bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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
Derivative Design of Axial Fan Range: From Academia to Industry
Authors: Bonanni Tommaso , Cardillo Lucio , Corsini Alessandro , Delibra Giovanni , Sheard Anthony G. , Volponi David 
Published: September 2016

The work presented in this paper concerns a useful method for axial fans preliminary design based on the “Derivative Design” concept. The emphasis is, on one side, on education and, on the other, on the practical help that such method can provide in the early preliminary design process.
A complete data set of an axial fan measured with ISO 5801 standards is the start point for the investigation and the prediction of the multiple possible performance that different fan configurations can provide, in terms of dimensionless duty coefficients. In particular, configurations with different number of blades, and hence of solidity, are studied. The typical options of derivative design are explored and relations for performance prediction are presented.
A detailed description of the derivative design methodology is followed by tests and validation. The tools employed are a fully three dimensional code, the Advanceded Actuator Disk Mode (AADM), and two other in-house codes, the Meanline Axisymmetric Calculation (MAC) and Axisymmetric Laboratory (AXLAB).
Results of the derivative design method are reported, showing a good accuracy against the AADM data. The MAC and AXLAB ensure still acceptable results when increasing the solidity of the machine. On the contrary, a decrease of solidity leads to higher relative errors in the prediction of the load coefficient.
In conclusion, an exploration of the possible fields of operation of a blade profile can be carried out by a correct prediction of the stage diffusion factor.
Influence of Honeycomb Land Geometry on Seal Performance
Authors: Frączek Daniel , Bochon Krzysztof , Wróblewski Włodzimierz 
Published: September 2016

The aim of this study was to identify the best structures of the honeycomb (or structures used instead of it) that can be applied to a seal cavity labyrinth in order to improve the sealing performance. The problem was investigated numerically using the ANSYS CFX commercial software.
The paper presents geometrical data concerning the proposed solutions to the labyrinth seal land structure. A simple straight-through labyrinth geometry with two leaned fins is analysed. Such a simple structure of the flow conditions was chosen to reduce the influence of other effects on the seal performance. Three-dimensional models of the labyrinth seal were elaborated for each honeycomb or honeycomb-like land structure. The following concepts were analysed: an inclination of the honeycomb cells, a land with different cell shapes (squeezed honeycomb) and honeycomb cells filled with a porous material. The labyrinth seals with different land structures were compared with two reference cases: a seal with a standard honeycomb land (with 1/8-inch cell size) and a seal with a smooth land. Calculations were performed for the pressure ratio values ranging from 1.08 to 1.8 and for varied sizes of the clearance.
Main parameters of the leakage flows are discussed. Additionally, the influence of the inlet narrowing on the seal performance is investigated. A qualitative assessment of the seal concepts is made and the most promising solutions are pointed out.
Non-Invasive Parameter Identification in Rotordynamics via Fluid Film Bearings: Linking Active Lubrication and Operational Modal Analysis
Authors: Santos Ilmar Ferreira , Svendsen Peter Kjær 
Published: September 2016

In recent years, theoretical and experimental efforts have transformed the conventional tilting-pad journal bearing (TPJB) into a smart mechatronic machine element. The application of electromechanical elements into rotating systems makes feasible the generation of controllable forces over the rotor as a function of a suitable control signal. The servovalve input signal and the radial injection pressure are the two main parameters responsible for dynamically modifying the journal oil film pressure and generating active fluid film forces in controllable fluid film bearings. Such fluid film forces, resulting from a strong coupling between hydrodynamic, hydrostatic and controllable lubrication regimes, can be used either to control or to excite rotor lateral vibrations. If non-invasive forces are generated via lubricant fluid film, in situ parameter identification can be carried out, enabling evaluation of the mechanical condition of the rotating machine.
Using the lubricant fluid film as a non-invasive calibrated shaker is troublesome, once several transfer functions among mechanical, hydraulic and electronic components become necessary. In this framework the main original contribution of this paper is to show experimentally that the knowledge about the several transfer functions can be bypassed by using output-only identification techniques. The manuscript links controllable (active) lubrication techniques with operational modal analysis, allowing for in-situ parameter identification in rotordynamics, i.e. estimation of damping ratio and natural frequencies.
The experimental analysis is carried out on a rigid rotor-level system supported by one single pair of pads. The estimation of damping and natural frequencies is performed using classical experimental modal analysis (EMA) and operational modal analysis (OMA). Very good agreements between the two experimental approaches are found. Maximum values of the main input parameters, namely servovalve voltage and radial injection pressure, are experimentally found with the objective of defining ranges of non-invasive perturbation forces.
Mechanical Integrity and Design Analysis Suite (MIDAS): A Tool for Rapid Finite Element Analysis (FEA) of Steam Turbine Blades
Authors: Lolis Periklis , Guardino Cesare , Brown Trevor , Henson Jonathan 
Published: September 2016

Even though Finite Element Analysis (FEA) is considered to be an accurate static and dynamic simulation method, it is used only to verify the Mechanical Integrity (MI) of Steam Turbine (ST) blades, due to the time required to set up and perform a typical FEA. Furthermore, the complexity of the blade model results in convergence issues that further increase the analysis time, which can last several days. Instead, faster, lower order empirical tools with increased conservatism are preferred for the design phase.
Based on parametric steam turbine blades definition, the Mechanical Integrity and Design Analysis Suite (MIDAS) provides a platform for rapid, fully-automated 3D model generation and FEA. The analysis applies simplified contact interactions on a fully structured mesh, aiming primarily for model convergence in a short time, whilst maintaining the required accuracy. In order to verify that, an extended comparison of MIDAS static and vibrational analysis results with the state-of-the-art FEA and experimental measurements is performed.
Therefore, with MIDAS an accurate full FEA is completed within few minutes for each blade, speeding up the MI validation process and enabling its use at the design of every ST blade. Furthermore, the use of FEA contributes to an extended blade application envelope and optimised blade geometry. As a result, MIDAS presents several benefits to new and existing ST customers including increased operational flexibility, extended blade life, faster delivery of the ST cylinders at a lower acquisition cost and extended outage intervals.
Steam Turbine Rotor Transient Thermo-Structural Analysis and Lifetime Prediction
Authors: Moroz Leonid , Frolov Boris , Kochurov Roman 
Published: September 2016

Market requirements for faster and more frequent power unit start-up events result in a much faster deterioration of equipment, and a shorter equipment lifespan. Significant heat exchange occurs between steam and turbine rotors during the start-up process and even more intensive heat exchange takes place during the condensation phase in cold start-up mode, which leads to further thermal stresses and lifetime reduction. Therefore, the accuracy of lifetime prediction is strongly affected and dependent on the accuracy of transient thermal state prediction.
In this study, transient thermal and structural analyses of a 30 MW steam turbine for a combined High and Intermediate pressures (HPIP) rotor during a full cold start cycle is performed and special attention is paid to initial start-up phase with ‘condensation’ thermal BC. All steps for rotor design and the thermal model preparation were done using the AxSTREAM™* software platform. It included the development of a two dimensional model of the rotor, thermal zones and corresponding thermal boundary conditions (heat transfer coefficients and steam temperatures) calculation during turbine start-up and shut down operation. Rotor thermal and structural simulations were done using commercial FE analysis software to evaluate the thermo-stress-strain state of the turbine rotor. Calculation and validation of thermal and structural state of the rotor was done using actual start-up cycle and measured data from a power plant, and it showed good agreement of the calculated and the measured data. Based on the results of thermo-structural analysis, the evaluation of rotor lifetime by means of a low cycle fatigue approach was performed and presented in this paper.
Aerodynamics of Darrieus Wind Turbines Airfoils During Start-Up
Authors: Bianchini Alessandro , Balduzzi Francesco , Ferrara Giovanni , Ferrari Lorenzo 
Published: September 2016

Recent studies have demonstrated that, when rotating around an axis orthogonal to the flow direction, airfoils are virtually transformed into equivalent airfoils with a camber line defined by their arc of rotation. In these conditions, the symmetric airfoils commonly used for Darrieus blades actually behaves like virtually cambered ones or, equivalently, rotors have to be manufactured with counter-cambered blades in order to have the performance of a symmetric airfoil.
To complete these analyses, the present study focuses the attention on the airfoils’ aerodynamics during the start-up of the rotors. This phase of turbines’ functioning is indeed of particular interest since it actually defines the cut-in speed of the rotors and then notably impacts on the annual energy production, especially in case of small-size machines.
In the work, unsteady CFD simulations have been carried out in start-up like conditions on three airfoils, i.e. a NACA 0018 and two modified profiles based on the same airfoil. The modified profiles have been conformally transformed to fit their camber lines to the arc of a circle, such that the ratio of the airfoil chord to the circle’s radius is 0.114 or 0.25.
The study demonstrates that all the conventional theories based on one-dimensional aerodynamic coefficients (e.g. blade element momentum models) are affected by an intrinsic error in evaluating the starting torque profiles. Symmetric airfoils in fact exhibit a counter-intuitive non symmetric starting torque over the revolution. Conversely, airfoils compensated for the virtual camber effect show a substantially different starting torque profile, with a more symmetric distribution between the upwind and the downwind halves. This behavior is due to the effect of the pitching moment, which is usually neglected in lumped parameters models. At very low revolution speeds, its contribution becomes significant due to the very high angles of attack experienced by the blade. In particular, the pitching moment is non symmetric between the upwind and the downwind halves of the revolution. For upwind azimuthal positions the pitching moment reduces the overall torque output, while it changes sign in the downwind section, increasing the torque.
The importance of accounting for the pitching moment contribution in low-order models (e.g. a blade element momentum model) is finally discussed by comparing the predicted torque profiles with those obtained by CFD.