bluuebunny/crossref_metadata_2025 huggingface dataset:
A Prototype Left Ventricular Assist Artificial Heart Pump: An Integrated Permanent Magnet and Active Magnetic Bearing Suspension System
Authors: Allaire Paul , Jiang Wei , Kailasan Arunvel , Dimond Timothy
Published: September 2014

The progress in the development of ventricular assist artificial heart pumps is continuing. This paper describes the magnetic suspension for a unique prototype axial flow pump designed for approximately 6 L/min at 100 mm Hg performance with an operating speed of approximately 7,000 rpm. The integrated magnetic suspension design provides a direct non-contact blood flow path through the pump with no obstructions which might create low flow areas and thrombosis (blood clots). The magnetic suspension is a combination of permanent magnets (PMs) and active magnetic bearings (AMBs). There are two radial AMBs which support the four degrees of freedom at the ends of the axial pump impeller and an axial PM thrust bearing. The axial PM bearing supports the direction of the largest fluid force on the impeller. A major objective of artificial hearts is to have extremely low power consumption. Thus the integrated PM and AMB suspension system has an operating magnetic suspension power of approximately 2 watts. The design, numerical modeling, and testing of the magnetic suspension system to support the fluid loads and the g loads are described in the paper.
Alternative Method to Simulate a Sub-Idle Engine Operation in Order to Synthesize Its Control System
Authors: Sukhovii Sergii I. , Sirenko Feliks F. , Yepifanov Sergiy V. , Loboda Igor
Published: September 2014

The steady-state and transient engine performances of gas turbine control system development are usually evaluated by applying full thermodynamic engine models. Most models only address the operating range between the idle and maximum power points, but more recently, they also address a sub-idle operating range.

The lack of information about the component maps at the sub-idle modes creates major challenges for the starting system and control system designers. A common method to cope with the problem extrapolates the performances of the engine components to the sub-idle operation range. Precise extrapolation is a challenge to be studied by many scientists. As a rule, many scientists are only concerned about particular aspects of the problem such as the lighting combustion chamber or the turbine operation under the turned-off conditions of the combustion chamber. However, there are no known reports about a model that considers all of these mentioned aspects and simulates the engine starting.

To synthesize a thermodynamic model of starting, most known methods require the performance of the components in the sub-idle range. The proposed paper addresses a new method that simulates the engine starting. The method substitutes the non-linear thermodynamic model with a linear dynamic model, which is supplemented with a simplified static model. The latter model is the set of direct relations between parameters that are used in the control algorithms instead of commonly used component performances. Specifically, the static model consists of simplified relations between the gas path parameters and the corrected rotational speed.

The paper also describes an algorithm for model synthesis and its practical application to real data.
Probabilistic Lifetime Prediction of Thermal Barrier Coating Systems Depending on Manufacturing Scatter
Authors: Bossmann Hans-Peter , Duda Thomas , Krueckels Joerg , Mihm Sebastian , Mücke Roland , Witz Gregoire
Published: September 2014

The assessment of Bondcoat/Thermal barrier coating systems is an inherent part of the lifing process of gas turbine component. On the one hand, coatings are considered in the constitutive modelling — e.g. in the thermal model and for the prediction of eigenfrequencies of gas turbine blades. On the other hand, the influence of the coating system on the lifetime of the part (target cyclic life and target operation hours) needs to be assessed. This paper addresses the prediction of coating lifetime. Lifing models of Bondcoat/Thermal barrier coating systems (BC/TBC) are commonly built using isothermal furnace cyclic tests (FCT). The lifetime of the BC/TBC under such test conditions has been shown to depend on multiple coating parameters like TBC thickness, TBC porosity, BC thickness, BC roughness, and also on testing temperature. For example, the TBC life (defined as time to partial TBC spallation) is reduced with increasing temperature, with increasing TBC thickness and decreasing porosity and BC roughness. When operating in a gas turbine (GT), the TBC surface temperature and the BC temperature depend on engine operating conditions, heat transfer of combustion gas and cooling air, coating microstructure and thickness. For instance, a TBC with high porosity typically demonstrates a lower thermal conductivity than that with low porosity. For otherwise same boundary conditions, the BC temperature will decrease with increasing TBC porosity and increasing TBC thickness. The benefit of having a high coating porosity observed in FCT is further amplified by its impact on reducing the BC temperature in GT operation. To the contrary, the positive impact of a reduced TBC thickness observed in FCT is reduced by its negative impact on an increased BC temperature during GT operation. Taking these effects into account a probabilistic lifing model is proposed based on Monte Carlo simulations. Using this model the impact of the manufacturing scatter on the BC/TBC life can be assessed, and enables improved manufacturing by focusing on those parameters that are most critical for coating lifetime.
A CFD-Based Parametric Study on Modification of Discrete Sister Holes Location for the Film Cooling Flow
Authors: Khajehhasani Siavash , Jubran Bassam
Published: September 2014

A numerical study on the effects of sister holes locations on film cooling performance is presented. This includes the change of the location of the individual discrete sister holes in the streamwise and spanwise directions, where each one of these directions includes 9 different locations, The simulations are performed using three-dimensional Reynolds-Averaged Navier Stokes analysis with the realizable k–ε model combined with the standard wall function. The variation of the sister holes in the streamwise direction provides similar film cooling performance as the base case for both blowing ratios of 0.5 and 1. On the other hand, the spanwise variation of the sister holes’ location has a more prominent effect on the effectiveness. In some cases, as a result of the anti-vortices generated from the sister holes and the repositioning of the sister holes in the spanwise direction, the jet lift-off effect notably decreases and more volume of coolant is distributed in the spanwise direction.
Validation Results for a Diverse Set of Turbomachinery Cases Using a Density Based OpenFOAM® Solver
Authors: Anderson Mark R. , Bonhaus Daryl L.
Published: September 2014

A validation study of a variety of compressible flow turbomachinery cases is presented with comparisons to test data using OpenFOAM. OpenFOAM is open-source code consisting of various solvers and computational libraries focused on CFD. The study used a particular solver version with a density based approach that was derived from the “extended” branch of OpenFOAM. The example cases all consisted of single blade row designs at steady state and were run fully viscous (unless noted otherwise) with various turbulence models.

The results showed a definite superiority of the density based solver over other OpenFOAM solvers in a test suite of simplified cases as well as in more complex examples in actual turbomachinery designs. A typical Laval nozzle case and transonic bump case are presented demonstrating the basic ability of the solver to capture shocks and to handle transonic flow in general. Actual turbomachinery applications consisted of a two-dimensional transonic compressor cascade, a moderately supersonic two-dimensional turbine cascade, two radial compressor cases, and a radial inflow turbine.

The results showed the solver to be very capable of capturing pressure distributions and, most importantly, aerodynamic loss through the machines. The ability of the solver to accurately model performance in a wide range of different designs and across the entire performance map was demonstrated. Detailed comparisons to highly regarded test data are shown.

Special examination was made of the computational costs of the solver which were quite high with run times coming in at about 10 times longer than other commercial compressible flow solvers. Several acceleration methods are discussed which significantly improved run time performance.
An Engine System Approach to Improve Turbocharger Fatigue Life
Authors: Sun Harold , Hu Liangjun , Zhang Jizhong , Alashe Waheed , Hanna Dave , Curtis Eric , Yi James
Published: September 2014

The ultimate goal of an advanced turbocharger development is to have a superior aerodynamic performance while having the turbocharger survive various real world customer applications. Due to the uncertainty of customer usage and driving pattern, the fatigue life prediction is considered one of the most ambiguous analyses in the entire design and analyses processes of the turbocharger. The turbocharger system may have various resonant frequencies, which may be within the range of turbocharger operation for automotive applications. A turbocharger may operate with excessive stresses when running near resonant frequencies. The turbocharger may experience fatigue failures if the accumulative cycles of the turbocharger running across the resonant frequencies exceeds a certain limit.

In this study, the authors propose an alternative approach to mitigate this kind of fatigue issues: i.e. engine system approach to improve turbocharger fatigue life via avoiding operating the turbocharger near resonant speeds for extended period of time. A preliminary numerical study was made and presented in this paper to assess the feasibility of such an engine system approach, which is followed by an engine dynamometer test for engine performance sensitivity evaluation when the turbocharger operation condition was adjusted to improve the high cycle fatigue life. The study shows that for a modern diesel engine equipped with electrically controlled variable geometry turbine and EGR for emission control, through the engine calibration and control upgrade, turbocharger operation speed can be altered to stay away from certain critical speeds if necessary.

The combined 1D and 3D numerical simulation shows the bandwidth of the turbine “risk zone” near one of the resonant speeds and the potential impact on engine performances if the turbocharger speed has to be shifted out of the “risk zone.”
Aerodynamic Robustness of End Wall Contouring Against Rim Seal Purge Flow
Authors: Regina K. , Kalfas A. I. , Abhari R. S. , Lohaus A. , Voelker S. , auf dem Kampe T.
Published: September 2014

In the present study, the results of an experimental investigation are presented, which have been undertaken in the axial turbine facility LISA at ETH Zurich. The two test configurations consist of a one-and-a-half stage, unshrouded, highly loaded axial turbine with 3-dimensionally shaped blading representative of modern high pressure gas turbines. The two test configurations differ in the hub end walls: while one design has cylindrical end walls, the other design features non-axisymmetric end wall contouring (EWC).

Both turbine designs have not been especially designed for the unsteady and complex interaction mechanisms of the hub rim seal purge flow with the main annulus flow. However, these turbine designs have been subject to measurements without (nominal) and with purge flow (0.8% of the main mass flow) with the purpose of studying the aerodynamic robustness of the performance of the stages with respect to the rim seal purge flow. In order to further analyze the robustness of both turbine designs, also measurements at off-design conditions have been taken.

The steady and unsteady aerodynamic effects are measured, respectively, with pneumatic probes as well as with the in-house developed and manufactured Fast Response Aerodynamic Probe (FRAP) technology. With the aim of evaluating the aerodynamic performance and robustness of the end wall design, the one result of the experimental investigation is the quantification of the sensitivity of the stage efficiency with respect to the case with and without purge flow for both turbine designs. By means of the analysis of the time-resolved flow field and characterization of the secondary flow features, their reaction to the presence of purge flow is highlighted and used as an explanation for the efficiency deficits caused by the purge flow.

The measurements show a benefit in stage efficiency of +0.2% by using the end wall contouring in the nominal case, confirming the design intention and effectiveness of the contoured end walls. However, the beneficial impact of the end wall contouring is taken back by a higher sensitivity of the stage efficiency with respect to the purge flow, which causes the efficiency benefit to vanish with the investigated purge flow injection rate of 0.8%. The off-design measurements show that also the sensitivity of the stage with end wall contouring with respect to the reduction of stage loading factor is by 1/3 higher than the one of the cylindrical end walls.

The measurements imply that the cost of higher stage efficiency at nominal conditions by the use of end wall contouring is paid with a higher sensitivity of the stage to changes in the rotor incoming flow field and thus with a lower aerodynamic robustness of the turbine design.
Aeromechanical Modelling of Fan Blades to Investigate High-Cycle and Low-Cycle Fatigue Interaction
Authors: Dhopade Priyanka , Neely Andrew J.
Published: September 2014

Gas turbine engine components are subject to both low-cycle fatigue (LCF) and high-cycle fatigue (HCF) loads. To improve engine reliability, durability and maintenance, it is necessary to understand the interaction of LCF and HCF in these components, which can adversely affect the overall life of the engine while they are occurring simultaneously during a flight cycle. A fully coupled aeromechanical fluid-structure interaction (FSI) analysis in conjunction with a fracture mechanics analysis was numerically performed to predict the effect of representative fluctuating loads on the fatigue life of blisk fan blades. This was achieved by comparing an isolated rotor to a rotor in the presence of upstream inlet guide vanes (IGVs). A fracture mechanics analysis was used to combine the HCF loading spectrum with an LCF loading spectrum from a simplified engine flight cycle in order to determine the extent of the fatigue life reduction due to the interaction of the HCF and LCF loads occurring simultaneously. The results demonstrate the reduced fatigue life of the blades predicted by a combined loading of HCF and LCF cycles from a crack growth analysis, as compared to the effect of the individual cycles. In addition, the HCF aerodynamic forcing from the IGVs excited a higher natural frequency of vibration of the rotor blade, which was shown to have a detrimental effect on the fatigue life. The findings suggest that FSI, blade-row interaction and HCF/LCF interaction are important considerations when predicting blade life at the design stage of the engine.
Engineering Precursors to Forewarn the Onset of an Impending Combustion Instability
Authors: Nair Vineeth , Thampi Gireeshkumaran , Sujith R. I.
Published: September 2014

The present study aims at arming an operator of fielded turbulent combustors with a repertoire of mathematical measures for real-time monitoring to forewarn the onset of impending combustion instability. In turbulent combustors, the route to high-amplitude, periodic, combustion-driven oscillations from conditions of low-amplitude, chaotic, combustion noise happens through an intermediate regime in flow conditions where the measured pressure fluctuations display bursts of intermittent, high-amplitude, periodic oscillations that appear in a near-random manner amidst chaotic fluctuations. This loss of chaos from combustion noise to combustion instability can be quantified to serve as a precursor to impending instability. The recurrence properties of intermittent burst oscillations can be quantified using dynamical systems theory by tracking the distribution of the aperiodic segments in the measured signals. Several statistical measures may be constructed through such recurrence quantification that provide robust early warning signals to an impending instability. Further, the transition to combustion driven oscillations leads to a collapse of the number of relevant time scales involved in the problem. This collapse in time scales can be quantified using generalized Hurst exponents which serve as an additional measure that captures the onset of an impending combustion instability well in advance. The various patent pending measures illustrated in this paper serve as precursors due to the inevitable presence of an intermittent regime of burst oscillations in turbulent combustors.
Transient Thermal Analysis and Visco-Plastic Damage Model for Life Prediction of Turbine Components
Authors: Staroselsky A. , Martin T. J. , Cassenti B.
Published: September 2014

This paper reports the process and computer methodology for a physics-based prediction of overall deformation and local failure modes in cooled turbine airfoils, blade outer air seals, and other turbomachinery parts operating in severe high temperature and high stress environments. The computational analysis work incorporated time-accurate, coupled aerothermal CFD with non-linear deformation thermal-structural FEM with a slip-based constitutive model, evaluated at real engine characteristic mission times and flight points for part life prediction. The methodology utilizes a fully-coupled elastic-viscoplastic model that was based on crystal morphology, and a semi-empirical lifing model introduced the use of dissipated energy to estimate the remaining part life in terms of cycles to failure. The method was effective for use with three-dimensional finite element models of realistic turbine airfoils using commercial finite element applications. The computationally predicted part life was calibrated and verified against test data for deformation and crack growth.
Steam Turbine Valve Hard-Facings: Experience and Latest Developments
Authors: Brussk S. , Schrey A. , Barnikel J. , Weltersbach D. , Starwald H.
Published: September 2014

The modern energy mix demands a flexible operation with an increased number of fast starts, and this results in enhanced requirements for the steam turbine and its components. Turbine admission valves, which are increasingly operated under instationary conditions to follow the changing power grid requirements, are mainly in charge. Therefore, continuous improvement of the tribological characteristics and oxidation resistance of valve components is required.

This paper discusses technical experience in steam turbine valve hard-facings over time, the current status and developments in this regard. Typical wear and crack findings of CoCr-based hard-facings are presented. The relevant investigations on the crack formation mechanism resulted in requirements and influences for the development of the current hard-facings. These concepts made for new products and service applications are introduced.

Furthermore, in consideration of a future increase in flexibility and efficiency demands, technical requirements for functional coatings are specified, and the development results of an integrated material concept are depicted.
Endwall Contour Optimization of a Turning Mid Turbine Frame Using an Adjoint Method
Authors: Akin M. Bugra , Sanz Wolfgang , Pieringer Paul
Published: September 2014

This paper presents the application of a viscous adjoint method in the optimization of the endwall contour of a turning mid turbine frame (TMTF). The adjoint method is a gradient based optimization method that allows for the computation of the complete gradient information by solving the governing flow equations and their corresponding adjoint equations only once per function of interest (objective and constraints), so that the computation time of the optimization is nearly independent of the number of parameters. With the use of a greater number of parameters a more detailed definition of endwall contours is possible, so that an optimum can be approached more precisely. A Navier-Stokes flow solver coupled with Menter’s SST k–ω turbulence model is utilized for the CFD simulations, whereas the adjoint formulation is based on the constant eddy viscosity approximation for turbulence. The total pressure ratio is used as the objective function in the optimization. The effect of contouring on the secondary flows is evaluated and the performance of the axisymmetric TMTF is calculated and compared with the optimized design.
The Influence of Transition on CFD Calculations of a Two-Stage Counter-Rotating Turbine
Authors: Akin M. Bugra , Sanz Wolfgang
Published: September 2014

Accurate numerical simulations depend on the correct prediction of all relevant flow phenomena. For many aeronautical devices such as turbomachinery the behaviour of boundary layers, wall shear stress and wall heat transfer are significant for the performance. Turbulence and transition may influence such flow characteristics. Onset and the extent of transition can therefore be of high importance for the design process.

In this paper three-dimensional steady-state simulations of a two-stage turbine with and without modeling of transition are performed. The configuration consists of a transonic high pressure turbine stage followed by an S-shaped turning mid turbine frame and a counter-rotating low pressure turbine rotor. The in-house Reynolds-averaged Navier-Stokes solver has been applied to this configuration with the correlation based γ–Reθ transition model developed by Menter et al. which has been added to the SST turbulence model. Also, calculations without transition with the SST and the Spalart-Allmaras turbulence model have been performed. This configuration is also the subject of experimental investigations at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology, so that measurement data at two planes are used for the verification of the simulations. After verification and flow analysis, the results are also discussed to evaluate the effect of modeling transition phenomena. An analysis of the overall efficiency of the turbine and the efficiency losses in the blade and vane rows are finally presented.
Large Eddy Simulation of ALSTOM’s Reheat Combustor Using Tabulated Chemistry and Stochastic Fields-Combustion Model
Authors: Kulkarni Rohit , Bunkute Birute , Biagioli Fernando , Duesing Michael , Polifke Wolfgang
Published: September 2014

Large Eddy Simulations (LES) of natural gas ignition and combustion in turbulent flows are performed using a novel combustion model based on a composite progress variable, a tabulated chemistry ansatz and the stochastic-fields turbulence-chemistry interaction model. It is a significant advantage of this approach that it can be applied to industrial configurations with multi-stream mixing at relatively low computational cost and modeling complexity. The computational cost is independent of the chemical mechanism or the type of fuel, but increases linearly with the number of streams. The model is validated successfully against the Cabra methane flame and Delft Jet in Hot Coflow (DJFC) flame. Both cases constitute fuel jets in a vitiated coflow. The DJFC flame coflow has a non-uniform mixture of air and hot gases. The model considers this non-uniformity by an additional mixture fraction dimension, emulating a ternary mixing case. The model not only predicts flame location, but also the temperature distribution quantitatively. The LES combustion model is further extended to consider four stream mixing. It has been successfully validated for ALSTOM’s reheat combustor at atmospheric conditions. Compared to the past steady-state RANS (Reynolds Averaged Navier-Stokes) simulations [1], the LES simulations provide an even better understanding of the turbulent flame characteristics, which helps in the burner optimization.
The Influence of Manufacturing Tolerances on Swirler Durability
Authors: Rudrapatna Nagaraja S. , Bohman Richard R. , Anderson Jonathan K. , Dudebout Rudolph , Hausen Richard
Published: September 2014

Jet fuel flowing through the fuel injector is atomized and then mixed with high temperature compressed air flowing through the swirler to create a combustible mixture inside a gas turbine combustor. Individual geometric and flow features are carefully tuned at a component level to deliver optimum combustion performance. In a critical interface such as the fuel injector and swirler, manufacturing tolerances not only have an impact on combustor performance and operability but also on durability, as the relative position of the fuel injector to the swirler significantly impacts the swirler temperature. This paper studies the influence of manufacturing tolerances on component assembly and the resulting impact on swirler temperature. The oxidation damage mechanism of the swirler is used as a measure to assess swirler durability. A Pareto chart of the effect of manufacturing tolerances on metal temperature is used to highlight the key influencing parameters. Probability distribution associated with manufacturing tolerances is gathered with Monte Carlo simulation to guide the design.
On the Optimisation of a Geared Fan Intercooled Core Engine Design
Authors: Kyprianidis Konstantinos G. , Rolt Andrew M.
Published: September 2014

Reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. Thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to further analyse the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. The proposed design methodology is capable, with the utilised tool, of exploring the interaction of design criteria and providing critical design insight at engine-aircraft system level.

Previous work by the authors focused on understanding the design space for this particular configuration with minimum specific fuel consumption, engine weight and mission fuel in mind. This was achieved by means of a parametric analysis, varying several engine design parameters — but only one at a time. The present work attempts to identify “globally” fuel burn optimal values for a set of engine design parameters by varying them all simultaneously. This permits the non-linear interactions between the parameters to be accounted. Special attention has been given to the fuel burn impact of the reduced HPC efficiency levels associated with low last stage blade heights.

Three fuel optimal designs are considered, based on different assumptions. The results indicate that it is preferable to trade overall pressure ratio and pressure ratio split exponent, rather than specific thrust, as means of increasing blade height and hence reducing the associated fuel consumption penalties. It is interesting to note that even when considering the effect of HPC last stage blade height on efficiency there is still an equivalently good design at a reduced overall pressure ratio. This provides evidence that the overall economic optimum could be for a lower overall pressure ratio cycle. Customer requirements such as take-off distance and time to height play a very important role in determining a fuel optimal engine design. Tougher customer requirements result in bigger and heavier engines that burn more fuel. Higher overall pressure ratio intercooled engine cycles clearly become more attractive in aircraft applications that require larger engine sizes.
Increasing On-Shore Wind Generated Electricity in Germany’s Transmission Grid
Authors: Singh A. , Willi D. , Chokani N. , Abhari R. S.
Published: September 2014

An increase in the penetration of renewables generated electricity has technical and economic impacts on power transmission systems because of the renewables’ variable characteristics. However, due to concerns of energy security, operational information of power infrastructure is scarce, making it challenging for policy-makers and independent power producers to assess these systems for the development of new energy projects. This paper presents an analysis of Germany’s power generation and transmission infrastructure using integrated, geographically-indexed production, demand and grid models. The paper assesses the impact of growth of renewables on Germany’s grid in a scenario of slow growth of grid infrastructure to show that the length of transmission lines needing reinforcement increases from 650 km in 2011 to 1090 km in 2020, if Germany’s transmission grid is to keep pace with the increased penetration of renewable energy. Mesoscale model simulations of the weather are used in the year 2020 scenario to assess the economic development of the competing renewables — wind and solar — in relation to the available grid capacity. It is shown that if the grid development lags the development of then targeted 35% renewables portfolio, then 6.5% of generated power by wind and solar energy will face risk of curtailment.
An Experimental Investigation of a Tandem Stator Flow Characteristic in a Low Speed Axial Research Compressor
Authors: Tesch Alrik , Lange Martin , Vogeler Konrad , Ortmanns Jens , Johann Erik , Gümmer Volker
Published: September 2014

A major goal in axial compressor development is to increase the efficiency and to reduce the weight of the module. In order to do so the power density has to be increased by raising the work per stage. Higher capability to do work can be achieved by increasing the circumferential velocity component of the fluid. Tandem stators might offer the ability to turn high swirling flow with lower losses compared to a single blade stator. In terms of higher aerodynamic loading the use of tandem vanes can be a key feature to allow the design of highly efficient and compact compressor modules.

This paper presents the design and experimental validation of a single stage low speed axial compressor with a tandem outlet guide vane, representative for a modern jet engine high pressure compressor. Additionally to the overall compressor performance the 3D flow field of the tandem stator has been measured with a five hole probe at different operating points. The results will be discussed in comparison with numerical results. Furthermore, oil flow pictures are used to get a deeper insight into flow conditions inside the vane passage and to validate the numerically predicted secondary flow structures.
Aerodynamics Prediction and Design of a Steam Turbine Exhaust Hood
Authors: Zhou Daiwei , Liu Bo , Zhu Xiaocheng , Du Zhaohui
Published: September 2014

The exhaust hood of a low pressure steam turbine is a component that has the potential to be improved considerably in terms of aerodynamic efficiency. In the present study, flow structures in the exhaust hood model of the low pressure stream turbine are investigated with experimental measurement and numerical simulation. The flow field in a modern type of exhaust hood is illustrated. The flow field predicted by CFD is validated by experimental measurement. Then, this paper introduces an aerodynamic optimization system to further improve the pressure recovery capability of low pressure turbine exhaust hood. The optimization system is developed with the Kriging surrogate model and the CFD method. The aerodynamic benefit provided by the optimal exhaust hood is explained. Finally, to scrutinize the static pressure recovery capability of the optimized exhaust hood, a full-scale exhaust hood coupled with last three stages is used to numerically evaluate the optimal design at four different flow rates. It is demonstrated that the optimal design from the air model can be used in the actual exhaust hood in different operation conditions.
Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge
Authors: Babu Harish , Sarkar S.
Published: September 2014

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using Large Eddy Simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair and DSSN vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.
Effects of the Steady Wake-Tip Clearance Vortex Interaction in a Compressor Cascade: Part II — Numerical Investigations
Authors: Busse Peter , Krug Andreas , Vogeler Konrad
Published: September 2014

An important aspect of the aerodynamic flow field in the tip region of axial compressor rotors is the unsteady interaction between the tip clearance vortex and the incoming stator wakes. In order to gain an improved understanding of the mechanics involved, systematic studies need to be performed. As a first step towards the characterisation of the dynamic effects caused by the relative movement of the blade rows, the impact of a stationary wake-induced inlet disturbance on a linear compressor cascade with tip clearance will be analyzed. The wakes were generated by a fixed grid of cylindrical bars with variable pitch being placed at discrete pitchwise positions.

Part II of this two-part paper focuses on the numerical studies conducted with the scientific flow solver TRACE. Selected measurements, which are discussed in detail in the first part of this paper, are compared with steady state RANS simulation data to determine the validity of the computational model. For this purpose, the flow field obtained in the passage (PIV), at the cascade exit (five-hole probes) and the endwall pressure distributions were used. The presented numerical results show potentials and limitations of the steady state CFD for the prediction of the investigated flow phenomena. The computations provide the initial conditions for future unsteady calculations, and enable a separate depiction of potential effects of steady and unsteady wake-tip clearance vortex interaction.
Experimental Investigation Into the Performance of Shallow Aeroengine Off-Takes
Authors: Simmons Kathy , Chandra Budi
Published: September 2014

Oil removal (scavenge) from aeroengine bearing chambers is an ongoing challenge for aeroengine designers. Effective scavenging of oil is necessary to avoid excessive heat generation, degradation of oil properties and deterioration in heat transfer functionality. However the task of oil removal is not trivial. Oil is entrained in a highly rotating environment induced by the rotating shafts. Simply removing a larger volume of fluid from the chamber with the scavenge pump can create higher air flowrates but lead to oil becoming trapped in the chamber and so no reduction in residence volume (the amount of oil present in the chamber during operation).

The University of Nottingham Technology Centre in Gas Turbine Transmissions Systems has been conducting experiments investigating two phase behaviour within a simplified aeroengine bearing chamber operating at ambient pressures with water as the working liquid. The rig is constructed from polycarbonate enabling good visual access. In the chamber offtake region a number of behaviours can be observed relating to the hydraulic uplift and general flow behaviour as gas and liquid exit the chamber. Chandra et al [1] reports a parametric study using a design of experiments approach into geometrical variants of a shallow offtake region defined by curved approaches and a small offtake volume. Phenomenlogical factors were quantified and used to identify the best performing geometry. Previous work at the UTC [2, 3] has used residence volume as the primary comparative performance parameter.

In this paper residence volume data is obtained for two sumps for which phenomenological data exists. The paper compares performance on the basis of these visual factors with performance on the basis of residence volume and concludes that although both frameworks have value, they do not lead to identical conclusions for all operating conditions. In film dominated cases significant hydraulic uplift usually corresponds to larger residence volume but for droplet dominated cases this is not necessarily so.
NOx Formation in a Reacting Premixed Jet in Hot Cross Flow
Authors: Ahrens Denise , Kolb Michael , Hirsch Christoph , Sattelmayer Thomas
Published: September 2014

The NOx emissions of a premixed jet in hot cross flow configuration have been studied experimentally and with simple Cantera models. Staged combustion is realized by a first reaction zone providing a flow of fully combusted products and a secondary combustion stage downstream which consists of a premixed jet injected into the hot cross flow. The focus of the study lies on the overall NOx emission reduction potential of this generic configuration with respect to single stage premixed combustion employed in the high load regime of most large gas turbines for power generation. Cantera benchmark calculations were made to address that question. The second stage reaction was modeled using two different configurations: The worst case scenario being the combustion of the mixture in the jet without any interaction with the hot cross flow, and the most favorable case being the jet and the cross flows perfectly mixed and then burned. All calculations were performed under atmospheric and high pressure conditions to illustrate the influence of pressure on the potential of staging on the reduction of NOx emissions. In parallel to the modeling the NOx formation was studied in an atmospheric test rig. For that purpose emission and temperature data were collected with single orifice probe traverses four jet diameters downstream. The thermocouple probe was calibrated against CO-equilibrium concentration data from thermodynamic modeling. Furthermore, a planar laser diagnostic technique using Mie scattering was applied for determining the mixing of jet and cross flow. The mixture field was statistically analyzed to detect differences in spatial and temporal mixing. Finally all data were used to study NOx formation under atmospheric pressure and to transfer the results to gas turbine combustor conditions.
An Energy-Based Framework to Determine the Fatigue Strength and Fatigue Ductility Parameters for LCF/HCF Life Assessment of Turbine Materials
Authors: Shen M.-H. Herman , Akanda Sajedur
Published: September 2014

An energy-based framework is developed to determine the fatigue strength parameters of Basquin equation and the fatigue ductility parameters of Manson-Coffin equation to predict fatigue life of a steam turbine material. The proposed framework is based on assessing the complete energy necessary to cause fatigue failure of a material. This energy is considered as a fundamental material property and is known as fatigue toughness. As a first approximation, the fatigue toughness is equivalent to the monotonic tension energy of a material. This assumption was experimentally verified for weld metal of a weld joint constituent of a turbine rotor and for aluminum 6061-T6. However, in case of base metal of the weld joint constituent, the fatigue toughness was found to be higher than the monotonic energy. From the fatigue toughness and the experimentally determined fatigue life at two different stress levels, the cyclic parameters of Ramberg-Osgood constitutive relation that describes the hysteresis stress-strain loop were calculated. Next, the coefficients and exponents of Basquin and Manson-Coffin equations were expressed as functions of fatigue toughness and cyclic parameters of a material. The predicted fatigue life obtained from the present energy-based framework was found to be in a good agreement with the experimental data.
Numerical Investigation of an Integrated Impingement and Pin-Fin Cooling Configuration in a Wedge Duct
Authors: Feng Xiaoxing , Tian Shuqing , Bai Jiangtao , Zhang Hong , Wang Kefei , Wang Hui
Published: September 2014

In the gas turbine blade cooling design, impingement insert and pin-fins arranged as an array in the trailing region are usually used to enhance the heat transfer. To investigate the heat transfer characteristics of the integrated impingement and the pin-fin cooling configuration in wedge channels, the numerical simulations with k-ε turbulence model and scalable wall function algorithm are carried out using a commercial CFD code.

To reveal the factors that enhance the heat transfer in the blade internal trailing channel, heat transfer characteristics of pin-fins with impingement slot are compared with that without impingement slot. The effect of the ratio of jet impingement distance to pin-fin diameter on the heat transfer is analyzed. The convergence angle of the channel is studied. The heat transfer characteristics of the integrated impingement and pin-fin cooling configuration in the wedge channels are evaluated.

The results reveal that the impinging jet enhances largely the heat transfer in the first two rows. In the studied range of L/D = 0.5∼2.0, the heat transfer of the pin-fins with impingement is about 20%∼25% higher than that without impingement. The averaged Nusselt numbers on the endwall surface, the pin surface, and the overall surfaces respectively in the wedge duct increase linearly with the increase of Reynolds number, decrease gradually with the increase of the impingement distance and increase with the increase of the convergence angle.
Design Optimization of Profiled Endwall in a High Work Turbine
Authors: Tang Huimin , Liu Shuaiqiang , Luo Hualing
Published: September 2014

In this paper, a method based on non-uniform rational B-spline surface (NURBS) technique coupled with mesh deforming technique is implemented to design the profiled endwall of turbines. This method has the advantages of flexible geometry representation and automatic rapid remeshing. An optimization procedure has been implemented by integrating the in-house geometry manipulator, a commercial three-dimensional CFD flow solver and the optimization driver, IsightTM.

This procedure is applied to design the profiled endwalls of the first stage of a one-and-half stage high work axial flow turbine. Genetic Algorithm is used in the optimization process, and the aim is to minimize the total pressure loss.

The influences of the profiled endwalls on the secondary flow in the stator and rotor have been analyzed by steady simulation. The results indicate a 0.4% improvement in stage efficiency. The secondary loss as well as the profile loss has been significantly reduced, and the increase of the reaction which influences the turbine efficiency is also observed.

The unsteady simulations are also presented in this paper to confirm the improved performance of the optimum profiled endwalls.
Bleed-Induced Distortion in Axial Compressors
Authors: Grimshaw S. D. , Pullan G. , Walker T.
Published: September 2014

In this paper, the influence of non-uniform bleed extraction on the stability of an axial flow compressor is quantified. Non-uniformity can be caused by several geometric factors (for example, plenum chamber size or number of off-take ducts) and a range of configurations is examined experimentally in a single stage compressor. It is shown that non-uniform bleed leads to a circumferential distribution of flow coefficient and swirl angle at inlet to the downstream stage. The resultant distribution of rotor incidence causes stall to occur at a higher flow coefficient than if the same total bleed rate had been extracted uniformly around the circumference. The loss of operating range caused by the non-uniform inlet flow correlates with the peak sector-averaged bleed non-uniformity for all the bleed configurations tested. A connection is made between the analysis of non-uniform bleed extraction and the familiar “DCθ” criterion used to characterize inlet total pressure distortion.
Design and Flow Analysis of a Supersonic Small Scale ORC Turbine Stator With High Molecular Complexity Working Fluid
Authors: Uusitalo Antti , Turunen-Saaresti Teemu , Guardone Alberto , Grönman Aki
Published: September 2014

In small scale and low temperature waste heat recovery systems, Organic Rankine Cycle (ORC) technology can be identified as a promising solution in converting low-grade heat into electricity. The principle of ORC is based on a conventional Rankine process but an organic working fluid is adopted instead of steam. The use of high molecular complexity working fluids enables the design of high efficiency ORCs and are characterized by dry expansion and high pressure ratios over the turbine, as well as low speed of sound, which typically leads to highly supersonic flows in the ORC turbine stator.

In order to design supersonic ORC turbines, the geometry of the turbine stator has to be based on design methods that accurately take into account the real gas effects of the working fluid during the expansion. In this study, a highly supersonic small scale ORC turbine stator using siloxane MDM as working fluid, is studied. The accurate real gas model was implemented in a CFD-flow solver in order to predict the flow field in the stator in design and in off-design conditions. The results of this study gives valuable information on realising small capacity ORC turbomachinery, characterized by highly supersonic stators, and on the off-design performance of supersonic radial turbine stator that has not been documented or discussed in the previous studies.
Development of New Engine Control for ETF40B Marine Turboshaft Engine
Authors: Luebs Alan
Published: September 2014

Vericor Power Systems (Vericor), the manufacturer of the ETF40B turboshaft engine used on the US Navy Landing Craft Air Cushion (LCAC) vehicles, has introduced a new Full Authority Digital Engine Control (FADEC) to replace the original FADEC currently in service in the Navy LCAC fleet. After several attempts to improve the reliability of the original FADEC to meet an acceptable standard, the original FADEC has remained unreliable in service.

In 2008 Vericor initiated a self-funded development program to replace the original engine control. Alternative FADEC design approaches were considered and ultimately Safran Electronics Canada (SE-C) was selected to design and manufacture a single-channel purpose built embedded controller that would control ETF40B engine/LCAC application as well as other Vericor gas turbine engines.

The design effort began in August 2010 and the first on-engine tests occurred in July 2011. Environmental/EMI qualification testing was accomplished to aggressive temperature, shock, vibration and Mil-Std-461F requirements leading to field deployment in the spring of 2013. This paper describes the requirements for this FADEC, its design pedigree, and the development and testing of the unit leading to US Navy use on the ETF40B equipped LCACs.