bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Thermo-Acoustic Properties of Combustors and Afterburners
Authors: Jourdain Guillaume , Eriksson Lars-Erik
Published: January 2011

Predicting thermo-acoustic instabilities in combustion chambers remains an important issue. These instabilities mainly contain hydrodynamic and acoustic waves and can lead to severe structural damage if the energy feedback due to combustion builds up high amplitudes. In order to predict their behavior, linearized flow solvers have been developed in combination with an Arnoldi extraction method to compute several of the least damped eigenmodes of combustor flows. This technique has been validated against an atmospheric combustor test rig, named Validation Rig I, in which both low frequency buzz and high frequency screech modes could be induced. Both types of modes have also been found computationally, by matching frequencies and modes shapes. A post-processing mode stability analysis procedure has also been developed with which any computed eigenmode may be analyzed with respect to the Rayleigh criterion. The results of the mode stability analysis are consistent with the corresponding unsteady RANS simulations, but not with the experimental data. Understanding the modes coupled with combustion can provide useful knowledge regarding the the possibility to suppress them.
Engine Distress Detection in Gas Turbines With Electrostatic Sensors
Authors: Wilcox Melissa , Ransom David , Henry Meron , Platt John
Published: January 2011

Failures in gas turbines such as fretting at combustor assembly interfaces, blade rub, Thermal Barrier Coating (TBC) spalling, minor amounts of domestic or foreign object damage can be detected by mechanical vibration or gas turbine performance degradation, but it is usually too late for damage control by the time the failure is significant enough to be detected with these methods. Electrostatic charge sensors present a potential method for identifying the failure modes at an earlier stage before significant damage has occurred. In a gas turbine, there are potentially two sources of electrostatic charge in the exhaust gas flow stream: ionized plasma that is a natural byproduct of high temperature combustion, and any form of debris that has originated either in the compressor, combustor, or turbine sections of the gas turbine engine as a result of vibration or fatigue. For this reason, the electrostatic charge monitor becomes a very useful device for monitoring both combustion performance problems as well as potential damage related to debris in the exhaust stream. Electrostatic sensing technology has been proven to work in detecting ingested debris and engine debris on aerospace jet engines. However, the use of the sensors in industrial applications has shown that much research is still required especially in the areas of sensor placement and failure identification. This paper discusses results from testing conducted to identify the optimal placement location for the electrostatic charge sensors in a gas turbine exhaust stream. The results are presented for various sensor locations on small (112 kW) and medium (1.185 MW) frame gas turbines to evaluate distance, velocity, radial location, and gas turbine geometry effects. These tests are completed with the gas turbine ingesting varying amounts of TBC upstream of the compressor and administering power level changes to the gas turbine. The results of this experimental program demonstrate a clear sensitivity to sensor placement along the exhaust duct of a gas turbine as well as the radial location. There are variations in the particle flow pathlines in the exhaust duct at different gas turbine operating conditions. These variations influence the sensors response. Best results are obtained when the sensors are placed at the location with the fastest and hottest exhaust gas. Multiple sensors may be required to obtain comprehensive coverage for practical event detection.
Thermoeconomic Analysis of Micro Gas Turbine Design in the Range 25–500 kWe
Authors: Galanti Leandro , Massardo Aristide F.
Published: January 2011

The main aim of this paper is the thermoeconomic analysis of micro gas turbines in the range 25–500 kWe. This thermoeconomic analysis is based on the Thermoeconomic Functional Analysis (TFA) approach developed by the Authors over the last twenty years and is strongly related to the need for minimizing of the specific capital cost which is still considered high, and for optimizing MGT size to match customers’ needs. The investigation has been carried out using WTEMP code (Web-based ThermoEconomic Modular Program), developed by the Thermochemical Power Group of the University of Genoa [1][2][3]. The thermoeconomic analysis was performed on the basis of the thermodynamic, geometric and capital cost parameters of the main MGT devices (i.e. recuperator effectiveness, turbine inlet temperature, compressor pressure ratio, etc.) and on the economic scenario (fuel costs, cost of electricity, etc.). The subjects of the analysis were the existing Regenerative MGT (R-MGT) cycles [4][5] and new Inter-cooled Regenerative (ICR-MGT) cycles; for the sake of simplicity in this study, the economic value of heat in the case with CHP configuration was not considered.
Aeromechanic Validation of a New Steam Turbine LP Section: Test Major Outcomes
Authors: Piraccini Francesco , Biondi Roberto , Cosi Lorenzo
Published: January 2011

To enhance the Steam Turbine product line rotating speed and efficiency, GE Company has developed a new generation of high rotating speed Steam Turbine Low Pressure (LP) Sections named HS family (see also Cosi at al., [1.]). The master component of the family, and its smallest size, is the 4-stage LP section HS8, capable of variable speed operation up to 11250 rpm. The aeromechanical validation of HS8 was carried out in two steps: a full-scale rotating test in a vacuum chamber (so called wheel Box Test, WBT) and a full-size test vehicle campaign in steam (Low Pressure Development Turbine, LPDT). During both tests the 4-stage rotors were equipped with a reliable system of strain gages and thermocouples. Aim of the present paper is to present an overview of the experimental results and post-processed data from both tests. Measured blades modes frequencies, responses and quality factors from both WBT and LPDT are described and compared, and the behavior of these parameters at different mass-flows and backpressures is explored. Then, interesting results from the comparison of damping (or Q factors), in WBT and LPDT test are presented. Finally, a methodology for nodal diameter configuration identification is described. To the best of authors’ knowledge the present paper is the deepest investigation about damping in WBT and prototypical test for steam turbine last stage blades.
Describing Function Analysis of Limit Cycles in a Multiple Flame Combustor
Authors: Boudy Fre´de´ric , Durox Daniel , Schuller Thierry , Jomaas Grunde , Candel Se´bastien
Published: January 2011

A recently developed nonlinear Flame Describing Function (FDF) is used to analyze combustion instabilities in a system where the feeding manifold has a variable size and where the flame is confined by quartz tubes of variable length. Self-sustained combustion oscillations are observed when the geometry is changed. Regimes of oscillation are characterized at the limit cycle and also during the onset of oscillations. Theoretical predictions of the oscillation frequencies and levels are obtained using the FDF. This generalizes the concept of flame transfer function by including a dependence on the frequency and on the level of oscillation. Predictions are compared with experimental results for two different lengths of the confinement tube. These results are in turn used to predict most of the experimentally observed phenomena and in particular the correct oscillation levels and frequencies at limit cycles.
Flash Atomization: A New Concept to Control Combustion Instability in Water Injected Gas Turbines
Authors: Iyengar Vishwas , Simmons Harold , Ransom David , Holzschuh Thomas
Published: January 2011

The objective of this work is to develop and explore methods to reduce combustor rumble in an industrial gas turbine in co-generation service that is operated with water injection reducing NOX emissions. Attempts to use water injection as a means to reduce NOX emissions in gas turbines have been largely unsuccessful because of increased combustion instability levels experienced. The increase in pulsation causes chronic fretting, wear, and fatigue that damages combustor components resulting in higher operation costs due to repair or replacement of parts. This combustion instability can be tied to the insufficient atomization of injected water; relatively large water droplets evaporate non-uniformly that lead to energy absorption in non-uniform chaotic pulses. This added pulsation is amplified by the combustion process and acoustic resonance. Effervescent atomization, where a gas bubbles are injected with the liquid, is beneficial in producing finely atomized droplets, because the gas bubbles burst as they exit the nozzles creating additional energy to disperse the liquid. A new concept for effervescent atomization dubbed “Flash Atomization” is presented where water is heated to just below its boiling point in the supply line so that some of it will flash to steam as it leaves the nozzle. An advantage of Flash Atomization is that available heat energy can be used rather than mechanical energy to compress injection gas for conventional effervescent atomization.
Simulations of Multi-Phase Particle Deposition on Endwall Film-Cooling
Authors: Lawson Seth A. , Thole Karen A.
Published: January 2011

Demand for clean energy has increased motivation to design gas turbines capable of burning alternative fuels such as coal derived synthesis gas (syngas). One challenge associated with burning coal derived syngas is that trace amounts of particulate matter in the fuel and air can deposit on turbine hardware reducing the effectiveness of film cooling. For the current study, a method was developed to dynamically simulate multi-phase particle deposition through injection of a low melting temperature wax. The method was developed so the effects of deposition on endwall film cooling could be quantified using a large scale vane cascade in a low speed wind tunnel. A microcrystalline wax was injected into the mainstream flow using atomizing spray nozzles to simulate both solid and molten particulate matter in a turbine gas path. Infrared thermography was used to quantify cooling effectiveness with and without deposition at various locations on a film cooled endwall. Measured results indicated reductions in adiabatic effectiveness by as much as 30% whereby the reduction was highly dependent upon the location of the film-cooling holes relative to the vane.
Impact of Fan Gap Flow to the Centrifugal Impeller Aerodynamics
Authors: Lee Yu-Tai
Published: January 2011

The effect of a gap between an inlet duct and a rotating impeller in a centrifugal fan is often neglected in the impeller design calculations or design-related CFD analyses. This leads to an arbitrary determination of the gap size for the final fan configuration. Since the gap guides the volute flow back to the impeller flow field near the shroud high-curvature turning area, the low-momentum jet formed by the gap flow could prevent local flow from separation, reducing the local flow turning losses. However, this jet flow has enlarged flow separation in the blade passage producing shedding vorticity in the downstream passage flow. The passage-flow separation and the downstream volute flow, which is also affected by the passage-flow separation, have a higher impact on flow losses than the blade leading-edge separation. If the gap size is not selected carefully, the combined effect of the passage-flow separation and downstream volute-flow losses reduces the fan’s overall performance between 2% points and 5% points as demonstrated in the current study. In this paper, local impeller velocity distributions obtained from both design-CFD and analysis-CFD calculations are compared along the shroud from the gap to the blade trailing edge. The overall impeller flow fields with and without the gap and volute effects are also compared and discussed based on the CFD solutions. Finally, an example of controlling the gap effect is shown.
Reduction of Pressure Forces in Turbine Labyrinth Seals
Authors: Kosowski Krzysztof , Ste˛pien´ Robert
Published: January 2011

The paper describes a chamber seal reducing the aerodynamic forces created in shroud seals. This kind of turbine seal was patented and tested. The investigations into the pressure field in the shroud gap were performed by means of CFD Fluent Code and compared with the results measured on a single-stage air model turbine of the impulse type. Special attention was paid to the pressure field in the rotor blade shroud clearance in the situation when rotor-stator eccentricity led to asymmetrical flows in blade passages and shroud gaps. The investigations were carried out for different types of shrouds, various shapes and dimensions of the chambers, and for different turbine working conditions. The calculations were verified by the experimental research. The performed investigations proved that the chamber seal could remarkably reduce aerodynamic forces generated in turbine clearances due to rotor-stator eccentricity. The results proved that: - the proposed chamber seal can reduce pressure forces acting on the blade shroud by about 30%–60%, depending on the type of the shroud; - the chamber seals are specially effective in the case of relatively small radial clearances; - the proposed method may be applied in active control of aerodynamic forces generated in turbine shroud seals; - the presented seal modification can be easily introduced to turbines in operation and to the newly-designed ones. It must be emphasized that according to the calculations and experiments the application of the chamber to typical labyrinth shroud seals does not affect the flows in the turbine blade channels.
Derivation of Temperature-Estimation Equation Based on Microstructural Changes in Coatings of In-Service Blades of Gas Turbines
Authors: Okada Mitsutoshi , Hisamatsu Tohru , Fujioka Terutaka
Published: January 2011

A CoNiCrAlY-coated blade of an in-service gas turbine is analyzed, and a diffusion layer is formed along the boundary between the coating and the substrate due to the interdiffusion in the middle and tip of the blade. Such a layer is not observed in the vicinity of the blade root because of a comparatively low temperature during the operation. Coated specimens are prepared from the portions of the blade devoid of the diffusion layers, and the specimens are exposed to a high temperature in air. On the basis of the increase in the diffusion layer thickness, an equation for estimating the temperature of the blade is derived. Analysis of another in-service blade with a thermal barrier coating (TBC) is carried out. The aluminum-content decreases below the bond coat surface due to Al diffusion caused by the Al-oxide formation. This results in the formation of an Al-decreased layer (ADL) along the leading and trailing edges. The ADL is not observed at the center of the blade chord. The specimens are extracted from the portions of the blade that are devoid of ADL, and they are subjected to a high temperature in air. On the basis of the increase in the ADL thickness, a temperature-estimation equation is derived.
Numerical Investigation of Heat Transfer and Flow Characteristics in a Steam-Cooled Square Ribbed Duct
Authors: Shui Linqi , Gao Jianmin , Xu Liang , Wang Xinjun
Published: January 2011

In order to increase entry gas temperature and improve the efficiency of gas turbine, steam is used as a coolant instead of air. Much research has been carried out on the closed circuit steam cooling of vanes substituted with film-cooling using compressor air in recent years. Furthermore, by studying the steam flow and heat transfer characteristics in rib ducts, this investigation focuses on establishing the basis of steam cooling technology application in complex flow field of internally-cooled turbine vane. In this paper, a report and assessment of RSM method based on SSG turbulence model is performed with commercial computational fluid dynamics software ANSYS CFX. The numerical results of heat transfer coefficient and friction factors in square channels with 90 degree rib turbulators for Reynolds numbers of 10 000, 30 000 and 60 000 are compared with the experimental data from Han’s. It is found that the obtained heat transfer coefficient distributions and friction factors match well with SSG turbulence model. In addition, the heat transfer distribution and pressure drop of steam-cooled ducts are predicted under the same work conditions by using dry real gas model. The Reynolds number could be correlated with the Nusselt number. The impact of steam physical properties on heat transfer performance are researched detailedly by respectively changing the steam superheat and entry pressure. The results indicate that the RSM method with a suitable turbulence model is valuable for the air-cooled and steam-cooled duct with the acceptable engineering accuracy (less than 20%). Comparing the cooling efficiency between steam and air under the same operation condition, the advantage of using cooling steam is evident than using cooling air. Furthermore, the efficiency of the whole gas turbine system will be greatly improved through using the closed loop steam cooling system. Changing the steam superheat and entry pressure, it has little effect on the steam flow and heat transfer characteristics. Increasing the steam overheat would raise the friction factor. Contrarily, enhancing the entry pressure would decrease the friction factor.
Identification of Acoustic Dipole Sources in a Propylene Centrifugal Compressor Stage
Authors: Tang Hongtao , Qi Datong , Lu Fuan
Published: January 2011

Three-dimensional unsteady turbulent flow in a propylene centrifugal compressor stage was numerically studied in order to identify primary acoustic dipole sources. The investigated model is the last stage of a propylene compressor used in the megaton ethylene production. The leakage clearance between the impeller and diffuser was simplified and modeled to capture the rotor-stator interaction accurately. A series of sixth-order polynomials, the use of which significantly sped up the computation compared with directly using Helmholtz real gas equation as the gas model, were fitted with a relative error less than 0.03% based on the thermodynamic data of propylene obtained by the Helmholtz equation. According to Lowson’s equation, the root mean square of the partial derivative of static pressure with respect to time during two revolutions of the impeller was taken as the parameter to measure dipole source intensity. The spatial distribution and frequency characteristics of the dipole sources were also investigated intensively. As a result of the present study, the primary dipole source is located at the junction of the impeller and diffuser, and its intensity is dominated by the components at the impeller blade passing frequency (BPF) and its higher harmonics, which are induced by the strong rotor-stator interaction. The spectrum analysis downstream of the impeller indicates that the higher harmonic components of dipole sources attenuate faster than the BPF component along the streamwise direction, and it is the BPF that dominates the noise characteristic in the volute casing of the studied model.
Particle-Image Velocimetry Measurements of Film Cooling in an Adverse Pressure Gradient Flow
Authors: Jessen Wilhelm , Konopka Martin , Schro¨der Wolfgang
Published: January 2011

The turbulent flow field of a film cooling flow is investigated using the particle-image velocimetry (PIV) technique. Cooling jets are injected from a multi-row hole configuration into a turbulent boundary layer flow of a flat plate in the presence of a zero and an adverse pressure gradient. The investigations focus on full-coverage film cooling. Therefore, the film cooling configuration consists of three staggered rows of holes with a lateral spacing of p/D = 3 and a streamwise row distance of l/D = 6. The inclined cooling holes feature a fan-shaped exit geometry with lateral and streamwise expansions. Jets of air and CO2 are injected separately at different blowing ratios into a boundary layer to examine the effects of the density ratio between coolant and mainstream on the mixing behavior and consequently, the cooling efficiency. For the zero pressure gradient case the measurement results indicate the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The mainstream velocity distributions evidence the growth of the boundary layer thickness at increasing row number. The interaction between the undisturbed boundary layer and first two rows leads to maximum values of turbulent kinetic energy. The presence of an adverse pressure gradient in the mainstream clearly intensifies the growth of the boundary layer thickness and increases the velocity fluctuations in the upper mixing zone. The measurements considering an increased density ratio show higher turbulence intensities in the shear zone between the jets and the main flow leading to a more pronounced mixing in this area. The results of the experimental measurements are used to validate numerical findings from a large-eddy simulation. This comparison shows a very good agreement for mean velocity distributions and velocity fluctuations.
Combustion Modeling of Partially Premixed Flames
Authors: Zimmermann Ilona , Pfitzner Michael
Published: January 2011

Accurate and properly validated turbulence-chemistry interaction models for RANS combustion computational fluid dynamics (CCFD) simulations are required in support of the development process of modern gas turbine combustors. Although standard models are available for fully premixed and purely non premixed turbulent combustion, models describing partially pre-mixed combustion are still under development. A new model for the simulation of turbulent partially premixed combustion is presented, which combines features of non premixed and fully pre-mixed combustion models and reduces to these respective standard models in the limiting cases. Transport equations for mixture fraction and its variance as well as one progress variable are solved. Fluctuations of mixture fraction are taken into account through a presumed beta PDF assumption. The laminar flame speed for the whole range of mixture fractions is evaluated using correlations for lean and rich extinction limits based on experimental results from the literature. The model is validated using hydrogen and methane jet flames.
Effect of Blade Geometry and Foreign Object Kinetic Energy on Blades Damage
Authors: Nikhamkin Mickhail S. , Voronov Leonid V. , Semenova Irina V.
Published: January 2011

One of the main reasons of engine failure is foreign object damage (FOD) of compressor blades. Engine manufactures are constantly searching for blade endurance increasing methods. The problem solution requires investigation in the field of the structural factor effects on the blade damageability. The paper describes numerical analysis method of the damage process. Based on “the typical damage case” concept, this method can simulate typical blade damages: dents, tears, notches. The numerical analysis is performed by the finite element method (FEM). Material behavior is described with an elastic-plastic strain rate dependent model. Blade damage numerical model is thoroughly verified by the results of special experiments. To implement the experimental modeling, actual blades were damaged, a special experimental setup based on a pneumatic gun being used. The foreign object kinematic parameters before and after the impact, a blade leading edge displacements and residual deformation fields registered in the experiment are used as verification criteria for the numerical model. The blade leading edge thickness and a foreign object energy effect on the blade damageability is investigated. The research showed there are some foreign object kinetic energy critical values at which the damage mechanism and type are changed.
Porosity and Thermal Cycling Behavior of Plasma Sprayed and EBPVD Thermal Barrier Coatings
Authors: Agu Ogad , Diwan Ravinder , Mensah Patrick F. , Silva Monica B. , Guo S. M.
Published: January 2011

Traditionally, thermal barrier coatings (TBCs) are used in gas turbine engines to create an insulation layer between the metallic components and the gases in the hot section. Atmospheric plasma spray (APS) is a common method used to produce TBCs. The goal of this study is to study the porosity and thermal cycling behavior of standard (STD) and vertically cracked (VC) thermal barrier coatings (TBCs) fabricated by Atmospheric Plasma Spray (APS) for two different thicknesses, 300 and 600 μm respectively. Electron Beam Physical Vapor Deposition (EBPVD) coatings with 300 micron thickness prepared under tumbled and non-tumbled conditions were studied. For this study, mercury porosimeter equipment (POREMASTER 33) by Quantachrome Instruments was used to measure porosity, and pore size distribution. Scanning Electron Microscopy (SEM) images were obtained for all the samples. The images showed clear microstructural difference between the APS and EBPVD coatings. All the coatings were thermal cycled to 1200°C and the conventional APS-STD (300μm) performed the best followed by APS-VC coatings and EBPVD coatings which performed similarly.
An Experimental Study on the Effects of Fischer-Tropsch (FT) Blends With Diesel #2 and JP5 on the Performance of a Rolls-Royce Model 250-C20B Gas Turbine Engine
Authors: Islin J. Alexander , Cerza Martin , Jenkins Peter E.
Published: January 2011

Fischer-Tropsch fuel is created using a catalyzed reaction in which a blend of carbon monoxide hydrogen gas (syngas) is converted into liquid hydrocarbons over a metal catalyst. The length of the carbon chain completely depends on the reaction parameters (mainly on temperature), empowering the manufacturer to produce different types of fuel. In this experiment, a fuel known as FT8 was created using this method. It is a synthetic form of JP8, a common jet fuel used extensively in the U.S. Navy as well as many commercial applications. This synthetic fuel, unlike conventional Diesel fuels, is colorless and lacks the impurities found in fossil fuels. Because of the lack of additives in the fuel required by the Rolls-Royce Model 250-C20B, the fuel was mixed in varying quantities up to 50% with Diesel #2 and JP5. Utilizing specific equipment, the Model 250-C20B’s exhaust gas composition, power output, and thermodynamic efficiency were measured. Temperatures and pressures were measured for each of the gas turbine’s five state points. Exhaust gas composition and output shaft torque and speed were also measured. The results of these tests were compared with baseline runs conducted with 100% conventional fuels used. It was determined that the blending of fuels did not affect performance, positively or negatively, to any great degree. Power output, fuel consumption, and exhaust gas composition were not significantly affected by the use of mixing the Fischer-Tropsch fuel with the conventional fuels used. However, it was determined that some blends did outperform the baseline tests. It did appear that the 20%–40% blend ratio does slightly increase the fuel’s performance in the engine in most areas.
Airport PM10 Emissions: Development of a First Order Approximation (FOA) Methodology for Aircraft and Airport Particulate Mass Emissions
Authors: Andrews Gordon E. , Andrews Ian D. , Dixon-Hardy Darren W. , Gibbs Bernard M. , Li Hu , Wright Stephen
Published: January 2011

The application the FOA-Leeds method for PM10 estimation at airports was undertaken using a small regional airport as an example. Some further justification of the FOA-Leeds method is also given using the EU PartEmis data together with some industrial gas turbine measurements of particulate mass. The ICAO LTO cycle is appropriate to large airport but not to smaller regional airport as the aircraft movement times are much shorter in smaller airports. Data is presented for observed taxi, take off, climb out and approach times and it is shown that taxi times are much shorter than in the ICAO LTO and take off times are shorter in modern aircraft. This data was applied to the annual operations of a regional airport and every plane using the airport was identified and their engines. The ICAO LTO cycle database was used to determine the EI in each mode and the SN, but the measured LTO times were used to determine the total mass emissions. These were compared with the ICAO LTO cycle times and the estimated PM10 mass emissions were significantly lower. The total aircraft movements for the summer period were analysed and the total PM10 mass emissions were estimated.
Identification of Rotordynamic Force Coefficients of a Metal Mesh Foil Bearing Using Impact Load Excitations
Authors: San Andre´s Luis , Chirathadam Thomas Abraham
Published: January 2011

Metal mesh foil bearings (MMFB) are an inexpensive compliant gas bearing type that aims to enable high speed, high temperature operation of small turbomachinery. A MMFB with an inner diameter of 28.00 mm and length of 28.05 mm is constructed with low cost and common materials. The bearing incorporates a copper mesh ring, 20% in compactness and offering large material damping, beneath a 0.127mm thick preformed top foil. Prior experimentation (published papers) provide the bearing structure force coefficients and the break away torque for bearing lift off. Presently, the MMFB replaces a compressor in a small turbocharger driven test rig. Impact load tests aid to identify the direct and cross-coupled rotor dynamic force coefficients of the floating MMFB while operating at a speed of 50 krpm. Tests conducted with and without shaft rotation show the MMFB direct stiffness is less than its structural (static) stiffness, ∼25% lower at an excitation frequency of 200 Hz. The thin air film acting in series with the metal mesh support, and separating the rotating shaft and the bearing inner surface while airborne, reduces the bearing stiffness. The equivalent viscous damping is nearly identical with and without shaft rotation. The identified loss factor, best representing the hysteretic type damping from the metal mesh, is high at ∼0.50 in the frequency range 0–200 Hz. This magnitude reveals large mechanical energy dissipation ability from the MMFB. The measurements also show appreciable cross directional motions from the unidirectional impact loads, thus generating appreciable cross coupled force coefficients. Rotor speed coast down measurements reveal pronounced subsynchronous whirl motion amplitudes locked at distinct frequencies. The MMFB stiffness hardening nonlinearity produces the rich frequency forced response. The synchronous as well as subsynchronous motions peak while the shaft traverses its critical speeds. The measurements establish reliable operation of the test MMFB while airborne.
Set Up of an Experimental Facility for the Investigation of Wet Compression on a Multistage Compressor
Authors: Bettocchi R. , Morini M. , Pinelli M. , Spina P. R. , Venturini M. , Torsello G.
Published: January 2011

At present, inlet fogging and wet compression are two of the most widely used approaches to enhance gas turbine performance, especially during hot seasons. However, potentially negative effects of these practices on long-term operational integrity of gas turbines should be evaluated carefully; in particular, wet compression may lead to the erosion of first compressor stages, due to the impact of water droplets within the flow at compressor intake. This issue is still controversial in technical literature, since only limited historical field operating data and information are available. Therefore, a test facility was specifically set up in the laboratories of the University of Ferrara, to evaluate the effects of wet compression on a small-size compressor. This paper presents the experimental facility developed for wet compression investigation and some preliminary results.
A Prediction Model for Corner Separation/Stall in Axial Compressors
Authors: Yu Xianjun , Liu Baojie
Published: January 2011

Endwall corner stall can cause significant aerodynamic blockage and losses production. Hence, pre-prediction of it during the preliminary processes of compressors is important. However, Lieblein’s diffusion factor often fails near the endwall region for the strong three-dimensionality flow effects. A new model for predicting endwall corner stall phenomenon in axial compressors was developed based on the methodology used by Lei et al. [1] (J. Turbomach. 2008, 031006). At first, the influencing factors for the flows of endwall corner separation/stall were analyzed by numerical simulations. The results showed that, besides the parameters determining the loading of a two-dimensional blade profile, blade aspect ratio was also a key factor. Then, by using both the theoretical and empirical methods, a modified diffusion parameter, which can be used as a criterion for axial compressor corner stall, was defined to consider the combined effects of three factors: the streamwise pressure gradient, the circumferential pressure gradient and the passage mass-flow-rate redistribution effect (controlled mainly by blade aspect ratio). Finally, the stall criterion was validated by experimental results of various test facilities with different blade geometries and experimental conditions. The results showed that the modified diffusion parameter can predict the corner separation/stall flows in a good agreement with the experimental results in axial compressors without blade three-dimensional designs.
Accelerated Deterioration by Saltwater Ingestion in Gas Turbine Intake Air Filters
Authors: Brekke Olaf , Bakken Lars E.
Published: January 2011

There is currently no international standard for evaluating and documenting the performance of the complete gas turbine intake air system in offshore applications. Several suppliers document the performance of their filters in accordance with applicable Heating, Ventilation, and Air Conditioning (HVAC) air-filtration standards for general ventilation. These standards fail to address the offshore-specific challenges related to salt removal and moist and wet operation and cannot be used to accurately predict operational performance or life. It is therefore desirable to develop suitable test methods and standards that can be used to better predict operational performance and life before filters and complete inlet air systems are put into operation offshore. An experimental test rig has been built in the laboratory at the Norwegian University of Science and Technology (NTNU) in order to increase understanding of the fundamentals related to gas turbine inlet air filtration. This paper presents the results from an experimental test program where the test rig was used to evaluate the effect of accelerated deterioration of high-efficiency filter elements for gas turbine inlet air filtration. High-efficiency filter elements from different suppliers were deteriorated by ingesting a saltwater solution. The performance of the filters exposed to accelerated deterioration was evaluated for different levels of contamination and compared to the performance of filter elements that have accumulated comparable amounts of contaminants in offshore operation.
Non-Equilibrium Condensation Effects on the Flow Field and the Performance of a Low Pressure Steam Turbine
Authors: Starzmann Jo¨rg , Casey Michael , Sieverding Frank
Published: January 2011

The influence of non-equilibrium condensation on the flow field and performance of a three stage low pressure model steam turbine is examined using modern three dimensional CFD techniques. An equilibrium steam model and a non-equilibrium steam model, which accounts for both subcooling and condensation effects, are used, and have been verified by comparison with test data in an earlier publication [1]. The differences in the calculated flow field and turbine performance with these models show that the latent heat released during condensation influences both the thermodynamic and the aerodynamic performance of the turbine, leading to a change in inlet flow angles of about 5°. The calculated three dimensional flowfield is used to investigate the magnitude and distribution of the additional thermodynamic wetness loss arising from steam condensation under non-equilibrium flow conditions. Three simple methods are described to calculate this, and all show that this amounts to around 6.5% of the total losses at the design condition. At other load conditions the wetness losses change in magnitude and axial distribution in the turbine.
Performance Evaluation of the CVC With Open Rotor Engine Technologies as Propulsion Systems for Subsonic Aircraft
Authors: Khani Nqobile , Doulgeris Georgios , Singh Riti
Published: January 2011

This paper evaluates the constant volume combustion (CVC), the open rotor (OR) and constant volume combustion with open rotor (CVCOR) engine technologies as propulsion systems in subsonic aircraft. Available simulation codes are used to compare different engine technologies assuming the same level of technology investment, to identify the cycle optimum, to calculate the thrust specific fuel consumption (SFC) and to determine flight mission fuel burn for a short range and a long range aircraft. Compared to turbofans of current and of equal technology, it is concluded the novel cycles give better uninstalled SFC performance and better fuel burn performance installed for short and long range missions. Within the constraints of this study, it is concluded the novel cycles offer better thermal efficiencies, increasingly higher overall pressure ratios and yield a lower fuel burn compared to turbofans of current and of equal technology. The novel cycles would be viable as future propulsion systems if the primary design target is fuel consumption. The CVCOR and OR would be comparable based on SFC alone. However installation losses make the CVCOR a better prospect considering the effects of OPR and BPR. Against the impact of increasing fuel costs, it would be beneficial to use the novel cycles.
Steady/Unsteady Reynolds Averaged Navier-Stokes and Large Eddy Simulations of a Turbine Blade at High Subsonic Outlet Mach Number
Authors: Le´onard Thomas , Duchaine Florent , Gourdain Nicolas , Gicquel Laurent Y. M.
Published: January 2011

Reynolds Averaged Navier-Stokes (RANS), Unsteady RANS (URANS) and Large Eddy Simulation (LES) numerical approaches are clear candidates for the understanding of turbine blade flows. For such blades, the flow unsteady nature appears critical in certain situations and URANS or LES should provide more physical understanding as illustrated here for a laboratory high outlet subsonic Mach blade specifically designed to ease numerical validation. Although RANS offers good estimates of the mean isentropic Mach number and boundary layer thickness, LES and URANS are the only approaches that reproduce the trailing edge flow. URANS predicts the mean trailing edge wake but only LES offers a detailed view of the flow. Indeed LES’s identify flow phenomena in agreement with the experiment, with sound waves emitted from the trailing edge separation point that propagate upstream and interact with the lower blade suction side.
Modernization of Existing US Navy Steam Turbines: Efficiency, Reliability and Maintainability
Authors: Golinkin Samuel L. , Lipski Michael J. , Conlow Frank J.
Published: January 2011

Earlier steam plant design requirements for the US Navy steam turbines were focused on reliability and maintainability. Simplicity of design implied easy operation, maintenance and service. Efficiency was not a top priority. Now, in an atmosphere of operating budget cuts and skyrocketing fuel costs along with environmental responsibilities, efficiency improvements are expected, and in some cases demanded on main propulsion units. Additional load due to modern electronic combat systems places extra demand on SSTG sets. Modernization with improved efficiency, reliability and maintainability, while retaining design simplicity is the optimal solution. Meanwhile during the last 50 years, the turbomachinery industry has developed numerous innovative improvements through extensive R&D efforts, advanced computerized simulation of aerodynamics and flow field analysis along with finite element modeling, new manufacturing methods and improved metallurgy and surface treatments. These advances allow efficiency improvements without adding complexity to the design. Modern airfoil design, the optimized transition from partial-arc to full-arc steam admission, tangential leaning vanes, advanced seal designs, streamlined steam path configuration and improved moisture removal are major areas worthy of consideration. Mechanical reliability can be improved with Taumel (orbital) peened tenons for blade packets or integral shrouds which give a 360 degree connection to all of the blades in a row. Electron beam welded diaphragms with EDM cut horizontal joints help to minimize thermal distortions and flow irregularities, particularly at the split lines. Improved welding procedures for casing, diaphragm and rotor repairs can result in shorter repair cycles and lower costs to further promote extension of the turbine’s life cycle. Maintainability can be improved with advanced materials that no longer require regular service, such as anti-lube (greaseless) bushings and replaceable components that don’t require in place machining. Combinations of the above improvements have been used successfully within the industry in upgrading hundreds of turbines, compressors and pumps in various applications including power generation, petrochemical, oil and gas, commercial marine, and other fields. Typical examples of efficiency improvement are 8%–14% over current operating parameters. [1, 2, 3, 4, 5] This paper presents various proven advanced turbine components used to upgrade existing steam turbines, which can be successfully used in US Navy applications as well.
Aerodynamic Comparison and Validation of RANS, URANS and SAS Simulations of Flat Plate Film-Cooling
Authors: Voigt Stefan , Noll Berthold , Aigner Manfred
Published: January 2011

The present paper deals with the detailed numerical simulation of film cooling including conjugate heat transfer. Five different turbulence models are used to simulate a film cooling configuration. The models include three steady and two unsteady models. The steady RANS models are the Shear stress transport (SST) model of Menter, the Reynolds stress model of Speziale, Sarkar and Gatski and a k-ε explicit algebraic Reynolds stress model. The unsteady models are a URANS formulation of the SST model and a scale-adaptive simulation (SAS). The solver used in this study is the commercial code ANSYS CFX 11.0. The results are compared to available experimental data. These data include velocity and turbulence intensity fields in several planes. It is shown that the steady RANS approach has difficulties with predicting the flow field due to the high 3-dimensional unsteadiness. The URANS and SAS simulations on the other hand show good agreement with the experimental data. The deviation from the experimental data in velocity values in the steady cases is about 20% whereas the error in the unsteady cases is below 10%.
A CFD Approach to Fluid Dynamic Optimum Design of Steam Turbine Stages With Stator and Rotor Blades
Authors: Yuan Xin , Tanuma Tadashi , Zhu Xiaofeng , Lin Zhirong , Nomura Daisuke
Published: January 2011

An advanced aerodynamic design optimization system for steam turbine stages considering rotor blade tip leakage and blade end-wall non-axis-symmetric contouring has been developed. Using this system, fluid dynamic optimizations were carried out for a steam turbine stage with stator and rotor blades. The system includes parametric modeling of blade and end-wall contouring, evaluation system with in-house or package CFD software and optimization strategy module. The designs of rotor blade and hub end-wall surface in a typical large-scale high-pressure steam turbine stage were optimized in order to know this design optimization impact on enhancing the stage efficiency. Results show that: from the current well designed high pressure steam turbine stage, the demonstrated efficiency enhancement with the present optimum design is around 0.2% under consideration of rotor tip leakage. Design cycle could be greatly shortened by parallel optimization algorithm and cluster PC, and especially four days could be sufficient for an optimization with one thousand iterations on 20 CPUs of 2.0G cluster PC.
Reverse Engineering Gas Turbine Emission Performance: Applied to an Aircraft Auxiliary Power Unit
Authors: Leong Christopher C. , Rye Lucas J. , Blakey Simon , Wilson Christopher W.
Published: January 2011

Environmental and future supply pressures are expected to drive aviation towards alternative fuel sources. However little is available in the literature on aircraft landing-takeoff (LTO) cycle gaseous emissions resulting from the combustion of alternative fuels. Considering the different engine configurations existing in today’s commercial aviation fleet, emission experiments of alternative fuels on all engine types are almost impossible. Modelling may provide a solution but the availability of combustor data (geometry and air split details) in the public domain is limited. A reverse engineering technique is developed to recover the air splits and combustion process in gas turbine engine by a CRN and forward predicting the emissions from the engine exhaust. The model was developed and optimised with a Genetic Algorithm against the Jet A-1 experimental emission data obtained from an APU. Results from the optimised CRN emission predictions closely matched the Jet A-1 gaseous emission data. The modelling technique also successfully demonstrated an ability to predict APU gaseous emission data obtained for Synthetic Paraffinic Kerosene (SPK) (neat and 50–50 blended with Jet A-1) and biodiesel. This technique is expected to enhance the emission databank of aircraft and airside emissions.
The Influence of the Total Pressure Profile on the Performance of Axial Gas Turbine Diffusers
Authors: Hirschmann A. , Volkmer S. , Schatz M. , Finzel C. , Casey M. , Montgomery M.
Published: January 2011

Large industrial gas turbines for combined heat and power generation normally have axial diffusers leading to the heat recovery steam generator. The diffusers operate with high inlet axial Mach number (0.6) and with a non-uniform inlet total pressure profile from the turbine. Tests have been carried out on a generic highly loaded axial diffuser in a scaled axial diffuser test rig, with different inlet total pressure profiles including those that might be met in practice. The results show that the inlet total pressure profile has a strong effect on the position of flow separation, whereby a hub-strong profile tends to separate at the casing and the tip-strong profile on the hub. Steady CFD simulations using the SST turbulence model have been carried out based on extensive studies of the best way to model the inlet boundary conditions. These simulations provide good agreement with the prediction of separation in the diffuser but the separated regions often persist too long so that, in this highly loaded case with flow separation, the calculated diffuser pressure recovery can be in error by up to 30%.