bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
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.
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.
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.