bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Modelling of Three Dimensional Honeycomb Labyrinth Seals Employing a Simplified Approach
Authors: Collins Dermot , Teixeira Joao Amaral , Crudgington Pete , Ivey Paul C.
Published: September 2008

This paper numerically analyses the flow through abradable honeycomb labyrinth seals using CFD. Three-dimensional CFD simulations using a single tooth have been compared to representative two-dimensional simulations. Two sizes of honeycomb (1.60mm and 3.20mm) have been analysed at pressure ratios from 1.20 up to 1.60. The seal geometry was kept constant throughout with a running clearance of 1.00mm. The honeycomb has been oriented in two planes with respect to the labyrinth teeth. The two-dimensional planes show equivalence both in terms of overall performance and inter-cavity pressure profiles. Comparisons of Cd typically agree within 2.5%, having an average variation of 1.3%. Total pressure profiles at the middle of the upstream and downstream cavity have been compared. These reveal typical average RMS variations of less than 3% between 3-D and 2-D profiles. It has also been shown that the honeycomb surface causes velocity effects in 3-D that propagate into the seal cavity. The technique used has achieved significant reductions in modelling times.
Double-Jet Ejection of Cooling Air for Improved Film-Cooling
Authors: Kusterer Karsten , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo
Published: September 2008

Film-cooling in gas turbines leads to aerodynamic mixing losses and reduced temperatures of the gas flow. Improvements of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount and by establishing a more equal distribution of the cooling fluid along the surface. It is well known that vortex systems in the cooling jets are the origin of reduced film-cooling effectiveness. For the streamwise ejection case, kidney-vortices result in a lift-off of the cooling jets; for the lateral ejection case, usually only one dominating vortex remains, leading to hot gas flow underneath the jet from one side. Based on the results of numerical analyses, a new cooling technology has been introduced by the authors, which reaches high film-cooling effectiveness as a result of a well-designed cooling hole arrangement for interaction of two neighbouring cooling jets (Double-jet Film-cooling DJFC). The results show that configurations exist, where an improved film-cooling effectiveness can be reached because an anti-kidney vortex pair is established in the double-jet. The paper aims on following major contributions: • to introduce the Double-jet Film-cooling (DJFC) as an alternative film-cooling technology to conventional film-cooling design. • to explain the major phenomena, which lead to the improvement of the film-cooling effectiveness by application of the DJFC. • to prove basic applicability of the DJFC to a realistic blade cooling configuration and present first test results under machine operating conditions.
The Effects of Unintentional Deviations Due to Manufacturing of Cooling Holes and Operation on Transpiration Cooling Efficiency
Authors: Bohn Dieter , Krewinkel Robert
Published: September 2008

A full-coverage cooled multi-layer plate configuration is investigated numerically by application of a 3-D conjugate fluid flow and heat transfer solver, CHTflow. The geometrical setup and the fluid flow conditions derive from modern gas turbine combustion chambers and bladings. The numerical grid contains the coolant supply (plenum), the solid body and the main flow area on the plate. The full-coverage cooling is realized by finest drilled holes with a diameter of 0.2 mm that are shaped in the region of the thermal barrier coating. Two different effects will be considered in this paper. First, the effects of deviations in the cooling hole geometry due to the manufacturing process will be discussed, then the effects of an obstruction in one of the cooling holes will be looked at. The numerical investigation focuses on the cooling efficiency on the plate surface and on the cooling hole surface as well as the aerodynamics in the main flow. The scientific work is embedded in the Collaborative Research Center 561 at RWTH Aachen University.
A Solar Gas Turbine Cycle With Super-Critical Carbon Dioxide as a Working Fluid
Authors: Utamura Motoaki , Tamaura Yutaka
Published: September 2008

Solar thermal power generation system equipped with molten salt thermal storage offers continuous operation at a rated power independent of the variation of insolation. A gas turbine cycle for solar applications is studied which works in a moderate temperature range (600–850K) where molten salt stays as liquid stably. It is found that a closed cycle with super-critical state of carbon dioxide as a working fluid is a promising candidate for solar application. The cycle featured in smaller compressor work would achieve high cycle efficiency if cycle configuration and operation conditions are chosen properly. The temperature effectiveness of a regenerative heat exchanger is shown to govern the efficiency. Under the condition of 98% temperature effectiveness, the regenerative cycle with pre- and inter-cooling provides cycle efficiency of as much as 47%. A novel heat exchanger design to realize such a high temperature effectiveness is also presented.
Effect of Feed Channel Width on Heat Transfer in a Rectangular Duct With an Array of Off-Set Jets
Authors: Al-Hadhrami Luai M.
Published: September 2008

Experimental investigation was carried out to study the heat transfer characteristics in a rectangular duct cooled by an array of impinging jets. Air ejected from an array of orifices is aimed at the heated target surface and exits from the radial outlets. The effect of feed channel widths (5 ≤ H / d ≤ 9), jet to target plate distance (4 ≤ S/d ≤ 8), outflow orientation and jet Reynolds numbers (9300 ≤ Rej ≤ 18800) with a single array of equally spaced off-set orifice jets of diameter d = 0.5 cm on heat transfer was studied. Results indicated that the outflow orientation causing crossflow effect significantly affects the Nusselt number distributions on the target surface. Relatively higher Nusselt number values were obtained for the outflow orientation where the flow exits in both the directions. The feed channel width H/d = 7 gave relatively higher values of heat transfer compared to the other two feed channel widths. The jet-to-plate distance S/d = 4 resulted in higher heat transfer compared to the other jet-to-plate distances.
Flame Ionization Distribution and Dynamics Monitoring in a Turbulent Premixed Combustor
Authors: Chorpening B. T. , Huckaby E. D. , Morris M. L. , Thornton J. D. , Benson K. J.
Published: September 2008

To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented which operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blowoff, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio, and progress has been made on detecting and measuring combustion instabilities. In support of this development, a highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the ultraviolet flame emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the ultraviolet (mostly OH*) emission and the corresponding electron and ion distribution near the walls of the combustor. During testing the combustion dynamics were controlled using a fuel feed impedance control technique. This provided flame ionization measurements for both steady and unsteady combustion, without changing the operating parameters of the combustor. Previous testing in this combustor had fewer data acquisition channels, and did not include a full implementation of a CCADS centerbody. This testing included both the guard and sense CCADS electrodes installed on the nozzle centerbody, and an array of 14 wall mounted spark plugs to monitor the flame ionization downstream along the walls of the combustor. This paper reports the results of this testing, focusing on the relationship between the flame ionization, ultraviolet flame emission, and pressure oscillations. Tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with inlet reference velocities of 20 and 25 m/s. The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Data processing included computing the logarithm of the real-time current signal from the guard electrode, to compensate for the exponential decay of the potential field from the electrode. The data show the standard deviation of the guard current to be the most promising statistic investigated for correlation with the standard deviation of the chamber pressure. This correlation could expand the capabilities of CCADS to allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.
Effects of Swirl Combination and Mixing Tube Geometry on Combustion Instabilities in a Premixed Combustor
Authors: Koyama Masamichi , Fujiwara Hiroshi , Zimmer Laurent , Tachibana Shigeru
Published: September 2008

In this paper, flow fields inside a premixed combustor have been investigated by CFD analysis and PIV measurement in a preheating, non-reacting condition. Four types of premixer are examined. The design of the premixer is determined by the combination of swirlers and mixing tubes. There are two variations of triple-concentric swirlers and three variations of mixing tubes. Comparisons are made among mean velocity distributions derived from CFD and PIV. PDF analysis is performed on the data from PIV to discuss the possibility of the occurrence of flashback. Combustion rig tests have been carried out also on similar condition to see combustion instabilities depending on the choice of premixers and operating conditions. Flame is directly observed from crystal windows placed on the side and downstream of the combustion chamber. A glass rod is installed on the wall of the mixing tube so as to see light emissions inside the tube, i.e. evidence of flashback. Pressure fluctuations at the combustor liner are measured in one position. The spectra of pressure fluctuations are computed to look at the possibility of combustion oscillations. Discussions are made on the relation between the global flame structure and pressure modes. Finally, proper premixer configurations to prevent combustion instabilities are proposed.
Active Combustion Control System for Reduction of NOx and Pulsation Levels in Gas Turbines
Authors: Kokanovic´ Stanka , Guidati Gianfranco , Torchalla Stephan , Schuermans Bruno
Published: September 2008

This paper presents two different active combustion control systems (ACCS) for the reduction of NOx levels, and suppression of thermo-acoustic instabilities within stationary gas turbines. Dependent on the actual measurement the ACCSs steer the fuel split between different burner groups or within the burner itself in order to find an optimum operation point. In a first step, an active control system has been developed for the ALSTOM GT13E2 gas turbine where the fuel ratio between two burner groups has to be handled to optimise NOx and pulsation levels. Since perturbations in combustion operating conditions have a direct effect on combustion pulsation behaviour, it is possible to control combustor equivalence ratio by using combustion pulsation measurements as an input for the control system. By doing that, lower operating NOx emissions are achieved as operating safety margin to lean blow out (LBO) may be reduced by more than 50% due to a more accurate and controlled handling of combustor equivalence ratio. Although combustion instabilities due to lean blow out are of minor concern within the GT26, the success of this combustion control approach has led to the development of a more advanced method where both, NOx levels and pulsation amplitudes are feedback-controlled simultaneously in order to track the optimum operating point. By using two premixed stages in the burners fuel supply, the equivalence ratio within the combustor is adapted. Engine and single burner test results confirmed control model dynamics predictions. This paper illustrates the applied closed-loop controls concepts and the successful controller verification on single burner and on engine level.
Automated Laser Re-Opening of Film Cooling Holes
Authors: Hoebel M. , Fehrmann B. , Franitza K. , Kohles C. , Lang P.
Published: September 2008

The re-opening of film cooling holes is currently one of the major challenges for the commercial repair of latest generation gas turbine noble parts. Protective coatings consumed in the course of a C-Interval must be replaced. An undesired side effect is that the new coating material plugs existing cooling channels. The use of reconditioned parts critically depends upon the capability to restore the original efficiency of the advanced cooling system. We present a novel process for that purpose, which has been developed at the ALSTOM Technology Center combining robotic vision and laser material processing. As a first step accurate information about cooling hole positions and orientation is obtained from a robotic vision system. This data is used to guide a short-pulse drilling laser in a subsequent machining operation. Typical overspray conditions for a great variety of film cooling geometries have been simulated and the results have been used to create a database of 3D overspray models. From these models a CAD/CAM postprocessor automatically generates individualized laser machining programs. Overspray coating material is then removed through an ablation process using a tailored 5+2 axes laser machining center equipped with an industrial q-switch Nd-YAG laser and a galvano-scanner. Airflow measurement results show that the new process is capable of meeting the cooling airflow requirements for heavily loaded hot-gas parts of the first gas turbine stage. This allows high quality reconditioning of film-cooled gas turbine components such as those in ALSTOM’s GT24/GT26 fleet.
Modelling of PV-Powered Water Electrolysers
Authors: Crosa Giampaolo , Lubiano Maurizio , Trucco Angela
Published: September 2008

In the near future the hydrogen production by means of advanced water electrolysers powered by renewable hybrid energy systems (Photovoltaic solar/wind) could help to resolve the electricity supply and environmental problems relating to the use of fossil fuels. In the light of this perspective the hydrogen represents an alternative energy carrier, helping to overcome all the problems related to the intermittent nature of solar and wind sources. A non linear dynamic simulator of a photovoltaic-hydrogen energy system has been realised, aiming to provide a useful instrument for the development of innovative strategies for plant control and plant operating guidance. The lumped parameter physical approach has been used, applying the fundamental conservation laws of mass, energy and momentum to every component of the plant. The water electrolyser model has been tailored on the characteristics of an advanced pressurised system, using a Casale Chemicals S.A. advanced cell bipolar design, with alkaline electrolyte (KOH solution), whose mathematical models was described by the authors in previous papers. A first version of this simulator has been improved by introducing a reliable thermal model, able to predict the solar panel temperature profile that affects the PV array performance; the panel model has been modified in order to reproduce precisely the I/V characteristics of any PV module, starting from its nominal data. Thanks to this model improvement, the simulator allowed to be used to maximise the PV power production, evaluating different control strategies: a Maximum Power Point Tracking (M.P.P.T) block has been then introduced in the model to optimise the generated power by the photovoltaic plant. The Joule losses due to the PV field internal wiring and to its feeding connection with the electrolyser have been also considered: it consents to separately compute the energy losses in the different PV-electrolyser coupling configurations, thus evaluating the best panel disposition in order to minimise the electric power dissipation. The simulator proved to be able to robustly predict the performance of the PV-electrolysis system for different configurations, operating conditions and control strategies. A steady-state analysis not appears in fact to be an adequate tool for these purposes.
Advanced Seal Test Rig Validation and Operation
Authors: Kool Gerrit A. , Kloosterman Arjen B. , Rademaker Edward R. , Soemarwoto Bambang I. , Bingen Fons M. G. , Paolillo Roger E. , Cloud David F.
Published: September 2008

Advanced seals have been identified as critical in meeting engine goals for specific fuel consumption, thrust-to-weight ratio, emissions, durability, and operating costs. In a direct effort to reduce the parasitic leakage, a high-temperature, high-speed seal test rig with Active Clearance Control (ACC) has been designed, built and validated by the National Aerospace Laboratory (NLR) in the Netherlands within a collaborative program with Sulzer Metco Turbine Components (SMTC) and Pratt & Whitney (P&W). NLR’s new seal test rig is capable to evaluate seals for the next generation gas turbine engines. It will test air seals (i.e., labyrinth, brush, and new seal concepts) in near gas turbine engine environment conditions of high temperature to 815 °C (1500 °F), high pressure to 2400 kPa (335 psid), high surface speeds to 365 m/s (1200 ft/s). Seal flows for typical engine seal clearances between 0.12 mm (0.005 inch) and 0.65 mm (0.025 inch) can be measured without changing test articles but by using the ACC system. A compressed air facility at the German-Dutch Windtunnel, located at the NLR site, delivers the required compressed clean and dry air. This paper describes the design, the instrumentation, the control system and the validation of the test rig. The rig certification was achieved by validating test measurements using a known three knife-edges stepped labyrinth seal. This paper also addresses the NLR’s CFD and engineering tool development to predict the seal performance.
Numerical Modeling of Stationary But Developing Premixed Turbulent Flames
Authors: Sathiah Pratap , Lipatnikov Andrei N.
Published: September 2008

A typical stationary premixed turbulent flame is the developing flame, as indicated by the growth of mean flame thickness with distance from flame-stabilization point. The goal of this work is to assess the importance of modeling flame development for RANS simulations of confined stationary premixed turbulent flames. For this purpose, submodels for developing turbulent diffusivity and developing turbulent burning velocity, which were early suggested by our group (FSC model) and validated for expanding spherical flames [4], have been incorporated into the so-called Zimont model of premixed turbulent combustion and have been implemented into the CFD package Fluent 6.2. The code has been run to simulate a stationary premixed turbulent flame stabilized behind a triangular bluff body in a rectangular channel using both the original and extended models. Results of these simulations show that the mean temperature and velocity fields in the flame are markedly affected by the development of turbulent diffusivity and burning velocity.
Laser Cladding of Ti-6Al-4V Knife Edges
Authors: Shanker Kartik , Cuddy Jonathan , Willerton Roy
Published: September 2008

The effect of cladding of Ti-6Al-4V knife edges using wires and a CO2 laser power source was investigated. This method of cladding, in combination with conventional atmospheric shielding techniques, permits continuous deposition of thick (> 1mm) cladding of acceptable porosity and microstructural quality. The cladding width increased to 0.76–0.81mm irrespective of the knife edge width of 0.350–0.76mm. Continuous deposition of multiple layers was possible, at 0.125–0.150mm increase in thickness per pass, at part linear speeds as high as 762 mm/min. While the process is sensitive to practical considerations of wire feed, knife edge and laser alignment, no evidence of damage to the substrate from laser reflection was observed.
Combustion Optimization for the ALSTOM GT13E2 Gas Turbine
Authors: Steinbach Ch. , Ulibarri N. , Garay M. , Lu¨bcke H. , Meeuwissen Th. , Haffner K. , Aubry J. , Kodim D.
Published: September 2008

The NOx emissions of low NOx premix combustors are not only determined by the burner design, but also by the multi burner interaction and the related distribution of air and fuel flows to the individual burners. Often the factors that have a positive impact on NOx emission have a negative impact on the flame stability, so the main challenge is to find an optimum point with the lowest achievable NOx while maintaining good flame stability. The hottest flame zones are where most of the NOx is formed. Avoiding such zones in the combustor (by homogenization of the flame temperature) reduces NOx emissions significantly. Improving the flame stability and the combustion control allows the combustor to operate at a lower average flame temperature and NOx emissions. ALSTOM developed a combustion optimization package for the GT13E2. The optimization package development focused on three major issues: • Flame stability; • Homogenization of flame temperature distribution in the combustor; • Combustion control logic. The solution introduced consists of: • The reduction of cooling air entrainment in the primary flame zone for improved flame stability; • The optical measurement of the individual burner flame temperatures and their homogenization by burner tuning valves; • Closed loop control logic to control the combustion dependent on the pulsation signal. This paper shows how fundamental combustion research methods were applied to derive effective optimization measures. The flame temperature measurement technique will be presented along with results of the measurement and their application in homogenization of the combustor temperature distribution in an engine equipped with measures to improve flame stabilization. The main results achieved are: • Widening of the main burner group operation range; • Improved use of the low NOx operation range; • NOx reduction at the combustor pulsation limit and hence, large margins to the European emission limit (50 mg/m3 @ 15%O2).
CFD Based Analysis of Burner Fuel Air Mixing Over a Range of Air Inlet and Fuel Pre-Heat Temperatures for a Siemens V94.3A Gas Turbine Burner
Authors: Darbyshire O. R. , Wilson C. W. , Evans A. , Beck S. B. M.
Published: September 2008

The homogeneity of the fuel/air mix entering the combustion chamber of a gas turbine is known to be a factor in both the emissions performance (with poor mixing resulting in local hotspots and the formation of thermal NOx) and the generation of acoustic vibrations (humming). Obviously it is desirable to reduce both pollutants and unwanted acoustics as far as possible. The aim of this paper is to study the relationship between the local inlet conditions and the mixing of the fuel and air, specifically looking at the effects of fuel gas preheating and inlet air temperature on mixedness at the combustor inlet. A CFD model of the lean pre-mixed combustor for a Siemens v94.3A gas turbine was used to analyse the problem. The 3-dimensional model employs a structured mesh scheme and uses the symmetry of the burner to reduce computational effort. The model was solved using a 2nd order discretisation of the momentum and continuity equations along with the RNG k-ε turbulence model to provide closure. The boundary conditions for the model were taken from data obtained from in service measurements. Several runs were made using air inlet temperatures varying from −10°C to 30°C and gas inlet temperatures from 10°C to 450°C. The data obtained from the CFD simulations was processed to give an indication of the quality of the fuel/air mixing for each set of inlet conditions. This was then used to create a tool which can be used to determine the amount of gas pre-heat required to achieve the best possible mixing for a given set of ambient conditions. An estimation of the NOx produced at different conditions was derived from the mixing data. Analysis of the results showed that increasing the gas preheat produces an improvement in the mixing of the fuel and air in the burner. This improvement in mixing also resulted in a reduction in the estimated amount of NOx produced.
Numerical Modeling of Thermoacoustic Oscillations in a Gas Turbine Combustion Chamber
Authors: Nowak Dariusz , Bellucci Valter , Cerny Jan , Engelbrecht Geoffrey
Published: September 2008

The prediction of high-frequency acoustic oscillations in gas turbine combustors is an important issue, related to engine performance, NOx emissions, component lifetime and engine operational flexibility. Different methods with increasing complexity and predictive ability have been discussed in a number of papers. Application of these methods requires large computational capacity and long computational times. Therefore, a limited number of variants of small combustor models or small sectors can be analyzed in a reasonable time. This paper presents an approximate approach, applicable under certain specific conditions. It is based on an understanding that the acoustic pressure oscillations are tied to the oscillation in heat release rate. The interaction is taking place in the heat release zone, independent of the type of the feedback mechanism. For a typical gas turbine combustion chamber, many acoustic modes exist in the frequency range of interest. However, only a few of these modes are excited by the combustion process and thus are relevant. The mode excitation depends both on combustion noise (due to flame excitation contribution independent of the acoustic field) and combustion instability (acoustic mode made unstable by the flame transfer function). With a flame surface obtained from steady state CFD simulation, and with acoustic mode shapes obtained from a Finite Element package, the forced acoustic response of the combustion system to the flame excitation was calculated. In a first validation step, this method has been tested on a single burner atmospheric test facility. In a second step, the method will be applied to an annular SEV combustion chamber of a GT26 ALSTOM gas turbine. The strength of this approach is that large models can be analyzed quickly to show the influence of changes in a flame position and effect of the combustor geometry. The weakness is that combustion instabilities can not be addressed by such a method. Furthermore, the phase relation of the excitation between different parts of the flame is frequency dependant and needs to be given as an input, which requires an experience and expert knowledge.
Impulse Response Processing of Transient Heat Transfer Gauge Signals
Authors: Oldfield M. L. G.
Published: September 2008

A new, computationally-efficient method is presented for processing transient thin-film heat transfer gauge signals. These gauges are widely used in gas turbine heat transfer research, where, historically, the desired experimental heat transfer flux signals, q, are derived from transient measured surface-temperature signals, T, using numerical approximations to the solutions of the linear differential equations relating the two. The new method uses known pairs of exact solutions, such as the T response due to a step in q, to derive a sampled approximation of the impulse response of the gauge system. This impulse response is then used as a finite impulse response digital filter to process the sampled T signal to derive the required sampled q signal. This is computationally efficient because the impulse response need only be derived once for each gauge for a given sample rate, but can be re-used repeatedly, using optimised Matlab filter routines and is highly accurate. The impulse response method can be used for most types of heat flux gauge. In fact, the method is universal for any linear measurement systems which can be described by linear differential equations where theoretical solution pairs exist between input and output. Examples using the new method to process turbomachinery heat flux signals are given.
Towards the Multiobjective Optimisation of Gas Turbine Combustors
Authors: Wyse S. G. , Parks G. T. , Cant R. S.
Published: September 2008

Gas turbine combustor design entails multiple, and often contradictory, requirements for the designer to consider. Multiobjective optimisation on a low-fidelity linear-network-based code is suggested as a way of investigating the design space. The ability of the Tabu Search optimiser to minimise NOx and CO, as well as several acoustic objective functions, is investigated, and the resulting “good” design vectors presented. An analysis of the importance of the flame transfer function in the model is also given. The mass flow and the combustion chamber width and area are shown to be very important. The length of the plenum and the widths of the plenum exit and combustor exit also influence the design space.
Impact of Impurities in CO2-Fluids on CO2 Transport Process
Authors: Li H. , Yan J.
Published: September 2008

There are four possible transportation means that could be used to deliver CO2: motor carriers, railway carriers, water carriers, and pipeline. The impurities in CO2-fluids have significant impacts on the thermodynamic properties that will further affect the design, operation and cost of CO2 transport. This paper focuses on how impurities in CO2-fluids affect thermodynamic properties, and how the changes of properties affect CO2 transport process. Vapor-liquid equilibrium (VLE), critical point and densities are essential thermodynamic properties for designing a CO2 transport process. Studies on these properties will be carried out for CO2-mixtures based on the combinations of the common impurities such as SO2, H2S, CH4, Ar, O2 and N2. Moreover with a real case of pipeline for CO2 transport, the impact of impurities on transport process will be demonstrated in more details.
Validation of a Partially-Premixed Combustion Model for Gas Turbine Applications
Authors: Caracciolo L. , Rubini P. A.
Published: September 2008

The principal requirements of industry, with respect to the numerical simulation of gas turbine combustors, are computational efficiency and algorithm robustness, together with an accurate representation of the complex fundamental processes. This paper examines the performance of the premixed combustion models implemented in the commercial CFD package Fluent™, in order to validate the ability to model combustion in the context of a premixed gas turbine combustor. The predictions of the model are found to compare well with the experimental results available, demonstrating robustness and computational efficiency.
Skeletal Mechanisms for n-Heptane Combustion
Authors: Slavinskaya N. , Noll B.
Published: September 2008

In order to predict with CFD codes the ignition of kerosene including pollution formation it is necessary to develop a reduced mechanism, which can be incorporated into the code and applied without dramatically increasing the turn-around time. The practical global chemical schemes, which reflect the combustion properties for large a range of parameters in the combustion chamber, can be developed on the base of a skeletal mechanism. These mechanisms are established applying analytical reduction methods to detailed mechanisms. The first reduction of n-heptane detailed mechanism, which is a part of a reference model for practical fuels, was performed to model the heat release of kerosene for equivalent ratios of 0.5–2, initial temperatures of 700–1400 K and initial pressures of 6.5–55.0 bar. The final skeletal mechanism consists of 47 species and 378 irreversible reactions and predicts reasonably well the experimental data of ignition delay times for the given combustion parameters.
Rim Seal Ingestion Characteristics for Axial Gap Rim Seals in a Closely-Spaced Turbine Stage From a Numerical Simulation
Authors: Wang Cheng-Zhang , Johnson Bruce V. , Cloud David F. , Paolillo Roger E. , Vashist T. K. , Roy Ramendra P.
Published: September 2008

Turbine rim seal ingestion in gas turbines is influenced by many geometric and flow parameters. For turbine stages where the vanes and blades are closely spaced, the time-dependent pressure and flow fields near the seal strongly influence the rim seal ingestion. Numerical simulations of a close-spaced configuration, similar to that used in previous experiments, were made to determine the complex 3-D, time-dependent flow and ingestion characteristics of an axial gap rim seal. The calculated pressure fields were in general agreement with previously published experimental data. The radial velocities inward and outward in the axial gap seal were appreciable fractions of the hub tangential velocity and varied with position across the airfoil pitch and the axial location in the seal. The tangential velocities in the gap varied with flow direction, generally greater than hub velocity for flow ingress and less than hub velocity for flow ingress and less than hub velocity for flow egress. Velocity jets upstream of the blade leading edge penetrated into the disk cavity approximately 10 times the seal width. The ingestion velocities for this configuration were dominated by the blade bow wave pressure field. One conclusion of the authors is that the blade pressure field can be as or more significant than the vane trailing pressure field in influencing rim seal ingestion.
Heat Transfer Measurements in a Rotating Equilateral Triangular Channel With Various Rib Arrangements
Authors: Lee Dong Hyun , Rhee Dong-Ho , Cho Hyung Hee , Moon Hee-Koo
Published: September 2008

The present research investigates the heat transfer characteristics in an equilateral triangular channel to simulate the leading edge cooling passage of a gas turbine blade. The experiments are conducted for the stationary and rotating ribbed channel with three different attack angles (45°, 90° and 135°). Square ribs are installed in a staggered manner on the pressure and suction side surfaces of the channel. The rib height to channel hydraulic diameter ratio (e/Dh) is 0.079 and the rib-to-rib pitch (p) is 8 times of the rib height. To measure regional-averaged heat transfer coefficients in the channel, two rows of copper blocks with heaters are installed on each surface. The rotation number ranges from 0.0 to 0.1 for the fixed Reynolds number of 10,000. Inlet coolant-to-surface density ratio is about 0.2. For the channel with 90° ribs, the heat transfer rates of all regions have similar values for stationary case. However, for the rotating channel, heat transfer coefficients on the pressure side surface are significantly increased while the suction side surface has quite low heat transfer coefficients due to a single rotating secondary flow induced by Coriolis force. For the channel with angled rib arrangements, a pair of counter-rotating vortices is induced by the angled rib arrangements. High heat transfer coefficients are obtained on the regions near the inner wall for 45° angled ribbed channel and near the leading edge for the 135° angled ribbed channel. The heat transfer coefficients in rotating channel with angled ribs are almost the same as those of stationary case for the tested conditions because the secondary flow dominates the heat transfer. The channel with angled ribs consistently yields better thermal performance than the transverse ribbed channel for the test conditions of the present study.
Design of a Lean Premixed Prevaporized Can Combustor
Authors: Charest M. R. J. , Gauthier J. E. D. , Huang X.
Published: September 2008

Increasingly, more stringent emissions regulations have necessitated new gas turbine combustor designs with low pollutant emissions. Radically different modern designs have been developed to meet these requirements while maintaining high combustion efficiencies and good flame stability. While several published methodologies for conventional combustor design exist, none exist for modern ones. This paper describes the development of a new preliminary design algorithm for a modern lean premixed prevaporized (LPP) combustor. It also introduces a new LPP combustor concept. The approach used is multi-disciplinary in nature, applying empirical and semi-empirical models in the algorithm to capture complex processes such as droplet evaporation, chemical reaction, jet mixing, and heat transfer. The resulting set of procedures allows a designer to quickly define the detailed geometry of the combustor and provides an assessment of its performance. The preliminary design procedures were verified using the advanced numerical techniques of computational fluid dynamics (CFD). Reasonable agreement between predictions from the preliminary design and numerical analysis was achieved which indicated that the design procedures have been developed successfully.
A Probabilistic Risk-Based Approach to Assess NASA Aeronautics Technologies
Authors: Tong Michael T.
Published: September 2008

NASA’s aeronautics research program invests in air-transportation technologies to protect the environment, makes air travel more accessible and affordable for Americans, enables exploration through new aerospace missions, and augments national security. The program will address critical public needs related to reduction of aircraft noise and emissions, and enable new science missions. In this paper, a probabilistic risk-based approach is presented to provide guidance for developing a robust technology portfolio, and to prioritize the most promising technologies required to achieve aeronautics program goals. An assessment of subsonic aircraft emission-reduction technologies is performed to demonstrate how the approach can be used to guide technology investment in the context of limited NASA funding for aeronautics technology research.
Thermal Analysis and Durability Design Strategies for Gas Turbine Airfoils
Authors: Cunha F. J. , Abdel-Messeh W. , Chyu M. K.
Published: September 2008

Aircraft propulsion engines, land-based power generation, and industrial machines have, as a primary component, the turbine as means to produce thrust or generate power. In the turbine section of the engine, airfoil components are subjected to extremely complex and damaging environments. The combination of high gas temperatures and pressures, strong gradients, abrupt geometry changes, viscous forces, rotational forces, and unsteady turbine vane/blade interactions, all combine to offer a formidable challenge in terms of turbine durability. Nevertheless, the ultimate goal is to maintain or even improve the highest level of turbine performance and simultaneously reduce the amount of cooling flow needed to achieve this end. As such, coolant flow is a penalty to the cycle and thermal efficiency. Cooling strategies are developed and presented to determine ways for coolant flow management. The main variables include film cooling configurations, and convective efficiency schemes to balance turbine airfoil thermal loads for target overall cooling effectiveness. The desired targets are determined by the turbine airfoil durability requirements of oxidation and fatigue on a local scale and for creep on the bulk scale. Emphasis is provided to the general modes of cooling including film cooling, impingement cooling, and convective cooling for different parts of the airfoil such as leading edge, mid-body, trailing edge, tip and endwalls. Convective cooling is presented in terms of fundamental cooling enhancements, such as turbulating trip strips and pedestals. Recent literature dealing with these topics is listed.
Numerical Study of Instability Mechanisms Leading to Transition in Separation Bubbles
Authors: McAuliffe B. R. , Yaras M. I.
Published: September 2008

In this paper, transition in a separation bubble is examined through numerical simulation. The flow Reynolds number and streamwise pressure distribution are typical of the conditions encountered on the suction side of low-pressure turbine blades of gas-turbine engines. The spatial and temporal resolutions utilized in the present computations correspond to a coarse direct numerical simulation, wherein the majority of turbulence scales, including the inertial subrange, are adequately resolved. The accuracy of the simulation results is demonstrated through favorable comparisons with experimental data corresponding to the same flow conditions. The results of the simulation show linear Tollmien-Schlichting (T-S) instability growth downstream of the point of separation, leading to the roll-up of spanwise vorticity into disctete vortical structures, characteristic of Kelvin-Helmholtz (K-H) instability growth. The extent of cross-stream momentum exchange associated with packets of amplified T-S waves is examined, along with details of the time-periodic breakdown into turbulence occurring upon the development of the K-H instability. Reynolds-averaged properties of the separation bubble are presented, and provide evidence of the strong three-dimensional nature of the reattachment process.
Experimental and Theoretical Studies on Air Humidification by a Water Spray for Humid Air Turbine Cycle
Authors: Xu Zhen , Xiao Yunhan , Wang Yue
Published: September 2008

Humidification of compressed air is important for humid air turbine cycle. Earlier studies paid more attention to packed bed towers. However, a spray tower has inherent advantages such as less pressure loss and low cost. In this study, a pressurized model spray tower was established for the experiments. A specially designed air diffuser was installed to achieve uniform air velocity profiles over the cross section and a mist eliminator was used to trap the water droplets in the outlet air. Performance of the tower was tested at different pressures and water/air ratios. Pressure loss was measured and analyzed at different air velocities. A comprehensive analysis of the humidification process in the spray tower was carried out. A mathematical model considering droplet motion and conservation of heat and mass was developed to predict heat and mass transfer in the water droplet-air two-phase flow. Local heat and mass transfer coefficients over height of the tower were calculated. It has been shown that the parameters of outlet air and water can be calculated within a maximal error of 7.3% compared with the experiment results. Droplet size is a main parameter that affects operating performance of the spray tower. It has also been indicated that pressure loss in the spray tower is low and this will benefit its application in HAT.
Fully Automated Model Based Performance Analysis Procedure for Online and Offline Applications
Authors: Bauer Michael , Staudacher Stephan
Published: September 2008

The development of modern gas turbines is accompanied by an extensive prototype testing. To evaluate performance, the engines are fitted with a substantial number of sensors measuring pressures, temperatures, shaft speeds etc. The test data is analyzed by procedures calculating data that is not directly measured, e. g. component efficiencies and turbine temperatures. Engine manufacturers usually apply such procedures for a detailed analysis after the test (offline) as well as to ensure a safe and efficient engine operation during the test (online). Especially for the latter application, a fast and reliable assessment of the performance of the engine and its components as well as a fast and reliable detection of measurement faults is required. The paper describes a fully automated performance analysis procedure for offline as well as for online applications. Basis of the procedure is a full thermodynamic model representing the expected behavior of the engine to be tested. By such a model-based analysis procedure a comparison between test data and the expected engine behavior is performed. The way the comparison is done allows detecting and isolating measurement faults and component malfunctions. In case of a detected measurement fault, the measurement will be excluded automatically from the analysis. At MTU Aero Engines GmbH the procedure is regularly applied for online and offline test data analysis of different engine types. Compared to the procedures used so far, a lot of measurement faults can be detected quickly and reliably.
Application of Inlet Fogging for Power Augmentation of Mechanical Drive Turbines in the Oil and Gas Sector
Authors: Al-Amiri Abdalla M. , Zamzam Montaser M. , Chaker Mustapha A. , Meher-Homji Cyrus B.
Published: September 2008

The use of inlet fogging systems to boost the power for gas turbine engines is well known and extensively applied in the power generation field. In this paper the application of inlet fogging of gas turbine engines utilized in the oil and gas sector for mechanical drive applications is covered. Extracting oil from a well is often limited by the rate of gas extraction, and consequently by the gas turbine power and efficiency. In hot and dry air climates, such as desert areas of the gulf countries, gas turbine engine power output is dramatically reduced because of the reduction in gas turbine air mass flow. This effect is even more predominant with aeroderivative units that are commonly used in this sector. Cooling the air to the wet bulb temperature, will increase the density of the air, increase the air mass flow, and boost the power and efficiency. Consequently the amount of extracted gas, and therefore oil, will be substantially increased. With such a cooling potential, and the current trend in oil prices, inlet fogging can have a very rapid payback. In this paper, the behavior of gas turbines with and without fog injection will be analyzed in detail based on actual field data. Critical parameters such as the power turbine inlet temperature, exhaust temperatures, compressor discharge pressure, the gas generator and power turbine speeds, as increasing stages of fogging are applied are covered. Furthermore, specific issues relating to the design and control of fogging as applied to aeroderivative engines will be discussed.