bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance and Cost Analysis of Advanced Gas Turbine Cycles With Pre-Combustion CO2 Capture
Authors: Hoffmann Ste´phanie , Bartlett Michael , Finkenrath Matthias , Evulet Andrei , Ursin Tord Peter
Published: August 2009

This paper presents the results of an evaluation of advanced combined cycle gas turbine plants with pre-combustion capture of CO2 from natural gas. In particular, the designs are carried out with the objectives of high efficiency, low capital cost and low emissions of carbon dioxide to the atmosphere. The novel cycles introduced in this paper are comprised of a high-pressure syngas generation island, in which an air-blown POX reformer is used to generate syngas from natural gas, and a power island, in which a CO2-lean syngas is burnt in a large frame machine. In order to reduce the efficiency penalty of natural gas reforming, a significant effort is spent evaluating and optimizing alternatives to recover the heat released during the process. CO2 is removed from the shifted syngas using either CO2 absorbing solvents or a CO2 membrane. CO2 separation membranes, in particular, have the potential for considerable cost or energy savings compared to conventional solvent-based separation and benefit from the high pressure level of the syngas generation island. A feasibility analysis and a cycle performance evaluation are carried out for large frame gas turbines such as the 9FB. Both short term and long term solutions have been investigated. An analysis of the cost of CO2 avoided is presented, including an evaluation of the cost of modifying the combined cycle due to CO2 separation. The paper describes a power plant reaching the performance targets of 50% net cycle efficiency and 80% CO2 capture, as well as the cost target of 30$ per ton of CO2 avoided. This paper indicates a development path to this power plant that minimizes technical risks by incremental implementation of new technology.
Optimum Design and Sensitivity Analysis of Axial Flow Compressor With Combination of Analytical Method, Qualitative and Quantitative Rules and Genetic Algorithm
Authors: Soltani Mohsen Reza , Khaledi Hiwa , Ghofrani Mohammad Bagher , Rezaei Amir Abbas
Published: August 2009

Simulation and prediction of gas turbine performance is a very important issue in design process or in actual behavior analysis. In these models physical behavior of components such as compressors, combustion chambers and turbines are simulated related to each other. The compressor is the most important part of simulation. This paper presents a model for simulating a compressor using stage stacking procedure with the aid of a genetic algorithm. The most important feature of the proposed method is that qualitative and quantitative rules based on turbo-machinery knowledge of compressors are used as constraints to the genetic algorithm to find the corrected situations of design. This knowledge is evaluated with both industrial and aero gas turbine engines (501F & CF6 (LM2500)). The model is based on an analytical solution and provides an insight into the effects of choices made during the compressor design process on performance and off-design stage matching. The results of the model highlight the capability of the method which accurately reproduces the available data. In addition to obtaining design conditions, this model can find and calculate stages that are highly loaded and this information is vital to control the compressor.
Forced Response of Shrouded Blades With Intermittent Dry Friction Force
Authors: Gu Weiwei , Xu Zili , Qiang Lv
Published: August 2009

The gap friction damper model is presented in this paper, which is employed to simulate the friction forces at the contact points of the shroud interface. Using the harmonic balance method (HBM), the friction force can be approximated by a series of harmonic functions. The governing differential equations of blade motion are transformed into a set of nonlinear algebraic equations, which can be solved iteratively to yield the steady-state response. The results show that the forced response is attenuated due to the additional damping introduced by frictional slip. The predicted results agree well with those of the Runge-Kutta method. In addition, the effect of parameters of damping structures such as the gap size, friction coefficient and normal load on the forced response of blades were studied. The results show that increasing the damper gap size causes a increase in resonant response. However, the increment isn’t obvious. In addition, an increase in friction coefficient or normal load decreases the forced response of blade.
A Conceptual Design Study for a New High Temperature Fast Response Cooled Total Pressure Probe
Authors: Brouckaert Jean-Franc¸ois , Mersinligil Mehmet , Pau Marco
Published: August 2009

The present paper proposes a concept for a water cooled high temperature unsteady total pressure probe, intended for measurements in the hot sections of industrial gas turbines or aero-engines. This concept is based on the use of a conventional miniature piezo-resistive pressure sensor, located at the probe tip to achieve a bandwidth of at least 40kHz. Due to extremely harsh conditions and the intention to immerse the probe continuously into the hot gas stream, the probe and sensor must be heavily cooled. The short term objective of this design is to gain the capability of performing measurements at the temperature conditions typically found at high pressure turbine exit (1100–1400K) and in the long term at combustor exit (2000K or higher).
Evaluation of Impact Loads of Clutch Engaging Within Single Shaft Applications for Power Generation
Authors: Lu¨neburg Bernd , Klocke Meinolf , Kulig Stefan , Joswig Frank
Published: August 2009

Combined Cycle Power Plants (CCPP) in single shaft arrangements consist of a gas turbine, a generator and a steam turbine on one shaft line. In order to enhance the plant availability and operational flexibility, Siemens Fossil Power Generation introduces a switchable clutch between steam turbine and generator. The clutch is a synchronous self-shifting device that engages automatically at rated speed as soon as the steam turbine overruns the gas turbine-generator. It disengages automatically when the steam turbine speed drops below the speed of the gas turbine. A rather complicated mechanism consisting pawls and ratchets and a thread of helical splines including damper mechanisms is used to provide the required coupling functions. The primary reason for the clutch is to ensure independent gas turbine and steam turbine operation below steam turbine rated speed. The clutch is especially advantageous during startup and gas turbine simple-cycle operation. Next to these advantages, the clutch engaging processes could introduce significant impact loading to the shaft components which differ from other. Next to the normal engaging process fault cases like engaging processes after gas turbine trip at high acceleration values due to the gas turbine compressor losses must be sustained by all rotor train components. This paper documents a nonlinear torsional analysis of the single shaft arrangement to assess the impact loading due to clutch engaging processes. A dynamic three-mass-model of the clutch including nonlinear stiffness and damping functions is set up and applied for the simulations. The coupling of the translatory and the rotatory inertia effects of the main sliding component of the clutch has been taken into account. Different load case scenarios in different single shaft component arrangements respectively different inertia ranges of the steam turbine rotor train are investigated in detail by the transient analyses. Based on this procedure, it is ensured that the mechanical layout of the single shaft components is sufficiently designed to withstand all operational loads under normal and faulty operating conditions.
Improvement of Performance Prediction by Automated Assimilation of Gas Turbine Component Maps
Authors: Zwingenberg M. , Benra F.-K. , Werner K.
Published: August 2009

The performance data of most Siemens heavy-duty gas turbines which have been built in the last 20 years are stored in so-called typefiles. These typefiles contain the description of the thermodynamic operating behavior for each gas turbine type using several component maps, e.g., for the compressor, the turbine and the combustion chamber. In addition to all available high-accuracy performance test results, modern IT technology enables the user to handle a tremendous volume of measured data via remote access. This allows the user to determine and to guarantee the performance of modifications and upgrades with sufficient precision, even for older gas turbine types. The method for automated generation of typefiles based on the entire volume of available data and its corresponding Matlab® based software solution are the focus of this contribution. Although this method offers a very promising source of data from various sites, the obtainable data sets usually do not cover the entire temperature and rotational speed range that is necessary to create a map suitable for all requisite operating conditions. Thus, theoretically-based additional information combined with special extrapolation methods are necessary.
Shroud Leakage Modeling of the Flow in a Two Stage Axial Test Turbine
Authors: Pau M. , Cambuli F. , Mandas N.
Published: August 2009

Three dimensional steady multistage calculations, using mixing plane approach, are presented for two different blade geometries in a two stage axial test turbine with shrouded blades. A 3D multiblock Navier-Stokes finite volume solver (TBLOCK) has been used in all the simulations. In order to study shroud leakage flow effects the whole shroud cavity geometry has been modeled, overcoming most of the limitations of simple shroud leakage model in calculating fluid flow over complex geometries. Numerical investigations are mainly focused on assessing the ability of the solver to be used as multistage design tool for modeling leakage-mainstream flow interaction. Several calculations are compared. The first computes the main blade flow path with no modeling of the shroud cavities. The second includes the modeling of the shroud cavities for a zero leakage mass flow rate. Finally a multiblock calculation which models all the leakage flow paths and shroud cavities has been carried out for two different levels of shroud seal clearance. It is found that neglecting shroud leakage significantly alters the computed velocity profiles and loss distributions, for both the computed blade geometries. A numerically predicted shroud leakage offset loss is presented for the two considered blade geometries, focusing on the relative importance of the leakage flow, re-entry mixing losses, and inlet and exit shroud cavity effect. Results demonstrates that full calculation of leakage flow paths and cavities is required to obtain reliable results, indicating the different effects of the leakage-to-mainstream flow interaction on the blade geometries computed. Despite a slight increase in the computational time, multiblock approach in handling leakage flow problem can now-days be used as a practical tool in the blade design process and routine shroud leakage calculations.
A New Test Rig for Film Cooling Experiments on Turbine Endwalls
Authors: Kunze Martin , Preibisch Stefan , Vogeler Konrad , Landis Kenneth , Heselhaus Andreas
Published: August 2009

Endwall film cooling has been subject to many investigations over the past years. Since the coolant is injected into the wall boundary layer, it is primarily affected by the complex three-dimensional flow structure which is developed near the endwall inside turbine bladings. Little information can be found in the literature about how load variation affects endwall film cooling. As the secondary flow, driven by the circumferential and radial pressure gradient, is intensified with higher cascade load, strong interaction of the coolant injected in the near-wall cross flow is expected. Therefore, an airfoil cascade rig has been designed with an endwall cooling configuration containing multiple rows of expanded film holes. The film rows are combined to groups which can be supplied with different types of coolant gas through individual plenum cavities. Additionally, basic film cooling experiments have been conducted on a flat surface to validate the temperature measurement technique on results available in the literature. Film cooling injection is established through a row of 7 cylindrical holes inclined streamwise at 35° for a blowing rate ranging from 0.35 to 1.5. Experiments are conducted at constant main flow conditions at ReD = 4200 and at low turbulence level Tu = 1.5% with CO2 (DR = 1.37) and Air (DR = 0.9) used as coolant gas. Centerline effectiveness for selected blowing rates is compared to results available from previous literature.
Endwall Performance of Outlet Guide Vane Cascades With Different Blade Loading Distributions
Authors: Sonoda Toyotaka , Schreiber Heinz-Adolf , Arima Toshiyuki
Published: August 2009

As a part of an innovative aerodynamic design concept for a single stage low pressure turbine, a high turning outlet guide vane is required to remove the swirl from the hot gas. The airfoil of the vane is a highly loaded compressor airfoil that has to operate at very low Reynolds numbers (Re∼120,000). Recently published numerical design studies and experimental analysis on alternatively designed airfoils showed that blade profiles with an extreme front loaded pressure distribution are advantageous for low Reynolds number conditions. This paper experimentally and numerically discusses about the three-dimensional performance near the end-wall of two alternatively designed cascades, the end-wall performance of a baseline cascade with controlled diffusion airfoils (CDA) and a cascade with extreme front loaded airfoils. The results showed that although the end-wall pressure gradients are different, the characteristics of the secondary flow are very similar for both of the cascades. Both, experiment and numerical analysis showed that the losses close to the end-wall of the extreme front loaded airfoils are even lower in relation to those of the CDA airfoils. The flow mechanism on the superiority of the extreme front loaded airfoils around the end-wall region is discussed.
Dynamic Analysis of Fretting-Wear in Friction Contact Interfaces
Authors: Salles Loi¨c , Blanc Laurent , Thouverez Fabrice , Gouskov Alexander M.
Published: August 2009

Fretting wear is a very important phenomenon occurring in bladed disks. It causes that blades must be replaced in turbomachines during their life-cycle. Methods exist to predict fretting-wear in quasi-static analysis. However they don’t predict all the phenomena observed in blade attachments on real turbomachines. That’s why this study assumes that dynamics plays a role in fretting-wear. This paper is devoted to the realistic modelling and calculation of fretting-wear and dynamical response of structures in unilateral contact with friction. Vibration and wear phenomena present very different scales both in time and space. Therefore the difficulty is in finding methods that enable one to solve the non-linear problem with a good compromise between the approximations made about the dynamical aspects and those linked with fretting-wear issues. Here, phenomenological examples are studied. They involve a small number of degrees of freedom with a view to understanding the complex coupling between vibration and fretting-wear. This way, they will show the relative importance of parameters.
Development of Lean-Burn Low-NOx Combustion Technology at Rolls-Royce Deutschland
Authors: Lazik W. , Doerr Th. , Bake S. , v. d. Bank R. , Rackwitz L.
Published: August 2009

Lean-burn combustion technology is identified to be the key technology for aero-engine combustion systems to achieve future legislative requirements for NOx. The lean-burn low NOx combustor development at Rolls-Royce Deutschland RRD for the upcoming generation of aero-engines is presented, which has been supported by the German aeronautical research programme. The down selection process of different injector concepts is described in detail to develop lean-burn fuel injection technology up to a technology level for engine application. Initial concept validation with testing on single sector combustion rigs applying advanced laser measurement techniques is followed by high power single sector emission tests to prove low emission characteristics. Climbing the level of technology readiness, which is in each phase substantiated by intense CFD simulations, the most promising low emissions design concepts have been investigated for unrestricted combustor operability compared to conventional rich burn systems. Altitude relight, weak extinction margins, fuel staging optimisation and combustion efficiency in the vicinity of staging points have been optimised on different sub-atmospheric, atmospheric, medium and high-pressure test vehicles. The validation process concludes with sub-atmospheric and high-pressure testing within a fully annular test environment before the final lean-burn fuel injector configuration has been selected for core engine testing to prove emission performance and operability of the fuel-staged combustion system. Two fuel injector configurations were successfully tested in a high-pressure fully annular rig. The combustor module and both injector standards have been cleared for core engine operation.
Online and Offline Vibration Analysis of Stator End Windings of Large Power Generators
Authors: Thien Dagmar , Romanowski Holger , Strack Sebastian , Kempen Stefan , Krol Thorsten , Langmann Axel
Published: August 2009

An overview of different techniques to monitor vibrations of the generator end winding (impact tests, online vibration measurements using fiber optic accelerometers or a laser vibrometer) are presented. Data from online vibration measurements to investigate the vibration modal shapes of the stator end winding basket during operation is correlated with the generator operation parameters. These analyses are compared to results of finite-element-model calculations of a stator end winding. To evaluate the vibrations of a generator stator end winding during operation, it is necessary to relate vibrational modes to the generator operation parameters. In situ recording of, i.e. local accelerations or strain together with generator operating parameters allows deeper insight into the correlation of operating parameters and vibrations of the stator end windings.
Multi-Objective Optimization in Axial Compressor Design Using a Linked CFD-Solver
Authors: Becker Kai , Lawerenz Martin , Voß Christian , Mo¨nig Reinhard
Published: August 2009

In combination with a multi-objective 3D optimization strategy, a linked CFD-solver is presented in this paper, combining 3D-Reynolds-averaged-Navier-Stokes and an inviscid throughflow method. It enables the adjustment of the 3D boundary conditions for any design variation and contains new options for configuring the objective functions. The link is achieved by matching the flow information between both CFD codes in an iterative procedure. Compared to an individual 3D-CFD calculation, the convergence does not take significantly longer. The potential of the linked CFD-solver is demonstrated in a multi-objective optimization for one blade row to be optimized and one operating point at a 3-stage axial compressor with inlet guide vane. Within the optimization, the objective functions are formulated, so that the performance of the axial compressor is enhanced in addition to the improved efficiency of the 3D-cascade.
Skeletal Mechanism for C2H4 Combustion With PAH Formation
Authors: Slavinskaya N. , Zizin A. , Braun-Unkhoff M. , Lenfers C.
Published: August 2009

A semi-detailed kinetic mechanism with 100 species and 816 reactions for ethylene combustion including PAH formation was elaborated. The model includes the C2H5OH sub mechanism combustion as well. This mechanism has in view to be the base of further kinetic schemes of practical fuels (reference fuels). The mechanism was reduced to a skeletal model with 72 species and 580 reactions. The elaborated models were validated on experimental data bases of heat release as well as formation of polyaromatic hydrocarbons and soot in laminar premixed C2H4, C2H4 / C2H5OH flames taken from literature. The calculated ignition delay times, laminar flame speeds, as well as temporal profiles of small and large aromatics and also soot particles are in good agreement with experimental data obtained for pressures 1 – 5 bar, temperatures T0 = 1100 – 2300 K, fuel/oxygen equivalence ratio φ = 0.5 – 2.
A New Energy-Based Multiaxial Fatigue Life Prediction Procedure
Authors: Tarar Wasim , Scott-Emuakpor Onome , Shen M.-H. Herman , George Tommy , Cross Charles
Published: August 2009

An energy-based fatigue life prediction framework was previously developed by the authors for prediction of axial and bending fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. In this study, energy expressions that construct the constitutive law are equated in the form of total strain energy and the distortion energy dissipated in a fatigue cycle. The resulting equation is further evaluated to acquire the equivalent stress per cycle using energy based methodologies. The equivalent stress expressions are developed both for biaxial and multiaxial fatigue loads and are used to predict the number of cycles to failure based on previously developed prediction criterion. The equivalent stress expressions developed in this study are further used in a new finite element procedure to predict the fatigue life for two and three dimensional structures. The final output of this finite element analysis is in the form of number of cycles to failure for each element on a scale in ascending or descending order. Therefore, the new finite element framework can provide the number of cycles to failure at each location in gas turbine engine structural components. In order to obtain experimental data for comparison, an Al6061-T6 plate is tested using a previously developed vibration based testing framework. The finite element analysis is performed for Al6061-T6 aluminum and the results are compared with experimental results.
Detailed Flow Investigation Using PIV in a Rotating Square-Sectioned Two-Pass Cooling System With Ribbed Walls
Authors: Elfert M. , Voges M. , Klinner J.
Published: August 2009

In a 2-pass cooling system the pressure driven air flow distribution is investigated experimentally using the non-intrusive PIV Technique. The generic model as part of a complex and sophisticated cooling system consists of two square-sectioned ducts with a length of 20 diameters and an inherent 180 degree bend. The system has been investigated basically with smooth walls (case 0) and, later on, with two different kinds of ribbed walls in both legs. Ribs are applied to enhance the cooling performance; they are placed on two opposite walls of both legs in a symmetric (case A) and an asymmetric manner (case B), respectively. The ribs are inclined with an angle of 45 degrees versus the duct axis (i.e. main flow direction). The applied rib lay-out is well-proved and optimized with respect to heat transfer improvement and the inherent pressure drop increase. The system rotates about an axis orthogonal to the centreline of the straight passes. The configuration was analyzed with the planar the two-component Particle Image Velocimetry (2C PIV), which is capable of obtaining complete maps of the instantaneous as well as the averaged flow field even at high turbulence levels, which are typically present within duct turns, near ribs and, above all, during rotation. The presented investigations were conducted in stationary and rotating mode. Especially in the bend region separation phenomena and vortices with high local turbulence are apparent. The presence of ribs changes the fluid motion by generating additional vortices impinging the side walls. Flow visualization with injected oil smoke using the laser light sheet visualization technique was helpful to detect vortex structures and separations. Especially in the bend area separation regions and vortices with high local turbulence are apparent. The results shown in this paper demonstrate the effect of the 180 degree bend in combination with the two rib turbulator geometries for isothermal flow conditions excluding any buoyancy with and without rotation. Turbulent channel flow was investigated at a Reynolds number of 50,000, derived with the hydraulic diameter of the pass, non-rotating and at a rotation number of 0.02 which was chosen still moderate. Engine relevant rotation numbers are in order of .1 or higher. A reconstruction of model mountings will allow higher values for the next tests. Future work will expand to higher rotational speed and, also, will include buoyancy effects. This investigation shall help to clarify the complex flow phenomena due to the interaction of several vortices, present in two-pass cooling systems. The flow maps obtained with PIV are of good quality and high spatial resolution and therefore provide a test case for the development and validation of numerical simulation tools like the DLR flow solver TRACE which is not a topic of this paper.
Impact of Fuel Supply Impedance on Combustion Stability of Gas Turbines
Authors: Huber Andreas , Polifke Wolfgang
Published: August 2009

In the development of gas turbines the prevention of thermoacoustic instabilities plays an important role. The present study analyzes the influence of the acoustic impedance of the fuel supply system on combustion stability in a generic configuration representative of practical lean-premix combustors. Transient Computational Fluid Dynamics (CFD) of turbulent reacting flow and system identification (SI) are combined to obtain a description of the combustion dynamics in terms of two flame transfer functions, which describe the response of heat release rate to fluctuations of velocity and equivalence ratio, respectively. In this way, the mixing and transport of the fuel from the injector to the flame, the kinematic response of the flame to upstream flow fluctuations, and combined effects like the perturbation of flame speed and position due to equivalence ratio perturbations are all captured. The flame transfer functions obtained are combined with a network model for the system acoustics in such a way that results from a single CFD simulation can be used to investigate a wide variety of combustor and fuel supply configurations in a quantitative and very efficient manner. It is demonstrated that a change of the fuel supply impedance can significantly influence the amplitude of equivalence ratio fluctuations as well as the relative phase of the two transfer functions, and thereby provide a means for control of combustion instabilities.
Improved Understanding of Blow-Down in Filament Seals
Authors: Franceschini Gervas , Jones Terry V. , Gillespie David R. H.
Published: August 2009

Brush seals are used to provide flow resistance between rotating and stationary components in gas turbines. Compliant filament seals such as brush seals exhibit a phenomenon called blow-down where the filaments deflect towards the rotor surface when a differential pressure is applied across the seal. This phenomenon is desirable as it enables seal contact to be maintained during rotor contractions and eccentric excursions. This paper describes an aerodynamic mechanism which can cause the blow-down of bristles. Importantly it shows that distortion of the bristle pack is not necessary to achieve blow-down. Experimental and computational investigations of a large scale model representative of a section of a brush seal are also reported. The measured and predicted detailed pressure distributions thus obtained are used to validate the model of blow-down presented.
Nonlinear Vibration Analysis of an Unbalanced Flexible Rotor Supported by Ball Bearings With Radial Internal Clearance
Authors: Gupta T. C. , Gupta K. , Sehgal D. K.
Published: August 2009

In the present work, the nonlinear dynamic response of an unbalanced horizontal flexible rotor supported by deep groove ball bearing is studied. Nonlinearity effects in rolling element bearings arise from Hertzian contact force deformation relationship and clearance between rolling elements and races. The system is bi-periodically excited due to varying compliance of ball bearing and rotating unbalance. The flexible rotor bearing system is modeled by finite element method, taking into account the gyroscopic moments, rotary inertia, shear deformation, proportional damping, nonlinear stiffness and radial internal clearance of ball bearing. The implicit type numerical time integration scheme Newmark-β and Newton-Raphson methods are used to numerically solve the nonlinear equations of motion. The mathematical model is validated for the natural frequencies of the flexible shaft and whirl frequencies. On account of variation in the ball bearing stiffness, the variation in natural frequencies of the rotor ball bearing system is estimated. The influence of ball bearing nonlinearity on dynamic behavior is analyzed by time histories of steady state response, phase portraits and power spectra. Effect of radial internal clearance and varying compliance on the unbalance response of flexible rotor is studied in detail.
Experimental Characterisation of the Stiffness and Leakage of a Prototype Leaf Seal for Turbine Applications
Authors: Jahn Ingo H. J. , Owen Andrew K. , Franceschini Gervas , Gillespie David
Published: August 2009

The leaf seal, a seal comprising multiple flexible elements, offers similar leakage to a brush seal, but may have other benefits that make it a more attractive option in some applications. This paper details an experimental investigation of the leakage and stiffness of a pair of prototype leaf seals carried out in a slow speed rotating rig at differential pressures of up to 0, 4 MPa. The stiffness is characterised by measuring the force required to create excursions of the housing relative to the seal. The results are presented in terms of the effective annular clearance of an idealised labyrinth seal. For a single seal design, in which contact between the leaf tips causes inherent damping in the seal, the effect of changes in seal housing geometry are reported. The results observed are explained with reference to the flow field in the leaf pack.
The Effect of Ribs and Tip Wall Distance on Heat Transfer for a Varying Aspect Ratio Two-Pass Ribbed Internal Cooling Channel
Authors: Jenkins Sean C. , Zehnder Frank , Shevchuk Igor V. , von Wolfersdorf Jens , Weigand Bernhard , Schnieder Martin
Published: August 2009

Internal cooling channels with differing aspect ratios are typically found in gas turbine blades due to the varying thickness of the blade from the leading to trailing edge. These serpentine passages often contain several 180° bends, which are sharp edged in the region of the blade tip. The 180° bend has a pronounced effect on the heat transfer characteristics in the outlet channel and tip wall, where a strong influence is seen due to the divider wall-to-tip wall distance in the bend. The present study investigates the effect of the divider wall-to-tip wall distance for a ribbed two-pass cooling channel with a 2:1 inlet and 1:1 outlet channel. Spatially resolved heat transfer measurements were made using the transient thermochromic liquid crystal technique for a smooth and a ribbed configuration using parallel 45° ribs. Effects of the 180° bend on heat transfer and rib-induced enhancements were identified separately and bend effects were found to dominate the heat transfer increase in the outlet channel near the bend. Pressure losses due to the bend and ribs were also independently evaluated for a range of tip wall distances. Results show that the smaller tip wall distances increase heat transfer on the tip wall and outlet channel, but at the cost of an increased pressure loss. An optimum tip wall position is suggested, forming a compromise between heat transfer improvement and increased pressure losses.
Improving the Performance of a Bent Ejector With Inlet Swirl
Authors: Maqsood Asim , Birk A. M.
Published: August 2009

Ejectors are commonly employed in gas turbine exhaust systems for reasons such as space ventilation and IR suppression. Ejectors may incorporate bends in the geometry for various reasons. Studies have shown that the bend has a deteriorating effect on the performance of an ejector. This work was aimed to investigate the effect of exhaust gas swirl on improving the performance of a bent ejector. Four short oblong ejectors with different degrees of bend in the mixing tube and four swirl conditions were tested in this study. The primary nozzle, in all the cases, was composed of a circular to oblong transition. Testing was performed at ambient and hot primary flow with 0, 10, 20 and 30° swirl angles. It was observed that the swirl had a strong affect on the performance of a bent ejector. Improvement of up to 55, 96 and 180% was obtained in the pumping ratio, pressure rise and total efficiency respectively with a 20° swirl in the exhaust gas.
Three-Dimensional Aerodynamic Design of Turbine Blades Using the Adjoint Method
Authors: Li Yingchen , Feng Zhenping
Published: August 2009

The adjoint method is attractive because of its low computational cost and high efficiency. Although it has been one of the hot issues in aerodynamic design, it is not so widely used in turbomachinery applications as it is in the aeronautical field. The purpose of this work is to apply the adjoint method to three-dimensional (3D) aerodynamic inverse design of axial turbine blades for inviscid compressible flow. The 3D continuous adjoint system of Euler equations is formulated for turbine internal flow. The 3D blade profile is parameterized with Non-uniform B-Spline patch, and the coordinates of the B-Spline control points are selected as the design variables. Characteristic analysis of adjoint equations is taken to set inlet/outlet boundary conditions. To avoid the discontinuity of boundary conditions of adjoint equations in the spanwise direction, a method for solving an ordinary differential equation is developed to smooth the residual distribution of aerodynamic parameter on blade surface. 3D adjoint equations are numerically solved by using time-marching method and finite volume method. Finally, combining the grid perturbation technique, CFD technique and quasi-Newton algorithm, the aerodynamic design approach for 3D axial turbine blades is presented and several numerical examples are demonstrated to validate this approach.
Prototype Design of a Two-Stage High-Speed Motor Driven Air Compressor
Authors: Backman Jari L. H. , Turunen-Saaresti Teemu , Saari Juha
Published: August 2009

Oil-free pressurized air is needed in several industrial fields, i.e. paper mills and in electronics manufacturing. The pressure level is rather high, 600 – 900 kPa, and the compressor type usually used in these applications are dry screw compressors and gearbox-driven centrifugal compressors. However, drawbacks of these kinds of compressors are wearing of the components, high maintenance costs and increased energy consumptions during the life-time. To tackle these drawbacks, the prototype of a two-stage centrifugal compressor was designed, manufactured and tested. Both compressor impellers and the electric motor are on the same shaft, and magnetic bearings are used to make the machine oil-free. Due to the high pressure level and two compressor stages, the centrifugal compressor needs to run at relatively high rotation speed. When the compressor has more than one wheel, the compressor power can be reduced and the overall efficiency increased with intercooling. In a two-stage compressor this means that the pressurized air after the first stage is cooled near to ambient temperature. As a result the compressor consumes less power, but intercooling causes a pressure loss to the system, which has to be taken into account. The compromise is needed with the same mass flow rate compressor stages is very restrictive, as the specific speeds can not vary much. The main difference comes from the different volume flows, as the density in the second stage is higher than in the first stage. The final optimizing of the efficiency takes into account the mechanical requirements with shaft critical speeds. The operation of the two-stage air compressor driven by a high-speed motor is rated at the point 800 kPa(g), 0.9 kgs−1, 300 kW and 60 000 rpm, respectively. The compressor stages are equipped with vaneless diffusers to maximize the operational range. The aerodynamic design based on the traditional in-house practice is verified with computerized flow dynamics using the Finflo-solver. The calculation does not include the volute, and the differences between the CFD results and the in-house design results are larger in the first stage of the compressor. Both compressor stages have been properly measured in a comprehensive test program following the measurement standards. The performances of the compressor stages at 80% speed are similar to the design data. At design speed both the efficiencies and pressures are lower than expected and the results indicate a need to improve the aerodynamic design.
Dynamic Analysis of Compressor Trips in the Sno̸hvit LNG Refrigerant Circuits
Authors: Schjo̸lberg Ingrid , Hyllseth Morten , Skofteland Gunleiv , Nordhus Ha˚vard
Published: August 2009

Compressors are key components in the refrigerant circuits of the Sno̸hvit LNG plant and contain large amounts of mechanical energy. Thus it is imperative that the control system is able to keep the compressor out of surge in case of driver trip. A dynamic process simulator describing the total LNG plant has been developed by Kongsberg Process Simulation and the simulator has been applied in the engineering phase for the design and process verification. The simulator has also been used to verify the robustness of the closed loop refrigerant circuits and to verify that the refrigerant compressors are sufficiently protected after a driver trip. The presented work demonstrates the value of dynamic simulations for verification of compressor protection systems. In addition it shows the importance of using correct data for polar inertia of the rotating equipment, as well as the opening and dead times of the anti-surge valves. It is recommended to include a sensitivity analysis of these parameters as part of plant verification studies.
Analysis of Stalled Compressor and Application to a Nuclear Gas Turbine Plant
Authors: Tauveron N.
Published: August 2009

The general context of this work is the modelling of closed cycle gas turbine with a nuclear heat source. In this context, a description of the turbomachinery has been developed, based on a one dimensional approach. However this type of model requires closure relations as input data. The objective of this paper is to provide models, which are able to describe compressor behaviour in off-design conditions and especially full stall condition. The present model is a derivation from analytical developments and Computational Fluid Dynamics (CFD) simulation results (Large Eddy Simulations with a two-layer approximate boundary conditions). An important part of this work consists to establish and validate a model of stalled compressor by comparison with representative experimental data. This preliminary validation process shows that the stall model has not the same accuracy as those used for stable off-design conditions. The model is applied to circulators of High Temperature Nuclear Reactors.
Unsteady Analysis of Blade and Tip Heat Transfer as Influenced by the Upstream Momentum and Thermal Wakes
Authors: Ameri Ali A. , Rigby David L. , Steinthorsson Erlendur , Heidmann James , Fabian John C.
Published: August 2009

The effect of the upstream wake on the blade heat transfer has been numerically examined. The geometry and the flow conditions of the first stage turbine blade of GE’s E3 engine with a tip clearance equal to 2% of the span was utilized. Based on numerical calculations of the vane, a set of wake boundary conditions were approximated which were subsequently imposed upon the downstream blade. This set consisted of the momentum and thermal wakes as well as the variation in modeled turbulence quantities of turbulence intensity and the length scale. Using a one blade periodic domain, the distributions of unsteady heat transfer rate on the turbine blade and its tip, as affected by the wake, were determined. Such heat transfer coefficient distribution was computed using the wall heat flux and the adiabatic wall temperature to desensitize the heat transfer coefficient to the wall temperature. For the determination of the wall heat flux and the adiabatic wall temperatures, two set of computations were required. The results were used in a phase-locked manner to compute the unsteady or steady heat transfer coefficients. It has been found that the unsteady wake has some effect on the distribution of the time averaged heat transfer coefficient on the blade and that this distribution is different from the distribution that is obtainable from a steady computation. This difference was found to be as large as 20 percent of the average heat transfer on the blade surface. On the tip surface, this difference is comparatively smaller and can be as large as four percent of the average.
In Situ Measurement and Validation of Gaseous Species Concentrations of a Gas Turbine Model Combustor by Tunable Diode Laser Absorption Spectroscopy (TDLAS)
Authors: Behrendt Thomas , Hassa Christoph , Mohamed Ajmal , Faleni Jean-Pierre
Published: August 2009

In the framework of a European research project, ONERA and DLR have studied the applicability of infrared laser techniques to gas turbine combustor measurements. The final goal is to replace gas analysis with probe measurements by optical techniques fulfilling the ICAO standards for engine emission measurements. Infrared laser absorption spectroscopy has the potential for fast, high spatial resolution measurements of combustion species with rugged equipment and therefore might contribute to the reduction of combustor development time and cost. Furthermore, the measurement of minor species in the combustor could help the understanding of the combustion process in the gas turbine. The tunable diode laser absorption technique of ONERA was used to probe CO, CO2, NO and H2O. The apparatus and measurement procedure including the upgrades for the combustor measurements are described. Successful measurements were achieved with CO inside and outside of the combustor. The reactive flow field of the model combustor was characterized with conventional measurement techniques. The CO measurements by TDLAS were compared with probe measurements that could be weighted by temperature and velocity measurements. Furthermore, temperature information was derived from the Laser measurements. The results are compared and further improvements are discussed.
Fuel Interchangeability for Lean Premixed Combustion in Gas Turbine Engines
Authors: Ferguson Don , Richard Geo. A. , Straub Doug
Published: August 2009

In response to environmental concerns of NOx emissions, gas turbine manufacturers have developed engines that operate under lean, pre-mixed fuel and air conditions. While this has proven to reduce NOx emissions by lowering peak flame temperatures, it is not without its limitations as engines utilizing this technology are more susceptible to combustion dynamics. Although dependent on a number of mechanisms, changes in fuel composition can alter the dynamic response of a given combustion system. This is of particular interest as increases in demand of domestic natural gas have fueled efforts to utilize alternatives such as coal derived syngas, imported liquefied natural gas and hydrogen or hydrogen augmented fuels. However, prior to changing the fuel supply end-users need to understand how their system will respond. A variety of historical parameters have been utilized to determine fuel interchangeability such as Wobbe and Weaver Indices, however these parameters were never optimized for today’s engines operating under lean pre-mixed combustion. This paper provides a discussion of currently available parameters to describe fuel interchangeability. Through the analysis of the dynamic response of a lab-scale Rijke tube combustor operating on various fuel blends, it is shown that commonly used indices are inadequate for describing combustion specific phenomena.
Improving the Turbine Cooling Conceptual Design Process
Authors: Bell Chris , Clarkson P. John , Dawes William N.
Published: August 2009

A method is introduced to improve the conceptual design of turbine blade cooling systems. It delivers greater insights, enables flexibility to explore the design space and provides a more mature start to a conventional design cycle. System representations are rapidly developed using 3-D sketch-based computer models based on idealised, imprecise geometry. Process bottlenecks are eliminated, accelerating design feedback to guide changes. Computational fluid dynamics models provide qualitative coolant flow information. Rapid-prototype models indicate core suitability. An example is presented: coolant flow and core quality are progressively improved and changes made to transform the system style.
Towards an Automated Simulation Process in Combined Thermal, Flow and Stress in Turbine Blade Cooling Analyses
Authors: Davison Joel B. , Ferguson Stephen W. , Mendonc¸a Fred G. , Peck Adam F. , Thompson Allan
Published: August 2009

In recognition of continuing difficulties that are experienced in performing computational analyses (CAE) on real turbine blades, this paper explores current developments in areas of integrated geometry handling, multi-domain meshing and multi-disciplinary analysis. The application of an integrated software framework first for CAD repair, then for surface and volume meshing, and finally for combined fluid, thermal and stress analysis can go some way to easing pains. The focus here is to demonstrate how it is possible in a single simulation environment, and using a finite volume methodology, to deal with real turbine blade geometries in terms of CAD handling, and then to perform conjugate-heat transfer and stress analyses using one mesh which is generated to be continuous through the fluid (external and internal passages) and blade metal. Possible gains to productivity become obvious.