bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integrated Weld Quality Concept: A Holistic Design Approach for Steam Turbine Rotor Weld Joints
Authors: Borgmann C. , Dumstorff P. , Kern T.-U. , Almstedt H. , Niepold K. 
Published: August 2015

The today’s energy market requires highly efficient power plants under flexible operating conditions. Especially, the fluctuating availability of renewables demands higher cycling of fossil fired power plants. The need for highly efficient steam turbines is driven by CO2 reduction programs and depletion of fossil resources. Increased efficiency requires higher steam temperatures up to 630°C in today’s units or even more for future steam power plants. The gap between material properties in the hot and cold running parts of a steam turbine rotor is widened by increased live steam temperatures and the increased demand for flexibility. These technical challenges are accompanied by economic aspects, i.e. the market requirements have to be met at reasonable costs.
The welding of steam turbine rotors is one measure to balance required material properties and economical solutions. The rotor is a core component of the steam turbine and its long-term integrity is a key factor for reliable and safe operation of the power plant. An important aspect of weld quality is the determination of permissible size of weld imperfections assessed by fracture mechanics methods. The integrity of rotor weld joints is assured by ultrasonic inspection after the final post weld heat treatment with respect to fracture mechanics allowable flaw sizes. This procedure usually does not take credit from the quality measures applied during monitoring of the welding process.
This paper provides an overview of an holistic design approach for steam turbine rotor weld joints comprising the welding process and its improved online monitoring, non-destructive evaluation, material technology, and its fracture mechanics assessment. The corresponding quality measures and their interaction with fracture mechanics design of the weld joint are described. The application of this concept allows to exploit the potentials of weld joints and to assure a safe turbine operation over life time.
Surrogate-Based Optimisation for a Mixed-Variable Design Space: Proof of Concept and Opportunities for Turbomachinery Applications
Authors: Baert Lieven , Beauthier Charlotte , Leborgne Michaël , Lepot Ingrid 
Published: August 2015

State-of-the-art turbomachinery design processes rely more and more on the extensive use of numerical simulations. To deal with expensive high-fidelity computations, surrogate-based optimisation (SBO) has become a very interesting approach. In order to cope with industrial cases, the capability to handle variables of a mixed nature appears key.
Innovative and auto-adaptive surrogates have been implemented within Minamo that are capable of natively handling the different natures of the design parameters. The present work discusses this mixed-variable SBO framework applied to a multi-profile combinational problem inside the bypass duct. A proof of concept is given followed by a more advanced application. It is demonstrated that the proposed mixed-variable SBO efficiently delivers reliable results and that it offers many opportunities during a conceptual design phase.
A Large Scale Turbine Test Rig for the Investigation of High Pressure Turbine Aerodynamics and Heat Transfer With Variable Inflow Conditions
Authors: Krichbaum Alexander , Werschnik Holger , Wilhelm Manuel , Schiffer Heinz-Peter , Lehmann Knut 
Published: August 2015

Focusing on the experimental analysis of the effect of variable inlet flows on aerodynamics, efficiency and heat transfer of a modern high pressure turbine, the Large Scale Turbine Rig (LSTR) at Technische Universität Darmstadt has been extensively redesigned.
The LSTR is a full annular, rotating low speed turbine test rig carrying a scaled 1.5-stage (NGV1 - Rotor - NGV2) axial high-pressure turbine geometry designed by Rolls-Royce Deutschland to match engine-realistic Reynolds numbers. To simulate real turbine inflow conditions, the LSTR is equipped with a combustor simulator module including exchangeable swirlers. Other inflow conditions include axial or turbulent inflow as well as altered relative positions of swirl cores and NGVs by traversing. To investigate combustor-turbine interaction, the LSTR offers a large variety of optical and physical access ports as well as high flexibility to the application of measurement techniques.
An elaborate secondary air system enables the simulation of various cooling air flows. The turbine section is equipped with film-cooled NGVs, a hub side seal air injection between NGVs and rotor, as well as a hub side RIDN cooling air injection module designed to provide realistic turbine flow conditions. Exchangeable hub side RIDN-plates allow for investigation of different coolant injection geometries.
Measurement capabilities include 5-hole-probes, Pitot and total temperature rakes, as well as static pressure taps distributed along NGV radial sections and at the hub side passage endwall. The NGV passage flow can be visualized by means of Particle Image Velocimetry (PIV). Hot Wire Anemometry (HWA) will be used for time-resolved measurements of the turbulence level at several positions. The distributions of heat transfer and film cooling effectiveness are acquired using infrared thermography and CO2-gas tracing.
Alstom Gas Turbine Technology Overview: Status 2014
Authors: Kappis Wolfgang , Florjancic Stefan , Ruedel Uwe 
Published: August 2015

Market requirements for the heavy duty gas turbine power generation business have significantly changed over the last few years. With high gas prices in former times, all users have been mainly focusing on efficiency in addition to overall life cycle costs. Today individual countries see different requirements, which is easily explainable picking three typical trends. In the United States, with the exploitation of shale gas, gas prices are at a very low level. Hence, many gas turbines are used as base load engines, i.e. nearly constant loads for extended times. For these engines reliability is of main importance and efficiency somewhat less. In Japan gas prices are extremely high, and therefore the need for efficiency is significantly higher. Due to the challenge to partly replace nuclear plants, these engines as well are mainly intended for base load operation. In Europe, with the mid and long term carbon reduction strategy, heavy duty gas turbines is mainly used to compensate for intermittent renewable power generation. As a consequence, very high cyclic operation including fast and reliable start-up, very high loading gradients, including frequency response, and extended minimum and maximum operating ranges are required.
Additionally, there are other features that are frequently requested. Fuel flexibility is a major demand, reaching from fuels of lower purity, i.e. with higher carbon (C2+), content up to possible combustion of gases generated by electrolysis (H2). Lifecycle optimization, as another important request, relies on new technologies for reconditioning, lifetime monitoring, and improved lifetime prediction methods.
Out of Alstom’s recent research and development activities the following items are specifically addressed in this paper. Thermodynamic engine modelling and associated tasks are discussed, as well as the improvement and introduction of new operating concepts. Furthermore extended applications of design methodologies are shown. An additional focus is set ono improve emission behaviour understanding and increased fuel flexibility.
Finally, some applications of the new technologies in Alstom products are given, indicating the focus on market requirements and customer care.
Life Prediction of Power Turbine Components for High Exhaust Back Pressure Applications: Part II — Power Turbine Exhaust System
Authors: Dua Dipankar , Shaffer Don , Short Graeme 
Published: August 2015

Industrial and aeroderivative gas turbines when used in CHP and CCPP applications typically experience an increased exhaust back pressure due to losses from the downstream balance-of-plant systems. Also, gas turbines for mechanical drive application have a wide operating envelope which leads to a fluctuating back pressure that varies with change in exhaust flows. This increased back pressure on the power turbine results in increased exhaust gas temperatures and aerodynamic loading that can influence the mechanical integrity and life of Power Turbine Exhaust System.
This Paper discusses the Impact to Fatigue and Creep life of free power turbine exhaust system subjected to high back pressure applications using Siemens Energy approach.
Steady state and transient temperature fields were predicted using finite element method. These predictions were validated using full-scale engine test and are found to correlate well with the test results.
Full Scale strain gauge survey of the exhaust hood was undertaken at ambient conditions at various pressure levels to validate the structural boundary conditions of lifing models. Strain Predictions were found in good agreement with measured strain gauge data.
Steady State and Transient stress fields have been estimated using validated structural and thermal finite element models. Walker Strain Initiation model [1] is utilized to predict Low Cycle Fatigue Life and Larson Miller Parameter Creep Model has been used to estimate creep damage to the exhaust system.
The Life Prediction Study shows that the exhaust system design for high back pressure applications meets the product design standards.
Reduced Order Modeling of Aeroacoustic Systems for Stability Analyses of Thermoacoustically Non-Compact Gas Turbine Combustors
Authors: Hummel Tobias , Temmler Constanze , Schuermans Bruno , Sattelmayer Thomas 
Published: August 2015

A methodology is presented to model non-compact thermoacoustic phenomena using Reduced Order Models (ROM) based on the Linearized Navier-Stokes Equations (LNSE). The method is applicable to geometries with a complex flow field as in a gas turbine combustion chamber. The LNSE, and thus the resulting ROM, include coupling effects between acoustics and mean fluid flow, and are hence capable of describing propagation and (e.g. vortical) damping of the acoustic fluctuations within the considered volume. Such a ROM then constitutes the main building block for a novel thermoacoustic stability analysis method via a low-order hybrid approach. This method presents an expansion to state-of-the-art low-order stability tools, and is conceptually based on three core features: Firstly, the multi-dimensional and volumetric nature of the ROM establishes access to account spatial variability and non-compact effects on heat release fluctuations. As a result, it is particularly useful for high frequency phenomena such as screech. Secondly, the LNSE basis grants the ROM the capability to reconstruct complex acoustic performances physically accurate. Thirdly, the formulation of the ROM in state-space allows convenient access to the frequency and time domain. In the time domain, non-linear saturation mechanisms can be included, which reproduce the non-linear stochastic limit cycle behavior of thermoacoustic oscillations.
In order to demonstrate and verify the ROM’s underlying methodology, a test case using an orifice-tube geometry as the acoustic volume is performed. The generation of the ROM of the orifice-tube is conducted in a two-step procedure. As the first step, the geometrical domain is aeroacoustically characterized through the LNSE in frequency domain, and discretized via the Finite Element Method (FEM). The second step concerns the actual derivation of the ROM. The high-order dynamical system from the LNSE discretization is subjected to a modal reduction as order reduction technique. Mathematically, this modal reduction is the projection of the high-order (N ∼200,000) system into its truncated left eigenspace. An order reduction of several magnitudes (ROM order: Nr ∼100) is achieved. The resulting ROM contains all essential information about propagation and damping of the acoustic variables, and efficiently reproduces the aeroacoustic performance of the orifice-tube. Validation is achieved by comparing ROM results against numerical and experimental benchmarks from LNSE-FEM simulations and test rig measurements, respectively. Excellent agreement is found, which grants the ROM modeling approach full eligibility for further usage in the context of thermoacoustic stability modeling. This work is concluded by a methodological demonstration of performing stability analyses of non-compact thermoacoustic systems using the herein presented ROMs.
Optically Accessible Multisector Combustor: Application and Challenges of Laser Techniques at Realistic Operating Conditions
Authors: Meier U. , Heinze J. , Magens E. , Schroll M. , Hassa C. , Bake S. , Doerr Th. 
Published: August 2015

For their application in a multisector combustor, several laser-based measurement techniques underwent further development to generate useful results in the demanding environment of highly luminous flames under elevated pressures. The techniques were applied to two burner configurations and the results were used to explain their respective behavior.
Multisector combustors at elevated pressure present formidable difficulties to the operation of laser based techniques, as the optical path length is longer than for a single sector while the optical density of the flowing medium can be quite high. Hence, the techniques have to be set up to perform under low signal to noise levels. Nevertheless for a validation exercise geared at multidimensional simulation, quantitative results are requested. Here the modification of standard Laser Induced Incandescence as a means to measure soot concentrations with higher dynamic range is described. For situations where the optical density is too high for the application of imaging techniques, laser absorption was used and its application in the multisector combustor is presented.
Since combustion and soot formation is closely coupled to flowfield and mixing, velocity measurements are highly desired for comparison with computed flowfields. Although with Laser-Doppler Anemometry a well-established technique is at hand, the high operating costs of a multisector combustor cannot be supported for the needed time of operation. Therefore an effort was made to make the Particle Imaging Velocimetry technique operable in highly luminous flames by using a second camera. The two-camera system and its operation are described in the paper.
Finally the application on two different burner configurations is reported together with chemiluminescence as a tracer for heat release, and differences in soot production are related to the measured flow field.
Auto-Ignition of In-Line Injected Hydrogen/Nitrogen Fuel Mixtures at Reheat Combustor Operating Conditions
Authors: Schmalhofer Christoph , Griebel Peter , Stöhr Michael , Aigner Manfred , Wind Torsten 
Published: August 2015

De-carbonization of the power generation sector becomes increasingly important in order to achieve the European climate targets. Coal or biomass gasification together with a pre-combustion carbon capture process might be a solution resulting in hydrogen-rich gas turbine (GT) fuels. However, the high reactivity of these fuels poses challenges to the operability of lean premixed gas turbine combustion systems because of a higher auto-ignition and flashback risk. Investigation of these phenomena at GT relevant operating conditions is needed to gain knowledge and to derive design guidelines for a safe and reliable operation.
The present investigation focusses on the influence of the fuel injector configuration on auto-ignition and kernel development at reheat combustor relevant operating conditions. Auto-ignition of H2-rich fuels was investigated in the optically accessible mixing section of a generic reheat combustor. Two different geometrical in-line configurations were investigated. In the premixed configuration, the fuel mixture (H2 / N2) and the carrier medium nitrogen (N2) were homogeneously premixed before injection, whereas in the co-flow configuration the fuel (H2 / N2) jet was embedded in a carrier medium (N2 or air) co-flow. High-speed imaging was used to detect auto-ignition and to record the temporal and spatial development of auto-ignition kernels in the mixing section.
A high temperature sensitivity of the auto-ignition limits were observed for all configurations investigated. The lowest auto-ignition limits are measured for the premixed in-line injection. Significantly higher auto-ignition limits were determined in the co-flow in-line configuration. The analysis of auto-ignition kernels clearly showed the inhibiting influence of fuel dilution for all configurations.
Influence of Tip Jet Mass Flow and Blowing Rate on the Performance of an Axial Diffuser at Different Inlet Total Pressure Profiles
Authors: Thomas Rojas , Schatz Markus , Kuschel Benjamin , Brouwer Silke , Pradeep A. M. , Vogt Damian , Roy Bhaskar 
Published: August 2015

The present paper evaluates the impact of casing energized jet flow on the performance of an annular-conical exhaust diffuser. Two different inflow profiles, namely a uniform total pressure and a hub-strong total pressure inlet profile were studied. For both profiles, the flow is observed to separate at the casing. Experiments were performed at different tip jet mass flow rates and two different tip gap heights to understand their effect on the diffuser performance. Apart from wall pressure readings, probe measurements have been done at various locations within the diffuser to study the flow behaviour in more detail.
The results show that at the diffuser inlet already small tip jet flows help to prevent casing separation and hence improve pressure recovery noticeably, especially in the front section of the diffuser. On the other hand, higher tip jet flows tend to weaken the core flow at the diffuser exit, thus generating an inhomogeneous outflow velocity profile.
To enhance the interpretation of the experimental data, results from Computational Fluid Dynamics (CFD) simulations are used. Interestingly, the experimental results indicate that while the blowing ratio seems to be the major parameter for the improvement of pressure recovery for a hub-strong inlet profile, the pressure recovery for a uniform profile appears to be more sensitive to the tip jet mass flow rate. However, the numerical results do not show this trend.
Investigation of the Accuracy of RANS Models to Predict the Flow Through a Low-Pressure Turbine
Authors: Pichler R. , Sandberg R. D. , Michelassi V. , Bhaskaran R. 
Published: August 2015

In the present paper direct numerical simulation data of a low pressure turbine is investigated in light of turbulence modelling. Many compressible turbulence models use Favre average transport equations of the conservative variables and turbulent kinetic energy along with other modelling equation. First a general discussion on the turbulence modelling error propagation prescribed by transport equations is presented, leading to the terms that are considered to be of interest for turbulence model improvement. In order to give turbulence modellers means of validating their models the terms appearing in the Favre averaged momentum equations are presented along pitchwise profiles at three axial position. These three positions have been chosen such that they represent regions with different flow characteristics.
General trends indicate that terms related with thermodynamic fluctuations and Favre fluctuations are small and can be neglected for most of the flow field. The largest errors arise close to the trailing edge region where vortex shedding occurs. Finally, linear models and the scope for their improvement are discussed. Using locally optimized turbulence viscosities, the improvement potential of state of the art models is shown. On the other hand this study also highlights the danger of pure local optimization.
Simulations of Unsteady Blade Row Interactions Using Linear and Non-Linear Frequency Domain Methods
Authors: Frey Christian , Ashcroft Graham , Kersken Hans-Peter 
Published: August 2015

This paper compares various approaches to simulate unsteady blade row interactions in turbomachinery. Unsteady simulations of turbomachinery flows have gained importance over the last years since increasing computing power allows the user to consider 3D unsteady flows for industrially relevant configurations. Furthermore, for turbomachinery flows, the last two decades have seen considerable efforts in developing adequate CFD methods which exploit the rotational symmetries of blade rows and are therefore up to several orders of magnitude more efficient than the standard unsteady approach for full wheel configurations.
This paper focusses on the harmonic balance method which has been developed recently by the authors. The system of equations as well as the iterative solver are formulated in the frequency domain.
The aim of this paper is to compare the harmonic balance method with the time-linearized as well as the non-linear unsteady approach. For the latter the unsteady flow fields in a fan stage are compared to reference results obtained with a highly resolved unsteady simulation. Moreover the amplitudes of the acoustic modes which are due to the rotor stator interaction are compared to measurement data available for this fan stage.
The harmonic balance results for different sets of harmonics in the blade rows are used to explain the minor discrepancies between the time-linearized and unsteady results published by the authors in previous publications. The results show that the differences are primarily due to the neglection of the two-way coupling in the time-linearized simulations.
A Dynamic Clearance Seal for Steam Turbine Application
Authors: Messenger Andrew , Williams Richard , Ingram Grant , Hogg Simon , Tibos Stacie , Seaton Jon 
Published: August 2015

Effective sealing in turbomachinery reduces the leakage flow bypassing the turbine blades and also reduces the losses where the leakage flow mixes with the primary flow. In general the clearance should be as small as possible but is limited by thermal and mechanical effects which vary with load. In recent years intermittent energy sources, particularly wind and solar, have appeared in greater numbers on the power network. As a consequence conventional power plants need to become more flexible to accommodate renewable energy generation. A sealing technology which can accommodate rapid changes in load and maintain seal performance would be a valuable development.
This paper presents a novel seal design for steam turbines. The seal is designed to be capable of maintaining a smaller clearance than that of conventional labyrinth seals whilst allowing for dynamic movement with the rotor. The paper describes the seal concept and the analytic al work undertaken to demonstrate the concept. The seal design has also been tested in test facilities at Durham and the initial experimental results are included. They show that the concept works as intended.