bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of Gas Turbine Intake Air Filtration in a 420 MW Cogeneration Plant
Authors: Ingistov Steve , Milos Michael , Bhargava Rakesh K.
Published: September 2014

A suitable inlet air filter system is required for a gas turbine, depending on installation site and its environmental conditions, to minimize contaminants entering the compressor section in order to maintain gas turbine performance. This paper describes evolution of inlet air filter systems utilized at the 420 MW Watson Cogeneration Plant consisting of four GE 7EA gas turbines since commissioning of the plant in November 1987. Changes to the inlet air filtration system became necessary due to system limitations, a desire to reduce operational and maintenance costs, and enhance overall plant performance. Based on approximately 2 years of operational data with the latest filtration system combined with other operational experiences of more than 25 years, it is shown that implementation of the high efficiency particulate air filter system provides reduced number of crank washes, gas turbine performance improvement and significant economic benefits compared to the traditional synthetic media type filters. Reasons for improved gas turbine performance and associated economic benefits, observed via actual operational data, with use of the latest filter system are discussed in this paper.
Experimental and Theoretical Rotordynamic Coefficients of Smooth and Round-Hole Pattern Water Fed Annular Seals
Authors: Jolly Pascal , Hassini Amine , Arghir Mihaï , Bonneau Olivier
Published: September 2014

The present work presents the comparison between experimental and theoretical results obtained for three straight annular seals. One of the annular seals has smooth rotor and stator while the others have a textured stator; the textures are equally spaced shallow round holes, with two different depths. The experimental results were obtained on a test rig dedicated to the identification of the dynamic coefficients of high Reynolds bearings and annular seals. The test rig uses hot water (<50°C) as a working fluid. Dynamic excitations imposed by piezoelectric shakers to the rotor enable the identification of dynamic coefficients via complex impedances. Theoretical results compared with experimental findings were obtained by numerically solving the “Bulk Flow” equations (film thickness averaged equations dominated by inertia effects). The numerical model was extensively validated for smooth annular seals but is less confident for textured surfaces. The present comparisons between experimental and numerical results enable to estimate the accuracy of the numerical model employed for the textured seals.
Compressible Direct Numerical Simulation of Low-Pressure Turbines: Part I — Methodology
Authors: Sandberg Richard D. , Pichler Richard , Chen Liwei , Johnstone Roderick , Michelassi Vittorio
Published: September 2014

Modern low pressure turbines (LPT) feature high pressure ratios and moderate Mach and Reynolds numbers, increasing the possibility of laminar boundary-layer separation on the blades. Upstream disturbances including background turbulence and incoming wakes have a profound effect on the behavior of separation bubbles and the type/location of laminar-turbulent transition and therefore need to be considered in LPT design. URANS are often found inadequate to resolve the complex wake dynamics and impact of these environmental parameters on the boundary layers and may not drive the design to the best aerodynamic efficiency. LES can partly improve the accuracy, but has difficulties in predicting boundary layer transition and capturing the delay of laminar separation with varying inlet turbulence levels. Direct Numerical Simulation (DNS) is able to overcome these limitations but has to date been considered too computationally expensive. Here a novel compressible DNS code is presented and validated, promising to make DNS practical for LPT studies. Also, the sensitivity of wake loss coefficient with respect to freestream turbulence levels below 1% is discussed.
Research of an Advanced Turbine Disk for High Thrust-Weight Ratio Engine
Authors: Shen Xiuli , Dong Shaojing , Chen Zhiying
Published: September 2014

To meet the design requirements of the high thrust-weight ratio engine, the twin-web turbine disk is systematically investigated. The structural topology optimization is carried out with the evolutionary structural optimization method based on the conventional turbine disk, and a new shape of the twin-web turbine disk is presented. It is similar to the existing ones but with significant improvement for the strengthened ring is not needed. Then the finite element analysis and size optimization are conducted according to the results of topology optimization. The weight of the twin-web disk is reduced by 23.6% compared to the conventional design with the same stress level. Then a preliminary analysis of the welding residual stress is performed. Finally, a rotating three-dimensional photoelastic test is carried out to verify the rationality of the design and the accuracy of the calculation results.
Integrated Overtopping Wave Energy Converter in a Hybrid Offshore Wind Turbine Power Generation System
Authors: Ioannou Artemis , Kalfas Anestis I. , Karambas Theofanis V.
Published: September 2014

Marine construction technologies could be designed to offer power generation in addition to their sea defence and coastal erosion prevention function. This paper aims to evaluate and optimize the performance of an Overtopping Wave Energy Converter (OWEC) as part of a hybrid generation system integrated into an offshore wind turbine. For that purpose, two configurations have been investigated. A 100kW OWEC was combined with a micro-gas turbine of 80kW at the first configuration and the same OWEC with a wind turbine (WT) of 200kW at the second. The preliminary design of an integrated offshore OWEC/WT is presented.

The findings of the present investigation have been applied to a specific test case of a small, off–grid island, in the Aegean archipelago. Regarding its power requirement, Donoussa island currently relies exclusively on fossil fuel. At the same time, a high wave and wind power potential is available. A representative set of wind data have been obtained and numerically analyzed. A wave simulation, overtopping prediction and power output has been carried out. Moreover, a techno-economic and environmental assessment of the proposed offshore integrated design is presented. The stand alone coastal OWEC, and a single offshore wind turbine have been evaluated versus the proposed offshore hybrid power generation scheme.

The OWEC is expected to generate 320MWh per year, thus covering half of the island’s estimated power demand. Using both wave and wind power generation, energy autonomy of the island could be achieved. In order to cover the requirements of extreme cases, a micro gas-turbine power generation unit has been considered, in parallel to the existing fossil fuel power generation unit. From the techno-economic assessment point of view, the coastal OWEC construction has a shorter return on investment time of 11 years as compared to 13 years of the proposed integrated design but lower profitable investment. Besides providing sufficient electrical power for the island, the additional environmental benefit of the proposed system is that it can be used to counter coastal erosion.

The integrated offshore OWEC/WT design could potentially double the power output of each and every offshore wind turbine installation. This result could therefore be interpreted either as halving of the required number of offshore wind turbines erections or as doubling of the power output of an offshore wind park.
Numerical Studies Into Intake Flow for Fan Forcing Assessment
Authors: Carnevale Mauro , Green Jeffrey S. , Di Mare Luca
Published: September 2014

Recent trends in design for civil intakes lead towards shorter diffuser sections, unorthodox installations and more loaded lips. All these features increase the risk of lip stall in flight at incidence or in cross wind and increase the level of forcing seen by the fan blades because of the interaction with non-uniform flow from the intake.

In this study we analyze the behavior of prediction tools for intake distortion. In particular we compare the performance of popular turbulence models for standard intake flows and we discuss their behavior on the grounds of their behavior for elementary flows.

We conclude our study by comparing forcing and distortion figures of merit from different models.
Quantifying Loss Mechanisms in Turbine Tip Shroud Cavity Flows
Authors: Palmer Timothy R. , Tan Choon S. , Zuniga Humberto , Little David , Montgomery Matthew , Malandra Anthony
Published: September 2014

Numerical calculations, steady as well as unsteady, of flow in a turbine stage with a tip shroud cavity elucidate that the loss generating flow features consist of tip seal leakage jet, the interaction of cavity exit flow with main flow, the partially recirculating cavity inlet flow interaction with vane wakes, and injection of leakage flow into the shroud cavity. The first two flow features, namely the tip seal leakage flow and mixing of cavity exit flow with main flow, dominate while the injection of leakage flow plays an indirect role in affecting the loss generation associated with cavity exit flow. The tip shroud cavity flow essentially consists of a system of toroidal vortices, the configuration of which is set by the cavity geometry and changes when subject to unsteady vane-rotor interaction. The role which the toroidal vortices play in setting the cavity inlet recirculating flow pattern and loss generation is delineated. It is suggested that there exists a link between the inlet cavity sizing and the toroidal vortical structure. The computed results appear to indicate that the main flow path approximately perceives the presence of the tip shroud cavity as a doublet; as such a flow model based on this approximation is formulated. Loss variations with tip gap height and leakage flow injection are assessed. Results show that the expected loss due to mixing has a functional dependence on the square of the difference in their velocity magnitude and swirl. The tip seal leakage jet loss scales approximately linearly with the corrected mass flow rate per unit area over the range of tip gaps investigated.
Turbine Blade Tip Film-Cooling and Heat Transfer Measurements at High Blowing Ratios
Authors: Narzary Diganta , Liu Kevin , Han Je-Chin , Mhetras Shantanu , Landis Kenneth
Published: September 2014

Film-cooling and heat transfer characteristics of a gas turbine blade tip with a suction side rail was investigated in a stationary 3-blade rectilinear cascade. Mounted at the end of a blow-down facility the cascade operated at inlet and exit Mach numbers of 0.29 and 0.75, respectively. The rail was marginally offset from the suction side edge of the tip and extended from the leading to the trailing edge. A total of 17 film-cooling holes were placed along the near-tip pressure side surface and 3 on the near-tip leading edge surface with the objective of providing coolant to the tip. The tip surface itself did not carry any film-cooling holes. Relatively high blowing ratios of 2.0, 3.0, 4.0, and 4.5 and three tip gaps of 0.87%, 1.6%, and 2.3% of blade span made up the test matrix. Pressure sensitive paint (PSP) and Thermo-Chromic Liquid Crystal (TLC) were the experimental techniques employed to measure film-cooling effectiveness and heat transfer coefficient, respectively. Results indicated that when the tip gap was increased, film-cooling effectiveness on the tip surface decreased and heat transfer to the tip surface increased. On the other hand, when the blowing ratio was increased, film effectiveness increased but the effect on heat transfer coefficient was relatively small. The highest heat transfer coefficient levels were found atop the suction side rail, especially in the downstream two-thirds of its length whereas the lowest levels were found on the tip floor in the widest section of the blade.
Effects of Curvature Continuity of Compressor Blade Profiles on Their Performances
Authors: Song Yin , Gu Chunwei
Published: September 2014

Curvature discontinuity may exist in the surface, especially at the leading edge, of a compressor blade. The importance of curvature continuity or discontinuity has been realized, but its definite influences and mechanisms still need research. In this paper, an optimization method is proposed to design continuous-curvature blade profiles from datum blades, and a Reynolds-Averaged Navier-Stokes (RANS) solver with a transition model is used to examine the flowfields and performances of different blade profiles. Large eddy simulations of several cases are also presented to validate the RANS results. The effects of leading-edge-blend-point curvature continuity and the main-surface curvature continuity are studied separately. The results show that the curvature continuity at the leading-edge blend point helps to eliminate the separation bubble, and thus improves the blade performance. The main-surface curvature continuity is also found beneficial, although its effects are much smaller than those of the blend-point curvature continuity. Boundary-layer equations of the blade profiles are analyzed in terms of order of magnitude to further study the different curvature-continuity effects of the blend point and main surface theoretically. The analysis reveals the physical facts that produce the pressure spike around a leading-edge blend point with a discontinuous curvature, and thus explains how the optimized continuous-curvature leading edge removes the pressure spike and the related separation. The analysis also finds that the high spike appearing near the nose of a continuous-curvature leading edge at larger incidences is controlled by the large nose curvature rather than curvature discontinuity. The dual separation mechanisms also help to solve the so-called sharp leading edge paradox.
Effects of Streamwise Pressure Gradient and Convex Curvature on Film Cooling Effectiveness
Authors: Qin Yanmin , Ren Jing , Jiang Hongde
Published: September 2014

The effects of streamwise pressure gradient and convex wall curvature on film cooling effectiveness are investigated using PSP technology. Film cooling under five different main stream pressure gradients on both flat and convex wall is examined. The cooling hole has an inclined angle of 30° and no compound angle with a hole length of L/D = 4. The convex wall has a constant radius of r/D = 30. Numerical simulations are also conducted to gain more flow field information. For the flat wall case, film cooling effectiveness is higher with greater favorable pressure gradient for low blowing ratios. While for high blowing ratio cases, cooling effectiveness doesn’t vary much with streamwise pressure gradient. Film cooling effectiveness is increased significantly on convex wall compared with flat wall for M<0.5. The effect of streamwise pressure gradient is greater on convex wall and becomes unneglectable. The influence of streamwise pressure gradient and convex wall curvature is conjugated and should be discussed together. For all blowing ratios, film cooling effectiveness is apparently higher for larger mainstream favorable pressure gradient on convex wall.
Investigation of Applicability of Transporting Water Mist for Cooling Turbine Blades
Authors: Wang Ting , Ragab Reda
Published: September 2014

This paper presents a numerical study to investigate the feasibility of transporting water mist to the rotating blades of a high pressure turbine. The idea of using mist film cooling to enhance conventional air cooling has been proven to be a feasible technique under laboratory conditions. However, there are challenges in implementing this scheme for real gas turbine systems. The first challenge is how to transport the mist to the rotating blades and the second challenge is delivering the mist to the injection holes and getting the particles to survive within the harsh gas turbine environment. Both a zero-dimensional mist evaporation analytical model and a 3D computational fluid dynamics (CFD) scheme are employed for analysis. In the CFD simulation, the Lagrangian-Eulerian method is used along with the discrete phase model (DPM) to track the evaporation process of each individual water droplet.

For transporting the mist to the blades, the high-pressure water mist is injected into the stream of cooling air extracted from the compressor through two different passages. The first passage passes through the rotor cover-plate cavity before entering the blade base. The second passage passes through a diaphragm box on the base of the second vane, then tangentially through a cooling passage in the rotating shaft, and eventually to the blade base. The results show that it is feasible to transport the mist from the turbine casing to the blade through both passages, provided that droplets with sufficient particle diameter and mist loading are used. The shorter passage, through the nozzle diaphragm, alleviates a lot of challenges facing the passage through the blade cavity, and seems to be more practical. A side benefit of transporting mist through the internal passages is the additional cooling of the pre-swirler and rotor cover plates. The results are encouraging for implementing the mist cooling technique under real gas turbine conditions.
A Comparative Numerical Study of Aerodynamics and Heat Transfer on Transitional Flow Around a Highly Loaded Turbine Blade With Flow Separation Using RANS, URANS and LES
Authors: Schobeiri Meinhard T. , Nikparto Ali
Published: September 2014

The paper numerically and experimentally investigates the behavior of the boundary layer development and heat transfer along the suction and pressure surfaces of a highly loaded turbine blade with separation. To evaluate and compare the predictive capability of different numerical methods, Reynolds Averaged Navier-Stokes based solvers (RANS), Unsteady Reynolds Averaged Navier Stokes equation (URANS) as well as Large Eddy Simulation (LES) are used. The results of each individual numerical method are compared with the measurements. For this purpose, extensive boundary layer and heat transfer measurements were performed in the unsteady boundary layer cascade facility of the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. Aerodynamics experiments include measuring the onset of the boundary, its transition, separation and re-attachment using miniature hot wire probes. Heat transfer measurements along the suction and pressure surfaces were conducted utilizing a specially designed heat transfer blade that was instrumented with liquid crystal coating. Comparisons of the experimental and numerical results detail differences in predictive capabilities of the RANS based solvers and LES.
Influence of Intake on Fan Blade Flutter
Authors: Vahdati Mehdi , Smith Nigel , Zhao Fanzhou
Published: September 2014

The main aim of this paper is to study the influence of upstream reflections on flutter of a fan blade. To achieve this goal, flutter analysis of a complete fan assembly with an intake duct and the downstream OGVs (whole LP domain) is undertaken using a validated CFD model. The computed results show good correlation with measured data. Due to space constraints, only upstream (intake) reflections are analyzed in this paper. It will be shown that the correct prediction of flutter boundary for a fan blade requires modeling of the intake and different intakes would produce different flutter boundaries for the same fan blade. However, the ‘blade only’ and intake damping are independent and the total damping can be obtained from the sum of the two contributions.

In order to gain further insight into the physics of the problem, the pressure waves created by blade vibration are split into an upstream and a downstream traveling wave in the intake. The splitting of the pressure wave allows one to establish a relationship between the phase and amplitude of the reflected waves and flutter stability of the blade. By using this approach, a simple reflection model can be used to model the intake effects.
Investigation of a Separated Boundary Layer and its Influence on Secondary Flow of a Transonic Turbine Profile
Authors: Brachmanski Roland E. , Niehuis Reinhard , Bosco Arianna
Published: September 2014

Profile losses of the turbine blade and secondary flow losses are the main source of aerodynamic loss in a low pressure turbine. However, not much attention has been paid in the interaction between these two loss sources. This paper investigates the interaction mechanisms between a separated boundary layer on the suction side and the secondary flow in blade passages.

The high speed cascade wind tunnel of the University of the Federal Armed Forces Germany has been used to achieve the required operation conditions, generating a flow separation on the suction side. The profile of this cascade has been chosen due to the flow separation behavior on the suction side of the blade at low Reynolds numbers. Different measurements techniques are conducted to further investigate the effects seen in CFD.

The aim of this paper is to investigate the interaction phenomena between the secondary flow and a separation bubble at different Reynolds numbers. The development and change of the boundary layer in the axial and radial directions on the suction side of the turbine blade are presented and discussed. The results show discrepancies between the numerical prediction and the experimental data on the suction side of the blade rise as the effects of the secondary flow increase. Furthermore, the increasing influence of the radial pressure gradient of the secondary flow leads to a noticeable reduction in the length of the separation bubble close to the endwall region.
On the Predicted Performance of Oil Lubricated Thrust Collars in Integrally Geared Compressors
Authors: San Andrés Luis , Cable Travis A. , Wygant Karl , Morton Andron
Published: September 2014

Integrally geared compressors (IGCs) comprise of single stage impellers installed on the ends of pinion shafts, all driven by a main bull gear (BG) and shaft system. When compared to single shaft multistage centrifugal compressors, the benefits of IGCs include better thermal efficiency, reduced footprint and simple foundation, dispensing with a high speed coupling, as well as better access for maintenance and overhauls. In IGCs the compression of the process gas induces axial loads on the pinion shafts that are transmitted via thrust collars (TCs) to the main drive shaft and balanced by a single thrust bearing. The TCs, located on either side of pinion gears, slightly overlap with the BG outer diameter to form lentil-shaped lubricant-wetted regions. Archival literature on the design and optimization of TCs is scant, in spite of their widespread usage as they are comprised of simple geometry mechanical elements. This paper presents an analysis of the hydrodynamic film pressure generated in a lubricated TC due to the rotation of both thrust collar and bull gears and specified taper angles for both bodies. The model solves the Reynolds equation of hydrodynamic lubrication to predict the operating film thickness that generates a pressure field reacting to impellers’ thrust loads; these forces being a function of the pinion speed and the process gas physical properties. The model also predicts performance parameters such as power loss and axial stiffness and damping force coefficients. A parametric study brings out the taper angles in the TC and BG that balance the transmitted load with a lesser friction factor and peak pressure, along with large axial stiffness and damping.
Exhaust Diffuser Characteristics at Off-Design Conditions
Authors: Vassiliev Vladimir , Sommer Thomas P. , Granovsky Andrei , Prozorov Sergey
Published: September 2014

In todays electricity market with a strong mix of renewables and traditional energy sources, heavy-duty gas turbines often have to operate at part load with decreased exhaust mass flow. Decreased mass flow leads to reduced Mach number and this factor drives the exhaust loss down. At the same time off-design conditions lead to reduction of diffuser pressure recovery, and this factor drives loss up. The latter is normally stronger, and therefore the losses at GT low load are higher than at base load.

Traditionally exhaust diffusers were optimised for base load operation, and their characteristics were analysed in range close to this regime. However with increased part load operation it became important to investigate strong off-design conditions as well. In this work the numerical analysis of diffuser flow at different conditions corresponding to GT base load and different part loads is performed.

In the first part of the paper the numerical model and results of calculations are discussed. The calculations are compared with measurements in real engine, and this comparison demonstrates that numerical model provides good predictions not only for design conditions, but for off-design conditions as well.

The validated numerical model was then applied to analysis of diffuser geometry impact on the off design conditions, and the second part of the paper describes the results of these calculations. The analysis showed that modification of central body and front part of diffuser have negligible impact on losses at off design conditions, but significantly reduce performance at base load leading to non-optimal redistribution of losses between different regimes. Therefore original diffuser configuration provides the best compromise for wide operational window.
Simulation of the Near-Field Region of Film Cooling Jets Using RANS and Hybrid URANS/LES Models
Authors: Foroutan Hosein , Yavuzkurt Savas
Published: September 2014

This paper investigates the flow field and heat transfer in the near-field region of film cooling jets through numerical simulations using RANS and hybrid URANS/LES models. Detailed simulations of flow and thermal fields of a single row of film cooling cylindrical holes with 30° inline injection on a flat plate are obtained for low (M = 0.5) and high (M = 1.5) blowing ratios under high free stream turbulence (10%). The realizable k-ε model is used within the RANS framework and a realizable k-ε-based detached eddy simulation (DES) is used as a hybrid URANS/LES model. Both models are used together with the two-layer zonal model for near-wall simulations. Steady and time-averaged unsteady film cooling effectiveness obtained using these models in ANSYS-FLUENT are compared with available experimental data. It is shown that hybrid URANS/LES models (DES in the present paper) predict more mixing both in the wall-normal and spanwise directions compared to RANS models, while unsteady asymmetric vortical structures of the flow can also be captured. The turbulent heat flux components predicted by the DES model are higher than those obtained by the RANS simulations, resulting in enhanced turbulent heat transfer between the jet and mainstream, and consequently better predictions of the effectiveness. Furthermore, the unsteady physics of jet and crossflow interactions and the jet lift-off under high free stream turbulence is studied using the present DES results.
Compression Mechanics of the SC-MR Support for Rotor System
Authors: Ma Yanhong , Zhu Haixiong , Wang Chan , Qiao Hengwen , Hong Jie
Published: September 2014

The elastic damping support for rotor system which is combined of squirrel cage and metal rubber (also called metal mesh) and named SC-MR support for short is presented here. The SC-MR support is designed for flexible rotor system in turbo machineries, such as turbo-pumps and aeroengines. The SC-MR support realizes the function of both the elastic support and damping, which can provide a wonderful solution to the vibration problems. The squirrel cage supplies the main support stiffness and the Metal Rubber supplies the main damping and parallel stiffness. By controlling the parameters of the squirrel cage and the Metal Rubber, the stiffness and damping of the support could be designed to certain ranges.

The stiffness of the squirrel cage and the SC-MR support was simulated by FEM models and the values are 2.13e7 N/m and 2.51e7 N/m respectively. The squirrel cage supplies more than 80% of the stiffness and the MR supplies minor parallel stiffness, which perfectly meets the design purpose.

The effects of the installation state on the mechanical characteristics of the support were researched by compression tests. The Quasi-static tests on the squirrel cage show that its stiffness is 2.19e7 N/m, almost the same as simulated result. The compression tests on the SC-MR support were conducted while the Metal rubber was assembled with several prescribed prestrains. The results show that the support stiffness exhibits an increasing trend with either the radial prestrain or the axial prestrain, and it is more sensitive to the former one. The damping also appears to show an increasing trend with the prestrains and the loss factor is always larger than 0.02, distributing in range 0.02–0.08. The parallel stiffness of the MR increases severely with the prestrain. Therefore, the effect of the installation should be taken into account during the structure design process.
An Experimental Investigation of Thermal Wetness Loss in the Full Scale Size Low Pressure Turbine
Authors: Tsukuda Tomohiko , Sato Hiroki , Nomura Daisuke , Kawasaki Sakae , Shibukawa Naoki
Published: September 2014

Experimental investigation with a full scale low pressure steam turbine is carried out to reveal the thermal wetness loss. This paper focuses on thermal wetness loss of the last stage in a six-stage low pressure turbine. The temperature of superheating at the inlet of the last stage varies within a range of several tens of degrees under the condition that enthalpy at the stage outlet is below the saturation point. Radial distributions of pressure and temperature at the stage inlet and outlet are measured with rake probes and traverse probes, whereas the stage outlet enthalpy is identified by using the generator output and turbine mass flow rate. Higher stage efficiency is obtained the superheating inlet temperature becomes higher in this experimental condition. A three-dimensional CFD taking into consideration a non-equilibrium/equilibrium condensation model is carried out to understand the experimental results. A non-equilibrium condensation model can take into account the thermal wetness loss associated with supercooling and non-equilibrium condensation. The amount of thermal wetness loss is evaluated by comparing the results of non-equilibrium and equilibrium condensation models. The results show that the degree of superheating at the inlet of the stage affects the supercooling temperature distribution in the last stage flow path, resulting in lower thermal wetness loss at a higher inlet superheat condition.
Analysis Versus Synthesis for Trending of Gas-Path Measurement Time Series
Authors: Borguet S. , Léonard O. , Dewallef P.
Published: September 2014

Gas-path measurements used to assess the health condition of an engine are corrupted by noise. Generally, a data cleaning step occurs before proceeding with fault detection and isolation. Classical linear filters such as the exponentially weighted moving average filter are traditionally used for noise removal. Unfortunately, these low-pass filters distort trend shifts indicative of faults, which increases the detection delay.

The present paper investigates two new approaches to non-linear filtering of time series. On one hand, the synthesis approach reconstructs the signal as a combination of elementary signals chosen from a pre-defined library. On the other hand, the analysis approach imposes a constraint on the shape of the signal (e.g., piecewise constant). Both approaches incorporate prior information about the signal in a different way, but they lead to trend filters that are very capable at noise removal while preserving at the same time sharp edges in the signal. This is highlighted through the comparison with a classical linear filter on a batch of synthetic data representative of typical engine fault profiles.
Aerodynamic and Heat Transfer Measurements on an Intermediate Turbine Duct Vane
Authors: Johansson Martin , Povey Thomas , Chana Kam , Wallin Fredrik , Abrahamsson Hans
Published: September 2014

Flow in a turbine duct is highly complex, influenced by the upstream turbine stage flow structures, including tip leakage flow and non-uniformities originating from the upstream HP vane and rotor. The complexity of the flow makes the prediction using CFD methods difficult, hence there exists a need for experimental validation.

This paper presents a new design of an intermediate turbine duct with a structural vane that has been designed, manufactured and integrated into the Oxford Turbine Research Facility. This is a short duration high speed test facility enabling the use of an engine sized turbine, operating at the correct non-dimensional parameters relevant for aerodynamic and heat transfer measurements. The current configuration consists of a HP stage and a downstream duct including a low-aspect ratio vane, representative for a counter rotating turbine configuration.

Aerodynamic and heat transfer measurements are conducted to generate a database with which current CFD methods can be validated. The instrumentation presented here includes static pressure tappings and thin film heat transfer gauges on the ITD vane surface and endwalls.

The time averaged measurements show the impact of different clocking positions of the ITD vane with respect to the up-stream HP vane. This demonstrates the requirements of addressing the influence of vane counts and stator-stator clocking when designing new components. The measurements are compared with CFD predictions.
Design and Analysis of a Unique Flywheel Energy Storage System: An Integrated Flywheel, Motor/Generator and Magnetic Bearing Configuration
Authors: Kailasan Arunvel , Dimond Timothy , Allaire Paul , Sheffler David
Published: September 2014

Energy storage is becoming increasingly important with the rising need to accommodate the energy needs of a greater population. Energy storage is especially important with intermittent sources such as solar and wind. Flywheel energy storage systems store kinetic energy by constantly spinning a compact rotor in a low-friction environment. When short-term back-up power is required as a result of utility power loss or fluctuations, the rotor’s inertia allows it to continue spinning and the resulting kinetic energy is converted to electricity. Unlike fossil-fuel power plants and batteries, the flywheel based energy storage systems do not emit any harmful byproducts during their operation and have attracted interest recently. A typical flywheel system is comprised of an energy storage rotor, a motor-generator system, bearings, power electronics, controls and a containment housing. Conventional outer flywheel designs have a large diameter energy storage rotor attached to a smaller diameter section which is used as a motor/generator. The cost to build and maintain such a system can be substantial. This paper presents a unique concept design for a 1 kW-hr inside-out integrated flywheel energy storage system. The flywheel operates at a nominal speed of 40,000 rpm. This design can potentially scaled up for higher energy storage capacity. It uses a single composite rotor to perform the functions of energy storage. The flywheel design incoporates a 5-axis active magnetic bearing system. The flywheel is also encased in a double layered housing to ensure safe operation. IGBT based power electronics are adopted as well. The design targets cost savings from reduced material and manufacturing costs. This paper focuses on the rotor design, the active magnetic bearing design, the associated rotordynamics and a preliminary closed-loop controller.
The Effects of Component Defects on Utility Gas Turbine Operational Risk and Mitigation Practices
Authors: Narcus Andrew R. , Appleby John W. , Jones Russell B.
Published: September 2014

Component deterioration is observed in fleet gas turbine units during overhaul and maintenance activities of utilities providing electric power, co-generation or mechanical drive operations. Affected components include those provided by Original Equipment Manufacturers (OEM) and newly-manufactured and repaired hardware from OEM or aftermarket suppliers. This study details: i) the gas turbine flow path component deterioration and distress typically observed from operation, ii) some of the typical reasons (expected and abnormal) for the component damages, iii) the resulting effects and detriment to the utilities, and iv) a means for reducing the potential for component damages and operational risk to the utilities.

Abnormal gas path component deterioration is one of the leading causes for forced opening of IGT units. Unscheduled opening of production gas turbine units during normal and critical operating time periods can result in significant costs to the utilities and insurance providers due to unplanned overhaul and maintenance costs, replacement components costs, and lost production revenue during the outage. Often the majority of the premature component deterioration within a set can be attributed to the quality of manufacturing or repair processing and inadequate inspections of the components.

Escapes in quality assurance can occur resulting in components being supplied to utilities that do not meet design intent, such as debris contamination, coatings issues, and mis-machined features. Additionally, component suppliers are often pressured to meet production deadlines and provide delivery of the components to the utilities to avoid contractual penalties. This scenario can result in the potential for reduced focus on the quality of the components and quality-control escapes of design-deviated components delivered to the utilities for unit operation. Any uncontrolled deviations, damage, and discrepancies that result from hardware manufacturing and repair processes can have a significant impact on the long term durability of turbomachinery components. These component “damages” and manufacturing defects can be reduced or eliminated through proper functional quality inspections and component assessment, prior to unit installation. Additional issues concerning, improper tooling and methods employed during component removal and re-installation during maintenance activity can also result in damage to components and premature deterioration.

This study focuses on how utilities can perform or audit the functional checks on components prior to unit installation in an effort to reduce component degradation, operational risk and potential of forced outage of units resulting in additional maintenance costs and lost revenue.
Closed Loop Nonlinear System Identification Applied to Gas Turbine Analytics
Authors: Holcomb Chad M. , de Callafon Raymond A. , Bitmead Robert E.
Published: September 2014

Intelligent engine condition monitoring and early fault detection is becoming a necessity for modern gas turbines to achieve availability and reliability requirements. Degradation or failure of critical control components negatively affects reliability and safety as well as the ability to perform condition monitoring of the engine. Model-based approaches for analytics and condition monitoring show great promise with advances in remote connectivity and available computational power. Development of diagnostics for analytics requires focus on the target machine as well as the integrity of measurement and actuation systems to correctly identify and classify degradation indicators that discriminate between actuation and measurement faults from deterioration in machine performance. In this paper, a method is proposed to use data obtained in closed-loop operation to identify system models that separate the dynamic responses and non-linear characteristics for use in analytics. This is demonstrated on high-fidelity simulation data from a Taurus™ 60 gas turbine generator. The system is modeled with a feedback connection of a known controller in series with a block Hammerstein system.
Enhanced CFD Modelling and LDA Measurements for the Air-Flow in an Aero-Engine Front Bearing Chamber: Part I
Authors: Aidarinis J. , Goulas A.
Published: September 2014

Modern aero-engine development requires also a gradual increase in the overall effectiveness of lubrication systems. This particularly applies to bearing chambers where a complex two-phase flow is formed by the interaction of the sealing air and the lubrication oil. It is important to increase the level of understanding of the flow field inside the bearing chamber and to develop engineering tools in order to optimize its design and improve its performance. To achieve this an experimental and a computational study of the whole front bearing chamber were carried out for a range of shaft rotational speeds and sealing air mass flow.

The experimental measurements of the air velocity inside the chamber were carried out using a Laser Doppler Anemometer (LDA) in two-phase air/oil flow conditions. The experimental facility is a 1:1 scale model of the front bearing chamber of an aero-engine.

Computational 3D modeling of the bearing chamber was performed. The bearing gap and the presence of lubrication oil was modeled as an anisotropic porous medium with functions relating the pressure loss of the air coming through the gap and the tangential component of velocity of the air exiting the gap of the ball bearing with the air-flow rate through the gap and the rotational speed of the shaft. The methodology to obtain the above mentioned functions and the results of the detailed study are given in [1].

The enhanced computational model of the chamber implementing the law of pressure drop of the ‘lubricated’ bearing and the function of modeling the tangential velocity of the air exiting the bearing, was used to calculate the flow field for the full range of the measurements. A limiting curve dividing the operational map of the bearing chamber into two areas was predicted. Large vortical and swirling structures dominate the flow and they vary in size according to the position of the operation point relative to the limiting curve. Operation above the limiting curve leads to flow classified as type I with air going through the ball bearing while for operation below the limiting curve line the flow is classified as type II, there is no air-flow through the bearing gap.
Interpretation of Unexpected Aggregation of Condensate in Shrouded HP-Stages of an Industrial Steam Turbine
Authors: Schinnerl Mario , Beer Wolfgang , Willinger Reinhard
Published: September 2014

Unexplainable rotor oscillations occured at an industrial steam turbine with air condenser shortly after startup of the plant, but already at specified load points. These oscillations led to immediate shutdowns and were not explainable with conventional reasons at that time. After several oscillation measurements and analysis a hypothesis was developed to explain the oscillation phenomena: The reason of the oscillations is an aggregation of condensate in a labyrinth seal of one or more turbine stages which acts like additional bearings and shifts the eigenfrequencies of the whole system.

This work presents an analytical steady-state heat transfer model to explain, how condensation can occur in high-pressure sections of a steam turbine. With this model it is possible to take into account heat exchange in single turbine stages. The occurring heat fluxes are calculated row by row in each stator and rotor blade row. A new approach for considering the heat fluxes due to heat conduction between guide blades and guide blade carrier is presented. Due to the absence of measured surface temperatures the determination of convective heat transfer coefficients plays a major role in this work.
Comparison of the Aerodynamics of Acoustically Designed EGVs and a State-of-the-Art EGV
Authors: Marn Andreas , Selic Thorsten , Schönleitner Florian , Heitmeir Franz , Broszat Dominik
Published: September 2014

Within previous EU projects, possible modifications to the engine architecture have been investigated, that would allow for an optimised aerodynamic or acoustic design of the exit guide vanes (EGV) of the turbine exit casing (TEC). However, the engine weight should not be increased and the aerodynamic performance must be at least the same.

This paper compares a state-of-the art TEC (reference TEC) with typical EGVs with an acoustically optimised TEC configuration for the engine operating point approach. It is shown that a reduction in sound power level for the fundamental tone (1 blade passing frequency) for this acoustically important operating point can be achieved. It is also shown that the weight of the acoustically optimised EGVs (only bladings considered) is almost equal to the Reference TEC, but a reduction in engine length can be achieved.

Measurements were conducted in the subsonic test turbine facility (STTF) at the Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology. The inlet guide vanes, the low pressure turbine (LPT) stage, and the EGVs have been designed by MTU Aero Engines.
A Conceptual Design Study of an Open Rotor Powered Regional Aircraft
Authors: Larsson Linda , Lundbladh Anders , Grönstedt Tomas
Published: September 2014

Today many of the routes between small to medium sized airports and large hubs are operated by regional aircraft, powered by turboprop or turbofan engines. In the future the open rotor engine might provide an alternative option. The open rotor would combine the possibility of high cruise speed with high propulsive efficiency. Also, since the open rotor essentially is a turboprop with the possibility to fly fast, there is a benefit of high specific range at low cruising speeds, thus giving it a wide range cruise operation.

In this paper a regional aircraft for 70 passengers and 3000 km range is studied. The aircraft is evaluated with both a counter rotating open rotor and a turbofan engine. Aircraft design parameters such as wing area and sweep are varied together with engine parameters such as engine power and propeller disc loading.

Results show that the open rotor aircraft has a 17.0 % higher specific range at the optimal cruise Mach number compared to the turbofan aircraft. For higher speeds, at Mach 0.78, the difference is reduced to 15.0 %. The long range cruise Mach number is around Mach 0.7 for the open rotor aircraft while for the turbofan aircraft it is slightly higher, around Mach 0.72.
Multistage Coupling of Mistuned Aircraft Engine Bladed Discs in a Forced Vibration Analysis
Authors: Rzadkowski Romuald , Maurin Artur
Published: September 2014

Considered here is the effect of multistage coupling on the dynamics of an aircraft engine rotor with eight mistuned bladed discs on a drum-disc shaft. Each disc had a different number of rotor blades. Free and forced vibrations were examined using finite element models of single rotating blades, bladed discs, and an entire rotor. Calculations of the global rotating mode shapes of flexible mistuned bladed discs-shaft assemblies took into account the excitation of the turbine bladed disc with 0EO, 1EO and 2EO forces. The thus obtained maximal stress values of all of the rotor blades were carefully examined and compared with a tuned system to discover resonance conditions and coupling effects. Mistuning changes the stress distribution in individual rotor blades and the level of maximum stress increases or decreases as compared to bladed discs which are analyzed without the shaft.