bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Flame Transfer Functions Measured With Locally Resolved Full-Field-Vibrometry and OH*-Chemiluminescence
Authors: Greiffenhagen Felix , Woisetschläger Jakob , Gürtler Johannes , Scholz Heiko , Kuschmierz Robert , Czarske Jürgen
Published: August 2018

Information about heat release can be used to discuss the flame dynamics and stability behavior of turbulent combustion systems. The most common experimental approach to determine heat release fluctuations is the recording of OH*-chemiluminescence. Since there is a strong dependence of chemiluminescence on strain rate and mixture gradients, spatial information must be judged with care. As already shown in previous work, Laser Interferometric Vibrometry (LIV) directly detects the line-of-sight values of density fluctuations along the laser beam axis. Neglecting friction, losses of thermal radiation and conduction and assuming only small fluctuations of pressure in the reaction zone, heat release fluctuations can be calculated directly from density fluctuations. With available LIV techniques only pointwise scanning was feasible, resulting in time-consuming traversing of the flame to cover the whole flame field. A new camera-based full-field-LIV-system, developed at Technische Universität Dresden, is capable to simultaneously determine spatial information of heat release within the whole field with only one measurement, lasting a few minutes. This leads to a dramatical reduction of measurement time and furthermore reduces experimental efforts. Since the system is able to measure the complete flame at once, it is also possible to get information about the transient behavior of the combustion process. In this work the full-field-LIV system was applied for the first time on a swirl stabilized, lean and premixed methane flame. The results of this newly developed technique were checked against those of a commercially available single-beam LIV-system. Finally, the flame transfer function (FTF) was recorded with full-field-LIV and OH*-chemiluminescence and compared against each other.
Part-Load Limit Reduction of a Frame 9E Using a Precursor for Combustion Dynamics
Authors: Rouwenhorst Driek , Widhopf-Fenk Robert , Hermann Jakob , Häringer Matthias , Becker Julius , Gerhard Jürgen , Niedermeier Julian
Published: August 2018

In a test campaign to lower the minimum part-load of a combined cycle plant, a series of turndown tests on two GE Frame 9E gas turbines with DLN1 combustor technology were carried out under premix operation by Stadtwerke München (SWM). It has been found that the load can be reduced significantly compared to the conventional turndown ratio, before either CO emissions or combustion dynamics form the limiting factor of the turndown test. To exploit this potential safely and operate the gas turbines close to these physical limits, emissions and combustion dynamics must be monitored online. The azimuthal thermoacoustic mode that is observed in the can-annular machines is monitored with the IfTA PreCursor, based on the online determination of the modal decay rate. For this method, the acoustic pressure is measured at the cans around the gas turbine circumference to observe the azimuthal acoustic propagation that is enabled by the cross-firing tubes between the cans. Using this strategy to monitor CO emissions and thermoacoustic stability in real-time, a reduction of the minimal part-load limit by approximately 20% is achieved for the considered gas turbines. In must-run situations without demand for electricity generation, the operating costs can be directly reduced by the fuel savings. As an additional benefit, SWM can offer a broader power reserve for grid stabilization on the energy market. This monitoring strategy has been fully implemented in the control system and first experiences of the extended part-load limit are currently being gathered.
Open-Loop Control of the Precessing Vortex Core in a Swirl-Stabilized Combustor: Impact on Flame Shape and Flame Stability
Authors: Lückoff Finn , Sieber Moritz , Oberleithner Kilian
Published: August 2018

In this study, we apply periodic flow excitation of the PVC at the centerbody of a generic swirl-stabilized combustor to investigate the impact of the precessing vortex core (PVC) on flame shape and flame dynamics. Previous studies revealed considerable influence of the PVC on combustion properties such as flame dynamics and fuel/air mixing. We employ time-resolved OH*-chemiluminescence and pressure measurements to investigate the influence of the PVC on flame dynamics and flame shape transition. The PVC is typically present in flames which are detached from the burner outlet. This lift-off is observed for increasingly lean mixtures in this study. With the help of the PVC actuation, studied in this work, the transition point between attached and detached flame is shifted towards richer mixtures. Moreover, the dynamics of heat release rate fluctuations that are related to PVC and thermoacoustic instabilities are extracted from the OH*-chemiluminescence data. This reveals a considerable damping of the thermoacoustic oscillations due to the PVC actuation under technically premixed conditions and the rise of additional modes due to the interaction of both dynamics.
The Determination of Steady-State Movements Using Blade Tip Timing Data
Authors: Mohamed Mohamed , Bonello Philip , Russhard Peter
Published: August 2018

One of the main challenges of the Blade Tip Timing (BTT) measurement method is to be able to determine the sensing position of the probe relative to the blade tip. It is highly important to identify the measurement point of BTT since each point of the blade tip may have a different vibration response. This means that a change in measurement position will affect the amplitude, phase and DC component of the results obtained from BTT data. This increases the uncertainty in the correlation between BTT measurements and Finite Element (FE) modelling. Also, the measurement point should ideally be located to measure as many modes as possible. This means that the probe’s position should not coincide with a node, or a position at which the sensor misses the blade tip. Changes in the sensing position usually arise from the steady state movements of the blades (change in mean displacement). Such movements are caused by changes to the static (thermal and pressure) loading conditions that result from changes in the rotational speed. Such movements usually have a constant direction at normal operating conditions, but the direction may fluctuate if the machine develops a fault. There are three main types of movements of the sensing position that are considered in this paper: (1) axial movement; (2) blade lean; (3) blade untwist. Ideally, the sensing position is known based on the geometries of both the blade and the probe, but due to different types of movements of the blade this position is lost. Very few works have researched the extraction of the sensing position. Such preliminary works have required a pre-knowledge of mode shapes and additional instrumentation. The aim of this paper is to present a novel method for the identification of the BTT sensing position of the probes relative to a blade tip, which can be used to quantify the above movements. The developed method works by extracting the steady state offset from measurements of blade tip displacements over a number of revolutions as the speed changes from zero to a certain value. Hence, that part of the offset that is due to the angular positioning error of the probes (outside the scope of this work) is cancelled out (since it is independent of speed). The change in steady state offset is then processed to identify the three possible movements. The new method is validated using a novel BTT simulator that is based on the modal model of the FE model of a bladed disk (“blisk”). The simulator generates BTT data for prescribed changes to the sensing position. The validation tests show that the novel algorithm can identify such movements within a 2% margin of error.
An Investigation of Flow Characteristics and Parameter Effects for a New Concept of Hybrid SVC Nozzle
Authors: Song F. , Shi J. W. , Zhou L. , Wang Z. X. , Zhang X. B.
Published: August 2018

Lighter weight, simpler structure, higher vectoring efficiency and faster vector response are recent trends in development of aircraft engine exhaust system. To meet these new challenges, a concept of hybrid SVC nozzle was proposed in this work to achieve thrust vectoring by adopting a rotatable valve and by introducing a secondary flow injection. In this paper, we numerically investigated the flow mechanism of the hybrid SVC nozzle. Nozzle performance (e.g. the thrust vector angle and the thrust coefficient) was studied with consideration of the influence of aerodynamic and geometric parameters, such as the nozzle pressure ratio (NPR), the secondary pressure ratio (SPR) and the deflection angle of the rotatable valve (θ). The numerical results indicate that the introductions of the rotatable valve and the secondary injection induce an asymmetrically distributed static pressure to nozzle internal walls. Such static pressure distribution generates a side force on the primary flow, thereby achieving thrust vectoring. Both the thrust vector angle and vectoring efficiency can be enhanced by reducing NPR or by increasing θ. A maximum vector angle of 16.7 ° is attained while NPR is 3 and the corresponding vectoring efficiency is 6.33 °/%. The vector angle first increases and then decreases along with the elevation of SPR, and there exists an optimum value of SPR for maximum thrust vector angle. The effects of θ and SPR on the thrust coefficient were found to be insignificant. The rotatable valve can be utilized to improve vectoring efficiency and to control the vector angle as expected.
Performance Characterization of a Twin Scroll Volute for Turbocharging Applications
Authors: Cravero Carlo , La Rocca Mario , Ottonello Andrea
Published: August 2018

The use of twin scroll volutes in radial turbine for turbocharging applications has several advantages over single passage volute related to the engine matching and to the overall compactness. Twin scroll volutes are of increasing interest in power unit development but the open scientific literature on their performance and modelling is still quite limited. In the present work the performance of a twin scroll volute for a turbocharger radial turbine are investigated in some detail in a wide range of operating conditions at both full and partial admission. A CFD model for the volute have been developed and preliminary validated against experimental data available for the radial turbine. Then the numerical model has been used to generate the database of solutions that have been investigated and used to extract the performance. Different parameters and indices are introduced to describe the volute aerodynamic performance in the wide range of operating conditions chosen. The above parameters can be used for volute development or matching with a given rotor or efficiently implemented in automatic design optimization strategies.
The Identification and Prediction of Helical Modes Induced by a Multi-Passage Swirl Stabilised Lean Burn Aero-Engine Fuel Injector Under Steady State and Acoustically Forced Conditions
Authors: Treleaven Nicholas C. W. , Su Jialin , Garmory Andrew , Page Gary J. , Juniper Matthew
Published: August 2018

Thermoacoustic instabilities in gas turbine combustion systems, caused by a feedback loop between acoustic fluctuations and the flame, can be a major factor in determining the durability of the combustor. Of interest here are helical modes caused by a Kelvin-Helmholtz instability emanating from a region of high shear close to the outlet of the fuel injector. A liquid fuelled lean burn fuel injector, containing three air flow passages is studied in the present work using non-reacting compressible unsteady RANS CFD simulations. An acoustic wave is injected at the downstream boundary with excitation frequencies of 300Hz and 450Hz to compare to an unforced case. Analysis of the flow response is carried out using linear stability analysis, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). The linear stability analysis required interpolation of the solution from the unstructured CFD grid onto a uniform cylindrical polar mesh. The analysis found an absolute instability in the shear region between two passages. This m = −2 mode is unstable over frequencies from 400Hz to 1000Hz with wavelengths of 1.08 to 1.41 of the injector outer diameter. For the unforced case the POD identifies the first two modes with azimuthal wave number m = 1 and these are seen to spiral from the splitter plate inwards to disturb the pilot and outwards to the main. The dominant frequency is around 450Hz which is consistent with measurements and close to the linear stability analysis value. For the 300Hz forced case POD identifies the first four modes as being helical but has difficulty determining the dominant azimuthal wave number. There is shown to be a significant interaction between the acoustic and helical modes and double the total resolved kinetic energy as compared to the unforced case. The 450Hz forced case shows the asymmetric m = 1 mode to be damped and the m = 2 helical mode is relatively unchanged. The resolved kinetic energy was only marginally higher than the unforced case and significantly lower than the 300Hz forced case. The DMD analysis showed how, as the forcing increased the flow through the injector, the flow is simultaneously pushed radially inwards and accelerated azimuthally. It also identified the region downstream of the splitter plate with significant fluctuations and is likely to be the wavemaker region responsible for the generation of helical instabilities. This work improves understanding of how helical modes of different azimuthal wave numbers react to acoustic forcing. The ability to manipulate the strength of these modes through alteration of the fuel injector geometry gives designers an additional tool to control thermo-acoustic instabilities.
Validation of a Physics-Based Low-Order Thermo-Acoustic Model of Combustion Driven Oscillations in a Liquid Fueled Gas Turbine Combustor
Authors: Knadler M. , Caley T. , Lee J. G. , Jung S. , Kim S. , Park H.
Published: August 2018

Validation test results of a low-order thermoacoustic model of combustion dynamics in a liquid-fueled, gas turbine combustor are presented. A finite element model designed in COMSOL Multiphysics is used as a tool for predicting naturally occurring combustion instabilities. The combustion rig consists of an inlet plenum, nozzle, combustor, and variable length transition tube. The combustor is run at pilot only mode at high pressure (up to 4 atm), resulting in sooty fuel-rich flame. The global flame transfer function is measured using flame emission at OH* band (307±5 nm) from the whole flame with inlet velocity fluctuation which is measured using multi-microphone measurement. The impedances at the choked inlet and exit of combustor are measured using a multi-microphone method, showing that the actual impedances of choked inlet and exit are different from theoretical values. Using the measured flame transfer function and impedances, the model’s capability to predict the instabilities is examined for two different rig configurations: one with a 10”-long transition tube and the other with a 20”-long transition tube. The modelling results are shown to converge to eigenfrequencies close to those measured experimentally. They correctly predict the stability regime of each of the tested conditions and frequencies of oscillations to within a maximum of 4% error. Using measured acoustic boundary conditions at the inlet and exit orifice improves the prediction of instability frequency.
Large Eddy Simulation of Boundary Layer Transition Mechanisms in a Gas-Turbine Compressor Cascade
Authors: Scillitoe Ashley D. , Tucker Paul G. , Adami Paolo
Published: August 2018

Large Eddy Simulation (LES) is used to explore the boundary layer transition mechanisms in two rectilinear compressor cascades. To reduce numerical dissipation, a novel locally adaptive smoothing scheme is added to an unstructured finite-volume solver. The performance of a number of Sub-Grid Scale (SGS) models is explored.

With the first cascade, numerical results at two different freestream turbulence intensities (Ti’s), 3.25% and 10%, are compared. At both Ti’s, time-averaged skin-friction and pressure coefficient distributions agree well with previous Direct Numerical Simulations (DNS). At Ti = 3.25%, separation induced transition occurs on the suction surface, whilst it is bypassed on the pressure surface. The pressure surface transition is dominated by modes originating from the convection of Tollmien-Schlichting waves by Klebanoff streaks. However, they do not resembled a classical bypass transition. Instead, they display characteristics of the “overlap” and “inner” transition modes observed in the previous DNS. At Ti = 10%, classical bypass transition occurs, with Klebanoff streaks incepting turbulent spots.

With the second cascade, the influence of unsteady wakes on transition is examined. Wake-amplified Klebanoff streaks were found to instigate turbulent spots, which periodically shorten the suction surface separation bubble. The celerity line corresponding to 70% of the free-stream velocity, which is associated with the convection speed of the amplified Klebanoff streaks, was found to be important.
Heat Transfer and Pressure Drop in a Converging Pedestal Array With Exit Area Variation
Authors: Soma L. W. , Ames F. E. , Acharya S.
Published: August 2018

The trailing edge of a vane is one of the most difficult areas to cool due to a narrowing flow path, high external heat transfer rates, and deteriorating external film cooling protection. Converging pedestal arrays are often used as a means to provide internal cooling in this region. The thermally induced stresses in the trailing edge region of these converging arrays have been known to cause failure in the pedestals of conventional solidity arrays. The present paper documents the heat transfer and pressure drop through two high solidity converging rounded diamond pedestal arrays. These arrays have a 45 percent pedestal solidity. One array which was tested has nine rows of pedestals with an exit area in the last row consistent with the convergence. The other array has eight rows with an expanded exit in the last row to enable a higher cooling air flow rate. The expanded exit of the eight row array allows a 30% increase in the coolant flow rate compared with the nine row array for the same pressure drop. Heat transfer levels correlate well based on local Reynolds numbers but fall slightly below non converging arrays. The pressure drop across the array naturally increases toward the trailing edge with the convergence of the flow passage. A portion of the cooling air pressure drop can be attributed to acceleration while a portion can be attributed to flow path losses. Detailed array static pressure measurements provide a means to develop a correlation for the prediction of pressure drop across the cooling channel. Measurements have been acquired over Reynolds numbers based on exit flow conditions and the characteristic pedestal length scale ranging from 5000 to over 70,000.
The Assessment of Assemblability and Dissassemblability of Aero Engines During Preliminary Design
Authors: Mall Jochen , Staudacher Stephan , Koch Christian
Published: August 2018

With a continuous annual growth of air traffic by nearly 5%, an additional paradigm change towards industrially producible products is necessary to meet future demands of new airplanes and aero engines. To ensure the producibility of more and more sophisticated aero engines, an assessment of assemblability and disassemblability during preliminary design becomes necessary in this context. Major cost drivers can be identified at an early stage in the product development process regarding assembly-feasible design of the product and the corresponding assembly system. This paper introduces a 3D preliminary design model and a methodology to assess the assemblability and disassemblability of civil aero engines during preliminary design. Based on a systematic evaluation of three different variants of low-pressure turbine modules, implications for a reduction of the assembly and disassembly time can be deduced. Hence, optimization potentials for product design as well as for the design of the corresponding assembly system are identified. The generic models and parametric evaluation methodology of the presented approach allow an application on further aero engine modules, new aero engine technologies as well as other fields.
Learning From Success Mixing Different Brands of Turbomachinery Lube Oil ISO VG32 at Badak LNG Plant Bontang
Authors: Junaedi Achmad
Published: August 2018

Badak LNG Plant Bontang have succeeded in mixing different brands of turbomachinery lube oil ISO VG32 which intended to increase flexibility of lube oil usage and eliminate to one brand dependency during operational. The methodology referred to ASTM D7155 Standard Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils and ASTM D4378 Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas and Combined Cycle Turbines. The study was started from lube oil compatibility test at laboratory. After that, a ratio 70:30 of ISO VG32 existing lube oil (DTE Light) and new lube oil (Turbolube XT32) were mixed and trialed to Fuel Gas Compressor and its Turbine Driver. Lube oil and equipment operating parameter such as viscosity, color, water content, total acid number, foaming tendency, oxidation, metal content, flash point, bearing temperature, filter differential pressure, and vibration were collected and compared to baseline data to analyze deterioration indication of lube oil. As long as eight month trial test, there was no deterioration indication of lube oil mixture and no significant influence to the equipment operating performance. Badak LNG have decided to continue lube oil mixing.
The Influence of Rotor-Wakes on Boundary Layer Development in an Axial Compressor and its Numerical Prediction
Authors: Frieling Dominik , Griebel Achim , Wein Lars , Seume Joerg R. , Herbst Florian
Published: August 2018

This paper provides an analysis and discussion of the development of rotor wakes, and their influence on the boundary layer along a downstream axial compressor vane. Numerical investigations are carried out by means of unsteady RANS and Scale-Adaptive Simulations which apply the Shear Stress Transport turbulence model coupled to the γ-Reθ transition model. Numerical results are compared with the previously published and newly measured experimental data of a two-stage low-speed axial research compressor with IGV. In order to determine the differences between the numerical simulations and experimental data, space-time diagrams of wall shear stress and shape factor on the surface of the first vane are used together with upstream turbulence intensity. Special emphasis is put on differences in the wake development downstream of the blade, and their influence on the vane’s boundary layer development. It is shown, that there are still crucial limitations in the prediction of the wake development, especially the wake width and intensity. The badly-predicted wakes lead to an inaccurate prediction of the boundary layer development. A possibility to overcome the inaccurate prediction of the boundary layer development is proposed. The apparent advantage of the Scale-Adaptive Simulations, i.e allowing to resolve turbulent structures and large-scale unsteadiness, does not lead to a better prediction of transition processes. On the contrary, coupling the γ–Reθ transition model to Scale-Adaptive Simulations lead to further disadvantages.
Non-Linear Vibration of Rotating Co-Rotational Two-Dimensional Beams With Large Displacement
Authors: Shen Zihan , Chouvion Benjamin , Thouverez Fabrice , Beley Aline , Beley Jean-Daniel
Published: August 2018

In order to achieve better performances and reduce fuel consumption, the new generation of turbomachines uses larger and lighter design, for instance the “open-rotor” concept, and is conceived to rotate at higher speeds. Parts of the structure become then even more likely to undergo large amplitude vibrations. Consequently, the conception of future aero-engine requires a sound and robust technique to predict the rotating machine vibrations considering geometrical nonlinearities (large displacements and large deformation). In this paper, the nonlinear vibrations of rotating beams with large displacements is investigated by the use of the Co-Rotational (C-R) finite element method. In the C-R approach, the full motion of each element is decomposed into a rigid body part and a pure deformational part by introducing a local coordinate system attached to the element. The utilization of the C-R method offers the possibility to treat geometrical nonlinearity directly with pre-extracted rigid body motion displacements. The originality we propose in this study is to derive its formulation in a rotating reference frame and include both centrifugal and gyroscopic effects. The nonlinear governing equations are obtained from Lagrange’s equations using a consistent expression for the kinetic energy. With this formulation, the spin-stiffening effect from geometrical nonlinearities due to large displacements is accurately handled. The proposed approach is then applied to several types of mechanical analysis (static large deformation, modal analysis at different spin speeds, and transient analysis after an impulsive force) to verify its accuracy and demonstrate its efficiency.
Steady CFD Simulation of a High Pressure Turbine Rotor With Hub and Shroud Purge Flow
Authors: Sanz Wolfgang , Zerobin Stefan , Egger Manfred , Bader Pascal , Pieringer Paul , Göttlich Emil , Heitmeir Franz
Published: August 2018

Purge air is injected at the hub and shroud of axial turbines in order to avoid hot gas entering the gaps between stationary and rotating blade rows. The purge flows considerably interact with the main flow and influence the secondary flow like the tip leakage vortex. Therefore, at Graz University of Technology the flow in a product-representative one-and-a-half stage test turbine under the influence of purge flows was investigated. Four individual purge mass flows differing in flow rate, pressure, and temperature were injected through hub and tip cavities before and after the unshrouded high-pressure turbine rotor.

In order to get more insight into the cavity flows and the flow evolution in the rotor this configuration is studied with a steady CFD simulation with and without purge flows. It was found that the secondary flow and especially the tip leakage vortex is significantly influenced by the purge flow which varies in circumferential direction. The differences between purge and zero-purge flow conditions are discussed with the help of radial distributions and contour plots of stream-wise vorticity. Streamlines allow to follow the path of the purge flows in the rotor and show the radial displacement of the secondary flow vortices. Wall streamlines describe the changes in the boundary layer flow and their effect on the vorticity after the trailing edge.
Conjugate Heat Transfer Methodology for Thermal Design and Verification of Gas Turbine Cooled Components
Authors: Winchler Lorenzo , Andreini Antonio , Facchini Bruno , Andrei Luca , Bonini Alessio , Innocenti Luca
Published: August 2018

Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature, justified by a corresponding increase of cycle efficiency and power output. In such way turbine components heat load management has become a compulsory activity and then, a reliable procedure to evaluate the blades and vanes metal temperatures, is, nowadays, a crucial aspect for a safe components design.

In the framework of the design and validation process of HPT (High Pressure Turbine) cooled components of the BHGE NovaLT™ 16 gas turbine, a decoupled methodology for conjugate heat transfer prediction has been applied and validated against measurement data. The procedure consists of a conjugate heat transfer analysis in which the internal cooling system (for both airfoils and platforms) is modeled by an in-house one-dimensional thermo-fluid network solver, the external heat loads and pressure distribution are evaluated through 3D CFD analysis and the heat conduction in the solid is carried out through a 3D FEM solution. Film cooling effect has been treated by means of a dedicated CFD analysis, implementing a source term approach.

Predicted metal temperatures are finally compared with measurements from an extensive test campaign of the engine, in order to validate the presented procedure.
Uncertainty Quantification Analysis of Back Facing Steps Film Cooling Configurations
Authors: Sakai Eiji , Bai Meng , Ahlfeld Richard , Montomoli Francesco
Published: August 2018

This paper compares two back step film-cooling configurations under an uncertainty quantification framework. An important limit of such configurations is their reliability under geometrical variations, which is taken into account in this study.

For the back step configurations, a straight and a curved step is used. Detached eddy simulations with k-ω turbulence model are performed using OpenFOAM ver. 4.0. The Reynolds number is based on the main stream velocity and film cooling hole diameter, d, and is Re = 15,300. The investigated step heights are 0.5d and 0.75d, and the blowing ratios, BR, are 0.5 and 1.0. The straight and the curved steps are found to enhance lateral spreading of coolant flow, resulting in higher film cooling effectiveness compared to the baseline case without the step at comparatively higher BR conditions. The curved step shows better performance than the straight one in particular from BR = 1.0 upwards with the step height of 0.5d.

At lower BR with lower H/d, and at higher BR with higher H/d, deterministic simulations are not able to identify the best performer. However when the performance of the two configurations is evaluated considering the stochastic variation of step height and the cooling condition, the benefit of the curved step becomes clear. In particular, the curved step shows better mean performance and has a higher probability to achieve a better performance than the other one. The uncertainty in the film cooling effectiveness caused by the uncertainty of the step height and the BR is investigated using Sparse Approximation of Moment-Based Arbitrary polynomial chaos (SAMBA).
Development of Blade Tip Repair for SGT-700 Turbine Blade Stage 1, With Oxidation Resistant Weld Alloy
Authors: Barhanko Dikran A. , Åberg Niclas R. , Andersson Olov H.
Published: August 2018

The SGT-700 gas turbine currently rated at 33 MW (simple cycle) and with an efficiency of ∼ 37% has been in service since 2002. In order to reduce life cycle cost, a repair process with an acceptable repair yield needed to be developed for turbine blade stage 1. The stage 1 blade is made from the polycrystalline cast alloy IN792, and the blade is coated with PtAl or MCrAlY+TBC depending on engine model. The blade is internally air cooled. After the row 1 vane, the stage 1 blade is forced to withstand the highest temperatures. The combination of high temperatures, and thermomechanical fatigue loading results in blade tip degradation, which leads to a loss of thermal efficiency. The blade tip repair process described in this document is one step in a continuous repair development plan for the SGT-700. To ensure quality in each reparation, the blade tip repair described here was developed using Siemens’ Product Development Process (PDP).

The development of the repair procedure include:

• Coating removal

• Pre- and post-weld heat treatment

• Machining of oxidized areas

• Hot box welding with manual GTAW

• Grinding to final air foil shape

• Re-opening of the cooling holes with EDM

• EDM to restore the squealer tip

• Recoating and air flow check

This technical paper describes the repair process developed together with a sub-supplier. The project resulted in a successful repair process for the component as well as repaired blades with higher blade tip oxidation resistance compared with the original design.
Importance of Boundary Layer Transition in a High-Pressure Turbine Cascade Using LES
Authors: Seguí Luis M. , Gicquel L. Y. M. , Duchaine F. , de Laborderie J.
Published: August 2018

In the context of smooth surfaces where no industrial process modifies the flow and where no roughness affects the boundary layer flow, there are configurations today where the correct heat flux prediction is still unattained for certain operating points. This is the case of the LS89 configuration that has shown to be of great difficulty to accurately simulate the thermal fields for high Reynolds number flows even when performing wall-resolved Large Eddy Simulations (LES). The physics of the studied operating point (MUR235) are especially complex due to the interaction of a transitioning boundary layer, shock waves and free-stream turbulence injected at the inlet. In this paper, free-stream turbulent specifications are seen to be important towards the capture of the heat transfer profile on most regions of the blade. The boundary layer is found to be transitional when either artificially raising the level of turbulence at the inlet or by using a highly refined mesh that induces the generation of turbulent spots that increase the heat transfer. The important refinement done improves the heat flux predictions to the point it is approaching the experimental data.
Flowfield of a Shaped Film Cooling Hole Over a Range of Compound Angles
Authors: Haydt Shane , Lynch Stephen
Published: August 2018

Film cooling holes are a well-established cooling technique used in gas turbines to keep component metal temperatures in an acceptable range. A streamwise-oriented film cooling hole creates a symmetric counter-rotating vortex pair (CRVP) due to the jet interaction with the crossflow. As the orientation of the film cooling hole is incrementally misaligned with the streamwise direction (known as a compound angle), one of the vortices in the CRVP gains strength at the expense of the other until there is a single streamwise vortex that dominates the flowfield. This vortex diffuses the coolant jet and impinges hot gas onto the surface, which can augment heat transfer coefficients in a region uncovered by coolant. Although this has been well studied for cylindrical holes, there is less understanding about the nature of this phenomenon for shaped holes, which are intended to diffuse coolant laterally to minimize flowfield interaction. In the present study, particle image velocimetry (PIV) was used to measure the flowfield of compound angled shaped film cooling holes at several downstream planes normal to the streamwise direction. Five compound angled 7-7-7 holes were tested, from a streamwise oriented hole (0° compound angle) to a 60° compound angle hole, in increments of 15°. All cases were tested at a density ratio of 1.0 and blowing ratios ranging from 1.0 to 4.0. Experimental data shows that the circulation increases as compound angle increases because the flowfield transitions from a CRVP to a single streamwise vortex. For large compound angles, the streamwise vortex lifts the core of the jet off of the surface, isolating the coolant from the endwall. Measurements also indicate hole-to-hole interaction downstream for cases with high blowing ratio and large compound angle. Flowfield results are compared with adiabatic effectiveness results from a companion study in order to explain hole-to-hole interaction trends.
Performance of the Automotive Turbocharger Compressor With Various CO2-Air Mixtures
Authors: Duda Tomasz , Copeland Colin
Published: August 2018

The automotive low pressure exhaust gas recirculation or closed-cycle gas turbine engines are among applications where an alternative fluids to air are used. This paper analyses compressor performance measured while operating with substitute gas. Several compressor performance maps were generated and compared on a steady-state turbocharger test facility run in a closed-loop mode. The automotive centrifugal compressor was mapped with pure air, CO2-air mixtures (3%, 5%, 10% CO2 by mass) and pure CO2. The analysis of the obtained data has indicated that the use of reduced speed parameter and reduced mass flow parameter formulas worked well in the process of the compressor map correction for the CO2-air mixtures. The corrected (with reduced mass flow and speed parameters) compressor performance map generated for the case of pure CO2 has shown a shift in both choke and surge lines and changes in measured pressure ratio and efficiency. Further efficiency and pressure ratio corrections based on the method proposed by Roberts and Sjolander [1] have shown no match between the predicted and measured values of efficiency for CO2. The series of adiabatic 3D CFD simulations indicated that this was likely caused by the heat transfer between the uninsulated turbomachinery components.
Approximate Solution of the Fokker-Planck Equation for a Multi-Degree of Freedom Frictionally Damped Bladed Disk Under Random Excitation
Authors: Förster Alwin , Panning-von Scheidt Lars , Wallaschek Jörg
Published: August 2018

Bladed Disks are subjected to different types of excitations, which cannot in any case be described in a deterministic manner. Fuzzy factors, such as slightly varying airflow or density fluctuation, can lead to an uncertain excitation in terms of amplitude and frequency, which has to be described by random variables. The computation of frictionally damped blades under random excitation becomes highly complex due to the presence of nonlinearities. Only a few publications are dedicated to this particular problem. Most of these deal with systems of only one or two degrees of freedom and use computational expensive methods, like finite element method (FEM) or finite differences method (FDM), to solve the determining differential equation. The stochastic stationary response of a mechanical system is characterized by the joint probability density function (JPDF), which is driven by the Fokker-Planck equation (FPE). Exact stationary solutions of the FPE only exist for a few classes of mechanical systems. This paper presents the application of a semi-analytical Galerkin-type method to a frictionally damped bladed disk under influence of Gaussian white noise (GWN) excitation in order to calculate its stationary response. One of the main difficulties is the selection of a proper initial approximate solution, which is applicable as a weighting function. Comparing the presented results with those from the FDM, Monte-Carlo Simulation (MCS) as well as analytical solutions proves the applicability of the methodology.
Numerical Investigation of Spray Development in a Micro Gas Turbine LPP Combustor With Airblast Atomizer
Authors: Annunziata Gianluca , Cameretti Maria Cristina , De Robbio Roberta , Tuccillo Raffaele
Published: August 2018

The purpose of the paper is the investigation of the combustion development in a Lean Premixed Prevaporized (LPP) combustor supplied with liquid fuels of a Micro Gas Turbine. The injection system is equipped by an airblast atomizer with three air inlets.

In such a study the analysis is performed by a CFD tool that can simulate the injection conditions, by isolating and studying some specific phenomena. A 3-D fluid dynamic code (the FLUENT® flow solver) has been used to simulate the spray pattern in the chamber fuelled by kerosene fuel. Preliminarily, the numerical simulation refers to cold flow conditions, in order to validate the estimation of the fundamental spray parameters, such as the spray angle and Sauter Mean Diameter of the droplets; in a second step, the calculations employ boundary conditions close to those occurring in the actual combustor operation, in order to predict the fuel vapour distribution throughout the premixing chamber. In particular, the fuel is injected under the typical conditions that occur in the injection system of a gas turbine LPP combustor and in all cases examined, the boundary information is introduced in terms of air and fuel mass flow rates and of inlet characteristics of the air flow entering the revalorizing chamber, in order to estimate the fuel vapour formation and its distribution.

In a third phase the combustion phenomenon is simulated and the NO emissions calculated. Finally, the best solution obtained is also tested by using a bio-fuel to compare the combustion performance and NO amount.
Experimental and Numerical Investigation of a Shower Head Advanced Jet Impingement on Concave Surfaces
Authors: Singh Alankrita , Prasad Bhamidi V. S. S. S.
Published: August 2018

A novel configuration of jet impingement cooling for leading edge of a gas turbine blade is proposed in this paper. The new configuration is obtained by rearranging the jet impingement holes in a shower head fashion with a combination of circular and elliptic holes. The entire configuration is simulated by a jet impingement pipe (JIP) to experimentally investigate the improved performance of cooling of concave target surfaces. The central JIP has circular ends, remaining four neighboring JIP have 45° chamfer at one of its ends facing target surface to ensure uniformity and extension in cooling coverage. The heat transfer characteristics of jet impingement were investigated both experimentally and numerically by varying jet Reynolds number and gap ratio. Simulations are also carried out for different curvature ratios to determine the relative surface curvature effect on jet impingement heat transfer. This is accomplished by varying diameter of concave surface. The augmentation in heat transfer by both the elliptic (chamfered JIP) and circular (whose all JIP ends are circular) shower head arrangements are compared.
Acoustic Properties of Perforated Liners With Perpendicular Arrangements of Narrow Slots
Authors: Jetté François-Xavier , Shanian Ali , Schaenzer Megan , Pham Minh Quan , Bourgeois Geneviève , Farhangi Mehran , Sanchez Fabian , Innes Matt
Published: August 2018

Cooling holes in combustion liners are typically circular, as are the holes used for acoustic damping of combustor instabilities. This hole geometry is chosen for several reasons, which include manufacturability, stress concentration considerations, and because the behavior of round holes is well understood. However, developments in both manufacturing techniques and modeling methods now allow other hole geometries to be considered, such as perpendicular arrangements of narrow slots carefully shaped to prevent high stress concentrations (patent pending). The latter have been demonstrated to provide more efficient cooling and lower stress compared to round holes. However, the acoustic properties of such arrangements are not straightforward to model yet since it is not known how some important factors are affected by this geometry change.

In order to study the acoustic behavior of such arrangements of holes, a series of tests were conducted in an impedance tube (in reflection) for various slot shapes, width and spacing, with a backing cavity and purge flow (controlled via pressure drop). Some baseline measurements for circular holes were also obtained in an attempt to quantify any difference resulting from the change in hole shape.

The results have shown that at any pressure drop, the maximum absorption coefficient for narrow perpendicular slots and round holes is nearly equal when the hole area corrected by the discharge coefficient (i.e. the effective area) is also nearly the same, and that narrow perpendicular slots give more broadband absorption on the high frequency side of the absorption peak for a given cavity. It is suggested that since the maximum absorption between round holes and narrow perpendicular slots are nearly equal at an equivalent effective area, the resistance (real part of impedance) of the holes depends on the maximum flow velocity through the hole rather than the average velocity, for the particular combinations of hole dimension and sample plate thickness tested. It is also suggested that the greater broadband absorption at high frequencies for the narrow slots could be due to the fact that their high length to width ratio would result in a characteristic dimension dominated by their small width (similar to the airfoil thickness being the representative dimension of the size of the wake for an airfoil) hence a lower Strouhal number.
Improved Smith Chart for Axial Compressor Design
Authors: Anderson Mark R.
Published: August 2018

Preliminary design of a turbomachinery stage usually begins with target flow states, represented by a velocity triangle. Guidance for these target velocities comes from a variety of sources, which include some physics-based rules but, more often than not, have a significant empirical basis.

The best-known guidelines for axial designs are the so-called “Smith Charts”. This approach was documented in detail by Smith [1] and quickly became a preferred approach for initial design of axial turbines stages. The method was based on a significant set of test data for various turbine designs, corrected for complicating factors, such as various clearance gaps and so on. Similar, but less well-documented methods, have been developed for axial compressor design. Despite the widespread use of the Smith chart method, these approaches have a very limited substantiation and no clear pedigree. Most attempts to develop Smith-like charts for compressor design guidance are based on fairly simplified models that carry significant unknowns, particularly at high loading.

This paper details the development of new Smith charts for axial compressor designs, by making extensive use of optimization techniques. Profile designs are optimized for a range of target flow coefficients and work coefficients. The result is a performance map, representing the maximum possible performance for a given set of coefficient values. The analysis was limited to 2D profile design (quasi-3D analysis) and a reaction of 50%, the theoretical ideal reaction rate for 2D flow.

Using the newly developed maps of maximum performance potential, the accuracy of various modeling methods is examined, along with their ability to determine the optimum design condition. Improvements to profile loss methods, based on the new data, are suggested.
Rib Turbulator Effects on Crossflow-Fed Shaped Film Cooling Holes
Authors: Fox Dale W. , Jones Fraser B. , McClintic John W. , Bogard David G. , Dyson Thomas E. , Webster Zachary
Published: August 2018

Most studies of turbine airfoil film cooling in laboratory test facilities have used relatively large plenums to feed flow into the coolant holes. However, a more realistic inlet condition for the film cooling holes is a relatively small channel. Previous studies have shown that the film cooling performance is significantly degraded when fed by perpendicular internal crossflow in a smooth channel. In this study, angled rib turbulators were installed in two geometric configurations inside the internal crossflow channel, at 45° and 135°, to assess the impact on film cooling effectiveness. Film cooling hole inlets were positioned in both pre-rib and post-rib locations to test the effect of hole inlet position on film cooling performance. A test was performed independently varying channel velocity ratio and jet to mainstream velocity ratio. These results were compared to the film cooling performance of previously measured shaped holes fed by a smooth internal channel. The film cooling hole discharge coefficients and channel friction factors were also measured for both rib configurations with varying channel and inlet velocity ratios. Spatially-averaged film cooling effectiveness is largely similar to the holes fed by the smooth internal crossflow channel, but hole-to-hole variation due to inlet position was observed.