bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Investigation of Stator Clocking Effects in a Two-Stage Low-Speed Axial Compressor
Authors: Sta¨ding J. , Wulff D. , Kosyna G. , Becker B. , Gu¨mmer V.
Published: May 2012

The impact of stator clocking on performance and flow of a 2.5-stage axial compressor has been investigated. Stator clocking, the circumferential indexing of adjacent stator rows with equal blade counts, is known as a potential means to modify the flow field in multistage turbomachinery and increase overall efficiencies of both turbines and compressors. These potential effects on turbomachine performance are due to wake-airfoil interactions and primarily depend on the alignment of the downstream stator row with the upstream stator wake path. The present survey describes and discusses the experimental research on stator clocking effects in a low-speed 2.5-stage axial flow compressor, using front loaded CDA blade sections and cantilevered stator rows with identical blade counts. Conventional static pressure tappings were used to locate global peaks in compressor performance for varying Stator 2 clocking positions at different flow coefficients. Results of unsteady total pressure measurements obtained by means of a high-frequency pressure transducer, embedded in the Stator 2 leading edge, give information on Stator 1 wake propagation. Traverse data from pneumatic 5-hole probes show the impact of stator indexing on Stator 2 exit total pressure at different blade spans. Regardless of flow coefficient, the variations of overall compressor efficiency due to Stator 2 clocking are around 0.2% and are exhibiting a near-sinusoidal trend over the clocking angle. It is shown that total pressure measurements at mid-span of Stator 2 leading edge suggest best overall performances for design and low loading conditions, if the Stator 1 wakes pass through mid-passage of Stator 2. At high loading, however, maximum efficiency locates the wake path directly at the leading edge. Due to a considerable span-wise skewness of the upstream stator wake, the aerodynamic clocking position for Stator 2 varies from hub to tip. While it is shown again that this effect weakens the advantages of airfoil indexing on a global scale, stator clocking shows much more potential if only a single blade section is considered.
Experiment Study of Simulated Effect of Rotor Stator Interaction: Effect of Axial Spacing and Rotor Blade Film Cooling Air Injection Ratio
Authors: Sridhar Murari , Prasad B. V. S. S. S. , Sitaram N.
Published: May 2012

The effect of inlet wake and air injection on blade surface temperature distribution is experimentally determined in the present paper. A flat plate with smoothly curved leading edge and a symmetric beveled trailing edge is used to produce inlet wake. Experiments are performed on a seven-airfoil linear cascade in a low speed wind tunnel at the chord Reynolds number of 5.3×105. Three blades in the middle of the cascade are provided with multiple rows of air injection holes on both pressure surface and suction surface. The distance between the trailing edge of the wake plate and leading edge of the cascade blade is kept at three axial locations, i.e. 0.25, 0.35 and 0.5 (all measured in terms of percent blade chord), at seven transverse locations for each axial location. The detailed temperature distributions on the blade surface are measured using “T-Type” thermocouples connected to a data logger. The results are obtained in terms of film cooling effectiveness for a density ratio (between the hot fluid through air injection holes and cold main flow fluid) of 1.1 and injection mass flow rates of 1.1, 2.5, 3.0 and 5.0 percent of main flow. A significant change in the film cooling effectiveness is observed with increase in the injection mass flow rate and change in the axial spacing.
Investigation of the Influence of Different Rim Seal Geometries in a Low-Pressure Turbine
Authors: Schuler P. , Dullenkopf K. , Bauer H.-J.
Published: May 2012

The sealing of the machine’s inside against hot-gas ingestion is commonly provided by blowing relative cold compressor air radially out through the turbine wheelspace. Rim-seals located inside the wheelspace are primarily designed to keep the required amount of sealing at a minimum. A further possible function of the rim-seal follows from the desire to reduce the aerodynamic losses contributed by the interaction of the emerging sealing flow with the boundary layer of the incoming main flow. Investigations performend in the EU project MAGPI concentrate on the interaction between the sealing flow and the main gas flow and in particular on the effect of different rim seal designs regarding the loss-mechanism in a low-pressure turbine passage. Two different rim seal designs inside a linear low-pressure turbine cascade rig have been analysed in detail. Both, the simple axial gap and the more complex compound design were investigated under the influence of different sealing mass flow rates. Furthermore, a configuration without any cavity in the main gas flow served as a reference case. Extensive measurements of the total pressure loss over the turbine blade have been conducted by means of a five-hole probe. Additionally, the blade loading has been measured at several blade heights. A considerable increase of total pressure losses was observed due to the presence of a cavity with any rim seal design, even for no sealing flow. Higher sealing mass flow rates intensified this effect which becomes manifested in a strengthening of the secondary flows downstream the cascade. Experiments revealed also significant differences in loss-increment depending on the rim seal design used. Deeper insight into the interaction of the flows close to the rim seal is given by results of Laser-Doppler-Velocimetry measurements. The rounded shape of the compound design, which implies an axial overlapping, represents a promising prevention against hot-gas ingestion. While the axial gap design is characterized by higher losses, it also suffers considerable hot-gas ingestion in front of the blade leading edge. A parametric study regarding a possible optimization of the axial gap design is presented in this work.
Parametric Study of Emissions From Low Calorific Value Syn-Gas Combustion, With Variation of Fuel Distribution, in a Prototype Three Sector Burner
Authors: Sigfrid Ivan R. , Whiddon Ronald , Alde´n Marcus , Klingmann Jens
Published: May 2012

The emission composition is measured for a prototype burner while varying the equivalence ratio in discrete portions of the burner. The burner is a three sector system, consisting of a separate igniter, pilot/stabilizer and main burner. The design allows for discrete control of equivalence ratio in each of the three sectors. The ignition sector, designated RPL (Rich-Pilot-Lean), operates from rich to lean equivalence values, and serves to ignite the pilot sector, which, in turn, stabilizes the main combustion sector. All three burner sections are premixed. The burner is operated at atmospheric pressure with inlet flows heated to 650 K (±8 K). Tests were performed for three gases: methane, a model syngas (10% CH4, 22.5% CO, 67.5% H2), and dilute syngas. The dilute gas includes sufficient nitrogen to lower the heating value to 15 MJ/m3. The model syngas and diluted syngas are representative of fuels produced by gasification process. The burner emissions, specifically, CO, CO2, O2 and NOx, are measured while holding the RPL equivalence value constant and varying the equivalence ratio of the pilot and main sectors. The equivalence ratios for pilot and main sectors are chosen such that the total burner equivalence ratios remain constant during a test sequence. The target total equivalence ratio for each gas is chosen such that all experiments should have the same flame temperature.
Transition Mechanisms in Laminar Separated Flow Under Simulated Low Pressure Turbine Airfoil Conditions
Authors: Da¨hnert Jerrit , Lyko Christoph , Peitsch Dieter
Published: May 2012

Based on detailed experimental work conducted at a low speed test facility, this paper describes the transition process in the presence of a separation bubble with low Reynolds number, low free-stream turbulence, and steady main flow conditions. A pressure distribution has been created on a long flat plate by means of a contoured wall opposite of the plate, matching the suction side of a modern low-pressure turbine aerofoil. The main flow conditions for four Reynolds numbers, based on suction surface length and nominal exit velocity, were varied from 80,000 to 300,000, which covers the typical range of flight conditions. Velocity profiles and the overall flow field were acquired in the boundary layer at several streamwise locations using hot-wire anemometry. The data given is in the form of contours for velocity, turbulence intensity, and turbulent intermittency. The results highlight the effects of Reynolds number, the mechanisms of separation, transition, and reattachment, which feature laminar separation-long bubble and laminar separation-short bubble modes. For each Reynolds number, the onset of transition, the transition length, and the general characteristics of separated flow are determined. These findings are compared to the measurement results found in the literature. Furthermore, the experimental data is compared with two categories of correlation functions also given in the open literature: (1) correlations predicting the onset of transition and (2) correlations predicting the mode of separated flow transition. Moreover, it is shown that the type of instability involved corresponds to the inviscid Kelvin-Helmholtz instability mode at a dominant frequency that is in agreement with the typical ranges occurring in published studies of separated and free-shear layers.
Heat Transfer in Turbine Hub Cavities Adjacent to the Main Gas Path Including FE-CFD Coupled Thermal Analysis
Authors: Guijarro Valencia Antonio , Dixon Jeffrey A. , Guardini Attilio , Coren Daniel D. , Eastwood Daniel
Published: May 2012

Reliable means of predicting heat transfer in cavities adjacent to the main gas path are increasingly being sought by engineers involved in the design of gas turbines. In this paper an up-dated analysis of the interim results from an extended research programme, MAGPI, sponsored by the EU and several leading gas turbine manufactures and universities, will be presented. Extensive use is made of CFD and FE modelling techniques to understand the thermo-mechanical behaviour and convective heat transfer of a turbine stator well cavity, including the interaction of cooling air supply with the main annulus gas. It is also important to establish the hot running seal clearances for a full understanding of the cooling flow distribution and heat transfer in the cavity. The objective of the study has been to provide a means of optimising the design of such cavities (see Figure 1) for maintaining a safe environment for critical parts, such as disc rims and blade fixings, whilst maximising the turbine efficiency by means of reducing the fuel burn and emissions penalties associated with the secondary airflow system. The modelling methods employed have been validated against data gathered from a dedicated two-stage turbine rig, running at engine representative conditions. Extensive measurements are available for a range of flow conditions and alternative cooling arrangements. The analysis method has been used to inform a design change which will be tested in a second test phase. Data from this test will also be used to further benchmark the analysis method. Comparisons are provided between the predictions and measurements from the original configuration, turbine stator well component temperature survey, including the use of a coupled analysis technique between FE and CFD solutions.
Combustion of Natural Gas, Hydrogen and Bio-Fuels at Ultra-Wet Conditions
Authors: Go¨ke Sebastian , Terhaar Steffen , Schimek Sebastian , Go¨ckeler Katharina , Paschereit Christian O.
Published: May 2012

Humidified Gas Turbines promise a significant increase in efficiency compared to the dry gas turbine cycle. In single cycle applications, efficiencies up to 60% seem possible with humidified turbines. Additionally, the steam effectively inhibits the formation of NOx emissions and also allows for operating the gas turbine on hydrogen-rich fuels. The current study is conducted within the European Advanced Grant Research Project GREENEST. The premixed combustion at ultra wet conditions is investigated for natural gas, hydrogen, and mixtures of both fuels, covering lower heating values between 27 MJ/kg and 120 MJ/kg. In addition to the experiments, the combustion process is also examined numerically. The flow field and the fuel-air mixing of the burner were investigated in a water tunnel using Particle Image Velocimetry and Laser Induced Fluorescence. Gas-fired tests were conducted at atmospheric pressure, inlet temperatures between 200°C and 370°C, and degrees of humidity from 0% to 50%. Steam efficiently inhibits the formation of NOx emissions. For all tested fuels, both NOx and CO emissions of below 10 ppm were measured up to near-stoichiometric gas composition at wet conditions. Operation on pure hydrogen is possible up to very high degrees of humidity, but even a relatively low steam content prevents flame flashback. Increasing hydrogen content leads to a more compact flame, which is anchored closer to the burner outlet, while increasing steam content moves the flame downstream and increases the flame volume. In addition to the experiments, the combustion process was modeled using a reactor network. The predicted NOx and CO emission levels agree well with the experimental results over a wide range of temperatures, steam content, and fuel composition.
Effects of Contact Interface Parameters on Vibration of Turbine Bladed Disks With Underplatform Dampers
Authors: Schwingshackl C. W. , Petrov E. P. , Ewins D. J.
Published: May 2012

The design of high cycle fatigue resistant bladed disks requires the ability to predict the expected damping of the structure in order to evaluate the dynamic behaviour and ensure structural integrity. Highly sophisticated software codes are available today for this nonlinear analysis but their correct use requires a good understanding of the correct model generation and the input parameters involved to ensure a reliable prediction of the blade behaviour. The aim of the work described in this paper is to determine the suitability of current modelling approaches and to enhance the quality of the nonlinear modelling of turbine blades with underplatform dampers. This includes an investigation of a choice of the required input parameters, an evaluation of their best use in nonlinear friction analysis, and an assessment of the sensitivity of the response to variations in these parameters. Part of the problem is that the input parameters come with varying degrees of uncertainty, since some are experimentally determined, others are derived from analysis and a final set are often based on estimates from previous experience. In this investigation the model of a commercial turbine bladed disc with an underplatform damper is studied and its first flap, first torsion and first edgewise modes are considered for 6EO and 36EO excitation. The influence of different contact interface meshes on the results is investigated, together with several distributions of the static normal contact loads to enhance the model setup and hence increase accuracy in the response predictions of the blade with an underplatform damper. A parametric analysis is carried out on the friction contact parameters and the correct setup of the nonlinear contact model to determine their influence on the dynamic response and to define the required accuracy of the input parameters.
Development of H2-Rich Syngas Fuelled GT for Future IGCC Power Plants: Establishment of a Baseline
Authors: Sipo¨cz Nikolett , Mansouri Mohammad , Breuhaus Peter , Assadi Mohsen
Published: May 2012

As part of the European Union (EU) funded H2-IGCC project this work presents the establishment of a baseline Integrated Gasification Combined Cycle (IGCC) power plant configuration under a new set of boundary conditions such as the combustion of undiluted hydrogen-rich syngas and high fuel flexibility. This means solving the problems with high NOx emitting diffusion burners, as this technology requires the costly dilution of the syngas with high flow rates of N2 and/or H2O. An overall goal of the project is to provide an IGCC configuration with a state-of-the-art (SOA) gas turbine (GT) with minor modifications to the existing SOA GT and with the ability to operate on a variety of fuels (H2-rich, syngas and natural gas) to meet the requirements of a future clean power generation. Therefore a detailed thermodynamic analysis of a SOA IGCC plant based on Shell gasification technology and Siemens/Ansaldo gas turbine with and without CO2 capture is presented. A special emphasis has been dedicated to evaluate at an intermediate stage of the project the GT performance and identify current technical constraints for the realization of the targeted fuel flexibility. The work shows that introduction of the low calorific fuel (H2 rich fuel more than 89 mol% H2) has rather small impact on the gas turbine from the system level study point of view. The study has indicated that the combustion of undiluted syngas has the potential of increasing the overall IGCC efficiency.
Application of Forecasting Methodologies to Predict Gas Turbine Behavior Over Time
Authors: Cavarzere A. , Venturini M.
Published: May 2012

The growing need to increase the competitiveness of industrial systems continuously requires a reduction of maintenance costs, without compromising safe plant operation. Therefore, forecasting the future behavior of a system allows planning maintenance actions and saving costs, because unexpected stops can be avoided. In this paper, four different methodologies are applied to predict gas turbine behavior over time: Linear and Non Linear Regression, One Parameter Double Exponential Smoothing, Baesyan Forecasting Method and Kalman Filter. The four methodologies are used to provide a prediction of the time when a performance limit will be exceeded in the future, as a function of the current trend of the considered parameter. The application considers different scenarios which may be representative of the trend over time of some significant parameters for gas turbines. Moreover, the Baesyan Forecasting Method, which allows the detection of discontinuities in time series, is also tested for predicting system behavior after two consecutive trends. The results presented in this paper aim to select the most suitable methodology that allows both trending and forecasting as a function of data trend over time, in order to predict time evolution of gas turbine characteristic parameters and to provide an estimate of the occurrence of a failure.
A Validation of Commerical Flow Solver Performance on Hybridised Octree Meshes
Authors: Kellar W. P. , Harvey S. A. , Dawes W. N.
Published: May 2012

In recent years we have been developing a meshing system which is aimed at eliminating the bottleneck represented by building meshes for real-world, complex turbomachinery configurations. This system is based on a rapid octree meshing technology which is then made conformal to the bodies present. The objective of this paper is to demonstrate that this class of mesh is not only very fast to produce but also fit-for-purpose in the sense that simulations generated with third-party commercial flow solvers like Fluent have the same accuracy as those performed on more conventional meshes. A range of standard examples and test cases will be presented.
Impact of Manufacturing Variability and Non-Axisymmetry on High-Pressure Compressor Stage Performance
Authors: Lange Alexander , Voigt Matthias , Vogeler Konrad , Schrapp Henner , Johann Erik , Gu¨mmer Volker
Published: May 2012

This paper introduces an approach for considering manufacturing variability leading to a non–axisymmetric blading in CFD simulation of a high–pressure compressor stage. A set of 150 rotor blades from a high–pressure compressor stage was 3D scanned to obtain the manufacturing variability. The obtained point clouds were parameterized using a parametric blade model, which uses typical profile parameters for translating the geometric variability into a numerical model. Probabilistic simulation methods allow for generation of a sampled set of blades that statistically corresponds to the measured one. This technique was applied to generate 4000 sampled blades to investigate the influence of a non–axisymmetric blading. It was found that the aerodynamic performance is considerably influenced by a variation of passage cross section. Nevertheless, this influence decreases with an increasing number of independently sampled blades and thus independently shaped passage cross sections. Due to a more accurate consideration of the geometric variability, the presented methodology allows for a more realistic performance analysis of an HPC stage.
Biomass Utilization in Dual Combustion Gas Turbines for Distributed Power Generation in Mediterranean Countries
Authors: Camporeale Sergio Mario , Fortunato Bernardo , Pantaleo Antonio Marco , Sciacovelli Domenico
Published: May 2012

In Mediterranean regions, such as Puglia in Italy, the supply chain constraints (i.e. local biomass availability, logistics of supply, storage and seasonality issues) limit the optimal size of a biomass fired power plant in a range of 5–15 MWe. In this scenario, innovative Dual Combustion Externally Fired Gas Turbine (DCGT) Power Plants cofired by natural gas and biomass are examined. For this purpose, biomass external firing is explored under two alternatives: direct combustion of solid biomass and atmospheric fixed bed biomass gasification with air. The proposed cycles are analyzed considering both the Net Overall Electric Efficiency and the Marginal Efficiency of biomass energy conversion, defined for the cofiring of biomass and natural gas. Since natural gas represents a quite expensive fossil fuel resource, a Marginal Efficiency higher than zero indicates the convenience to burn natural gas in this typology of power plant rather than in traditional Combined Cycle with higher efficiency. The energy analysis has been carried out by varying pressure ratio, turbine inlet temperature, heat exchanger efficiency and considering the further option of steam injection. The results of the thermodynamic assessment highlight that the gasification should be preferred to the direct combustion of biomass because of the higher marginal efficiency, although the net overall electric efficiencies of the two plants are almost the same (31%).
Innovative Variable Turbine Concept for Turbochargers
Authors: Chebli Elias , Casey Michael , Mu¨ller Markus , Sumser Siegfried , Hertweck Gernot , Schmid Wolfram
Published: May 2012

New concepts for the optimisation of supercharging systems have been analysed to improve fuel consumption, emissions and transient diesel engine response. In addition to the conventional VTG (Variable Turbine Geometry) where the variability takes place upstream of the turbine impeller, a new innovative variable turbine geometry called VOT (Variable Outlet Turbine) is investigated in this paper where the variability takes place at impeller exit. The flow variability is achieved by variation of the flow cross-section at the turbine outlet using an axial displacement of a sliding sleeve over the exducer and provides a simple solution for flow variability. The flow field of the VOT is calculated by means of steady state 3D-CFD simulations to predict the aerodynamic performance as well as to analyse the loss mechanisms. The VOT design is optimised by finding a good balance between clearance and outlet losses to improve the turbine efficiency. Furthermore, experimental results of the VOT are presented and compared to a turbine equipped with a waste gate (WG) that verify the efficiency advantage of the VOT. In general, it is found that the use of the VOT at high specific speed is important to reduce the outlet losses and to improve the turbine efficiency over a wide operating range.
Design of a Rich Internet Application for Gas Turbine Engine Simulations
Authors: Johnson Crosby , Paolini Christopher , Bhattacharjee Subrata
Published: May 2012

Modeling the performance and emissions characteristics of gas turbine engines can involve sequentially solving multiple thermodynamic states of a representative fluid flowing through the engine, evaluating cycle performance, and evaluating the chemical equilibrium of the fluid at select states. The states are defined by the combination of specified thermodynamic conditions, process assumptions derived from established theory of gas turbine engines, and thermodynamic properties of the representative fluid. Internet based applications such as TEST allow experienced analysts to structure and evaluate thermodynamic models of gas turbine engines and separately evaluate the chemical equilibrium of air-fuel mixtures to predict exhaust emissions. Although the TEST thermodynamic and chemical equilibrium data retrieval is automated, analysts are required to first structure the system model. The Internet based software described in this paper allows analysts to combine the modeling of performance and emissions characteristics of gas turbine engines without the need to first structure a model, broadening the range of potential analysts beyond the thermodynamic and chemical equilibrium communities. The software presented in this work combines a visually rich and Internet based interface to input specifications and display results, a communication mechanism to obtain Internet based thermodynamic and chemical equilibrium data, and a solution architecture to autonomously interpret user inputs and Web based data and model engine parameters. This software also allows analysts to modify the model complexity, accounting for irreversibilities and auxiliary devices such as regenerators, reheaters, and intercoolers as required. Data reduction features such as graphical representation of parametric studies and combustion product distribution are also available within the software.
Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades
Authors: Patil Sunil , Tafti Danesh
Published: May 2012

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the LES framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of Rau et al. [1], and Han et al. [2], and wall resolved LES data of Tafti [3]. Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.
Evaluation of a Wire-Mesh Duct Burner Premixer Using LSI Techniques
Authors: Ramadan Omar B. , Hughes Patrick M. , Gauthier J. E. Donald
Published: May 2012

The mixing of fuel and oxidizer is critical for the reduction of NOx emissions from premixed combustion burners. The mixing process in a pre-mixer of a natural gas-fired conical wire-mesh duct burner (DB) was studied experimentally using the laser sheet illumination (LSI) technique. A quasi-quantitative technique was used to rank the relative mixing performance of the different geometrical and flow combinations tested (mixer geometry, fuel injection angle and fuel air momentum ratio). The present paper presents some of the results used in the design and analysis of the burner. This burner was integrated and tested with a micro-turbine cogeneration system (MT70 kW Ingersoll Rand (IR) CHP unit). The DB provides supplementary firing in the exhaust gas stream of the microturbine to increase and control the thermal output of the micro-cogeneration system. The combination provided near perfect premixing and low emissions. The DB successfully raised the micro-turbine exhaust gas temperature from about 227°C to as high as 700°C with NOx and CO emissions of less than 5 ppm and 10 ppmv (corrected to 15 percent O2) respectively. The DB also displayed stable, low emissions operation throughout the surface firing rate range of 148 kW to 328 kW (1574 kW/m2 to 3489 kw/m2). The results show that LSI technique can provide invaluable information about the overall flow field structure. Many important observations are discussed such as mixing, fuel spread, and fuel jet penetration. Samples of the LSI images and 3D plots for selected cases are presented. The two best geometrical combinations ranked during the LSI test were used in the actual combustion test of the DB. Some of the combustion results which prove the effectiveness of the LSI technique are presented.
Simulation of Combustor Damage Mechanisms and Material System Performance via a Sub-Element Configured Specimen Test
Authors: Rudrapatna Nagaraja , Peterson Benjamin H.
Published: May 2012

Modern gas turbine combustors are made of high temperature alloys, employ effusion cooling and are protected by a Thermal Barrier Coating (TBC). Standard material characterization tests such as creep, oxidation and low cycle fatigue are indicators of a material’s potential performance but they neither fully represent the combustor geometric/material system nor fully represent the thermal fatigue conditions a combustor is subjected to during engine operation. Combustor rig tests and/or engine cyclic endurance tests to determine the suitability of new material systems for combustors are time consuming and costly. Therefore, a simple test method for screening material systems under representative combustor conditions is needed. This experimental system was recently developed at Honeywell Aerospace to characterize various gas turbine combustor damage mechanisms and assess state-of-the-art and developmental materials. A configured specimen is fabricated using materials and processes similarly to actual combustor hardware, including sheet metal forming, welding, TBC coating, and effusion hole laser drilling. The configured specimen is cyclically exposed to hot spot thermal gradients typically experienced by fielded hardware using a jet-fueled burner and heated cooling air. Damage mechanisms simulated include bond coat oxidation, TBC spallation, thermal fatigue and distortion. A summary of these damage mechanisms and lessons learned from test development are presented. Results from recent combustor liner, bond coat, and top coat material modifications are also discussed. The effect of combustor liner material creep and thermal fatigue resistance, bond coat composition and processing, and TBC composition and structure on combustor durability is presented.
Reduced Modelling for Turbine Rotor-Blade Coupled Bending Vibration Analysis
Authors: Okabe Akira , Kudo Takeshi , Shiohata Koki , Matsushita Osami , Fujiwara Hiroyuki , Yoda Hideo , Sakurai Shigeo
Published: May 2012

In a traditional turbine-generator set, rotor shaft designers and blade designers have their own models and design process which neglects the coupled effect. Since longer blade systems have recently been employed[1] for advanced turbine sets to get higher output and efficiency, additional consideration is required concerning rotor bending vibrations coupled with a one-nodal (k = 1) blade system. Rotor-blade coupled bending conditions generally include two types so that the parallel and tilting modes of the shaft vibrations are respectively coupled with in-plane and out-of-plane modes of blade vibrations with a one-nodal diameter (k = 1). This paper proposes a method to calculate the natural frequency of a shaft blade coupled system. According to this modeling technique, a certain blade mode is reduced to a single mass system, which is connected to the displacement and angle motions of the shaft. The former motion is modeled by the m-k system to be equivalent to the blade on the rotating coordinate. The latter motion is commonly modeled in discrete form using the beam FEM on an inertia coordinate. Eigenvalues of the hybrid system covering both coordinates provide the natural frequency of the coupled system. In order to solve the eigenfrequencies of the coupled system, a tracking solver method based on sliding mode control concept is used. An eight-blade system attached to a cantilever bar is used for an example to calculate a coupled vibration with a one-nodal diameter between the blade and shaft.
Time-Accurate Calculations of a Passive Shroud Bleed Configuration and Implications for Unsteady Blade Loading
Authors: Deng Xiangyang , Lurie Elizabeth A. , Feng Jinzhang
Published: May 2012

A time-accurate simulation of the flow through a centrifugal compressor stage consisting of a radial inlet with bleed air injection holes, an impeller with air bleed exit holes, and vaneless diffuser is performed for the peak efficiency and near-stall conditions to address fundamental questions regarding the time-varying flowfield. Unsteady results at near-stall point are compared to three steady-state simulations: (1) a simulation without recirculating bleed air at near-stall point; (2) a simulation with axisymmetric slot bleed at near-stall point; and (3) a simulation without recirculating bleed air at an increased inlet mass flow rate that accounts for the additional throughflow associated with the amount of bleed air. By these analyses, it is established that representing the bleed flow as axisymmetric, hence steady state in the rotating frame of reference, provides assessment of the time-average compressor performance; that the time-average loading is similar in both qualitative and quantitative manner to the steady state model; that the unsteady blade loading is dominated by first and second harmonic of bleed hole passing frequency and of similar magnitude to mean loading; and that the blade hole alters the local blade loading as far down as 60% span.
Vibration Control of a Turbo Molecular Pump Suspended by Active Magnetic Bearings
Authors: Zhang Kai , Dong Jinping , Dai Xingjian , Zhang Xiaozhang
Published: May 2012

In a turbo molecular pump suspended by active magnetic bearings (AMBs), vibration caused by the rotor’s bending modes, gyroscopic effects and structure vibration modes influenced the pump performance and even cause instability. Different methods were used to deal with these problems. A Cross Feedback method was effective in restraining the nutation and precession of the rotor. A Phase Shaping method provided sufficient damping for the 1st bending mode of the rotor. The structure vibration instability was avoided by adjusting the joint strength between two parts of the pump housing. The gyroscopic effects also destroyed the stability of unbalance control algorithms for the AMBs at a high rotation speed. It was shown that, to ensure the stability of the controller when the unbalance control algorithms were applied, the 1st bending frequency of the rotor should be increased. Experiment results concerning the problems discussed above were provided. With a suitable controller design and an appropriate consideration of the dynamic problems, the rotor was successfully accelerated to 27 000 rpm.
Experimental Investigation on Ignition Performance of LESS Combustor
Authors: Fu Zhenbo , Lin Yuzhen , Li Jibao , Sung Chih-Jen
Published: May 2012

In the design of next-generation civil aviation gas turbine combustors, there is high demand to improve the efficiency of combustion technology to decrease the amount of fuel consumed and to reduce the emissions in an effort to lessen the environmental impacts. This paper introduces a novel, ultra-low emissions combustor, namely Low Emission Stirred Swirl (LESS) combustor, employing the lean premixed prevaporized (LPP) approach. The LESS combustor is a single annular layout. Its dome is comprised of two stages — the pilot stage and the main stage. The pilot stage is a typical swirl cup design which uses a pressure swirl atomizer with dual counter-rotating radial swirlers to atomize the fuel and form a diffusion flame, and is located in the centerline of the combustion chamber. The main stage surrounding coaxially the pilot stage includes one annulus as premixer and 14 plain orifice atomizers with 14 small dual counter-rotating radial swirlers arranged uniformly on the dome of the annulus, which lead to the main premixed flame. Five different igniter locations are chosen according to the CFX-simulated non-reacting flow field of a simplified mainstage combustor. Only the pilot pressure swirl atomizer is operated in the present ignition performance tests. The model combustor is a single module rectangular combustor with normal inlet temperature and normal inlet pressure. Under the test conditions of air pressure drop of 0.5%–9%, the ignition performance of the model LESS combustor is analyzed. The lean lightoff fuel/air ratio (LLO FAR), characterizing the ignition performance of a combustor, is investigated herein. In addition, the effects of igniter locations and pilot fuel nozzles on LLO FAR are studied. Specific to the LESS combustor, the igniter location has minor effect on the LLO FAR values. However, as expected, the combustor dome pressure drop and attendant reference velocity along with spray SMD impact LLO FAR. Furthermore, CFX-simulated results of the flow field, spray characteristics, and gas-liquid interactions under the typical condition of combustor operation are presented and discussed to provide insight into the ignition processes and performance.
Experimental Investigations of Flame Stabilization of a Gas Turbine Combustor
Authors: Lu¨ckerath Rainer , Lammel Oliver , Sto¨hr Michael , Boxx Isaac , Stopper Ulrich , Meier Wolfgang , Janus Bertram , Wegner Bernhard
Published: May 2012

While today’s gas turbine (GT) combustion systems are designed for specific fuels there is an urgent demand for fuel-flexible stationary GT combustors capable of burning natural gas as well as hydrogen-rich fuels in future. For the development of a fuel flexible, low-emission, and reliable combustion system a better understanding of the flow field – flame interaction and the flame stabilization mechanism is necessary. For this purpose, a down-scaled staged can combustion system provided with an optical combustion chamber was investigated in a high pressure test rig. Different optical diagnostic methods were used to analyze the combustion behavior with a focus on flame stabilization and to generate a comprehensive set of data for validation of numerical simulation methods (CFD) employed in the industrial design process. For different operating conditions the size and position of the flame zone were visualized by OH* chemiluminescence measurements. Additionally, the exhaust gas emissions (NOx and CO) and the acoustic flame oscillations were monitored. Besides many different operating conditions with natural gas different fuel mixtures of natural gas and hydrogen were investigated in order to characterize the flashback behavior monitored with OH* chemiluminescence. For selected operating conditions detailed laser diagnostic experiments were performed. The main flow field with the inner recirculation zone was measured with two-dimensional particle image velocimetry (PIV) in different measuring planes. One-dimensional laser Raman spectroscopy was successfully applied for the measurement of the major species concentration and the temperature. These results show the variation of the local mixture fraction allowing conclusions to be drawn about the good premix quality. Furthermore, mixing effects of unburnt fuel/air and fully reacted combustion products are studied giving insights into the process of the turbulence-chemistry interaction and reaction progress.
Tip Leakage Losses in Subsonic and Transonic Blade-Rows
Authors: Wheeler Andrew P. S. , Korakianitis Theodosios , Banneheke Shashimal
Published: May 2012

In this paper the effect of blade-exit Mach number on unshrouded turbine tip-leakage flows is investigated. Previously published experimental data of a high-pressure turbine blade are used to validate a CFD code, which is then used to study the tip-leakage flow at blade-exit Mach numbers from 0.6 to 1.4. Three-dimensional calculations are performed of a flat-tip and a cavity-tip blade. Two-dimensional calculations are also performed to show the effect of various squealer-tip geometries on an idealized tip-flow. The results show that as the blade-exit Mach number is increased the tip leakage flow becomes choked. Therefore the tip-leakage flow becomes independent of the pressure difference across the tip and hence the blade-loading. Thus the effect of the tip-leakage flow on overall blade loss reduces at blade-exit Mach numbers greater than 1.0. The results suggest that for transonic blade-rows it should be possible to raise blade loading within the tip region without increasing tip-leakage loss.
Inverse Problem for Isentropic Mach-Number on Blade Wall in Aerodynamic Shape Design of Turbomachinery Cascades by Using Adjoint Method
Authors: Li Haitao , Song Liming , Zhang Pengfei , Feng Zhenping
Published: May 2012

This paper presents an approach of the continuous adjoint system deduction based on the variation in grid node coordinates, in which the variation in the gradient of flow quantity is converted into the gradient of the variation in flow quantity and the gradient of the variation in grid node coordinates, which avoids the coordinate system transforming in the traditional derivation process of adjoint system and make the adjoint system much more sententious. By introducing the Jacobian matrix of viscous flux to the gradient of flow variables, the adjoint system for turbomachinery aerodynamic design optimization governed by compressible Navier-Stokes equations is derived in details. Given the general expression of objective functions consisted of both boundary integral and field integral, the adjoint equations and their boundary conditions are derived, and the final expression of the objective function gradient including only boundary integrals is formulated to reduce the CPU cost. Then the adjoint system is numerically solved by using the finite volume method with an explicit 5-step Runge-Kutta scheme and Riemann approximate solution of Roe’s scheme combined with multi-grid technique and local time step to accelerate the convergence procedure. Finally, the application of the method is illustrated through a turbine cascade inverse problem with an objective function of isentropic Mach number distribution on the blade wall.
Detailed Local Heat Transfer Measurements in a Model of a Dendritic Gas Turbine Blade Cooling Design
Authors: Batstone James , Gillespie David , Romero Eduardo
Published: May 2012

A novel form of gas turbine blade or vane cooling in which passages repeatedly branch within the wall of the cooled component is introduced in this paper. These so called dendritic cooling geometries offer particular performance improvements compared to traditional cooling holes where the external cross flow is low, and conventional films have a tendency to lift off the surface. In these regions improved internal cooling efficiency is achieved, while the coolant film is ejected at a low momentum ratio resulting in reduced aerodynamic losses between the film and hot gases, and a more effective surface film. By varying the number of branches of the systems at a particular location it is possible to tune the flow and heat transfer to the requirements at that location whilst maintaining the pressure margin. The additional loss introduced using the internal branching structure allows a full film-coverage arrangement of holes at the external blade surface. In this paper the results of transient heat transfer experiments characterising the internal heat transfer coefficient distribution in large scale models of dendritic passages are reported. Experiments were conducted with 1, 2 and 3 internal flow branches at a range of engine representative Reynolds numbers and exit momentum ratios. CFD models are used to help explain the flow field in the cooling passages. Furthermore the sensitivity of the pressure loss to the blowing ratio at the exit of the cooling holes is characterised and found to be inversely proportional to the number of branches in the dendritic system. Surprisingly the highly branched systems generally do not exhibit the highest pressure losses.
LES of Pre-Vaporized Kerosene Combustion at High Pressures in a Single Sector Combustor Taking Advantage of the Flamelet Generated Manifolds Method
Authors: Pantangi Pradeep , Sadiki Amsini , Janicka Johannes , Hage Michael , Dreizler Andreas , van Oijen J. A. , Hassa Christoph , Heinze Johannes , Meier Ulrich
Published: May 2012

This paper summarizes the development of an LES based model for reliable description of combustion in a gas turbine combustion chamber. Combustion is described by means of the flamelet generated manifolds (FGM) method. A Smagorinsky-model with dynamic procedure is applied to determine the subgrid scale stresses. A gradient ansatz model is used to represent the sub-grid scale scalar flux in the mixture fraction and in the reaction progress variable equations. Soot formation and radiation are not considered. In order to evaluate the capability of the model for predicting combustion processes induced by complex real fuels a high pressure single sector combustor (SSC) is investigated. This combustion chamber is fuelled with pre-vaporized kerosene fuel and features very complex unsteady swirling flow and partially premixed combustion properties. The validation of the designed tool along with the prediction analysis is carried out in terms of comparison between experimental data (achieved with a nozzle fired at 0.6 Mpa) and numerical results. This reveals that the proposed LES model is able to capture satisfactorily the flow and combustion properties involving. In particular the flame is predicted to be not always attached to the nozzle. It fluctuates between a lifted and an attached regime. This agrees with experimental findings.
On a Numerical Method for the Simulation of Steady Jet Array Interaction With Rotating Components
Authors: Kostege Valery , Chernyshev Sergey , Vassiliev Vladimir
Published: May 2012

Experimental and theoretical investigations show that unsteady effects like moving wakes, tip vortices, passing shocks, pulsating injections and other similar structures significantly affect the aerodynamic characteristics of turbines and compressors. They also influence the thermal state and lifetime of components. Therefore it is very important for designers of turbomachines to properly simulate these effects. On the other hand, time-accurate computations are still expensive and require substantial resources in CPU and computer memory. Moreover the elapsed time is high. However in certain cases the numerical model for unsteady calculations can be simplified, allowing proper capture of the unsteadiness impact, but with much less required computing capacity. This makes the approach acceptable for design applications. Such a simplified method, applicable to a simulation of a steady jets array interaction with rotating components, is described in this paper. The advantages and limitations are discussed, and the validation results and application examples are presented.