bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of NOx Formation in a Hydrogen Fueled Gas Turbine Engine
Authors: Therkelsen Peter , Werts Tavis , McDonell Vincent , Samuelsen Scott
Published: August 2009

A commercially available natural gas fueled gas turbine engine was operated on hydrogen. Three sets of fuel injectors were developed to facilitate stable operation while generating differing levels of fuel/air premixing. One set was designed to produce near uniform mixing while the others have differing degrees of non-uniformity. The emissions performance of the engine over its full range of loads is characterized for each of the injector sets. In addition, the performance is also assessed for the set with near uniform mixing as operated on natural gas. The results show that improved mixing and lower equivalence ratio decreases NO emission levels as expected. However, even with nearly perfect premixing, it is found that the engine, when operated on hydrogen, produces a higher amount of NO than when operated with natural gas. Much of this attributed to the higher equivalence ratios that the engine operates on when firing hydrogen. However, even at the lowest equivalence ratios run at low power conditions, higher NO was observed. Analysis of the potential NO formation effects of residence time, kinetic pathways of NO production via NNH, and the kinetics of the dilute combustion strategy used are evaluated. While no one mechanism appears to explain the reasons for the higher NO, it is concluded that each may be contributing to the higher NO emissions observed with hydrogen. In the present configuration with the commercial control system operating normally, it is evident that system level effects are also contributing to the observed NO emission differences between hydrogen and natural gas.
A Numerical Study of Anti-Vortex Film Cooling Designs at High Blowing Ratio
Authors: Heidmann James D.
Published: August 2009

A concept for mitigating the adverse effects of jet vorticity and lift-off at high blowing ratios for turbine film cooling flows has been developed and studied at NASA Glenn Research Center. This “anti-vortex” film cooling concept proposes the addition of two branched holes from each primary hole in order to produce a vorticity counter to the detrimental kidney vortices from the main jet. These vortices typically entrain hot freestream gas and are associated with jet separation from the turbine blade surface. The anti-vortex design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The anti-vortex film cooling hole concept has been modeled computationally for a single row of 30 degree angled holes on a flat surface using the 3D Navier-Stokes solver Glenn-HT. A modification of the anti-vortex concept whereby the branched holes exit adjacent to the main hole has been studied computationally for blowing ratios of 1.0 and 2.0 and at density ratios of 1.0 and 2.0. This modified concept was selected because it has shown the most promise in recent experimental studies. The computational results show that the modified design improves the film cooling effectiveness relative to the round hole baseline and previous anti-vortex cases, in confirmation of the experimental studies.
Numerical Simulation of Endwall Fence on the Secondary Flow in Compressor Cascade
Authors: Zhong Jingjun , Han Ji-Ang , Liu Yanming , Tian Fu
Published: August 2009

In this paper, based on the experimental data, a detailed numerical simulation has been carried out for the compressor cascade composed of CDA blades with fences on the endwall. There are several different configurations of the endwall fences, such as length, height, and pitch-wise location for the endwall fence. The optimum lengths, height, pitch-wise or span-wise location of the fences on the cascade end walls are obtained. The process of endwall fence’s controlling secondary flow in the compressor cascade mainly lies in two ways: hindering crosswise flow from pressure surface to suction surface near the endwall of the cascade; forming and developing of fence vortex, in which the fence blockage effect is more important. Endwall fences has a significant effect on the vortices distribution, in which the formation and development of fence vortex is important. Its formation has a close relationship with the strength of the crossflow at the region between the pressure surface and fence, which is mainly due to the relative airflow movement when the pressure side branch of the horseshoe vortex rolls up and lift along the fence. For the fence vortex and passage vortex have the different rotation direction, it plays an important role in decreasing the secondary flow loss, furthermore, reducing the strength of the passage vortex. In general, stronger crosswise flow induces stronger fence vortex. As height and length of the fence increased, the blockage effect is more obvious, but the additional fence losses increased at the same time. Numerical results show that the fences, with one third of height of the inlet boundary layer thickness and the length of 75 percent axial chord, are most effective when they are located 30 percent of pitch far from the pressure surface of the blade. For all the computational cases, they reduce the cascade loss furthest respectively.
Test-Model Correlation of Dry-Friction Damping Phenomena in Aero-Engines
Authors: Jean P. , Gibert C. , Dupont C. , Lombard J.-P.
Published: August 2009

In order to control the risk of high cycle fatigue of bladed disks, it is important to predict precisely the vibration levels and to design damping solutions to attenuate them. Therefore, Snecma has made some efforts in the last years in order to characterize better the damping in aero-engines. Among the various damping sources, friction damping is particularly difficult to model due to its non-linear behaviour [1]. For that purpose, two methods based on multi-harmonic balance strategy have been especially developed for Snecma, dedicated to the study of the non-linear forced response of bladed disks. The first one enables to model the bladed disk equipped with dry-friction dampers [2], and the second one takes into account intrinsic friction located in disk-blade interface [3]. To validate both models experimentally, a test campaign has been carried out in a vacuum chamber on a rotating bladed disk excited by piezoelectric actuators. The blade shanks have been softened in order to increase friction effects. Experimental results show a regular and reproducible behaviour of the non-linear forced response, over various rotation speed and excitation levels. The contributions of friction dampers and friction in blade attachment have been decoupled thanks to glue applied in the blade root. Both friction phenomena that were observed experimentally at resonance of the blade first bending mode have been reproduced numerically. After updating modeling parameters, an acceptable correlation was found on resonance frequencies, amplitudes and damping levels over the full experimental setup range, which validates these numerical tools for their use in design process.
Toward the Expansion of Low-Pressure-Turbine Airfoil Design Space
Authors: Praisner T. J. , Grover E. A. , Knezevici D. C. , Popovic I. , Sjolander S. A. , Clark J. P. , Sondergaard R.
Published: August 2009

Future engine requirements, including high-altitude flight of unmanned air vehicles, as well as an impetus to reduce engine cost and weight, are challenging the current state of the art in low-pressure-turbine airfoil design. These new requirements present low-Reynolds number challenges as well as the need for high-performance, high-lift design concepts. Here we report on an effort to expand the relatively well established aerodynamic design space for low-pressure turbine airfoils through the application of recent developments in transition modeling to airfoil design. Analytical and experimental mid-span performance data and predicted loadings are presented for four high-lift airfoil designs based on the Pack B velocity triangles. The new designs represent a systematic expansion of low-pressure turbine airfoil design space through the application of high-lift design concepts for front- and aft-loaded airfoils. All four designs performed as predicted across a range of operationally representative Reynolds numbers. Full-span loss data for the new high-lift designs reveal increased endwall losses, which, with the application of non-axisymmetric endwall contouring, have been substantially reduced. Taken holistically, the results presented here demonstrate that accurate transition modeling provides a reliable method to develop optimized, very high-lift airfoil designs. However, further improvements in endwall-loss mitigation technologies are required to enable the implementation of the very high-lift technology presented here in engine systems.
Experimental Investigation of a Single Stage Helium Axial Compressor of HTGR-10 Power Conversion Unit
Authors: Zhu Rongkai , Zheng Qun , Zou Jiguo , Bhargava Rakesh
Published: August 2009

This paper focuses on an experimental investigation of a helium compressor, a major component of the Power Conversion Unit (PCU), used in a High Temperature Gas Cooled Reactor (HTGR). The PCU system uses a direct Helium Brayton cycle for the power conversion. In this configuration, there is a strong coupling between the helium compressor and the other components of the PCU system. The estimations of compressor performance in stable and transient operational states are of high importance for the designer. Because of the difficulties in testing a compressor with helium as a working fluid, simulations methods using air to replace helium as a compressor working fluid in the experiments are researched. An experimental compressor system is built to investigate the performance of a helium compressor. Under different operating conditions, the compressor performance characteristics are obtained and compared with that of an air compressor. The possibility and the effective approach of designing a helium compressor based on the experimental data of an air compressor are studied. The experimental results showed that air under the correct flow conditions, identified using similitude analysis, can be used to test a helium compressor instead of far more expensive helium.
Investigation of the Flow in Centrifugal Compressor Volute
Authors: Xu C. , Amano R. S.
Published: August 2009

Volute is used to collect and transport swirling gas produced by impeller or diffuser. Design of the volute not only impacts compressor efficiency but also influences the operating ranges of the compressor. In this study, Navier-Stokes equations combined with an algebra turbulence model were used to simulate flows inside a single stage compressor. Detailed flow simulations for a large cut back tongue volute are presented and discussed. A rounded tongue volute was tested in a single stage test rig. The compressor stage performance tests were conducted in the test lab and static pressure taps were used to measure static pressures at volute internal walls at locations of θ = 240° and 360°. Thermal couples and other static pressure probes were instrumented at inlet and outlet of the compressor for performance tests. The numerical results were compared with experiments and good agreements are found. Studies showed that a large cut back rounded tongue volute provided good operating range without dramatically dropping compressor peak efficiency.
Researches of Similitude Theory for Axial Flow Helium Compressor
Authors: Zhu Rongkai , Zheng Qun , Yue Guoqiang , Zou Jiguo
Published: August 2009

In designing of a helium axial compressor from its homologous air compressor, the similarities between them have to be investigated. Such as how to establish the similarity criterion, how to prescribe the experimental air compressor’s parameters by the similitude laws, how to get the performance data of helium compressor from the air compressor test data etc, are important for the accurate design. The first stage of a high pressure helium compressor is taken as experimental model, with air as the working fluids in the experiments. The differences of physical parameters of helium and air, like density, viscosity, adiabatic exponent have been considered. The similitude laws used in the experiment have been established, and the reasons of deviation and correcting methods are analyzed. These results are useful references for the aerodynamic design of helium compressor.
Experimental and Theoretical Investigation of Centrifugal Compressor Performance Characteristics
Authors: Motavalli Sayyed Mostafa , Hajilouy-Benisi Ali , Nili-Ahmadabadi Mahdi
Published: August 2009

Prediction of compressor performance is a basic step in design of this turbomachine, while designer can optimize plan by considering various conditions and calculating machine performance. Flow field in centrifugal compressor is three-dimensional and intricate. Since 2-D and 3-D methods are very costly, consequently the mean line method usually is used for predicting compressor performance. The energy loss coefficients are used for this method. Because of the intricacy in flow and analysis of losses, most energy loss coefficients are attained by experimental procedures, however just some of them are determined according to theory and nature of the flow field. The purpose of this work is experimental and theoretical investigation on performance of the centrifugal compressor. The computer code based on 1-D modeling with energy loss coefficients is provided and it is modified according to the effects of splitters. In this model most of the various relations in the literature are examined. Finally experimental results are used for investigation of correctness of the model. Experimental studies are carried out on compressor of a S2B model of Shwitzer turbocharger at Sharif University of Technology turbocharger lab. Experimental and model results comparison demonstrates close correspondence between modified model results and compressor performance.
Design Procedure of a Novel Micro-Turbine Low NOx Conical Wire-Mesh Duct Burner
Authors: Ramadan Omar B. , Gauthier J. E. Donald , Hughes Patrick M. , Brandon Robert
Published: August 2009

Nowadays, air pollution and climate change have become a global environmental problem. As a result, government regulations worldwide are becoming increasingly stringent. This has led to an urgent need to develop new designs and methods for improving combustion systems to minimize the production of toxic emissions, such as nitrogen oxides. Micro-turbine based cogeneration units are one of the interesting alternatives for combined electrical power and heat generation (CHP). Micro-turbine CHP technology still needs to be developed to increase efficiency, heat-to-power ratio and improve operating flexibility. This can all be obtained by adding a duct burner to the CHP unit. This paper documents the design process for a novel low NOx conical wire-mesh duct burner for the development of a more efficient micro-cogeneration unit. This burner provides the thermal energy necessary to raise the micro-turbine exhaust gases temperature to increase the heat recovery capability. The duct burner implements both lean premixed and surface combustion techniques to achieve low NOx and CO emission levels. The design process includes a set of preliminary design procedures relating the use of empirical and semi-empirical models. The preliminary design procedures were verified and validated for key components, such as the duct burner premixer, using Laser sheet illumination technique (LSI). The LSI was used to study the mixing process inside the premixer fitted with different swirlers. The designed duct burner was successfully operated in a blue flame mode over a wide range of conditions with NOx emissions of less than 5 ppmv and CO emissions of less than 10 ppmv (corrected to 15% O2).
Optimum Planning of Electricity Production
Authors: Cerri Giovanni , Gazzino Marco , Iacobone Francesca Alessandra , Giovannelli Ambra
Published: August 2009

The power production planning problem has been deeply investigated. Maintenance management and load allocation problems have been assumed as crucial aspects for achieving maximum plant profitability. Modelling of life consumption of hot section components has been considered as one of the key feature necessary to simulate the plant behaviour. The approach takes market scenarios, as well as actual status and performance of plant components into account. A supervisor algorithm provides the operating parameters needed to establish each plant loading. Economic implications related to maintenance strategies including postponement or anticipation of maintenance interventions are investigated and results obtained by the numerical simulation are presented and widely discussed.
Numerical Simulation of the Flow Pulsations Origin in Cascades of the Rear Blade Rows in a Gas Turbine Axial Compressor Using Low Calorific Fuel
Authors: Cyrus Vaclav , Polansky Jiri
Published: August 2009

Fatigue failure of the last three stator rows vanes (S17, EGV1 and EGV2) in the seventeen stage gas turbine axial compressor occurred in the power plant where low calorific fuel, syngas, was used. Causes of this dangerous phenomenon were flow pulsations with the frequency of 380 to 400 Hz that were found by the experimental investigation of the duty gas turbine. Mechanism of the flow unsteadiness origin was studied with the help of flow simulations in 2D stator cascade system. Three numerical experiments were carried out. The first experiment investigated the flow simulation in the stator cascades system with a steady undisturbed inlet flow with increased turbulence intensity. Obtained data did not meet the standards of the actual compressor operations. In the remaining two numerical experiments a purposely designed rotor cascade was located in front of the stator cascades. Shedding of vortex structures from the cascade profile surfaces at positive incidence angles is responsible for the flow pulsation origin. The interaction of rotor wakes / stator S17 cascade plays an important role in the investigated phenomenon, as follows from CFD data. Aerodynamic loading of both cascades is equal in the second group of numerical experiments. Computed results were in a good qualitative agreement with the experimental ones. As the flow in rotor cascade was not separated, owing to the different aerodynamic loading of rotor and stator S17 cascades, the vortices shedding in stator cascade S17 had a significantly higher frequency of f = 2200 to 2300 Hz than in other investigated cases.
Numerical Simulation to Determine Ejection Device Geometry for Turbo-Shaft Driven Water Pump
Authors: Popescu Jeni A. , Vilag Valeriu A. , Petcu Romulus , Vataman Ion , Silivestru Valentin
Published: August 2009

Turbo-engines with known performances reaching the end of their useful flying life can become useful assets in the execution of industrial projects. One such project reported in this paper is to install a high capacity complex device which will clear out the water in cases of floods. The partnership created in order to accomplish the task includes specialists in energetic, turbo-machinery, amelioration, hydraulic and action logistics fields and is aiming to acquire knowledge, results and experience and to transfer the information to economic and social environment. The TV2-117A turbo-shaft is the main component of the power group representing the energy source of the installation. It is connected to a reducer gear-box and a high capacity water pump. Considering the purpose of the installation to be realised, a device destined to handle natural calamities effects, the solution must fulfil several very important conditions: mobility, power and reliability. Being known the fact that moving elements have lower reliability conducts to the idea of an oil cooling system without mechanical or electrical driven fans. This is possible through using the ejection effect in a system based on the exhausted hot gases from the turbo-engine. The ejection device is a tubular structure using three concentric tubes on the outlet. The central one absorbs the hot gases and drives the cool air from the surrounding environment through the other two to accomplish both the oil and turbo-engine box cooling. The numerical analysis, using a CFD code, is still in progress and the paper presents intermediate results. The CFD conditions were imposed by the turbo-engine experimental data obtained in previous tests and the known working conditions established for the device to be created. The preliminary results helped to eliminate many flow problems caused by geometric dimensions and to establish the necessary adjustments in order to obtain the expected mass flow and speed values for the cooling devices. The adjustments on the geometry consisted in modifying the lengths, the bending and the diameters of the tubes. The final and most suitable geometry is still to be determined using the CFD code.
Experimental Study of Combustion on a Micro Gas Turbine Combustor
Authors: Wang Feng-Shan , Kong Wen-Jun , Wang Bao-Rui
Published: August 2009

A research program is in development in China as a demonstrator of combined cooling, heating and power system (CCHP). In this program, a micro gas turbine with net electrical output around 100kW is designed and developed. The combustor is designed for natural gas operation and oil fuel operation, respectively. In this paper, a prototype can combustor for the oil fuel was studied by the experiments. In this paper, the combustor was tested using the ambient pressure combustor test facility. The sensors were equipped to measure the combustion performance; the exhaust gas was sampled and analyzed by a gas analyzer device. From the tests and experiments, combustion efficiency, pattern factor at the exit, the surface temperature profile of the outer liner wall, the total pressure loss factor of the combustion chamber with and without burning, and the pollutants emission fraction at the combustor exit were obtained. It is also found that with increasing of the inlet temperature, the combustion efficiency and the total pressure loss factor increased, while the exit pattern factor coefficient reduced. The emissions of CO and unburned hydrogen carbon (UHC) significantly reduced, but the emission of NOx significantly increased.
EVITA Study: Evaluation of Unscheduled Aircraft and Industrial Gas Turbine Part Failure Cases
Authors: Kool Gerrit , van den Elshout Jacques , Vogelaar Eric , van Gestel Ron , Mom Andre´
Published: August 2009

Maintenance costs of gas turbines are mainly driven by replacement costs of expensive parts. Reconditioning of these parts is considered to decrease the costs significantly, but it is the impression that re-used parts tend to be more involved in part failures. This is sometimes related to microstructural changes in the substrate materials owing to part repair. One hundred and nine (109) unscheduled gas turbine component failure cases have been collected and analyzed to identify causes of failure and contributing factors, and also to provide guidance on corrective measures such as design changes, new repair methods, missing information links and future R&D efforts. It was found that the most frequently reported failure mechanisms are mechanical and thermal fatigue and changes in the microstructure. Fifty percent (50%) of the reported failure cases have a root cause in the original component design and repair design, and consequently permanent solutions can be achieved by design modifications only. The paper concludes with the identification of knowledge gaps.
Compliant Hybrid Journal Bearings Using Integral Wire Mesh Dampers
Authors: Ertas Bugra H.
Published: August 2009

The following work presents a new type of hybrid journal bearing developed for enabling oil-free operation of high performance turbomachinery. The new design integrates compliant hydrostatic-hydrodynamic partitioned bearing pads with two flexibly mounted integral wire mesh dampers (IWMD). The primary aim of the new bearing configuration was to maximize the load carrying capacity and effective damping levels while maintaining adequate compliance to misalignment and variations in rotor geometry. The concept of operation is discussed along with the description of the bearing design. Several experiments using room temperature air as the working fluid were performed that demonstrate proof of concept, which include lift-off tests, bearing load tests, and rotordynamic characterization tests. The experiments demonstrate stable operation to 40,000 rpm (2.8 million DN) of a 2.750 in (70 mm) diameter bearing. In addition to the experimental results, an analytical model is presented for the compliant bearing system. The aeroelastic theory couples the steady state numerical solution of the compressible Reynolds flow equation with a flexible structure possessing translational and rotational compliance. This was achieved by formulating a fluid-structure force balance for each partitioned bearing pad while maintaining a global mass flow balance through the hydrostatic restrictors and bearing lands. Example numerical results for pad pressure profile, film thickness, torque, and leakage are shown.
Turbocharger Performance Maps Building Using a Hot Gas Test Stand
Authors: Venson Giuliano Gardolinski , Barros Jose´ Eduardo Mautone
Published: August 2009

This work presents the experimental methodology used in turbochargers tests using a hot gas test stand. The test consists in recording the characteristic curves of the turbochargers, known as flow maps or performance maps. A tubular combustion chamber, designed to operate burning gaseous fuels, is used to drive the set. By using a hot gas generator it’s possible to simulate the real operational condition of the turbine. The experimental configuration allows reproducing the self-sustained turbocharger operation. The test stand instrumentation is based on virtual instrumentation, where acquisition of the sensors and control are made by computer. For the performance maps obtainment, the experimental data are treated through an empirical model based in a quadratic equation involving two variables, mass flow rate and rotational speed. The results present the performance and efficiency maps for the APL-240 Master Power turbocharger, used in commercial heavy trucks. With the results is made a comparison between the experimental maps with the maps gotten through a semi-empirical model based in modified Euler equation. The maximum deviation for compressor and turbine semi-empirical pressure ratios are respectively 8% and 14% in relation to the experimental data.
Generation of a Quasi 3-D Map of a Half-Embedded Ultra High Bypass Ratio Turbofan Intake on the Wing of a Broad Delta Wing Airframe
Authors: Rousselot S. , Truffi D. , Doulgeris G. , Mistry S. , Pachidis V. , Pilidis P.
Published: August 2009

The need for low fuel consumption, emissions and noise drives future propulsion systems towards ultra high bypass ratio turbofan configurations. One of the arising challenges is the installation of such an engine, due to its high diameter. An alternative to under-the-wing podded installation is half embedding it into a thick wing. An ideal airframe has been found to be the Broad Delta (BD) wing, featuring high wing-root thickness. Two conventional nacelles have been integrated into each wing of a four-engine BD body. The performance of a half embedded turbofan intake has been studied, with the use of 3-D Computational Fluid Dynamics. This qualitative analysis comprises of full scale aircraft simulation with special focus on the flow-field upstream and inside the novel installation. The study required the creation of a detailed map of the intake for cruise and take-off flight conditions. The map comprises of radial pressure recovery profiles in various circumferential positions for enhanced representation of fan-inlet total pressure distortion. It is produced using a decoupled zooming process, where ‘matching’ between a 0-D gas turbine performance code and 3-D CFD is achieved for each operating point.
Employing Inverted Brayton Cycle to Solve Stack Temperature Problems After Water Recovery From HAT Cycle Exhaust Gas
Authors: Wan Kuifang , Xiao Yunhan , Zhang Shijie
Published: August 2009

By adding an induced draft fan or exhaust compressor between flue gas condenser and stack to make the turbine expand to a pressure much lower than ambient pressure, this paper actually employed inverted Brayton cycle to solve stack temperature problems after water recovery from Humid Air Turbine (HAT) cycle exhaust gas and compare the effect of different discharging methods on the system’s performance. Comparing with the methods of gas discharged directly or recuperated, this scenario can obtain the highest electrical efficiency under certain pressure ratio and turbine inlet temperature. Due to the introduction of induced draft fan, in spite of one intercooler, there are twice intercoolings during the whole compression since the flue gas condenser is equivalent to an intercooler but without additional pressure loss. So the compression work decreases. In addition, the working pressure of humidifier and its outlet water temperature are lowered for certain total pressure ratio to recover more exhaust heat. These enhance the electrical efficiency altogether. Calculation results show that the electrical efficiency is about 49% when the pressure ratio of the induced draft fan is 1.3∼1.5 and 1.5 percentage points higher than that of HAT with exhaust gas recuperated. The specific works among different discharging methods are very closely. However, water recovery is some extent difficult for HAT employing inverted Brayton cycle.
Low Leakage Designs for Rotor Teeth and Honeycomb Lands in Labyrinth Seals
Authors: Chougule Hasham H. , Ramerth Douglas , Ramachandran Dhinagaran
Published: August 2009

Design improvements on labyrinth seal teeth and a honeycomb land are examined by three-dimensional CFD numerical modeling of the flow field. The only objective is reduction of the total leakage through the new seal. CFD assumptions and analysis was validated by comparison with leakage data from labyrinth seal experiments conducted by Stocker [1]. The baseline chosen for comparison of sealing effectiveness is a conventional low clearance straight-through labyrinth seal with four teeth and a honeycomb land of symmetrical hexagonal cells. The proposed new seal has a staggered honeycomb land and straight teeth with an inclined notch. CFD predicts ∼17% reduction in seal leakage at a radial clearance of 0.005 inch (0.122mm) due to higher wall friction and flow turbulence.
Comparison the Cooling Performance of Cylindrical and Fan-Shaped Cooling Holes With Special Emphasis on the Effect of Internal Coolant Cross-Flow
Authors: Saumweber Christian , Schulz Achmed
Published: August 2009

Cooling holes in real gas turbine applications are prevalently exposed to cross-flow in the coolant passage. The majority of the studies available in literature do not consider the effects of flow in the coolant passage. Our own studies however reveal that especially diffuser holes are very susceptible in respect to cross-flow at the hole entrance, if the orientation of the cross-flow is perpendicular to the symmetry plane of the cooling hole. The effect of coolant cross-flow will be discussed in detail. The superordinate target is to identify the dominating mechanisms, which determine the flow field within the diffuser hole and hence limit the potential of cooling performance augmentation. For this reason a fan-shaped hole with 14° expansion angle will be compared to a simple cylindrical hole. Both holes have a length-to-diameter ratio of 6 and an inclination angle of 30°. The comparison will be performed by means of experimentally gained discharge coefficients, local and laterally averaged adiabatic film cooling effectiveness, and heat transfer coefficients. Numerical simulations of the cooling flow will support the interpretation of the experimental results.
Simulation of Hydrogen Production From Biomass Pyrolysis Gas by Secondary Steam Reforming
Authors: Lin Leteng , Sun Li , Zhang Xiaodong , Yi Xiaolu , Xu Min
Published: August 2009

Hydrogen is currently being widely regarded as a futural energy carrier to reduce carbon emissions and other NOx and SOx pollutants. Many researchers have proved that hydrogen can be efficiently used in solid oxide fuel cells -gas turbine system (SOFC-GT) and molten carbonate fuel cells-gas turbine system (MCFC-GT). Hydrogen production from biomass resources offers the advantage of providing a renewable energy carrier for extensive reduction of the CO2 emission. A secondary steam reforming process which consists of steam reforming of methane and water gas shift was proposed to further convert CH4, CO and other hydrocarbons in biomass pyrolysis gas for promoting hydrogen yield. According to respective reaction mechanism, simulating calculations were carried out in two reforming processes separately. With the favor of PRO/II, the effects of reaction temperature and steam to carbon ratio on hydrogen yield were discussed in details in the steam reforming of methane. A reasonable calculation method was established for simulating the water gas shift process in which the effects of temperature and steam to CO ratio was investigated. The simulation made good results in optimizing reaction conditions for two reformers and predicting the volume rate of all gas components. It is proved by simulation that hydrogen-rich gas with >68 mol% H2 could be produced, and the hydrogen yield could reach 48.18 mol H2/(Kg Biomass) and 45.85 mol/(Kg Biomass) respectively when using corn straw and rice husk as feedstock. The experiment data from a related reference was adopted to prove the reasonability of the simulation results which could show the feasibility of secondary steam reforming process, as well as provide good references for practical process operation.
Investigation of Innovative Trailing Edge Cooling Configurations With Enlarged Pedestals and Square or Semicircular Ribs: Part II—Numerical Results
Authors: Di Carmine Emiliano , Facchini Bruno , Mangani Luca
Published: August 2009

Trailing edge is a critical region for turbine airfoils since this part of the blade has to match aerodynamic, cooling and structural requirements at the same time. In fact aerodynamic losses are strictly related to trailing edge thickness which, on the contrary, tends to be increased to implement an internal cooling system, in order to face high thermal loads. At the moment the most employed devices consist of pin fins of various shapes, which contribute to both heat transfer enhancement and structural resistance improvement. Enlarged pedestals decrease pressure losses in comparison with multirow pin fins, even if the heat transfer increase is limited. This work deals with the investigation of the usage of enlarged pedestals, inserted in a wedge shaped duct, in conjunction with square or semicircular rib turbulators. The aim of the analysis is the evaluation of the convective Heat Transfer Coefficient (HTC) distribution over the endwall surface and the pressure drop of the converging duct. Numerical analysis used 3D RANS calculations. An in-house modified object-oriented CFD code and a commercial one were used. Several turbulence models and mesh types were tested. Numerical calculations were compared with experimental results obtained on the same geometries using a transient Thermochromic Liquid Crystals (TLC) based technique. Goals of this comparison are both the evaluation of the accuracy of CFD packages with standard two equation turbulence models in heat transfer problems with complex geometries and the analysis of flow details to complete and support experimental activity.
Numerical and Experimental Damping Prediction of a Nonlinearly Coupled Low Pressure Steam Turbine Blading
Authors: Siewert Christian , Panning Lars , Gerber Christoph , Masserey Pierre-Alain
Published: August 2009

The rotor blades of a low pressure steam turbine stage are subjected to fluctuating steam forces during operation that cause blade vibrations. One of the main tasks in the design of low pressure steam turbine blading is the vibration amplitude reduction in order to avoid high dynamic stresses that could damage the blading. The vibration amplitudes of the blades in the last row of a low pressure steam turbine stage can be reduced significantly to a reasonable amount if adjacent blades are coupled by shroud and snubber contacts that reinforce the blading. Furthermore, in the case of blade vibrations, relative displacements between neighboring blades occur in the contacts and friction forces are generated that provide additional damping to the structure due to the energy dissipation caused by microslip effects. A three dimensional structural dynamics model including an appropriate spatial contact model is necessary to predict the generalized contact forces induced by the shroud and the snubber contacts and to describe the vibrational behavior of the blading with sufficient accuracy. To reduce the numerical effort to compute the vibration response, the Harmonic Balance Method (HBM) is applied to solve the resulting nonlinear equations of motion in the frequency domain.
Emission Characteristics of a Premixed Cyclic-Periodical-Mixing Combustor Operated With Hydrogen-Natural Gas Fuel Mixtures
Authors: Bru¨ckner-Kalb Jochen R. , Kro¨sser Michael , Hirsch Christoph , Sattelmayer Thomas
Published: August 2009

The concept of the cyclic periodical mixing combustion process (CPMCP) [1, 2] for the extension of the lean blowout limit had been implemented in an atmospheric experimental combustor for testing with both external perfect [3] and technical [4] premixing of reactants. It had been tested with natural gas and has now been tested with a mixture of 70%Vol of hydrogen and 30%Vol of natural gas (98% CH4) as fuel. With natural gas the NOx emissions are unaffected by the limited technical premixing quality, as long as the air preheat is in the design range of the premixers [4]. Then, for adiabatic flame temperatures of up to 1630 K NOx emissions are below 1 ppm(v) with CO emissions below 8 ppm(v) in the whole operation range of the test combustor (15% O2, dry). With the “70%Vol H2 – 30%Vol CH4” mixture the NOx emissions increase by nearly one order of magnitude. Then, NOx emissions below 7 ppm(v) (15% O2, dry) are achieved for adiabatic flame temperatures of up to 1600 K. They approach the 1 ppm(v) level only for flame temperatures below 1450 K. CO emissions are below 4 ppm(v). The reason for the increase of the NOx emissions is the higher reactivity of the mixture, which leads to earlier ignition in zones of still elevated unmixedness of reactants near the premixer-injector exits. This effect was investigated by chemical reactor network simulations, analyzing a pressure effect and an additional chemical effect of hydrogen combustion on NOx formation.
Design and Optimization of the Internal Cooling Channels of a HP Turbine Blade: Part I—Methodology
Authors: Amaral Sergio , Verstraete Tom , Van den Braembussche Rene´ , Arts Tony
Published: August 2009

This first paper describes the Conjugate Heat Transfer (CHT) method and its application to the performance and lifetime prediction of a high pressure turbine blade operating at a very high inlet temperature. It is the analysis tool for the aerothermal optimization described in a second paper. The CHT method uses three separate solvers: a Navier-Stokes (NS) solver to predict the non-adiabatic external flow and heat flux, a Finite Element Analysis (FEA) to compute the heat conduction and stress within the solid, and a 1D aero-thermal model based on friction and heat transfer correlations for smooth and rib-roughened cooling channels. Special attention is given to the boundary conditions linking these solvers and to the stability of the complete CHT calculation procedure. The Larson-Miller parameter model is used to determine the creep-to-rupture failure lifetime of the blade. This model requires both the temperature and thermal stress inside the blade, calculated by the CHT and FEA. The CHT method is validated on two test cases: a gas turbine rotor blade without cooling and one with 5 cooling channels evenly distributed along the camber line. The metal temperature and thermal stress distribution in both blades are presented and the impact of the cooling channel geometry on lifetime is discussed.
Insights Into Discrepancies Between Results of Nonlinear and Linear Vibration Analyses of Rigid Rotors on Journal Bearings
Authors: Zachariadis Demetrio C.
Published: August 2009

A comparison between results of nonlinear and linear vibration analyses of rigid rotors supported on hydrodynamic journal bearings and subjected to standard unbalance loads shows that the discrepancies are relevant. Such discrepancies are attributed to the incompatibility between the vibration levels caused by these standard unbalance loads and the assumption of the existence of static equilibrium positions for the calculation of stiffness and damping coefficients.
An Experimental Study of Vane Clocking Effects on Embedded Compressor Stage Performance
Authors: Key Nicole L. , Lawless Patrick B. , Fleeter Sanford
Published: August 2009

Previous research has shown that vane clocking, the circumferential indexing of adjacent vane rows with similar vane counts, can be an effective means to increase stage performance, reduce discrete frequency noise, and/or reduce the unsteady blade forces that can lead to high cycle fatigue. The objective of this research was to experimentally investigate the effects of vane clocking in an embedded compressor stage, focusing on stage performance. Experiments were performed in the intermediate-speed Purdue 3-Stage Compressor, which consists of an IGV followed by three stages. The IGV, Stator 1, and Stator 2 vane rows have identical vane counts, and the effects of vane clocking were studied on Stage 2. Much effort went into refining performance measurements to enable the detection of small changes in stage efficiency associated with vane clocking. At design loading, the change in stage efficiency between the maximum and minimum efficiency clocking configurations was 0.27 points. The maximum efficiency clocking configuration positioned the Stator 1 wake at the Stator 2 leading edge. This condition produced a shallower and thinner Stator 2 wake compared to the clocking configuration that located the wake in the middle of the Stator 2 passage. At high loading, the change in Stage 2 efficiency associated with vane clocking effects increased to 1.07 points; however, the maximum efficiency clocking configuration was the case where the Stator 1 wake passed through the middle of the downstream vane passage. Thus, impingement of the upstream vane wake on the downstream vane leading edge resulted in the best performance at design point but provided the lowest efficiency at an off-design condition.
Test Results From the Advanced Humid Air Turbine System Pilot Plant: Part 2—Humidification, Water Recovery and Water Quality
Authors: Araki Hidefumi , Higuchi Shinichi , Koganezawa Tomomi , Marushima Shinya , Hatamiya Shigeo , Tsukamoto Moriaki
Published: August 2009

The AHAT (advanced humid air turbine) system has been studied to improve thermal efficiency of gas turbine power generation. This is an original gas turbine power generation system which substitutes the WAC (water atomization cooling) system for the intercooler system of the HAT cycle. A pilot plant was built to verify feasibility of the AHAT system, which is composed of a gas turbine, a humidification tower, a recuperator and a water recovery system. Firstly, characteristics of the humidification tower were examined. The experimental results of the humidification rate agreed with the calculation results within a deviation of 1%. Humidification increased the heat recovery, and the electrical efficiency exceeded 40%. Secondly, characteristics of the spray-type water recovery system were examined. 95% of water consumed by the humidification tower was recovered, and a significant reduction of the make-up water for the HAT cycle was confirmed. Thirdly, concentrations of impurities within the circulating water of the AHAT system were measured when the recovered water was recycled without any purification process.
An Investigation of the Flow Physics of Vane Clocking Using Unsteady Flow Measurements
Authors: Key Nicole L. , Lawless Patrick B. , Fleeter Sanford
Published: August 2009

Vane clocking, the circumferential indexing of adjacent vane rows with similar vane counts, has been shown to affect stage efficiency in compressors and turbines. Steady flow measurements acquired in the embedded stage of the Purdue 3-Stage Compressor showed a change in stage efficiency with vane clocking, as discussed in a companion paper. The optimum efficiency condition at design loading occurred when the upstream vane wake impinged on the downstream vane, as had been reported by other vane clocking studies. However, at high loading, the impingement of the upstream vane wake triggered a vane suction side boundary layer separation and resulted in the worst efficiency condition. The objective of this research is to experimentally investigate the maximum and minimum efficiency clocking configurations with unsteady flow measurements to illuminate the flow physics associated with the measured changes in Stage 2 performance. Vane exit unsteady total pressure, velocity, and flow angle measurements were acquired at 50 pitchwise locations spanning one vane passage. Fourier decomposition is used to identify the impact of the upstream rotor wake on the shedding characteristics of the Stator 2 boundary layer and how the placement of the upstream vane wake affects this phenomenon. For the clocking configuration that located the Stator 1 wake at the leading edge of the Stator 2 vane at design loading, it dampened the boundary layer response to the fluctuating incidence associated with rotor wake chopping, leading to a reduction in the size of the structures shed in the Stator 2 vane wake. At the high loading condition, the placement of the Stator 1 wake at the leading edge of Stator 2 triggered a suction side boundary layer separation, resulting in an absence of the upstream rotor blade pass frequency in the spectrum measured in the Stator 2 wake.
Acoustic Thermography Testing of Industrial Gas Turbine Blades in the Service Stage
Authors: Broddega˚rd Mattias , Homma Christian
Published: August 2009

Gas turbine blades are operating under very demanding conditions. In modern industrial gas turbines, the rotating blades and the guide vanes of the first stages are hollow to allow internal cooling. This means that there is a possibility of having crack initiation on the internal surface of the components. Due to the complex casting geometry, this type of defects is very difficult to detect with conventional nondestructive testing techniques such as ultrasonic and radiographic testing. Siemens has developed a new non-destructive testing technique based on acoustic thermography, SIEMAT. The test object is energized by an ultrasonic excitation device. Due to the vibrations, a very slight heating will develop at cracks in the test object. The local increase of temperature is captured by a highly sensitive IR camera. The SIEMAT technique is capable of detecting both surface-breaking and internal cracks, including cracks under coatings. The testing time is very short, and the IR sequences are recorded for subsequent analysis. A major advantage for service applications is that the technique is mostly sensitive to closed defects such as cracks, since open defects where no contact between the faces is present, for example pores and scratch marks, will not cause any heat generation. Siemens is currently implementing the SIEMAT technique for assessment of service-exposed turbine blades from medium size gas turbines, which are due for reconditioning. By being able to verify that no internal cracks are present, the reliability of the reconditioned blades will be increased. This paper describes the SIEMAT testing technique, and the results obtained when applied on service-exposed industrial gas turbine blades.