bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Validation of Fretting Fatigue Strength and Fretting Wear Rate at Contact Surface of Turbine-Blade-Shroud Cover
Authors: Asai Kunio , Kudo Takeshi , Yoda Hideo
Published: December 2013

In continuously coupled blade structures, fretting fatigue and wear have to be considered as supposed failure modes at the contact surface of the shroud cover, which is subject to steady contact pressure from centrifugal force and the vibratory load of the blade. We did unique fretting tests that modeled the structure of the shroud cover, where the vibratory load is only carried by the contact friction force, i.e., a type of friction. What was investigated in this study are fretting fatigue strength, wear rate, and friction characteristics, such as friction coefficient and slip-range of 12%-Cr steel blade material. The friction-type tests showed that fretting fatigue strength decreases with the contact pressure and a critical normal contact force exists under which fretting fatigue failure does not occur at any vibratory load. This differs from knowledge obtained through pad-type load carry tests that fretting fatigue strength decreases with the increase of contact pressure and that it almost saturates under a certain contact pressure. Our detailed observation in the friction-type tests clarified that this mechanism was the low contact pressure narrowing the contact area and a resulting high stress concentration at a local area. The fretting wear rate was explained by the dissipated energy rate per cycle obtained from the measured hysteresis loop between the relative slip range and the tangential contact force. This fretting wear rate per cycle is almost the same as the general adhesion wear rate when energy dissipation per cycle is high, and the former is smaller than the latter as the dissipated energy decreases. Finally, to prevent fretting fatigue and wear, we propose an evaluation design chart of the contact surface of the shroud cover based on our friction-type fretting tests.
Robust Design of Friction Interfaces of Bladed Disks With Respect to Parameter Uncertainties
Authors: Krack Malte , Panning Lars , Wallaschek Jörg , Siewert Christian , Hartung Andreas
Published: December 2013

Friction damping is a well-known technology in the field of turbomachinery. The design of friction contacts is subject to various uncertainties in the contact parameters and operating conditions. In order to obtain a robust design, it is thus necessary not only to optimize the design for a specific set of parameters but also to assess the performance of the design regarding sensitivities with respect to changes in the parameters. An optimization method for the design of friction interfaces for bladed disks subject to uncertainties has been developed. The nonlinear forced vibrations are computed by efficiently solving the equation of motion using the Multi-Harmonic Balance Method. Coulomb friction and unilateral normal contact constraints are enforced employing an analytical formulation of the Dynamic Lagrangian method. Resonance response levels and frequencies are directly computed with respect to design parameters. Analytically derived sensitivities are then used to obtain the probability for that a certain response level is not exceeded. The method is applied to a tuned blisk in order to obtain the optimum normal preload in the nonlinear shroud coupling subject to a given uncertainty in the level of excitation, for example.
Metallurgical Investigation of LM2500 High Pressure Turbine (HPT) Blade Failures
Authors: Driscoll Matthew , McFetridge Eric , Neff Robert , Descar Peter
Published: December 2013

The General Electric LM2500 gas turbine is utilized as the propulsion engine aboard the Navy’s newest surface combatants including the FFG 7, CG 47 and DDG 51 Class ships. The US Navy owns and operates 450 LM2500 engines. Several instances of high pressure turbine blade failures have required engines to be removed from service and returned to the depot. This paper assesses the reasons for these removals including a shipboard service life assessment of each failure and root cause investigation. Detailed metallurgical findings from two of the Navy’s HPT blade failures are presented and proposed operational risk mitigation strategies are offered for LM2500 engine users.
Effect of Adjacent Blade Motion on the Aerodynamics of a Linear Cascade Blade
Authors: Naresh Babu K. , Kushari A. , Venkatesan C.
Published: December 2013

Due to the trend of increasing power and reducing weight, the fan and compressor blades of turbo machinery might be more sensitive to flutter, which must strictly be avoided in the design process. In order to increase our understanding of the flutter phenomena for fan and compressor cascades, aero-elastic investigations are essential. In the present work experiments were performed in the specifically designed Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics forces and moments acting on a blade in a linear cascade of blades when the instrumented blade is stationary and the two adjacent blades on both sides of the instrumented blade are executing torsion-mode oscillations about their mid-chord. A 5-component strain gage balance was used to measure the unsteady aerodynamic forces on the model blade. The forces were measured for six inter-blade phase angles (i.e., the phase angle between the moving blade motions at a given frequency where the central blade is stationary) at low subsonic conditions, different reduced frequencies and different stagger. The time-variant forces were analyzed and variation of lift and drag coefficients for different inter-blade phase angles and reduced frequencies were plotted. The experimental results indicate that the inter-blade phase angle had a major effect on the variation of the unsteady forces and that reduced frequency had a somewhat less significant effect. Also in order to investigate the influence of the reduced frequency and inter-blade phase angles on the global stability of the cascade and its local contributions, experiments were performed for different reduced frequencies and phase angles. At the higher inter-blade phase angles (180°) the blade remains aerodynamically stable at 0° stagger, but the stability reduces at higher stagger angles. The blade is usually unstable when the interblade phase angle is 0°. At different flow conditions, some of the inter-blade phase angles appear to be aerodynamically unstable.
Scaling 3-36kW Microturbines
Authors: Head Adam Joseph , Visser W. P. J.
Published: December 2013

Microturbine performance and losses are strongly dependent on scale, especially at very small sizes. As a consequence, prediction of these scale effects is important within the framework of conceptual design and sizing studies where the power output is varied in order to optimize the application in which the microturbine is integrated. The scale effects can be addressed for the individual gas path and mechanical components which include turbomachinery, ducting, bearings, recuperators, combustors etc. Absolute prediction of efficiencies at the initial design stage, or at any other stage, is difficult, and the designer usually relies upon empirical loss models and correlations. Using both empirical and physical analysis, these relations can be extended to include size as a variable providing a means to predict changes of losses relative to a known reference case. This paper describes the results from an analysis of size-related loss mechanisms in small turbomachinery derived from turbochargers. A microturbine cycle performance analysis is presented in order to illuminate how these effects influence efficiency at varying design power levels. In addition, geometric size and weight relations are derived for prediction of physical dimensions as a function of design power. A case study is presented scaling microturbine concepts in the range of 10–36kW for an electric vehicle range extender application.
Fuelling an EGR Equipped Micro Gas Turbine With Bio-Fuels
Authors: Cameretti Maria Cristina , Tuccillo Raffaele , Piazzesi Renzo
Published: December 2013

The authors discuss in this paper some aspects related to the employment of liquid and gaseous bio-fuels in a micro-gas turbine. Besides the purpose of checking the effectiveness of supplying the micro-turbine with fuels from renewable sources, the attention is focused on the need of controlling the pollutant emission. To this aim, several solutions are experienced by means of CFD numerical simulations. For the liquid fuel supply, a new shape and location of the main fuel injector is combined with a modified position of the pilot injector. In the case of the biogas fuelling, an external EGR option is considered as activated. Both methods aim at the reduction of the thermal and prompt NO formation by approaching the flameless combustion concept.
Non-Linear Time and Frequency Domain Methods for Multi-Row Aeromechanical Analysis
Authors: Rahmati M. T. , He L. , Wang D. X. , Li Y. S. , Wells R. G. , Krishnababu S. K.
Published: December 2013

An unsteady Navier-Stokes solution system for aeromechanical analysis of multiple blade row configurations is presented. A distinctive feature of the solver is that unified numerical methods and boundary condition treatments are consistently used for both a nonlinear time-domain solution mode and a frequency-domain one. This not only enables a wider range of physical aeromechanical problems to be tackled, but also provides a consistent basis for validating different computational models, identifying and understanding their relative merits and adequate working ranges. An emphasis of the present work is on a highly efficient frequency-domain method for multi-row aeromechanic analysis. With a new interface treatment, propagations and reflections of pressure waves between adjacent blade rows are modeled within a domain consisting of only a single passage in each blade row. The computational model and methods are firstly described. Then, extensive validations of the frequency-domain method against both experimental data and the nonlinear time-domain solutions are described. Finally the computational analysis and demonstration of the intra-row reflection effects on the rotor aerodynamic damping are presented.
Performance Study and Instability Analysis of Steam Turbine Control Valve
Authors: Engeda Abraham
Published: December 2013

Industrial steam turbines represent one of the largest fractions of prime movers. Regardless of the steam-turbine application being considered, speed and/or load control will be required. Speed control is the primary control loop for all turbine applications, industrial as well as utility. The inlet of industrial steam turbine is usually controlled by a single valve, or a series of valves (multi-valve assembly) working in concert. As a turbine governing valve, the venturi valve, has been widely used in steam turbines to regulate inlet flow in the last 40 years. But as turbine output power become larger, a number of valve failure incidences started to be reported and improving the valve designs became a high priority. But despite numerous investigations to eliminate valve failure, the attempts were not fully successful due to the complicated nature of the fluid-structure interaction mechanisms, and the basic mechanism causing valve vibration and failure is still far from being fully understood. Steam control valves are required to operate under wide ranges of valve openings and pressure ratios.

As a continuation of previous valve designs, a newly designed valve with two different seat configurations has been investigated experimentally and studied. This paper reports the results of one of the newly designed valves with a short seat configuration. This paper presents detailed experimental investigations to clarify the mechanisms of valve instability caused by unsteady flows around the valve. A result of the asymmetric unstable flow, noise and vibration characteristics of the valve together with an overall performance assessment of the valve is presented.
Operation and Simulation of Hybrid Wind and Gas Turbine Power System Employing Wind Power Forecasting
Authors: Xia Junrong , Zhao Pan , Dai Yiping
Published: December 2013

Due to the intermittence and fluctuation of wind resource, the integration of large wind farms in a power grid introduces an additional stochastic component to power system scheduling. This always brings challenges to maintain the stability of power system. Integrating gas turbine units with wind farms can compensate their output fluctuation. In this paper, a methodology for the operation scheduling of a hybrid power system that consists of a large wind farm and gas turbine units is presented. A statistical model based on numerical weather prediction is used to forecast power output of the wind farm for the next 24 hours at quarter-hour intervals. Forecasts of wind power are used for optimizing the operation scheduling. In order to study the dynamic performance of the proposed hybrid power system, dynamic modeling of this hybrid power system is addressed. Wind farm and gas turbine units are integrated through an AC bus, and then connected to a power grid. An aggregated model of the wind farm and detailed models of gas turbine units are developed, and are implemented using MATLAB/Simulink. Simulation studies are carried out to evaluate the system performance using real weather data. The simulation results show that the proposed hybrid power system can compensate fluctuating wind power effectively and make wind power more reliable.
MS5002C and D “Power Crystal™ Kit” Heavy Duty Gas Turbine Development and Operating Experience
Authors: Del Turco Paolo , D’Ercole Michele , Fouad Ahmed Ossama , Carta Riccardo , Russo Alessandro , Lombardi Gaetano , Calicchio Vincenzo , Gori Stefano
Published: December 2013

Given the constant increase in world energy demand, gas turbine operators are continuously looking for turbo-machinery improvements, both in terms of increased power and extended maintenance intervals, limiting, as much as possible, the downtime for upgrading.

In 2006, GE Oil & Gas engineers launched the Power Crystal™ development program to enhance the output power or extend the maintenance interval of the MS5002C and D heavy duty gas turbines.

This effort resulted in an upgrade kit potentially to be installed during a standard major inspection, which include a single crystal material 1st stage high pressure turbine blade and additional improvements, such as new coatings for combustor hardware and improved cooling of the 1st stage high pressure turbine nozzle and 1st stage high pressure turbine wheel.

The upgrade kit was validated through an extensive test campaign, which included test-rig component tests in advance of the First Engine to Test (FETT).

All critical-to-quality parameters of the gas turbine were investigated, such as turbine gas path component temperatures and stresses, performance and operability.

This paper describes the background for the upgrade, discusses the new kit features, how the test program was built and conducted, and reports the experience accumulated on the gas turbine during the initial field operation.
Performance Study of an Air-Oil Pump and Separator Solution
Authors: Steimes Johan , Gruselle François , Hendrick Patrick
Published: December 2013

Many applications need to extract a certain phase from a multiphase flow like in oil extraction, flow in nuclear power plants, aircraft lubrication systems, etc. The Aero-Thermo-Mechanics (ATM) Department of Universiteé Libre de Bruxelles (ULB) is developing an original system to extract the gas from a liquid-gas flow together with increasing the pressure of the liquid phase. This system will help to reduce the complexity and the oil consumption of aeroengine lubrication systems.

This paper will summarise the results of a first air/oil prototype. It will also present the guidelines learned from this prototype and used to design a second version of the integrated pump and separator. A newly developed oil consumption measurement system will also be presented. Based on previous results, on litterature review and on an in-house theoretical model, the paper will explain theoretically how the separation efficiency is affected by the particle distribution at the inlet of the prototype, and by the key parameters identified in different studies. Finally the conclusions will present the lessons learned through the design and tests of these two prototypes and the future work will be presented.
Component Testing and Prototype Commissioning of MAN’s New Gas Turbine in the 6 MW-Class
Authors: Wiedermann Alexander , Orth Ulrich , Aschenbruck Emil , Reiss Frank , Krüger Dietmar , Wiers Sven-Hendrik
Published: December 2013

MAN Diesel & Turbo has developed a new gas turbine in the 6 MW-class for both mechanical drive and power generation applications. The lay-out of the Gas Turbine has been driven by opportunities in current and future markets and the positioning of the competition, and this has determined the characteristics and technical parameters which have been optimized in the 6 MW design.

The design makes use of extremely high precision engineering so that the assembly of sub components to modules is a smooth flowing process and can guarantee both the high standards in quality and performance which MAN Diesel & Turbo is aiming for. Individual components have been tested and thoroughly validated. These tests include in particular the compressor of the gas turbine and the combustion chamber.

The commissioning of the gas turbine prototype engine had been prepared with a numerous number of measuring probes and carried out at the Oberhausen plant gas turbine test field. Results of component and the gas turbine prototype tests will be presented and discussed.
Design Methodology of Supercritical CO2 Brayton Cycle Turbomachineries
Authors: Lee Jekyoung , Lee Jeong Ik , Ahn Yoonhan , Yoon Hojoon
Published: December 2013

The supercritical CO2(S-CO2) Brayton Cycle is gaining attention due to its high thermal efficiency at relatively low turbine inlet temperature and compactness of turbomachineries. For designing turbomachineries of the S-CO2 Cycle, however, most of existing codes based on ideal gas assumption are not proven yet to be accurate near the supercritical condition. Furthermore, many of existing design computer programs usually focuses on a specific type of turbomachinery, e.g. axial or radial, which makes hard to compare performance of both types at the same design condition. Since both axial and radial types of turbomachineries were pointed out as an equally possible candidate for the S-CO2 Brayton cycle, in order to compare and determine the best effective type of turbomachinery requires considering both types under the same design conditions. Taking into consideration of these facts, some modifications to the conventional design methodology of gas cycle turbomachinery are necessary to design a turbomachinery for the S-CO2 cycle. Especially, a modified design method should consider non-linear property variation of CO2 near the critical point to obtain an accurate result. Thus, the modified design method for the S-CO2 Brayton cycle turbomachineries is suggested in this paper and the method was implemented in the in-house code. In addition, some preliminary results will be discussed with the plan for validation and verification of the code.
Dynamic Response Analysis of Rotor System With Uncertain Parameters via Interval Analysis Method
Authors: Hong Jie , Wang Jun , Chen Meng , Ma Yanhong
Published: December 2013

The support stiffness and connecting structure stiffness change with different assembly conditions and operating conditions. The phase and amount of rotor unbalance in different operating cycle changes due to wear of blade tip and connecting structures in different working cycles. These parameters which have significant effect on rotordynamics are “uncertain but bounded”, in another word, the distributions of the parameters are unknown, but the intervals of uncertain parameters are always got easier.

An interval analysis method, which solves the dynamic response with these uncertain parameters, has presented. Based on interval mathematics and modal superposition method, interval analysis method simplifies the uncertain parameters to interval vectors so that it can get the intervals within which the dynamic response varies when less information of structure is known. The interval analysis method is efficient under the condition that probability approach cannot work because of small samples and sparse statistics characteristics. The formulation of rotor dynamic response using interval modal superposition analysis method is formulated. A numerical example of comparison between interval analysis method and Monte Carlo method is given, and the results illustrate the interval analysis method.
Development of Advanced USC Technologies for 700°C Class High Temperature Steam Turbines
Authors: Tanaka Y. , Magoshi R. , Nishimoto S. , Setoyama M. , Yamamoto R. , Hirakawa Y. , Kawasaki K.
Published: December 2013

Global warming due to increased CO2 levels in the atmosphere and resource saving have been the focus of world attention in the past decades. Efforts to improve generating efficiency by increasing the turbine inlet steam temperature and pressure in large capacity fossil-fuel and combined-cycle power plants are being made together with efforts to improve the internal efficiency. Most of MHI’s modern steam turbines, including the combined cycle plants, have a 600°C class USC inlet steam conditions. 700°C class Advanced USC (A-USC) technology is one of the remarkable technologies being developed to reduce CO2 emissions, and one, which was chosen by Japan’s ‘Cool Earth - Innovative Energy Technology Program’, which was launched in 2008 to contribute to substantial reductions in CO2 emissions. Major Japanese manufacturers of boilers and turbines joined forces with research institutes to bring the project to reality. This paper illustrates the features and benefits of A-USC technologies for MHI’s 700°C class high temperature steam turbines, including cycle design, conceptual design (structure and alloy), and the development of candidate materials.
A Study of Nonlinear Vibrations in a Frictionally-Damped Turbine Bladed Disc With Comprehensive Modelling of Aerodynamic Effects
Authors: Petrov E. P. , Zachariadis Z.-I. , Beretta A. , Elliott R.
Published: December 2013

A new effective method for comprehensive modelling of gas flow effects on vibration of nonlinear vibration of bladed discs has been developed for a case when effect of the gas flow on the mode shapes is significant.

The method separates completely the structural dynamics calculations from the significantly more computationally expensive computational fluid dynamics (CFD) calculations while provides the high accuracy of modelling for aerodynamic effects.

A comprehensive analysis of the forced response using the new method has been performed for a realistic turbine bladed disc with root-disc joints, tip and underplatform dampers. The full chain of aerodynamic and structural calculations are performed: (i) determination of boundary conditions for CFD; (ii) CFD analysis; (iii) calculation of the aerodynamic characteristics required by the new method; (iv) nonlinear forced response analysis using the MAIM. The efficiency of the friction damping devices has been studied and compared for several resonance frequencies and engine orders. Advantages of the method for aerodynamic effect modelling have been demonstrated.
Improving High-Dimensional Physics Models Through Bayesian Calibration With Uncertain Data
Authors: Kumar Natarajan Chennimalai , Subramaniyan Arun K. , Wang Liping
Published: December 2013

We address the problem of calibrating model parameters in computational models to match uncertain and limited experimental data using a Bayesian framework. We employ a modified version of the Bayesian calibration framework proposed by Kennedy and O’Hagan [15], to perform calibration of large dimensional industrial problems. Results for two nonlinear industrial problems with 15 and 100 calibration parameters are presented. The unique advantages of the Bayesian framework are presented along with a discussion on the challenges in calibrating large number of parameters with uncertain and limited data.
Development of a Robust Structural Health Monitoring System for Wind Turbine Foundations
Authors: Currie Magnus , Saafi Mohamed , Quail Francis
Published: December 2013

The construction of onshore wind turbines has rapidly been increasing as the UK attempts to meet its renewable energy targets. As the UK’s future energy depends more on wind farms, safety and security are critical to the success of this renewable energy source. Structural integrity is a critical element of this security of supply. With the stochastic nature of the load regime a bespoke low cost structural health monitoring system is required to monitor integrity. This paper presents an assessment of ‘embedded can’ style foundation failure modes in large onshore wind turbines and proposes a novel condition based monitoring solution to aid in early warning of failure.
The Effect of Compressive Damage on Tensile Loading Failure of Titanium 6Al-4V
Authors: Scott-Emuakpor Onome , George Tommy , Wertz John , Holycross Casey
Published: December 2013

In order to explore the belief that total strain energy accumulation during monotonic tensile fracture is a universal damage parameter, the effect of compressive preloads on specimens failed via tensile loading is analyzed. The motivation behind this analysis is due to the theory of an energy-based life prediction model, which states that the total strain energy required for monotonic tensile fracture is defined as the physical damage quantity for the fatigue lifing model. Two things are observed in order to determine the effects of a compressive preload on tensile monotonic fracture. First, the compressive work is viewed as accumulated damage, thus adding to the total work necessary for failure. Second, tensile works of fractured specimens with and without stored compressive energy are compared to see if the damage parameter is affected. The analysis is conducted through experimental data acquisition from round stock Titanium 6Al-4V dogbone specimens. The results from this study show that compressive damage has a negligible effect on monotonic tensile work to fracture, and combined half-cycle tension and compression preloads have an unnoticeable effect on the tensile work of the final pull to fracture. These results contradict the theory and research validations of the energy-based predictions; however, they provide a platform for future efforts to understand the strain energy correlation between monotonic, low cycle and high cycle failures.
Experimental Testing of a Magnetically Levitated Rotor With a Neural Network Controller
Authors: Veloz Alejandro , Romero Quintini Juan C. , Parada Mónica , Diaz Sergio E.
Published: December 2013

Magnetic bearings represent a solution for high rotating speeds and sterile environments where lubrication fluids could contaminate. They can also be used in systems where maintenance is difficult or inaccessible, because they don’t require auxiliary lubrication systems and don’t suffer mechanic wear as they work with no contact between rotor and bearing stator. An important part of magnetic bearings is the controller; which is needed to stabilize the system. This controller is generally a PID in which tuning and/or filters design can be complicated for not well known systems. This work presents results of the development of a neural network controller, which is potentially easier to implement, to control the position of a magnetically suspended rotor.

The proposed controller is based in the identification of the system inverse model. This is achieved first by implementing a simple PID capable of levitating the rotor, and then some excitations are applied to the rotor in order to acquire data of the position of the rotor and current in the actuators. Current and position data is used to train the artificial neural network for the controller.

The controller was implemented in a numerical model and also in an experimental system with a rotor of 1.06kg and 300mm in length. The implementation of SISO, MISO and MIMO neural controllers (both with offline and online training) and a conventional PID with neural network compensation are compared.

Structures and architectures of networks are shown. Vibration responses to: a constant force; a controlled impact and a constant acceleration ramp between 0 and 12500rpm are compared. Results in both, numeric model and experimental system, show that neural network controllers are capable of hovering the rotor and control vibrations. Peak-Peak amplitudes vs. rpm plots are similar to a conventional PID. In most cases, the neural network controllers show amplitudes slightly lowers on low frequencies and slightly higher on higher frequencies, except the conventional PID with neural network compensation case, were the system responses as with higher damping. Finally, a discussion is made about future steps in research to improve implementation of a neural controller that is potentially simpler and faster in terms of tuning and with a comparable performance to a conventional magnetic bearing PID controller.
Fatigue Life Estimation Method Considering Inelastic Behavior of Ni-Based Directionally Solidified Superalloy With Multiple Holes
Authors: Yokoyama Takashi , Sekihara Masaru
Published: December 2013

Low cycle fatigue tests at high temperature were conducted on test specimens with small holes made of a Ni-based directionally solidified superalloy, which are intended as the cooling structures formed in the components in the fossil fuel power plant. The tests included those cases with and without a strain holding process, i.e., fatigue creep interaction (FCI) tests and low cycle fatigue (LCF) tests, respectively. The number of LCF crack initiation cycles of the one- and seven-hole specimens decreased compared to that of the smooth one. The number of FCI crack initiation cycles of a compressive hold case for the seven-hole specimen decreased compared to that of the LCF test, while that of a tensile hold case decreased further. The test results were evaluated based on the inelastic behavior around the center hole of the specimens, where the most serious inelastic strain occurred, using finite element analysis that takes into account the inelastic anisotropy of material properties. The number of crack initiation cycles of the LCF and the compressive FCI tests correlated with the maximum tensile stress around the hole, while that of all the tests correlated with the frequency-modified strain energy. We propose a method for evaluating cyclic inelastic behavior around a hole using cyclic Neuber’s rule for anisotropic materials to simply evaluate the failure life of actual components.
Modelling of Flange Joints for the Nonlinear Dynamic Analysis of Gas Turbine Engine Casings
Authors: Schwingshackl C. W. , Petrov E. P.
Published: December 2013

The finite element analysis of individual components of aircraft engine casings provides high accuracy and a good agreement with the measured response data. However, when these components are assembled, the accuracy of such predictions can significantly deteriorate since models describing stiffness and friction properties of joints are linearised.

A full nonlinear analysis of the casing flanges is required to fully include the influence of the bolted joints, model the flexibility in the contact interface, and consider the nonlinear behaviour of the contact due to partial slip and separation. In this paper different nonlinear models of casings are investigated with an available nonlinear analysis tool; A parametric study of the contact interface meshes is conducted to identify a satisfying analysis approach. The dynamic flange behaviour is analysed in detail, including effects of the bolt and normal load distribution. A comparison of the introduced nonlinear modelling with more traditional rigid or linear-elastic flange joint models is carried out to evaluate the effect of the nonlinear approach.

The study demonstrates the nonlinear nature of a casing flange joint and highlights the need to include them in the analysis. The detailed modelling of the contact interaction of joints, gives an insight in the nonlinear contact behaviour of flanges of aircraft engine casings, and the predictive capabilities for the nonlinear analysis of gas turbine engines.
A System Identification Method for Excitation-Frequency Dependent Rotordynamic Coefficients
Authors: Dimond Timothy W. , Younan Amir A. , Allaire Paul
Published: December 2013

Experimental identification of rotordynamic systems presents unique challenges. Gyroscopics, generally damped systems, and non-self-adjoint systems due to fluid structure interaction forces mean that symmetry cannot be used to reduce the number of parameters to be identified. Rotordynamic system experimental measurements are often noisy, which complicates comparisons with theory. When linearized, the resulting dynamic coefficients are also often a function of excitation frequency, as distinct from operating speed.

In this paper, a frequency domain system identification technique is presented that addresses these issues for rigid-rotor test rigs. The method employs power spectral density functions and forward and backward whirl orbits to obtain the excitation frequency dependent effective stiffness and damping. The method is highly suited for use with experiments that employ active magnetic exciters that can perturb the rotor in the forward and backward whirl directions. Simulation examples are provided for excitation-frequency reduced tilting pad bearing dynamic coefficients. In the simulations, 20 and 50 percent Gaussian output noise was considered. Based on ensemble averages of the coefficient estimates, the 95 percent confidence intervals due to noise effects were within 1.2% of the identified value.

The method is suitable for identification of linear dynamic coefficients for rotordynamic system components referenced to shaft motion. The method can be used to reduce the effect of noise on measurement uncertainty. The statistical framework can also be used to make decisions about experimental run times and acceptable levels of measurement uncertainty. The data obtained from such an experimental design can be used to verify component models and give rotordynamicists greater confidence in the design of turbomachinery.
A Tribological Study of Partial-Arc Bearings With Egg-Shaped Surface Texture for Microturbine Applications
Authors: Bompos D. A. , Nikolakopoulos P. G. , Papadopoulos C. I. , Kaiktsis L.
Published: December 2013

Recent research has demonstrated that proper use of texture geometries can improve the performance of journal and thrust bearings. In particular, for journal bearings, elliptical and egg-shaped texture patterns appear as promising candidates for improving bearing performance, in terms of load carrying capacity and friction coefficient. The expected advantages should also hold for partial-arc bearings, which, for small scale – high speed applications, are characterized by significant advantages, in comparison to full bearings. In the present paper, a tribological study of partial-arc journal bearings with periodic egg-shaped texture applied on the stator surface is presented. Computational Fluid Dynamics (CFD) simulations are performed and processed to yield the bearing performance indices. Here, the bearing geometry and the texture characteristics are defined parametrically; a wide range of bearing designs is thus accounted for. Flow simulations are based on the numerical solution of the Navier-Stokes equations for incompressible isothermal flow. The effects of dimple shape, bearing eccentricity, bearing arc angle, and slenderness ratio on the bearing performance are investigated. The present results demonstrate that a substantial improvement of journal bearing performance, especially in terms of the friction coefficient, in comparison to that of smooth bearings, is feasible.
Numerical Simulation of Unsteady Flow Around Oscillating Blade
Authors: Zagitov R. A. , Shuvaev N. V. , Dushko A. N. , Shmotin Yu. N.
Published: December 2013

The paper is pointed to the problem of numerical simulation of unsteady flow around an oscillating blade in jet engine compressor. Single compressor rotor blade row is considered. It is assumed that mode shape and frequency of blade oscillation is not influenced by airflow. The system of governing equations is transformed to a moving coordinate system to describe blade oscillations. Multi-block structured “H-O” grid is used for spatial discretization. Inner boundary of “O”-grid (representing blade airfoil surface) is moved to describe blade airfoil oscillation. To minimize discretization error, special morphing procedure was developed for “O”-grid to accommodate blade airfoil surface motion. Other grid blocks remain steady. Nonlinear harmonic method is applied to integrate Euler equations on time variable. For spatial derivation Dispersion-Relation-Preserving methodology is applied. To maintain solution accuracy nonreflecting boundary conditions are implemented on artificial boundaries (inlet and outlet). Resulting system of nonlinear algebraic equations is resolved numerically. As an alternative, time-marching method is realized in ANSYS CFX by means of user routines. Numerical and experimental cascade results are compared.
Analytical Prediction of Fatigue Crack Growth Behavior Under Biaxial Loadings
Authors: Kannusamy Ragupathy , Ramesh K.
Published: December 2013

Aircraft and pressure vessel components experience stresses that are negative biaxial or multiaxial in nature. Biaxiality is defined as the ratio of stress applied parallel and normal to the crack front. In recent years many experimental studies have been conducted on fatigue crack growth under various biaxial loading conditions. Biaxial loadings affect crack front stresses and strains, fatigue crack growth rate and direction, and crack tip plastic zone size and shape. Many of these studies have focused on positive biaxial loading cases. No conclusive study has been reported out yet that accurately quantifies the influence of negative biaxiality on fatigue crack growth behavior. Lacking validation, implementation on real life problems remains questionable. To ensure safe and optimum designs, it is necessary to better understand and quantify the effect of negative biaxial loading on fatigue crack behavior.

In this paper, attempts were made to quantify the effect of biaxial load cases ranging from B = −0.5 to 1.0 on fatigue crack growth behavior. Also an attempt has been made to establish a simplified approach to incorporate the effect of biaxiality into da/dN curves generated from uniaxial loading using an analytical approach without conducting expensive biaxial crack growth testing. Sensitivity studies were performed with existing test data available for AA2014-T6 aluminum alloy. Detailed elastic–plastic finite element analyses were performed with different stress ranges and stress ratios with various crack sizes and shapes on notched and un-notched geometries. Constant amplitude loads were applied for the current work and comparison studies were made between uniaxial and different biaxial loading cases. It was observed from the study that negative biaxiality has a very pronounced effect on the crack growth rate and direction for AA2014-T6 if the externally applied load exceeds 20% of the yield strength as compared with 40% of externally applied load for alloy of steel quoted in the literature.
Effects of Manufacturing Noise on Microturbine Centrifugal Impeller Performance
Authors: Javed A. , Pecnik R. , Olivero M. , van Buijtenen J. P.
Published: December 2013

This paper presents a study on a small centrifugal impeller for microturbine application from a manufacturing perspective. The aim is to analyze the impact of geometric deviations on part performance using adequate performance modeling tools and statistical methods. A one-dimensional (1D) performance analysis tool has been developed in-house derived from the meanline and two-zone modeling methods. The 1D model has proved to be a simple and computationally inexpensive tool for having a quick performance analysis of the impeller using basic geometric information extracted from part drawings. For the sensitivity analysis, a total of eight input geometric parameters including radii, tip-clearance and blade angles have been varied individually within specific limits in the 1D tool for classifying their influence on the output performance. Since the 1D model is a simplified version of a much complex three-dimensional (3D) model, a commercial computational fluid dynamics (CFD) tool has been used to provide a comparison with the 1D model and scrutinize the effects of such deviations on the fluid behavior inside the impeller passage at a detailed level. For uncertainty quantification, Monte Carlo simulation has been performed using the 1D model to assess the variability of overall impeller output performance to simultaneous random deviations in the input geometric parameters. The study is useful to evaluate the possibility of designing gas turbine parts for manufacturability and superior production cost-effectiveness.
Computational Engineering Design for Micro-Scale Combustors
Authors: Saddawi Salwan David , Kipouros Timoleon , Savill Mark
Published: December 2013

At present, optimisation is an enabling technology in innovation. Multi-objective and multi-disciplinary design tools are essential in the engineering design process, and have been applied successfully in aerospace and turbomachinery applications extensively. These approaches give insight into the design space and identify the trade-offs between the competing performance measures satisfying a number of constraints at the same time. It is anticipated here that the same benefits can be obtained for the design of micro-scale combustors. In this paper, a multi-disciplinary automated design optimisation system was developed for this purpose, which comprises a commercial computational fluid dynamics package and a multi-objective variant of the Tabu Search optimisation algorithm. The main objectives that are considered in this study are to optimise the main micro-scale combustor design characteristics and to satisfy manufacturability considerations from the very beginning of the whole design operation. Hydrogen-air combustion as well as 14 geometrical and 2 operational parameters are used to describe and model the design problem. Two illustrative test cases will be presented, in which the most important device operational requirements are optimised, and the efficiency of the developed optimisation system is demonstrated. The identification, assessment and suitability of the optimum design configurations are discussed in detail.
Modal Tests and Analysis of a Radial Impeller at Rest: Influence of Surrounding Air on Damping
Authors: Gibert C. , Blanc L. , Almeida P. , Leblanc X. , Ousty J.-P. , Thouverez F. , Laîné J.-P.
Published: December 2013

HCF risk assessment for turbomachinery blades requires the prediction of vibratory levels, which in turn requires fine damping quantification. This issue is especially sensitive for structures with low structural damping such as monobloc centrifugal compressor disks (blisks). The material composing blisks and aero-dynamic flow both contribute to damping phenomena. A strategy for non-aerodynamic damping characterization is to perform experiments in vacuum.

This paper focuses on the use of modal tests in vacuum to estimate material damping under non-rotating conditions. Experiments are performed on an isolated impeller manufactured from a single piece in a vacuum chamber at different air pressure levels ranging from 10 mbar to 1 bar. Strong dependency of damping ratios on pressure can be found on the first flexural mode, leading to two types of application.

Firstly, measurements enable assessing the validity of extrapolations of non-aerodynamic damping from measurements sometimes performed under less thorough vacuum conditions. Basic fluid-structure interaction models are used to interpret and quantify the evolution of modal quantities when air is progressively removed. Secondly, vacuum measurements can give frequency response functions (FRFs) with much greater separation between resonance peaks. In this study, the damping ratio found in vacuum condition are 3% of these at ambient pressure corresponding to a magnitude 30dB higher at resonance peaks. This contrasts with in-air measurements on cyclic symmetry structures, like blisks, with high modal density that make the direct interpretation of FRFs and their modal analysis more difficult.
Feasibility Study of an Oil-Free Turbocharger Supported on Gas Foil Bearings via On-Road Tests of a 2-Liter Class Diesel Vehicle
Authors: Sim Kyuho , Kwon Suk Bum , Kim Tae Ho , Lee Yong-Bok
Published: December 2013

This paper presents the feasibility study of an oil-free turbocharger (TC) supported on gas foil bearings (GFBs) via on-road tests of a 2-liter class diesel vehicle. The oil-free TC is constructed using a hollow rotor with a radial turbine at one end and a compressor impeller at the other end, a center housing with journal and thrust GFBs, and turbine and compressor casings. The oil-free TC reuses parts of a commercial variable geometry turbocharger except for the rotor-bearing system. In a test rig driven by a diesel vehicle engine (EG), the rotordynamic performance of the oil-free TC is evaluated up to the rotor speed of 130 krpm, while being measured at the compressor end. The journal GFBs are modified to enhance the rotordynamic performance by inserting three metal shims between the bump-strip layers and bearing housing. The rotordynamic performance is also measured during on-road tests by replacing the original TC of the test diesel vehicle with the constructed oil-free TC. The journal GFBs have a relatively large bearing clearance and no metal shims to generate sub-synchronous motions at low TC and EG speeds. During normal vehicle driving, the TC rotor motions show steady rotordynamic operations. The oil-free TC rotates at 25 krpm ∼50 krpm while the vehicle runs at 20 km/h ∼30 km/h on the roads. Sub-synchronous rotor motions initiate with a frequency of ∼100 Hz at the TC speed of ∼37 krpm. The TC rotor motion also shows multiple EG-induced harmonics, as expected. Upon external shocks given by passing the vehicle on road-bumps, the sub-synchronous motions are excited only when the rotor rotates above the initiation speed of sub-synchronous motion. The excitation is non-destructive because the vehicle suspension absorbs most of the external shock. Incidentally, the external shocks appear to have no influence on the synchronous motion and engine-induced harmonics of the TC rotor.