chiyuki , Imai Ryouji , Matsuno Shinsuke , Yoshida Toyoaki , Mimura Fujio , Kumada Masaya
Published: February 2009

The cooling configuration adopted in this study integrates impingement cooling and pin fin cooling devices into one body, the aim being enhancement of the effective heat transfer area. The purpose of the study is to confirm improvement of cooling effectiveness for two different pin density configurations by experimental verification. Experiments were conducted in similar conditions to actual engines using large-scaled flat-plate specimens manufactured by a new rapid prototype casting technique. The results were compared with predictions by one-dimensional analysis adopting the fin efficiency theory. Although the coarse pin density, one pin in a unit area, shows good agreement with the prediction, the fine pin density, four pins in the unit area, was overpredicted. It was found by numerical analysis that heat transfer of the new pin geometry did not increase, so that its surface area increased. CFD-aided prediction was proposed and validated with two specimen’s data.
Effect of Leading-Edge Geometry on Separation Bubble on a Compressor Blade
Authors: Liu Huoxing , Liu Baojie , Li Ling , Jiang Haokang
Published: February 2009

Accurate prediction of flow field is the most important factor during the design of high performance compressors. In some cases the agreement of pressure ratio and efficiency between predicted and measured is excellent, but it is common for the efficiency to be in error by perhaps one or two percent. This error is enough to render the calculation unable to replace expensive experiment testing. One of the important matters in need of more study is the mechanism of boundary layer transition from laminar to turbulent flow. The objective of this fundamental research work is to acquire the detailed structure of separation bubbles on the suction side of the blade by using the PIV and pressure taps. This paper presents an experimental study of the influence of 2d leading-edge geometry on behavior of separation bubbles. The measurements on a nose of enlarged blade were conducted on a special large-scale experimental facility, the pressure distribution and flowfield of flow were measured. The test model used in this study consists of circular leading edge and elliptic leading edge. Results are presented for a range of incidence. The measurement result indicated that the leading edge shape has a large influence on flow details separation and transition as well as the boundary layer properties after reattached point. The wedge angle appears to be an important role in leading edge geometry parameters.
Feasibility of Applying Active Lubrication to Reduce Vibration in Industrial Compressors
Authors: Santos Ilmar F. , Nicoletti Rodrigo , Scalabrin Alexandre
Published: February 2009

In this paper the complete set of modified Reynolds’ equations for the active lubrication is presented. The solution of such a set of equations allows the determination of stiffness and damping coefficients of actively lubricated bearings. These coefficients are not just dependent on Sommerfeld number, as it would be the case of conventional hydrodynamic bearings, but they are also dependent on the excitation frequencies and gains of the control loop. Stiffness as well as damping coefficients can be strongly influenced by the choice of the control strategy, servo valve dynamics and geometry of the orifices distributed over the sliding surface. The dynamic coefficients of tilting-pad bearings with and without active lubrication and their influence on an industrial compressor of 391 Kg, which operates with a maximum speed of 10,200 rpm, are analyzed. In the original compressor design, the bearing housings are mounted on squeeze-film dampers in order to ensure reasonable stability margins during full load condition (high maximum continuous speed). Instead of having a combination of tilting-pad bearings and squeeze-film dampers, another design solution is proposed and theoretically investigated in the present paper, i.e. using actively lubricated bearings. By choosing a suitable set of control gains, it is possible not only to increase the stability of the rotor-bearing system, but also enlarge its operational frequency range.
Prediction of Turbulent Heat Transfer and Fluid Flow in 2D Channels Roughened by Square and Deformed Ribs
Authors: Jia Rongguang , Sunde´n Bengt
Published: February 2009

Introduction of roughness by ribs in flow passages is a popular method of enhancing heat transfer in the cooling passages, e.g., of turbine blades and combustors. It is essential to accurately predict the enhancement of heat transfer generated by the ribs to ensure good design decisions. In most of the studies square ribs have been considered, but in practice such ribs may appear rounded due to improper manufacturing or wear during operation. This study is focused on the effect of the rib deformations, based on computational fluid dynamics (CFD). One of the main difficulties in CFD is the reliable modeling of the underlying physics of the turbulence. This paper describes some recent efforts to validate and apply RANS-based models for predictions of turbulent flow and heat transfer in ribbed ducts, relevant to gas turbine cooling. The evaluated turbulence models include a basic low-Re k-ε model (AKN), and two promising higher order models: namely, the explicit algebraic stress model (EASM), and the V2F model. All these models are validated with available 2D experimental heat transfer and fluid flow data. Some conclusions are reached on their suitable application situations. The effect of the roundedness on heat transfer and fluid flow is presented in detail. Some possible improvements, i.e., of the deformed ribs, are proposed to suppress the hot spots, and/or to enhance the overall thermal and hydraulic performance.
Pyrolysis Systematics for Co-Utilization Applications
Authors: Green Alex E. S. , Chaube Ritesh P.
Published: February 2009

A semi-empirical model (SEM) of slow pyrolysis (SP) of carbonaceous material along nature’s coalification path has been under development to facilitate blending of various feedstocks in fuel conversion systems (pyrolyzers, combustors, gasifiers, liquefiers and carbonizers). The model was adjusted to coal data in the literature and our own drop tube pyrolysis measurements with various types of biomass. The latest version of the model is here adapted to represent the flash pyrolysis (FP) yields of 15 products (CaHbOc) for 17 coal types measured by Xu and Tomita (XT) at 1037°K and at 5 additional temperatures for 8 of the coals. A good analytical representation of yields vs. C, H and O wt%s and temperature is found that makes the Xu-Tomita FP measurements conveniently available for many fuel conversion applications. Our larger objective is to help bring order into the fundamentals underlying humankind’s oldest technologies, the extraction of energy out of wood and coal.
Cooling Air Temperature Reduction in a Direct Transfer Preswirl System
Authors: Geis T. , Dittmann M. , Dullenkopf K.
Published: February 2009

This paper describes an experimental study of the cooling efficiency of a preswirl rotor-stator system equipped with a small number of preswirl nozzles of circular shape, located on a radius equal to that of the receiver disk holes. In the direct transfer cooling air system, total air temperatures were measured in the relative frame, i.e. inside the receiver holes by means of small total temperature probes for different throughflow rates, rotational Reynolds numbers and swirl ratios. The experimental data were compared with a simple theoretical model which predicts air temperatures in an “ideal” preswirl system. This comparison served to quantify the efficiency of this cooling scheme. In a subsequent one-dimensional analysis which took into account flow data obtained in an earlier experimental study by the same authors, two different mechanisms responsible for the elevated cooling air temperatures were determined. The new model considers in addition to the observed reduction of swirl due to viscous drag on the stator and mixing inside the rotor-stator cavity, the work put in by the rotor at high disk rotational Reynolds numbers and low cooling air flow rates.
Model Based Gas Turbine Parameter Corrections
Authors: Kurzke Joachim
Published: February 2009

Ambient conditions have a significant impact on the temperatures and pressures in the flow path and on the fuel flow of any gas turbine. Making observed data comparable requires a correction of the raw data to sea level Standard Day conditions. The most widely applied gas turbine parameter correction method is based on keeping some dimensionless Mach number similarity parameters invariant. These similarity parameters are composed of the quantity to be corrected multiplied by temperature to the power ‘a’ and pressure to the power ‘b’ with exponent ‘a’ being theoretically either 0, +0.5 or −0.5 and ‘b’ either 0 or 1.0. To improve the accuracy of this approach it is common practice to empirically adapt the temperature and pressure exponents ‘a’ and ‘b’ in such a way that the correction process leads to a better correlation of the data. Finding empirical exponents requires either many consistently measured data that cover a wide range of ambient temperatures and pressures or a computer model of the engine. A high fidelity model is especially well suited for creating optimally matched exponents and for exploring the phenomena that make these exponents deviate from their theoretical value. This paper discusses the questions that arise when creating empirical exponents with a thermodynamic model of the gas turbine. The gas turbine parameter correction method based on Mach number similarity parameters can get complex if effects like humidity, bleed air or power off-take, free power turbines, switching between various fuel types (Diesel and natural gas), water respectively steam injection, variable geometry or afterburners have to be considered. In such a case it might be simpler — and certainly more accurate — to use the thermodynamic model for the gas turbine parameter correction. Computing power required for running a model is nowadays of no relevance and the better consistency of the data available for engine performance monitoring can yield a significantly improved performance diagnostic capability.
Analysis of Cycle Configurations for the Modernization of Combined Heat and Power Plant by Fitting a Gas Turbine System
Authors: Chmielniak Tadeusz , Kosman Gerard , Kosman Wojciech
Published: February 2009

The application of a gas turbine generally allows to increase the number of possible configurations of cogenerated heat and electrical power systems, which became a significant substitute for classic, coal-fired power plants. They are characterized by better thermodynamical, economical, ecological and operating indexes. Gas turbine units are also the best option for the moderinization of existing power plants. This paper discusses the effectiveness of various technological configurations with gas turbines, which are to be applied during modernization projects of already existing conventional combined heat and power plants. In the analysis and entropy methods were applied. Algorithms of the entropy method allow to determine the entropy generation in each section of a combined heat and power (CHP) plant. Several criteria were taken into consideration while analyzing the effectiveness of technological cycle configurations with gas turbines. These include the energy effectiveness, the efficiency of the HRSG and the steam cycle, the efficiency of the whole thermal electric power station, the exergetic efficiency of the HRSG and the steam cycle, and the fuel efficiency index. It was assumed that gas turbines operate under their nominal conditions. The composite curves were also taken into consideration while choosing the type of the turbine. The modernization project tends not to eliminate those exiqsting power plant sections (machines and equipment), which are able to operate further. The project suggests that those units should remain in the system, which satisfy the applied durability criterion. The last phase of the optimization project focuses on the sensibility verification of several steam-gas CHP plant parameters and their influence on the whole system.