bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Performance of a Radially Rotating Twin-Pass Smooth-Walled Parallelogram Channel
Authors: Liou Tong-Miin , Chang Shyy Woei , Yang Chun-Chang , Lan Yi-An
Published: September 2014

An experimental study was performed to measure the detailed heat transfer distributions, Fanning friction factors (f) and thermal performance factors (TPF) of a radially rotating twin-pass parallelogram channel. Laboratory scale full field Nusselt number (Nu) distributions over Leading Endwall (Leading-E) and Trailing Endwall (Trailing-E) of the rotating channel are measured at the test conditions of 5000 < Re < 20000, 0 < Ro < 0.3 and 0.028 < Δρ/ρ < 0.12. A selection of Nu data illustrates the individual and interactive impacts of Re, Ro and buoyancy (Bu) numbers on local and area-averaged heat transfer properties. Without the additional flow complexities induced by the turbulators, the degrees of Bu impacts are significantly amplified from those developed in an enhanced rotating ribbed channel. Relative to the similar rotating square twin-pass channel, the heat transfer recovery over the stable wall proceeds at the lower Ro for present rotating parallelogram channel. Accompanying with the improved heat transfer performances from the square-channel counterparts, the f values are raised. With a set of f correlations generated using the f data collected from the Leading Sidewall (Leading-S) and Trailing Sidewall (Trailing-S) at isothermal conditions; the TPF values at various rotating conditions were evaluated. The heat transfer correlations that determine the area-averaged Nusselt numbers over the inlet and outlet legs and over the turning region are generated. The area-averaged Nu, f factors and TPF determined from the present rotating parallelogram channel are compared with those reported for the rotating twin-pass channels to determine the comparatively thermal performances of the parallelogram rotating channel for turbine rotor blade cooling.
Aerodynamic Data for Two Variants of Root Turbine Blade Sections for a 54″ Turbine Rotor Blade
Authors: Šimurda David , Luxa Martin , Šafařík Pavel , Synáč Jaroslav , Rudas Bartoloměj
Published: September 2014

Aerodynamic investigations were performed on planar blade cascades representing two alternative root sections of rotor blades 54″ in length with straight fir-tree root. Each of the variants was designed for different number of blades in the rotor. This paper presents the results of measurements showing the dependency of the kinetic energy loss coefficient and the exit flow angle on the exit isoentropic Mach number and the angle of incidence. Images of the flow fields are also presented. The experimental data is analyzed to assess and document the difference between the two root section designs.

Results show that requirement of straight fir tree root leading to high design incidence angles significantly limit operation range. Also in case of root sections with high exit Mach numbers a limit load conditions are an issue. In order to utilize available pressure drop blade cascade throat/pitch ratios should be kept as high as possible which favorites variant with lower number of blades and higher outlet metal angle (relative to axial direction).
The Effect of Vortex Core Distribution on Heat Transfer in Steam Cooling of Gas Turbine Blade Internal Ribbed Channels
Authors: Zhu Jiangnan , Gao Tieyu , Li Jun , Li Guojun , Gong Jianying
Published: September 2014

Steam has already been used as coolant of gas turbine blade internal cooling. A lot of investigations have been carried out to research the heat transfer performance of steam in ribbed rectangular channels. However, the micro-structure of the flow field especially the vortex distribution is not very clear. As the vortex caused by ribs is one of the main factors that enhance heat and mass transfer, it is very necessary to investigate the distribution of vortex in steam-cooled ribbed channels. The numerical simulation of steam flow field in 45° rib channels were carried out by using ANSYS CFX commercial program. The inlet Reynolds numbers are 30000 and 60000. The wall heat flux and inlet static pressure is 10kW/m2 and 0.3MPa, respectively. In order to find out the distribution and shape of all the main vortices, the technology of vortex core is applied, which is based on the critical point theory and Eigen-values of velocity gradient tensor. The distribution and shape of vortex core clearly indicates that the heat transfer strength of vortices positions is relatively higher than other places. There are four high strength vortices at the near-wall region between every two neighbored ribs. At the side wall which is located at the front side of ribs, high strength vortex exists and washes over the most part of the side wall. In the main flow region, the secondary flow caused by angled ribs can also be seen. The heat and mass transfer performance of steam in angled rib channels can be illustrated by the location and shape of vortex core.
The Effect of Endwall Manufacturing Variations on Turbine Performance
Authors: Grewe Robert P. , Miller Robert J. , Hodson Howard P.
Published: September 2014

Turbine blades and vanes of modern aero-engines are commonly manufactured by casting. The casting process often introduces slight geometry variations. In the endwall region this leads to inter-platform steps, gaps and leakage flows. This paper determines the underlying loss mechanisms associated with each of these geometric features and guides designers in minimizing their impact on efficiency.

The paper shows that the presence of an inter-platform step causes a pair of vortical structures to be superimposed onto the blade existing secondary flow structure. These are shown to always increase loss. When manufacture variations are considered the optimal design intent blade is shown to be one where the suction side endwall is lower than the pressure side endwall.

The paper shows that when leakage mass flow is introduced the presence of a step can either raise or reduce loss. A correlation which gives the optimal step height for a set leakage mass flow is presented. In the final part of the paper measured engine vane geometries are used to determine the impact of endwall geometry variation on turbine stage efficiency.
A Laser-Optical Sensor System for Simultaneous Tip Clearance and Vibration Monitoring of Compressor Rotor Blades
Authors: Neumann M. , Dreier F. , Günther P. , Fischer A. , Czarske J. , Holzinger F. , Schiffer H.-P.
Published: September 2014

In order to improve the efficiency and increase the life-time of compressors and turbines, online monitoring of operating parameters is an essential tool. One aim is to predict critical events like stall or flutter by observing blade vibrations and deformations. Due to superior material properties ceramic, carbon-fiber and glass-fiber reinforced composite blades become more and more popular. Hence, conventional measurement systems like capacitive probes are not able to deliver the necessary precision or, in the worst case, are not able to measure at all. Therefore, we developed a fiber-coupled, laser-optical sensor, named laser Doppler distance sensor (LDDS), which overcomes this drawback. The sensor is able to resolve the circumferential blade tip velocity as well as the radial expansion of each blade. Moreover, conventional blade tip timing measurements are possible as well.

Our aim is to provide a universal stall prediction and monitoring sensor system that is applicable to all types of blades.
Row Removal Heat Transfer Study for Pin Fin Arrays
Authors: Kirsch Kathryn L. , Ostanek Jason K. , Thole Karen A. , Kaufman Eleanor
Published: September 2014

Arrays of variably-spaced pin fins are used as a conventional means to conduct and convect heat from internal turbine surfaces. The most common pin shape for this purpose is a circular cylinder. Literature has shown that beyond the first few rows of pin fins, the heat transfer augmentation in the array levels off and slightly decreases. This paper provides experimental results from two studies seeking to understand the effects of gaps in pin spacing (row removals) and alternative pin geometries placed in these gaps. The alternative pin geometries included large cylindrical pins and oblong pins with different aspect ratios. Results from the row removal study at high Reynolds number showed that when rows four through eight were removed, the flow returned to a fully-developed channel flow in the gap between pin rows. When larger alternative geometries replaced the fourth row, heat transfer increased further downstream into the array.
A Simplified Method for Determining Gas Turbine Performance Parameters Based Upon Available Catalogue Data
Authors: Ranasinghe Chamila , Noor Hina , Jayasuriya Jeevan
Published: September 2014

Overall theoretical performance analysis of gas turbines can be conducted by applying design parameters into several thermodynamic theories and equations. However, limited availability of the design parameters will not provide sufficient room for a detailed analysis. Gas turbine manufacturers publish only a limited amount of design/performance data, while important parameters remained hidden and the available information is not sufficiently enough for obtaining a complete gas turbine performance dataset. Five main parameters commonly provided by a gas turbine manufacturer’s catalogues; pressure ratio of the compressor, exhaust mass flow rate, exhaust temperature of flue gas, overall efficiency, and electrical output. A theoretical model developed based on Mathcad software as documented in literature is used to reveal other hidden gas turbine parameters. A similar theoretical model using another solver was developed to obtain a complete dataset by using the available catalogue data with additional assumptions, which correspond to the commercial state of the art.

The engineering equation solver (EES) software has been used as a platform to rebuild the theoretical model. As the main development, a graphical user interphase (GUI) has been introduced to the new program with the aim to make it more user friendly. Furthermore on top of obtaining the hidden thermodynamic parameters for the gas turbine, performing flue gas analysis and an exergy analysis has now become possible through this program. The developed EES program is expected to be run in the learning laboratory at the Division of Heat and Power Technology, Department of Energy Technology, Royal Institute of Technology (KTH), Stockholm and finally it is going to be incorporated into CompEdu Learning Platform of the same division.
Slot Film Cooling in an Accelerating Boundary Layer With High Free-Stream Turbulence
Authors: Busche Mitch L. , Kingery Joseph E. , Ames Forrest E.
Published: September 2014

Slot film cooling and downstream heat transfer measurements have been acquired in the accelerating flows over two cylindrical leading edge test surfaces. Measurements were conducted at four blowing ratios, two Reynolds numbers and six well documented turbulence conditions for each test surface. Film cooling measurements were acquired over a four to one range in blowing ratio at the lower Reynolds number and at the two lower blowing ratios for the higher Reynolds numbers. The film cooling measurements were acquired at a coolant to free-stream density ratio of approximately 1.04. The flows were subjected to a low turbulence condition (Tu = 0.7%), two levels of turbulence for a smaller sized grid (Tu = 3.5%, and 7.9%), one turbulence level for a larger grid (8.1%), and two levels of turbulence generated using a mock aero-combustor (Tu = 9.3% and 13.7%). Turbulence level is shown to have a significant influence in mixing away film cooling coverage progressively as the flow develops in the streamwise direction. Effectiveness levels for the aero-combustor turbulence condition are reduced to as low as 20% of low turbulence values by the furthest downstream region. The slot in each case is located close to the stagnation region of the leading edge and the upstream boundary layers are very thin and accelerating. The slot is angled at 30° to the surface. Film cooling data, from the larger cylindrical stagnation region test surface, show that transitional flows have significantly improved effectiveness levels compared with turbulent flows. These data are expected to be very useful in grounding computational predictions of slot film cooling with elevated turbulence levels and acceleration.
Non-Axisymmetric Turbine Endwall Aerodynamic Optimization Design: Part II — Turbine Stage Design and Unsteady Flow Characteristics Analysis
Authors: Sun Hao , Song Liming , Li Jun , Feng Zhenping
Published: September 2014

Aerodynamic optimization design and experimental validation for the non-axisymmetric endwall profiles of the turbine cascade have been completed in the part I of this research work. Non-axisymmetric endwall profile optimization design of the turbine stage and corresponding steady and unsteady flow characteristics were presented in the part II. Aerodynamic optimization design for the non-axisymmetric endwall profile of the turbine stage was conducted when the maximization of the total-total isentropic efficiency was set as the design objective with constraint on the mass flow rate. The aerodynamic performance of the designed turbine stage was evaluated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions. The non-axisymmetric endwall profiles of the stator hub and shroud as well as the rotor hub in the turbine stage were optimized using developed endwall profile method in the part I. A total of 15 design variables were employed in the optimization for the stator and rotor endwalls. The global optimization method of the adaptive rang differential evolution algorithm was used to search the optimal non-axisymmetric endwall profile. The total-total isentropic efficiency of the turbine stage with the optimized non-axisymmetric endwall profile increases 0.26% by comparison of the referenced axisymmetric endwall design when the effects of the rotor tip clearance were also considered. The secondary flow losses of the stator and rotor were significantly reduced in the optimized non-axisymmetric endwall stage, as well as the tip leakage flow losses. In addition, the unsteady aerodynamic performance of the turbine stage with the optimized non-axisymmetric endwall profile and referenced axisymmetric endwall were numerically investigated and compared. The numerical results indicate that the fluctuating velocity in the rotor blade passage of the optimized non-axisymmetric endwall stage significantly decreases since the stator wake and secondary flow losses are reduced. Thus, the intensity of the unsteady interaction between the stator upstream flow and the flow in the rotor passage decreases. The time-averaged results indicated that the aerodynamic efficiency and output power of the turbine stage with the optimized non-axisymmetric endwall profile are higher than that of the referenced axisymmetric endwall stage. Meanwhile, the transient results at different time steps show that the periodic fluctuating amplitude of the efficiency and power of the optimized non-axisymmetric endwall stage were smaller than that of the referenced axisymmetric endwall stage due to the weaker stator/rotor unsteady interaction effects.
Heat Transfer Measurements of Oblong Pins
Authors: Kirsch Kathryn L. , Thole Karen A.
Published: September 2014

Pin fin arrays are employed as an effective means for heat transfer enhancement in the internal passages of a gas turbine blade, specifically in the blade’s trailing edge. Various shapes of the pin itself have been used in such arrays.

In this study, oblong pin fins are investigated whereby their long axis is perpendicular to the flow direction. Heat transfer measurements were taken at the pin mid-span with unheated endwalls to isolate the pin heat transfer. Results show important differences in the heat transfer patterns between a pin in the first row and a pin in the third row. In the third row, wider spanwise spacing allows for two peaks in heat transfer over the pin surface. Additionally, closer streamwise spacing leads to consistently higher heat transfer for the same spanwise spacing. Due to the blunt orientation of the pins, the peak in heat transfer occurs off the stagnation point.
Investigation on the Effect of Dimension on the Compression Mechanics of Metal Rubber
Authors: Ma Yanhong , Gao Di , Hong Jie
Published: September 2014

Metal Rubber (MR) is an attractive porous material used in vibration absorbers within extremely harsh environments. It is in general acknowledged that the sliding friction existing at the contact points between individual wires dominates the damping performance of MR products, but few people concern the effects of the dimension of metal rubber on the mechanical characteristics including modulus and damping. In order to discover the influencing laws of initial height and initial bearing area of metal rubber on its properties, three batches of MR specimens were fabricated and a series of experiments were carried out.

This study describes the manufacturing and testing of metal rubber (MR) samples made of stainless steel, and subjected to compression-compression loading in quasi-static regime. Three batches of MRs with different dimensions and similar relative density have been fabricated, and their mechanical properties (tangent modulus and loss factor) have been investigated and compared at different strains and under cyclic loading. The experiments show the significant effect of the MRs’ initial height and bearing area over the global mechanical compression properties, with the loss factor decreasing in samples with higher height and smaller bearing area, and the tangent modulus increasing with higher height. The phenomenon was explained by the MR spiral wire model, which employed MR’s boundary effect and different contact types of interaction. When a metal rubber sample is manufactured, the final process is to be formed in a specially designed mold by applying a compressive force, the MR is then shaped in the mold, and when the compressive force gradually decreases, the MR will rebound along molding direction, but restricted by the mold along the non-molding directions. This manufacturing process causes the different properties between the boundary and the inner part of the metal rubber solid, and the different contact types between individual wires contribute to the different properties. In this work, MR samples with different height were tested and compared, the results were consistent with the analysis that the boundary part along molding direction has more slip interaction, and samples with different bearing area were tested and compared to investigate the boundary effect along non-molding directions, the results were consistent with the analysis that this boundary part has more stick interaction. The results show that the dimension effect should be considered in the design of vibration dampers made with MR material, and we can control the mechanical properties of MR component by changing the size and combination form.
Thermo Fluid Dynamic Analysis of a Gas Turbine Transition-Piece
Authors: Da Soghe Riccardo , Bianchini Cosimo , Andreini Antonio , Mazzei Lorenzo , Riccio Giovanni , Marini Alessandro , Ciani Alessandro
Published: September 2014

The transition-piece of a gas turbine engine is subjected to high thermal loads as it collects high temperature combustion products from the gas generator to a turbine. This generally produces high thermal stress levels in the casing of the transition piece, strongly limiting its life expectations and making it one of the most critical components of the entire engine. The reliable prediction of such thermal loads is hence a crucial aspect to increase the transition-piece life span and to assure safe operations. The present study aims to investigate the aero-thermal behaviour of a gas turbine engine transition-piece and in particular to evaluate working temperatures of the casing in relation to the flow and heat transfer situation inside and outside the transition-piece. Typical operating conditions are considered to determine the amount of heat transfer from the gas to the casing by means of CFD. Both conjugate approach and wall fixed temperature have been considered to compute the heat transfer coefficient, and more in general, the transition-piece thermal loads. Finally a discussion on the most convenient heat transfer coefficient expression is provided.
Fluid Properties at Gas Turbine Inlet due to Fogging Considering Evaporation and Condensation Phenomena as Well as Icing Risk
Authors: Günther Christoph , Joos Franz
Published: September 2014

This study reports on numerically calculated thermophysical properties of air entering a gas turbine compressor after passing through an intake duct affected by different cooling techniques. Case of reference is unaffected ambient air (referenced to as unaffected) passing the intake duct. Furthermore ambient air cooled down to wet bulb temperature by (overspray) fogging (referenced to as wet) was considered. The third case shows air cooled down to the same temperature as it was reached in the wet case but by using chillers (referenced to as chilled). Equilibrium and non-equilibrium properties according to the occurring evaporation and condensation phenomena were compared. Equilibrium conditions seems to have a reduced inlet icing risk for the wet case compared to the chilled case. However comparing the wet case to the unaffected case showed a higher icing risk for the wet case at low ambient relative humidity. In contrast to equilibrium conditions a consideration of non-equilibrium conditions resulted in an increased icing risk due to almost negligible condensation rates.
Experimental Investigation of a Fuel Flexible Generic Gas Turbine Combustor With External Flue Gas Recirculation
Authors: Fischer Stefan , Kluß David , Joos Franz
Published: September 2014

Flue gas recirculation in combined cycle power plants using hydrocarbon fuels is a promising technology for increasing the efficiency of the post combustion carbon capture and storage process. However, the operation with flue gas recirculation significantly changes the combustion behavior within the gas turbine.

In this paper the effects of external flue gas recirculation on the combustion behavior of a generic gas turbine combustor was experimentally investigated. While prior studies have been performed with natural gas, the focus of this paper lies on the investigation of the combustion behavior of alternative fuel gases at atmospheric conditions, namely typical biogas mixtures and syngas. The flue gas recirculation ratio and the fuel mass flow were varied to establish the operating region of stable flammability.

In addition to the experimental investigations, a numerical study of the combustive reactivity under flue gas recirculation conditions was performed.

Finally, a prediction of blowout limits was performed using a perfectly stirred reactor approach and the experimental natural gas lean extinction data as a reference. The extinction limits under normal (non-vitiated) and flue gas recirculation conditions can be predicted well for all the fuels investigated.
Design and Characterization of an Inlet Duct for Mass Flow Measurement in a Micro Gas Turbine Test Rig
Authors: Buratto C. , Carandina A. , Morini M. , Pavan C. , Pinelli M. , Spina P. R.
Published: September 2014

In this paper, a test rig for experimentation on a micro gas turbine is presented. The test rig consists of a micro gas turbine Solar T-62T-32, which, coupled with a 50 kVA alternator, can supply electrical energy to a calibrated resistive load bank. Particular attention is paid to the design of the inlet duct for the mass flow rate measurement. The basic issue was to create the intake duct for a micro gas turbine (MGT) test rig, in order to provide precise data about the mass flow rate and the thermodynamic air characteristics in the MGT inlet section. The inlet duct is also designed in order to allow future tests on inlet cooling technologies.

The MGT is incorporated in a chassis for noise reduction, the dimensions of which are 540 mm (height), 570 mm (width) and 940 mm (length). These small dimensions lead to problems with the insertion of the duct. Moreover, the intake of the compressor is not axial but radial, and this means that a volute must be foreseen to convey the flux into the MGT.

Several shapes of volute are analyzed in this paper, considering the effects on the pressure loss and the induction of turbulence. The challenge was to develop a fluid-dynamically efficient duct with the hindrance of a very small available space between the compressor casing, the gearbox and the fuel pipes inside the narrow noise-reduction chassis.

The mass flow rate will be computed by means of the differential static pressure between the upstream and the downstream section of a Venturi tube. The choice of a Venturi was due to the fact that it produces a pressure loss lower than any other device, such as orifice plates or other nozzle shapes. Furthermore, the expected mass flow rate would lead to high fluid speeds and, as a consequence, the diameter ratio between the duct and the throat of the Venturi was chosen to be as high as possible.
Uncertainty Quantification, Rare Events and Mission Optimization: Stochastic Variations of Metal Temperature During a Transient
Authors: Montomoli F. , Amirante D. , Hills N. , Shahpar S. , Massini M.
Published: September 2014

Gas turbines are designed to follow specific missions and the metal temperature is usually predicted with deterministic methods. However, in real life the mission is subjected to strong variations which can affect the thermal response of the components. This paper presents a stochastic analysis of the metal temperature variations during a gas turbine transient.

A Monte Carlo Method (MCM) with Meta Model is used to evaluate the probability distribution of the stator disk temperature. The MCM is applied to a series of CFD simulations of a stator well, whose geometry is modified according to the deformations predicted during the engine cycle by a coupled thermo-mechanical analysis of the metal components. It is shown that even considering a narrow band for the stochastic output, +/− σ, the transient thermal gradients can be up to two orders of magnitude greater than those obtained with a standard deterministic analysis. Moreover, a small variation in the tail of the input probability density function, a rare event, can have serious consequences on the uncertainty level of the temperature.

Rare events although inevitable they are not usually considered during the design phase. In this paper it is shown for the first time that is possible to mitigate their effect, minimizing the maximum standard deviation induced by the tail of the input PDF. The mission optimization reduces the maximum standard deviation by 15% and the mean standard deviation of about 12%. The maximum thermal gradients are also reduced by 10%, although this was not the parameter used as the goal in the optimisation study.
Air Distribution Over a Combustor Liner
Authors: Jiang Leiyong , Corber P. Andrew
Published: September 2014

The splitting of the airflow that passes through the openings in the combustor liner is vital to its performance. Traditionally, numerical simulations of the gas turbine combustor have limited the computational domain to only the flow field inside the liner, while the airflow distribution over the liner is estimated based on semi-empirical correlations. In addition, the airflow rates are assumed to be the same through the identical open passages at each combustor axial cross-section. In the present study, the internal and external flow fields of a practical gas turbine combustor liner are directly coupled, so the air splitting is determined by comprehensive simulations. The predicted results for the air distribution are closely correlated to the dataset estimated from recently improved semi-empirical correlations for passage discharge-coefficients. The simulations also show that the effects of the combustion process on the air splitting can be neglected. Lastly, the results reveal that the airflow through identical passages at the same axial cross-section are not equal, and can vary by up to ±25% of the mean. In summary, the present study suggests that when performing computational models of gas turbine combustor flows, the simulations should couple the liner’s internal and external air splits whenever possible.
Smoothing Techniques for Real-Time Turbine Speed Sensors
Authors: Gutierrez Louis Alberto , Pezzini Paolo , Tucker David , Banta Larry
Published: September 2014

A data noise reduction model for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (HyPer) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior.

The system is controlled by an embedded real-time control platform provided by Woodward Industrial Control. Every sensor is monitored by the platform, and an overall strategy drives the system from start-up to shut-down. Fuel is regulated by a valve which reacts based on the speed of the turbine. There are three optical encoder sensors which are used to monitor turbine speed, and the average of these three sensors is used as feedback for a PID controller, which works to regulate fuel consumption to the combustor. The turbine speed has demonstrated fluctuation in certain conditions, which may be a result of data noise combined with a systemic instability in the flow to the turbine.

This research introduces the method of Double Exponential Smoothing as it is applied to data noise reduction in an embedded control platform. An experimental test was conducted to evaluate the performance of the fuel valve speed control when filtered by a real-time Double Exponential Smoothing Algorithm. The results demonstrate, that when compared with traditional filtering techniques, Double Exponential Smoothing offers a significant improvement in both signal volatility and data latency.
Flame Response Analysis of Syngas
Authors: Gorski Jan , Chishty Wajid Ali , Johnson Matthew
Published: September 2014

The motivation for the work comes from the requirement to assess the feasibility of using alternative fuels in lean-premixed land-based stationary gas turbine combustion systems. Lean-premixed systems are prone to combustion instability issues and the need is to determine how the use of alternative fuels would affect such instabilities.

The paper presents the results of an acoustically-forced laminar flat flame study that was conducted to measure the influence of flow velocity oscillations on the response of syngas flames under various operating conditions and in comparison to natural gas flames.

The results indicate that syngas concentration in a methane-syngas-air mixture significantly affects the flame response. On the other hand, the ratio of hydrogen-to-carbon monoxide in the syngas was found to have a negligible effect on the flame response for a fuel blend made up of 50% methane and 50% syngas. Flame liftoff distance and flame speed were found to be important parameters that govern the flame transfer function magnitude and resonant frequency for a thermally stabilized flat flame. The paper also presents insights into flame transfer function scaling based on a refined Strouhal definition.
The Use of CO2 to Improve Stability and Emissions of an IGCC Combustor
Authors: Lewis Jonathan , Marsh Richard , Valera-Medina Agustin , Morris Steven , Baej Hesham
Published: September 2014

The use of gas for power generation is likely to increase in the medium term. Also, the introduction of new fuels will ensure a higher generation with lower emissions under continuous operation. These scenarios lead to the conclusion that there will be a considerably more diverse range of fuel supply. However, the use of these new fuels contrasts with recent experiences of global operators who report increasing emissions and difficult combustion dynamics with even moderate variations in their fuel characteristics. Clearly there are significant challenges for fuel flexible gas turbines, particularly emission control, combustor dynamics and flame stability.

Trials using a power derivative gas turbine combustor and a high hydrogen content fuel produced unusual flashback events, in that flashback was induced by either leaning of the fuel mixture by the increase of combustion air, or by a change in composition through the reduction of methane pilot fuel. The introduction of CO2 through the combustors pilot injector prevented flashback from occurring under these circumstances. The resulting reduction of temperature in the combustion zone, indicated by lower burner tip temperatures causes a reduction in the emissions of nitrous oxides, whilst there is minimal effect on the effective turbine inlet temperature, only a 2.3% reduction.

Investigations using a ‘generic’, radial swirl burner and stereo PIV demonstrated how the flashback depended on a combination of flow structure augmentation and changes in mixture burning rate. The injection of methane or CO2 had differing effect on these parameters of the combustion zone, but both produced combinations that facilitated stability.
Modeling and Simulation of the Dynamic Operating Behavior of a High Solar Share Gas Turbine System
Authors: Felsmann Christian , Heide Stephan , Gampe Uwe , Freimark Manfred
Published: September 2014

Solar gas turbine (GT) systems provide the opportunity to utilize solar heat at a much higher temperature than solar thermal power plants based on steam turbine cycles. Therefore gas turbine technology has the potential to improve the efficiency of future solar thermal power plants. Nevertheless, to achieve mature technology for commercial application, further development steps are required. Knowledge of the operational behavior of the solar GT system is the basis for the development of the systems control architecture and safety concept.

The paper addresses dynamic simulation of high solar share GT systems, which are characterized by primary input of solar heat to the gas turbine. To analyze the dynamic operating behavior, a model with parallel arrangement of the combustion chamber and the solar receiver was set up. By using the Heaviside step function, the system dynamics were translated into transfer functions which are used to develop controllers for the particular system configuration. Two operating conditions were simulated to test the controller performance. The first case is the slow increase and decrease of solar heat flow, as part of a regular operation. The second case is an assumed rapid change of solar heat flow, which can be caused by clouds. For all cases time plots of critical system parameters are shown and analyzed.

The simulation results show much more complex system behavior compared to conventional GT systems. This is due to the additional solar heat source, large volumes and stored thermal energy as well as the time delay of energy transportation caused by the piping system.
Numerical Simulation of Enhancing the Exhaust Mixing by the Air-Tab Technique
Authors: Gu Rui , Xu Jinglei
Published: September 2014

In order to reduce the infrared radiation, and to improve the survival rates of the fighter, it is necessary to further enhance the mixing of the nozzle exhaust jet with the ambient air. A novel technology known as air-tab is adopted to enhance the exhaust mixing with the environment air in high bypass turbofan nozzle model. Numerical results show that: 1)The technology can flexibly adapt to the every condition of nozzle and keep the best mixing effect all the time, with very little flowfield loss; 2)The parameters present zigzag distribution. 3) High temperature region area has been reduced nearly 50% by the air-tab with the second mass flow rate only about 3% of total mass flow rate.
HAYNES NS-163 Alloy: A Novel Nitride Dispersion-Strengthened Co-Base Alloy
Authors: Fahrmann Michael G. , Deodeshmukh Vinay P. , Srivastava S. Krishna
Published: September 2014

HAYNES® NS-163® alloy was developed by Haynes International Inc. for high-temperature structural applications with a dual manufacturing approach in mind: the fabrication of components in the readily weldable and formable mill-annealed condition, and their subsequent strengthening by means of a gas nitriding process. The alloy was designed to be conducive to dispersion strengthening by virtue of the formation of internal Ti- and Nb-rich nitrides. Since this process is diffusion-controlled, component section thicknesses are presently limited to approximately 2.0 mm (0.080″). The paper presents key parameters of the devised commercial nitridation process and the resulting microstructures and mechanical properties of sheet samples, which originated from a production-scale heat. Oxidation resistance and the need for coatings at temperatures exceeding 980°C (1800°F) are addressed as well. It is shown that this new alloy has the potential to fill the gap between today’s strongest solid-solution strengthened alloys and the oxide-dispersion strengthened mechanically alloyed materials.
Experimental Investigations of Spark Ignition in a Model Combustor With Synthesis Gas
Authors: Zhang Xiaoyu , Zhong Di , Weng Fanglong , Zhu Min
Published: September 2014

The components of syngas derived from coal, biomass and waste are significantly different from those of typical gas turbine fuels, such as natural gas and fuel oils. The variations of hydrogen and inert gases can modify both the fluid and the combustion dynamics in the combustor. In particular, the characteristics of spark ignition can be profoundly affected. To understand the correlation between the varying fuel components and the reliability of ignition, a test system for spark ignition was established. The model combustor with a partial-premixed swirl burner was employed. The blending fuel with five components, hydrogen, carbon monoxide, methane, carbon dioxide and nitrogen, was used to model the synthesis gas used in industry. The ignition energy and the number of sparks leading to successful ignition were recorded. By varying the fuel components, the synthesis gases altered from medium to lower heat value fuels. The ignition time, ignition limit and subsequent flame developments with variations of air mass flow rates and fuel components were systematically investigated. With the increase of air flow, the syngas with a lower hydrogen content has a shorter ignition time compared with higher hydrogen syngas in the lean condition, whereas in the rich condition, syngas with a higher hydrogen content has a shorter ignition time. The effects of the hydrogen content, inlet air Reynolds number and spark energy on the ignition limit were investigated. The ignition limit was enlarged with increase in the hydrogen content and spark energy. Meanwhile, three distinct flame patterns after ignition were investigated. Finally, a map for the characteristics of the ignition and subsequent flame development was obtained. The results are expected to provide valuable information for the design and operation of stable syngas combustion systems and also provide experimental data for the validations of theoretical modelling and numerical computations.
A Novel Intake Concept for Flue Gas Recirculation to Enhance CCS in an Industrial Gas Turbine
Authors: Payne Robin C. , Arias Manuel , Stefanis Vassilis
Published: September 2014

For the next generation of combined cycles, it is essential to not only improve the performance of a gas turbine combined cycle power plant, but also reduce its environmental impact. Flue Gas Recirculation is a useful method to increase CO2 concentration in the exhaust stream, allowing a smaller and lower cost carbon capture plant than would be required without FGR. Conventional FGR methodology requires a complex mixer with long mixing section to achieve acceptable inlet conditions for the GT compressor. A novel approach is presented, where the method of introducing the flue gas to the compressor has been substantially rethought to provide a low cost and robust FGR solution for carbon capture and sequestration applications. In this paper, CFD analysis of the flow in the intake section is used to demonstrate the operating principle of such a method, and cycle modelling calculations to compare its performance with a more conventional approach.
Numerical Aero-Thermal Analysis of a Rib-Roughened Trailing Edge Cooling Channel at Different Rotation Numbers and Channel Orientations
Authors: Pascotto Matteo , Armellini Alessandro , Casarsa Luca , Spring Sebastian
Published: September 2014

The present work considers the aero-thermal characterization of a rib-roughened cooling channel for the trailing edge of gas turbine blades, and is based on previous findings from a smooth channel configuration. The passage is characterized by a trapezoidal cross section with high aspect-ratio, radial inlet flow, and coolant discharge at both model tip and trailing side, where seven elongated pedestals are installed. In this study, heat transfer augmentation is achieved by placing inclined squared ribs on the channel central portion.

RANS simulations with a SST turbulence model were performed using the commercial solver ANSYS CFX®v14. The numerical tool was first validated on the available experimental data and, subsequently, its capabilities were exploited in a wider range of working conditions, namely at higher rotation speed and different channel orientation. In this way it was possible to highlight the effects that ribs and working conditions have on the development of both flow and thermal fields.

The results show that rotation and channel orientation produce contrasting effects. On the rib-roughened wall, rotation/orientation generates an increase/decrease of the heat transfer; conversely, on the trailing side region rotation/orientation has a negative/positive effect on the thermal field.
An Experimental Study of the Load-Orientation Sensitivity of Three-Lobe Bearings
Authors: Khatri Rasish , Childs Dara W.
Published: September 2014

Static and dynamic performance test results are provided for a three-lobe bearing evaluated over the following range of radial static-load orientations (taken from the leading edge of the loaded pad): 0°, 20°, 30°, 40°, 80°, 90°, and 100°. Static and dynamic test results are evaluated to determine the sensitivity of the bearing to changes in the static load direction.

The bearing has the following specifications: 100o arc angle, 0.52 preload, 70% offset, 101.74 mm minimum bore diameter, 0.116 mm radial pad clearance, and 76.3 mm axial length. The bearing is tested at 6750 rpm, 9000 rpm, 10800 rpm, and 13200 rpm, and at five different unit loads. Static measurements include hot and cold clearances, static eccentricities, and pad metal temperatures. Dynamic results include stiffness coefficients, damping coefficients, and whirl-frequency ratios (WFRs).

Dynamic tests show that the three-lobe bearing is very sensitive to load orientation at low speeds and high loads. Kxx is highest for the 80°, 90°, and 100° load orientations. Kyy is highest for the 20°, 30°, and 40° load orientations. Kxy is highest for the 80°, 90°, and 100° load orientations. The magnitude of Kyx is highest for the 0° and 20° load orientations. Cxx is largest for the 80°, 90°, and 100° load orientations, and Cyy is largest for the 0°, 20°, 30°, and 40° load orientations.

In terms of WFRs, it is generally dynamically advantageous to orient the static load vector for this bearing towards the leading edge of the pad. WFRs at 6750 rpm with loads of 1149 kPa, 1723 kPa, and 2298 kPa are equal to zero when the static load vector is pointed towards the leading edge of the pad and between 0.25 and 0.5 when the static load vector points towards the trailing edge of the pad. The bearing is not sensitive to load orientation at high speeds and light loads. At 13200 rpm, measured WFRs are between 0.2 and 0.6 at all loads and for all load orientations. Measured WFRs at the no-load condition are approximately 0.5 at all speeds.

Static data showed that the 30° and 90° load orientations yielded slightly higher measured maximum pad-metal-temperature increases at each speed relative to the other load orientations. At the highest static-load magnitudes, the pad metal temperatures are not as dependent on load orientation. The 20°, 30°, and 40° load orientations had the smallest measured eccentricity ratio, and thus the highest static stiffness.
Comparative Study of Impinging Jet Array Heat Transfer on a Flat Plate Cooled by Superheated Steam and Air
Authors: Ma Chao , Wang Jianfei , Zang Shusheng , Ji Yongbin
Published: September 2014

In modern gas turbine, using superheated steam to cool the vane and the liner of combustion chamber is a promising alternative to traditional compressor air. Infrared camera was applied to measure the spatial distribution of the impingement heat transfer coefficient on a flat plate cooled by superheated steam and air in this paper. The experimental study revealed the distribution of local heat transfer coefficients over a flat plate cooled by steam and air in an array of 3×5 impinging jets module. Results showed that the impingement cooling heat transfer is enhanced by the increase of mass flow rate, and the superheated steam cooling could improve area averaged heat transfer performance 35.3∼83.0% more than air cooling in the same mass flow rate conditions in the experiment. The influence of the jet-to-plate spacing ratio (Zn/d) and the jet-to-jet spacing ratio (Yn/d) on heat transfer were also investigated. It was concluded that the heat transfer is enhanced with the increase of Yn/d or the decrease of Zn/d based on the same area. Furthermore, three-dimensional and steady state computations had been carried out for experimental operating conditions. The Numerical results and experimental data have good agreements with each other for both the area averaged Nu and the local Nu, so results of the numerical model are expecting reliable. Results based Numerical models showed detailed characteristics of the distribution of the velocity and turbulence level, which revealed underlying mechanisms of pressure loss and flow structure for steam cooing and air cooling respectively.
Effect of Corrugated Orifice and Pin-Fin on Multiple Array Impingement Cooling With Low Nozzle to Target Distance
Authors: Yang Li , Li Weihong , Chi Zhongran , Ren Jing , Jiang Hongde
Published: September 2014

Impingement cooling is widely used in turbine vanes and combustors. With the increase of turbine inlet temperature, high heat transfer coefficient and low pressure drop are required for cooling structures. A series of new impingement configurations combined with corrugated orifice and pin-fins were developed in the present work. Both transient liquid crystal (TLC) and pressure measurement were applied on the impingement cooling structures. A 3D numerical method was also used for conjugate heat transfer simulation. Corrugated orifice helps decrease the pressure drop by decreasing the speed of cross flow. Experimental data show that, corrugated orifice is helpful in reducing pin-fin induced pressure drop but contributes little to heat transfer. Pin-fins increases both the heat transfer and pressure drop lightly. Conjugate heat transfer simulation shows that pin-fins significantly reduce the metal temperature by conduction. Structures with pin-fins can make a good use of the large surface area of corrugated orifices.