bluuebunny/crossref_metadata_2025 huggingface dataset:
Expedient Estimation of the Maximum Amplification Factor in Damped Mistuned Bladed Disks
Authors: Han Yun , Xiao Bing , Mignolet Marc P.
Published: March 2009

This paper focuses on the formulation and validation of a novel approach for the expedient estimation of the maximum amplification factor induced by mistuning in damped bladed disks. This computational approach is based on earlier analytical results yielding an upper bound of the maximum amplification factor in the limit of zero damping. Extensions of these results are derived first to broaden the applicability of the methodology. Next, the computational technique is described: it involves the components of one of the mode shapes of the mistuned disk and the associated frequency as the variables over which the optimization is carried out. Further, the initial guess for these variables is obtained from the analytical estimates of the upper bound. This approach removes the limitations of earlier analytical efforts, i.e. damping is considered, and the actual value of the maximum amplification factor and the corresponding mistuning of the blade properties are obtained. Limitations on the magnitude of the mistuning could also be considered in the algorithm if desired. This novel approach was applied for the parametric study of the maximum amplification factor as a function of damping in two single-degree-of-freedom per blade disk models as well as in a reduced order model of a blisk. The results obtained in connection with the two single-degree-of-freedom systems very closely match the global maxima predicted by an existing, more tedious algorithm introduced earlier to avoid convergence to one of the many local maxima known to often exist.
Study of Influence of Different Types of Cooling, Fuel Heating and Steam Generation States on Performance of Simple Gas/Steam Combined Cycle
Authors: Yadav J. P. , Singh Onkar
Published: March 2009

This paper deals with the study of influence of different types of cooling, fuel heating and steam generation states on performance of simple gas / steam combined cycle with varying cycle pressure ratio and turbine inlet temperature (TIT). Open and closed loop cooling using air / steam and water has been considered to evaluate cycle performance for optimum values of TIT and cycle pressure ratio for single, dual and triple pressure steam generation in heat recovery steam generator (HRSG). Influence of fuel heating on cycle efficiency and cycle work output of combined cycle is also presented here. In this paper the study of combined cycle having single or dual / triple pressure steam generation in HRSG has been done using computer program in C++ language for maximum cycle efficiency and cycle specific work output for the variation of cycle pressure ratio from 12 to 18, turbine inlet temperature from 1400 K to 1700 K for both open and closed loop air / steam and water cooled gas turbines.
Investigation of Combustion Oscillations in a Lean Gas Turbine Model Combustor
Authors: Diers Olaf , Schneider Denis , Voges Melanie , Weigand Peter , Hassa Christoph
Published: March 2009

This contribution is a continuation of ASME-GT2006-90300. While still working at atmospheric pressure, the range of operating conditions was extended to more realistic reduced mass flows to reproduce the engine pressure loss and air preheat up to 700K. The thermoacoustic behaviour of the burner was mapped over that operating range. Two different types of oscillations were observed for flames anchored at the nozzle or lifted from it. Both exhibited a frequency dependence on the Strouhal number for constant reduced mass flows. For a selected operating point with the lifted flame at a preheat temperature of 600K and a reduced mass flow of 0.3kg K0.5/(s bar), the thermoacoustic behaviour of the burner was characterised by phase locked Particle Image Velocimetry as well as phase locked OH- and OH-T- LIF measurements and correlated to the acoustic pressure signal obtained by microphones. The combined data showed pulsating combustion being supported through periodic reignition of the main flame zone by a recirculating volume of hot, OH-rich gas, the cycle time being connected to the observed frequency. The characterization of the preheated operating point was completed with a heat balance investigation quantifying the non-adiabatic combustion conditions of the uncooled combustor.
Optimum Operation of Export Compressors
Authors: No̸rstebo̸ Vibeke Stærkebye , Bakken Lars E. , Dahl Hans Jo̸rgen
Published: March 2009

Natural gas from the Norwegian continental shelf (NCS) is processed at the Kollsnes gas treatment plant in western Norway and exported through two pipelines to continental Europe. The export facility consists of five parallel compressor trains and a crossover leg between the two export pipelines. Customers have the opportunity to make varying nominations, which the plant must satisfy. Several compressors operating in parallel, crossover possibilities and alternating pipeline pressures and nominations present challenges for identifying optimum operation procedures at the export facility. Several different ways to operate the facility are available. Each of these may be equal in terms of meeting system requirements, but may differ for energy efficiency. The objective of the work is to establish guidelines for optimum operation of the compressor station. This implies increasing system energy efficiency by minimizing specific power consumption and maintaining operational flexibility.
The Role of the Recirculating Gases at the Mild Combustion Regime Formation
Authors: Levy Y. , Sherbaum V. , Erenburg V.
Published: March 2009

The present work is concerned with the thermodynamic and chemical kinetics of gas turbine combustor operating in the Moderate or Intense Low-oxygen Dilution (MILD) combustion regime. The objective of the present study is to evaluate analytically the effect of the recirculation rate of combustion products within the FLOXCOM gas turbine combustor on a number of combustion parameters, mainly on the ignition delay time, NOx and CO emission, minimum ignition temperature, rate of pollutant formation and the dilution rate. The study also refers to the mechanism of influence of the recirculation rate on these values. Combustion pressure and inlet air temperature are used as parameters. The gas turbine is fueled with methane. The analysis is mainly based on CHEMKIN simulations where the calculation scheme of the combustion process in the combustor is modeled by a combination of plug reactors and mixers. Due to the unique characteristics of gas turbines, inlet air temperature is directly linked to combustion pressure while assuming conventional adiabatic compression efficiencies. It is shown that free radicals, which are part of the reaction products and exists for only a short period of time within the recirculated gases, decrease ignition delay time. The importance of shortening the ignition delay is further highlighted because of the adverse effect oxygen dilution has on this parameter (dilution of the reactants by the reaction products). It was found that there is an optimal recirculation rate, which corresponds to maximum heat density. In addition, results indicate that CO emission values rise with the recirculation rate, however the NOX values are more complicated. NOX depends on recirculation rate when flame temperatures are kept held constant. The NOX emission increases and the CO emission decreases with compressor pressure ratio. The CO concentration that is evaluated in the combustion process is further reduced during last dilution stage. Finally, basic rules for design optimization of the combustor are drafted. These are based on conventional one-dimensional fluid and thermodynamic relations and on the CHEMKIN simulations.
Modeling a Non-Premixed Industrial Gas Turbine Combustor by a Transported PDF Approach With ILDM Chemistry
Authors: Harder Sebastian , Joos Franz
Published: March 2009

The combustion process in a typical can combustor of an industrial gas turbine is determined by the nature of turbulent flow, the chemical reaction and the interaction with each other. Turbulent non-premixed combustion can be divided into different flame regimes in terms of time- and length scales. A typical non-premixed turbulent diffusion flame in a gas turbine combustor covers all regimes. PDF methods are suitable to describe the entire combustion regime without any limitation to a certain regime. In this paper a hybrid pdf/RANS method is presented. The pdf model is based on the transported composition pdf equation, coupled with a commercial three dimensional CFD solver. A stochastic particle system in a Lagrangian framework is used to solve the pdf equation. The chemistry is described by an ILDM approach. The numerical results have been validated with measurements. The test rig consists of an non-premixed gas turbine can combustor with a typical primary and secondary zone. A main air swirler stabilizes the natural gas/air mixture in the primary zone, followed by a burnout and a mixing zone. The setup is investigated using conventional measurement techniques. Field measurements of compositions and mixture fraction as well as temperature are compared with the pdf/RANS calculations. The benefit of this approach is a realistic prediction of all relevant species. The complete one point statistics of the numerical calculations are used to identify the different combustion regimes from the combustor to the exit. The numerical comparison of pdf-, edm- and flamelet-model shows that the pdf approach can be used to describe a realistic gas turbine combustor. In the past, pdf-methods were applied only on simple generic model flames. The purpose of the presented paper is to demonstrate the application of a transported-pdf approach to a realistic gas turbine combustor.
Film Cooling Measurements for Cratered Cylindrical Inclined Holes
Authors: Lu Yiping , Dhungel Alok , Ekkad Srinath V. , Bunker Ronald S.
Published: March 2009

Film cooling performance is studied for cylindrical holes embedded in craters. Different crater geometries are considered for a typical crater depth. Cratered holes may occur when blades are coated with thermal barrier coating layers by masking the hole area during TBC spraying resulting in hole surrounded by TBC layer. The film performance and behavior is expected to be different for the cratered holes compared to standard cylindrical holes. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5 and 2.0. The results show that film cooling effectiveness is slightly enhanced by cratering of holes but a substantial increase in heat transfer enhancement negates the benefits of higher film effectiveness. Three different crater geometries are studied and compared to a baseline flush cylindrical hole, a trenched hole, and a typical diffuser shaped hole. CFD simulation using Fluent was also performed to determine the jet-mainstream interactions associated with the experimental surface measurements.
Gill Slot Trailing Edge Aerodynamics: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Aerodynamics Losses and Pressure Distribution
Authors: Ames F. E. , Johnson J. D. , Fiala N. J.
Published: March 2009

Gill slots (also called cutbacks) are a common method to cool the trailing edge of vanes and blades and to eject spent cooling air. Exit surveys detailing total pressure loss, turning angle, and secondary velocities have been acquired for a gill slot vane in a large scale low speed cascade facility. These measurements are compared with exit surveys of the base (solid) vane configuration. Exit surveys have been taken over a four to one range in chord Reynolds numbers (500,000,1,000,000, and 2,000,000) based on exit conditions and for low (0.7%), grid (8.5%), and aero-combustor (13.5%) turbulence conditions with varying blowing rate (50%, 100%, 150%, and 200% design flow). Exit loss, angle, and secondary velocity measurements were acquired in the facility using a five-hole cone probe at two stations representing axial chord spacings of 0.25 and 0.50. Differences between losses with and without the gill slot for a given turbulence condition and Reynolds number are compared providing evidence of coolant ejection losses and losses due to the separation off the gill slot lip. Additionally, differences in the level of losses, distribution of losses, and secondary flow vectors are presented for the different turbulence conditions and at the different Reynolds numbers. The turbulence condition has been found to have only a small affect on the increase in losses due to the gill slot. However, decreasing Reynolds number has been found to produce an increasing increment in losses. The present paper together with a companion paper, which documents gill slot heat transfer, is intended to provide designers with the heat transfer and aerodynamic loss information needed to compare competing trailing edge designs.
Training Future Gas Turbine Performance Engineers
Authors: Pachidis V. , Pilidis P. , Li I.
Published: March 2009

The performance analysis of modern gas turbine engine systems has led industry to the development of sophisticated gas turbine performance simulation tools and the utilization of skilled operators who must possess the ability to balance environmental, performance and economic requirements. Academic institutions, in their training of potential gas turbine performance engineers have to be able to meet these new challenges, at least at a postgraduate level. This paper describes in detail the “Gas Turbine Performance Simulation” module of the “Thermal Power” MSc course at Cranfield University in the UK, and particularly its practical content. This covers a laboratory test of a small Auxiliary Power Unit (APU) gas turbine engine, the simulation of the ‘clean’ engine performance using a sophisticated gas turbine performance simulation tool, as well as the simulation of the degraded performance of the engine. Through this exercise students are expected to gain a basic understanding of compressor and turbine operation, gain experience in gas turbine engine testing and test data collection and assessment, develop a clear, analytical approach to gas turbine performance simulation issues, improve their technical communication skills and finally gain experience in writing a proper technical report.
Turbine Stator Well CFD Studies: Effect of Upstream Egress Ingestion
Authors: Georgakis C. , Whitney C. , Woollatt G. , Stefanis V. , Childs P.
Published: March 2009

There is a constant demand in the turbomachinery industry to improve engine performance, meet stringent environmental and safety regulations, and reduce the time and cost of new product development. As improvements in component efficiencies become increasingly difficult to achieve and new material development has become more expensive over the years, more attention is focusing on other areas of gas turbine technology. Internal cooling air systems, in particular, have been subject to significant research, in order to reduce the effect of parasitic losses on the overall engine performance. Often, part of the compressor flow passes directly into turbine inter-stage cavities primarily for rotor disc cooling. The advantages such a concept offers are (a) better thermal effectiveness on the rotor disc by having lower wall temperature (b) preventing, to some degree, the ingestion of mainstream hot gases into the cavity. These enhancements have to be integrated into the turbine stage without, of course, sacrificing the overall performance. Detailed knowledge of the flow and heat transfer within these cavities is needed if such improvements are to be further pursued. The material presented in this paper investigates the effect of upstream coolant injection into the mainstream flow being ingested into a turbine stator well. The coolant injection comes from an upstream rim seal, and so called egress. The CFD domain modelled includes both the main gas path and stator well. CFD studies have been performed to predict the flow physics in the cavity, and this has included an investigation of both steady and unsteady effects. This study is extended beyond the cavity flows, and it gives an insight of the mainstream flow particularly behind the blade rows. The CFD results are compared with dedicated aerodynamic 3D-blade design codes. These CFD studies have contributed significantly in understanding the effect on flow and heat transfer of upstream turbine coolant injection being subsequently ingested into a downstream stator well. Most importantly, these CFD studies enhanced the optimisation of turbine stator well design and limited the coolant flow ingested into the rotating cavities whilst maintaining overall performance.
Optimizing the Performance of Air-Air Ejectors With Triangular Tabbed Driving Nozzles
Authors: McBean S. F. , Birk A. M.
Published: March 2009

This paper describes an experimental investigation into optimizing the performance of air-air ejectors with triangular tabbed driving nozzles. Mixing tabs have been shown to improve ejector performance, but at the cost of increased back-pressure. Ejector performance was evaluated on the basis of pumping, mixing, and back-pressure. It was discovered that mixing-tube inlet treatment influenced the ability of ejectors to entrain ambient air. It was also found that although mixing improved as a function of increased mixingtube length, maximum pumping occurred when the mixing-tube was approximately four nozzle diameters in length. Lastly, for a given overall ejector length, increased standoff was found to be more beneficial than increased mixing-tube length. Optimal ejector geometry was defined by the configuration that generated maximum mixing and maximum pumping for minimal increases in back-pressure.
Film Cooling From a Row of Holes Supplemented With Anti Vortex Holes
Authors: Dhungel Alok , Lu Yiping , Phillips Wynn , Ekkad Srinath V. , Heidmann James
Published: March 2009

The primary focus of this paper is to study the film cooling performance for a row of cylindrical holes each supplemented with two symmetrical anti vortex holes which branch out from the main holes. The anti-vortex design was originally developed at NASA-Glenn Research Center by Dr. James Heidmann, co-author of this paper. This “anti-vortex” design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film cooling holes. The geometry and orientation of the anti vortex holes greatly affect the cooling performance downstream, which is thoroughly investigated. By performing experiments at a single mainstream Reynolds number of 9683 based on the free stream velocity and film hole diameter at four different coolant-to-mainstream blowing ratio of 0.5, 1, 1.5, 2 and using the transient IR thermography technique, detailed film cooling effectiveness and heat transfer coefficients are obtained simultaneously from a single test. When the anti vortex holes are nearer to the primary film cooling holes and are developing from the base of the primary holes, better film cooling is accomplished as compared to other anti vortex hole orientations. When the anti vortex holes are laid back in the upstream region, film cooling diminishes considerably. Although an enhancement in heat transfer coefficient is seen in cases with high film cooling effectiveness, the overall heat flux ratio as compared to standard cylindrical holes is much lower. Thus cases with anti vortex holes placed near the main holes certainly show promising results.
Computational Investigations in the Trailing Edge Region of Cooled Turbine Vane: Comparison of Different Channel Shapes
Authors: Kulasekharan N. , Prasad B. V. S. S. S.
Published: March 2009

Thermal hydraulic characteristics of coolant flow through passages consisting of rib turbulators, pin fin array and trailing edge slot are reported. Channels of straight, trapezoidal and curved shapes are considered. Continuity, momentum and energy equations for a three dimensional incompressible flows are solved. A constant heat flux value is specified over the coolant channel walls, rib surfaces and circumferential faces of the pin-fins. Total pressure loss coefficient, pin end-wall and pin surface averaged Nusselt number are estimated and presented for the pin array, for Reynolds number ranging from 20,000 to 40,000. Cambered channels showed highest pin end wall averaged heat transfer than trapezoidal channel, which is higher than the straight channel.
A New Finite Element for Gas Turbine Engine Fatigue Life Prediction
Authors: Tarar Wasim , Scott-Emuakpor Onome , Shen M.-H. Herman
Published: March 2009

An energy-based fatigue life prediction framework was previously developed by the authors [1–4] for prediction of axial and bending fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. In this study, the energy expressions that construct the new constitutive law is integrated into minimum potential energy formulation to develop a new finite element for fatigue life prediction. The comparison of Finite element method (FEM) results to existing experimental fatigue data, verifies the new finite element method for fatigue life prediction. The final output of this finite element analysis is in the form of number of cycles to failure for each element in ascending or descending order. Therefore, the new finite element framework can provide the number of cycles to failure for each element in gas turbine engine structural components. The performance of the fatigue finite element is demonstrated by the fatigue life predictions from 6061-T6 aluminum and Ti-6Al-4V. Results are compared with experimental results and analytical predictions [1].
Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical End Seal: Centered Circular Orbit Tests
Authors: San Andre´s Luis , Delgado Adolfo
Published: March 2009

The paper presents parameter identification measurements conducted on a squeeze film damper (SFD) featuring a non-rotating mechanical seal that effectively eliminates lubricant side leakage. The SFD-seal arrangement generates dissipative forces due to viscous and dry-friction effects from the lubricant film and surfaces in contact, respectively. The test damper reproduces an aircraft application that must contain the lubricant for extended periods of time. The test damper journal is 2.54 cm in length and 12.7 cm in diameter, with a nominal clearance of 0.127 mm. The damper feed end opens to a plenum filled with lubricant, and at its discharge grooved section, four orifice ports evacuate the lubricant. In prior publications (ASME Paper GT2006-90782, IJTC2006-12041), single frequency force excitation tests were conducted, without and with lubricant in the squeeze film land, to determine the seal dry-friction force and viscous damping force coefficients. Presently, further measurements are conducted to identify the test system and SFD force coefficients using two sets of flow restrictor orifice sizes (2.8 mm and 1.1 mm in diameter). The flow restrictors regulate the discharge flow area, and thus control the oil flow through the squeeze film. The experiments also include measurements of dynamic pressures at the squeeze film land and at the discharge groove. The magnitude of dynamic pressure in the squeeze film land is nearly identical for both sets of flow restrictors, and for small orbit radii, dynamic pressures in the discharge groove have peak values similar to those in the squeeze film land. The identified parameters include the test system damping and the individual contributions from the squeeze film, dry friction in the mechanical seal and structure remnant damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry friction interaction at the mechanical seal interface. Squeeze film force coefficients, damping and added mass, are in agreement with simple predictive formulas for an uncavitated lubricant condition and are similar for both flow restrictor sizes. The SFD-mechanical seal arrangement effectively prevents air ingestion and entrapment and generates predicable force coefficients for the range of frequencies tested.
Vorticity Dynamics in Axial Compressor Flow Diagnosis and Design
Authors: Yang Yantao , Wu Hong , Li Qiushi , Zhou Sheng , Wu Jiezhi
Published: March 2009

The role of vorticity dynamics in the axial compressor diagnosis and design is investigated analytically and numerically, in terms of the stagnation-pressure flux that controls the compressor’s performance. The stagnation-pressure flux is found to be dominated by the distribution of circumferential vorticity. The circumferential vorticity is directly expressible by the circulation distribution which is the significant parameter in the throughflow compressor design. Some principles of controlling compressor performance are thereby proposed, which are demonstrated by two rotor blades, designed by throughflow procedure and evaluated by three-dimensional Reynolds-average Navier-Stokes simulation.
Experimental Study of Humid Air Diffusion Flames in HAT Cycle
Authors: Ge Bing , Zang Shu-Sheng , Gu Xin
Published: March 2009

Combustion with humid air is a key process of humid air turbine (HAT) cycles. Many studies have been undertaken to understand the influence of moisture in air on combustion fields. This study focuses on investigating the differences between the propane/humid air turbulent diffusion flame in a bluff-body burner and the same flame with normal dry air. The moisture levels were achieved by injecting steam into dry air. Particle image velocimetry was used to study the velocity fields experimentally in the humid reactive burner flow and the equivalent non-humid flow. The temperature fields of flames were measured using high temperature thermocouples, and the NO distributions were obtained with gas detection instruments. The results show that although humid air reactive flow fields are similar to the non-humid flow fields in general, there are some differences in the humid air combustion flow field comparing to the same combustion flow field with normal dry air: the center of the reversed-flow region goes forward; the dimension of the reversed-flow region is smaller. An analysis of NO formation revealed NO reduction of humid air flames due to the presence of steam. It is suggested that humid air combustion is helpful to shorten the axial length of combustor, and reduce the formation of pollution.
Strategies to Enhance the Part-Load Performance of a SOFC/GT Hybrid System
Authors: Yang Jin Sik , Sohn Jeong L. , Ro Sung Tack
Published: March 2009

In spite of the high performance characteristics of the solid oxide fuel cell / gas turbine (SOFC/GT) hybrid system, it is very difficult to maintain the high level performance under real application conditions, which generally require part-load operations. The performance loss of SOFC/GT hybrid systems under part-load operating conditions is closely related to that of the gas turbine. The power generated by the gas turbine in a hybrid system is much smaller than that generated by the SOFC. However, its contribution to the system efficiency is very important especially at part-load operating conditions. Therefore, to enhance the part-load performance of hybrid systems, it is useful to reduce the relative amount of power generated by a gas turbine that delivers lower performance than a SOFC. In the present study, several part-load operation strategies related to the gas turbine are studied and their impacts on the performance of a SOFC/GT hybrid system are discussed.
Blade Loading Influence on Unsteady Flow Interactions in Axial Steam Turbines
Authors: Tashima Tsuguhisa , Sasaki Takashi , Kalfas Anestis I. , Abhari Reza S.
Published: March 2009

This paper presents the results of a comparative experimental investigation of two turbine test cases with different second stage stator count. The objective is to investigate the possibility of reducing the product cost and weights by reducing stator count while improving overall turbine performance. The experiment was performed in a two-stage axial research turbine facility. The blade geometries under investigations are of typical of the high-pressure section of steam-turbines and the blade rows except the second stage stator are identical between the two test cases. The low solidity stator has 3/4 blades count of the high solidity stator while keeping the same axial chord length. Unsteady and steady data were obtained using the fast response probe and the miniature pneumatic probes at the exit of the first rotor, at the exit of the second stator and the second rotor. The prime interest is focused on the way that performance is changed by the different number of wakes and vortices transporting through the downstream blade rows. In the reduced blade count case, the unsteady flow interactions causes the larger distributions of all flow properties measured. A marked difference is observed near 10 to 35% span where the hub passage vortex is dominant. In the low solidity stator case, the time dependent vorticity variation was found to be 40% larger compared to the high solidity stator case. In correspondence to the vorticity variation, the loss coefficient also varies depending on time. Pneumatic measurements show that the difference of second rotor loss coefficient between the cases is within 1.5% except the tip area. However, unsteady loss variation differs between the test cases depending on the change of the flow structures. The mechanism of this unsteady loss variation is analyzed in detail.
Turbine Blade Thermal Design Process Enhancements for Increased Firing Temperatures and Reduced Coolant Flow
Authors: Kru¨ckels J. , Arzel T. , Kingston T. R. , Schnieder M.
Published: March 2009

A successful implementation of a cooled turbine blade design for a heavy duty gas turbine engine is a technology challenge that requires a stringent engineering approach. The increased spread of hot gas versus metal temperature, the flatter temperature profiles for reduced emissions and the aerodynamic 3D-profile shape requirement and all at a reduced cooling air consumption place the specification of a new turbine blade, that is put forward to the aerothermal engineers, as a technical challenge. It is also desired to reduce the available development time to be able to introduce new technology features faster into the market. The paper aims to demonstrate turbine blade cooling and heat transfer design process enhancements that allow: increased thermal predictability, increased capturing of three dimensional effects and reduced engineering development cycle time from initial design to full engine validation. Selected items will be shown for demonstration. One example is the use of symmetry and parameterization to move CFD from an analysis tool into an available design tool to capture effects as rotation or three-dimensionality. Another example is the use of heat sinks within a finite element model to represent individual cooling holes instead of hole geometry.
Study on SOFC-IGCC Hybrid Power System With High Efficiency
Authors: Duan Liqiang , Yang Yongping , Xu Ershu
Published: March 2009

Due to its high efficiency and good environmental performance, solid oxide fuel cell (SOFC) system is very attractive for future power generation, especially integrated with the conventional power generation system. However, how to effectively integrate SOFC with the conventional thermal power system and build the hybrid system with high efficiency is still a research focus. This paper studies a novel SOFC-IGCC (integrated gasification combined cycle) hybrid power system with high efficiency. On the base of the integration idea of total energy system, a novel SOFC-IGCC hybrid power system is proposed in this paper. The energy conversion mechanism of SOFC from chemical energy to electrical energy is analyzed. The maximum potential of improving the total system performance is also analyzed. The system characteristics of the hybrid system have been studied. The optimal rules of main parameters of hybrid system are revealed. The research results obtained in this paper show that integration with SOFC system will result in a significant performance improve of the total hybrid system. The integration degree of SOFC with IGCC greatly influences the system performance of the hybrid system. Compared with the base IGCC system (the system thermal efficiency is 46%), the efficiency of SOFC-IGCC hybrid system is greatly improved and increased to approximately 52%. The achievements acquired results from this paper will provide a feasible way to develop hybrid power system and valuable information for further study on IGCC system with high efficiency.
Predictions of Adiabatic Film Cooling Effectiveness for Effusion Film Cooling
Authors: Yusop Nadiahnor Md. , Andrews Gordon E. , Ingham Derek B. , Khalifa I. M. , Mkpadi Mike C. , Pourkashanian Mohammed
Published: March 2009

This paper presents computational predictions of adiabatic film cooling effectiveness for effusion cooling systems with 90° and 30° holes. Predictions are performed for a range of coolant injection mass flow rates per unit surface area, G, of 0.1kg/sm2 - 1.6 kg/sm2 for 90° holes with constant pitch-to-diameter ratio of X/D = 11 and 10 rows of holes and for 30° inclined holes with X/D = 11 and 15 rows of holes over a 152mm surface length. The computational works performed are steady-state and the turbulent governing equations are solved by a control-volume-based finite difference method with second-order upwind scheme and the k-epsilon turbulence model. The velocity and pressure terms of momentum equations are solved by the SIMPLE method. The CFD prediction were validated by comparing the predictions with literature data for single rows of inclined holes and then applied to effusion cooling. The predictions included the use of a tracer gas in the coolant, which was used to predict the mixing of the coolant with the hot mainstream gases. Also the surface distribution of the tracer gas was a direct prediction of the cooling effectiveness. The mixing of coolant with the mainstream was studied and boundary layer temperature and coolant mixing profiles were predicted. These were compared with temperature measurement in a hot effusion cooling test rig.
Adaptive Control of Combustion Instabilities for Non-Minimum Phase Systems
Authors: Morgans Aimee S. , Annaswamy Anuradha M.
Published: March 2009

Model-based adaptive controllers, or self-tuning regulators, offer an efficient means of stabilising combustion instabilities over a range of operating conditions. They utilise some general properties satisfied by a wide range of combustion systems and thus avoid the need for on-line system identification. One of the required properties is that the open-loop system is minimum-phase i.e. that it does not contain any right-half plane (RHP) zeros. It is shown in this work that for some combustion systems in which a pressure measurement is used as a sensor signal, right-half plane zeros arise due to reflections from boundaries. This may either occur due to the reflection of acoustic waves, or due to the acceleration of entropy waves. A method of eliminating the right-half plane zeros by using a modified pressure measurement is proposed, which also maintains the relative degree of the system. The modified sensor signal is applied to numerical models of unstable combustion systems with large reflections from boundaries, and the self-tuning regulator is demonstrated to work in cases where it fails with a single pressure measurement. This is demonstrated for several different unstable combustion systems, confirming that the approach remains independent of the system details.
The Zimont TFC Model Applied to Premixed Bluff Body Stabilized Combustion Using Four Different RANS Turbulence Models
Authors: Eriksson Pontus
Published: March 2009

The Volvo Aero Corp. (VAC) Triangular Bluff Body Stabilized Combustion rig VR-1 has been extensively researched both in terms of experiments and theoretical treatment. Previous CFD work has concentrated on Reynolds Averaged Navier-Stokes (RANS) models combined with the Level Set Flamelet Library approach. Large Eddy Simulation (LES) has also been applied to the case. In this paper the Zimont Turbulent Flame Closure (TFC) model has been investigated in conjunction with the k-ε, k-ω, SST k-ω and RSM RANS model implementations in ANSYS CFX 10.0. It is shown that the various RANS models generate significantly different results in terms of turbulent velocity and integral length scale fields. These parameters influence the computed turbulent flame speed. The turbulent viscosity fields also differ substantially between the various RANS models. This will affect the computed degree of flame front diffusion. For the investigated case; the TFC model combined with the k-ω model fairly accurately captures the recirculation zone length and overall turbulent flame speed. The measured case however displays Kelvin-Helmholtz induced oscillations of the shear layers behind the bluff body. This will combine with the free-stream turbulence and turbulence generated along the upstream surfaces of the bluff body to distort the flame sheets. The two flame fronts will also be subjected to other (unquantified) combustion related instabilities. The combined effect is not captured well in steady state RANS. The analysis is therefore seen to grossly under-predict flame front diffusion, regardless of turbulence model.
Turbomachinery Simulation in Design Point and Part-Load Operation for Advanced CO2 Capture Power Plant Cycles
Authors: Haag J.-Ch. , Hildebrandt A. , Ho¨nen H. , Assadi M. , Kneer R.
Published: March 2009

In this paper two different power plant processes with their current optimized layouts of the AZEP project and the recently started OXYCOAL-AC project are presented. Both processes are designed for CO2-capture combined with oxygen membrane technology. As a consequence of the implementation of a membrane module there will be essential changes in the plant layout involving modifications to the turbomachinery designs due to the different working medium and interactions of different cycle components. Furthermore, there are different loops included for recirculation of the combustion gas constituents CO2 and H2O. Although, the processes presented have different boundary conditions regarding the selection of fuel and gross power output, they have in common the need for new turbomachinery designs. These two processes are thermodynamically analyzed and compared both at design point and at off-design (part-load operation) mode. Main focus are the different operation modes of AZEP and different turbomachinery layouts for OXYCOAL-AC. Special attention is paid to the modeling of the crucial components common for both power plant processes e.g. the oxygen membrane, the turbine and the compressors. The thermodynamic studies aim at analyzing a) the requirements on turbomachinery at the design point, b) how to reduce the level of requirements for the compressor and the turbine and c) the operation and potential of mismatch for the turbomachinery during part-load operation. Simplified turbomachinery maps and a simplified black box 1-D model of the membrane module and the heat exchangers are used within a commercial heat- and mass-balance program for simulation of part-load operation of both processes. The objective of this conceptual study is the investigation of parameter changes caused by the interaction of process components.
Tensile Creep Behavior of Melt-Infiltrated SiC-SiC Composites for Gas Turbine Engine Applications
Authors: Pujar Vijay V. , Morscher Gregory N.
Published: March 2009

SiC-SiC ceramic matrix composites (CMCs) manufactured by the melt-infiltration (MI) process are considered leading candidates for hot-section turbine engine components. MI composites consisting of different commercially available SiC fibers were fabricated and their room temperature and elevated temperature performance was evaluated. In this paper, results on the performance of composites under tensile creep conditions and the properties of these materials retained after creep are discussed. Specimens were subjected to 100-h creep tests at different stress levels. For samples that did not rupture during creep, retained tensile properties were measured after creep and compared to those on the as-produced samples. Interestingly, the after-creep specimens show higher 0.005% offset stresses (or matrix cracking strengths) relative to those in the as-produced materials, which is attributed to redistribution of stresses among the constituents during the tensile creep test. That is, the results show that the offset stresses in these materials can actually improve with use under tensile creep conditions, which is a desirable attribute for components of these materials for turbine engines.
Fuel Variability Effects on Turbulent, Lean Premixed Flames at High Pressures
Authors: Boschek E. , Griebel P. , Jansohn P.
Published: March 2009

Fuel flexibility will be a key issue for the operation of future stationary gas turbines because of the increasing amount of off-spec natural gas qualities from new resources and upcoming new fuels derived from biomass which will be more important in the near future. The performance of gas turbines in terms of flame stability and low emission combustion must be at least maintained also with these new fuels. Therefore, the impact of fuel variation on combustion characteristics must be known for the combustor design. This paper addresses the effect of hydrogen and propane addition on flame characteristics like lean blowout (LBO), emissions (NOx, CO), flame positions and turbulent flame speeds for flames at gas turbine relevant conditions. Hydrogen enriched fuels are typical constituents of gasification fuels such as those obtained from biomass, while propane is considered a typical higher hydrocarbon present in off-spec natural gas. Turbulent, lean premixed flames of different fuels (methane, methane/hydrogen and methane/propane) have been studied in a generic, axis-symmetric, high-pressure gas turbine combustor. Flame stabilization is achieved aerodynamically via a recirculation zone induced by the combustor geometry with sudden expansion. Turbulence at the combustor inlet is generated using a turbulence grid (perforated plate). LBO limits are detected using the global OH chemiluminescence flame signal collected with a photo-multiplier and a data acquisition system together with the exhaust gas temperature measured with a thermocouple. The species concentrations (CO2, O2, CO, NOx) are measured by exhaust gas analyzers. Flame front positions and turbulent flame speeds are determined with Laser Induced Fluorescence measurements of the OH radical (OH-PLIF). Flame characteristics will be presented for the following fuel/air mixtures at a mixture preheating temperature of 673 K: pure methane, H2-enriched flames containing up to 50% hydrogen by volume, methane/propane mixtures containing up to 50% propane by volume. LBO limits, NOx emissions will be presented for different pressures. Most probable flame front positions and turbulent flame speeds are presented at a pressure of 5 bars for fuel mixtures between pure methane and 50% of each additive (propane and hydrogen). Experiments have revealed that a premixed mixture of 50% hydrogen and 50% methane, by volume, can significantly extend the lean blowout limit by up to 22% compared to pure methane. Because of a 120 K lower flame temperature a drastic reduction of the NOx emission (about 57%) is observed. Addition of hydrogen also significantly decreases the flame position (50%), changes the shape of the flame front and because of a higher global reaction rate increases the turbulent flame speed. Experiments with different methane/propane mixtures showed an increase (approximately 25–30%) of the NOx concentration at a propane content of 50%. Additionally, the flame stabilizes closer to the combustor inlet for higher propane contents.
Heat Transfer Predictions of Film Cooled Stationary Turbine Airfoils
Authors: Laskowski Gregory M. , Tolpadi Anil K. , Ostrowski Michael C.
Published: March 2009

Conventional heat transfer design methods for high temperature gas turbine airfoils decouple the internal and external flow. Thermal boundary conditions from these decoupled analyses are applied to the blade surfaces to predict turbine life. Typically, the domain for the external flow includes the hot gas path and the film cooling holes while the domain for the internal flow includes the internal flow passages and film cooling holes. The solid blade itself couples the external and internal flow and heat transfer. Since film cooling flow physics can play a significant role on the overall turbine blade heat transfer, there has been increased interest in capturing these effects by including the hole geometry in the solution procedure. Ideally, the complete turbine blade heat transfer analysis would be provided by efficient CFD simulations for the coupled problem including the internal passages, film cooling holes and hot gas path. By prescribing both the external flow and internal flow inflow/outflow boundary conditions, the hole physics can be included in the solution. The current paper presents results obtained for coupled simulations of the NASA C3X vane and VKI rotor which models the internal passages, hole geometries and hot gas path. In both cases, cooling is achieved by rows of pressure-side, leading-edge and suction-side film cooling holes. The rows are independently fed by span-wise, constant area plenums. The former has a total of 152 cylindrical cooling holes whereas the later has a total of 110 cylindrical/shaped holes. In addition, the C3X vane consists of 10 internal radial cooling passages of cylindrical cross-section. The simulations were conducted with the Shear Stress Transport (SST) model on a grid that extended into the viscous sub-layer along all surfaces. The computed surface pressure and external heat transfer coefficient distributions at mid-span are compared to experimental data for both cases. Internal heat transfer predictions are also presented and discussed.
The Effect of Unsteady Aerodynamic Asymmetric Perturbations on Flutter
Authors: Kielb Robert E. , Hall Kenneth C. , Miyakozawa Tomokazu
Published: March 2009

Nearly all turbomachinery aeroelastic analyses assume that the blades are “tuned” aerodynamically. That is, all blades experience identical steady and unsteady loads (except for an interblade phase shift). This paper presents the results of a perturbations sensitivity study of the effects of aerodynamic asymmetries on flutter of bladed disks. A high fidelity model including both structural and aerodynamic coupling is used. The types of asymmetry considered are single blade, symmetric group, and random. For the case of one blade perturbation, and symmetry group of 2 perturbations, the effect is to suppress flutter. This is similar to the effect of frequency mistuning. However, the results from random perturbations of all blades suggest that manufacturing variations or field damage may cause an engine to flutter. This provides a strong motivation to conduct additional research in this area.