bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavior of Tilting–Pad Journal Bearings With Large Machining Error on Pads
Authors: Dang Phuoc Vinh , Chatterton Steven , Pennacchi Paolo , Vania Andrea , Cangioli Filippo
Published: September 2016

The use of tilting pad journal bearings (TPJBs) has increased in recent years due to their stabilizing effects on the rotor bearing system. Most of the studies addressing steady state and dynamic behaviors of TPJBs have been evaluated by means of thermo-hydrodynamic (THD) models, assuming nominal dimensions for the bearing, (i.e., the physical dimensions of all pads are identical and loads applied along the vertical direction). However machining errors could lead to actual bearing geometry and dimensions different from the nominal ones. In particular, for TPJB the asymmetry of the bearing geometry has not been well-investigated and can lead to an unexpected behavior of the bearing. The asymmetry of the bearing geometry can arise from large machining errors on only one or more pads, as a consequence of a pivot failure or after bad-mounting of the pads during assembly. These conditions can sometimes be detected by high values of the pad temperature, as measured by the temperature probes installed on the bearing pads, or by the abnormal vibration caused by pad-flutter phenomena.

In this paper the authors investigate large machining errors on the pad thickness for a five-pad TPJB and analyze their effects on the bearing operating characteristics. Pad thickness errors correspond to a different preload factor or clearance for each pad. A sensitivity analysis was performed for several combinations of pad thickness using a THD model and the behavior of the bearing was analyzed, including dynamic stiffness and damping coefficients, clearance profile, shaft locus, minimum oil-film thickness, power loss, flow rate, and maximum pressure.

The experimental case of a five pads TPJB with an intentional large machining error on the thickness of the pads is also described in the paper. The bearing has a nominal diameter of 100 mm, a diameter to length ratio (L/D) equal to 0.7 and can run at up to 3000 rpm. The experimental measurements are compared with the results obtained from the analytical model. The results show that the effects of asymmetry of the bearing geometry are more evident if the direction of the static load applied on the rotor bearing system, which is different from the vertical load, is also considered. For instance, the shape of shaft locus obtained by experimental tests changing the static load direction at a constant speed is an irregular pentagon if it is compared to the case of the nominal bearing.

Based on our findings, we concludes that the machining error on the pads has a large influence on the shaft locus, minimum oil-film thickness and maximum pressure on pads, especially at high rotational speed, but has little effect on the flow rate and power loss. In addition, this error significantly affects the dynamic stiffness and damping coefficients, both in terms of rotational speed and load direction.
Effects of Airfoil’s Polar Data in the Stall Region on the Estimation of Darrieus Wind Turbine Performance
Authors: Marten David , Bianchini Alessandro , Pechlivanoglou Georgios , Balduzzi Francesco , Nayeri Christian Navid , Ferrara Giovanni , Paschereit Christian Oliver , Ferrari Lorenzo
Published: September 2016

Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 90’s, in favour of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT concept, especially in the Darrieus configuration, may outweigh their disadvantages in specific applications, like the urban context or floating platforms.

To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guidelines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the Blade Element Momentum Theory for HAWTs’ applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the Double Multiple Streamtubes (DMS) Theory, based on momentum balances, and the Lifting Line Theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces.

Since the incidence angles range experienced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition towards the “thin plate like” behaviour has a large effect on simulation results. This paper will demonstrate the importance of stall and post-stall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of post-stall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna-Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and torque are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both simulation methods is highlighted and discussed.
A Simple Physics-Based Model for Particle Rebound and Deposition in Turbomachinery
Authors: Bons J. P. , Prenter R. , Whitaker S.
Published: September 2016

A new model is proposed for predicting particle rebound and deposition in environments relevant for gas turbine engines. The model includes the following physical phenomena: elastic deformation, plastic deformation, adhesion, and shear removal. It also incorporates material property sensitivity to temperature and tangential-normal rebound velocity cross-dependencies observed in experiments. The model is well-suited for incorporation in CFD simulations of complex gas turbine flows due to its algebraic (explicit) formulation. Model predictions are compared to coefficient of restitution data available in the open literature as well as deposition results from two different high temperature turbine deposition facilities. While the model comparisons with experiments are in many cases promising, several key aspects of particle deposition remain elusive. The simple phenomenological nature of the model allows for parametric dependencies to be evaluated in a straightforward manner. It is hoped that this feature of the model will aid in identifying and resolving the remaining stubborn holdouts that prevent a universal model for particle deposition.
Scaling Laws of Radial Clearance and Bump Stiffness of Radial Foil Bearings
Authors: Honavara Prasad Srikanth , Kim Daejong
Published: September 2016

Design and analysis of foil bearings involve consideration to various physical aspects such as fluid pressure, structural deformation and heat generation due to viscous effects within the bearing. These complex physical interactions are mathematically governed by highly nonlinear partial differential equations. Therefore, foil bearing design involves detailed calculations of flow fields (velocities, pressures), bump deflections (structural compliance) and heat transfer phenomena (viscous dissipation in the fluid, frictional heating, temperature profile etc.). The computational effort in terms of time and hardware requirements make high level engineering analyses tedious which presents an opportunity for development of rule of thumb laws for design guidelines.

Scaling laws for bearing clearance and bump stiffness of radial foil bearings of various sizes are presented in this paper. The scaling laws are developed from first principles using the scale invariant Reynolds equation and bump deflection equation. Power law relationships are established between the 1) radial clearance and bearing radius and 2) bump stiffness and bearing radius. Simulation results of static and dynamic performance of various bearing sizes following the proposed scaling laws are presented.
Full 3D Rotor/Stator Interaction Simulations in Aircraft Engines With Time-Dependent Angular Speed
Authors: Batailly Alain , Legrand Mathias , Pierre Christophe
Published: September 2016

Modern aircraft engine designs feature reduced clearances that may initiate structural contacts between rotating and static components. A numerical strategy dedicated to the simulation of such interactions is here enriched in order to account for time-dependent angular speeds. This contribution first details the evolution of the numerical strategy before validating the developments by comparing numerical results with experimental observations made on an industrial test bench. Further numerical investigations allow to assess the sensitivity of numerical results to acceleration and deceleration rates. Results, obtained with and without abradable coating, underline the fundamental nonlinear nature of the analysed system. It is found that lower acceleration rates favour the arisal of interaction phenomena and that amplitudes of vibration at a given angular speed are generally lower when the blade decelerates.
Effect of Turbulence and Transition Models on the CFD-Based Performance Prediction of Wind Turbines
Authors: Ernst Benedikt , Seume Joerg R. , Herbst Florian
Published: September 2016

Computational Fluid Dynamics (CFD) simulations are becoming increasingly important to enhancing the understanding of rotor aerodynamics and improving blade design for wind turbines. The present study addresses the effect of turbulence treatment on the CFD-based performance assessment of wind turbines by successively increasing the modeling depth. A process for 2D and 3D CFD simulations is described, which is based on the geometry of the NREL 5MW reference wind turbine. It is shown that the main differences between fully turbulent computations and transition model simulations with and without additional curvature correction model occur in the inner blade region, and increase in 3D flow regimes. Literature and the findings of the present study lead to the conclusion that simulations with the transition model in conjunction with the curvature correction model should be preferred. The resulting power output of this setup is also in good agreement with the Blade Element Momentum (BEM) calculation.
CFD and Thermal Analysis of Leaf Seals for Aero-Engine Application
Authors: Fico Vincenzo , Pekris Michael J. , Barnes Christopher J. , Jha Rakesh Kumar , Gillespie David
Published: September 2016

Aero-engine gas turbine performance and efficiency can be improved through the application of compliant shaft seal types to certain sealing locations within the secondary air system. Leaf seals offer better performance than traditional labyrinth seals, giving lower leakage flows at design duties. However, for aeroengine applications, seal designs must be able to cope with relatively large off-design seal closures and closure uncertainties. The two-way coupling between temperatures of seal components and seal closures, through the frictional heat generated at the leaf-rotor interface when in contact, represents an important challenge for leaf seal analysis and design. This coupling can lead to leaf wear and loss, rotor overheating, and possibly to unstable sealing system behaviour (thermal runaway). In this paper we use CFD, FE thermal analysis, and experimental data to characterise the thermal behaviour of leaf seals. This sets the basis for a study of the coupled thermo-mechanical behaviour. CFD is used to understand the fluid-mechanics of a leaf pack. The leaf seal tested at the Oxford Osney Laboratory is used for the study. Simulations for four seal axial Reynolds number are conducted; for each value of the Reynolds number, leaf tip-rotor contact and clearance are considered. Distribution of mass flow within the leaf pack, distribution of heat transfer coefficient at the leaf surface, and swirl velocity pick-up across the pack predicted using CFD are discussed. The experimental data obtained from the Oxford rig is used to develop a set of thermal boundary conditions for the leaf pack. An FE thermal model of the rig is devised, informed by the aforementioned CFD study. Four experiments are simulated; thermal boundary conditions are calibrated to match predicted metal temperatures to those measured on the rig. A sensitivity analysis of the rotor temperature predictions to the heat transfer assumptions is carried out. The calibrated set of thermal boundary conditions is shown to accurately predict the measured rotor temperatures.
Influence of Temperature and Pressure Fluctuations on the Mechanical Behavior of a Seal Structure in Steam Valve Under In-Service Conditions
Authors: Hong Hui , Wang Weizhe , Zhao Nailong , Cai Zhenwei , Liu Yingzheng
Published: September 2016

Most sealing components are designed under an idealized service condition with no fluctuation in steam temperature and pressure. However, the fluctuations during stable operation phase influences the mechanical behavior of sealing component in terms of fatigue and sealing performance. The correlation of these temperature and pressure fluctuations and corresponding strain amplitudes are established by FE analysis. The sealing performance under in-service conditions is compared with that of idealized operation conditions.
FE Analysis of the Effects of TGO Thickness and Interface Asperity on the Cracking Behavior Between the TGO and the Bond Coat
Authors: Jiang Jishen , Xu Bingqian , Wang Weizhe , Adjei Richard Amankwa , Zhao Xiaofeng , Liu Yingzheng
Published: September 2016

Finite element simulations based on an interface cohesive zone model (CZM) have been developed to mimic the interfacial cracking behavior between the α-Al2O3 thermally grown oxide (TGO) and the aluminum rich Pt–Al metallic bond coat (BC) during cooling from high temperature to ambient temperature. A two dimensional half-periodic sinusoidal geometry corresponding to interface undulation is modelled. The effects of TGO thickness and interface asperity on the stress distribution and the cracking behavior are examined by parametric studies.

The simulation results show that cracking behavior due to residual stress and interface asperity during cooling process leads to stress redistribution around the rough interface. The TGO thickness has strong influence on the maximum tensile stress of TGO and the interfacial crack development. For the sinusoidal asperities, there exist a critical amplitude above which interfacial cracking is energetically favored. For any specific TGO thickness, crack initiation is dominated by the amplitude while crack propagation is restricted to the combine actions of the wavelength and the amplitude of the sinusoidal asperity.
Altitude Effects on the Performance of Small Radial Turbomachinery: Part I — Compressor Impellers
Authors: Verstraete Dries , Lunnan Kjersti
Published: September 2016

Small unmanned aircraft are currently limited to flight ceilings below 20,000 ft due to the lack of an appropriate propulsion system. One of the most critical technological hurdles for an increased flight ceiling of small platforms is the impact of reduced Reynolds number conditions at altitude on the performance of small radial turbomachinery. The current article investigates the influence of Reynolds number on the efficiency and pressure ratio of two small centrifugal compressor impellers using a one-dimensional meanline performance analysis code. The results show that the efficiency and pressure ratio of the 60 mm baseline compressor at the design rotational speed drops with 6–9% from sea-level to 70,000 ft. The impact on the smaller 20 mm compressor is slightly more pronounced and amounts to 6–10%. Off-design changes at low rotational speeds are significantly higher and can amount to up to 15%. Whereas existing correlations show a good match for the efficiency drop at the design rotational speed, they fail to predict efficiency changes with rotational speed. A modified version is therefore proposed.
Altitude Effects on the Performance of Small Radial Turbomachinery: Part II — Turbine Impellers
Authors: Verstraete Dries , Lunnan Kjersti
Published: September 2016

Small unmanned aircraft are currently limited to flight ceilings below 20,000 ft (6.1 km) due to the lack of an appropriate propulsion system. One of the most critical technological hurdles for an increased flight ceiling of small platforms is the impact of the low Reynolds number conditions at altitude on the performance of small radial turbomachinery. The current article investigates the influence of Reynolds number on the efficiency and pressure ratio of 5 radial turbines using a 1D meanline performance analysis code. The results show that the efficiency at the design rotational speed drops by up to 30% from sea-level to 70,000 feet. However, the bulk of this efficiency loss occurs above approximately 20,000 feet where the flow in most turbines transitions to laminar flow. Existing turbine scaling correlations do not predict this efficiency loss well. However, an adapted method from compressor scaling research is shown to be fairly accurate.
Combined Influence of Surface Deposition and Hole-Blockage on Film-Cooling Performances
Authors: Wang Xue-yi , Pu Jian , Yuan Rui-ming , Wang Jian-hua
Published: September 2016

Commercial aero-engines may operate in dust-laden environments, such as taking off and landing on desert ground or flying through volcano dust cloud, and foreign particles frequently deposit at hot surface and film hole-exits, which results in partial blockage of film holes, clog of cooling air, reduction in cooling effect, and could induce catastrophic damage. This problem has not been well solved up to now. This paper presents an experimental investigation on two surface deposition models (deposition limited to upstream of hole with a peak height of 1.5 diameter of hole called D1.5, and downstream forming a trench with a peak height of 1.0 diameter of hole, called D1) and two blockage models (leading edge of hole LB, and trailing edge TB), as well as two combined models D1.5-LB, and D1-TB. The experiments are conducted in a low speed water tunnel using Planar Laser Induced Fluorescence (PLIF) technique. Through this experiment, the following interesting phenomena, which were not reported in previous literatures, are reveled: 1) The effect of blockage ratio at leading edge on cooling performance of combined D1.5-LB is opposite to individual LB, i.e. in the case of combined D1.5-LB, a higher blockage ratio corresponds to a lower cooling effectiveness; whereas, for individual LB, the cooling effectiveness increases with the blockage ratios in the tested range. 2) At all blowing ratios, the cooling performances of combined D1.5-LB are better than that of perfect model D0-B0 (without deposition and blockage). At all blockage ratios tested in this experiment, in the case of combined D1.5-LB, a higher blowing ratio corresponds to a higher cooling effectiveness and a lager film coverage length. 3) At lower blockage ratios of 0.1 and 0.3, the overall-averaged cooling effectiveness of combined D1-TB is higher than that of perfect model D0-B0. At large blockage ratio 0.5, the blockage effect is dominant, and the averaged cooling effectiveness of combined model D1-TB is lower than that of D0-B0. In the case of individual deposition model D1-B0, although the lateral-averaged film cooling effectiveness is augmented, the area of film cooling is reduced.
Power Dip Impact on Compressor System Stability
Authors: Bakken Lars E. , Lunde Erling , Løes Morten
Published: September 2016

Knowledge of compressor system behaviour during a trip is essential to obtain reliable operation. Experience at a gas treatment plant has shown that the export compressors (43 MW) may enter the unstable area of the performance characteristics and suffer from surge and rotating stall in situations with voltage drops in the electricity grid.

A detailed dynamic simulation model has been established to analyse the impact of different mechanical, process and control tuning aspects. The electric motor driven compressor, the protection valves and piping have been modelled and dynamic analyses performed to reveal the transient response.

The main challenges are related to the compressor system/process design and to the compressor and variable speed drive (VSD) response during power dip or compressor trip. Based on experiences detailed sensitivity analyses have been performed, covering the impact of: compressor discharge volumes, performance characteristics — head rise to surge, dimensions of the recycle piping as well as the sizing, characteristics and trip signal delay of the recycle protection valve(s).

This paper reports experience from analyses of the export compressor and driver behaviour during the first 3 seconds of an electric power/voltage dip. It is partly based on earlier tests and dynamic simulations performed for the facility, and partly on new technology challenges and opportunities. The main objective has been to study the compressor system sensitivity related to variation in available driver power during power dip and its impact on the transient rundown trajectory and recovery phase.
Development of an Inside-Out Ceramic Turbine
Authors: Landry C. , Dubois P. K. , Courtois N. , Charron F. , Picard M. , Plante J.-S.
Published: September 2016

Ceramic turbines could substantially increase operating temperatures of turbomachinery without the need of blade cooling, leading to higher conversion efficiency and power density. However, the inherent brittleness and low tensile strength of ceramic materials limits the use of hub-based ceramic turbines. This paper presents a novel inside-out turbine architecture, permitting the use of monolithic ceramic blades. The proposed architecture uses a carbon-polymer composite rim which converts the rotor radial loads to tangential hoop stress. The blades mainly support compressive loads, minimizing tensile stresses within the blade and thus crack propagation. This allows the use of low tensile strength ceramics which cannot be used in standard hub-based turbines. The rotor hub is comprised of two radially flexible C-shaped hubs, which have sufficient compliance to follow radial displacement of the heavily loaded composite rim. The feasibility of the proposed inside-out ceramic turbine is demonstrated by addressing the four key challenges of the architecture using proof-of-concept prototypes, namely: (1) rotor dynamics of the flexible hub; (2) thermal viability of the composite rim (3) local tensile stress in the blades, and (4) thermal shock in the ceramic blades in transient mode. Experimental validation with an alumina blade confirms that this architecture supports the use of low tensile strength, brittle ceramic blades.
Analysis of Historical Dry Gas Seal Failure Data
Authors: Day Meera , Allison Tim
Published: September 2016

While proper design and maintenance of dry gas seals is a well-understood topic, dry gas seal failures are still relatively common. These failures can result in frequent repairs and costly downtime. Although several case studies of individual failures are available, relatively few large-scale dry gas seal failure studies exist. Based on a review of existing literature, very little has been published on failure statistics aimed at improving seal reliability. As a part of an industry-funded dry gas seal reliability project, a failure database has been populated with information provided by both end users and original equipment manufacturers. The database includes details on dry gas seal and separation seal configuration, seal gas supply, operating history, conditions at time of failure, and failure symptoms, including any results from failure analyses performed by the survey respondent. In total, eight companies contributed 194 failures. Of these, 144 cases had root causes provided.

From this database of failures, statistical analysis is used to determine common reasons behind dry gas seal failures in gas compression service. Failure trends are identified based on data collected, and corresponding recommendations are provided for improving dry gas seal reliability.
Combustor-Turbine Aerothermal Interaction in an Axial Turbine: Influence of Varied Inflow Conditions on Endwall Heat Transfer and Film Cooling Effectiveness
Authors: Werschnik Holger , Hilgert Jonathan , Bruschewski Martin , Schiffer Heinz-Peter
Published: September 2016

The Large Scale Turbine Rig (LSTR) at Technische Universit ät Darmstadt, Germany is used to examine the aerothermal interaction of combustor exit flow conditions on the subsequent turbine stage. The rig resembles a high pressure turbine and is scaled to low Mach number conditions. A baseline configuration with axial, low-turbulent inflow and an aerodynamic inflow condition of a state-of-the-art lean combustor is modeled by the means of swirl generators, whose clocking position towards the nozzle guide vane’s leading edge can be varied. A hub side coolant injection consisting of a double-row of cylindrical holes is implemented to examine the impact on endwall cooling.

This paper is directed to study the effect of swirling inflow on heat transfer and film cooling effectiveness on the hub side endwall. Nusselt numbers are calculated using infrared thermography and the auxiliary wall method. This method allows for a high spatial resolution and in addition also yields adiabatic wall temperature data within the same measurement using a superposition approach. Aerodynamic measurements and numerical simulations complement the examination.

The results for the baseline case show Nusselt numbers to increase significantly with higher coolant mass flux rates for the whole endwall area. With swirling inflow, in general, a decrease of film cooling effectiveness and an increase of Nusselt numbers is observed for identical mass flux rates in comparison to the baseline case. The difference varies depending on clocking position.
An Unsteady Aerodynamics Model for Lifting Line Free Vortex Wake Simulations of HAWT and VAWT in QBlade
Authors: Wendler Juliane , Marten David , Pechlivanoglou George , Nayeri Christian Navid , Paschereit Christian Oliver
Published: September 2016

This paper describes the introduction of an unsteady aerodynamics model applicable for horizontal and vertical axis wind turbines (HAWT/VAWT) into the advanced blade design and simulation code QBlade, developed at the HFI of the TU Berlin. The software contains a module based on lifting line theory including a free vortex wake algorithm (LLFVW) which has recently been coupled to the structural solver of FAST to allow for time-resolved aeroelastic simulations of large, flexible wind turbine blades. The aerodynamic model yields an accuracy improvement with respect to Blade Element Momentum (BEM) theory and a more practical approach compared to higher fidelity methods such as Computational Fluid Dynamics (CFD) which are too computationally demanding for load case calculations. To capture the dynamics of flow separation, a semi-empirical method based on the Beddoes-Leishman model now extends the simple table lookups of static polar data by predicting the unsteady lift and drag coefficients from steady data and the current state of motion. The model modifications for wind turbines and the coupling to QBlade’s vortex method are described. A 2D validation of the implementation is presented in this paper to demonstrate the capability and reliability of the resulting simulation scheme. The applicability of the model is shown for exemplary HAWT and VAWT test cases. The modelling of the dynamic stall vortex, the empiric model constants as well as the influence of the dynamic coefficients on performance predictions are investigated.
Aerodynamic Excitation Analysis for Variable Tip Gap
Authors: Hauptmann Thomas , Seume Joerg R.
Published: September 2016

In jet engines, blade repair is often more economical than the replacement of damaged blades with spare parts. Besides such regeneration of turbine blades, blade rubbing and erosion lead to a deviation of the geometry in the tip region of the original blade. These geometric variations can introduce non-uniform flow conditions which in turn may lead to an excitation of the blades. An analysis of the aerodynamic excitation due to typical geometric variations of the radial tip gap, introduced through substantial wear, is numerically investigated using a fluid-structure interaction (FSI) approach. The model was previously validated against experimental data. The results of the analysis show up to 1.6 times higher excitation than in the reference case, because rotor blades are excited by the wakes of the stator vanes and are amplified by a modified tip flow in the rotor passage.
Additive Manufacturing of Hot Gas Path Parts and Engine Validation in a Heavy Duty GT
Authors: Schurb Julius , Hoebel Matthias , Haehnle Hartmut , Kissel Harald , Bogdanic Laura , Etter Thomas
Published: September 2016

Additive manufacturing and in particular Selective Laser Melting (SLM) are manufacturing technologies that can become a game changer for the production of future high performance hot gas path parts. SLM radically changes the design process giving unprecedented freedom of design and enabling a step change in part performance. Benefits are manifold, such as reduced cooling air consumption through more efficient cooling schemes, reduced emissions through better mixing in the combustion process and reduced cost through integrated part design. GE is already making use of SLM for its gas turbine components based on sound experience for new part production and reconditioning.

The paper focuses on:

a) Generic advantages of rapid manufacturing and design considerations for hot gas path parts

b) Qualification of processes and additive manufacturing of engine ready parts

c) SLM material considerations and properties validation

d) Installation and validation in a heavy duty GT

Additive Manufacturing (AM) of hot gas path components differs significantly from known process chains. All elements of this novel manufacturing route had to be established and validated. This starts with the selection of the powder alloy used for the SLM production and the determination of essential static and cyclic material properties.

SLM specific design features and built-in functionality allow to simplify part assembly and to shortcut manufacturing steps. In addition, the post-SLM machining steps for engine ready parts will be described.

As SLM is a novel manufacturing route, complementary quality tools are required to ensure part integrity. Powerful nondestructive methods, like 3D scanning and X-ray computer tomography have been used for that purpose. GE’s engine validation of SLM made parts in a heavy duty GT was done with selected hot gas path components in a rainbow arrangement including turbine blades with SLM tip caps.

Although SLM has major differences to conventional manufacturing the various challenges from design to engine ready parts have been successfully mastered. This has been confirmed after the completion of the test campaign in 2015. All disassembled SLM components were found in excellent condition. Subsequent assessments of the SLM parts including metallurgical investigations have confirmed the good part condition.
Setup, Validation and Probabilistic Robustness Estimation of a Model for Prediction of LCF in Steam Turbine Rotors
Authors: Pusch David , Voigt Matthias , Vogeler Konrad , Dumstorff Peter , Almstedt Henning
Published: September 2016

Flexibility and availability together with fast startup times become more and more important for steam turbine operation. Exact knowledge about the turbine components stresses and lifetime consumption during transient operation is a prerequisite in order to meet these requirements.

A transient FE model of an intermediate pressure steam turbine rotor was generated, allowing the prediction of temperature and elastic stress field during turbine startup, load changes and shutdown. Operating data of the steam parameters and of a thermocouple inside the wall of the turbine inner casing were used to indirectly validate the thermal FE model in order to reproduce the measured metal temperatures in a proper accuracy.

Subsequently a probabilistic sensitivity study was performed in order to identify the influence of scattering or not well known boundary conditions on the calculated lifetime consumption of the steam turbine rotor during a cold start. This in fact provides information about the accuracy of the prediction. The results of the sensitivity study also help to improve the model accuracy by identifying the boundary conditions with the largest impact on lifetime prediction uncertainty, i.e. the boundary conditions that need further investigation.
The Role of Advanced Fracture Mechanics Evaluation Methods for Turbine Components
Authors: Almstedt Henning , Kern Torsten-Ulf , Segletes David , Loehr Michael
Published: September 2016

The demand for higher plant cycling operation and reduced life-cycle costs are the main drivers for the design and assessment of turbine components today. Heavy cyclic loading increases the potential of fully utilizing the fatigue capabilities of the material which might lead to crack initiation and subsequent crack propagation.

Fracture mechanics methods and evaluation concepts are widely applied to assess the integrity of components with defects or crack-like findings. The realistic modelling of the failure mechanism plays a key role for the accurate prediction of crack sizes at failure state.

A basic treatment of material toughness typically leads to conservative assessments for components with sufficient ductility. A standard approach to describe material behavior with high ductility is to use the start of stable crack extension as a dimensioning parameter for the analysis. By definition a critical condition for a component is reached when the crack driving force is equal to the characteristic material parameter. On the other hand, advanced analysis methods allow determination of the instability point (ductile tearing analysis).

This paper will discuss two cases for practical analysis from steam turbine design showing clear advantages for service application by using advanced analysis methods.
Pre-Optimization of Asymmetrical Underplatform Dampers
Authors: Gastaldi Chiara , Gola Muzio M.
Published: September 2016

The numerical coupled optimization of an underplatform damper is the exploration of its dynamics through a finite element model which includes both the damper and the blades. This is an effective approach if the initial damper mass and geometry have been previously selected in such a way that those parameter combinations leading to undesirable damper behavior (i.e. contact point lift-off, jamming, excessive contact forces) are ruled out a priori. This can be obtained through a pre-optimization where, after choosing the damper type the following main steps are followed:

1. ensure that damper jamming is avoided through an appropriate choice of platform angles, in function of the friction coefficients;

2. ensure that damper lift-off is avoided through an appropriate choice of the shape and position of the damper-platform flat contact surface and the position of the damper mass center;

3. set upper and lower limits to the value of damper-platform contact forces (as a multiple of the damper centrifugal force), the first being related to friction and wear problems, the second to the very existence of bilateral contacts;

4. check the model, and in particular the values of friction coefficients and contact stiffness, against experimental results.

Once the above knowledge concerning the most desirable damper shape has been gathered an effective coupled-optimization can safely be performed. This is done by finding the most effective match between the damper size/mass and the bladed disk through a non-linear dynamic calculation (not examined in this paper). The outcome of both the pre-optimization and the coupled optimization are strongly dependent on the assumed values of friction coefficients, which depend on the contact surface type (then, different for the left and right side of the damper) and the contact pressure.

The paper capitalizes on already developed tools, presented in previous ASME papers, such as the test rig developed by the AERMEC lab to draw the appropriate values of contact parameters, the numerical model representing the stand-alone dynamics of the damper between the platforms and the automatic random sampling tuning procedure. The purpose of the paper is to illustrate the procedure through the analysis of a family of rigid bar dampers with a curved-flat cross section.
Comparison of Two Methods for Sensitivity Analysis of Compressor Blades
Authors: Schmidt Robin , Voigt Matthias , Vogeler Konrad , Meyer Marcus
Published: September 2016

This paper will compare two approaches of sensitivity analysis, namely (i) the adjoint method which is used to obtain an initial estimate of the geometric sensitivity of the gas-washed surfaces to aerodynamic quantities of interest and (ii) a Monte Carlo-type simulation with an efficient sampling strategy. For both approaches the geometry is parameterized using a modified NACA parameterization. First the sensitivity of those parameters is calculated using the linear (first order) adjoint model. Since the effort of the adjoint CFD solution is comparable to that of the initial flow CFD solution and the sensitivity calculation is simply a postprocessing step, this approach yields fast results. However, it relies on a linear model which may not be adequate to describe the relationship between relevant aerodynamic quantities and actual geometric shape variations for the derived amplitudes of shape variations.

In order to better capture nonlinear and interaction effects, secondly a Monte Carlo-type simulation with an efficient sampling strategy is used to carry out the sensitivity analysis. The sensitivities are expressed by means of the Coefficient of Importance, which is calculated based on modified polynomial regression and therefore able to describe relationships of higher order.

The methods are applied to a typical high pressure compressor stage. The impact of a variable rotor geometry is calculated by 3D CFD simulations using a steady RANS model. The geometric variability of the rotor is based on the analysis of a set of 400 blades which have been measured using high-precision 3D optical measurement techniques.
Development and Validation of an Efficient TEHD Model of Tilting Pad Journal Bearings
Authors: Conti R. , Frilli A. , Meli E. , Nocciolini D. , Panconi S. , Pugi L. , Rindi A. , Rossin S.
Published: September 2016

The large success of Tilting Pad Journal Bearings (TPJBs) for the use in high speed/high load applications is due to their intrinsic stability properties, which allow superior rotor dynamic performances. TPJBs operation involves different physical phenomena, like the pads flexibility and the heat exchange between solids and fluids: an accurate analysis of these phenomena is fundamental in order to successfully employ TPJBs. In this paper, the authors, in cooperation with General Electric Nuovo Pignone, develop an innovative 3D TPJB modelling approach that allows an accurate analysis of the interactions between the fluid dynamic and thermal phenomena with the elastic behaviour of the solid components (ThermoElastoHydroDynamic analysis). The main objective of the proposed model is to provide accurate 3D results with low computational times. The TPJB model has been also experimentally validated, focusing on the thermal characteristics of the system and the interactions due to the TEHD behaviour of the bearing system.
On the Scaling of Aeroelastic Parameters for High Pressure Applications in Centrifugal Compressors
Authors: Fruth Florian , Jeschke Peter , Franz Holger
Published: September 2016

A centrifugal compressor has been evaluated numerically for the scalability of aeroelastic parameters for different pressure levels. By maintaining the flow coefficient, as done in the development process, comparable aerodynamics for the compressor cases have been generated ranging from 0.96 bar to 40 bar inlet pressure. It has been found, that the mean static pressure as well as the aerodynamic damping can be scaled by the inlet density ratio. The gained results proofed for this case to be sufficient in magnitude and distribution for an early development stage. Harmonic pressure scaling for centrifugal compressors however has resulted in non-negligible errors. The origin of changes for the setup presented is found in the variation of Reynolds number. Especially the hub and tip sections are influenced and therefore also the secondary flow through the impeller tip gap. This generally results in lower scalability after the transition from axial to radial flow. Hence impeller trailing edge mode shapes have to be considered carefully. The Reynolds number effects become smaller however for higher temperature levels, reducing the scaling errors.
Performance Analysis of Hybrid Brush Pocket Damper Seals Using Computational Fluid Dynamics
Authors: Pugachev Alexander O. , Griebel Clemens , Tibos Stacie , Charnley Bernard
Published: September 2016

In this paper, a hybrid brush pocket damper seal is studied theoretically using computational fluid dynamics. In the hybrid sealing arrangement, the brush seal element with cold clearance is placed downstream of a 4-bladed, 8-pocket, fully partitioned pocket damper seal. The new seal geometry is derived based on designs of short brush-labyrinth seals studied in previous works. Transient CFD simulations coupled with the multi-frequency rotor excitation method are performed to determine frequency-dependent stiffness and damping coefficients of pocket damper seals. A moving mesh technique is applied to model the shaft motion on a predefined whirling orbit. The rotordynamic coefficients are calculated from impedances obtained in frequency domain. The pocket damper seal CFD model is validated against available experimental and numerical results found in the literature. Bristle pack in the brush seal CFD model is described as porous medium. The applied brush seal model is validated using the measurements obtained in previous works from two test rigs. Predicted leakage characteristics as well as stiffness and damping coefficients of the hybrid brush pocket damper seal are presented for different operating conditions. In this case, the rotordynamic coefficients are calculated using a single-frequency transient simulation. By adding the brush seal, direct stiffness is predicted to be significantly decreased while effective damping shows a more moderate or no reduction depending on excitation frequency. Effective clearance results indicate more than halved leakage compared to the case without brush seal.
Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals
Authors: Da Soghe Riccardo , Bianchini Cosimo , Sangan Carl M. , Scobie James A. , Lock Gary D.
Published: September 2016

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations.

With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement.

When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations.

Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.
Development of Advanced Thermal Barrier Coatings With Improved Temperature Capability
Authors: Witz Gregoire , Schaudinn Markus , Sopka Joerg , Buecklers Tobias
Published: September 2016

Continuously increasing hot gas temperatures in heavy duty gas turbines lead to increased thermal loadings of the hot gas path materials. Thermal barrier coatings are used to reduce the superalloys temperature and cooling air needs. Until now 6–8 wt% yttria stabilized zirconia is the first choice material for such coatings, but it is slowly reaching its maximum temperature capability due to the phase transformation at high temperature and sintering.

New thermal barrier coating material with increased temperature capability enable the next generation of gas turbine with >60% combined cycle efficiency. Such material solutions have been developed through a multi-stage selection process. In a first steps, critical material performance requirements for thermal barrier coating performance have been defined based on the understanding of standard TBC degradation mechanisms. Based on these requirements, more than 30 materials were a pre-selected and evaluated as potential coating materials. After carefully reviewing their properties both from literature data and laboratory test results on raw materials, five materials were selected for coating manufacturing and laboratory testing.

Based on the coating manufacturing trials and laboratory test results, two materials have been selected for engine testing, in a first step in GT26 Birr Test Power Plant and afterwards in customer engines. For such tests the original coating thickness has been increased such to achieve coating surface temperature ∼100K higher than with a standard thermal barrier coating. Both coatings performed as predicted in both GT26 Birr Test Power Plant and customer engines.
Establishment of a Competitive Additive Manufacturing Workshop
Authors: Ryan Paul , Schwerdtfeger Jan , Rodermann Markus
Published: September 2016

Compared to conventional manufacturing processes, additive manufacturing offers a degree of freedom that has the potential to revolutionize the turbine components supply chain. Additive manufacturing facilitates the design and manufacture of highly complex components in high performance materials with features that cannot currently be realized with other processes. In addition, shorter development and manufacturing lead-times are possible due to the flexibility of 3D based processing and the absence of expensive, complicated molds or dies.

Having been confined for many years to rapid prototyping or R&D applications, additive manufacturing is now making the move to the factory floor. However, a dearth of manufacturing experience makes the development effort and risk of costly mistakes a deterrent for many organizations that would otherwise be interested in exploring the benefits of additive manufacturing.

A former manufacturer of industrial gas turbines recently established an additive manufacturing workshop designed to deliver highly complex engine-ready components that can contribute to increased performance of the gas turbine. A strong emphasis on process validation and implementation of the organization’s best practice Lean and Quality methodologies has laid solid foundations for a highly capable manufacturing environment.

This paper describes the approach taken to ensure that the workshop achieves a high level of operational excellence. Process development topics explored in the paper include the following:

• Planning of process flow and cell layout to permit the maximum lean performance

• Strategy used to determine machine specification and selection method.

• Assessment of process capability

• Influence of design for manufacture on process efficiency and product quality

• Experience gained during actual production of first commercial components