bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Turbulence-Chemistry Interaction Modeling on the Structure and the Stability of a Swirl-Stabilized Flame
Authors: Lourier Jean-Michel , Eberle Christian , Noll Berthold , Aigner Manfred
Published: August 2015

Scale Adaptive Simulations (SAS) of the swirl-stabilized flame of the PRECCINSTA burner are presented. Within the computations a large share of velocity fluctuations as well as temperature and species fluctuations are resolved in combustion regions. With rising resolution of fluctuating quantities, the impact of the sub grid scale (SGS) turbulence and turbulence chemistry interaction (TCI) models decreases. The main topic of this paper is to investigate the residual influence of an SGS-TCI model in case of the SAS of the swirl-stabilized flame. As a first outcome, the data obtained in this work are in very good agreement with experimental and LES data from the literature. And secondly, the modeling of SGS-TCI is of minor importance for the resulting time-mean quantities due to the high share of resolved velocity, temperature and species fluctuations in the computations.
Influence of Trailing Edge Geometry on the Condensing Steam Flow in Low-Pressure Steam Turbine
Authors: Patel Giteshkumar , Patel Yogini , Turunen-Saaresti Teemu
Published: August 2015

The paper describes the influence of trailing edge geometries on the non-equilibrium homogeneously condensing steam flow in the stationary cascade of turbine blades. The computational fluid dynamics (CFD) simulations were performed with the ANSYS Fluent CFD code using the Eulerian-Eulerian approach. The condensation phenomena were simulated on the basis of the classical nucleation theory, and the steam properties were calculated with the real gas model. Flow turbulence was solved by employing the modified version of the shear-stress transport (SST) k-ω turbulence model. For this study, three trailing edge profiles; that is, conic, semicircular and square were considered. The influence of the trailing edge shapes were discussed together with experimental data available in the literature. The presented results show that the trailing edge geometries influence on the nucleation process, the droplet size, wetness fraction, the shock waves structure generated at trailing edge and its angles, the flow angle, the entropy generation and flow mixing in the wake. The cascade loss coefficients were calculated for the low inlet superheat case and for the high inlet superheat case. The presented results demonstrated that the losses that occur due to the irreversible heat and mass transfer during the condensation process were also influenced due to the trailing edge shapes.
Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low Pressure Turbine Blade
Authors: Cui J. , Nagabhushana Rao V. , Tucker P. G.
Published: August 2015

Using a range of high fidelity large eddy simulations, the contrasting flow physics on the suction surface, pressure surface and endwalls of a low pressure turbine blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at mid-span and (b) the impact of the state of the incoming boundary layer on endwall flow features.

On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high Free-Stream Turbulence (FST). The instantaneous flow features revealed that this reduction at high FST is due to the dominance of ‘streak-based’ transition over the ‘Kelvin-Helmholtz’ based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients.

On pressure surface, elongated vortices were observed at low FST. The possibility of the co-existence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence.

At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer when compared to an incoming laminar boundary layer. Multiple horse-shoe vortices, which constantly moved towards the leading edge due to a low-frequency unstable mechanism, were captured.
Low NOx SEV Lean Premix Reheat Combustion in Alstom GT24 Gas Turbines
Authors: Guyot Daniel , Tea Gabrielle , Appel Christoph
Published: August 2015

Reducing gas turbine emissions and increasing their operational flexibility are key targets in today’s gas turbine market. In order to further reduce emissions and increase the operational flexibility of its GT24 (60Hz) and GT26 (50Hz), Alstom has introduced an improved SEV burner and fuel lance into its GT24 upgrade 2011 and GT26 upgrade 2011 sequential reheat combustion system.

Sequential combustion is a key differentiator of Alstom GT24 engines in the F-class gas turbine market. The inlet temperature for the GT24 SEV combustor is around 1000 degC and reaction of the fuel/oxidant mixture is initiated through auto-ignition. The recent development of the Alstom sequential combustion system is a perfect example of evolutionary design optimizations and technology transfer between Alstom GT24 and GT26 engines. Better overall performance is achieved through improved SEV burner aerodynamics and fuel injection, while keeping the main features of the sequential burner technology.

The improved SEV burner/lance concept has been optimized towards rapid fuel/oxidant mixing for low emissions, improved fuel flexibility with regards to highly reactive fuels (higher C2+ and hydrogen content), and to sustain a wide operation window. In addition, the burner front panel features an improved cooling concept based on near-wall cooling as well as integrated acoustics damping devices designed to reduce combustion pulsations thus extending the SEV combustor’s operation window even further. After having been validated extensively in the Alstom high pressure sector rig test facility, the improved GT24 SEV burner has been retrofitted into a commercial GT24 field engine for full engine validation during long-term operation.

This paper presents the obtained high pressure sector rig and engine validation results for the GT24 (2011) SEV burner/lance hardware with a focus on reduced NOX and CO emissions and improved operational behavior of the SEV combustor. The high pressure tests demonstrated robust SEV burner/lance operation with up to 50% lower NOX formation and a more than 70K higher SEV burner inlet temperature compared to the GT24 (2006) hardware.

For the GT24 engine with retrofitted upgrade 2011 SEV burner/lance all validation targets were achieved including an extremely robust operation behavior, up to 40% lower GT NOX emissions, significantly lower CO emissions at partload and baseload, a very broad operation window (up to 100K width in SEV combustor inlet temperature) and all measured SEV burner/lance temperatures in the expected range. Sector rig and engine validation results have confirmed the expected SEV burner fuel flexibility (up to 18%-vol. C2+ and up to 5%-vol. hydrogen as standard).
Measurement and Prediction of Adiabatic Film Effectiveness of Combustor Representative Effusion Arrays
Authors: Krawciw Jason , Martin Damian , Denman Paul
Published: August 2015

Thermal protection of gas turbine combustors relies heavily upon the delivery of a carefully managed film of coolant air to the hot-side of the combustor liner. Furthermore, improvements in engine sfc and the trend to ever more aggressive engine cycles means greater emphasis is being placed upon more efficient use of the proportion of combustion system air made available for cooling. As a result, there is a requirement to better understand the development of cooling films deposited onto the hot-side of the liner through complex effusion arrays. This study, therefore, is concerned with the prediction and measurement of adiabatic film effectiveness of a number of engine-representative designs. A RANS based CFD approach is used to predict film effectiveness in which computational cost is minimised by solving first for a single coolant passage to provide high fidelity, near-exit boundary conditions to the effusion arrays. Equivalent measurements are made for each test case using a Pressure Sensitive Paint (PSP) technique in which the oxygen-quenched fluorescence properties of the paint are employed together with a Nitrogen gas cooling simulant to determine adiabatic film effectiveness. This study demonstrates that whist the model under-predicts the mixing of the coolant with the main-stream flow, and hence the film development over the surface, the approach works well at quantifying the relative performance of each design.
Heat Release Response to Forced Flow Oscillations of a Low-Order Modelled Laboratory Scale Dump Combustor
Authors: Orchini Alessandro , Juniper Matthew P.
Published: August 2015

In this study we investigate the heat release response to forced harmonic velocity fluctuations of a bluff body dump combustor. We use the kinematic G-equation as a low-order model for the flame and heat release dynamics. The geometry considered is based on an experimental setup developed by R. Balachandran and widely investigated in the literature, and we look for a qualitative comparison with experimental and numerical results. We model the flow field dynamics adapting the well-known travelling wave model, which was originally developed for conical flames, to the case of a bluff-body stabilized flame in a non-uniform mean flow field. We impose velocity fluctuations at the dump plane at various frequencies and amplitudes and we integrate the nonlinear flame and heat release dynamics. Results show that the model qualitatively reproduces the kinematic behaviour observed in the experiments, although some major quantitative differences are found. We conclude by discussing our results, and adjustments that could be introduced in future in the low-order model in order to improve it.
Vortexing Methods to Reduce Secondary Losses in a Low Reaction Industrial Turbine
Authors: Deshpande Srikanth , Thern Marcus , Genrup Magnus
Published: August 2015

Vortexing methods implemented on an industrial steam turbine vane in order to reduce secondary losses are discussed. Three vortexing methods presented are prismatic blade design, inverse vortex and parabolic forced vortex. Baseline industrial vane considered for study is a prismatic blade design. Modifications are analysed numerically using commercial code CFX. Modified vanes along with baseline rotor as a complete stage is considered for analysis. Steady state Reynolds averaged Navier Stokes equations are solved. Total pressure loss (TPL) is used as target functions to monitor reduction in secondary losses. Rotor considered for the study is the baseline industrial rotor for all design modifications of vane.
Impact of High Exhaust Back Pressure on Power Turbine Secondary Flows and Disc Thermals
Authors: Thirumurthy Deepak
Published: August 2015

Industrial and aeroderivative gas turbines use exhaust systems for flow diffusion and pressure recovery. The downstream balance-of-plant systems such as heat recovery steam generators or selective catalytic systems require, in general, a steady, uniform flow out of the exhaust system. One detrimental effect of having these downstream systems is the increased back pressure. These combined-cycle systems increase the back pressure on the free power turbine which results in decreased power output and efficiency.

Aeroderivative gas turbines for mechanical drive application have a wide operational envelope. In general, at baseload, the exhaust back pressure ranges from 1.5 to 2.5 kPa above ambient pressure. Increased exhaust back pressure results in changes to power turbine secondary flows by changing the cavity flow dynamics, sealing flows, and rim seal ingestion. This impacts the thermal characteristics of turbine rotor discs and their lives.

The primary motivation for this research and development work was to develop solution for secondary air system and investigate the impact of high exhaust back pressure on power turbine disc thermals. At first, 1-D system-level power turbine secondary flow analyses were carried out with normal back pressure (3.0 kPa) and with high back pressure (11.37 kPa). In addition, 3-D computational fluid dynamic simulations were performed to understand the cavity flow dynamics and disc heat transfer coefficient variations. These results were used in a high-fidelity 2-D thermal modeling of the power turbine to study the impact of back pressure on turbine disc thermal characteristics and their lives.

The fluid and thermal predictions were validated using normal back pressure full-scale full-load test results. Cooling mass flow rate, static pressure, air temperature, and metal temperature predictions are compared with test results over a wide operating range. The numerical predictions are in good agreement with test results.
A Comparison of a Mono, Twin and Double Scroll Turbine for Automotive Applications
Authors: Walkingshaw Jason , Iosifidis Georgios , Scheuermann Tobias , Filsinger Dietmar , Ikeya Nobuyuki
Published: August 2015

As a means of meeting ever increasing emissions and fuel economy demands car manufacturers are using aggressive engine downsizing. To maintain the power output of the engine turbocharging is typically used. Due to the miss-match of the mass flow characteristics of the engine to the turbocharger, at low engine mass flow rates, the turbocharger can suffer from slow response known as “Turbolag”. Mono-scroll turbines are capable of providing good performance at high mass flow rates and in conjunction with low inertia mixed flow turbines can offer some benefits for transient engine response. With a multi-entry system the individual volute sizing can be matched to the single mass flow pulse from the engine cylinders. The exhaust pulse energy can be better utilised by the turbocharger turbine improving turbocharger response, while the interaction of the engine exhaust pulses can be better avoided, improving the scavenging of the engine.

The behaviour of a mono-scroll turbocharger with the engine using engine simulation tools has been well established. What requires further investigation is the comparison with multi-entry turbines. CFD (Computational Fluid Dynamics) has been used to examine the single admission behaviour of a twin and double scroll turbine. Turbocharger gas stand maps of the multi-entry turbines have been measured at full and single admission. This data has been used in a 0D engine model. In addition, the turbine stage has been tested on the engine and a validation of the engine model against the engine test data is presented. Using the validated engine model a comparison has been made to understand the differences in the sizing requirements of the turbine and the interaction of the mono-scroll and multi-entry turbines with the engine. The impact of the different efficiency and mass flow rate trends of the mono and multi-entry turbochargers are discussed and the trade-offs between the design configurations regarding on engine behaviour are investigated.
Effects of Flow Path Height of Impeller Exit and Diffuser on Flow Fields in a Transonic Centrifugal Compressor
Authors: Tomita Isao , Ibaraki Seiichi , Wakashima Koji , Furukawa Masato , Yamada Kazutoyo , Kanzaki Dai
Published: August 2015

Today turbocharging has become a fundamental technology to realize engine downsizing, which is an attractive strategy for low carbon emissions. High efficiency and wide operating range are strongly required for the automotive turbochargers. Especially centrifugal compressors for automotive turbochargers are requested to operate with high efficiency from the surge limit to the choke limit. The internal flow in a centrifugal compressor is however three dimensional and shows very complex unsteady flow phenomena like a rotating stall and a surging, which have yet to be elucidated fully.

In this study the effect of flow path height of impeller and diffuser on flow fields in a transonic centrifugal compressor has been investigated both numerically and experimentally. Detached Eddy Simulation (DES) has been applied and revealed the reduction of impeller exit flow path affects the accumulation of low momentum flow at impeller inlet as well as impeller exit. Also it has been confirmed experimentally the 15% reduction of the impeller exit flow path height can halve the surging flow rate with same choking capacity at pressure ratio of 2.6.
Unsteady Work and Wake Recovery due to Pressure Wave Interaction in a LP Turbine
Authors: Marx Martin , Lipfert Martin , Rose Martin G. , Staudacher Stephan , Engel Karl
Published: August 2015

Recent publications have demonstrated the influence of unsteady work terms on the inviscid recovery of wake momentum. So far, this so-called wake differential work effect was only validated based on selected locations and time steps in turbine rotors. The magnitude of this effect over a whole blade passing cycle and the local unsteady work mechanisms causing it are still not fully understood. Using a numerical simulation, the unsteady static pressure field of a turbine rotor is assessed. Three regions are identified in which work is transfered unsteadily to the fluid, caused by the fluid interaction with the unsteady rotor pressure field. A Lagrangian analysis is performed to validate and quantify the wake differential work concept. To be representative, a large number of wake and free stream fluid particle paths are evaluated. Overall, a 7 per cent lower wake work in the rotor is identified, averaged over a whole blade passing cycle. From a particle point of view, the rotor pressure field acts as a pressure wave propagating in circumferential direction. Due to inviscid unsteady work, this pressure wave influences the stagnation enthalpy of the fluid particles. It is shown that this effect is more dominant for wake fluid, as the wake velocity is closer to the propagation velocity of the pressure wave. A mathematical model of this so-called “wake surfing effect” and the two other unteady work mechanisms reveals how the wake momentum is recovered depending on the initial wake velocity vector. If exploited well, this unsteady work mechanism could cause a reduction of wake mixing loss, leading to an increased turbine efficiency.
Aeroelastic Investigation of an Annular Transonic Compressor Cascade: Numerical Sensitivity Study for Validation Purposes
Authors: Chenaux Virginie Anne , Grüber Björn
Published: August 2015

The accuracy of flutter or forced response analyses of turbomachinery blade assemblies strongly depends on the correct prediction of the unsteady aerodynamic loads acting on the vibrating blades.

This paper presents the aeroelastic numerical results of an annular transonic compressor cascade subjected to harmonic oscillation conditions. The measurements associated were performed in an annular test facility for non-rotating cascades.

The aim of this investigation is to get a deeper understanding of the specific characteristics of this test facility as well as improving the flutter prediction procedure and accuracy.

For a subsonic and a transonic flow condition, the steady-state blade surface pressure distributions were predicted with two mesh configurations and results were compared to the experimental results. The first configuration omits the geometrical complexity of the experimental model and only models the blade passage. The second mesh configuration includes the cascade’s detailed geometry and cavities. The presence of leakage flows arisen due to the cascade’s slits and cavities are identified and their impact on the main flow field is analyzed and discussed.

For the flutter computations, two mesh resolutions were investigated. The global damping predicted with a fine and a coarse mesh was compared, as well as the local pressure amplitudes and phases predicted with both configurations.

Results show that even though similar global damping curves are predicted with both mesh resolution, for some IBPAs, local differences exist on the pressure amplitudes and phases. This highlights that only comparing the global damping coefficient, is not sufficient for code validation.
Experimental Analysis of Floating Ring Annular Seals and Comparisons With Theoretical Predictions
Authors: Mariot Antoine , Arghir Mihai , Hélies Pierre , Dehouve Jérôme
Published: August 2015

Floating ring annular seals represent one of the solutions for controlling leakage in high speed rotating machinery. They are generally made of a carbon ring mounted in a steel ring for preserving their integrity. Low leakage is ensured by the small clearance of the annular space between the carbon ring and the rotor. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor may occur when the annular seal is locked up against the stator and the amplitude of rotor vibrations are larger than the radial clearance. This situation is prohibited because it rapidly leads to the destruction of the carbon ring.

The present work presents experimental results obtained for floating ring annular seals of 38 mm, tandem mounted in a buffer seal arrangement. The rotation speed was comprised between 50 Hz and 350 Hz and maximum pressure drop was 7 bar. For these operating conditions the floating ring follows the rotor vibrations without any impacts.

Comparisons were made with a theoretical model based on the equations of motion of the floating ring driven by mass inertia forces, hydrostatic forces in the (main) annular seal and by friction forces on its radial face (also named the “nose” of the seal). The friction coefficient on the nose of the floating ring was estimated from Greenwood and Williamson’s model for mixed lubrication. The present analysis validates the theoretical model used for predicting the dynamic response of the floating ring for a given rotor motion.
Effect of High Freestream Turbulence on Flowfields of Shaped Film Cooling Holes
Authors: Schroeder Robert P. , Thole Karen A.
Published: August 2015

Shaped film cooling holes have become a standard geometry for protecting gas turbine components. Few studies, however, have reported flowfield measurements for moderately-expanded shaped holes and even fewer have reported on the effects of high freestream turbulence intensity relevant to gas turbine airfoils. This study presents detailed flowfield and adiabatic effectiveness measurements for a shaped hole at freestream turbulence intensities of 0.5% and 13%. Test conditions included blowing ratios of 1.5 and 3 at a density ratio of 1.5. Measured flowfields revealed a counter-rotating vortex pair and high jet penetration into the mainstream at the blowing ratio of 3. Elevated freestream turbulence had a minimal effect on mean velocities and rather acted by increasing turbulence intensity around the coolant jet, resulting in increased lateral spreading of coolant.
Ignition and Flame Propagation in Oxy-Methane Mixtures Diluted With CO2
Authors: Almansour Bader , Thompson Luke , Lopez Joseph , Barari Ghazal , Vasu Subith S.
Published: August 2015

Ignition and flame propagation in methane/O2 mixtures diluted with CO2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBV) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation is recorded by using a high-speed camera in select experiments to visualize the effect of CO2 proportionality on the combustion behavior. The laminar burning velocity is studied for a range of equivalence ratios (ϕ =0.8–1.3, in steps of 0.1), and oxygen ratios, D=O2/(O2+CO2) (26–38% by volume). It was found that the LBV decreases by increasing the CO2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO2 proportionality increases. Current experiments are in very good agreement with existing literature data. The premixed flame model from CHEMKIN PRO [1] software and two mechanisms (GRI-Mech 3.0 [2] and ARAMCO Mech 1.3 [3]) are used to simulate the current data. In general, simulations are in reasonable agreement with current data though the mechanisms predict slower flame speeds. The LBV values obtained by the ARAMCO 1.3 mechanism are closer to the experimental values. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.
Fixed Geometry Bearing Analysis Using 2 Dimensional Pad Data
Authors: Li Wei , Thorat Manish
Published: August 2015

A fast and efficient method for evaluating bearing coefficients of the fixed geometry bearings is presented. In a typical industrial application, where the accuracy of the solution is desired, this paper presents a method whose accuracy is verified to be good by the benchmark study. Reynolds equation is solved to obtain non-dimensionalised static and rotor-dynamic characteristics for a pre-defined bearing pad geometry. The solution in the form of non-dimensional functions is obtained for a 2 dimensional space representing all possible journal loci for any load vector orientation. Laminar flow is considered in the analysis, although the method of analysis can be extended to Turbulent flow regime. The analysis method is most efficient for isoviscous boundary condition. A pad assembly method for the fixed pad journal bearings is presented. Any fixed pad bearing geometry including multi-pad bearings, preload with any load vector orientation can be evaluated using this method. In this paper, demonstrating cases for a four-pad bearing are presented.
The Role of Three-Dimensional Interactions in Fluidic Control of Shock-Induced Separation on a Transonic Turbine Blade
Authors: Bernardini Chiara , Sacco Craig , Bons Jeffrey P. , Chen Jen-Ping , Martelli Francesco
Published: August 2015

An experimental and numerical investigation is conducted to assess the fluid dynamic mechanisms of control by vortex-generator jets for shock-induced separation in a highly loaded low pressure turbine (LPT) blade. Two- and three-dimensional steady RANS computations are performed to evaluate their ability to reproduce the main features of such a complex flow. The test blade is part of a compressible LPT cascade that exhibits shock-induced separation at an exit Mach number of 0.8. Active flow control is implemented through a spanwise row of discrete vortex-generator jets (VGJs) located on the suction surface. The control performance of VGJs in these transonic conditions has an optimum blowing ratio beyond which losses increase. Three-dimensionalities in the flow field are established by discrete VGJ-boundary layer interaction as suggested by Particle-Image Velocimetry (PIV) acquisitions at different spanwise locations. Blade pressure distributions and wake total pressure losses are acquired to evaluate the control performance and compared with calculations. Two-dimensional numerical investigations by RANS simulations suggest that the effect of increased expansion over the passage is a product of massflow injection only. Three-dimensional RANS results are interrogated to give a more detailed representation of the flow features around the jets, such as the jet vortex dynamics and spanwise modulation of the potential field. The analysis of this experimental and numerical information identifies the mechanisms contributing to the performance of skewed jets for control of shock induced separation in a highly loaded LPT blade. The results provide indications on the accuracy of RANS simulations, identifying the challenges of using RANS (2D or 3D) to solve such complex flows.
Implementation of Explicit Density-Based Unstructured CFD Solver for Turbomachinery Applications on Graphical Processing Units
Authors: Romanelli G. , Mangani L. , Casartelli E. , Gadda A. , Favale M.
Published: August 2015

For the aerodynamic design of multistage compressors and turbines Computational Fluid Dynamics (CFD) plays a fundamental role. In fact it allows the characterization of the complex behaviour of turbomachinery components with high fidelity.

Together with the availability of more and more powerful computing resources, current trends pursue the adoption of such high-fidelity tools and state-of-the-art technology even in the preliminary design phases. Within such a framework Graphical Processing Units (GPUs) yield further growth potential, allowing a significant reduction of CFD process turn-around times at relatively low costs.

The target of the present work is to illustrate the design and implementation of an explicit density-based RANS coupled solver for the efficient and accurate numerical simulation of multi-dimensional time-dependent compressible fluid flows on polyhedral unstructured meshes. The solver has been developed within the object-oriented OpenFOAM framework, using OpenCL bindings to interface CPU and GPU and using MPI to interface multiple GPUs.

The overall structure of the code, the numerical strategies adopted and the algorithms implemented are specifically designed in order to best exploit the huge computational peak power offered by modern GPUs, by minimizing memory transfers between CPUs and GPUs and potential branch divergence occurrences. This has a significant impact in terms of the speedup factor and is especially challenging within a polyhedral unstructured mesh framework. Specific tools for turbomachinery applications, such as Arbitrary Mesh Interface (AMI) and mixing-plane (MP), are implemented within the GPU context.

The credibility of the proposed CFD solver is assessed by tackling a number of benchmark test problems, including Rotor 67 axial compressor, C3X stator blade with conjugate heat transfer and Aachen multi-stage turbine. An average GPU speedup factor of approximately S ≃ 50 with respect to CPU is achieved (single precision, both GPU and CPU in 100 USD price range). Preliminary parallel scalability test run on multiple GPUs show a parallel efficiency factor of approximately E ≃ 75%.
Premixed Swirling Flame Response to Acoustic Forcing Studied With High-Speed PIV and OH* Chemiluminescence
Authors: Denisov Alexey , Ravi Abhishek
Published: August 2015

Studies of swirling flames have been boosted by technological advances in high-speed lasers and cameras. Temporal and spatial evolution of swirling flows has been revealed by high-speed particle image velocimetry (PIV). We have studied the response of a perfectly premixed swirling flame to weak acoustic perturbations induced by a pair of loudspeakers upstream of the burner. Phase-resolved response of the flame was observed with PIV and OH* chemiluminescence measurements running at 12 times the forcing frequency. The flow dynamics was not affected by the flame compared to non-reacting conditions and the flame responded to flow variations by changing its angle. Proper orthogonal decomposition analysis revealed that the strongest coherent structure in the flow was precessing vortex core that caused transversal variation of the heat release without producing acoustic oscillations. Axisymmetric vortices were not observed at this level of acoustic forcing, but precession modes were modulated at acoustic frequency as additional frequency peaks appeared at the sum and the difference of precession and forcing frequencies. Average time of vortex convection from the burner to the flame is close to the delay of the flame response to acoustic forcing, measured by microphones. This supports the importance of vortex propagation to acoustic modulation of flame heat release.
Development of a Discontinuous Galerkin Solver for High Quality Wall-Resolved/Modelled DNS and LES of Practical Turbomachinery Flows on Fully Unstructured Meshes
Authors: Carton de Wiart Corentin , Hillewaert Koen , Lorriaux Etienne , Verheylewegen Guillaume
Published: August 2015

The development of a high-order CFD solver for LES of turbomachinery is discussed. It is integrated in a flexible multiphysics platform Argo based on the discontinuous Galerkin Method. The DGM bridges the gap between the flexibility of the industrial solvers and the accuracy of the academic methods, as it is able to reach high order of accuracy on fully unstructured and hybrid meshes. Due to its inherent data locality, it also features high serial and parallel efficiency. The method provides a natural framework for adaptation of mesh size and interpolation order, which can be used later to further reduce computational cost and at the same time increase reliability of industrial DNS and LES. The paper mainly focuses on the physical modelling aspects and their interaction with the discretisation. In particular implicit LES and wall modelling is discussed. The approaches are tested on the wall-resolved and modelled LES of the turbulent channel flow. Finally the approach is applied to resolved LES of the near-transonic transitional flows in a low-pressure turbine cascade at Re = 9.4 × 104 and a compressor cascade at Re = 6.0 × 105. Either cases feature the full span and include end wall effects.
Development and Application of a Multi-Disciplinary Multi-Regime Design Methodology of a Low-Noise Contra-Rotating Open-Rotor
Authors: Leborgne Michaël , Lonfils Timothée , Lepot Ingrid
Published: August 2015

This paper focuses on the development and exploitation of a multi-disciplinary, optimization-assisted, design methodology for contra-rotating open-rotors. The design procedure relies on a two-step approach. An aero-mechanical optimization is first performed to generate a geometry with good performances over several high-speed points representative of a mission. This geometry is subsequently used as the baseline of an aero-mechanical-acoustic optimization focusing on interaction noise reduction at Cutback and Sideline low-speed points. In terms of design parameters, both rotors are modified for the first phase but only the upper part of the front rotor is altered for the noise minimization. A fully-automatic high-fidelity aero-mechanical-acoustic computational chain with fluid-structure coupling is exploited in combination with evolutionary algorithms assisted by surrogate models for the constrained-optimization process. The acoustic footprint is estimated by a simplified but fast and relevant formulation combining an unsteady lifting-line and an acoustic propagation method. The best geometry of the first design gains 1.2pt in weighted efficiency while respecting all the aero-mechanical constraints. The acoustic optimization shows that noise reduction at Sideline and Cutback points is strongly antagonistic. However, significant Sideline noise reduction from 3.5 to 5.5dB depending on the harmonics is achieved while maintaining Cutback noise and without major degradation of high-speed efficiency.
Influence of Fuel Characteristics in a Correlation to Predict Lean Blowout of Bluff-Body Stabilized Flames
Authors: Huelskamp Bethany C. , Kiel Barry V. , Gokulakrishnan Ponnuthurai
Published: August 2015

This study employed experimental data collected at the Air Force Research Laboratory (AFRL) as well as data from a review of past literature to develop a correlation for predicting lean blowout through the use of a least-squares curve-fit method. Combining data from the literature with data from AFRL allowed significant variations within the dataset with regard to velocity, flameholder diameter and shape, pressure, temperature, and fuel. Gaseous, single-component fuels as well as multi-component jet fuels were included in the study. The study reports new jet fuel blowout data. The laminar flame speed and ignition delay time calculated using detailed chemical kinetics mechanisms were used in the correlations to determine the chemical timescales relevant to lean blowout.

The correlation presented here indicates that the lean blowout of bluff-body stabilized flames is dependent on the Damköhler number, with fuel variation being a significant factor. The ratio of the flameholder diameter to the lip velocity was found to influence the lean blowout. This ratio represents the fluid-mechanic timescale in the Damköhler number. Pressure, temperature, and the hydrogen-to-carbon ratio of the fuel affect the reactivity of the mixture, contributing to the chemical timescale in the Damköhler number. For a limited dataset, the ignition delay time is an adequate representation of the chemical timescale.
Introduction of Circumferentially Non-Uniform Variable Guide Vanes in the Inlet Plenum of a Centrifugal Compressor for Minimum Losses and Flow Distortion
Authors: Sezal Ismail , Lang Matthias , Aalburg Christian , Chen Nan , Erhard Wolfgang , Scotti Del Greco Alberto , Tapinassi Libero , Gadamsetty Rajesh Kumar V.
Published: August 2015

In the Oil & Gas industry, large variations in flow rates are often encountered which require compression trains with a wide operating range. If the stable operating range at constant speed is insufficient, variable speed drivers can be used to meet the requirements. Alternatively, variable guide vanes (IGVs) can be introduced into the inlet plenum to provide pre- or counter-swirl to the first stage impeller, possibly eliminating the need for variable speed. This paper presents the development and validation of circumferentially non-uniform IGVs that were specifically designed to provide maximum angle variation at minimum losses and flow distortion for the downstream impeller. This includes the comparison of three concepts: a baseline design based on circumferentially uniform and symmetric profiles and two circumferentially non-uniform concepts based on uniquely cambered airfoils at each circumferential position and a multi airfoil configuration consisting of a uniquely cambered fixed part and a movable part. The idea behind the circumferentially non-uniform designs was to take into account non-symmetric flow features inside the plenum and a bias towards large preswirl angles rather than counter-swirl during practical operation. The designs were carried out by CFD and first tested in a steady, full-annulus cascade in order to quantify pressure losses and flow quality at the inlet to the impeller at different IGV setting angles (ranging from −20° to +60°) and flow rates. Subsequently, the designs were mounted in front of a typical Oil & Gas impeller on a high speed rotating rig in order to determine the impact of flow distortion on the impeller performance. The results show that pressure losses in the inlet plenum could be reduced by up to 40% with the circumferentially non-uniform designs over the symmetric baseline configuration. Furthermore, a significant reduction in circumferential distortion could be achieved with the circumferentially non-uniform designs. The resulting improvement in impeller performance contributed approx. 40% to the overall efficiency gains for inlet plenum and impeller combined.
Experimental Study on the Effect of Non-Uniform Inlet Velocity Profile on Internal Cooling in Rectangular Channels With Multi-Features
Authors: Huang S. , Yan Y. Y. , Maltson J. D.
Published: August 2015

Experiments were conducted to investigate the overall thermal performance of rectangular channels with a non-uniform inlet velocity profile. Two test sections with multiple internal cooling features had been used. One test section was implemented with two circular staggered pin-fin arrays with different pin diameters. The other one was implemented with a combination of a staggered pin-fin array and a perforated blockage array. The average surface heat transfer coefficient of the pedestal and perforated blockage and the local distribution of heat transfer coefficient on endwall were measured by the lumped capacitance method and transient liquid crystal method, respectively. The pressure drop across each array was measured. The heat transfer coefficients were measured over the Reynolds number range from 9,000 to 17,000. The spanwise pitches of the upstream pin-fin arrays were 2.33 and 4.66 for the channel with the multiple pin-fin array and the channel with perforated blockage, respectively. The effect of a non-uniform velocity profile on local heat transfer pattern and row-resolved heat transfer coefficient has been investigated.
The TMF Life Assessment of First-Stage W501F Turbine Blade Under Different Operating Temperatures
Authors: Choi Woosung , Chang Sung Yong , Kim Beom Soo , Chen Ying , Liu Yuan , Zhao Jun , Banerjee Avisekh
Published: August 2015

Thermal Mechanical Fatigue (TMF) is emerging to be a major damage accumulation mode in the first-stage turbine blades of the F class industrial turbines. In this work, the effect of engine operating temperatures on the TMF life of the first-stage W501F turbine blade has been studied. The turbine inlet temperature (TIT) for the base load engine operation is predicted using thermodynamics based engine analysis. A computational fluid dynamics (CFD) based cascade analysis of the gas path was performed to predict the metal temperatures and temperature gradients. A higher average TIT with a sharper gradient compared to the TIT profile for the base load was also assumed to numerically represent a more severe engine operating test case. A material physics based TMF life prediction approach was adopted to identify the fracture critical locations (FCL). The cyclic life to crack nucleation under different engine operating conditions was also predicted. The predicted FCL and life matched with field experience. A FCL was also predicted inside the cooling channels of the blade, suggesting the need to develop suitable inspection techniques.
Detailed Performance Analysis of a Centrifugal Compressor Stage With Pipe Diffuser and Immerged Tandem Deswirler
Authors: Schmidt Johannes , Schwarz Philipp , Wilkosz Benjamin , Jeschke Peter , Smythe Caitlin
Published: August 2015

Commonly, the pipe diffuser and deswirler are aerodynamically decoupled from each other to ensure better mixing of the inhomogeneous pipe flow before entering the deswirler and to prevent upstream effects of the deswirler bend and blading on the pipe diffuser. Close-coupling of these two components, however, can lead to a significantly lower radial extent of the stage, resulting in a decrease of stage weight and engine frontal area. The geometry investigated includes a centrifugal compressor stage with a compact diffusion system, including a pipe diffuser and tandem deswirler whose first blade row is immerged into the pipe diffuser. Stage and component performance of this compact configuration is compared to two different stage configurations with decoupled deswirlers. Performance maps and 1-D pressure build-up data show that the compact stage is able to reach efficiency and pressure build-up of the compared stages which contain the same impeller and same diffuser inlet geometry. The performance of one of the compared stages with significantly higher radial stage extent is even exceeded. However, a loss in surge margin of about 2% has been detected which seems to be the major problem in reducing stage size by close-coupling the deswirl system to the pipe diffuser, since this can have a major effect on the diffuser inlet pressure build-up.
Lifetime Assessment of Steam Turbine Casing
Authors: Hu Yifeng , Jiang Puning , Ye Xingzhu , Chen Gang , Zhang Junhui , Hao Zhenzhen , Xiao Lei
Published: August 2015

Nowadays, in order to accommodate electrical grids that include fluctuating supplies of green energy, more and more fossil power plants are increasingly required to start up and shut down frequently. The increased number of stress cycles leads to a significant reduction of lifetime. In this paper, numerous load cycles of steam turbine casing including various start up and shut down conditions were numerically investigated by using the finite element analysis (FEA). The total strain throughout the cycles was directly calculated by the elastic-plastic material model. The delta equivalent total strain was determined by rainflow count method, and the assessment of lifetime was evaluated.
Stochastic Methods for Nonlinear Rotordynamics With Uncertainties
Authors: Peradotto Edoardo , Panunzio Alfonso M. , Salles Loïc , Schwingshackl Christoph
Published: August 2015

The calculated dynamic response of an excited rotating system can be significantly affected by uncertainties in its mechanical properties, such as mass, stiffness, geometrical imperfections, or loadings. For this reason, it is essential to understand and quantify the influence of uncertain parameters on the predicted rotor response.

This paper aims to optimize the propagation of random input uncertainties for a rotordynamic problem and assess their influence on the dynamic behaviour of an unbalanced rotor. The Harmonic balance method (HBM) and a non-intrusive Polynomial Chaos Expansion (PCE) are used to evaluate the stochastic response of a finite element rotor. The proposed stochastic approach is based on a numerical quadrature calculation of integrals for finding the coefficients of the PCE.

The method is initially applied to evaluate the stochastic response of a linear rotodynamic system, leading to the original concept of stochastic Campbell diagram and further extended to nonlinear rotordynamic problems, using the Asymptotic Numerical Method (ANM).