bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Silo Combustor Liners Transient Behavior for Advanced Design Upgrade
Authors: Fedorov Ilya , Vassiliev Vladimir , Arkhipov Alexandre , Magni Fulvio
Published: August 2015

Many Alstom heavy-duty gas turbines with a silo combustor are in service and moreover undergoing upgrades for performance augmentation, lifetime extension, and emission reduction. The combustor liners, which are exposed to high gas temperatures, may require design tuning for these upgrades, and therefore reliable simulation of their behavior is of utmost importance.

This paper focuses on a case study of transient behavior of the Hot Gas Casing, a transition liner between compressor, turbine and silo combustor. Following a three-dimensional thermal assessment based on computational fluid dynamics, detailed structural analysis is done to identify the drivers behind different types of Hot Gas Casing deformation, observed after upgraded combustor introduction.

Thermal Barrier Coating application is proposed to reduce Hot Gas Casing bending. The solution was confirmed analytically and successfully introduced in the field. Good correlation of field findings and finite element prediction was found. It is shown that only a combined effect of thermal deformation, cyclic loading and creep may explain the observed behavior of the part.

A detailed design sensitivity study is performed, comparing different approaches to deformation reduction: application of ribs, corrugations and wall thickness increase. The best solution in terms of manufacturability and its impact on part deformation is chosen. It is found that wall corrugation does not provide the desired effect due to the nature of part deformation.
Efficiency Increase in Centrifugal Compressor With Open Impeller by Using Curvilinear Element Blade
Authors: Tsukamoto Kazuhiro , Hiradate Kiyotaka , Sakamoto Kiyohide , Chiba Haruaki , Shinkawa Yasushi
Published: August 2015

The effect of curvilinear element blade on open-type centrifugal impeller is numerically examined in this research. We compared four different open-type centrifugal impellers. Two of them were linear element blade impellers: one has a positive tangential lean to the rotation at the outlet and the other has negative tangential lean. The other two were curvilinear element blade impellers having different tangential lean profiles. Numerical simulation of steady flow was conducted in one-blade path model with inlet, impeller and vane-less diffuser regions.

The simulation confirm that impellers with negative tangential lean profiles improve the stage efficiency under the flow rate at the design point and the curvilinear element blade improve the stage efficiency not only at the design point but the lower flow rate regions also. The efficiency increase at the design point is obtained not in the vane-less diffuser region but in the impeller region since the negative lean profile reduce the tip-leakage loss near the impeller outlet region. The negative tangential lean profile changes the pressure distribution in the flow passage between two impeller blades. The pressure difference between the pressure surface and the suction surface of one blade near the tip region decrease because of the pressure distribution change. Hence, the mass flow rate of the tip leakage decreases and reduces the loss generation. In addition, the reason why the stage efficiency increases under the lower flow rate conditions by using curvilinear element blade is the suppression effect of the flow separation in the vane-less diffuser. This result indicates that there is a design criteria both tangential lean angle and the inflection point of the profile from positive to negative to suppress the flow separation at the hub side in the vane-less diffuser.
Flow Evolution in a One and a Half Axial Steam Turbine Stage Under Different Operating Conditions
Authors: Paradiso Berardo , Mora Alessandro , Dossena Vincenzo , Gatti Giacomo , Nesti Andrea , Arcangeli Lorenzo , Maceli Nicola
Published: August 2015

In order to investigate in detail the performance of steam turbine stages the Low Speed Test Rig at Politecnico di Milano has been adapted. The setup consists of a one and an half turbine stage with an inlet guide vane. Two kind of experimental approaches are planned in the project: the first, denominated “performance”, has been carried out by the OGTL department of GE Oil&Gas Florence while, at the same time, Politecnico di Milano performed detailed inter-stage measurements with steady probes and time resolved high response pressure probes. An axial steam turbine stage was tested under several operating conditions in terms of rotational speed, mass flow and inlet angle with the aim to provide the functional curves of the machine together with detailed flow-field measurements. In this paper, a detailed description of the inter-stage flow-field is presented for the most relevant operating condition. Then, a comparison between three different points at the same rotational speed (but different mass flow) is proposed. Finally, the effects of different axial gaps on the overall performance of the stage are discussed.

In particular, two different vane-rotor axial gaps have been tested by traversing pressure and temperature probes in three different axial planes. The first measurement plane is located at the first stator exit with the aim to provide details of the inlet swirl angle and 3D flow-field generated by the IGV. In the second plane, located at the rotor exit, the effect of different load conditions on the rotor performance and average flow-field is discussed. Finally, the measurements obtained in the third plane, placed at the second stator exit, are afterwards compared with the one obtained in the first plane, in order to evidence the influence of an unsteady inlet flow-field on the stator behaviour. The aim of the work is to provide very detailed aerodynamic measurements; this large amount of data will be used to validate the results of the CFD simulation carried out in the design stage. In this paper the preliminary findings of the steady flow-field will be presented as the basis for further analysis.
The Characteristics of Rotating Instabilities in Low Pressure Steam Turbines at Low Volume Flow Operation
Authors: Sigg Roland , Rice Timothy
Published: August 2015

For flexible operation steam turbines may operate occasionally at low load. Operation away from the original design regime looks set to be an increasing trend mainly due to the presence of intermittently available renewable energy sources in the grid. This paper sets out an approach for considering low flow effects on turbine designs.

At low load operating conditions rotating instabilities (RIS) can occur in the rear stages of LP steam turbines. The instabilities are comparable in many ways to rotating stall in compressors. Ideally the turbine blade natural frequencies should be designed to avoid the frequencies generated by the RIS system.

The characteristics of RIS systems were experimentally investigated to understand the dependency with both flow coefficient and exhaust configuration. Correlations have been developed to characterize the dynamic pressure amplitudes and the fractional speed of the RIS moving around the wheel. The presented correlation based method is shown calibrated for a specific blade design.

Two different test rigs provide the basis for the work presented. A low pressure model steam turbine provided detailed information for key blade/exhaust combinations. A simplified small scale air turbine was used to provide additional input for the behavior with alternative exhaust back wall position. Observations of the characteristic RIS behavior from model turbine tests are set in context with observed changes in the flow field.
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.
Application of Adjoint Solver to Optimization of Fin Heat Exchanger
Authors: Wang Cheng-Zhang , Nagisetty Kondala Rao , Montanari Federico , Hill D. Chris
Published: August 2015

This paper presents an investigation to improve the design of a generic fin heat exchanger, using novel discrete adjoint solver tools in the computational fluid dynamics (CFD) software FLUENT. A baseline design is analyzed initially to evaluate flow resistance and heat transfer. Optimization is conducted by deploying the adjoint solver. The heat load and the drag force are combined into an objective function using a Reynolds analogy approach. Sensitivities of the objective function to geometric changes are predicted by the adjoint, and then the mesh is morphed, and the predictions are verified by the full CFD solutions. Predetermined, engineering driven, geometric changes are explored and compared, and the range of validity of the predictions is evaluated. An algorithm is then developed to implement steepest descent, constrained optimization based on the adjoint solution. The algorithm is applied iteratively on the fin heat exchanger, and a comparison is performed between the change in objective function predicted by the adjoint, and that calculated in full CFD solutions on morphed meshes. The insight gained on the directions of design changes and attending quantitative improvement of the design objective function is very useful to guide the optimization process. This is enabled by the adjoint solver’s capability to robustly evaluate the sensitivities of the objective function to all solution variables, and predict changes in observables.
Second Law Analysis of Thermodynamic Cycles for Aero Engines
Authors: Kerber Eva , Weigand Bernhard , Schmidt Florian , Staudacher Stephan
Published: August 2015

This paper presents an evaluation of thermodynamic cycles with the help of second law thermodynamics. In common studies thermodynamic cycles are analyzed and judged mostly just by thermal efficiency and specific power output. Another way to describe the efficiency of a cycle and to identify the potential is the analysis of the entropy production of the system. In a previous study a general investigation of thermodynamic cycles was carried out [1]. The promising technologies identified were isothermal compression and expansion, internal heat transfer and constant-volume heat addition. Based on these theoretical and idealized investigations, estimations for component efficiencies and losses were made. The present study investigates the entropy production of the thermodynamic cycles including these promising technologies. This helps to understand the interaction of the components and the effect of single components and their losses on the whole cycle. Furthermore a distinction between internal and external entropy production is made. This identifies which part of the losses occurs in the components and which amount of exergy leaves the system unused. The results finally lead to a gas turbine cycle involving compression with intercooling, internal heat transfer and constant-volume heat addition.
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.
Numerical and Experimental Investigation on Spray Flux Distribution Produced by Liquid Sheet Atomization
Authors: Inoue Chihiro , Shimizu Atsushi , Watanabe Toshinori , Himeno Takehiro , Uzawa Seiji
Published: August 2015

Eulerian-Lagrangian hybrid method is implemented for the prediction of liquid atomization phenomena produced by 2 liquid water jets impinging by an angle of 40 deg. in quiet ambient air. To calculate the flow fields with liquid/gas interface, Eulerian analyses are conducted inside a fixed computational grid system. After the atomization occurs, every droplet is converted to a spherical particle. The motion of particles are tracked in Lagrangian form. For the validation of the developed Eulerian-Lagrangian hybrid method, flow visualization by using a high-speed video camera is carried out. To obtain quantitative values of spray characteristics, the liquid mass flux distribution in space is measured by utilizing a patternator. Numerical and experimental results of atomization process and mass flux distribution of spray show a similarity, and thus the developed method is evaluated that it has potential to predict spray characteristics produced by liquid sheet atomization. The developed numerical method can calculate unsteady spray distributions not only at the plane close to the injector but also far downstream. The spray mass flux distribution in the transient state, which is hard to measure by experiment, is demonstrated.
Design Method for High Ma Number Counter Rotating Turbine Blades
Authors: Wei Shi , Kun Zhou
Published: August 2015

The relative Ma number from rotor outlet is often quite large in high pressure turbine, especially in vaneless counter rotating turbine. Therefore, it is necessary that appropriate blades are adopted for high Ma working circumstances. In this paper, 13 design parameters are firstly chosen through analysis of the key factors that affecting the high Ma turbine performance. Then the non-uniform rational B spline method is employed to parameterize the model of turbine blade, and made the dynamic parameters of key geometric parameters associate. Furthermore, a parametric modeling method is developed for high Ma turbine cascade. Later, the method is applied to design a big bend angle and high Ma turbine blade used for a counter rotating turbine of VCE. Simulations are carried out to verify the modeling and the results prove that design demands under both working patterns can be satisfied, which implies that the blades modelling method developed in this paper is appropriate for high Ma turbine blades.
Impact of Flow Non-Axisymmetry on Swirling Flow Dynamics and Receptivity to Acoustics
Authors: Hansford Samuel , O’Connor Jacqueline , Manoharan Kiran , Hemchandra Santosh
Published: August 2015

In this study, we experimentally investigate both the intrinsic instability characteristics and forced response to transverse acoustic excitation of a non-reacting, swirling flow for application to combustion instability in annular gas turbine engines. The non-axisymmetry of the velocity field is quantified using an azimuthal mode decomposition of the time-averaged velocity field that shows that (1) the flow field is largely axisymmetric, (2) axisymmetry decreases with downstream distance, and (3) forcing does not significantly alter the time-averaged shape of the flow field. The flow field is analyzed in a companion linear stability analysis that shows that the most unstable modes in the flow field are m=−1 and m=−2, which agrees with the experimental observations and shows that the intrinsic dynamics of this flow field are non-axisymmetric with respect to the jet axis. The linear stability analysis captures the spatial variation of mode strength for certain modes, particularly mode m=−1, but there are some deviations from the experimental results. Most notably, these deviations occur for mode m=0 at radii away from the jet axis. Experimental results of the forced response of the flow indicate that the intrinsic instability characteristics of the flow field have an impact on the forced-response dynamics. Response of the flow field to a velocity anti-node in a standing transverse acoustic field shows non-axisymmetric vortex rollup and the dominance of the m=−1 and m=1 azimuthal modes in the fluctuating flow field. In the presence of a pressure anti-node, the m=0 mode of the fluctuating flow field is very strong at the jet exit, indicating an axisymmetric response, and ring vortex shedding is apparent in the flow measurements from high-speed PIV. However, further downstream, the strength of the axisymmetric mode decreases and the m=−1 and m=1 modes dominate, resulting in a tilting of the vortex ring as it convects downstream. Implications for flame response to transverse acoustic fields are discussed.
Three-Stage Low Pressure Compressor Modernization by Means of Optimization Methods
Authors: Goryachkin Evgenii , Popov Grigorii , Baturin Oleg , Kolmakova Daria
Published: August 2015

Low pressure compressor operation has some features. Firstly, the LPC stages work with cold air. For this reason there is transonic or subsonic flow in LPC. Secondly, the flow in LPC has complex spatial structure. Blade geometry of LPC is described by a large number of parameters. For this reason, it is difficult to pick up optimal combination of parameters manually. The solution of this problem is the usage of optimization methods to find the optimal combination of parameters. This approach was tested in this work. The main goal of this work was the LPC modernization for new parameters of gas turbine engine. Set of unimprovable solutions (Pareto set) was obtained as a result of solving optimization task. Pareto set was a compromise between the efficiency increase and the mass flow decrease. Each point from Pareto set had a correspondence with LPC unique geometry represented as an array of optimization parameters. One point of the Pareto set met all the required parameters of modernized LPC. The LPC geometry that guaranteed the efficiency increase by 1,3%, the total pressure ratio increase by 4% and mass flow rate decrease by 11% in comparison with the original LPC was obtained as a result of the investigation.
The Three Dimensional Flow Structure and Turbulence in the Tip Region of an Axial Flow Compressor
Authors: Tan David , Li Yuanchao , Chen Huang , Wilkes Ian , Katz Joseph
Published: August 2015

Continuing preliminary data submitted last year, this paper focuses on effect of operation point on the structure of a tip leakage vortex (TLV) in compressor-like settings. Experiments are being performed at the Johns Hopkins University refractive index-matched facility. The transparent acrylic blades of the one and a half stage compressor have the same geometry, but lower aspect ratio as the inlet guide vanes and the first stage of the Low Speed Axial Compressor facility at NASA Glenn. The refractive index of the liquid, an aqueous NaI solution is matched with that of the blades and transparent casing, facilitating unobstructed stereo-PIV measurements. As the flow rate is reduced close to stall conditions, the leakage flow is confined to rotor chordwise sections further towards the leading edge, and the TLV rollup occurs further upstream, and more radially inward. However, as the leakage flow stops in the aft part of the passage, the near-stall TLV migrates faster to the PS side of the next blade. Instantaneous realizations demonstrate that the TLV consists of multiple interlaced vortices and never rolls up into a single structure, but when phased-averaged, it appears as single structure. The circumferential velocity peak is located radially inward of the mean vorticity center. Turbulent kinetic energy (TKE) is high in the TLV center, in the shear layer connecting the suction side (SS) corner to the TLV feeding vorticity into it, as well as in the region of flow separation on the endwall casing where the leakage flow meets the passage flow. The normal and shear Reynolds stress demonstrate high inhomogeneity and anisotropy, with the streamwise velocity fluctuations being the largest contributor to TKE. The dominant inplane contributors to TKE production rate involve contraction in the region of endwall casing separation and near the SS tip corner, and shear production in the shear layer. Fragmentation and rapid growth of the TLV occurs at mid passage, moving upstream with decreasing flow rate.
High Resolution PIV and CH-PLIF Measurements and Analysis of a Shear Layer Stabilized Flame
Authors: Foley C. W. , Chterev I. , Seitzman J. , Lieuwen T.
Published: August 2015

Understanding the mechanisms and physics of flame stabilization and blowoff of premixed flames is critical towards the design of high velocity combustion devices. In the high bulk flow velocity situation typical of practical combustors, the flame anchors in shear layers where the local flow velocities are much lower. Within the shear layer, fluid strain deformation rates are very high and the flame can be subjected to significant stretch levels. The main goal of this work was to characterize the flow and stretch conditions that a premixed flame experiences in a practical combustor geometry and to compare these values to calculated extinction values. High resolution, simultaneous PIV and CH-PLIF measurements are used to capture the flame edge and near-field stabilization region. When approaching lean limit extinction conditions, we note characteristic changes in the stretch and flow conditions experienced by the flame. Most notably, the flame becomes less critically stretched when fuel/air ratio is decreased. However, at these lean conditions, the flame is subject to higher mean flow velocities at the edge, suggesting less favorable flow conditions are present at the attachment point of the flame as blowoff is approached. These measurements suggest that blowoff of the flame from the shear layer is not directly stretch extinction induced, but rather the result of an imbalance between the speed of the flame edge and local tangential flow velocity.
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.
High Speed Characterization of a Prototype Leaf Seal on an Advanced Seal Test Facility
Authors: Pekris Michael J. , Nasti Adele , Jahn Ingo H. J. , Franceschini Gervas
Published: August 2015

Advanced contacting seals, such as leaf seals or brush seals, can offer reduced leakage during engine operation when compared to conventional labyrinth seals. The flexible elements of these seals provide better compliance with the rotor during flight manoeuvres. The functionality and performance retention attributes of an engine-scale prototype leaf seal have been investigated on a seal test facility at Rolls-Royce that achieves engine-representative pressures and speeds and allows dynamic control of the seal position relative to the rotor, both concentric and eccentric. In this paper the experimental setup and the test method are described in detail, including the quantification of the measurement uncertainty developed to ASME standard PTC 19.1. Experimental data are presented that show the variations in leakage and torque over typical variations of the test parameters. Insight is gained into the interactions between the operating pressure and speed and the concentric and eccentric movements imposed on the seal.
An Uncertainty Quantification Framework Coupled With a 1D Physics-Based Model for the Prediction of NOx Emissions in a RQL Combustion Chamber
Authors: Musaefendic Haris , Mery Yoann , Noel Thomas
Published: August 2015

From one engine to another with same definition, aerodynamics and combustion may vary depending on several factors such as manufacturing tolerances or thermodynamic conditions. This dispersion has an influence on the physical conditions within the combustor and can impact the emission levels among other things. It is necessary to take into account this variability during all design phases in order to estimate the combustor performances. Uncertainty quantification (UQ) methods provide a set of capabilities for analyzing the impact of this variability. In this article, a non-intrusive UQ methodology is coupled with a 1D physics-based tool which models physical phenomena taking place in the combustor to estimate NOx emissions. A flow analysis is carried out to determine the flow distribution inside the combustor. Then, a simplified kinetic scheme calibrated on engine test results is used to compute the spatial distribution of species mass fractions. Accurate agreement with experiments is observed for several operating points and engines. The impact of the manufacturing tolerances of the diameter of chamber geometrical features on the combustor performances is evaluated. This method provides capabilities to better understand the physics involved improving our knowledge to design efficient combustors.
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.