bluuebunny/crossref_metadata_2025 huggingface dataset:
Cyclic Carbonation and Calcination Studies of Limestone and Dolomite for CO2 Separation From Combustion Flue Gases
Authors: Senthoorselvan Sivalingam , Gleis Stephan , Hartmut Spliethoff , Yrjas Patrik , Hupa Mikko
Published: August 2009

Naturally occurring limestone and dolomite samples, originating from different geographical locations, were tested as potential sorbents for carbonation/calcination based CO2 capture from combustion flue gases. Samples have been studied in a thermo gravimetric analyzer under a simulated flue gas conditions at three calcination temperatures, viz., 750°C, 875°C and 930°C for four Carbonation Calcination Reaction (CCR) cycles. The dolomite sample exhibited the highest rate of carbonation than the tested limestones. At 3rd cycle, its CO2 capture capacity per kg of sample was nearly equal to that of Gotland, the highest reacting limestone tested. At 4th cycle it surpassed Gotland, despite the fact that the CaCO3 content of Sibbo dolomite was only 2/3 of Gotland. Decay coefficients were calculated by a curve fitting exercise and its value is lowest for Sibbo dolomite. That means, most probably its capture capacity per kg of sample would remain higher, well beyond the 4th cycle. There was a strong correlation between the calcination temperature, specific surface area of the calcined samples and degree of carbonation. It was observed that higher the calcination temperature lower the sorbent reactivity. The BET measurements and SEM images provided quantitative and qualitative evidences to prove this. For a given limestone/dolomite sample, sorbent’s CO2 capture capacity was depend on the number of CCR cycles and the calcination temperature. In a CCR loop, if the sorbent is utilized only for a certain small number of cycles (<20), the CO2 capture capacity could be increased by lowering the calcination temperature. According to the equilibrium thermodynamics, the CO2 partial pressure in the calciner should be lowered to lower the calcination temperature. This can be achieved by additional steam supply into the calciner. Steam could then be condensed in an external condenser to single out the CO2 stream from the exit gas mixture of the calciner. A calciner design based on this concept is illustrated.
Remaining Life Assessment of Power Turbine Disks
Authors: Jin H. , Lowden P. , Pistor R.
Published: August 2009

This paper presents the results of a study conducted to determine the life expectancy of a power turbine disk. The purpose of the study is to revisit the original design calculations with current numerical computing techniques. By determining the state of stress and temperature in the vicinity of the stress concentrations, combined with material properties, the life expectancy of power turbine disks can be established.
Effect of Flame Structure on the Flame Transfer Function in a Premixed Gas Turbine Combustor
Authors: Kim Daesik , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic , Kim Kwanwoo , Srinivasan Shiva
Published: August 2009

The flame transfer function in a premixed gas turbine combustor is experimentally determined. The fuel (natural gas) is premixed with air upstream of a choked inlet to combustor. Therefore, the input to the flame transfer function is the imposed velocity fluctuations of the fuel/air mixture without equivalence ratio fluctuations. The inlet-velocity fluctuations are achieved by a variable-speed siren over the forcing frequency of 75–280 Hz and measured using a hot-wire-anemometer at the inlet to the combustor. The output function (heat release) is determined using chemiluminescence measurement from the whole flame. Flame images are recorded to understand how the flame structure plays a role in the global heat release response of flame to the inlet-velocity perturbation. The results show that the gain and phase of the flame transfer function depend on flame structure as well as the frequency and magnitude of inlet-velocity modulation and can be generalized in terms of the relative length scale of flame to convection length scale of inlet-velocity perturbation, which is represented by a Strouhal number. Non-linear flame response is characterized by a periodic vortex shedding from shear layer and the non-linearity occurs at lower magnitude of inlet-velocity fluctuation as the modulation frequency increases. However, for a given modulation frequency, the flame structure does not affect the magnitude of inlet-velocity fluctuation at which the non-linearity starts.
Dynamics and Stability Limits of Syngas Combustion in a Swirl-Stabilized Combustor
Authors: Speth Raymond L. , Altay H. Murat , Hudgins Duane E. , Ghoniem Ahmed F.
Published: August 2009

The combustion dynamics, stability bands and flame structure of syngas flames under different operating conditions are investigated in an atmospheric pressure swirl-stabilized combustor. Pressure measurements and high-speed video data are used to distinguish several operating modes. Increasing the equivalence ratio makes the flame more compact, and in general increases the overall sound pressure level. Very close to the lean blowout limit, a long stable flame anchored to the inner recirculation zone is observed. At higher equivalence ratios, a low frequency, low amplitude pulsing mode associated with the fluid dynamic instabilities of axial swirling flows is present. Further increasing the equivalence ratio produces unstable flames oscillating at frequencies coupled with the acoustic eigenmodes. Additionally, a second unstable mode, coupled with a lower eigen-mode of the system, is observed for flames with CO concentration higher than 50%. As the amount of hydrogen in the fuel is increased, the lean flammability limit is extended and transitions between operating regimes move to lower equivalence ratios.
Free-Stream Effects on the Cooling Performance of Cylindrical and Fan-Shaped Cooling Holes
Authors: Saumweber Christian , Schulz Achmed
Published: August 2009

From literature and our own studies it is known that the effects of hot gas cross-flow and in particular the turbulence of the hot gas flow highly influence the spreading of the coolant in the near hole vicinity. Moreover, the velocity of the hot gas flow expressed by a hot gas Mach number obviously plays a much more important role in case of diffuser holes than with simple cylindrical holes. To realize a certain blowing rate, a higher pressure ratio needs to be established in case of higher Mach numbers. This in turn may strongly affect the diffusion process in the expanded portion of a fan-shaped cooling hole. The said effects will be discussed in great detail. The effects of free-stream Mach number and free-stream turbulence, including turbulence intensity, integral length scale, and periodic unsteady wake flow will be considered. The comparative study is performed by means of discharge coefficients and by local and laterally averaged adiabatic film cooling effectiveness and heat transfer coefficients. Both cooling holes have a length-to-diameter ratio of 6 and an inclination angle of 30°. The fan-shaped hole has an expansion angle of 14°. The effect of the coolant cross-flow at the hole entrance is not considered in this study, i.e. plenum conditions exist at the hole entrance.
Experimental Investigation of Flow and Heat Transfer for Single and Multiple Rows of Circular Jets Impinging on a Concave Surface
Authors: Rama Kumar B. V. N. , Prasad B. V. S. S. S.
Published: August 2009

Flow and heat transfer characteristics for single and multiple rows of circular jets impinging on a concave surface are investigated experimentally. The dimensions of the concave target plate, impingement tube, orifice diameter, intra jet spacing are so selected that the present system represents a scaled-up (30:1) model for the leading edge of a typical gas turbine nozzle guide vane. The target plate is kept at a distance of one orifice diameter from the impingement tube, whilst the ratio of inter-jet distance to jet diameter is maintained at a value of 5.4. The parameters which are varied in the study include jet Reynolds number (Red = 2847–19300) and number of rows (nR = 1 and 5).The local dimensionless pressure and Nusselt number variations along the concave plate are presented at these parameters. A performance number named Thermo Hydrodynamic Performance Ratio (THPR) is introduced to evaluate different configurations on the basis of a combined pressure drop and heat transfer. Usage of multiple jets appears to offer much better THPR than that of single jet or single row of jets, for a chosen plenum condition.
Aeroelastic Properties of Closely Spaced Modes for a Highly Loaded Transonic Fan
Authors: Ma˚rtensson Hans , Gunnsteinsson Ste´fan Sturla , Vogt Damian M.
Published: August 2009

In the design of modern compressor blades of wide chord (low aspect ratio) type it is often hard to avoid having modes that are close to each other in frequency. Modes which are closely spaced can interact dynamically. Mistuning and localization of stresses are known problems with this. A potential problem with this is also the possibility of coalescence flutter of the modes. Even if the modes are frequency separated at zero rotational speed, the centrifugal stiffening may cause the modes to attract and even cross (or veer) at some rotational speed. In design, mode separation criteria are sometimes applied in order to minimize the risk of encountering unknown dynamic phenomena. This study is performed to better understand the dynamics of closely spaced modes with respect to risk for coalescence flutter. A reduced order aeroelastic system is then constructed that describes the interaction between the different modes. The aeroelastic couplings are then calculated for the 2 mode system. The method is general in terms of mode shapes and number of interacting modes. A parametrical study is performed in order to study how strongly the modes interact when the frequency separation is decreased and if there is a risk of destructive coalescence flutter. The investigation is performed on a high pressure ratio front stage fan blade. The tendency of the modes to interact depends on the strength of the coupling compared to the strength of the pure structural modes. The tendency towards instability was increased in cases where the stability margin was smaller of the single modes. The results can be considered to support a separation criterion of 2% for the lower. A re-evaluation should be considered if lighter blade material and increased loads are to be used.
Thermodynamic Equilibrium Analysis of Rice Husk Pyrolysis
Authors: Zhao Baofeng , Sun Li , Zhang Xiaodong , Chen Lei , Zhang Jie , Meng Guangfan , Meng Xiangmei
Published: August 2009

Pyrolysis of biomass materials can implement the efficient conversion of biomass to gaseous, liquid and solid energy products. Compared with experimental research which needs massive apparatus and funds and also takes long time, the computer simulation of biomass pyrolysis is more convenient and flexible to achieve the main characteristics of the process. Simulation of thermodynamic equilibrium for the pyrolysis of rice husk was studied in this paper. Based on the minimization of Gibbs free energy, MATLAB was used to calculate thermodynamic equilibrium for the pyrolysis of rice husk in the temperatures ranges from 523 K to 1723 K at intervals of 100 K. The results showed that the contents of H2 and CO increased rapidly with the temperature from 723 K to 1223 K, while the contents of H2O, CH4, CO2 and C decreased sharply. When the temperature was higher than 1223 K, the yields of H2 and CO reached the maximum of 51 mol% and 48 mol% respectively, and then kept stable. In order to be closer to experimental results, the constrain conditions of element C in tar was introduced in the calculations. The results indicated that, in the main components of tar from 523 K to 1223 K, the contents of naphthalene and toluene both decreased and then toluene vanished gradually. However, the content of benzene increased with increasing temperature and finally became the dominant product when the temperature was above 1300 K.
Weibull Distributions Applied to Cost and Risk Analysis for Aero Engines
Authors: Pascovici D. S. , Kyprianidis K. G. , Colmenares F. , Ogaji S. O. T. , Pilidis P.
Published: August 2009

This paper presents the use of Weibull formulation to the life analysis of different parts of the engine in order to estimate the cost of maintenance, the direct operating costs (DOC) and net present cost (NPC) of future type turbofan engines. The Weibull distribution is often used in the field of life data analysis due to its flexibility—it can mimic the behavior of other statistical distributions such as the normal and the exponential. The developed economic model is composed of three modules: a lifing module, an economic module and a risk module. The lifing module estimates the life of the high pressure turbine blades through the analysis of creep and fatigue over a full working cycle of the engine. The value of life calculated by the lifing is then taken as the baseline distribution to calculate the life of other important modules of the engine using the Weibull approach. Then the lower of the values of life of all the distributions is taken as time between overhaul (TBO), and used into the economic module calculations. The economic module uses the TBO together with the cost of labour and the cost of the engine (needed to determine the cost of spare parts) to estimate the cost of maintenance and DOC of the engine. In the present work five Weibull distributions are used for five important sources of interruption of the working life of the engine: Combustor, Life Limited Parts (LLP), High Pressure Compressor (HPC), General breakdowns and High Pressure Turbine (HPT). The risk analysis done in this work shows the impact of the breakdown of different parts of the engine on the NPC and DOC, the importance that each module of the engine has in its life, and how the application of the Weibull theory can help us in the risk assessment of future aero engines. A detailed explanation of the economic model is done in two other works (Pascovici et. al. [6] and Pascovici et. al. [7]), so in this paper only a general overview is done.
Investigation in the Eccentricity of Spoke Centered Turbomachinery Components
Authors: Stumvoll Alexander K. , Kau Hans-Peter
Published: August 2009

A spoke centered fixing arrangement is a typical design element in gas turbine machinery. It is used to mount two annular components concentrically allowing for free relative movement in radial direction due to different elongations caused by temperature gradients. In most cases the outer part represents the absolute coordinate system the inner ring has to be centered in reference to. Several tab slot combinations are used to provide the desired degree of freedom while guaranteeing the inner ring’s concentrical position. Typically the inner ring is equipped with pins sliding in the opposite lying slots of the outer ring. The arrangement requires at least three tab slot combinations, called spokes, between fixed and floating rings. A typical application is for example an inner air seal ring mounted concentrically to the guide vane ring of a gas turbine. Mountability demands clearance between tab and slot surfaces. Associated manufacturing tolerances lead to a certain eccentricity bandwidth for the floating inner ring. The eccentricity was investigated using commercial statistical tolerance analysis software. Since contact between the two rings is only established at three spokes according to acting forces and geometric proportions influenced by tolerances, a contact definition can’t be made before the actual simulation. Therefore, the software’s functionality had to be extended to allow automatic contact definition according to the above mentioned influences. An adaptable simulation model was developed in order to provide a basis of decision making regarding future spoke design parameters. Based on a typical spoke centering design a parameter study with respect to the number of spokes and with respect to a variation of tab and slot dimension tolerances was accomplished. The parameter study showed that the eccentricity mean value decreases with an increasing number of spokes. The mean value was found to approximate the nominal circumferential gap between tab and slot already at low spoke numbers. Lower mean values are hypothetically possible down to the minimum gap between tab and slot surface pairings. The number of spokes would therefore have to be infinite. The corresponding eccentricity standard deviation was also found to decrease with an increasing number of spokes. The investigation revealed that the eccentricity mean value interestingly also declines at higher spoke numbers with increasing tab and slot dimension tolerances. The standard deviation however increases in that case. This opposed effect may be neutralized, such that the upper limit of the eccentricity bandwidth and therefore the maximum eccentricity remains almost constant while broadening the tolerance bandwidths.
An Acoustic Modal Analysis of a DLE Combustion System
Authors: Yu Lingli , Cashmore Mick
Published: August 2009

This paper presents a methodology used in a study of acoustic modal properties of a DLE combustion system. An enclosure of a simple cylinder was taken as a benchmark study example of acoustics before the acoustic modal properties of the combustion system was examined. The FE code of ABAQUS was used for the acoustic simulation. The sine sweep excitation and known volume velocity technique was used for the acoustic testing. Excellent results were obtained on both test and simulation compared with the exact analytical solution for a given frequency range. The benchmark study shows that while for testing, a 3D microphone matrix (expensive instrumentation) is needed for measuring all potential natural frequencies and modeshapes, the FE code of ABAQUS can readily be used for a 3D system with a good degree of accuracy. Simulation and testing were then extended to a single leg of combustor model. Again good agreement was achieved between the test and simulation. The comparison shows that for frequencies within the given range, all predicted frequencies can be found in the test with errors less than 5%. The sensitivity of acoustic response to the varied acoustic boundary conditions was also studied using this model. The study suggested a complete model with all included combustion cans was necessary for a better prediction. Based on the studies above, A FE model was developed for the complete 8-can combustion system. The simulation of the complete model shows that the model is able to replicate the acoustic modal characteristic seen in engine test. Using this model the influence of cross-talk between the adjacent cans, the sensitivity of geometry configuration, the acoustic properties and boundaries can be examined.
Numerical Investigation of Flame Flashback Into Swirling Flow
Authors: Tangermann Eike , Pfitzner Michael
Published: August 2009

A lean premixed swirl burner configuration has been investigated numerically regarding its vulnerability with respect to flame flashback caused by combustion induced vortex breakdown (CIVB). The flashback phenomenon has been simulated using a simplified quasi two-dimensional URANS method to cover a large range of operational conditions and using Large-Eddy-Simulation to achieve a detailed view of the processes involved. The Lindsted-Vaos turbulent premixed combustion model supplemented with quenching models has been used in URANS simulations. In the LES the combustion has been modeled with a thickened flame model using a one-step reaction mechanism. The isothermal flow and the stable flame were validated and flashback limits for different operational conditions were determined.
Torsional Vibration, in Rotordynamic System, Identified by Monitoring Gearbox Behaviour
Authors: Naldi Lorenzo , Biondi Roberto , Rossi Valerio
Published: August 2009

Nowadays the wide diffusion of the electrical machines, used for power generation, or as driver/helper in Oil&Gas applications, have amplified the problematic related to train torsional excitation. The standard instrumentation installed on the train does not permit to monitor and analyze this kind of stress; therefore to define criteria to screen torsional alternating stress by lateral vibrations becomes extremely important. This paper describes the experience achieved by the authors in the study of rotordynamic behavior of some geared train with the goal to define a methodology to analyze torsional stresses adopting industrial proximity probes (installed in the gear) or a non intrusive measurement system (optical probes). In order to confirm the last technology, an additional classic strain gage torsional measurement has been adopted obtaining similar results. An extensive part of this paper is dedicated to illustrate several test campaigns performed in different site where customers highlighted abnormal vibration levels. Finally, a wide description of data post processing and consequent conclusions are offered.
Advanced TBC Systems by Vapor Deposition Using LPPS Thin Film
Authors: von Niessen K. , Eschendorff G. , Gindrat M. , Refke A.
Published: August 2009

LPPS-Thin Film is a vacuum plasma spray technology recently developed by Sulzer Metco. In comparison to conventional Vacuum Plasma Spraying (VPS) or Low Pressure Plasma Spraying (LPPS), LPPS-Thin Film uses a working pressure below 2 mbar and a high energy plasma gun. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An additional new feature of LPPS-Thin Film is the possibility to deposit a coating not only from liquid splats by melting the feed stock material but also from gas phase by vaporizing the injected material. The coatings produced from vapor phase show similar structures to EB-PVD layers. The coating thickness can vary from only a few microns up to more than 300 μm. The LPPS-Thin Film process fills the gap between conventional PVD/CVD technologies (≤ 1–5 μm) and standard thermal spray processes (≥ 50 μm). However the concept of “Thin-Film” not only refers to the thickness of the coating. In particular the vaporizing of ceramic coating material also enables new layer properties in a domain between thermal spray and EB-PVD. Yttria Stabilized Zirconia (YSZ) can be deposited with a columnar microstructure. Lab investigations show that these coatings have potential for lower thermal conductivity and higher thermal stress tolerance compared to standard EB-PVD layers.
Designing LP Turbines for Optimized Airfoil Lift
Authors: Gier Jochen , Franke Matthias , Hu¨bner Norbert , Schro¨der Thomas
Published: August 2009

In the last 10 to 15 years substantial effort has been spent on increasing the airfoil lift especially in aero engine low pressure turbines. This has been attractive, since increased airfoil lift can be used for airfoil count decrease leading to weight and hardware cost reduction. The challenge with this effort consequently has been to keep the efficiency at high levels. Depending on the baseline level of airfoil lift, an increase of 20% to 50% has been realized and at least partly incorporated in modern turbine designs. With respect to efficiency there is actually an optimum level of airfoil lift. Airfoil rows at a lift level below this optimum suffer from an excessive number of airfoils with too much wetted surface and especially increasing trailing edge losses. Airfoils at lift levels above this optimum suffer from growing losses due to high peak Mach numbers inside the airfoil row, higher rear diffusion on the airfoil suction sides and increasing secondary flow losses. Since fuel cost have been rising significantly as has been the awareness of the environmental impact of CO2, it becomes more and more important to design LP turbines for an optimal trade between efficiency and weight to achieve the lowest engine fuel burn. This paper summarizes work done recently and in the past to address the main influences and mechanisms of the airfoil lift level with respect to losses and efficiency as a basis for determination of optimal airfoil lift selection.
Micro Combined Plant With Gas Turbine and Organic Cycle
Authors: Caresana Flavio , Comodi Gabriele , Pelagalli Leonardo , Vagni Sandro
Published: August 2009

In this paper we discuss the usefulness of a bottoming cycle applied to a micro size gas turbine unit to enhance its electric performance. A commercial 100 kWe micro gas turbine is used as a topping system; a basic thermodynamic analysis is performed to define the principal characteristics of viable vapour bottoming cycles. The analysis points to a solution adopting an Organic Rankine Cycle (ORC) with R245fa as working fluid, due both to environmental constrains and to technical criteria.
Influence of Active Methods of Flow Control on Compressor Blade Cascade Flow
Authors: Matejka Milan , Popelka Lukas , Safarik Pavel , Nozicka Jiri
Published: August 2009

This paper deals with active methods of flow control, especially synthetic jet flow control. A synthetic jet was used for flow control in the compressor blade cascade to reduce the vortex structure and reduce the value of the loss coefficients. The output slot of the synthetic jet actuator was situated on the side wall on the connecting line of the leading edges of the blades. The direction of the synthetic jet was perpendicular to the main flow. The synthetic jet excitation is more effective and more efficient than a steady blowing or suction, and its great advantage is zero mass flux supplied to, or taken from the main flow. A positive influence of the synthetic jet on the flow field was proved. The flow field was also visualized.
Application of an Object-Oriented CFD Code to Heat Transfer Analysis
Authors: Mangani Luca , Andreini A.
Published: August 2009

This paper is aimed at showing the performances obtained with an open-source CFD code for heat transfer predictions after the addiction of specific modules. The development steps to make this code suitable for such simulations are described in order to point out its potentiality as a customizable CFD tool, appropriate for both academic and industrial research. The C++ library, named OpenFOAM, offers specific class and polyhedral finite volume operators thought for continuum mechanics simulations as well as built-in solvers and utilities. To make it robust, fast and reliable for RANS heat transfer predictions it was indeed necessary to implement additional submodules. The package coded by the authors within the OpenFOAM environment includes a suitable algorithm for compressible steady-state analysis. A SIMPLE like algorithm was specifically developed to extend the operability field to a wider range of Mach numbers. A set of Low-Reynolds eddy-viscosity turbulence models, chosen amongst the best performing in wall bounded flows, were developed. In addition an algebraic anisotropic correction, to increase jets lateral spreading, and an automatic wall treatment, to obtain mesh independence, were added. The results presented cover several types of flows amongst the most typical for turbomachinery and combustor gas turbine cooling devices. Impinging jets were investigated as well as film and effusion cooling flows, both in single and multi-hole configuration. Numerical predictions for wall effectiveness and wall heat transfer coefficient were tested against standard literature and in-house set-up experimental results. The numerical predictions obtained proves to be in-line with the equivalent models of commercial CFD packages obtaining a general good agreement with the experimental results. Moreover during the tests OpenFOAM code has shown a good accuracy and robustness, as well as an high flexibility in the implementation of user-defined submodules.
A Study of the Effect of Non-Linear Damping on Mistune Behaviour of a Turbine Rotor
Authors: Elliott Bob , Wardle Michael E. , Bellamy Robert A.
Published: August 2009

Numerous papers have been presented over the years by different researchers investigating the effects of mistuning on the dynamic behaviour of bladed disks in turbomachinery. There are probably also an equal number of studies into the use of friction dampers to control blade amplitudes in tuned bladed disk assemblies. The combined impact of these two effects (mistune and damping) however has received relatively little attention until recently. Significant progress has now been made in software developments that allow both phenomena to be modelled simultaneously in an efficient manner. By using one such proprietary code this paper investigates the relative contributions of local and whole system damping to the distribution of turbine blade amplitudes. The study then goes on to quantify what happens if damping is progressively lost through wear, environmental degradation or mis-assembly. Initially a statistical approach is used to establish the range of amplitudes in a simulated fleet of simple blisks with 24 blades. This is followed by more detailed studies of a subset of the rotors representing typical, lively & quiet arrangements. Finally, an example of a real bladed disk is presented to demonstrate how the effects observed and conclusions reached may be more generally applicable.
Cavity Effects on the Design of Turbine Profiled End Walls
Authors: Gisbert Fernando , Corral Roque , Chia Juan Mauricio , Lo´pez Carlos
Published: August 2009

The minimization of the secondary losses of a low-pressure turbine row by modifying its end walls, using a gradient-based optimization method is presented. The cavities of the turbine row are included in the simulation and the comparison with the case without cavities is discussed. It is concluded that the presence of the cavity alters significantly the horseshoe vortex and the profiled end-walls just affect the passage vortex and hence larger amplitudes are required to control the flow. A method for the fast and automatic meshing of the domain, which is essential for the optimization process, is also described.
The Dynamics of the Vorticity Field in a Low Solidity Axial Turbine
Authors: Barmpalias K. G. , Kalfas A. I. , Chokani N. , Abhari R. S.
Published: August 2009

A current trend in turbomachinery design is the use of low solidity axial turbines that can generate a given power with fewer blades. However, due to the higher turning of the flow, relative to a high solidity turbine, there is an increase in secondary flows and their associated losses. In order to increase the efficiency of these more highly loaded stages, an improved understanding of the mechanisms related to the development, evolution and unsteady interaction of the secondary flows is required. An experimental investigation of the unsteady vorticity field in highly loaded stages of a research turbine is presented here. The research turbine facility is equipped with a two-stage axial turbine that is representative of the high-pressure section of a steam turbine. Steady and unsteady area measurements are performed, with the use of miniature pneumatic and fast response aerodynamic probes, in closely spaced planes at the exits of each blade row. In addition to the 3D total pressure flowfield, the multi-plane measurements allow the full three-dimensional time-resolved vorticity and velocity fields to be determined. These measurements are then used to describe the development, evolution and unsteady interaction of the secondary flows and loss generation. Particular emphasis is given to the vortex stretching term of the vorticity transport equation, which gives new insight into the vortex tilting and stretching that is associated with the secondary loss generation.
Comparison of a Conventional Thermal Analysis of a Turbine Cascade to a Full Conjugate Heat Transfer Computation
Authors: Starke Christoph , Janke Erik , Hofer Toma´sˇ , Lengani Davide
Published: August 2009

Recent development in commercial CFD codes offers possibilities to include the solid body in order to perform conjugate heat transfer computations for complex geometries. The current paper aims to analyse the differences between a conjugate heat transfer computation and conventional uncoupled approaches where a heat transfer coefficient is first derived from a flow solution and then taken as boundary condition for a thermal conduction analysis of the solid part. Whereas the thermal analyses are done with a Rolls-Royce in-house finite element code, the CFD as well as the conjugate heat transfer computation are done using the new version 8 of the commercial code Fine Turbo from Numeca International. The analysed geometry is a turbine cascade that was tested by VKI in Brussels within the European FP6 project AITEB 2. First, the paper presents the aerodynamic results. The pure flow solutions are validated against pressure measurements of the cascade test. Then, the heat transfer from flow computations with wall temperature boundary conditions is compared to the measured heat transfer. Once validated, the heat transfer coefficients are used as boundary condition for three uncoupled thermal analyses of the blade to predict its surface temperatures in a steady state. The results are then compared to a conjugate heat transfer method. Therefore, a mesh of the solid blade was added to the validated flow computation. The paper will present and compare the results of conventional uncoupled thermal analyses with different strategies for the wall boundary condition to results of a conjugate heat transfer computation. As it turns out, the global results are similar but especially the over-tip region with its complex geometry and flow structure and where effective cooling is crucial shows remarkable differences because the conjugate heat transfer solution predicts lower blade tip temperatures. This will be explained by the missing coupling between the fluid and the solid domain.
Exhaust Gas Recirculation in DLN F-Class Gas Turbines for Post-Combustion CO2 Capture
Authors: ElKady Ahmed M. , Evulet Andrei , Brand Anthony , Ursin Tord Peter , Lynghjem Arne
Published: August 2009

This paper describes experimental work performed at General Electric, Global Research Center to evaluate the performance and understand the risks of using Dry Low NOx (DLN) technologies in Exhaust Gas Recirculation (EGR) conditions. Exhaust Gas Recirculation is viewed as an enabling technology for increasing the CO2 concentration of the flue gas while decreasing the volume of the post-combustion separation plant and therefore allowing a significant reduction in CO2 capture cost. A research combustor was developed for exploring the performance of nozzles operating in low O2 environment at representative pressures and temperatures. A series of experiments in a visually accessible test rig have been performed at gas turbine pressures and temperatures, in which inert gases such as N2/CO2 were used to vitiate the fresh air to the levels determined by cycle models. Moreover, the paper will discuss experimental work performed using a DLN nozzle used in GE’s F-class heavy-duty gas turbines. Experimental results using a research combustor operating in partially premixed mode, incorporate the effect of applying EGR on operability, efficiency and emissions performance under conditions of up to 40% EGR. Experiments performed in fully premixed mode using DLN single nozzle combustor revealed that further reductions in NOx could be achieved and at the same time still complying with CO emissions. While most existing studies concentrate on limitations related to the Minimum Oxygen Concentration (MOC) at the combustor exit, we report the importance of CO2 levels in the oxidizer. This limitation is as important as the MOC and it varies with the pressure and firing temperatures.
An Experimental Investigation of the Wake Shed From a High-Lift Low Pressure Turbine Cascade at Different Reynolds Numbers
Authors: Satta Francesca , Ubaldi Marina , Zunino Pietro , Schipani Claudia
Published: August 2009

The paper presents the results of an experimental investigation of the wake shed from a high-lift low-pressure turbine profile. Measurement campaigns have been carried out in a three-blade large-scale turbine linear cascade. The Reynolds number based on the chord length has been varied in the range 100000–500000, to differentiate the influence of the boundary layer separation on the wake development. Two Reynolds number conditions, representative of the typical working conditions of a low pressure aeroengine turbine, have been more extensively investigated. Mean velocity and Reynolds stress components within the wake shed from the central blade have been measured across the wake by means of a two-component crossed miniature hotwire probe. The measuring traverses were located at distances ranging between 2 and 100% of the blade chord from the central blade trailing edge. Moreover, wake integral parameters, at the two Reynolds conditions, have been evaluated and compared. Both velocity and total pressure results show a wider wake occurring at the lower Reynolds number, due to the separation affecting the suction side boundary layer. Furthermore, the momentum thickness has been found to be much higher at the lower Reynolds number, due to the higher losses related to the separation bubble occurring on the blade suction side. The Strouhal number associated with the vortex shedding seems to be influenced by the Reynolds number, due to the different conditions of the suction side boundary layers.
Prospects for Sub Sea Wet Gas Compression
Authors: Brenne Lars , Bjo̸rge Tor , Bakken Lars E. , Hundseid O̸yvind
Published: August 2009

Wet gas compression technology renders possible new opportunities for future gas/condensate fields by means of sub sea boosting and increased recovery for fields in tail-end production. In the paper arguments for the wet gas compression concept are given. At present no commercial wet gas compressor for the petroleum sector is available. StatoilHydro projects are currently investigating the wet gas compressors suitability to be used and integrated in gas field production. The centrifugal compressor is known as a robust concept and the use is dominant in the oil and gas industry. It has therefore been of specific interest to evaluate its capability of handling wet hydrocarbon fluids. Statoil initiated a wet gas test of a 2.8 MW single-stage compressor in 2003. A full load and pressure test was performed using a mixture of hydrocarbon gas and condensate or water. Results from these tests are presented. A reduction in compressor performance is evident as fluid liquid content is increased. The introduction of wet gas and the use of sub sea solutions make more stringent demands for the compressor corrosion and erosion tolerance. The mechanical stress of the impeller increases when handling wet gas fluids due to an increased mass flow rate. Testing of different impeller materials and coatings has been an important part of the Statoil wet gas compressor development program. Testing of full scale (6–8 MW) sub sea integrated motor-compressors (dry gas centrifugal machines) will begin in 2008. Program sponsor is the A˚sgard Licence in the North Sea and the testing takes place at K-lab, Norway. Shallow water testing of a full scale sub sea compressor station (12.5 MW) will begin in 2010 (2 years testing planned). Program sponsor is the Ormen Lange Licence.
Aerodynamic Asymmetry Analysis of Unsteady Flows in Turbomachinery
Authors: Ekici Kivanc , Kielb Robert E. , Hall Kenneth C.
Published: August 2009

A nonlinear harmonic balance technique for the analysis of aerodynamic asymmetry of unsteady flows in turbomachinery is presented. The present method uses a mixed time-domain/frequency-domain approach that allows one to compute the unsteady aerodynamic response of turbomachinery blades to self-excited vibrations. Traditionally, researchers have investigated the unsteady response of a blade row with the assumption that all the blades in the row are identical. With this assumption the entire wheel can be modeled using complex periodic boundary conditions and a computational grid spanning a single blade passage. In this study, the steady/unsteady aerodynamic asymmetry is modeled using multiple passages. Specifically, the method has been applied to aerodynamically asymmetric flutter problems for a rotor with a symmetry group of two. The effect of geometric asymmetries on the unsteady aerodynamic response of a blade row is illustrated. For the cases investigated in this paper, the change in the diagonal terms (blade on itself) dominated the change in stability. Very little mode coupling effect caused by the off-diagonal terms was found.
Unsteady Effects on Transonic Turbine Blade-Tip Heat Transfer
Authors: Atkins N. R. , Thorpe S. J. , Ainsworth R. W.
Published: August 2009

In a gas turbine engine the blade-tips of the high-pressure turbine are exposed to high levels of convective heat transfer due to the so-called tip-leakage phenomenon. The blade-lift distribution is known to control the flow distribution in the blade tip-gap. However, the interaction between upstream nozzle guide vanes and the rotor blades produces a time-varying flow field that induces varying flow conditions around the blade and within the tip-gap. Extensive measurements of the unsteady blade-tip heat transfer have been made in an engine representative transonic turbine. These include measurements along the mean camber line of the blade-tip which have revealed significant variation in both time-mean and time-varying heat flux. The influences of potential interaction and the vane trailing edge have been observed. Numerical calculations of the turbine stage using a Reynolds averaged Navier-Stokes based computational fluid dynamics code have also been conducted. In combination with the experimental results these have enabled the time-varying flow-field to be probed in the blade-relative frame of reference. This has allowed a deeper analysis of the unsteady heat transfer data, and the quantification of the impact of vane potential field and vane trailing edge interaction on the tip-region flow and heat transfer. In particular, the separate effects of time-varying flow temperature and heat transfer coefficient have been established.
Design of a Low Solidity Flow-Controlled Stator With Coanda Surface in a High Speed Compressor
Authors: Guendogdu Y. , Vorreiter A. , Seume J. R.
Published: August 2009

Aerofoil active flow control has been attempted to increase the permissible loading of boundary layers in gas turbine components. Steady suction and blowing, pulsing and synthetic jets are all means to remove low energy flow, replace momentum deficits, or promote mixing to inhibit boundary layer separation. A curved surface near the trailing edge (“Coanda surface”) is another technique used to control aerofoil boundary layer separation. This paper presents the design of a stator with active flow control for a high speed compressor using a Coanda surface. The Coanda surface is located behind an injection slot on the aerofoil suction side of the first stage of a four-stage high speed research compressor. The design method and the present results are based on steady numerical calculations. The design intent is to reduce the number of vanes. This active flow control is used to maintain the flow exit angle of the reference stator despite the resulting increase in stator loading. It is shown that the solidity of the flow-controlled stator can be decreased by 25% with a blowing rate of 0.5% of the main mass flow.
A Simple Approach to Determine Uncertainty Bounds on Bearing Rotordynamic Coefficients Identification
Authors: Medina Luis , Ruiz Rafael , Di´az Sergio
Published: August 2009

The majority of rotordynamic studies concerned with bearing properties identification estimate rotordynamic coefficients without addressing the issue of parameter uncertainties. Uncertainty quantification is required to establish the accuracy and therefore the robustness of the identified parameters. Accuracy on the identification methodology is hampered by measurement noise, experimental and modeling error, and numerical method. The aim of this article is to determine, by means of error analysis, the propagated uncertainty contributions in a parametric frequency-domain identification. The methodology is based on linearly independent excitations for a direct estimation of the bearing rotordynamic coefficients. Errors on measurable excitations and responses are considered in the identification strategy to evaluate uncertainties of the estimated parameters. General formulation using errors-in-variables noise model is presented for system identification, taking into account uncertainty propagation in bearing parameters estimation. Experimental measurements, obtained from a test rig, are employed to estimate rotordynamic coefficients of a three lobe air bearing and the associated uncertainties. Confidence intervals are suggested for the expected bearing coefficients. A Monte Carlo simulation is conducted to study the statistical behavior as a result of simulated stochastic uncertainty propagation for comparison purposes with the experimental evidence. Results are presented graphically to assess the influence of the uncertainty propagation on the bearing properties calculation.
Time-Varying Flame Ionization Sensing Applied to Natural Gas and Propane Blends in a Pressurized Lean Premixed (LPM) Combustor
Authors: Straub D. L. , Chorpening B. T. , Huckaby E. D. , Thornton J. D. , Fincham W. L.
Published: August 2009

In-situ monitoring of combustion phenomena is a critical need for optimal operation and control of advanced gas turbine combustion systems. The concept described in this paper is based on naturally occurring flame ionization processes that accompany the combustion of hydrocarbon fuels. Previous work has shown that flame ionization techniques may be applied to detect flashback, lean blowout, and some aspects of thermo-acoustic combustion instabilities. Previous work has focused on application of DC electric fields. By application of time-varying electric fields, significant improvements to sensor capabilities have been observed. These data have been collected in a lean premixed combustion test rig operating at 0.51–0.76 MPa (5–7.5 atm) with air preheated to 588 K (600°F). Five percent of the total fuel flow is injected through the centerbody tip as a diffusion pilot. The fuel composition is varied independently by blending approximately 5% (volume) propane with the pipeline natural gas. The reference velocity through the premixing annulus is kept constant for all conditions at a nominal value of 70 m/s. The fuel-air equivalence ratio is varied independently from 0.46 – 0.58. Relative to the DC field version, the time-varying combustion control and diagnostic sensor (TV-CCADS) shows a significant improvement in the correlation between the measured flame ionization current and local fuel-air equivalence ratio. In testing with different fuel compositions, the triangle wave data show the most distinct change in flame ionization current in response to an increase in propane content. Continued development of this sensor technology will improve the capability to control advanced gas turbine combustion systems, and help address issues associated with variations in fuel supplies.