bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximum Utilisation of Parts Process: A Method for Increased Precision of Component Lifetime Estimations in Medium Size Gas Turbines
Authors: Slottner Pontus , Wa¨rja Mathias , Broddega˚rd Mattias
Published: March 2009

The goal of a maintenance strategy should be to reach a Retirement For Cause, RFC, condition, where components are not replaced until a potential failure has been detected. Further, the inspection interval should be large enough to allow spare parts to be ordered and delivered during the time between failure detection and failure, with sufficient safety margins. This requires measurement techniques that can monitor how the turbine is operated, prognostics capabilities that foresee maintenance needs, and test methods that can determine the state of a component during maintenance events. In general there are two ways to determine the amount of damage a gas turbine component has been subjected to — calculations and examination of service exposed components. Optimum results should be obtained by using calculations as a basis and continuously review/modify their interpretation and the underlying damage models using best available experiences. This paper describes the Maximum Utilisation of Parts Process, MUPP — a process for systematic testing of used components, how process data can be turned into modifications to a gas turbines maintenance schedule with same or decreased risks, and the implications for equipment operator as well as maintenance provider. It is concluded that MUPP allows significantly lower maintenance costs in the medium to long time frame.
Tip Leakage Flow in Radial Inflow Rotor of a Microturbine With Varying Blade-Shroud Clearance
Authors: Deng Qinghua , Niu Jiufang , Feng Zhenping
Published: March 2009

In this paper, tip clearance flow in a radial inflow turbine rotor under the stage environment is investigated using a three-dimensional viscous flow simulation with three different blade-shroud gap heights of 1%, 2% and 3% of the local span. The results indicate that more relative casing motion increases the scraping effect on tip leakage flow at the rotor entrance. Also, the scraping flow can dominate the whole tip clearance at the rotor entrance when the velocity is high enough at the rotor tip diameter. Regardless of the transverse mass flow rates of the three tip clearances, the results strongly exhibit the characteristics of linearity when the relative meridional length S is greater than 40%. According to the analysis of leakage flow fields in the tip clearance, measures such as a circumference slot, axial slot, or honeycomb are proposed to be applied and placed at the shroud surface over the exducer of the rotor for effectively reducing the transverse flow.
High Pressure Water Mist Fire Protection Systems
Authors: Ka¨a¨ria¨inen Jaakko S.
Published: March 2009

Traditionally the industrial gas turbines have been protected with gaseous systems like CO2 or Halon. These systems depend much on the enclosure integrity because the concentration of the extinguishing media has to be kept on a certain level for a certain time. The enclosure integrity has to be tested periodically, and this often causes high maintenance costs. Most gaseous systems are dangerous to people. The enclosure has to be evacuated prior to discharge. This procedure takes typically 2-20 minutes. High pressure water mist fire protection technology provides a reliable system, which is not depending on enclosure integrity. Actually the testing of these systems has been done with the enclosure door open. Water mist systems are safe to personnel. They can be released immediately after the fire has been detected.
Aerodynamic Design of Turbine Blades by Using Adjoint-Based Method and N-S Equation
Authors: Li Yingchen , Feng Zhenping
Published: March 2009

Because of the low computational cost, adjoint method has been a highlight issue in aerodynamic design since being firstly introduced in aeronautical field. The purpose of this work is to expand the adjoint method into turbomachinery applications for viscous and compressible flow. The continuous adjoint method is formulated in two-dimensional blade design by using N-S equation. Combining Thompson’s theory of time-related boundary condition, we present the boundary conditions of the adjoint equation for internal flow and discuss the restrictions of cost function in the case of given surface temperature and adiabatic conditions on blade walls. Numerical techniques used in CFD are employed here to solve the adjoint linear PDE. In conjunction with quasi-Newton algorithm, the aerodynamic design approach for turbine blades is presented, which is independent of the N-S solver being used. Several numerical examples are implemented to validate this approach and then the pressure inverse design of a cascade blade is taken.
Full Scale Testing of a Cluster Nozzle Burner for the Advanced Humid Air Turbine
Authors: Koganezawa Tomomi , Miura Keisuke , Saito Takeo , Abe Kazuki , Inoue Hiroshi
Published: March 2009

The advanced humid air turbine (AHAT) system, which has a humidifier and a heat recovery system has the advantage of improving the thermal efficiency of gas turbine power generation without needing an extremely high firing temperature and pressure ratio. A pilot plant and a prototype gas turbine adapted to the AHAT system have been developed. Before the pilot plant test, an experimental study using a combustion test rig was carried out to obtain the characteristics of a prototype combustor and it is described in this presentation. The combustion conditions in the AHAT system are characterized by both high humidity and high temperature air (17.6wt%, 629C). It is expected that a low flame temperature caused by the high humidity condition will decrease NOx emission while the high temperature air condition will sustain flame stability. However, the latter condition has the disadvantage of causing NOx emission and autoignition of fuel. A cluster nozzle burner configuration, which has many fuel and air coaxial jet streams, was previously proposed. The cluster nozzle burner can mix fuel and air effectively within a short time which makes it suited to the AHAT system and able to cope with both flame stability and NOx reduction problems. The combustion rig test results showed good combustion performance for the developed cluster nozzle burner. Both the high temperature condition of the AHAT system and the recirculation zone generated by swirling of center burner air sustained flame stability at a level sufficient for the nozzle burner in AHAT operation. The low flame temperature due to the high humidity condition was effective in decreasing NOx emission, which was less than 10ppm at 50-100% load.
Effects of Pressure Ratio and Sealing Clearance on Leakage Flow Characteristics in the Rotating Honeycomb Labyrinth Seal
Authors: Li Jun , Yan Xin , Li Guojun , Feng Zhenping
Published: March 2009

Honeycomb stepped labyrinth seals in turbomachinery enhance aerodynamic efficiency by reducing leakage flow losses through the clearance between rotating and stationary components. The influence of pressure ratio and sealing clearance on the leakage flow characteristics in the honeycomb stepped labyrinth seal is numerically determined. The geometries investigated represent designs of the honeycomb labyrinth seal typical for modern turbomachinery. The leakage flow fields in the honeycomb and smooth stepped labyrinth seals are obtained by the Reynolds-Averaged Navier-Stokes solution using the commercial software FLUENT. Numerical simulations covered a range of pressure ratio and three sizes of sealing clearance for the honeycomb and smooth stepped labyrinth seals. The numerical discharge coefficients of the non-rotating honeycomb and smooth stepped labyrinth seals are in good agreement with previous experimental data. In addition rotational effects are also taken into account in numerical computations. The numerical results show that the leakage flow rate increases with the increasing pressure ratio at the fixed sealing clearance for the rotating and non-rotating honeycomb labyrinth seal. The influence of the sealing clearance on the leakage flow pattern for the rotating and non-rotating honeycomb labyrinth seal are observed. Moreover, the similar leakage flow rates are obtained at the same flow condition between the rotating and non-rotating honeycomb labyrinth seal due to the honeycomb acts to kill swirl velocity development for the rotating honeycomb labyrinth seal.
Nonlinear Dynamic Analysis of a Rotor System With Aerodynamic Journal Bearings
Authors: Shiau T. N. , Hsu W. C. , Deng B. W.
Published: March 2009

This paper investigates nonlinear dynamic characteristics of a rotor system with aerodynamic journal bearings. The Finite Difference Method (FDM) is employed to solve the Reynolds equation, which is used to determine the nonlinear compressible gas force of the aerodynamic bearing. By applying the gas bearing force to system equations of motion, the system response can be determined by the numerical integration method. Results show that the aerodynamic bearing will provide higher loading capacity to support the rotor when the eccentricity ratio is increased. The aerodynamic bearing force increases when the rotor is speeding up or the squeeze frequency is raised. The rotor trajectory presents aperiodic behavior, and it becomes significant as the rotor mass increases. When the squeeze frequency decreases or the rotor mass increases, the radius of the rotor trajectory will increase. Recursive Least Square Method and Kalman Filter Method are used to identify the aerodynamic bearing parameters from the system response. The parameters include the damping and stiffness coefficients of the aerodynamic bearing. According to the results of identification, both identified parameters by these two methods are in good accordance. The results show that the aerodynamic bearing force can be precisely identified and the system response can be quickly solved by the identified system with less computer time. But the identified system lost its accuracy as the rotor speed or the squeeze frequency increase because these will enhance the nonlinearity of the aerodynamic bearing force.
Development of Electric Power Generation Unit Driven by Waste Heat: Study on Working Fluids and Expansion Turbines
Authors: Inoue Naoyuki , Kaneko Atsushi , Watanabe Hiroyoshi , Uchimura Tomoyuki , Irie Kiichi
Published: March 2009

This paper presents the results of the development of a simple and compact power generator driven by waste heat, assuming hot water at a temperature of 80 to 90°C as a heat source. Firstly, a feasibility study on the characteristics of a low temperature power cycle (evaporated at 77°C, condensed at 42°C) was conducted. As a result, TFE (Trifluoroethanol CF3CH2OH), R123, F245fa were selected as suitable for the cycle to optimize the cycle efficiency. Experimental validation of the power generator in which TFE was adopted as a working fluid was also conducted. A radial turbine was adopted as an expander, and was newly designed using an inverse design method, whereby the 3-D blade geometry for specified blade loading distribution was numerically obtained. Turbine performance and flow fields were then validated by CFD (Computational Fluid Dynamics). The test equipment was driven by hot water as a heat source and cooling water as a cooling source, and the generated power was connected with the electric utility. The characteristics of the power generating cycle and those of the turbine were obtained experimentally. The experimental results of the expander turbine performance, using TFE as a working fluid, showed good agreement with CFD results.
An Integrated Software Procedure to Support Teaching of Radial Inflow Turbine Design
Authors: Cravero Carlo , Marini Martino
Published: March 2009

The authors decided to organize their design/analysis computational tools in an integrated software suite in order to help teaching radial turbine, taking advantage of their research background and a set of codes previously developed. The software is proposed for use during class works and the student can either use a single design/analysis tool or face a complete design loop consisting of iterations between design and analysis tools. The intended users are final year students in mechanical engineering. The codes output are discussed with two practical examples in order to highlight the turbomachinery performance at design and off-design conditions. The above suite gives the student the opportunity of getting used to different concepts (choking, blade loading, performance maps, …) that are encountered in turbomachinery design and of understanding the effects of the main design parameters.
The Development of 50kW Output Power Atmospheric Pressure Turbine (APT)
Authors: Tanaka K. , Inoue K. , Kitajima J. , Kazari M. , Nitta S. , Tsujikawa Y. , Kaneko K.
Published: March 2009

This research seeks to report the development of a 50kW output power atmospheric pressure turbine (APT), based on the Inverted Brayton Cycle, which puts new, distributed power generation technology to practical use by using as energy source gases at normal pressures and high temperature, from industrial furnaces, waste gasification furnaces, gas turbines, and fuel cells which work at high temperatures, (ex. MCFC: Molten Carbonate Fuel Cell, SOFC: Solid Oxide Fuel Cell) and attempts to save energy and reduce CO2. At the last conference (ASME Turbo Expo 2006 in Barcelona), we had presented a paper about the proposal of APT and the results of operation of a 3–5kw APT prototype. This paper describes the designing of a new 50kW output power APT, and shows performance analysis and a review of the effectiveness of its application to industrial furnaces and biomass gasification furnaces. This development is based on a 3–5 kW APT prototype we had built and operated, and evaluated results. The performance simulation results using a general process simulator “HYSYS” show that a new 50kW APT (with recuperating heat exchanger) has a net electric efficiency (LHV) of about 20%. Based on this simulation result, we calculated the power and economical performance of application to industrial furnaces and biomass boilers. The results of these calculations clarify the basic characteristics of a new APT, which can be used as a new system for distributed power generation using waste heat.
Vortical Flow Structure and Loss Generation Process in a Transonic Centrifugal Compressor Impeller
Authors: Ibaraki Seiichi , Furukawa Masato , Iwakiri Kenichiro , Takahashi Kazuya
Published: March 2009

Transonic centrifugal compressors are used in turbochargers and turboshaft engines because of their small dimensions, relatively high efficiency and wide operating range. The flow field of the transonic centrifugal compressor impeller is highly three dimensional, and is complicated by shock waves, tip leakage vortices, secondary flows and the interactions among them. In order to improve the performance, it is indispensable to understand these complicated flow phenomena in the impeller. Although experimental and numerical research on transonic impeller flow has been reported, thus providing important flow physics, some undetected flow phenomena remain. The authors of the present report carried out detailed Navier-Stokes computations of a transonic impeller flow measured by Laser Doppler Velocimetry (LDV) in previous work. The highly complicated vortical flow structure and the mechanism of loss generation were revealed by a visual data mining technique, namely vortex identification based on the critical point theory and limiting streamline mapping by means of line integral convolution. As a result, it was found that the tip leakage vortices have a significant impact on the flow field and vortex breakdowns that increase the blockage of the flow passage, and that these were caused by shock wave interaction.
On the Coupling of Foil Bearing Supported Rotors: Part 2 — Experiment
Authors: Tomaszewski Michael J. , Walton James F. , Heshmat Hooshang
Published: March 2009

The expanded application of high-speed rotor systems operating on compliant foil bearings will be greatly enhanced with the ability to adequately couple multiple shaft systems with differing bearing systems and dynamic performance. In this paper the results of a successful experimental program are presented. Test results are presented for three different foil bearing coupled rotor systems. First, a coupled 32 kW, 60,000 rpm induction motor drive supported on compliant foil bearings was coupled to an identical 32 kW 60,000 rpm generator rotor and operated to full speed. Next, a high-speed 30,000 rpm capable ball bearing mounted precision spindle was driven to full speed when coupled to a 32 kW foil bearing supported drive motor. Third, the 32 kW, 60,000 rpm foil bearing based motor drive was coupled to a foil bearing supported rotor having a bending critical speed at approximately 29,000 rpm. This combined system was operated successfully to 60,000 rpm. Results of this experimental test program confirm the rotor-bearing system dynamic analysis and demonstrate the feasibility of coupling foil bearing supported rotors to a wide array of other rotor-bearing systems.
Numerical Analysis of the Heat Transfer in Radial Turbine Wheels of Turbo Chargers
Authors: Heuer Tom , Engels Bertold
Published: March 2009

Increasing exhaust gas temperatures of turbocharged Otto and Diesel engines make great demands on the durability of turbine wheels. Hence, a substantiated knowledge about the temperature distribution inside the turbine wheel is crucial. To obtain these temperatures the CHT-method has been applied to a radial turbine of a commercial Diesel turbocharger. The geometry and physical conditions are taken from gas stand tests. Hence, the model includes the entire wheel, the twin scroll housing, and the inlet and outlet pipe. In addition to aerodynamic boundary conditions, thermal boundary conditions have been obtained from gas stand tests. Thermocouples have been applied to blades, hub, back, and shaft close to the piston ring and near to the bearings. The signals have been transmitted via telemetry. A heat transfer investigation clarifies the essential heat transfer mechanisms. The interaction between fluid and solid leads to a non-uniform heat transfer direction, i.e. in some wheel regions heat is even discharged. A discussion about the influence of boundary conditions proves the need to implement not only the turbine wheel solid walls but to include each wall as a solid domain. Since CFD-results are strongly dependent on the boundary conditions, different models are discussed and their influence on the temperature distribution is shown.
The Effect of Vane Clocking on the Unsteady Flowfield in a One and a Half Stage Transonic Turbine
Authors: Schennach O. , Pecnik R. , Paradiso B. , Go¨ttlich E. , Marn A. , Woisetschla¨ger J.
Published: March 2009

The current paper presents the results of numerical and experimental clocking investigations performed in a high-pressure transonic turbine with a downstream vane row. The objective was a detailed analysis of shock and wake interactions in such a 1.5 stage machine while clocking the vanes. Therefore a transient 3D-Navier Stokes calculation was done for two clocking positions and the three dimensional results are compared with Laser-Doppler-Velocimetry measurements at midspan. Additionally the second vane was equipped with fast response pressure transducers to record the instantaneous surface pressure for 20 different clocking positions at midspan.
The Effects of Freestream Turbulence, Turbulence Length Scale and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade
Authors: Carullo J. S. , Nasir S. , Cress R. D. , Ng W. F. , Thole K. A. , Zhang L. J. , Moon H. K.
Published: March 2009

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 × 105, 8 × 105, and 11 × 105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.
Opto-Acoustical Flame Monitoring of CCGT: Searching for Humming Precursors
Authors: Mastrovito Marco , Ferrante Antonio , Camporeale Sergio M. , Bonzani Federico , Ninni Rosanna
Published: March 2009

Modern gas turbines are prone to trigger and sustain pressure oscillations induced by heat release in their combustor; these oscillations, called humming, can cause severe damage on the machine structure, or, on a less detrimental level, can limit gas turbine performance from load point of view or NOx emissions, increasing their concentration in flue gas. Thermoacoustic oscillation problem, although deeply investigated during the last 15 years, is far from being solved, so that both theoretical and experimental approaches are being used in order to improve basic knowledge of this phenomenon. With this aim an optoelectronic detector based system has been developed to be installed on a 270MW gas turbine to detect radiative energy release fluctuations due to thermoacoustic oscillations. This optoelectronic device has been used in combination with standard piezoelectric sensors with the target to get a better insight of the humming phenomenon. A data analysis method based on well established data processing techniques has been applied to data gathered from the field. The ensemble of data processing techniques seems to offer a method to evaluate the actual risk of thermoacoustic instabilities. This is the very first application of the proposed tool, and a long way has to be run before it is assessed as a prognostic device. Nevertheless in the h.o. of the authors, this first application encourages the continuation of developing the tool extending the base of monitored plants.
The Effect of Fuel Density on Mixing Profiles in a DACRS Type Premixer: Experiments and Simulation
Authors: Davis Dustin W. , Nolan Junghwa , Brumberg Justin T. , Yilmaz Ertan , Varatharajan Balachandar , Goldmeer Jeffrey S. , Lacy Benjamin P.
Published: March 2009

A combined experimental and computational study was conducted to investigate the effect of fuel density variations on mixing from a double annular counter-rotating swirl (DACRS) nozzle operated at atmospheric pressure under non-reacting conditions using either helium (He) or a mixture of He and CO2 as fuel simulants. A small probe traversed through the flow collecting gas samples that were sent to gas analyzers measuring the concentration profiles. The resulting measurements are then used to validate the computational fluid dynamics (CFD) model. A commercial CFD code (CFX 10) with a Reynolds averaged Navier-Stokes (RANS) formulation was used to simulate the experiment. Multiple turbulence closures, such as standard and realizable k-ε and SSG Reynolds stress model were evaluated. Additionally, several geometrical considerations, such as modeling a 72° sector versus a full 360°, were tested. While at high fuel-to-air momentum flux ratios (J) the fuel simulant concentration profiles were outward-peaked, and at low J the profiles were center-peaked. An analysis of the experimental results clearly indicate the momentum flux ratio is the most influential parameter controlling mixing in a DACRS nozzle. The simulations produced quantitative agreement with the experimental measurements using the realizable k-ε turbulence closure and only modeling a 72° sector of the nozzle. The complexity of the studied problem required a considerable refinement of the grid to produce an accurate and grid independent solution. The validated model may now be used to explore the design space for optimization of a nozzle for utilization in a syngas application.
Performance Optimization of Compact Ceramic High Temperature Heat Exchangers
Authors: Chen Q. Y. , Zeng M. , Zhang D. H. , Wang Q. W.
Published: March 2009

In the present paper, the compact ceramic high temperature heat exchangers with parallel offset strip fins and inclined strip fins (inclined angle β = 0∼70°) are investigated with CFD method. The numerical simulations are carried out for high temperature (1500°C), without and with radiation heat transfer, and the periodic boundary is used in transverse direction. The fluid of high temperature side is the standard flue gas. The material of heat exchanger is SiC. NuS-G.R(with surface and gaseous radiation heat transfer) is averagely higher than NuNo.R (without radiation heat transfer) by 7% and fS-G.R is averagely higher than fNo.R by 5%. NuS-G.R(with surface and gaseous radiation heat transfer) is averagely higher than NuS.R (with only surface radiation heat transfer) by 0.8% and fS-G.R is averagely higher than fS.R by 3%. The thermal properties have significantly influence on the heat transfer and pressure drop characteristics, respectively. The heat transfer performance of the ceramic heat exchanger with inclined fins (β = 30°) is the best.
Genetic Algorithm Based Design and Optimization of an Outer-Fins and Inner-Fins Tube Heat Exchanger
Authors: Xie G. N. , Zeng M. , Wang Q. W.
Published: March 2009

One of passive enhancement techniques, Extended Surfaces, are commonly employed in many heat exchangers to enlarge the heat transfer area on gases side because of the low heat transfer coefficients, which may be 10 to 100 times smaller than those of liquids side. The use of extended surfaces (or referred to as finned surfaces) will reduce the thermal resistance of gases side. Enhanced heat transfer coefficient will be achieved by using the basic surface geometries: plate-fin and tube-fin. With respect to the tube-fin type heat exchanger, fins may be employed outside tubes (herein called outer-fins) to enhance the heat transfer of shell-side, and alternatively fins may be also employed inside tubes (herein called inner-fins) to increase the intensity of heat transfer of tube-side. The desire to accomplish the gas-to-gas heat exchange through the tubular heat exchangers will lead to develop heat transfer enhancement techniques for outside and inside tubes. Therefore based on integration with such two mechanisms, namely, outer-fins and inner-fins of enhancement heat transfer techniques, a kind of outer-fins and inner-fins tube heat exchanger has been preliminary proposed (ASME-IGTI, Paper No.2006-90260 [20]). Such heat exchanger is potentially used in gas-to-gas heat exchangers, especially used for highpressure operating conditions, where the plate-fin heat exchangers might not be applicable. In general, the design task is a complex trial-and-error process and there is always the possibility that the design results such as geometrical parameters are not the optimum. Therefore, the motivation of this paper is to conduct optimum designs of such heat exchanger (hereafter called Outer-Fins and Inner-Fins tube Heat Exchanger, OFIF HE). A computational intelligent technique, Genetic Algorithm (GA) is applied to search and optimize geometrical parameters of the OFIF HE. The minimum total volume or minimum total annual cost of such OFIF HE is taken as an objective function in the GA respectively. The results show that the optimized OFIF HE provides lower total volume or lower total annual cost than those presented in previous work. The method is universal and may be used for design and optimization of OFIF HEs under different specified duties and design objectives.
Heat Transfer Enhancement by Impingement Cooling in a Combustor Liner Heat Shield
Authors: Lauffer Diane , Weigand Bernhard , von Wolfersdorf Jens , Dahlke Stefan , Liebe Roland
Published: March 2009

As part of an industrial gas turbine research program, the present study provides the results of a basic investigation of the heat transfer in an impingement cooled combustor heat shield. Because of the complexity and the irregularity of the impingement pattern of the heat shield, standard correlations for regular impingement fields are insufficient and the investigation of local heat transfer enhancement is required therefore. The model to represent a simplified heat shield is made out of perspex, and heat transfer experiments are performed using a transient liquid crystal method. The local air temperature is measured at several positions within the model. The distributions of the Nusselt number on the impingement target plate as well as on the side rims and along the central bolt recess of the heat shield are shown for different impingement Reynolds numbers. The results are compared with respect to the local and overall heat transfer.
Rotating Stall Model and Simulation of Two-Stage Centrifugal Compressors
Authors: Scano Lorenzo , Arnulfi Gianmario L.
Published: March 2009

Often turbo-compressors exhibit the maximum efficiency condition very close to the stall limit, so that it would be highly interesting to have a deep comprehension of this phenomenon. Despite the large diffusion of the multi-stage centrifugal compressors in different fields of the technology, such as natural gas pipe-lines or chemical factories, at the best authors’ knowledge, to date no theoretical model exists for rotating stall in these machines. This paper deals with a model for simulating multi-stage centrifugal compressor flow pattern during rotating stall. The model is not able to capture the stall inception, so the velocity and pressure fields are calculated throughout the machine once rotating stall has developed. The model consists of an implementation of that proposed by Moore for single-stage centrifugal compressors, so the simplifying hypotheses are: irrotational upstream fluid flow, inviscid and incompressible flow, stationary flow in the frame rotating at the same frequency of the stall cell; infinite blades are supposed both in rotors and return channel. Even if these fluid-dynamic hypotheses are really strong, it is worth of note that the reference models for rotating stall simulation in turbo-compressors (namely the Moore’s models) are based, at the present time, on them. In a previous step of this research, the authors utilized a semi-empirical approach, with phases changes between first and second diffuser based on experimental data. Now this hypothesis is removed and the model is fully analytical. The mathematical model is solved by numerical way, leaving the original semi-analytical scheme of Moore, so allowing the stall cell propagation frequency to be calculated. The computer code is written in C language for Linux operating system. It was tested in single-stage configuration with results according to Moore’s theory; for two-stage setup, obtained results appear consistent and qualitatively according with experimental tests and, unlike the single stage analysis, only fast rotation waves were found.
Environmental Degradation of Heat-Resistant Alloys During Exposure to Simulated and Actual Gas Turbine Recuperator Environments
Authors: Rakowski James M. , Stinner Charles P. , Lipschutz Mark , Montague J. Preston
Published: March 2009

Primary surface recuperators (PSR’s) for land-based industrial gas turbines are typically constructed from heat-resistant alloys such as austenitic stainless steels or nickel-base superalloys. The water vapor present in gas turbine exhaust has been shown to increase the rate of chromium oxide volatility, which in turn can cause rapid oxidation of the underlying metal. As PSR’s are generally fabricated from thin foil materials, excessive degradation can cause perforation, leading to failure of components. The results of an extensive laboratory test program to characterize the performance of heat-resistant alloys will be summarized, outlining the different modes of attack and means for their mitigation. These results will be compared to an investigation carried out using sub-size recuperator components which were exposed to a full-flow exhaust stream during gas turbine operation for times ranging from a few weeks to over one year.
Thermodynamic Analysis of CO2 Capture Cycles Using Pre-Combustion Decarbonization and Membrane Technologies
Authors: Zausner Jack
Published: March 2009

Over the past 5–10 years, interest has increased significantly in CO2 free power generation cycles. This study focuses on precombustion decarbonization cycles that reform syngas, separating the CO2 using a membrane, and then burning hydrogen-rich fuel in a gas turbine. The syngas reforming section is comprised of 1) Auto-thermal reformer (ATR) used for syngas production 2) water gas shift reactor (WGSR) to shift CO into CO2 3) CO2 -separation membrane and 4) combustion with hydrogen rich fuel. Overall performance shows an efficiency loss of 8.4% and 10.6% compared to the baseline cycle for the high and low temperature CO2 membrane cycles examined. The operating temperatures of the membranes are limited by the exothermic CO shift reaction favoring lower temperatures. Furthermore, a chemical exergy analysis of the reformers in the decarbonization system is undertaken to understand the impact of fuel reforming.
Evaluation of Failsafe Performance for Hot Gas Filtration
Authors: Howard Nikia , Guan Xiaofeng , Martin Ruth Ann , Dahlin Robert S. , Landham E. Carl
Published: March 2009

The Power Systems Development Facility (PSDF) is an engineering-scale demonstration facility of advanced coal-fired power systems and high-temperature, high-pressure gas filtration systems. The PSDF was designed at sufficient size so that system components can be evaluated and assessed in an integrated fashion to provide data for commercial scale-up. The PSDF is funded by the U.S. Department of Energy, the Electric Power Research Institute, Southern Company, Siemens Power Generation, Kellogg Brown & Root (KBR), Peabody Energy, Burlington Northern Santa Fe Corporation, and the Lignite Energy Council. Coal gasification at the PSDF is achieved with the KBR Transport Gasifier. Particulate laden gas exiting the gasifier is filtered by a downstream particulate control device (PCD). The PCD is a hot-gas filter that can hold up to 91 filter elements arranged in two tiers, with 36 elements in the top cluster and up to 55 elements in the bottom cluster. More than 30 different types of sintered metal powder, metal fiber, and ceramic filter elements have been tested. As of October 2006, the longest exposure of an individual element was approximately 8550 hours, which was achieved with a Pall iron aluminide sintered metal powder element. The outlet particle loading during normal operation has been reliably maintained within the lower limit of measurement resolution (routinely less than 0.1 ppmw). Downstream of each filter element is a failsafe device to prevent particulate leakage in the event of a filter element failure. The failsafe device is a small filter element or other type of particle collector and serves as a backup to the primary filter element. Demonstration of reliable failsafes is a critical factor in advancing hot gas filtration technology and increasing readiness for commercialization. A failsafe test program was developed at the PSDF to identify failsafe devices that would provide satisfactory protection of a gas turbine from particulate damage. In tests that simulated the failure of a single filter element, both metallic and ceramic failsafe devices were typically able to produce an outlet particle loading below 0.1 ppmw after an initial period of seasoning. From the overall particulate collection efficiency point of view, the failsafes tested showed promising results of protecting a gas turbine from being damaged by particles in the event of a filter failure. This paper focuses on failsafe performance and effectiveness in preventing particulate leaking through the PCD in the event of a filter element failure.
Effect of Fuel Composition on Emissions From a Low-Swirl Burner
Authors: Sequera Daniel , Agrawal Ajay K.
Published: March 2009

Lean Premixed Combustion (LPM) is a widely used approach to effectively reduce pollutant emissions in advanced gas turbines. Most LPM combustion systems employ the swirling flow with a bluff body at the center to stabilize the flame. The flow recirculation region established downstream of the bluff-body brings combustion products in contact with fresh reactants to sustain the reactions. However, such systems are prone to combustion oscillations and flame flashback, especially if high hydrogen containing fuels are used. Low-Swirl Injector (LSI) is an innovative approach, whereby a freely propagating LPM flame is stabilized in a diverging flow field surrounded by a weakly-swirling flow. The LSI is devoid of the flow recirculation region in the reaction zone. In the present study, emissions measurements are reported for a LSI operated on mixtures of methane (CH4), hydrogen (H2), and carbon monoxide (CO) to simulate H2 synthetic gas produced by coal gasification. For a fixed adiabatic flame temperature and air flow rate, CH4 content of the fuel in atmospheric pressure experiments is varied from 100% to 50% (by volume) with the remainder of the fuel containing equal amounts of CO and H2. For each test case, the CO and nitric oxide (NOx) emissions are measured axially at the combustor center and radially at several axial locations. Results show that the LSI provides stable flame for a range of operating conditions and fuel mixtures. The emissions are relatively insensitive to the fuel composition within the operational range of the present experiments.
Performance of a Pulse Detonation Combustor-Based Hybrid Engine
Authors: Tangirala Venkat E. , Rasheed Adam , Dean Anthony J.
Published: March 2009

A key concept envisioned for Pulse Detonation Engine (PDE) technology is a hybrid engine, where a Pulse Detonation Combustor (PDC) replaces the combustor in a conventional gas turbine. A systems level performance estimation model for a PDC-based hybrid engine cycle was presented. A variable property formulation was used to estimate the cycle performance parameters namely the thermal efficiency (ηth) and the net specific work (Wnet). Performance estimations were obtained using a one-step finite-rate chemistry to simulate reactions, and the frozen reactions assumption to model the products of combustion. Two specific parametric studies are performed in which the compression ratio (CR) and the purge fraction (pf) were systematically varied. The predicted variations of ηth and Wnet with varying compression ratio and purge fraction are in agreement with the trends reported in the literature. For a range of values of CR (1-40), performance (ηth) advantage of a PDC-based hybrid engine is predicted, when compared to a conventional gas turbine engine. The present calculations show that the assumed unsteady turbine component efficiency (ηT) for the case of a PDC-based hybrid engine has a large effect on ηth. An experimental study investigating the operation of a multi-tube PDC-turbine hybrid system was performed to understand the effect of unsteady flows entering the turbine on the turbine component performance (ηT). An eight-tube PDC can-annular configuration was integrated with a single-stage axial turbine nominally rated for 10 lbm/s, 25000 RPM and 1000 hp. The system accumulated a total of 144 minutes of operation with long duration runs of approximately 5 minutes, in order for the rig to achieve thermal steady state and for the turbine to attain constant speed. The turbine component efficiency was found to be similar under PDC-fired operation and steady flow operation within the uncertainty of the measurement.
Numerical Assessment of SCAP: A Passive System for Preventing Thermoacoustic Oscillations in Gas Turbine Annular Combustors
Authors: Tiribuzi Stefano
Published: March 2009

ENEL operates a dozen combined cycle units whose V94.3A gas turbines are equipped with annular combustors. In such lean premixed gas turbines, particular operation conditions could trigger large pressure oscillations due to thermoacoustic instabilities. The ENEL Research unit is studying this phenomenon in order to find out methods which could avoid or mitigate such events. The use of effective numerical analysis techniques allowed us to investigate the realistic time evolution and behaviour of the acoustic fields associated with this phenomenon. KIEN, an in-house low diffusive URANS code capable of simulating 3D reactive flows, has been used in the Very Rough Grid approach. This approach permits the simulation, with a reasonable computational time, of quite long real transients with a computational domain extended over all the resonant volumes involved in the acoustic phenomenon. The V94.3A gas turbine model was set up with a full combustor 3D grid, going from the compressor outlet up to the turbine inlet, including both the annular plenum and the annular combustion chamber. The grid extends over the entire circular angle, including all the 24 premixed burners. Numerical runs were performed with the normal V94.3A combustor configuration, with input parameters set so as no oscillations develop in the standard ambient conditions. Wide pressure oscillations on the contrary are associated with the circumferential acoustic modes of the combustor, which have their onset and grow when winter ambient conditions are assumed. These results also confirmed that the sustaining mechanism is based on the equivalence ratio fluctuation of premix mixture and that plenum plays an important role in such mechanism. Based on these findings, a system for controlling the thermoacoustic oscillation has been conceived (Patent Pending), which acts on the plenum side of the combustor. This system, called SCAP (Segmentation of Combustor Annular Plenum), is based on the subdivision of the plenum annular volume by means of a few meridionally oriented walls. Repetition of KIEN runs with a SCAP configuration, in which a suitable number of segmentation walls were properly arranged in the annular plenum, demonstrated the effectiveness of this solution in preventing the development of wide thermoacoustic oscillations in the combustor.
The Influence of Blade Tip Gap Variation on the Flow Through an Aggressive S-Shaped Intermediate Turbine Duct Downstream a Transonic Turbine Stage: Part II — Time-Resolved Results and Surface Flow
Authors: Go¨ttlich E. , Marn A. , Pecnik R. , Malzacher F. J. , Schennach O. , Pirker H. P.
Published: March 2009

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters rotating at lower speed. Therefore it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at larger diameter without any separation or flow disturbances. Due to costs and weight this intermediate turbine duct has to be as short as possible leading to aggressive (high diffusion) S-shaped duct geometries. To investigate the influence of the blade tip gap size on such a nonseparating high diffusion duct flow a detailed test arrangement under engine representative conditions is necessary. Therefore the continuously operating Transonic Test Turbine Facility (TTTF) at Graz University of Technology has been adapted: An high diffusion intermediate duct is arranged downstream of a HP turbine stage providing an exit Mach number of about 0.6 and a swirl angle of −15 degrees. A LP vane row is located at the end of the duct and represents the counter rotating low pressure turbine at larger diameter. In order to determine the influence of the blade tip gap size on the flow through such an S-shaped turbine duct measurements were performed with two different tip gap sizes, 0.8 mm and 1.3 mm. The aerodynamic design was done by MTU Aero Engines. While Part I describes the investigation by means of five hole probes with thermo couples, boundary layer rakes and static pressure tappings Part II uses Laser-Doppler-Velocimetry (LDV) for measurements at duct inlet directly downstream the HP blades to obtain unsteady information about the inflow and to quantify the differences between the two tip gaps. Additionally oil-film visualization was used to discuss the surface flow at the outer and inner wall of the duct. A comparison with a numerical simulation is also given. This work is part of the EU-project AIDA (Aggressive Intermediate Duct Aerodynamics, Contract: AST3-CT-2003-502836).
Development and Testing of a Novel Centrifugal Gas Turbine Design: Combustor Development and Load Testing
Authors: Brun Klaus , Gernentz Ryan S.
Published: March 2009

A novel centrifugal gas turbine design was developed and prototype tested. The research effort consisted of the design, development, and full prototype testing of a 50 HP centrifugal gas turbine. The novelty of the centrifugal gas turbine concept is that it is based on a radial flow gas turbine consisting of a centrifugal compressor and impulse turbine mounted on the same side of a rotating wheel. The radial flow-vaned combustor is mounted on the wheel’s stationary shroud; consequently, there is no 180-degree flow turning required as in conventional radial flow gas turbines. This very simple and rugged gas turbine concept has the following major advantages: • Single rotating component (i.e., mechanically simple and compact gas turbine). • Portability. • Short axial span. • High tolerance to injection of particulate matter. • Simple construction; low manufacturing costs. This project included the conceptual design, structural and aerodynamic analysis, performance prediction modeling, detailed design, prototype fabrication, test rig instrumentation, compressor/turbine characterization, rotordynamic signature, combustor design, combustor testing, controls implementation, light-off testing, no-load testing, and performance testing of the gas turbine. Design analyses that were performed included 1-D thermodynamics, finite element structural and thermal, rotordynamic, 2-D blade path optimization, and 3-D Computational Fluid Dynamics (CFD). Testing of all individual gas turbine elements (compressor, combustor, and turbine) as well as the entire assembly was completed. Tests showed that stable gas turbine combustion was achieved up to 26,000 RPM. The gas turbine reached self-sustaining power at 21,000 RPM and 405°C firing temperature. Thus, the centrifugal gas turbine concept was demonstrated to function properly and to achieve positive power output. However, the design output power was not achieved because of combustion stability range limitations at speeds above 20,000 RPM. Maximum output power achieved was 1.4 kW at 23,000 RPM. Recommendations are provided to overcome these operational limitations in the next model centrifugal gas turbine.