bluuebunny/crossref_metadata_2025 huggingface dataset:
On Preliminary Experimental Experiences With Crude Oil Combustion in Strong Swirl Flow
Authors: Dobski Tomasz , Nowak Dariusz , Chmielewski Jan , Jankowski Radoslaw , Magni Fulvio
Published: January 2011

The paper presents preliminary experimental analyses of combustion processes for crude oil. The research is started from investigation of combustion of gas in a strong swirl flow as is intended to be an introductory step in studying the mechanism of stability and emission of pollutants in combustion of crude oil occurring in gas turbines. The areas of recirculation and pollutant emission in a strong swirl flow have been studied for the following three cases: - isothermal flow without combustion; - combustion of gas mixture with CH4 and N2 differently composed; - combustion of crude oil. All experiments are performed in the atmospheric test rig of a top-mounted combustor, briefly described in the paper. The velocity field in the combustion chamber is measured by laser doppler anemometry. The measured profiles of temperature and molar fraction of NOx, CO, CO2, O2 are discussed for natural gas and crude oil. Depending on the degree of the swirl of the flow and on the temperature of entering air, the distribution of molar fraction of most important chemical species has been established. This allows for better understanding the process of combustion in a strong swirl flow. The established characteristics of the flame blow-out make it possible to calculate the limits of capacity power generation available from a given size of a gas burner. For the burner geometry, similar to that with the know characteristic of gas combustion, the parameters for CO and NOx have been established for crude oil. Also, characteristics have been found for a specially designed oil nozzle with a large spray angle — sufficiently large for the optimum supply of fuel into the area of strong swirl flow with combustion established on the basis of the analysis of the burning of gas. It has been found that in cases of combustion crude oil a relatively small increase of the temperature of air supplied for combustion results in a significant drop in CO emission what has an impact on lower NOx emission.
Transonic Turbine Blade Tip Aero-Thermal Performance With Different Tip Gaps: Part I—Tip Heat Transfer
Authors: Zhang Q. , O’Dowd D. O. , He L. , Oldfield M. L. G. , Ligrani P. M.
Published: January 2011

A closely combined experimental and CFD study on a transonic blade tip aero-thermal performance at engine representative Mach and Reynolds numbers (Mexit = 1, Reexit = 1.27×106) is presented in this and its companion paper (Part II). The present paper considers surface heat transfer distributions on tip surfaces, and on suction and pressure side surfaces (near-tip region). Spatially-resolved surface heat transfer data are measured using infrared thermography and transient techniques within the Oxford University High Speed Linear Cascade research facility. The Rolls-Royce PLC HYDRA suite is employed for numerical predictions for the same tip configuration and flow conditions. The CFD results are generally in good agreement with experimental data, and show that the flow over a large portion of the blade tip is supersonic for all three tip gaps investigated. Mach numbers within the tip gap become lower as the tip gap decreases. For the flow regions near the leading edge of the tip gap, surface Nusselt numbers decrease as the tip gap decreases. Opposite trends are observed for the trailing edge region. Several ‘hot spot’ features on blade tip surfaces are attributed to enhanced turbulence thermal diffusion in local regions. Other surface heat transfer variations are attributed to flow variations induced by shock waves. Flow structure and surface heat transfer variations are also investigated numerically when a moving casing is present. The inclusion of moving casing leads to notable changes to flow structural characteristics and associated surface heat transfer variations. However, significant portions of the tip leakage flow remain transonic with clearly identifiable shock wave structures.
Aero-Thermal Performance of a Winglet at Engine Representative Mach and Reynolds Numbers
Authors: O’Dowd D. O. , Zhang Q. , He L. , Oldfield M. L. G. , Ligrani P. M. , Cheong B. C. Y. , Tibbott I.
Published: January 2011

This paper presents an experimental and numerical investigation of the aero-thermal performance of an uncooled winglet tip, under transonic conditions. Spatially-resolved heat transfer data, including winglet tip surface and near tip side walls, are obtained using the transient infrared thermography technique within the Oxford High Speed Linear Cascade test facility. CFD predictions are also conducted using the Rolls-Royce HYDRA suite. Most of the spatial heat transfer variations on the tip surface are well-captured by the CFD solver. The transonic flow pattern and its influence on heat transfer are analyzed, which shows that the turbine blade tip heat transfer is greatly influenced by the shock wave structure inside the tip gap. The effect of the casing relative motion is also numerically investigated. The CFD results indicate that the local heat transfer distribution on the tip is affected by the relative casing motion, but the tip flow choking and shock wave structure within the tip gap still exist in the aft region of the blade.
An Experimental Investigation of the Nonlinear Response of an Atmospheric Swirl-Stabilized Premixed Flame
Authors: Schimek Sebastian , Moeck Jonas P. , Paschereit Christian Oliver
Published: January 2011

Due to stringent emission restrictions, modern gas turbines mostly rely on lean premixed combustion. Since this combustion mode is susceptible to thermoacoustic instabilities, there is a need for modeling tools with predictive capabilities. Linear network models are able to predict the occurrence of thermoacoustic instabilities but yield no information on the oscillation amplitude. The prediction of the pulsation levels and hence an estimation whether a certain operating condition has to be avoided is only possible if information on the nonlinear flame response is available. Typically, the flame response shows saturation at high forcing amplitudes. A newly constructed atmospheric test rig, specifically designed for the realization of high excitation amplitudes over a broad frequency range, is used to generate extremely high acoustic forcing power with velocity fluctuations of up to 100% of the mean flow. The test rig consists of a generic combustor with a premixed swirl-stabilized natural gas flame, where the upstream part has a variable length to generate adaptive resonances of the acoustic field. The OH* chemiluminescence response, with respect to velocity fluctuations at the burner is measured for various excitation frequencies and amplitudes. From these measurements, an amplitude dependent flame transfer function is obtained. Phase-averaged OH* pictures are used to identify changes in the flame shape related to saturation mechanisms. For different frequency regimes, different saturation mechanisms are identified.
Impact of the Inflow Conditions on the Heavy-Duty Gas Turbine Exhaust Diffusers Performance
Authors: Vassiliev Vladimir , Irmisch Stefan , Abdel-Wahab Samer , Granovskiy Andrey
Published: January 2011

The flow in exhaust diffusers along with the channel geometry strongly depends on the inflow conditions, including Mach number level, total pressure distribution, flow angle, and turbulence. In the first part of this paper, the impact of these parameters is analyzed using CFD, experimental data from the test rig and field measurements. A widespread opinion is that the optimal condition for the diffuser is an axial uniform inflow. However, it is shown in this paper that non-uniform pressure distribution as compared to a uniform one can lead to better diffuser performance and that moderate residual swirl can improve the performance as well. In the second part of the paper, the minimization of exhaust losses in heavy-duty gas turbines is discussed and illustrated by two practical examples.
Structural Dynamic Design of a Rotating Hydrogen Co-Fired Multi-Fuel External Combustor
Authors: Heshmat Hooshang , Tomaszewski Michael J. , Walton James F. , Potgieter Deon J.
Published: January 2011

In the paper the authors will present the design and preliminary rotor-bearing dynamics test results for a hydrogen co-fired multi-fuel capable rotary burner. Hydrogen co-firing involves moving a stream of liquid or gaseous fuel through a zone of combusting hydrogen. The high-temperature of the hydrogen combustion zone initiates a vigorous combustion of the fuel stream moving through. Given the very high combustion temperatures of the rotating hydrogen flame fronts and close proximity of the rotating flame holder to the structural support, an integrated high temperature drive and bearing system was necessary to achieve reliable long term operation. Design space constraints for the rotary hydrogen burner head resulted in a drive and bearing system design that includes 150 mm diameter compliant foil journal bearing supports and an air driven reaction turbine closely integrated with the thrust foil bearings. Drive turbine design, rotor-bearing system dynamic tradeoffs and thermal management in the presence of high axial thermal gradients will be presented along with preliminary testing to design speeds of 7500 rpm (i.e, surface velocity of 100 m/s) under simulated thermal gradients with the rotating assembly face temperature reaching as high as 800°C.
Development of Air Cooled Combustor for Mitsubishi G Class Gas Turbine
Authors: Tsukagoshi Keizo , Arimura Hisato , Tanaka Katsunori , Nishida Koichi , Konishi Testu , Akamatsu Shinji , Kishida Hiroaki , Sato Kenji
Published: January 2011

Mitsubishi Heavy Industries (MHI) pioneered the introduction of steam cooling technology for gas turbines with the introduction of the M501G in 1997. To date, 62 Mitsubishi G units have been sold making this series the largest steam cooled fleet in the market. The turbine inlet temperature (TIT) for this gas turbine is 1500 deg. C. The original M501G has been upgraded for air cooling applications. This upgraded version is called as M501GAC (G Air Cooled). Several Dry Low NOx (DLN) and cooling technologies from existing F and G series were applied to the upgraded M501GAC. The new GAC combustor was installed in the in-house verification Combined Cycle Power Plant, called T-Point, and verification tests of the combustor were conducted from November 2008. The air cooled M501GAC combustor demonstrated less than 15ppm NOx operation, stable combustor dynamics at all load levels, and high combustor ignition reliability making it suitable for daily start and stop operation at T-Point. Long term verification test is currently under way.
Full-Scale Atmospheric Tests of Sequential Combustion
Authors: Ciani A. , Eroglu A. , Gu¨the F. , Paikert B.
Published: January 2011

Sequential combustion system of GT24 and GT26 engines from Alstom consists of a primary combustor, followed by a turbine and a re-heat combustor. This technology is capable of achieving the most rigorous emission targets at base-load operation, with an additional benefit of delivering very low NOx and CO emissions down to extremely low part load. This paper describes further development of the reheat technology with the help of multiple tools, with special consideration given to atmospheric tests. Prior to more demanding high-pressure combustion tests, full-scale atmospheric tests are utilized in order to down-select the most promising variants in a relatively cost-effective setup. Atmospheric tests are used additionally to gain insight into fundamental physics of reheat combustion, thanks to optical access and applicability of complicated measurement methods. A number of parameters, including NOx, CO, UHC emissions, temperature distribution, flashback margin, pressure drop and — to some extend — combustion dynamics can be assessed with the help of atmospheric tests. In order to increase the applicability of atmospheric test results to high-pressure conditions, the ignition and reaction characteristics of high-pressure flames must be reproduced at atmospheric conditions. This can be done through adjustment of operational parameters such as incoming temperature, as well as using fuel blends with modified ignition properties. The scaling methods as well as recent analyses on improvement areas for this unique combustion technology are discussed.
Endwall Effusion Cooling System Behaviour Within a High-Pressure Turbine Cascade: Part 1—Aerodynamic Measurements
Authors: Sacchi Marco , Simoni Daniele , Ubaldi Marina , Zunino Pietro , Zecchi Stefano
Published: January 2011

The secondary flow field in a large-scale high-pressure turbine cascade with micro-holed endwall cooling has been investigated at the Genova Laboratory of Aerodynamics and Turbomachinery in cooperation with Avio S.p.A in the framework of the European Project AITEB-2. The experimental investigation has been performed for the baseline configuration, with a smooth solid endwall installed, and for the cooled configuration with a micro-holed endwall providing micro-jets ejection from the wall. Two different cooling flow rates were investigated and the experimental results are reported in the paper. Different measurement techniques have been employed to analyze the secondary flow field along the channel and in a downstream tangential plane. Particle Image Velocimetry has been utilized to quantify the blade-to-blade velocity components in a plane located close to the endwall and in the midspan plane. Hot-wire measurements have been performed in a tangential plane downstream of the blade trailing edges in order to survey the micro-jets effects on the secondary flows behavior. The total pressure distributions, for the different blowing conditions, have been measured in the downstream tangential plane by means of a Kiel pneumatic probe. The results, represented in color plots of velocity, pressure loss coefficient and turbulent kinetic energy distributions, allow the identification of the endwall effusion cooling effects on location and strength of the secondary vortical structures. The thermal investigation of the effusion system is discussed in Part 2 of the paper.
Radial Inflow Turbine One and Tri-Dimensional Design Analysis of 600 kW Simple Cycle Gas Turbine Engine
Authors: Miranda Carrillo Rube´n A. , Nascimento Marco A. R. , Gutie´rrez Vela´squez Elkin I. , Moura Newton R.
Published: January 2011

Microturbines have been developed as an important power unit for distributed generation (DG) or distributed energy resource (DER) options [1]. They have been established and are widely used in aircraft and power applications, due to their easy installation, reliability, high performance, multi-fuel capabilities and low emission [2]. However, the aerothermodynamic design of a radial turbine still poses a challenge due to its high rotational speed and high inlet temperature, which influence the centrifugal stress and the rotor structural integrity. This paper presents the numerical investigations on the aerothermodynamic design of the nozzle and the radial inflow rotor for a 600 kW simple cycle gas turbine engine using a One-dimensional Computer FORTRAN Code (OFC) [3], on the grounds of non-dimensional parameters aimed at computational and work time reduction. This program utilizes a one-dimensional solution of flow conditions through the turbine along the meanline. The referred computer program is an effective performance prediction tool mostly in the initial stage of the preliminary design and can be used to quickly investigate and calculate the number of design options prior to any details of the vane and blade geometry. In order to find the most promising design option, a computational fluid dynamics (CFD) simulation has been used to study the performance, the aerothermodynamic design and the flow characteristics of the turbine components. The OFC results were compared with the CFD simulation, a computer program for the design analysis of radial inflow turbines, and analytical results taken from specialized literature showed the results were in agreement.
Fatigue Life Extension of Steam Turbine Alloys Using Low Plasticity Burnishing (LPB)
Authors: Preve´y Paul S. , Jayaraman Nayarananan , Ravindranath Ravi
Published: January 2011

Low Plasticity Burnishing (LPB) dramatically improves the damage tolerance of titanium alloy blades, mitigating blade-disk dovetail fretting and blade edge damage in gas turbines. LPB surface treatment of martensitic stainless steels Alloy 450 and 17-4PH subject to corrosion fatigue and pitting in the low-pressure sections of stream turbines has now been investigated. Condensation in the low-pressure steam turbine environment supports corrosion pitting and corrosion fatigue in martensitic stainless steels, primary failure mechanisms driving steam turbine repair and operational expense. Chloride corrosion fatigue results with and without high kf surface damage are compared for LPB, shot peened, and machined 17-4PH; and for ground and LPB treated Alloy 450. The depth and magnitude of compression achieved by the surface treatments are documented. LPB increased the undamaged fatigue strength of 17-4PH by 30% in neutral salt solution, and of Alloy 450 in acidic salt by 50%. In both alloys LPB mitigated damage to the 1 mm depth of compression. The cyclic stress corrosion component of corrosion fatigue was eliminated by the deep LPB compression, effectively restoring the endurance limit lost in active corrosion fatigue in both alloys.
Dental Air Turbine Performance Study Using CFD and Experimental Approach
Authors: Chiang Hsiao-Wei D. , Hsu Chih-Neng , Chang Ya-Yi , Chuang Shun-Yao
Published: January 2011

Dental air turbine handpieces have been widely used in clinical dentistry for over 30 years, however, little work has been reported on their performance. In dental air turbine handpieces, the types of flow channel and turbine blade shape can have very different designs. These different designs can have major influence on the torque, rotating speed, and power performance. This research is focused on the turbine blade and the flow channel designs. Using CFD and experiments, the key design parameters which influence the performance of dental hand pieces can be studied. Three types of dental air turbine designs with different turbine blades, nozzle angles, nozzle flow channels, and shroud clearances were tested and analyzed. Very good agreement was demonstrated between the CFD analyses and the experiments. Using the analytical model, parametric studies were performed to indentify key design parameters.
The Internal Structure of the Tip Leakage Vortex Within the Rotor of an Axial Waterjet Pump
Authors: Miorini Rinaldo L. , Wu Huixuan , Katz Joseph
Published: January 2011

The complex flow field in the tip region of a turbomachine rotor, including the tip leakage flow and tip leakage vortex (TLV), has been studied for decades. Yet many associated phenomena are still not understood. This paper provides detailed data on the instantaneous and phase averaged inner structure of the tip flow, and evolution of the TLV. Observations are based on series of high resolution planar particle image velocimetry measurements performed in a transparent waterjet pump fitted into an optical refractive index matched test facility. Velocity distributions and turbulence statistics are obtained in several meridional planes inside the rotor. We observe that the instantaneous TLV structure is composed of several unsteady vortex filaments that propagate into the blade passage. These filaments are first embedded into a vortex sheet generated at the suction side of the blade tip, and then they wrap around each other and roll up into the TLV. These vortices do not have sufficient time to merge into a single compact structure within the blade passage. We also find that the leakage vortex induces flow separation at the casing endwall and entrains the casing boundary layer with its counter-rotating vorticity. As it propagates in the rotor passage, the TLV migrates towards the pressure side of the neighboring blade. Unsteadiness associated with observed vortical structures is also investigated. We notice that, at early stages of the TLV evolution, turbulence is elevated in the vortex sheet, in the flow entrained from the endwall, and near the vortex core. Interestingly, the turbulence observed around the core is not consistent with the local distribution of turbulent kinetic energy production rate. This mismatch indicates that, given a TLV section, production likely occurs at preceding stages of the vortex evolution. Then, the turbulence is convected to the core of the TLV, and we suggest that this transport has substantial component along the vortex. Because we observe that the meandering of vortex filaments dominate the flow in the passage, we decompose the unsteadiness surrounding the TLV core to contributions from interlaced vortices and broadband turbulence. Results of this decomposition show that the two contributions are of the same order of magnitude. The TLV is investigated also beyond the trailing edge of the rotor blade. During these late stages of its evolution, the TLV approaches the pressure side of the neighboring blade and vortex breakdown occurs, causing rapid broadening of the phase average core, with little change in overall circulation. Associated turbulence occupies almost half the width of the blade passage and turbulence production there is also broadly distributed. Proximity of the TLV to the pressure side of the neighboring blade also affects entrainment of flow into the incoming tip region.
The Effect of Geometry on the Aerodynamics of a Prototype Gas Turbine Combustor
Authors: Mohammad Bassam , Jeng San-Mou
Published: January 2011

The method of admission of the swirling flow to the combustion chamber has a strong influence on the flow field structure in Gas Turbine Combustors (GTC). Two different exit configurations are studied. The first configuration is that of a swirl cup that ends only with a splash plate such that there is a sudden unguided expansion as the flow emanates from the swirl cup. The second is a swirl cup that ends with a splash plate and an asymmetric combustion dome. Laser Doppler Velocimetry (LDV) measurements are conducted in the horizontal plane (X-Y), for both configurations, 5mm from the flare exit. Also, LDV measurements are conducted in two vertical planes passing by the combustor centerline (X-Z and Y-Z). The results reveal a significant difference in the flow structure for both configurations. The combustion dome appears to reduce the turbulence activities close to the exit of the swirl cup. In addition, the presence of the combustion dome eliminates the corner recirculation zone and the low velocity region close to the combustor walls. It is interesting to see that the asymmetry of the combustion dome (9° difference in the expansion angle on both sides) results in a significant asymmetry in the velocity magnitude as well as the turbulence activities. Moreover, the asymmetry in the combustion dome results in a tilting of the CRZ toward the surface with the higher expansion angle. The results highlight the importance of the proper and careful design of the GTC front section. The experiments are conducted in a dump combustor (rectangular cross section). To study the effect of the chamber geometry on the flow field, the base configuration is installed in an annular combustor sector and LDV measurements are conducted in the axial radial plane (X-Z). The flow field as well as the shape of the CRZ are significantly different in both cases. The CRZ height reduced by 40% with the swirl cup installed to the SAC sector. The results emphasize the strong influence of the confinement on the flow structure.
The Highly Loaded Aerodynamic Design and Performance Enhancement of a Helium Compressor
Authors: Ke Tingfeng , Zheng Qun
Published: January 2011

A design study of the multistage axial helium compressor of a 300MWe nuclear gas turbine is presented in this paper. Helium compressor is characterized by shorter blades, narrow flow channels, numerous stages and longer slim rotor, which result in losses due to blade surface and end wall boundary layers growths, secondary flows and clearance leakage flows, any occurrence of flow separation and stage mismatch. Therefore, the purpose of this paper is to improve and optimize the aerodynamic design of the helium compressor. The property of helium is different from that of air, so how to choose the design parameters of a helium compressor is discussed first. And then how to shorten the length of the helium compressor or how to decrease the number of stages for a certain pressure ratio by increasing the stage loading are investigated. The new highly loaded helium compressor of larger flow coefficient and high reaction is designed and optimized. The three-dimensional flow patterns in a helium stage are simulated with CFD software (NUMECA). Adjusting the position of blade maximum camber deflection position; redistributing radial compression work; modifying the configuration of blade at inlet and outlet; using CDA technique to optimize blade profile; 3D blading techniques to mitigate end wall boundary layers and corner separation have improved the performance of the first stage of the helium compressor cascades.
Evaluation of High-Order Resonance of Blade Under Wake Excitation
Authors: Li Lin , Wang Peiyi
Published: January 2011

Avoiding the low-order resonances of blades is one of the main design goals for a mechanical structure designer of turbo machinery. However, we have to accept that there are resonance frequencies in the operating speed range of the blade, for the following reasons: Firstly, the natural frequencies of the blade are closely spaced sometimes, it is impossible to avoid them all. Secondly, in general, the higher of the resonance frequency, the lower the energy of resonance will be. But in recent 10 years, the high-order blade resonances present more and more frequently in turbo machinery, which induce a lot of HCF problems. As the considerations above, studies on the high-order vibration of blades become necessary and important. In the cascade, the high-order vibration of blades is mainly induced by the wakes from upstream. An obvious difference of the wake excitation from the common excitations resides in its asynchronism, that is, the maximum value of aerodynamic force from wakes at each point doesn’t appear at the same time, because except the frequency, the distribution of the aerodynamic force field depends on two parameters: not only amplitude but also phase angle. Both are functions of coordinates. In this paper, the related position in Euclidean Space between the asynchronous excitation field and the modal displacement of blade were deal with to evaluate the strength of the high-order resonance of blade. The effect of the asynchronous aerodynamic force field on the blade resonance was studied either. Finally a method for evaluation of high-order resonance of blade excited by wake fluid is proposed. A numerical case was studied either, which demonstrates that the proposed evaluation on high-order resonance is practical in engineering problem.
Experiment on Breakup Processes and Surface Waves of Round Liquid Jets in Crossflows
Authors: Zhu Ying , Huang Yong , Wang Fang , Wang Xiong-hui
Published: January 2011

An experiment was conducted to investigate the surface wave development and the breakup processes of round water jets in cross airflows at room temperature and pressure by high-speed photography. The jets were injected normal to the crossflow direction opposing gravitation forces from a plain orifice nozzle with the diameter of 0.3 mm and length-to-diameter ratio of 40. Successive images were recorded by a megapixel high-speed video camera with maximum frame rate frequency of 10000 Hz. The jet injection velocity varied from 3.8 m/s to 7.8 m/s. The crossflow velocity varied from 25.6 m/s to 35.1 m/s which resulted in the liquid-to-air momentum flux ratio varied from 10.2 to 80. The experimental results indicate that the surface of the liquid jet is smooth at first and then the initial surface wave appears a distance downstream along the jet column. The structure of the liquid jet would be successively deformed to a spiral wave in the cross airflow. When the amplitude grows large enough the liquid column is pinched into segments from the locations of wave troughs due to surface tension. With the increasing of the cross airflow velocity the aerodynamic forces, instead of the surface tension, begin to play an important role in the column breakup process. The liquid column is disintegrated by the cutting of the aerodynamic forces. The smooth length defined as the distance from where initial surface wave appears to the nozzle exit is correlated with the test operation parameters. The smooth length will be increased with the increasing of the jet injection velocity and decreased with the increasing of airflow velocity. The liquid jet column will bend and fluctuate in the crossflow and the normalized fluctuation displacement of the liquid column is correlated with the test operation parameters. The results depict that the increasing of jet injection velocity will diminish the jet column fluctuation whereas the increasing of airflow velocity will enhance it. The liquid column breakup points also fluctuate in the cross airflow. The coordinates of the time-averaged breakup locations are correlated with the liquid-to-air momentum ratio. The equation of the near-field liquid column trajectory curve before the column breakup point is concluded. The curves based on the equation agree well with the tested results.
Integrated Combustor and Vane Concept in Gas Turbines
Authors: Rosic Budimir , Denton John D. , Horlock John H. , Uchida Sumiu
Published: January 2011

This paper numerically investigates the interaction between multiple can combustors and the first vane in an industrial gas turbine with 16 can combustors and 32 vanes in order to find ways of reducing the overall cooling requirements. Two promising concepts for the overall cooling reduction are presented. In the first, by minimising the axial distance between the combustor wall and the vane, the stagnation region at the LE of every second vane can be effectively shielded from the hot mainstream gases. The LE shielding allows continuous cooling slots to be used (as an alternative to discrete cooling holes) to cool downstream parts of the vane using a portion of the saved LE showerhead cooling air. The second concept proposes a full combustor and first vane integration. In this novel concept the number of vanes is halved and the combustor walls are used to assist the flow turning. All remaining vanes are fully integrated into the combustor walls. In this way the total wetted area of the integrated system is reduced, and by shielding the LEs of the remaining vanes the total amount of cooling air can be reduced. The proposed combustor and first vane integration does not detrimentally affect the aerodynamics of the combustor and vane system. The concept also simplifies the design and should lower the manufacturing costs.
Flow Visualization Study of Passive Flow Control Features on a Film-Cooled Turbine Blade Leading Edge
Authors: Carroll Daniel R. , King Paul I. , Rutledge James L.
Published: January 2011

A water channel study was conducted on a cylindrical leading edge model of a film-cooled turbine blade to assess the effects of surface modifications on film spreading. A single radial coolant hole located 21.5° from the stagnation line, angled 20° to the surface and 90° to the flow direction supplied dyed coolant flow. Surface modifications included a variety of dimples upstream and downstream of the coolant hole and transverse trenches milled coincident with the coolant hole. Compared to the unmodified surface, a single row of small cylindrical or spherical dimples upstream of the coolant hole steadies the jet at blowing ratios up to M = 0.75. Medium and large spherical dimples downstream of the coolant hole have a similar effect, but none of the dimple geometries studied affect the coolant jet above M = 0.75. A single-depth, square-edged transverse trench spreads the coolant spanwise, increasing the coverage of a single coolant hole more than two times. This trench suffers from coolant blow-out above M = 0.50, but a deeper, tapered-depth trench entrains and spreads the coolant very effectively at blowing ratios above M = 0.50. The tapered trench prevents jet liftoff and is the only geometry studied that holds the coolant closer to the surface than the unmodified coolant hole.
Prediction of Aeroacoustic Resonance in Cavities of Hole-Pattern Stator Seals
Authors: Liliedahl David N. , Carpenter Forrest L. , Cizmas Paul G. A.
Published: January 2011

A Reynolds-averaged Navier-Stokes (RANS) solver developed in-house was used to simulate grazing channel flow past single and multiple cavities. The objective of this investigation was to predict fluid instabilities in hole-pattern stator seals. The numerical results generated with the RANS solver showed good agreement with those obtained using a commercial Large Eddy Simulation (LES) code. In addition, the numerical results agreed well with experimental data. Rossiter’s formula, a popular semi-empirical model used to predict frequencies of hole-tone acoustic instabilities caused by grazing fluid flow past open cavities, was modified using the RANS solver results to allow for its application to channel flows. This was done by modifying the empirical constant κ, the ratio of vortex velocity and the freestream velocity. The dominant frequencies predicted using the Rossiter’s formula with the new κ value matched well the experimental data for hole-pattern stator seals. The RANS solver accurately captured the salient features of the flow/acoustic interaction and predicted well the dominant acoustic frequencies measured in an experimental investigation. The flow solver also provided detailed physical insight into the cavity flow instability mechanism.
Effects of Pin Detached Space on Heat Transfer and From Pin Fin Arrays
Authors: Siw Sin Chien , Chyu Minking K. , Shih Tom I.-P. , Alvin Mary Anne
Published: January 2011

Heat transfer and pressure characteristics in a rectangular channel with pin-fin arrays of partial detachment from one of the endwalls have been experimentally studied. The overall channel geometry (W = 101.6 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (4:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = 1/4 E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e. C/D = 0, 1, 2, respectively. The Reynolds number, based on the hydraulic diameter of the un-obstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. Experimental results reveal that the presence of a detached space between the pin-tip and the endwall have a significant effect on the convective heat transfer and pressure loss in the channel. The presence of pin-to-endwall spacing promotes wall-flow interaction, generates additional separated shear layers, and augments turbulent transport. In general, an increase in detached spacing, or C/D leads to lower heat transfer enhancement and pressure drop. However, C/D = 1, i.e. H/D = 3, of a staggered array configuration exhibits the highest heat transfer enhancement, followed by the cases of C/D = 0 and C/D = 2, i.e. H/D = 4 or 2, respectively.
Force Feedback Control for Active Stabilization of Synchronous Whirl Orbits in Rotor Systems With Non-Linear Stiffness Elements
Authors: Cole Matthew O. T. , Chamroon Chakkapong , Ngamprapasom Prinya
Published: January 2011

Synchronous vibration in rotor systems having bearings, seals or other elements with non-linear stiffness characteristics is prone to amplitude jump when operating close to critical speeds as there may be two or more possible whirl responses for a given unbalance condition. This paper describes research on the use of active control methods for eliminating this potentially undesirable behavior. A control scheme based on direct feedback of rotor-stator interaction forces is considered. Model based conditions for stability of low amplitude whirl, derived using Lyapunov’s direct method, are used as a basis for synthesizing controller gains. Subsidiary requirements for existence of a static feedback control law that can achieve stabilization are also explained. An experimental validation is undertaken on a flexible rotor test rig where non-linear rotorstator contact interaction can occur across a small radial clearance in one transverse plane. A single radial active magnetic bearing is used to apply control forces in a separate transverse plane. The experiments confirm the conditions under which static feedback of the measured interaction force can prevent degenerate whirl responses so that the low amplitude contact-free orbit is the only possible steady-state response. The gain synthesis method leads to controllers that are physically realizable and can eliminate amplitude jump over a range of running speeds.
The Effect of Distributed Roughness on the Power Performance of Wind Turbines
Authors: Pechlivanoglou G. , Fuehr S. , Nayeri C. N. , Paschereit C. O.
Published: January 2011

The effects of distributed roughness on wind turbines are extensively investigated in this paper. The sources of roughness are identified and analyzed and their effects on airfoil are estimated from simulations and measured with wind tunnel measurements. In addition to the environmental and manufacturing induced roughness, several forms of roughness-related shape deviations are investigated and their effects on the aerodynamic performance of airfoils is qualitatively predicted through numerical simulations. The actual effects of roughness on wind turbine performance are also presented through power production measurements of wind turbines installed in sandy environments. These measurements are correlated with simulated power predictions, utilizing a steady state BEM code.
Novel High-Perfoming Single-Pressure Combined Cycle With CO2 Capture
Authors: Sipo¨cz Nikolett , Jonshagen Klas , Assadi Mohsen , Genrup Magnus
Published: January 2011

The European electric power industry has undergone considerable changes over the past two decades as a result of more stringent laws concerning environmental protection along with the deregulation and liberalization of the electric power market. However, the pressure to deliver solutions in regard to the issue of climate change has increased dramatically in the last few years and given the rise to the possibility that future natural gas-fired combined cycle (NGCC) plants will also be subject to CO2 capture requirements. At the same time, the interest in combined cycles with their high efficiency, low capital costs and complexity has grown as a consequence of addressing new challenges posed by the need to operate according to market demand in order to be economically viable. Considering that these challenges will also be imposed on new natural gas-fired power plants in the foreseeable future, this study presents a new process concept for natural gas combined cycle power plants with CO2 capture. The simulation tool IPSEpro is used to model a 400 MW single-pressure NGCC with post-combustion CO2 capture, using an amine-based absorption process with Monoethanolamine. To improve the costs of capture the gas turbine, GE 109FB, is utilizing exhaust gas recirculation, thereby increasing the CO2 content in the gas turbine working fluid to almost double that of conventional operating gas turbines. In addition, the concept advantageously uses approximately 20% less steam for solvent regeneration by utilizing preheated water extracted from HRSG. The further recovery of heat from exhaust gases for water preheating by use of an increased economizer flow results in an outlet stack temperature comparable to those achieved in combined cycle plants with multiple pressure levels. As a result, overall power plant efficiency as high as that achieved for a triple-pressure reheated NGCC with corresponding CO2 removal facility is attained. The concept thus provides a more cost-efficient option to triple-pressure combined cycles since the number of heat exchangers, boilers, etc. is reduced considerably.
Numerical and Experimental Analysis of the Temperature Distribution in a Hydrogen Fuelled Combustor for a 10 MW Gas Turbine
Authors: Masi Massimo , Gobbato Paolo , Toffolo Andrea , Lazzaretto Andrea , Cocchi Stefano
Published: January 2011

Proper cooling of the hot components and an optimal temperature distribution at the turbine inlet are fundamental targets for gas turbine combustors. In particular, the temperature distribution at the combustor discharge is a critical issue for the durability of the turbine blades and the high performance of the engine. At present, CFD is a widely used tool to simulate the reacting flow inside gas turbine combustors. This paper presents a numerical analysis of a single can type combustor designed to be fed both with hydrogen and natural gas. The combustor also features a steam injection system to restrain the NOx pollutants. The simulations were carried out to quantify the effect of fuel type and steam injection on the temperature field. The CFD model employs a computationally low cost approach, thus the physical domain is meshed with a coarse grid. A full-scale test campaign was performed on the combustor: temperatures at the liner wall and the combustor outlet were acquired at different operating conditions. These experimental data, which are discussed, were used to evaluate the capability of the present CFD model to predict temperature values for combustor operation with different fuels and steam-fuel ratios.
Numerical Analysis of the Effects of Non-Uniform Surface Roughness on Compressor Stage Performance
Authors: Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Venturini Mauro
Published: January 2011

Gas turbine performance degradation over time is mainly due to the deterioration of compressor and turbine blades, which, in turn, causes a modification of the compressor and turbine performance maps. Since detailed information about the actual modification of the compressor and turbine performance maps is usually unavailable, component performance can be modeled and investigated (i) by scaling the overall performance map, or (ii) by using stage-by-stage models of the compressor and turbine and by scaling each single stage performance map to account for each stage deterioration, or (iii) by performing 3D numerical simulations, which allow to both highlight the fluid-dynamic phenomena occurring in the faulty component and grasp the effect on the overall performance of the component. In this paper, the authors address the most common and experienced source of loss for a gas turbine, i.e. compressor fouling. With respect to the traditional approach, which mainly aims at the identification of the overall effects of fouling, authors investigate a micro-scale representation of compressor fouling (e.g. blade surface deterioration and flow deviation). This allows (i) a more detailed investigation of the fouling effects (e.g. mechanism, location along blade height, etc.), (ii) a more extensive analysis of the causes of performance deterioration and (iii) the assessment of the effect of fouling on stage performance coefficients and on stage performance maps. The effects of a non-uniform surface roughness on both rotor and stator blades of an axial compressor stage are investigated by using a commercial CFD code. The NASA Stage 37 test case was used as the baseline geometry. The numerical model already validated against experimental data available in literature was used for the simulations. Different non-uniform combinations of surface roughness levels on rotor and stator blades were imposed. This makes it possible to highlight how the localization of fouling on compressor blades affects compressor performance, both at an overall and at a fluid-dynamic level.
A High-Accuracy Model Reduction for Analysis of Nonlinear Vibrations in Structures With Contact Interfaces
Authors: Petrov E. P.
Published: January 2011

A highly accurate and computationally efficient method is proposed for reduced modelling of jointed structures in frequency domain analysis of nonlinear steady-state forced response. The method has significant advantages compared with the popular variety of mode synthesis methods or forced response matrix methods and can be easily implemented in the nonlinear forced response analysis using standard finite element codes. The superior qualities of the new method are demonstrated on a set of major problems of nonlinear forced response analysis of bladed discs with contact interfaces: (i) at blade roots; (ii) between interlock shrouds, and (iii) at under platform dampers. The numerical properties of the method are thoroughly studied on a number of special test cases.
Coating Pre-Cracking Effect in Combined Cycle Fatigue Tests of Superalloys for Gas Turbine Blades
Authors: Filippini Mauro , Foletti Stefano , Pasquero Giuseppe
Published: January 2011

In gas turbine engines for aerospace propulsion, the application of coatings on HP and LP stage blading where the highest temperatures are experienced is a common practice to prevent environmental degradation. However, since the strength of the coating is lower than that of the substrate material, upon loading the static strength of the coating may be exceeded and coating cracking may occur. In order to assess the effect of cracking in the coating on polycrystalline nickel superalloy MAR-M002, a number of combined cycle fatigue (CCF) and low cycle fatigue (LCF) tests with and without dwell have been carried out, at temperatures up to 870 °C. In order to experimentally assess the potential detrimental effect of coating cracking, controlled cracking in the coating prior to fatigue testing has been generated by using a special procedure. CCF tests have carried out by superimposing to strain controlled zero to maximum LCF cycles with dwell time stress controlled smaller HCF cycles, simulating the high loading ratio vibrations occurring in the blades. The loading mode applied in the CCF tests, even if much simpler than effective service conditions, is sufficiently representative of the loading experienced by the materials in correspondence of critical geometrical features of the turbine blades, where HCF amplitudes due to blade vibrations are superimposed to major (ground-air-ground) LCF cycles occurring during the regular service of the gas turbine engines. Comparison of the CCF and of the LCF tests with dwell with conventional LCF tests is presented herein, with special consideration of the effect of coating cracking.