bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the Dynamic Behavior of Two High-Pressure Turbines for the Possible Detection of Rub Symptoms
Authors: Cangioli Filippo , Pennacchi Paolo , Vania Andrea , Chatterton Steven , Dang Phuoc Vinh 
Published: September 2016

Physical contact between the rotor and stationary-elements is a main topic in the field of rotordynamics. In the last decades, many studies have investigated the causes and the consequences of this phenomenon; the so-called ‘rub’, resulting in several theories and mathematical models. Muszynska characterized the rub from a phenomenological point of view in different conditions, both steady-state and transient; her studies laid the foundations and inspired research in the following years in many universities and research centers. State-of-the-Art methods permit to recognize, in a simple way, the rub during machine operating condition but in spite of the amount of studies, it is still difficult to prevent the occurrence of rubbing.
This paper focuses on identifying what are the forerunner symptoms of rubbing without attach specific attention to the rub and even to the consequences on the machine behavior. The authors investigate how to prevent the occurrence of rub by detecting its symptoms by means of analysis of the vibration and of the diagnostic data. For this purpose, the conventional graphic tools are used: Bode plot, polar plot, cascade plot, waterfall plot, centerline plot, time-based plot etc.
The dynamic behavior of two high-pressure steam turbines, which have been damaged by a physical contact between the rotor and a stationary part, is analyzed. In order to investigate the evolutionary trend of the vibration for possible rub detection, a new graphic tool was developed by the authors.
This work is born thanks to an industrial interest about the identification of evidences in the dynamic behavior of the forthcoming rub.
The data are available in three different sets of measurements, for both the high-pressure turbines. The data cover a quite long period but they are not available during the rubbing.
It must be noticed that the rub has occurred, for both turbines, immediately after a trip of the machine, so it is not excludable, a priori, that the cause of the trip has not been the same cause of the rubbing.
Development of an Active Control System for Rotating Machinery by Means of Tilting Pad Journal Bearings
Authors: Chatterton Steven , Cangioli Filippo , Pennacchi Paolo , Vania Andrea , Dang Phuoc Vinh 
Published: September 2016

The current design trend of rotating machines like turbo-generators, compressors, turbines, and pumps is focused on obtaining both high dynamic performances and high versatility of machines in different operating conditions. The first target is nowadays achieved by equipping machines with tilting pad journal bearings. For the second target, State-of-the-Art researches are focused on the development of active systems able to adapt the dynamic behavior of the machine to the external environment and new operating conditions.
Typical causes of large vibration in rotating machines are faults, residual unbalance, resonance condition and instabilities. Aiming at vibration reduction, in recent years many studies are carried out to investigate different solutions; one of them is based on active tilting pad journal bearing.
In this paper, the authors investigate, by simulations, the reduction of shaft vibration by controlling the motion of the pads of a tilting pad journal bearing. The basic idea is to balance the exciting force on the shaft with a suitable resulting force of the oil-film pressure distribution.
In particular, a sliding mode controller has been considered and both angular rotation of the pads about the pivot and the radial motion of the pivot have been analyzed.
Sliding mode control guarantees high robustness of the control system in real applications that can be characterized by a strong non-linear behavior.
In the paper a general consideration about the bearing, the actuating methods and the control system have been provided. A numerical analysis of large size rotor equipped with active pads has been carried out in order to verify the effectiveness of the system in several conditions, even during the most critical operating phase, i.e. the lateral critical speed.
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.
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.
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.
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.
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.
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.