bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Rotor Tip Clearance on Tip Clearance Flow Potentially Leading to NSV in an Axial Compressor
Authors: Im Hong-Sik , Zha Ge-Cheng
Published: December 2013

This paper investigates non-synchronous vibration (NSV) mechanism of a high-speed axial compressor with three different rotor tip clearances. Numerical simulations for 1/7th annulus periodic sector are performed using an unsteady Reynolds-averaged Navier-Stokes(URANS) solver with a fully conservative sliding boundary condition to capture wake unsteadiness between the rotor and stator blades. The simulated NSV shows that the frequency and amplitude are strongly influenced by the tip clearance size and shape. The predicted NSV frequency is in good agreement with the experiment. The maximum amplitude of the NSV occurs at about 78% span of the rotor suction leading edge regardless of tip clearance due to a strong interaction of incoming flow, tip leakage flow and tip vortex. The instability of tornado like tip vortex oscillating in streamwise direction appears to be the main cause of the NSV observed in this study.
Development US Navy Gas Turbine Vibration Analysis Expertise: 501-K Vibration and Remote Monitoring of Gas Turbine Vibration
Authors: Thompson Bruce D. , Grobler Jurie
Published: December 2013

Until the advent of the 501-K34 engine the 501 did not have a history of high vibration levels. When the 501-K17 did exhibit high vibration levels, predictably, there was an identifiable cause. A few years after the introduction of the 501-K34, high levels of engine start vibration were frequently observed. Normally this would occur during engine “cold” start. When the 501-K34 was started “warm” or “hot” much lower engine start vibration levels were observed. This paper discusses 501-K vibration in general and the US Navy investigation into the mechanical causes for the high “cold start” 501-K34 vibration, as well as data analysis and problem mitigation. Because of the number of 501-K34s that have exhibited this problem and still appeared to be operating adequately, in other respects, the USN, over the last 7 years, to ensure the continued reliability of the 501-K34 engine has been monitoring remotely vibration and other important engine parameters. This was done through Integrated Performance Analysis Reports (IPAR), the Maintenance Engineering Library Server (MELS) and by accessing engine parameter data from the Full Authority Digital Controller (FADC). Using remote monitoring and understanding the vibrations mechanical aspects, it was realized that the 501-K34 could operate for a considerable period with high “cold start” vibration levels before the accumulated effect of this distress resulted in engine removal and subsequent repair.
Analysis of an Oscillating Airfoil in a Power-Extraction Regime Based on the Compressible Navier-Stokes Equations With Low-Speed Preconditioning
Authors: Campobasso M. Sergio , Drofelnik Jernej
Published: December 2013

A wing that is simultaneously heaving and pitching may extract energy from an oncoming air flow. The relationship between the aerodynamics and the theoretical performance of this device is here investigated by means of time-dependent laminar flow simulations performed with a research compressible Navier-Stokes solver. The presented analyses confirm the findings of other studies that the efficiency of the power extraction of this device can reach 34%, due to the favourable effects of a strong dynamic stall. In view of aeroacoustic applications, the developed flow solver uses the compressible Navier-Stokes equations with carefully optimized low-speed preconditioning. To demonstrate the modeling capabilities and the high computational performance of this approach, the unsteady aerodynamics of the energy-extracting device is simulated by using a computationally challenging freestream Mach number of 0.001. A fundamental element of novelty of this study is a thorough assessment of the proposed approach partly based on the challenging and realistic problem associated with the oscillating wing device.
Effects of Environments and Shot Peening on Creep and Creep-Fatigue Behaviors of Ni-Fe-Base Superalloy Inconel®Alloy 706
Authors: Yoshioka Yomei , Saito Daizo , Sumiya Rie , Ishibashi Kazutoshi , Ito Shoko , Kobayashi Daisuke , Itou Akihiro , Miyabe Masamichi , Kagiya Yukio
Published: December 2013

Fleet leader machines with non-shot-peened discs made of Inconel® alloy 706 were experienced to have cracks in the first stage gas turbine wheels. These were inter-granular cracking and observed to be highly stressed locations with less potential for oxidation, which is thought to be quasi-brittle inter-granular cracking due to stress induced atmospheric oxygen penetration, so called, hold-time cracking. To recognize this phenomenon, creep and creep-fatigue tests with smooth and notched specimens were conducted at 600 and 650°C in air and vacuum and confirmed the environmental effects on those lives and fracture modes.

The effectiveness of shot peening which was used as one of the countermeasures for this phenomenon was verified by using the creep-fatigue tests. The durability was also evaluated by thermal and stress aging tests at 450 and 500°C up to around 104 hours. Little relaxations were observed during the thermal agings after the initial rapid relaxation of the surface residual stress, but the effects of the loading stresses were observed above the yielding stress at each temperature.
CFD Predictions of Efficiency for Non-Equilibrium Steam 2D Cascades
Authors: Moraga Francisco J. , Vysohlid Martin , Gerber Andrew G. , Smelova Natalia , Atheya Sriram , Kanakala Vasudevarao
Published: December 2013

Most non-equilibrium wet steam CFD analyses in the open literature have concentrated on predicting blade pressure loadings, with very few studies emphasizing turbine efficiencies. One of the few exceptions is the work of Gerber et al. [1]. In light of this, in this paper we present CFD predictions of isokinetic efficiency and Markov Loss coefficients and comparisons with measurements for the 2D cascades of White et al. [2] and Bakhtar et al. [3, 4]. Predictions were obtained using an Eulerian-Eulerian multiphase formulation, which is an extension of General Electric’s proprietary CFD turbomachinery code, TACOMA. The formulation is optimized to capture the thermodynamic loss. There is no slip between the droplets and the surrounding vapor. Comparisons with other experimental quantities are also presented as needed to ensure that the non-equilibrium wet steam physics is accurately captured. Although the non-equilibrium models used cannot capture all the loss components present in actual flows, our efficiency predictions are much closer to experimental data than those of equilibrium simulations or the Baumann rule.
Contribution to the Understanding of Cold Pulsating Flow Influence in the Efficiency of Small Radial Turbines for Turbochargers
Authors: Serrano J. R. , Climent H. , Fajardo P. , Reyes-Belmonte M. A. , Vidal Fabrice
Published: December 2013

In the present paper an unsteady approach to determine the performance of a small radial inflow turbine working under cold pulsating flow is presented. It has been concluded that a reasonably good characterization of turbine behavior working with pulsating flow can be obtained using in a quasi-steady way models of the turbine isentropic efficiency and turbocharger mechanical efficiency. Both models have been fitted using data obtained from a steady flow characterization procedure.

Turbocharger measured parameters from the cold pulsating flow campaign have been compared with the ones obtained from one-dimensional gas-dynamics computational modeling. The modeling approach is based on quasi-steady isentropic and mechanical efficiency models. Reasonably good accuracy in compressor and turbine variables prediction has been obtained for most of the operative conditions. Influence of amplitude and frequency of the pulsating flow over the instantaneous and average turbine efficiency has been studied to put some light on the analysis of the involved physical phenomena. The main conclusion is that the biggest effect of unsteady flow on turbine efficiency is through the influence on blade jet to speed ratio. It has been also concluded that for the same average blade to jet speed ratio pulses amplitude does not influence turbine efficiency when it is closed but yes at other VGT positions. The effect of pulses frequency is less evident and only influences VGT performance at the highest VGT openings.
Development and Implementation of Alternative Repair Processes for Reconditioning of W501FD, Row 1 Vanes
Authors: Miglietti Warren , Crotty Kelly , Summerside Ian , Stampfli Matthias , Hoevel Simone
Published: December 2013

The W501FD (SGT6-5000F) engine, an “F” class machine has been in operation for more than a decade now. There are over 200 W501F’s in operation globally. Of importance to operators/users and owners of this gas turbine engine is the ability to recondition the turbine “hot-end section” components, in order to support maintenance requirements. The row 1 vane endures the highest temperature after combustion takes place and experiences severe thermal fatigue cracking. As a consequence, the row 1 vanes when compared to the other three rows of vanes, exhibits the worst degradation and is therefore a focus point of reconditioning for those in the industry. The technical objective is to develop a repair scheme for the row 1 vane, since this component has the highest frequency of replacement, when compared to the other three rows of vanes. Special processes have been developed for these components repairs, including but not limited to:

a) Machining off of the damaged and oxidized leading edge.

b) GTAW and GMAW of new leading edge coupons.

c) Optimizing elevated temperature solution heat treatments.

d) High frequency GTA weld repair of sidewall (platform) and airfoil cracks.

e) Vacuum diffusion braze repair of airfoil and sidewall (platform) craze-cracks.

f) Braze or Weld repair of damaged inward airfoil U-Groove/Channel (depending on severity of distress).

g) Straightening of ID and OD platforms.

h) Closure of air cooling holes via diffusion brazing and re-EDM’ing of a new cooling hole configuration.

i) Application of superior MCrAlY and TBC coating to that of the OEM.

This technical paper describes the all in-house reconditioning process development and implementation of the different stages of the repair schemes that resulted in a rapid turn-time, with high quality and achieved 100% repair yield. In addition this paper highlights the metallurgical and mechanical characteristics of the repaired regions of the component.
Numerical Analysis of Partial Admission Flow in an Industrial Steam Turbine
Authors: Kalkkuhl Tobias J. , Engelmann David , Harbecke Ulrich , Mailach Ronald
Published: December 2013

A partially admitted control stage is a typical feature of an industrial steam turbine. Its purpose is to provide efficient part-load operation and to reduce losses caused by an adverse blade height to tip gap ratio by closing segmental arcs of the inlet annulus. On the other hand partial admission naturally causes circumferential nonuniformity of the flow, because the flow enters the control stage rotor over only a portion of the annulus. This induces not only unsteady blade forces but also additional losses in comparison to a full-admission turbine. So the advantage of partial admission is reduced. In order to analyze partial admission flow effects a 3D CFD model of an industrial steam turbine needs to be developed. It consists of three parts: i) The nozzle groups covering only a portion of the annulus and the rotor of the impulse-type control stage, ii) a cross-over channel directing the flow to a reduced diameter, and iii) the downstream reaction-type turbine stages. The results show considerable flow nonuniformity downstream of the cross-over channel which affects performance of the adjacent full-admission stages. Different operating points of the turbine are investigated. Circumferential periodicity is utilized to minimize computational cost of the simulation. Customary guidelines to CFD-simulation are taken into account and simulation parameters are carefully checked for their influence on the results: turbulence models, meshing parameters and boundary conditions are varied. The influence of gap flow is checked. The results are finally compared to experimental data to check simulation quality.
A Generic Low Pressure Exhaust Diffuser for Steam Turbine Research
Authors: Burton Zoe , Hogg Simon , Ingram Grant
Published: December 2013

Durham University have embarked on a new research initiative in low pressure (LP) steam turbine exhaust hoods. An extensive literature review has highlighted the importance of applying representative conditions at inlet to the exhaust diffuser, specifically accurate total pressure and swirl angle distributions, in numerical simulations to generate flow fields within the hood in line with field data. With commercial sensitivity surrounding industrial designs for exhaust hoods and last stage blades, Durham University have developed a generic, research-level exhaust diffuser geometry and accompanying last stage blade to encourage the expansion of academic research in the field. Preliminary CFD calculations on the LP exhaust has shown the design produces a representative flow structure, capturing the primary sources of loss; the separation along the bearing cone and at the tip of the flow guide.
Reducing Energy Consumption in Active Magnetic Bearings by a Nonlinear Variable Bias Controller
Authors: Ueno Satoshi , Sahinkaya M. Necip
Published: December 2013

This paper presents a nonlinear variable bias controller for an active magnetic bearing (AMB). The nonlinear bearing force is analyzed theoretically and the control current for various bias current settings is derived from the nonlinear bearing equation. Then the power consumption is minimized to obtain the optimum bias current expression analytically. Results show that the optimum bias current can be calculated from the demand bearing force and the instantaneous rotor displacement. Moreover, the influences of magnetic bearing parameter errors are investigated and correction methods are introduced. Results of experimental rotational tests show that the rotor dynamics are not altered under variable bias currents if the proposed correction for parameter errors is implemented. The magnetic center of misalignment is also detected and compensated for. The proposed variable bias current controller provides not only significant energy savings, but also it is simple to implement and applicable to wide range of magnetic bearing systems without deterioration of the bearing dynamics.
Evaluating Materials and Fuels Using an Atmospheric-Pressure Low-Velocity Burner Rig: Factors to Consider to Avoid Unintended Consequences
Authors: Shifler David A. , Aprigliano Louis F. , Groghan Dan
Published: December 2013

The availability of petroleum-derived fuels is declining and the cost of petroleum can fluctuate wildly from $60 to $140 per barrel. These factors are causing a global desire to develop and use alternative fuels. While hydrogen, ethanol, and other non-hydrocarbon fuels are practical alternative fuels for the commercial sector, only liquid hydrocarbons meet the stringent needs of the military in terms of energy content, safety, handling and multi-platform use over the full range of operational conditions. Synthetic fuels will need to meet the current Naval petroleum-based physical, combustion, and chemistry specifications. Therefore, these fuels must be certified to meet Navy requirements and not have an adverse impact on current engine lives or performance.

It has been established that low-velocity, atmospheric-pressure burner rigs, when operated properly, simulate the corrosion and degradation of materials operating in Navy shipboard gas turbines. To evaluate new fuels to determine whether or not they will cause accelerated corrosion in a gas turbine, the corrosion of standard coated superalloys representative of materials in the hot section of gas turbines are exposed to the combustion gaseous products of the new fuels or fuel blends in the burner rig and compared to that of a standard Navy fuel. The control of parameters in all tests is critical if proper evaluation and interpretation is to be achieved. Failure to control the parameters leads to questions that could require more testing or deliver unsupportable, indeterminate conclusions. Two case studies will be presented on how these principles were used to conduct successful burner rig tests and how the learning from those cases were applied to make a decision as to how to conduct an alternate fuels test in a third case.
Simulation of Unsteady 3-D Wet-Steam Flows Through Three-Stage Stator-Rotor Blade Rows With Equilibrium and Nonequilibrium Condensations
Authors: Miyake Satoshi , Sasao Yasuhiro , Yamamoto Satoru , Tabata Soichiro , Miyawaki Toshihiro , Ooyama Hiroharu
Published: December 2013

Unsteady 3-D wet-steam flows through three-stage stator-rotor blade rows in a low-pressure steam turbine model developed by Mitsubishi Heavy Industry (MHI) are numerically investigated. In this study, a new and simple meshing strategy is introduced to improve the prediction of end-wall flows near the shroud and the hub. Dry and wet-steam conditions are taken into account and the calculated results changing the grid system are compared with the experiments. As a practical usage, coarse-grid computations using a PC cluster are also conducted and the results are compared with those using a fine grid and a supercomputer. In addition, a super-cooled condition is assumed and the computation is further conducted. Finally, the effect of homogeneous nucleation and the nonquilibrium condensation on the present flow is evaluated.
Integration of an Automatic Optimizer Functionality Into the Design Process of Industrial Steam Turbines
Authors: Drapkin Dimitri , Kores Franz , Polklas Thomas
Published: December 2013

Industrial steam turbines are mostly tailor made machinery, varying in a wide range of specifications. This feature introduces high requirements on the design process which has to be flexible, efficient and fast at the same time. Given live steam and design parameters as input, the geometry corresponding to the valid design scheme can be calculated together with the required thermodynamic, aerodynamic and mechanical characteristics. By variation of design parameters a design may be achieved which optimizes both, efficiency and cost. The optimization task is formulated mathematically, e.g. crucial optimization parameters, criteria for evaluation of different designs and other required constraints are selected. The structure of the resulting optimization problem is analyzed. Based on this analysis a modular optimization system design is proposed. The choice of Genetic Algorithms and Adaptive Particle Swarm Optimizer as optimization methods is discussed, recommendations for their proper use are given. A bicriterial optimization approach for a simultaneous optimization of efficiency and cost is developed.
Solar Hybrid Combined Cycle Performance Prediction: Influence of GT Model and Spool Arrangement
Authors: Barigozzi G. , Bonetti G. , Franchini G. , Perdichizzi A. , Ravelli S.
Published: December 2013

A modeling procedure was developed to simulate design and off-design operation of Hybrid Solar Gas Turbines in a combined cycle (CC) configuration. The system includes an heliostat field, a receiver and a commercial gas turbine interfaced with a conventional steam Rankine cycle. Solar power input is integrated in the GT combustor by natural gas. Advanced commercial software tools were combined together to get design and off-design performance prediction: TRNSYS® was used to model the solar field and the receiver while the gas turbine and steam cycle simulations were performed by means of Thermoflex®. Three GT models were considered, in the 35–45 MWe range: a single shaft engine (Siemens SGT800) and two two-shaft engines (the heavy-duty GT Siemens SGT750 and the aero derivative GE LM6000 PF). This in order to assess the influence of different GT spool arrangements and control strategies on GT solarization. The simulation method provided an accurate modeling of the daily solar hybrid CC behavior to be compared against the standard CC. The effects of solarization were estimated in terms of electric power and efficiency reduction, fossil fuel saving and solar energy to electricity conversion efficiency.
A Robust Optimization Technique for Calculating Scaling Coefficients in an Energy-Based Fatigue Life Prediction Method
Authors: Letcher Todd , Wertz John , Shen M.-H. Herman
Published: December 2013

The energy-based lifing method is based on the theory that the cumulative energy in all hysteresis loops of a specimens’ lifetime is equal to the energy in a monotonic tension test. Based on this theory, fatigue life can be calculated by dividing monotonic tensile energy by a hysteresis energy model, which is a function of stress amplitude. Due to variations in the empirically measured hysteresis loops and monotonic fracture area, fatigue life prediction with the energy-based method shows some variation as well. In order to account for these variations, a robust design optimization technique is employed. The robust optimization procedure uses an interval uncertainty technique, eliminating the need to know an exact probability density function for the uncertain parameters. The robust optimization framework ensures that the difference between the predicted lifetime at a given stress amplitude and the corresponding experimental fatigue data point is minimized and within a specified tolerance range while accounting for variations in hysteresis loop energy and fracture diameter measurements. Accounting for these experimental variations will boost confidence in the energy-based fatigue life prediction method despite a limited number of test specimens.
Design Parameters of Brush Seals and Their Impact on Seal Performance
Authors: Schwarz H. , Friedrichs J. , Flegler J.
Published: December 2013

Brush seals, which were originally designed for gas turbine applications, have been successfully applied to large-scale steam turbines within the past decade. From gas turbine applications, the fundamental behavior and designing levers are known. However, the application of brush seals to a steam turbine is still a challenge. This challenge is mainly due to the extreme load on the brush seal while operating under steam. Furthermore, it is difficult to test brush seals under realistic conditions, i.e. under live steam conditions with high pressure drops. Due to these insufficiencies, 2 test rigs were developed at the University of Technology Braunschweig, Germany. The first test rig is operated under pressurized air and allows testing specific brush seal characteristics concerning their general behavior. The knowledge gained from these tests can be validated in the second test rig, which is operated under steam at pressure drops of 45 bar and temperatures up to 450 °C. Using both the air test rig and the steam test rig helps keep the testing effort comparably small. Design variants can be pre-tested with air, and promising brush seal designs can consequently be tested in the steam seal test rig. The paper focuses on a clamped brush seal design which, amongst others, is used in steam turbine blade paths and shaft seals of current Siemens turbines. The consequences of the brush assembly on the brush appearance and brush performance are shown. The clamped brush seal design reveals several particularities compared to welded brushes. It could be shown that the clamped bristle pack tends to gape when clamping forces rise. Gapping results in an axially expanding bristle pack, where the bristle density per unit area and the leakage flow vary. Furthermore, the brush elements are usually assembled with an axial lay angle, i.e. the bristles are reclined against the backing plate. Hence, the axial lay angle is also part of the investigation.
The Limited-Torque Acceleration Through Critical Speed Phenomenon in Rotating Machinery
Authors: Srinivasan Anand , Thurston Trent W.
Published: December 2013

Rotor-bearing systems of modern day turbomachinery are generally designed to operate at speeds well above the lateral critical speed(s). Acceleration from rest to design speed of turbomachines is usually accomplished by a driver such as a motor or a turbine. The driver provides the torque required to bring the drive-train to full speed. If the torque delivered by the driver is less than the torque demanded by the driven machine, the drive-train stalls at a speed below running speed. If this speed coincides with a lateral critical speed of the turbomachine, the amplitude of vibration may increase to levels high enough to trip the machine. In extreme cases, damage due to rubs from vibration excursions may occur on the rotating components. Such a phenomenon is referred to as a limited-torque-acceleration of rotors through the critical speed. A theoretical analysis of this phenomenon requires a time-transient solution of the lateral equations of motion, with the acceleration rate determined from the torque equation. In this paper, the acceleration of the Jeffcott rotor model with a variable torque input has been studied, and the time-transient response of the shaft lateral displacements has been presented. Data recorded from a turbomachine that incurs vibration excursions during limited-torque acceleration through critical speed has also been presented. The importance of fast acceleration rates through critical speeds for rotating equipment has been stressed in this paper.
Life Prediction Feasibility in TMF via Stress/Strain Data From a Viscoplasticity-Based Numerical Model
Authors: Karl Justin , Gordon Ali P.
Published: December 2013

Contemporary computing packages handle a wide variety of stress analysis types, but are yet to provide an optimal way to handle certain load cases and geometries. Blades in gas turbine systems, for instance, undergo repetitive thermal and mechanical load cycles of varied shape and phasing. Complexly-shaped airfoils create non-uniform stress paths that exacerbate the problem of FEA software attempting to determine the correct states of stress and strain at any point during the load history. This research chronicles the update and integration of Miller’s original viscoplasticity model with ANSYS finite element analysis software. Elevated temperature strain-controlled LCF and strain-controlled TMF loadings were applied to single-element, uniaxial simulation runs and the results were then compared to data from duplicate experimental testing. Initial findings indicate that the model maintains significant accuracy through several cycles, but longer tests produce varying error in hysteretic response. A review of the modernized implementation of Miller’s viscoplasticity model is presented with a focus on modifications that may be used to improve future results.
Design and Investigations of a Micro-Turbine Flow Part
Authors: Kosowski Krzysztof , Piwowarski Marian , Stępień Robert , Włodarski Wojciech
Published: December 2013

The co-generative micro-power plant with the HFE7100 as a working medium was designed and built for experimental investigations. The heat output of the plant was assumed equal to 20 kW, while the electric output amounted to about 3kW.

In the paper a multi-stage micro-turbine with partial admission of all the stages is described in detail and the results of the particular experimental investigations and numerical calculations are shown, followed by an appropriate discussion and conclusions. The flow calculations were performed using ANSYS package and finally the axial multistage turbine was chosen. This allowed to apply typical nozzle and blade profiles. The turbine consists of 5 similar (almost identical) stages with constant section blades, the only difference being the increase of the admission arc (number of nozzles) in the successive stages. The rotor speed was assumed equal to 8000 rpm, mean rotor diameter −100 mm and blade height −10 mm. The stream lines, pressure and temperature distribution in the nominal and off-design conditions are presented and discussed in the paper. The micro-turbine was built and tested experimentally. The turbine performance was calculated for HFE7100 but also for air and nitrogen as a working medium for testing purposes. In the first stage of experiments the turbine behaviour was checked using these gases and the results were compared with the calculation data. The results of the experiments correspond very well with the appropriate CFD calculation data.
Novel Wind Turbine for Catabatic Winds
Authors: Jericha H. , Göttlich E. , Sanz W.
Published: December 2013

On many sea shores around the world high speed winds fall down from mountains and flow horizontally over the sea surface close to the shore. A new wind turbine design is presented which is able to catch this energy. The engine is intended to be mounted on a bridge between two ship bodies similar to a catamaran.

Wind enters horizontally — the wind turbine resembling a very large jet engine — and is reduced in speed by a diffuser. The blade arrangement is similar to a last stage steam turbine ahead of a condenser. Power is produced by this single stage reaction turbine. The deficiency of flow power at the turbine outlet is counteracted by energy from the surrounding air flow by feeding bypass air into the outlet area behind the rotor blades.

The now increased flow carries sufficient flow power to pass through the outlet diffuser and to reach the pressure conditions behind the wind turbine. The wind turbine rotor drives the electrical power generator via a planetary gear box. Hydrogen and Oxygen generated by electrolysers are proposed to be used as energy storage.
Investigations on the Rotordynamic Coefficients of Pocket Damper Seals Using the Multi-Frequency, One-Dimensional, Whirling Orbit Model and RANS Solutions
Authors: Li Jun , Li Zhigang , Feng Zhenping
Published: December 2013

The numerical approach using the multi-frequency one-dimensional whirling orbit model and Reynolds-Averaged Navier-Stokes (RANS) solution was proposed for prediction of rotordynamic coefficients of pocket damper seal (PDS). By conducting the multiple frequencies one-dimensional whirling orbit for rotor center as the excitation signal, the unsteady RANS solutions combined with mesh deformation method were utilized to calculate the transient response forces on the PDS rotor surface. Unlike the single frequency whirling orbit models which require a separate computation for each frequency, the multi-frequency whirling orbit model yields results for multiple frequencies and therefore requires only one computation for different frequencies. The rotor motion signal and response force signal were transformed to the frequency domain using the Fast Fourier Transform (FFT), then the eight rotordynamic coefficients of the PDS were determined at fourteen different vibration frequencies 20–300Hz. The numerical results of rotordynamic coefficients of the PDS were in good agreement with experimental data. The accuracy and availability of the proposed method was demonstrated. The effects of vibration frequencies and pressure ratios on the rotordynamic coefficients of PDS were also investigated using the presented numerical method. The multi-frequency one-dimensional whirling orbit model is a promising method for prediction of the rotordynamic coefficients of the PDS.
Steam Turbines for Flexible Load Operation in the Future Market of Power Generation
Authors: Wechsung Michael , Feldmüller Andreas , Lemmen Heiko
Published: December 2013

In a liberated electricity market with a steadily growing percentage of fluctuating renewables the load related requirements of modern steam power plants are noticeably changing. Whereas the past has seen mainly coal-fired units being operated in base load now highly efficient part load behavior becomes more and more important as well as quickly responding frequency support at minimized investment costs.

…In the article various approaches will be identified, discussed and evaluated under economical criteria focused on the above described challenges for future power generating technologies. One central idea is to shift the pure sliding pressure mode down to an intermediate load range where the upper limit is reached at around 70% and optimize the blade path efficiency according to this point. Along with this strategy concepts are presented which allow frequency support from primary to hour- reserve of maximized load steps. Moreover it shall be explained how it is principally possible to use the same cycle conditions for load steps and increasing part load efficiency at the same time. Another idea is to improve the plant performance at lower load ranges by raising the main and reheat steam temperature accompanied by special maintenance concepts. The ideas presented in this article are mainly derived from a steam turbine point of view. Nevertheless some requirements and effects on the overall plant are taken into account additionally.

The presented approaches can be applied for new apparatus as for the upgrade of existing units. As the drivers for a more flexible operation of steam plants are especially strong in markets which do not guarantee an attractive utilization of the plant in produced MWhrs/year, investment decisions for new plants have been delayed or cancelled due to the difficult market conditions. Therefore special attention will be paid in this paper to the application of the new flexibility features in power plants which are already in operating and which have been designed originally with the main focus on highest efficiencies in base load operation. The difficulties and limitations given with the existing plant design will most likely be compensated by the economical advantages of the more flexible plant operation after the modernization.
Use and Limitations of the Harmonic Balance Method for Rub-Impact Phenomena in Rotor-Stator Dynamics
Authors: Peletan Loïc , Baguet Sebastien , Jacquet-Richardet Georges , Torkhani Mohamed
Published: December 2013

In the present paper, a Harmonic Balance Method (HBM) coupled with a pseudo-arc length continuation algorithm is presented for the prediction of the steady state behaviour of a rotor-stator contact problem. The ability of the HBM to reproduce the four most common phenomena encountered during rotor to stator contact situations (i.e. ‘no-rub’, ‘full annular rub’, ‘partial rub’ and ‘backward whirl/whip’) is investigated. A modified Jeffcott rotor model is used and results of the proposed algorithm are compared with traditional time marching solutions and analytical predictions. The advantages and limitations of the HBM for this kind of problem are analyzed. It is shown that the HBM is orders of magnitude faster than transient simulations, and provides very accurate results. However, in its current form it is unable to predict quasi-periodic behaviour. Detailed analysis of the transient solutions yields valuable information for the future extension of the HBM to efficient quasi-periodic simulations.
Experimental Friction Damping Characteristic of a Steam Turbine Blade Coupled by Shroud and Snubber at Standstill Set-Up
Authors: Wu Jun , Xie Yonghui , Zhang Di , Zhang Minghui
Published: December 2013

In order to avoid the high cycle fatigue which leads to the failure of turbine blades, friction structural damping has been widely used in turbine blade designs to reduce vibratory stresses by energy dissipation. A method is developed here to analyze the influence of friction structural damping on the vibration characteristics of turbine blades. Vibratory responses of a long steam turbine blade with shroud and snubber are studied. Finite element contact analysis of the steam turbine blades which are modeled in 3-D solid elements is conducted to obtain the normal contact force on the shroud contact surface and snubber contact surface of adjacent blades under five different rotational speeds (2100rpm, 2200rpm, 2413rpm, 2600rpm and 3000rpm). A rig for the tests of non-rotating turbine blade with friction damping structure is built. The normal contact forces of the shroud and snubber are applied to the blade according to numerical results. The response curves and modal damping ratios of the blade under different normal contact forces, which each one is related to a different rotational speed, are obtained. The experimental results show that with increases in rotational speed, modal damping ratio of the blade experiences an increasing period followed by a decreasing period while the resonance amplitude decreases first and then increases when there is only shroud contact. The effects are similar when there are both shroud and snubber contact. The modal damping ratio of the blade is basically identical with that of the uncoupled blade for the rotational speed above 2600rpm. For this range of rotational speed, the resonance frequency increases with the increase of rotational speed, and the changes of the resonance frequency are very trivial.
Design Optimization of a Low Pressure Steam Turbine Radial Diffuser Using an Evolutionary Algorithm and 3D CFD
Authors: Verstraete Tom , Prinsier Johan , Di Sante Alberto , Della Gatta Stefania , Cosi Lorenzo
Published: December 2013

The design of the radial exhaust hood of a low pressure (LP) steam turbine has a strong impact on the overall performance of the LP turbine. A higher pressure recovery of the diffuser will lead to a substantial higher power output of the turbine. One of the most critical aspects in the diffuser design is the steam guide, which guides the flow near the shroud from axial to radial direction and has a high impact on the pressure recovery.

This paper presents a method for the design optimization of the steam guide of a steam turbine for industrial power generation and mechanical drive of centrifugal compressors. This development is in the frame of a continuous effort in GE Oil and Gas to develop more efficient steam turbines. An existing baseline exhaust and steam guide design is first analyzed together with the last LP turbine stage with a frozen rotor full 3D Computational Fluid Dynamics (CFD) calculation. The numerical prediction is compared to available steam test turbine data. The new exhaust box and a first attempt new steam guide design are then first analyzed by a CFD computation. The diffuser inlet boundary conditions are extracted from this simulation and used for improving the design of the steam guide.

The maximization of the pressure recovery is achieved by means of a numerical optimization method that uses a metamodel assisted differential evolution algorithm in combination with a 3D CFD solver. The profile of the steam guide is parameterized by a Bezier curve. This allows for a wide variety of shapes, respecting the manufacturability constraints of the design. In the design phase it is mandatory to achieve accurate results in terms of performance differences in a reasonable time. The pressure recovery coefficient is therefore computed through the 3D CFD solver excluding the last stage, to reduce the computational burden. Steam tables are used for the accurate prediction of the steam properties.

Finally, the optimized design is analyzed by a frozen rotor computation to validate the approach. Also off-design characteristics of the optimized diffuser are shown.
Prediction of Clearance in Industrial Gas Turbine Validated by Field Operation Data
Authors: Bordo Luca , Bruzzone Silvia , Perrone Andrea , Traversone Laura
Published: December 2013

During load operations the gas turbine is characterized by cyclic transients and long dwell times, resulting clearance variation occurs.

Tight clearances in both the compressor and the turbine section is one key to high component efficiencies. However, under any operating condition, some clearance must be maintained in order to avoid contact between rotating and stationary parts.

The optimization of the clearances during the running is one of the most relevant key to improve the engine performance, a Hydraulic Clearance Optimization (HCO) system is installed on the Ansaldo Energia gas-turbine models fleet in order to control turbine blade-tip clearances by appropriate shifting of the rotor against the flow direction and consequently reducing the radial gaps above the turbine blade tips.

In particular the proposed procedure takes into account the HCO effect on the blade clearances and their optimizing during the operation conditions.

The proposed procedure is based on a combination of 2D/3D FEM model of complete rotor-casing assembly and field operation data.

The computational approach is based on a 2D axi-symmetric finite element model of the engine rotor, including the stacked rotor discs and the connecting tie-rod. Particular care has been put in the definition of the boundary conditions which are: the centrifugal loads, the tierod pre-tightening, the thermal transient conditions. To take into account 3D effect of airfoil twisting and bending, the 3D models of the assembly blade-disk are built. The 3D FE displacements of the tip blades are combined with the 2D FE displacements of the complete rotor in the evaluation process. 3D casing FEM model are built to calculate the casing distortion due to temperature difference between cylindrical shell and horizontal flange. The procedure evaluates the axial and radial clearance combining the rotor/stator displacements.

The clearance and temperature values are measured and filed thanks to tip timing capacitive sensors and thermocouples sensors installed on same stages.

The proposed procedure gives results in good agreement with the measured clearances in all the transient operation conditions.
In-Scale and Up-Scale Full Turbine Stage Measurements as a Support for Small Turbine Units Development
Authors: Němec Martin , Jelínek Tomáš , Babák Martin
Published: December 2013

This paper summarizes experimental results of an aerodynamic performance study carried out on two full stage turbine test rigs. The stage under investigation was designed as a gas generator turbine for a small jet engine produced by PBS (the TJ100 engine with thrust of 1100 N and turbine tip diameter of 141 mm).

The investigation was carried out alternatively on two full-stage test rigs (in-scale and scaled-up) integrated into a cool flow closed-loop wind tunnel located at VZLU.

Firstly, the in-scale testing, focusing on an overall stage performance measured by means of a hydraulic dynamometer was arranged. Furthermore, some time-averaged flow field parameters in terms of total pressure, velocity and angles were acquired along the channel height upstream and downstream of the stage. The flow path authenticity and construction simplicity were strictly followed during the rig design phase and therefore original parts of the engine were mostly used.

Then, the verification of results was performed with the stage scaled-up by factor 2.27. The overall stage performance was measured and compared with results of the in-scale measurement. Moreover, detail unsteady flow field measurement at the rotor exit was performed. Time-resolved data were analysed in order to study the influences of the stage load on the stage performance.
Aerodynamic Performance Investigation of Modern Marine Gas Turbine Intake System
Authors: Sun Peng , Gao Haiyang , Zhong Jingjun , Yang Muxiao
Published: December 2013

Gas turbines (GTs) have been used on board for many years. To safe guard these engines working efficiently and stably, several types of air intake system have been employed. The aerodynamic performance of marine gas turbine intake system is one of the important aspects which is associated with the marine operating conditions and should be studied carefully.

In this paper, numerical simulation is carried out on the flow parameters of a vessel and her intake system. How vessel operating conditions and the environment conditions influence the intake system inlet boundary is studied firstly. Under some certain assumptions, the intake inlet total pressure value and the angle between wind and heading direction approximately follow the sine law. Then, unsteady simulation is carried out on the intake system. The total pressure loss variation and which measuring point can represent the pressure loss properly are discussed. It is found that the total pressure distribution varies with the measuring location. Following this, flow parameters at the volute outlet is analyzed in detail, especially the flow field structure and the distortion intensity. The total pressure distribution is non-uniform, which will influence the GT performance and stability significantly.
Modelling and Assessment of Compressor Faults on Marine Gas Turbines
Authors: Roumeliotis I. , Aretakis N. , Mathioudakis K. , Yfantis E. A.
Published: December 2013

Any prime mover exhibits the effects of wear and tear over time, especially when operating in a hostile environment. Marine gas turbines operation in the hostile marine environment results in the degradation of their performance characteristics. A method for predicting the effects of common compressor degradation mechanisms on the engine operation and performance by exploiting the “zooming” feature of current performance modelling techniques is presented. Specifically a 0D engine performance model is coupled with a higher fidelity compressor model which is based on the “stage stacking” method. In this way the compressor faults can be simulated in a physical meaningful way and the overall engine performance and off design operation of a faulty engine can be predicted. The method is applied to the case of a twin shaft engine, a configuration that is commonly used for marine propulsion.

In the case of marine propulsion the operating profile includes a large portion of off-design operation, thus in order to assess the engine’s faults effects, the engine operation should be examined with respect to the marine vessel’s operation. For this reason, the engine performance model is coupled to a marine vessel’s mission model that evaluates the prime mover’s operating conditions. In this way the effect of a faulty engine on vessels’ mission parameters like overall fuel consumption, maximum speed, pollutant emissions and mission duration can be quantified.
Combustion Assessment of a 50% Algae-Based HRD76 Fuel and 50% Conventional F76 Military Diesel Fuel Blend
Authors: MacKinnon Matthew T. , Shaw Jesse D. , Quiñones Martin
Published: December 2013

As part of the United States Navy green energy initiative, engineers at Rolls-Royce and NAVSEA conducted a combustion assessment for a blend of 50% algae-derived HRD76 biofuel and 50% conventional F76 military diesel. The assessment consisted of combustion rig testing with Rolls-Royce Model 501-K34 gas turbine combustion system hardware. Identical tests were performed with the biofuel blend and a baseline fuel consisting of 100% F76 military diesel. The test results quantified the impact of the alternative fuel blend on ignition, lean blow-out, combustor exit temperature profile, combustion system hardware temperatures, primary zone flame radiance, carbon deposition, and emissions. This paper discusses the methods and results of the combustion rig tests.