bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-Sustained Instabilities in an Annular Combustor Coupled by Azimuthal and Longitudinal Acoustic Modes
Authors: Bourgouin Jean-Francois , Durox Daniel , Moeck Jonas P. , Schuller Thierry , Candel Sébastien
Published: November 2013

Annular combustors may give rise to various types of combustion instabilities. Some of the resulting oscillations coupled by transverse acoustic modes are commonly observed in practice and their suppression or reduction is an important issue which needs to be considered. The present study is carried out in a system comprising an annular plenum feeding 16 swirling injectors confined by two cylindrical quartz tubes opened to the atmosphere. Calculations based on a Helmholtz solver provide a suitable estimate of frequencies observed experimentally and reveal the modal structure corresponding to the longitudinal and transverse oscillations. High speed images obtained under reactive conditions are then processed to extract the structure of heat release rate perturbations and match this structure with that of the coupling acoustic mode. It is found that the transverse instability is coupled by a first azimuthal mode which is characterized by a time varying spin ratio. This index gives the respective levels of rotating components in the azimuthal mode. Another instability arising at a lower frequency is coupled by a longitudinal acoustic mode giving rise to high-amplitude oscillations in heat release rate in which most of the flames (but not all) are synchronized and in phase with the pressure perturbation.
An Upwind Eulerian-Eulerian Model for Non-Equilibrium Condensation in Steam Turbines
Authors: Zhu Xiaofeng , Yuan Xin , Lin Zhirong , Shibukawa Naoki , Tsukuda Tomohiko , Niizeki Yoshiki , Tanuma Tadashi
Published: November 2013

The present paper proposes an Eulerian-Eulerian two-phase model for non-equilibrium condensing flow in steam turbines. This model is especially suitable for upwind finite volume scheme. An approximate Roe type flux using real water/vapor property is constructed to calculate the upwind wet-steam flux. This flux fully couples the wetness fraction with other conservative variables in the Jacobian Matrix whose eigen-vector and eigen-value are analitically derived. A novel treatment of real wet-steam property is developed by constructing a 3-DOFs TTSE table according to IAPWS97 formulas. The table is actually a cubic and uses the mixture’s density, the mixture’s internal energy and wetness as independent variables. Besides homogeneous condensation, heterogeneous condensing is also integrated into the model, which facilitates simulating the effect of salt impurities. The above methods are validated through two nozzle and one turbine cascade calculations and finally applied to a model LP steam turbine stage. Results show that the current model is very robust and is able to correctly capture the non-equilibrium condensation phenomena.
Modelling of Hydraulic Seals Using an Axisymmetric Volume of Fluid Method (VOF)
Authors: Mathews Hans-Christian , Morvan Hervé , Peduto Davide , Wang Yi , Young Colin , Bauer Hans-Jörg
Published: November 2013

Hydraulic seals are used in aero engines because of their excellent sealing properties. Sealing of oil inside bearing chambers is extremely important as leakage of oil into internal spaces of the engine increases the oil consumption and can result in undesirable effects, ranging from cosmetic to mechanical. A robust dimensioning of the seal is therefore essential. However, the maximum pressure capacity of the hydraulic seal is not always determined accurately enough with many of the existing design approaches, so a high safety factor must be used. It is desirable to keep improving the accuracy of these methods, in particular to handle ever larger pressure differences.

A new dimensionless design method is therefore introduced here to improve the determination of the maximum pressure capacity. This paper reports on a numerical CFD investigation using an axisymmetric Volume-of-Fluid (VOF) method building on the work of Young and Chew [1]. The numerical results are validated with the results of a two-shaft test rig, alongside analytical calculation results. Additionally, a parametric study based on CFD simulations is performed to identify dominant influence quantities. The parameters include the fluid properties of oil, the shaft speeds and the geometry parameters of the seal. Employing a data reduction approach, a new dimensionless number is introduced which allows the presentation of experimental and numerical results of the hydraulic seal in a dimensionless form. Based on this representation, a correlation is proposed, which shows a very promising trend.

This validated CFD investigation and subsequent correlation introduced here show significant potential for the dimensionless description of hydraulic seals and their maximum pressure capacity.
Large Eddy Simulation of Rotating Ribbed Channel
Authors: Fransen Rémy , Vial Laurence , Gicquel Laurent Y. M.
Published: November 2013

Large Eddy Simulation (LES) of isothermal flow in stationary and wall-normal rotating blade internal cooling system is evaluated against experimental data. The studied case is a 3D one wall ribbed straight channel for which time resolved two-dimensional Particle Image Velocimetry (PIV) measurements have been performed at the Von Karman Institute (VKI) in a near gas turbine operating condition. Thanks to these experimental mean and time-resolved quantities, advanced numerical computations can be adequately evaluated. In this work LES results show that this high fidelity CFD model is able to reproduce the turbulence increase (decrease) around the rib in destabilizing (stabilizing) rotation of the ribbed channel. Such effects are not only captured at the mean level but also at the unsteady level as confirmed by the comparison of the LES large-scale coherent motions with these obtained by PIV.
Aircraft Engine Gas Path Diagnostic Methods: Public Benchmarking Results
Authors: Simon Donald L. , Borguet Sébastien , Léonard Olivier , Zhang Xiaodong (Frank)
Published: November 2013

Recent technology reviews have identified the need for objective assessments of aircraft engine health management (EHM) technologies. To help address this issue, a gas path diagnostic benchmark problem has been created and made publicly available. This software tool, referred to as the Propulsion Diagnostic Method Evaluation Strategy (ProDiMES), has been constructed based on feedback provided by the aircraft EHM community. It provides a standard benchmark problem enabling users to develop, evaluate and compare diagnostic methods. This paper will present an overview of ProDiMES along with a description of four gas path diagnostic methods developed and applied to the problem. These methods, which include analytical and empirical diagnostic techniques, will be described and associated blind-test-case metric results will be presented and compared. Lessons learned along with recommendations for improving the public benchmarking processes will also be presented and discussed.
Experimental Characterization of Variable Bristle Diameter Brush Seal Leakage, Stiffness and Wear
Authors: Trivedi Deepak , Roy Binayak , Demiroglu Mehmet , Zheng Xiaoqing
Published: November 2013

Brush seals are used in a wide variety of turbomachinery for sealing rotor-stator and stator-stator clearances. Application of traditional brush seals is limited by their life and performance at high differential pressures. GE’s patent-pending Variable Bristle Diameter (VBD) brush seal overcomes the limitations of the traditional brush seal by sandwiching a layer of fine bristles, with better sealing capability, between adjacent rows of stiffer bristles capable of withstanding larger differential pressure and flow disturbance. The General Electric VBD design uses thick bristles both in front and back rows. In addition to leakage performance, for successful design it is important to understand the force interactions between a brush seal bristle pack and the rotor. The important failure mechanisms to avoid include overheating and rotor dynamic instabilities caused by excessive brush seal forces. Brush seal stiffness, defined as brush seal force per unit circumferential length per unit incursion of the rotor, depends on the complex interaction of the pressure-dependent inter-bristle forces, the blow-down forces and the friction forces between the backplate and the bristle pack. Furthermore, brush seals exhibit different hysteresis and wear behavior under different pressure loading conditions. In this article, we present experimentally measured leakage, stiffness and wear characteristics of three different VBD brush seal designs subjected to a wide range of pressure loading.
Side Weld and Bend Method of Manufacturing Compliant Plate Seals
Authors: Adis William E. , Mack Michael , Deo Hrishikesh V.
Published: November 2013

Compliant Plate Seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines and oil & gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around a rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter and an intermediate plate extends inwards into this slot from the stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip-clearance. Due to this self-correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and robust non-contact operation even in the presence of large rotor transients. Manufacturing of Compliant Plate Seals is a challenging problem and in this paper, we describe the development of a novel manufacturing technique called Side Weld And Bend (SWAB). The compliant plates are tightly packed with alternating spacer shims in a straight line fixture and welded to a top-plate from the side along a straight line. After removal of the spacer shims, the welded assembly is bent to form an arcuate seal of a desired diameter. The Side Weld And Bend (SWAB) manufacturing method reduces distortion, deformity, differential shrinkage and other associated problems with welding across gaps between adjacent compliant plate seals as is typical in current manufacturing processes.
Emissions and Operability of a Multi-Point Low NOx Staged Combustor at Intermediate Pressures
Authors: Villalva Rodrigo , Dolan Brian , Munday David , Gutmark Ephriam , Zink Gregory , Ryon Jason , Pack Spencer , Goeke Jerry
Published: November 2013

Emissions measurements were performed on a low-NOx emission combustor concept developed by United Technologies Aerospace Systems (formerly Goodrich) for NASA’s Environmentally Responsible Aircraft (ERA) program to meet N+2 emissions goals for a 70,000 pound thrust engine application. A key enabler of this goal is to improve combustion stability at low power conditions over that of previous work. The combustion system presented potentially substitutes five radially staged small injectors for a single row of larger injectors. The test combustor has a total of 13 individual fuel injectors distributed in five rows. NOx, CO, and UHC were measured for a variety of practical conditions, from lean blow-out to idle and simulated full power. Imaging provided insight on how the staged injectors perform and contribute to observed emissions. Conditions which yield significant NOx reductions were identified and correlate well to existing literature. In particular, evenly distributed combustion among all 13 fuel injectors reduced regions of high temperature and resulted in significant NOx reductions which correlate well with demonstrated performance of other multi-point combustors.
Experimental and Numerical Investigations of Effects of Flow Control Devices Upon Flat-Plate Film Cooling Performance
Authors: Kawabata Hirokazu , Funazaki Ken-ichi , Nakata Ryota , Takahashi Daichi
Published: November 2013

This study deals with the experimental and numerical studies of the effect of flow control devices (FCDs) on the film cooling performance of a circular cooling hole on a flat plate. Two types of FCDs with different heights are examined in this study, where each of them is mounted to the flat plate upstream of the cooling hole by changing its lateral position with respect to the hole centerline. In order to measure the film effectiveness as well as heat transfer downstream of the cooling hole with upstream FCD, a transient method using a high-resolution infrared camera is adopted. The velocity field downstream of the cooling hole is captured by 3D Laser Doppler Velocimeter (LDV). Furthermore, the aerodynamic loss associated with the cooling hole with/without FCD is measured by a total pressure probe rake. The experiments are carried out at blowing ratios ranging from 0.5 to 1.0. In addition, numerical simulations are also made to have a better understanding of the flow field. LES approach is employed to solve the flow field and visualize the vortex structure around the cooling hole with FCD. When a higher FCD is mounted to the plate, the film effectiveness tends to increase due to the vortex structure generated by the FCD. As FCD is laterally shifted from the centerline, the film effectiveness increases, while the lift-off of cooling air is also promoted when FCD is put on the center line.
Optimization of Reduced Kinetic Models for Reactive Flow Simulations
Authors: Gokulakrishnan P. , Joklik R. , Viehe D. , Trettel A. , Gonzalez-Juez E. , Klassen M.
Published: November 2013

A robust optimization scheme, known as rkmGen, for reaction rate parameter estimation has been developed for the generation of reduced kinetics models of practical interest for reactive flow simulations. It employs a stochastic optimization algorithm known as Simulated Annealing, and is implemented in C++ and coupled with Cantera, a chemical kinetics software package, to automate the reduced kinetic mechanism generation process. Reaction rate parameters in reduced order models can be estimated by optimizing against target data generated from a detailed model or by experiment. Target data may be of several different kinds: ignition delay time, blow-out time, laminar flame speed, species time-history profiles and species reactivity profiles. The software allows for simultaneous optimization against multiple target data sets over a wide range of temperatures, pressures and equivalence ratios.

In this paper, a detailed description of the optimization strategy used for the reaction parameter estimation is provided. To illustrate the performance of the software for reduced kinetic development, a number of test cases for various fuels were used: one-step, three-step and four-step global reduced kinetic models for ethylene, Jet-A and methane, respectively, and a fifty-step semi-global reduced kinetic model for methane. The fifty-step semi-global reduced kinetic model was implemented in the Star*CCM+ commercial CFD code to simulate Sandia Flame D using laminar flamelet libraries and compared with the experimental data. Simulations were also performed with the GRI3.0 mechanism for comparisons.
Manufacturing Influences on Pressure Losses of Channel Fed Holes
Authors: Barringer Michael , Thole Karen A. , Krishnan Vaidyanathan , Landrum Evan
Published: November 2013

Variations from manufacturing can influence the overall pressure drop and subsequent flow rates through supply holes in such applications as film-cooling, transpiration cooling, and impingement cooling that are supplied by micro-channels, pipe-flow systems, or secondary air systems. The inability to accurately predict flow rates has profound effects on engine operations. The objective of this study was to investigate the influence of several relevant manufacturing features that might occur for a cooling supply hole being fed by a range of channel configurations. The manufacturing variances included the ratio of hole diameter to channel width, the number of channel feeds (segments), the effect of hole overlap with respect to the channel sidewalls, and channel Reynolds number. Results showed that the friction factors for the typically long channels in this study, were independent of the inlet and exit hole configurations tested. Results also showed that the non-dimensional pressure loss coefficients for the flow passing through the channel inlet holes and through the channel exit holes were found to be independent of the channel flow Reynolds number over the range tested. The geometric scaling ratio of the hole cross-sectional area to the channel cross-sectional area collapsed the pressure loss coefficients the best for both one and two flow segments for both the channel inlet and channel exit hole.
Wild Cane Potential to Produce Gaseous Fuels via Air-Steam Thermal Gasification
Authors: Aponte Jorge Alberto , Gordillo Gerardo
Published: November 2013

Various alternative fuel technologies have been proposed as a solution to the negative environment impact caused by greenhouse emissions from fossil fuel combustion processes. One of those alternatives technologies is the inclusion of biomass (fuel crops and agricultural and municipal wastes) as feedstock to produce gaseous and liquid fuels via thermal gasification processes. Biomass thermal gasification is a clean technology, which does not increase the atmosphere carbon concentration since biomass is a neutral carbon energetic source. Wild cane is an invasive grass with a remarkable ability to establish and spread quickly. Thus, it has the potential to yield high biomass for the production of energy. Moreover, wild cane is considered as one of the species that most produces energy per hectare crop. Although wild cane occurs as a weed in most of the Colombian geography, it does not have an extensive potential use. However, wild cane can be included as feedstock for the production of bio-fuels via partial oxidation or thermal degradation (pyrolysis). Fuels produced through this technology can be used for heat o power generation in order to decrease the dependence of farms on fossil fuels. The current paper presents results on the wild cane potential to produce gaseous fuels through thermal gasification using air-steam mixtures for partial oxidation. Also, wild cane thermochemical properties are presented. The CEA (chemical equilibrium with applications) program from NASA was used to estimate the production of gaseous fuels as a function of the operating conditions, which include equivalence ratio (Φ) and steam to fuel ratio (S:F). Based on gas composition, the energy density of the gaseous fuels was estimated. Furthermore, the energy conversion was also calculated in order to estimate the efficiency of the gasification process. Wild cane thermochemical properties were obtained using ultimate, proximate, and thermogravimetric analyses (TGA). Thermogravimetric analyses were carried out using N2 as carrier gas and under different heating rates (β: 10, 20, and 35 °C/min). Based on TGA data and using the isoconversional method (i.e., free-model), the activation energy (E) was estimated. In general, the results show that the increase in operating conditions (equivalence ratio (Φ) and steam to fuel ratio (S:F)) results in gaseous mixtures rich in H2 and with a low CO content. On the other hand, the CH4 production is only possible at Φ > 4 and increases with increased Φ. The average activation energy was ∼ 162 KJ/Kmol.
Convex Curvature Effects on Film Cooling Adiabatic Effectiveness
Authors: Winka James R. , Anderson Joshua B. , Bogard David G. , Crawford Michael E. , Boyd Emily J.
Published: November 2013

Surface curvature is known to have significant effects on film cooling performance, with convex curvature inducing increased film effectiveness and concave curvature causing decreased film effectiveness. Generally, these curvature effects have been presumed to scale with 2r/d at the film cooling hole location, where r is the radius of curvature and d is coolant hole diameter. In this study, the validity of this scaling of curvature effects are examined by performing experiments in regions of large and low curvature on a model vane. Single rows of cylindrical holes were placed at various locations along the high curvature section of the suction side of the vane. For the first series of experiments, a single row of holes was placed at two locations with different local surface curvature. The coolant hole diameters were then adjusted to match 2r/d values. Results from these experiments showed that there was better correspondence of film performance when using the 2r/d scaling, but there was not an exact matching of performance. A second series of experiments focused on evaluating the effects of curvature downstream of the coolant holes. One row of holes was placed at a position upstream of the highest curvature, while another row was placed at a downstream position such that the radius of curvature was equivalent for the two rows of holes. Results indicated that the local radius of curvature is not sufficient in understanding the performance of film cooling. Instead, the curvature envelope downstream of the coolant holes plays a significant role on the performance of film cooling for cylindrical holes.
Numerical and Experimental Investigations of the Transient Thermal Behavior of a Steam Bypass Valve at Steam Temperatures Beyond 700 °C
Authors: Haj Ayed Anis , Kemper Martin , Kusterer Karsten , Tadesse Hailu , Wirsum Manfred , Czychon Karl-Heinz , Metzger Klaus , von Nordheim Dierk , Tebbenhoff Olaf , Bohn Dieter
Published: November 2013

Increasing the efficiency of steam cycle power plants is extremely important for the reduction of their CO2 emissions. Today’s best steam cycle power plants have a net plant efficiency of 46 %. Since the worldwide average efficiency is still in the range of 30 %, there exists a great potential in reduction of CO2 emissions by replacing old power stations with new ones. A further great potential lies in achieving even higher efficiencies by increasing live steam temperatures to more than 700 °C, so that the efficiency of steam power plants is pushed over the 50 % mark. Within a research project funded by the German government the challenges associated with material’s behaviour under elevated temperatures are investigated. In this project, a bypass-valve was installed in an experimental set-up in a real power station and is supplied with over 700 °C steam and investigated under long-term cyclic operation. Thermocouple measurements on reference points on the valve body and thermo graphic camera measurements deliver information about the real transient thermal behaviour of the valve. Numerical investigations aim to accurately model the transient thermal behaviour of the valve during cyclic operation and calculate corresponding three-dimensional temperature distributions, which are essential for conducting reliable mechanical integrity analysis for the applied Nickel-base material. Applying standard FEM thermal analyses that are based on heat transfer boundary conditions is often related with uncertainties regarding the convective heat transfer and corresponding coefficients. The application of a hybrid stepwise frozen conjugate heat transfer calculation approach aims to make use of the advantage of the conjugate heat transfer approach with respect to high accuracy in heat transfer calculation and reduce the calculation effort by freezing the fluid domain at different steps along the loading cycle and coupling it to the transient thermal load calculation in the solid domain. Both the standard FEM thermal analysis method and the hybrid stepwise frozen conjugate heat transfer calculation approach have been applied to calculate the transient thermal load in the valve. A validation of the numerical results has been performed for the reference points on the valve body and shows that the hybrid approach has better accuracy than the standard approach and shows very good agreement with the experimental results.
The FMT Criterion to Optimize the Quench Zone in RQL Combustors
Authors: Huang Yong , Liu Lei , Wang Fang , Wang Shaolin
Published: November 2013

As environmental protection is more and more important, pollution emission in aircraft combustors should be low. The RQL (rich-quench-lean) technique is one of the promising ways to control NOx emissions from combustors. In RQL combustors, NOx is mostly produced in quench zone. So the optimization of quench zone is very important to control NOx emissions.

According to thermal NOx mechanism, NOx emissions are determined by residence times. For a RQL combustor all the mainflow fuel should be burned out in quench zone. Then the maximum residence time is the time for the flame to transport the longest distance. Based on the first-principle analysis of the flow and combustion in the quench zone, the FMT (flame mixing time) criterion for the optimization of quench jets has been proposed.

There are two typical quench ducts. One is the annular shape and the other is the can shape. The two types of ducts are similar but there are some differences between them. In this paper both of them were analyzed in terms of the FMT criterion. The maximum residence times calculated by FMT criterion were compared with the experiments by Chiappetta et. al. [3] and Holdeman & Chang[13] for annular and can combustors, respectively. The comparison shows the very good agreement between the maximum residence times calculated by FMT criterion and the experiments. That means the FMT criterion can be validated by both annular and can shape combustors. And the FMT criterion could be used to optimize the configuration of quench zones.
Staged Lean Catalytic Combustion of Gasified Biomass for Gas Turbine Applications: An Experimental Approach to Investigate Performance of Catalysts
Authors: Manrique Carrera Arturo , Jayasuriya Jeevan , Fransson Torsten
Published: November 2013

Emission demands for gas turbine utilization will become more stringent in the coming years. Currently different techniques are used to reach low levels of NOx emissions. One possible solution is the Staged Lean Catalytic Combustion. In this concept a catalysts arrangement is used to generate high temperature combustion gases. The high temperature gases could be used to feed a second combustion stage in which more fuel is injected.

In this work a series of experiments were performed at the Catalytic Combustion High Pressure Test Facility at the Royal Institute of Technology (KTH) in Sweden. The fuel used was a simulated gasified biomass and the catalytic combustor consisted of an arrangement of different catalysts, e.g. bimetallic, hexaaluminates, and perovskites catalysts. These were used as, ignition catalyst, medium temperature catalyst and high temperature catalyst respectively.

The tests were performed between 5 and 13.5 bar, and the overall conversion varied between 60% and 70% and the temperature of flue gases could reach 750°C and contains high level of oxygen. The determining factor to control the exit gas temperature was the richness of the mixture (λ value). On the other hand, the increased pressure had a moderate negative effect in the overall fuel conversion. This effect is stronger at leaner mixtures compared to richer ones. Moreover, λ value and also pressure affected the temperature distribution along the reactor.

The utilization of a lean catalytic combustion approach makes possible the use of a post catalytic combustion. In this region additional fuel is injected to fully burn the exiting gases and increase the exit temperature to the desired levels. This staged lean catalytic combustion approach could resemble moderate levels exhaust gas recirculation techniques and/or high air temperature combustion and it is also briefly examined in the present work.
Comparative Study of Syngas Mild Combustion Characteristics in Swirl Diffusion and Coflow Diffusion Staged Combustor
Authors: Huang Mingming , Zhang Zhedian , Shao Weiwei , Xiong Yan , Liu Yan , Lei Fulin , Xiao Yunhan
Published: November 2013

MILD combustion is a promising combustion technology for the future gas turbine combustor due to its high combustion efficiency, low exhaust emissions and enhanced combustion stability. It utilizes the concept of exhaust gas recirculation to achieve combustion at reduced temperature and flat thermal field. To examine the role of gas recirculation level on MILD combustion performance, a laboratory-scale axially staged combustor constituted of gas generation zone, mixing zone and MILD combustion zone is presented. To realize ultra-low NOx emissions for syngas characterized by high flame temperature, it is necessary to select an appropriate combustion mode for the gas generation zone. This study compared combustion performance and gas/fuel/air mixing feature between two configurations, gas generation zone of which are based on swirl diffusion combustion and coflow diffusion combustion, respectively. The results are compared on flow field with numerical simulation, and global flame signatures and exhaust emissions with experiment. Both numerical simulation and experiment are performed at equivalence ratio of 0.4, heat load of 24.4 kW, using 10 MJ/Nm3 syngas as the fuel at atmospheric pressure and normal temperature fuel and air. More uniform oxidizer, lower flame temperature and less NOx production are observed in coflow diffusion staged combustion. MILD combustion zone is beneficial for the reduction of NOx and oxidation of CO exit from the gas generation zone.
Numerical Investigation of Delft-Jet-in-Hot-Coflow (DJHC) Burner Using Probability Density Function (PDF) Transport Modeling
Authors: De Ashoke , Dongre Akshay , Yadav Rakesh
Published: November 2013

In the present paper, the flames from DJHC burner, imitating MILD (Moderate and Intense Low Oxygen Dilution) combustion, are simulated using PDF transport modeling. Two different solution approaches have been used to resolve the joint composition PDF. First, a Lagrangian approach is used to solve the joint composition PDF, while in the second approach, the approximate solution is achieved by using presumed shape PDF and DQMOM-IEM modeling known as Multi-Environment Eulerian PDF (MEPDF). A quantitative comparison of the predictions from these two solution methods has been performed for two different jet Reynolds number, i.e. Re = 4100 & 8800. Moreover, the effect of molecular diffusion is also explored by comparing the predictions using different micro-mixing models such as Coalescence Dispersion (CD), Euclidean Minimum Spanning Tree (EMST), and Interaction-by-Exchange-with-Mean (IEM) model. The obtained numerical predictions from both approaches are compared with the experimental data to highlight the accuracy as well as the predictive capability of these models. In the case of low Reynolds number (Re = 4100), it is observed that the mean axial velocity and turbulent kinetic energy profiles are in good agreement with the measurements while the temperature profiles are slightly over-predicted in the downstream region. Although MEPDF results are in good agreement with the LPDF results, both the model predictions tend to exhibit discrepancies at higher Reynolds number.
Numerical Investigation on Flow and Heat Transfer in a Lattice (Matrix) Cooling Channel
Authors: Hagari Tomoko , Ishida Katsuhiko
Published: November 2013

Flow and heat transfer of lattice cooling channel are investigated numerically. Firstly, simulations are performed for two channels to reproduce the experimental results reported in open literatures. Based on the literatures, sub-channels consisting lattice network are designed with aspect ratio of near unity and crossing angle of 45 degrees. Predicted heat transfer patterns of primary surfaces have agreed qualitatively and quantitatively well with the experimental results. Cooling air turns mainly through turning at the end of each sub-channel. After impinging the sidewall, strong acceleration occurs at the entrance of the opposite sub-channel, which enhances local heat transfer.

Based on the above discussions, the present study also compares heat transfer coefficient of all surfaces (rib + primary) surrounding the sub-channel. The highest local heat transfer coefficient is found at rib surfaces. Predicted flow pattern indicates that a longitudinal vortex is formed in parallel to the sub-channel after impinging the sidewall, and that transient flow from one to another side of the sub-channels keeps the core of the vortex. This transient flow substantially contributes to the heat transfer enhancement at the upper edge of a rib surface, and more than half of total heat flux transfers through the rib. It follows that, in designing lattice cooling channel, rib surfaces should also be treated as heat transfer surface. Moreover, the effect of sub-channel (or rib) inclination angle on flow and heat transfer is examined. Rib inclination angle strongly affects translation flow between the lower and upper sub-channels and impingement at the sidewall. Further experimental investigation is expected in the near future.
Multi-Objective Optimization of a U-Bend for Minimal Pressure Loss and Maximal Heat Transfer Performance in Internal Cooling Channels
Authors: Verstraete Tom , Li Jing
Published: November 2013

A multi-objective design optimization is performed on a U-bend in serpentine internal cooling channels. The aim is to achieve both minimized total pressure loss and maximized heat transfer ability. The optimization technique used is a two-level routine developed at the Von Karman Institute for Fluid Dynamics (VKI), featuring a Differential Evolution algorithm assisted by a metamodel, which is continuously updated during the course of the optimization process to increase its accuracy The geometries are carefully parameterized by means of Bezier curves. In total, 26 geometrical parameters are used as design variables, allowing an extensive variation of the U-bend geometries. The fluid dynamic and heat transfer performances of the selected geometries are predicted by a Reynolds-averaged Navier-Stokes solver in OpenFOAM. The result shows that dozens of optimized geometries of enhanced performances in both design objectives can be obtained after a few numbers of iterations. The enhancement ranges from roughly 12∼30% decrease in total pressure loss and a 8∼17% increase in heat flow rate. A clear trade-off between pressure loss and heat transfer is observed, allowing designers to select a compromising geometry between both criteria after the optimization process, depending on the application type of the internal cooling channel. Generally, a stronger secondary flow motion in the channel will be responsible for higher heat transfer at the cost of increased losses. A discussion is held on the geometrical features that have an impact on the secondary flow motion strength and lead to general applicable conclusions.
Numerical Vibration Analysis of Supersonic Mixed-Compression Intake
Authors: Cheng Yao , Liu Zhansheng , Ma Ruixian , Zhang Guanghui
Published: November 2013

Vibration analysis of a supersonic mixed compression intake is carried out under periodic back pressure by using one-way fluid structure interaction method. Steady flow and transient flow in the intake are simulated with finite volume method. The total pressure recovery and the exit flow distortion of the steady flow solution are very close to Anderson and Wong’s experiment results. The frequency components of pressure transferring to the intake cowl wall are analyzed using FFT method for the unsteady flow, and are compared with the natural frequencies of the intake structure to avoid the resonance of the intake structure. The dynamic response of the intake structure is simulated with finite element method considering geometric nonlinearity. The displacement history of structure is obtained, and the region with large amplitude of vibration is identified. It indicates that the forced vibration occurs in the intake under the excitation of the oscillating back pressure. The static displacement is two times of the cowl wall thickness, while the peak value of the dynamic displacement is 10% of the cowl wall thickness.
Prediction of the Acoustic Losses of a Swirl Atomizer Nozzle Under Non-Reactive Conditions
Authors: Gikadi Jannis , Ullrich Wolfram C. , Sattelmayer Thomas , Turrini Fabio
Published: November 2013

When predicting combustion instabilities in gas turbine combustion chambers, the complex geometry and three dimensional flow configurations are often neglected. However, these may have significant influence on the overall acoustic damping behavior of the system. An important element governing the flow inside a combustion chamber is the swirl atomizer nozzle. Therein, the flow is accelerated and a swirling fluid motion is imposed. At its exit considerable high flow velocities are reached and multiple shear layers are formed which discharge into the combustion chamber. To predict damping effects in these environments, acoustic-flow interaction processes need to be taken into account. These involve scattering and refraction of incident acoustic waves in shear layers, acoustic interaction with the unstable hydrodynamic shear layers as well as acoustic wall interaction processes. Their combined effect can be studied using acoustic scattering matrices. In this paper the acoustic scattering behavior of a lean injection system developed by Avio is predicted under non-reactive conditions and compared to experiments. The numerical method is very general and works as follows: First, the fluid dynamic field is computed using a Reynolds averaged Navier-Stokes turbulence model. Then, the linearized Navier-Stokes equations are solved in frequency space around the previously computed mean flow state. The complex three dimensionality of the nozzle configuration is taken into account as well as its corresponding flow field. Results are compared against experimental measurements of a swirl atomizer nozzle at atmospheric and elevated inlet temperatures. It is shown that the scattering behavior and therefore the acoustic-flow interactions are captured accurately.
An Investigation of the Effects of Fuel Staging on Flame Structure in a Gas Turbine Model Combustor
Authors: Gounder J. D. , Boxx I. , Kutne P. , Biagioli F. , Luebcke H.
Published: November 2013

Gas turbine (GT) flames at lean operating conditions are susceptible to instabilities that can lead to unsteady operation, flame extinction, and thermoacoustic oscillations. High speed (10 kHz) laser and optical diagnostic techniques have been used to investigate the effect of fuel staging on the mechanisms involved in such instabilities and the overall performance of a gas turbine model combustor. The GT burner used in this study consists of coaxial swirlers which allow for fuel staging capability, where the fuel is varied from 100% to 20% fuel injection in the inner swirler. The burner is equipped with a combustion chamber with large quartz windows, allowing for the application of optical and laser diagnostics. Simultaneous high speed OH Planar Laser Induced Fluorescence (PLIF) and OH* chemiluminescence (CL) imaging, exhaust gas sampling and acoustic measurements were applied to characterize the flames and determine the operability limits of the combustor. Methane air flames at atmospheric pressure have been investigated at a constant thermal power of 58 kW. The global equivalence ratio was kept constant, while the fuel staging was varied. The bulk flow velocity at the exit plane was kept constant at 20 m/s. Simultaneous high speed particle image velocity (PIV) and OH PLIF measurements were performed at a repetition rate of 10 kHz on specifically chosen flames with a fixed staging and equivalence ratio. This paper will present the flame and the flow field structure resolved using the kHz measurement technique. The interaction between the velocity field and the flame front marked by the OH LIF will be presented. The mean PIV image provides the location of the inner and outer recirculation zones. The flame structure presented in this paper will also show the effectiveness of fuel mixing as the staging is varied. The changes in flame shape with variation in fuel staging is determined using the OH* chemiluminescence images. As the fuel flow in the inner swirler is reduced, the NOx and CO emissions also reduce and reach a minimum at a staging of 45% fuel being injected in the inner swirler. As fuel injection in the outer swirler increases beyond 60% the NOx and CO emissions start also increasing.
Numerical Analysis of Pressure Losses in Diffuser and Tube Steam Partition Valves
Authors: Bianchini C. , Micio M. , Tarchi L. , Cortese C. , Imparato E. , Tampucci D.
Published: November 2013

Control valves are one of the key steam turbine components both in terms of operational safety and flexibility. It is hence fundamental to correctly predict the valve characteristics at the various working conditions to accurately estimate machine performance and control logics. The aim of this work is to develop a simple method to predict pressure losses within the partition system to be used at preliminary design stage.

Two types of partition valves typically employed in real industrial steam turbines of different power (from 1MW to 100MW) are analysed. The first type exploits a diffuser-like shape to maximize the dynamic pressure recovery before the discharge into the impulse stage. The second type, based on simple tube geometry, increases the allowable flow rate, for the same valve seat, at the cost of higher pressure losses. Geometrical dimensions have been varied to cover a wide range of configurations employed in industrial applications. An exception is made for the diffuser angle and the relative fillet radius which were fixed to guarantee product standardization among the various machine sizes.

The flow is supposed axisymmetric and upstream reference condition for the entire study is 140 bar and 540 °C which are typical working conditions for such steam turbines. The influence of the shutter is also considered to properly characterize regulation of the steam flow on the basis of valve lift.

Pressure losses are first modelled dividing the partition valve into singular homogeneous parts such as the intake, the straight pipe, the diffuser and the discharge, for which simple correlations are available in literature. The overall characteristic curve is validated using CFD computations conducted with the steady state RANS solver available in the commercial code CFX exploiting the SST turbulence model.

The development of the correlation permitted to rapidly cover the selected range of geometries and conditions highlighting that dynamic pressure losses are the major sources of losses. Minimal passage area to discharge section ratio is hence a dimensionless value able to describe characteristic curves insensitively to any other geometrical parameter.
Internal Cooling Channels Design Investigations: Aerothermal Optimisation of Ribbed U-Bends
Authors: Lott Philippe T. , Lepot Ingrid , Chérière Emmanuel , Thirifay François , Semmler Klaus , Bénet Laura
Published: November 2013

The design of turbine cooling systems remains one of the most challenging processes in engine development. Modern turbine cooling systems indeed invariably combine internal convection cooling with external film cooling in complex flow systems. The heat transfer and cooling processes are at the limit of current understanding and engine designers heavily rely on empirical tools and engineering judgment to produce new designs. These designs are moreover developed in the context of continuously increasing Turbine Entry Temperature (TET) as the latter leads to improvement of Specific Fuel Consumption (SFC). The present contribution fits into the frame of the ongoing FP7 ER-ICKA project. It focuses on achieving a significant progress in understanding turbine blade passages internal cooling systems by gathering high quality experimental data and by developing cooling state-of-the-art design capabilities based upon computer codes calibrated through these experimental data.

In this context, the paper will describe the design optimisation and analysis work performed for two different internal cooling passages configurations, namely a static leading edge LP configuration passage (baseline experimentally tested at Stuttgart University) and a rotating mid-chord HP configuration passage (baseline experimentally tested at ONERA). The aim of the work was to develop a design methodology to optimise turbulence promoting ribs shape and arraying to improve the thermal behaviour of the internal cooling passages while avoiding excessive head loss. The optimisation was driven using decoupled rib design parameters for each ribbed wall to enhance flow interactions and maximise disturbances, to maximise potential increase in Heat Transfer Coefficients (HTCs). Any improvement in the thermal behaviour of the cooling system may indeed allow to either reduce the coolant mass flow rate requirements or increase the TET.

To drive these optimisations, the ultimate target was hence to reduce the maximum blade metal temperature. To this end, suitable cost functions (objectives and constraints) have been derived and implemented. They will first be presented and discussed along with the parameterisations, so as to define the complete optimisation specification. The computational chain setup, among which the challenging mesh regeneration choices set based on a mesh dependence study will then be detailed. Validation of the CFD evaluation against the experimental results will be described for the static baseline configuration at least (rotating test measurements are still ongoing) and the optimisation results, which have led to significant gains in HTCs, will finally be analysed, data mining techniques allow to identify key parameters, path taken in the conception space and major trends.
Experimental and Numerical Examinations of a Transonic Compressor-Stage With Casing Treatment
Authors: Schönweitz D. , Voges M. , Goinis G. , Enders G. , Johann E.
Published: November 2013

The flow in the blade tip vicinity of the transonic first stage of a multi-stage axial flow compressor with variable inlet guide vane (IGV) and casing treatment (CT) above the rotor is investigated experimentally and numerically with focus on the effects of the CT on flow structures and compressor performance.

For the experimental part of this study, conventional performance instrumentation is used to estimate the operating condition of the compressor. Radial distributions of total temperature and total pressure are taken at the leading edges of the stators for comparison with simulations as well as for adjusting the operating conditions of the compressor. The velocity field in the rear part of the first-rotor is determined with Particle Image Velocimetry (PIV) at 90% and 96% radial height using two periscope light sheet probes. The employed PIV setup allows a spatial resolution of 0.7 mm × 0.7mm and thus a similar resolution as the spatial discretization in the simulation. For the numerical part of the study, time-accurate simulations are conducted for the same operating conditions as during experiments. Additional simulations of the same configuration with smooth casing are conducted in order to estimate the effect of the CT on the flow.

The examination of PIV measurements and corresponding simulations exposes complex vortical structures originating from the interaction of the rotor bow shock with the IGV trailing edge, CT, IGV wake and the tip leakage vortex. The associated induced velocities together with the general passage flow form a complex flow field with significantly altered blockage compared to a common flow field in the tip vicinity. Position and trajectory of the tip leakage vortex are deduced from interactions between tip leakage vortex and IGV wake / CT.

The detailed comparison of the tip region of simulations with and without CT shows that the CT influences pressure rise and flow parameters in a wide radial range due to a radial redistribution of the flow. Correspondingly, a rotor with CT can achieve an increased total pressure rise compared to a rotor with smooth casing, with only minor effects on the efficiency.