bluuebunny/crossref_metadata_2025 huggingface dataset:
Convergence and Divergence: A Comparison between the Nordic School Curricula
Authors: Drakenberg Margareth , Malmgren Therese Vincenti
Published: August 2015

The aim of this article is to compare ethics and morality in the school systems in Denmark, Finland, Iceland, Norway and Sweden. What similarities and differences on ethical issues and values are to be found in the five countries? With a background knowledge in the Swedish curriculum, we want to study democracy, multiculturalism and human rights based on other countries’ curricula. Traditional theories and frameworks from literature on ethics and morality, for instance Begley’s frame of theory, and educational policy documents have been studied to understand the concepts in the school system. By using document analysis we have put this together to reach the aim of the study, which has a Nordic perspective, not only a Scandinavian one, which is the most usual ones. The main results are that there are both similarities and differences between the countries, but the Nordic countries regarding ethics and morality have especially to consider the main concepts democracy, multiculturalism and human rights in the school systems. Even if there are many similarities between the Nordic countries when it comes to democracy, multiculturalism and human rights there are differences between the Nordic countries how related concepts have been expressed.
Heat Transfer Augmentation due to Coolant Extraction on the Cold Side of Active Clearance Control Manifolds
Authors: Da Soghe Riccardo , Bianchini Cosimo , Andreini Antonio , Facchini Bruno , Mazzei Lorenzo
Published: August 2015

Jet array is an arrangement typically used to cool several gas turbine parts. Some examples of such applications can be found in the impingement cooled region of gas turbine airfoils or in the turbine blade tip clearances control of large aero-engines. In the open literature, several contributions focus on the impingement jets formation and deals with the heat transfer phenomena that take place on the impingement target surface. However, deficiencies of general studies emerges when the internal convective cooling of the impinging system feeding channels is concerned.

In this work an aero-thermal analysis of jet arrays for active clearance control was performed; the aim was the definition of a correlation for the internal (i.e. within the feeding channel) convective heat transfer coefficient augmentation due to the coolant extraction operated by the bleeding holes. The data were taken from a set of CFD RANS simulations, in which the behaviour of the cooling system was investigated over a wide range of fluid-dynamics conditions. More in detail, several different holes arrangements were investigated with the aim of evaluating the influence of the hole spacing on the heat transfer coefficient distribution. Tests were conducted by varying the feeding channel Reynolds number in a wide range of real engine operative conditions. An in depth analysis of the numerical data set has underlined the opportunity of an efficient reduction through the local suction ratio of hole and feeding pipe, local Reynolds number and manifold porosity: the dependence of the heat transfer coefficient enhancement factor from these parameter is roughly exponential.
Waste Heat Recovery in LNG Liquefaction Plants
Authors: Pillai P. , Meher-Homji C. , Meher-Homji F.
Published: August 2015

High thermal efficiency of LNG liquefaction plants is of importance in order to minimize feed usage and to reduce CO2 emissions. The need for high efficiency becomes important in gas constrained situations where savings in fuel auto consumption of the plant for liquefaction chilling and power generation can be converted into LNG production and also from the standpoint of CO2 reduction. This paper will provide a comprehensive overview of waste heat recovery approaches in LNG Liquefaction facilities as a measure to boost thermal efficiency and reduce fuel auto-consumption. The paper will cover types of heating media, the need and use of heat for process applications, the use of hot oil, steam and water for process applications and direct recovery of waste heat. Cogeneration and combined cycle approaches for LNG liquefaction will also be presented along with thermal designs. Parametric studies and cycle studies relating to waste heat recovery from gas turbines used in LNG liquefaction plants will be provided.

The economic viability of waste heat recovery and the extent to which heat integration is deployed will depend on the magnitude of the accrual of operating cost savings, and their ability to counteract the initial capital outlay. Savings can be in the form of reduced fuel gas costs and reduced carbon dioxide taxes. Ultimately the impact of these savings will depend on the owner’s measurement of the value of fuel gas; whether fuel usage is accounted for as lost feed or lost product. The negative impacts include the reduction in nitrogen rejection that occurs with reduced fuel gas usage and the power restrictions imposed on gas turbine drivers due to the increased exhaust system back-pressure caused by the presence of the WHRU. When steam systems are acceptable, a cogeneration type liquefaction facility can be attractive. In addition to steam generation and hot oil heating, newer concepts such as the use of ORCs or supercritical CO2 cycles will also be addressed.
An Introduction to Combustion, Fuels, Emissions, Fuel Contamination and Storage for Industrial Gas Turbines
Authors: Welch Michael , Igoe Brian
Published: August 2015

It is important that gas turbines used in Oil & Gas applications can burn a wide variety of fuels with the minimum impact on the environment or project economics. This paper is an introduction for those unfamiliar with gas turbine combustion in any detail into how emissions such as NOx are formed, and how the two most common types of gas turbine combustion system — the ‘conventional’ diffusion flame combustor and the Dry Low Emissions (DLE) combustor operate.

There are many types of gaseous and liquid fuels that can be used in Gas Turbines, which can come from a wide range of natural and industrial sources. These different potential fuels are discussed, along with the flexibility of the two different combustion systems to accept different types of fuel.

Some of the common contaminants found in these fuels are also discussed, along with the impact these have on the operability and maintenance of industrial and aero-derivative gas turbines, and methods to minimize the impact of these contaminants identified. Finally the paper looks at recommendations on liquid fuel storage to minimize operational issues on liquid fuels.
Performance Potential Analysis of Heavy-Duty Gas Turbines in Combined Cycle Power Plants
Authors: Seydel Carl Georg
Published: August 2015

Within the last decades heavy-duty gas turbines have become more relevant for the energy sector, especially due to the changing requirements on fossil power plants. In combination with high fluctuating renewables, such as wind and solar energy, combined cycle power plants provide the needed operational flexibility along with high thermal efficiency. In order to meet the ambitious reduction targets for future CO2 emissions, the extension of renewable power solutions is mandatory. Meanwhile further development of fossil power plants is important, to ensure a secure energy supply at all conditions and to back up the worldwide increasing power demand. Enhancements for heavy-duty gas turbines focus on higher thermal efficiency and increasing power output, whilst providing a high operational flexibility.

This study analyzes the future performance potential for heavy-duty gas turbines in combined cycle power plants, by further development of the main gas turbine components: compressor, combustion chamber and turbine, including the cooling system. The performance potential will be evaluated separately for each component and in combination for on- and off-design operation. The thermodynamic power plant design will be calculated with the performance software GTlab of the German Aerospace Center. Furthermore the fuel and CO2 savings for different levels of component technology development will be quantified. Concluding a potential evolution timeline for combined cycle power plants until the year 2050 will be given.

The results show that there is a high potential regarding to thermal efficiency and power output, by conventional component improvements of heavy-duty gas turbines. Also the improved components lead to a significant reduction of fuel consumption and CO2 emissions.
Aerodynamic Gas Turbine Compressor Design for an Oxy-Fuel Combined Cycle
Authors: Dahlquist Adrian , Genrup Magnus
Published: August 2015

A number of different CCS-technologies are currently being developed to reduce CO2 emissions from thermal power stations. One of these technologies is based on the oxy-fuel combined cycle process, the basics of which have been described in several publications. The key difference in this cycle is the working fluid, which requires further investigation. The working fluid in the topping gas turbine cycle of an OCC mainly consists of CO2 (80–95 wt%) and steam (5–15 wt%), with a few percentage of enriched N2 and Ar. The gas properties of this working fluid differ significantly from those of a conventional air-breathing gas turbine; hence, the gas turbine has to be designed accordingly.

The isentropic exponent is lower, for example, with the result that a higher pressure ratio is required in an oxy-fuel combined cycle gas turbine than in a conventional combined cycle to achieve exhaust gas conditions that fit the design of a conventional bottoming steam cycle. This higher pressure ratio results in additional challenges in the design of the aerodynamic compressor.

The amount of information in the public domain about designing an oxy-fuel gas turbine is sparse and is mainly limited to the cycle design. The main objective of this work is therefore to demonstrate the feasibility of achieving the aerodynamic compression in a single-spool compressor design, suitable for an oxy-fuel combined cycle application, with the aim of bringing the technology closer to commercialization.

The aerodynamic compressor design includes 1D mid-span and 2D through-flow design calculations, and a steady-state 3D analysis calculation for validation.

The compressor’s design suits an oxy-fuel combined cycle with a net plant power of 115 MWel.
The Implementation of Five-Dimensional FGM Combustion Model for the Simulation of a Gas Turbine Model Combustor
Authors: Donini Andrea , Bastiaans Robert J. M. , van Oijen Jeroen A. , de Goey L. Philip H.
Published: August 2015

Gas turbines are one of the most important energy conversion methods in the world today. This is because using gas turbines, large scale, high efficiency, low cost and low emission energy production is possible. For this type of engines, low pollutants emissions can be achieved by very lean premixed combustion systems. Numerical simulation is foreseen to provide a tremendous increase in gas turbine combustors design efficiency and quality over the next future. However, the numerical simulation of modern stationary gas-turbine combustion systems represents a very challenging task. Several numerical models have been developed in order to reduce the costs of flame simulations for engineering applications. In the present paper the Flamelet-Generated Manifold (FGM) chemistry reduction method is implemented and extended for the inclusion of all the features that are typically observed in stationary gas-turbine combustion. These consist of stratification effects, heat loss and turbulence. The latter is included by coupling FGM with the Reynolds Averaged Navier Stokes (RANS) model. Three control variables are included for the chemistry representation: the reaction evolution is described by the reaction progress variable, the heat loss is described by the enthalpy and the stratification effect is expressed by the mixture fraction. The interaction between chemistry and turbulence is considered through a presumed probability density function (PDF) approach, which is considered for progress variable and mixture fraction. This results in two extra control variables: progress variable variance and mixture fraction variance. The resulting manifold is therefore five-dimensional, in which the dimensions are progress variable, enthalpy, mixture fraction, progress variable variance and mixture fraction variance. A highly turbulent and swirling flame in a gas turbine model combustor is computed in order to test the 5-D FGM implementation. The use of FGM as a combustion model shows that combustion features at gas turbine conditions can be satisfactorily reproduced with a reasonable computational effort. The implemented combustion model retains most of the physical accuracy of a detailed simulation while drastically reducing its computational time, paving the way for new developments of alternative fuel usage in a cleaner and more efficient combustion.
Influencing Parameters of a Tip Blowing Interacting With Rotor Tip Flow
Authors: Guinet Cyril , Inzenhofer André , Gümmer Volker
Published: August 2015

The design space of axial-flow compressors is restricted by stability issues. Different axial-type casing treatments have shown their ability to enhance compressor stability and to influence efficiency. Casing treatments have proven to be effective, but there still is need for more detailed investigations and gain of understanding for the underlying flow mechanism. Casing treatments are known to have a multitude of effects on the near-casing 3D flow field. For transonic compressor rotors these are more complex, as super- and subsonic flow regions alternate while interacting with the casing treatment. To derive design rules it is important to quantify the influence of the casing treatment on the different tip flow phenomena. Designing a casing treatment in a way that it antagonizes only the deteriorating secondary flow effects can be seen as a method to enhance stability while increasing efficiency.

The numerical studies are carried out on a tip-critical rotor of a 1.5 stage transonic axial compressor. The examined recirculating tip blowing casing treatment, which consists of a recirculating channel with an air off-take above the rotor and an injection nozzle in front of the rotor. The design and functioning of the casing treatment is influenced by various parameters. A variation of the geometry of the tip blowing, more specifically the nozzle aspect ratio, the axial position or the tangential orientation of the injection port, was carried out to identify key levers.

The tip blowing casing treatment is defined as a parameterized geometric model and is automatically meshed. A sensitivity analysis of the respective design parameters of the tip blowing is carried out on a single rotor row. Their impact on overall efficiency and their ability to improve stall margin is evaluated. The study is carried out using URANS simulations.
Off-Nominal Component Performance in a Supercritical Carbon Dioxide Brayton Cycle
Authors: Clementoni Eric M. , Cox Timothy L. , King Martha A.
Published: August 2015

Bechtel Marine Propulsion Corporation (BMPC) is testing a supercritical carbon dioxide (S-CO2) Brayton system at the Bettis Atomic Power Laboratory. The Integrated System Test (IST) is a simple recuperated closed Brayton cycle with a variable-speed turbine-driven compressor and a constant-speed turbine-driven generator using S-CO2 as the working fluid designed to output 100 kWe. The main focus of the IST is to demonstrate operational, control, and performance characteristics of an S-CO2 Brayton power cycle over a wide range of conditions. Therefore, the IST was designed to operate in a configuration and at conditions that support demonstrating the controllability of the closed S-CO2 Brayton cycle. Operating at high system efficiency and meeting a specified efficiency target are not requirements of the IST. However, efficiency is a primary driver for many commercial applications of S-CO2 power cycles. This paper uses operational data to evaluate component off-nominal performance and predict that design system operation would be achievable.
Effect of Shaft Rotation, Hole and Annulus Geometry on the Discharge Behavior Through Rotating Radial Holes
Authors: Riedmüller Daniel , Sousek Jan , Pfitzner Michael
Published: August 2015

This paper reports on various effects on the flow through rotating radial holes (centrifugal, centripetal) in conjunction with the geometries of hole and surrounding annuli. The aerodynamic behavior of radial rotating holes is different from the one of axial and stationary holes due to the presence of centrifugal and Coriolis forces acting in the main flow direction. Furthermore, the geometry of the inlet and outlet region is often influencing the separation behavior of the flow at the holes. To investigate the flow phenomena and the discharge behavior of these radial holes in detail, an existing test rig containing two independently rotating shafts (co- and counter rotating) was used. Experimental and numerical investigations have been performed for both flow directions through the radial holes (centripetal and centrifugal), for different hole geometries (oblong holes and round holes), inlet types (rounded and sharp), length to diameter ratios (variation of either length or diameter) and gap widths between inner and outer shaft. For each of these geometrical variations flow properties have been varied such as pressure ratio across the holes, incident Mach number and rotational speed of both shafts. To enable large parametric studies and grid independency studies an optimization model with completely automatic grid generation, CFD simulation and post-processing has been set up. As a main result of the current studies it was found, that the shaft to hole diameter is another parameter of interest for the flow behavior through shaft holes. For a centripetal flow through the shaft holes and a decreasing inner gap width, the discharge coefficient was observed to increase initially before it drops significantly. In addition, measurements of centripetal flow though oblong holes revealed higher discharge coefficient in comparison with round holes and equal length to diameter ratio.
Isothermal and Cyclic Oxidation Performance of Vertically Cracked and Columnar TBC Structures Produced Using ASPS Process
Authors: Li Xiaolong , Huang Xiao , Yang Qi , Tang Zhaolin
Published: August 2015

Oxidation performance of thermal barrier coatings (TBCs) deposited by the axial suspension plasma spraying (ASPS) method was evaluated under isothermal and cyclic conditions with a peak temperature of 1080°C. The TBC systems are based on two nickel-based superalloy substrates (CMSX-4 and IN738LC), platinum aluminide bond coat, and yttria stabilized zirconia (8YSZ) top coat of either vertically cracked (VC) or columnar structure. Samples with IN738LC substrate exhibited longer isothermal oxidation lives whereas the ones with CMSX-4 substrate showed greater cyclic oxidation lives. Outward diffusion of W and Ta in TBC systems containing CMSX-4 was found to have progressed to the interface between TGO and top coat; this has contributed to the reduced isothermal oxidation life. The longer cyclic oxidation lives of TBC systems with CMSX-4 were attributed to less CTE mismatch between coating layers (reduced strain energy) and better creep resistance of diffusional bond coat on CMSX-4, hence less TGO rumpling. TBC systems with columnar YSZ had longer isothermal oxidation lives while those with vertically cracked YSZ seemed to result in longer cyclic lives.
Rolls Royce LCS Engine Health Monitoring Big Data Collection and Analysis
Authors: Moore Greg
Published: August 2015

This paper provides examples of LCS-1 Class Ships Environmental Health Monitoring (EHM), being performed on current US Navy class LCS-1 ships. The paper will be focused on normal vs. abnormal trending deciding where further analysis and troubleshooting is required. The paper will not present reasons for abnormal data trends, but will define the difference between normal and abnormal trends to precipitate further analysis.
United States Navy 501-K34 Gas Turbine Engine RADCON Effort
Authors: Patterson Jeffrey S. , Fauvell Kevin D. , McMahon Jay , Moralez Javier O.
Published: August 2015

On the afternoon of March 11, 2011 at 2:46pm, a 9.0 magnitude earthquake took place 231 miles northeast of Tokyo, Japan, at a depth of 15.2 miles. The earthquake caused a tsunami with 30 foot waves that damaged several nuclear reactors in the area. It was the fourth largest earthquake on record (since 1900) and the largest to hit Japan. On March 12, 2011, the United States Government launched Operation Tomodachi to provide humanitarian relief aid to Japan. In all, a total of 24,000 troops, 189 aircraft, 24 naval ships, supported this relief effort, at a cost of $90.0 million. The U.S. Navy provided material support, personnel movement, search and rescue missions and damage surveys. During the operation, 11 gas turbine U.S. warships operated within the radioactive plume. As a result, numerous gas turbine engines ingested radiological contaminants and are now operating under Radiological Controls (RADCON). This paper will describe the events that lead to Operation Tomodachi, as well as the resultant efforts on the U.S. Navy’s Japanese based gas turbine fleet. In addition, this paper will outline the U.S. Navy’s effort to decontaminate, overhaul and return these RADCON assets back into the fleet.
A Numerical Investigation on a New Pulse-Optimized Flow Control Method for Turbocharger Turbine Performance Improvement Under Pulsating Conditions
Authors: Cao K. , Yang M. , Martinez-Botas R. F.
Published: August 2015

A turbocharger turbine in an internal combustion engine is fed with continuously pulsating flow due to nature of the exhaust flow of a reciprocating engine. It is generally acknowledged that the performance of the turbine deteriorates due to this pulsation. In order to address the problem, a novel pulse-optimized flow control method is introduced in this paper, which involves a specially-designed nozzle ring upstream of the radial or mixed flow turbine. Unlike a traditional turbocharger, in which the nozzle ring is stationary, the nozzle ring is rotating. The inception of this new flow control method is based on the fact that the variable magnitude of the unsteady exhaust flow can be converted into the variation of the flow angle by means of the rotating nozzle ring. The new method is then validated by a steady-state, single passage numerical model. Calculations with different nozzle rotating speeds under both high and low mass flow rate conditions were executed and the results demonstrated significant improvements in both stage efficiency and power output. The results predicted that the new pulse-optimized flow control method was able to enhance the turbocharger performance to a great extent by means of addressing the potential energy within the highly dynamic exhaust flows.
Supporting Structure Performances Analysis of Heavy-Duty Gas Turbine Based on Fluid-Solid Coupling Method
Authors: Xu Guohui , Zhou Jian , Lu Mingjian , Geng Haipeng , Sun Yanhua , Yu Lie , Yang Lihua , Zhao Shiquan , Qi Xiaobing , Liu Xueyun , Fang Yu
Published: August 2015

In order to achieve high working efficiency, modern gas turbines operate at high temperature which is close to the melting points of metal alloys. However, the support of turbine end suffers the thermal deformation. And the journal center position is also changed due to the effects of high temperature and shaft gravity. Tangential or radial supporting structures, which are composed of supporting struts, diffuser cones, hot and cooling fluid channel, are widely used in gas turbine hot end. Cooling technology is usually used to keep the bearing temperature in a reasonable range to meet requirements of strength and deformation of the supporting struts. In this paper, three major assumptions are proposed: (a) radiation is not considered, (b) cooling flow system is only partially modeled and analysis assumes significantly higher cooling flow that is not typical for current engines, and (c) only steady state heat transfer is considered. And a 3D fluid-solid coupled model based on finite-element method (FEM) is built to analyze the performances of both the tangential and the radial support. The temperature distribution, thermal deformation and stress of supports are obtained from CFD and strength analysis. The results show that either the tangential or radial support is used in a 270MW gas turbine; the thermal stress is about 90.3% of total stress which is produced by both thermal effects and shaft gravity. Comparing to the results from radial supports, it can be seen that the struts stress and position variation of journal center of tangential support are smaller. Due to a rotational effect of the bearing housing caused by the deformation of the tangential struts, the thermal stress in these tangential struts can be relieved to some extent. When both thermal effect and shaft gravity are considered, the stress of each tangential supporting strut is almost uniformly distributed, which is beneficial to the stability of rotor system in the gas turbine.
A Method for Efficient Performance Prediction for Fan and Compressor Stages With Degraded Blades
Authors: Giebmanns A. , Schnell R. , Werner-Spatz C.
Published: August 2015

Over service time fan and compressor blades vary in their geometry. Due to the geometric irregularities it is difficult to reliably assess the fan or compressor performance. Therefore, in the present study, a method that allows an efficient and accurate estimation of the performance for fan and compressors with degraded blades is established.

In a first step, the blade regions mainly exposed to geometry variations are identified. Then, a simple parameterization that enables to easily describe the blade geometry as well as to independently represent the variations of all relevant geometric parameters is defined. For each geometric parameter (e.g. leading edge shape, rotor clearance gap height), the shifts of the operating points in the performance map due to the geometric variations are calculated. This is done with an adjoint flow solver which simultaneously provides the shifts for all extents of geometric parameter variations. As the geometric parameters are assumed to be independent of each other, the combination of variations in several geometric parameters is estimated by simply adding the shift vectors determined for the individual parameters.

The results for a subsonic compressor stage show a significant influence of the variations in the geometric parameters on the compressor performance. As validation with few nonlinear simulations demonstrates, this influence is well predicted by the method presented in this study. The relative deviation of the performance map parameters in the operating points around peak efficiency is less than 0.5 %. Compared to the nonlinear simulations, the numeric effort to determine the influence of seven geometric parameters on the performance map with the method based on adjoint simulations is considerably reduced by a factor of 35. In summary, the results demonstrate the feasibility of the method and encourage its application in an industrial context.
Aerodynamic Investigation of a Single-Stage Axial Compressor With a Casing Groove and Tip Injection Using Fluid-Structure Interaction Analysis
Authors: Ma Sang-Bum , Heo Man-Woong , Kim Kwang-Yong , Choi Jaeho
Published: August 2015

In this paper, a fluid-structure interaction (FSI) analysis was performed for a single-stage axial compressor with casing groove and tip injection using three-dimensional Reynolds-Averaged Navier-Stokes equations. The k-ε turbulence model and hexahedral grids system were used in the analysis. ANSYS solid 186 elements type was used to analyze the solid characteristic. In order to achieve robust stability of the transonic axial compressor, a casing groove was installed with tip injection on rotor tip region. FSI analysis was carried out to predict the deformation of the blades, and the results were compared to those of non-FSI analysis. Validation of the numerical results performed in comparison with experimental data, showed good agreements with experimental data for the adiabatic efficiency and total pressure ratio. It was found that deformation of blades affects the aerodynamic performance of the compressor to some extent. Stability of the axial compressor was enhanced by installing the casing groove with tip injection.
Characterization of Emissions From the Use of Alternative Aviation Fuels
Authors: Chan Tak W. , Chishty Wajid A. , Canteenwalla Pervez , Buote David , Davison Craig R.
Published: August 2015

Alternative fuels for aviation are now a reality. These fuels not only reduce reliance on conventional petroleum-based fuels as the primary propulsion source, but also offer promise for environmental sustainability. While these alternative fuels meet the aviation fuels standards and their overall properties resemble those of the conventional fuel, they are expected to demonstrate different exhaust emissions characteristics because of the inherent variations in their chemical composition resulting from the variations involved in the processing of these fuels.

This paper presents the results of back-to-back comparison of emissions characterization tests that were performed using three alternative aviation fuels in a GE CF-700-2D-2 engine core. The fuels used were an unblended synthetic kerosene fuel with aromatics (SKA), an unblended Fischer Tropsch synthetic paraffinic kerosene (SPK) and a semi-synthetic 50-50 blend of Jet A-1 and hydroprocessed SPK.

Results indicate that while there is little dissimilarity in the gaseous emissions profiles from these alternative fuels, there is however a significant difference in the particulate matter emissions from these fuels. These differences are primarily attributed to the variations in the aromatic and hydrogen contents in the fuels with some contributions from the hydrogen-to-carbon ratio of the fuels.
Feedback Control of Self-Sustained Nonlinear Combustion Oscillations
Authors: Li Xinyan , Zhao Dan
Published: August 2015

Detrimental combustion instability is unwanted in gas turbines, aeroengines and rocket motors. It is typically generated due to the dynamic coupling between unsteady heat release and acoustic pressure. To prevent the onset of combustion instability or dampen large-amplitude oscillations, the coupling must somehow be interrupted. In this work, we design and implement a sliding mode controller and observer to mitigate self-sustained combustion oscillations in an open-ended thermoacoustic system. An acoustically compact heat source is confined and modeled by using a modified form of King’s Law. Coupling the heat source model with a Galerkin series expansion of the acoustic pressure provides an approach to evaluate the performance of the sliding mode control. The thermoacoustic systems with different numbers of eigenmodes and actuators are considered. It is found that self-sustained limit cycle oscillations can be successfully produced from small perturbations in the thermoacoustic systems when the actuators are not actuated. Meanwhile, the system we modeled can be proved to be controllable and observable. In order to gain insight on the thermoacoustic mode selection and triggering, the acoustical energy exchange between neighboring eigenmodes are studied and discussed. As the controller-driven actuators are actuated, the limit cycle oscillations are quickly dampened. And both thermoacoustic systems are stabilized. The successful demonstration indicates that the sliding mode controller can be applied to stabilize unstable thermoacoustic systems, even with multiple eigenmodes.
Effects of Nonuniform Tip Clearance on Fan Performance and Flow Field
Authors: Chen Yingxiu , Hou Anping , Zhang Mingming , Li Jianxiong , Zhang Simu
Published: August 2015

Nonuniform tip clearance, caused by the deformation of the casing (casing ovalization), exists in all fans to some extent. However, description of the flow behavior with this kind of nonuniform clearance is seldom given in the open literature. In this paper, both steady and unsteady calculations are performed to study the influence of the nonuniform clearance on fan performance and flow field. The investigation method is based on three dimensional RANS equations, carried out by the ANSYS CFX fluid solver. A new factor τ, which is in the range of 0 to 1, is defined to represent the nonuniformity of the tip clearance. A series of numerical models with different tip clearance nonuniformities τ are investigated. In addition, the original, uniform tip clearance is also performed serving as a reference. The results indicate that the fan performance is mainly affected by two factors: the clearance nonuniformity τ and the average clearance level. There is a clear decreasing trend of the fan performance with increasing nonuniformity and average tip clearance level. The maximum clearance can contribute to the reduction of stall margin. Furthermore, the effects of nonuniform clearance on tip leakage vortex and aerodynamic force are also discussed in detail. The deformation of the casing can affect the pressure fluctuation and thus increase the amplitude of the aerodynamic force.
Innovative Approaches to Propellers Off-Design Performance Modeling
Authors: Tantot Nicolas , Brichler Thierry , Dubosc Matthieu , Ghebali Sacha
Published: August 2015

This article provides an overview on the challenges related to the prediction of propellers performance at preliminary design stage, ranging from numerical stability to simplicity required for being integrated into engine cycle models. After a description of the usual approach to propeller performance based on maps, and a discussion on its limitations, innovative methods are proposed, lying on the identification of losses trends combined with the use of propeller characteristic operating points over the whole usable area. These innovative approaches significantly reduce the number of required simulations or test cell points to be able to describe the full propeller range of operation, adding physics to the mathematical approach usually considered for turbomachinery component maps elaboration. Accuracy and stability of the considered approaches are discussed, along with an assessment of the required effort to set them up.
Dominant Damage Factors Determining for Single Crystal Nickel Superalloys Under Cyclic Loading Based on Principal Component Analysis
Authors: Wang Rongqiao , Jiang Kanghe , Jing Fulei , Hu Dianyin , Song Jun
Published: August 2015

A critical plane approach in combination with principal component analysis (PCA) for determining dominant damage factors (DDFs) was developed for single crystal nickel superalloys at elevated temperature. Maximum resolved shear stress (RSS), maximum slip rate and other 2 mesoscopic parameters on the critical plane, defined as the preferential slip plane, were selected as damage parameters. Correlation analysis results indicated that there were strong correlations (i.e. multicollinearity) among the selected parameters. To address this issue, PCA was performed to eliminate the effect of multicollinearity and the DDFs were determined as well. Based on the DDFs a life model was proposed and then validated by the fatigue experimental results. Most of the experimental lives are within the factor three of the predicted ones. The life model has a relatively simple form with reliable constants which facilitates the application in industry design.
Investigation of Flutter Mechanisms of a Contra-Rotating Open Rotor
Authors: Stapelfeldt Sina C. , Vahdati Mehdi , Parry Anthony B.
Published: August 2015

The growing pressure to reduce fuel consumption and cut emissions has triggered renewed interest in contra-rotating open rotor technologies. One of their potential issues is self-excited or forced vibration of the unducted, light-weight, highly swept blades. This paper presents a numerical study into the flutter behaviour of a contra-rotating open rotor rig at take-off conditions. The study presented in this paper aimed to validate the numerical approach and provide insights into the flutter mechanisms of the open rotor under investigation. For the initial validation, pressure profiles and thrust coefficients from steady state mixing plane calculations were compared against rig measurements. A full domain unsteady analysis predicted front rotor instability at low advance ratios. Flutter occured in the first torsional mode in 0ND and 1ND which agreed with experimental observations. Subsequent unsteady computations focussed on the isolated front rotor and first torsional mode. The flow field and aerodynamic damping over a range of advance ratios was studied. It was found that minimum aerodynamic damping occured at low advance ratios when the flow was highly three-dimensional on the suction side. A correlation between the quasi-steady loading on the blade and aeroelastic stability was made and related to the numerical results. The effects of variations in frequency were then investigated by linking local aerodynamic damping to the unsteady pressure on the blade surface.
Axial Flow Fan Design Experience for a Project Based Turbomachinery Class
Authors: Cardillo Lucio , Corsini Alessandro , Delibra Giovanni , Sheard Anthony G. , Volponi David
Published: August 2015

In consideration of the extremely rapid progress in turbomachinery technology after the WWII, when the first gas engine was run, modern turbomachinery could be considered a young subject. Developments in computational power and numerical techniques since the 1940s, totally changed designer’s perspectives, giving them the possibilities to increase power and sophistication of design tools consolidated by years of laboratory and field tests from the 1940’s and 1950’s. A huge database from which, we believe, “there is still so much to be learned” (Cumpsty, 1986) [1].

On the other hand turbomachinery performance correlations, or even design procedures, have tended to be developed in individualistic ways. A reason for this has been the use of different approaches within engineering companies and the development of customized design tools and correlation of previous experience or performance optimization.

These circumstances reflected in an extraordinary knowledge, hided by confidentiality and intellectual property issues. In this respect, proprietary design techniques acts as a barrier to the dissemination of concepts at the early stages such as the university.

This paper illustrates the design process of an industrial fan as taught at Sapienza, University of Rome, during lectures of Turbomachinery Design. Objective of the class was to help students learn to develop their own design tools from the available suggested literature Horlock (1958, 1962, 1966) [2] [3] [4], Dixon (1975) [5], Lakshminarayana (1995) [6], Cumpsty (1989) [1] and Lewis (1996) [8]. Moreover, the activities were oriented to the use of open source software, specifically Scilab, used to code preliminary design and optimization routines as well as OpenFoam for the CFD verification step.
The Loading Cycle of a H-Blade Type Vertical Axis Wind Turbine
Authors: Saverin Joseph , Frank Stefan
Published: August 2015

The loading cycle of a H-blade type vertical axis wind turbine was investigated. Two numerical models are used to predict turbine loading behaviour. An experimental benchmark case is used to verify that the loading cycle, at least from a quantitative perspective has been reproduced in the simulation. The blade angle of attack was used as a reference tool to explain the loading cycle and allow at least a first step towards a solid aerodynamic basis for understanding the loading undergone by a vertical axis wind turbine blade for a range of tip speed ratios. Additionally, a new method for improving numerical prediction of blade angle of attack and therewith blade loading is introduced and a preliminary study is undertaken to assess its validity.
Design and Analysis of a Real-Time Hot Gas Temperature Estimator for Heavy-Duty Gas Turbines
Authors: Müller Eric A. , Ticǎ Adrian
Published: August 2015

The knowledge about a relevant process and lifetime indicative quantity, such as the hot gas temperature, is crucial for the control of a gas turbine. Since this indicative process quantity usually cannot be directly measured, it has to be estimated. The paper describes a model-based method to accurately estimate in real-time the hot gas temperature of a heavy-duty gas turbine. The method follows a well-balanced trade-off between resulting prediction accuracy and involved computational complexity. It takes advantage of the capability of a component-level dynamic model to predict the system behaviour and of the capacity of a dynamic tracking filter to adapt to the current gas turbine conditions. In a simulation study, it is shown that the proposed design can provide an accurate hot gas temperature estimation over the entire gas turbine load range, along the gas turbine lifecycle, and during fast transient manoeuvres.
Sensitivity of Supersonic ORC Turbine Injector Designs to Fluctuating Operating Conditions
Authors: Bufi Elio A. , Cinnella Paola , Merle Xavier
Published: August 2015

The design of an efficient organic rankine cycle (ORC) expander needs to take properly into account strong real gas effects that may occur in given ranges of operating conditions, which can also be highly variable. In this work, we first design ORC turbine geometries by means of a fast 2-D design procedure based on the method of characteristics (MOC) for supersonic nozzles characterized by strong real gas effects. Thanks to a geometric post-processing procedure, the resulting nozzle shape is then adapted to generate an axial ORC blade vane geometry. Subsequently, the impact of uncertain operating conditions on turbine design is investigated by coupling the MOC algorithm with a Probabilistic Collocation Method (PCM) algorithm. Besides, the injector geometry generated at nominal operating conditions is simulated by means of an in-house CFD solver. The code is coupled to the PCM algorithm and a performance sensitivity analysis, in terms of adiabatic efficiency and power output, to variations of the operating conditions is carried out.
Characterization of Low Frequency Combustion Dynamics of Hot Blast Stoves by Means of a Flame Transfer Function Based on CFD Forced Response Simulations: Comparison of Different Hot Blast Stove Designs
Authors: Gövert Simon , Fratalocchi Virginia , Kok Jim B. W.
Published: August 2015

The combustion dynamics of thermo-acoustic systems like gas turbine combustors at elevated pressure and atmospheric industrial furnaces can be studied using a forced response approach. In this approach, the flame is excited by external perturbation of the upstream fuel or air mass flow. The flame transfer function can then be determined, which describes the response of the heat release rate in the combustor or furnace to the upstream velocity fluctuations. Subsequently, the flame transfer function can be used as an input for acoustic network models to further analyze the stability behavior of a given combustion system. Most of the applications of the flame transfer function analysis are for natural gas fired systems with dimensions such, that most of the relevant combustion dynamics is in the frequency range 100–500 Hz. The situation is different for hot blast stoves as used in the iron making process. Here the fuel is low calorific coal gas and the dimensions of the stove are huge, with heights of 30 m at a diameter of 5 m. This leads to a relevant frequency range for the combustion dynamics in interaction with acoustics of about 3–80 Hz. In order to cope with this combination of a large computational domain and extreme low frequent combustion dynamics in the response simulation, special attention was devoted to computational efficiency. In order to allow for a sufficient mesh resolution to capture the combustion characteristics while keeping the computational demands in a feasible range, the computational domain is to be drastically reduced by the use of symmetry assumptions. In a first step, the mesh dependency is studied and different combustion models are analyzed for a reference geometry on the basis of steady states results. The burning velocity model with adapted laminar flame speed description is subsequently chosen for the transient simulations. Transient numerical simulations are performed using a URANS turbulence model. The combustor is excited by a multi-harmonic perturbation of the fuel mass flow, to further reduce computational time. The flame transfer function is determined and compared for two different burner designs. The results show significant impact of combustor design on the acoustic behavior and combustion time scales. While the reference design acts like a low pass filter with a cut-off frequency of about 6 Hz, the modified design shows band-pass filter characteristics with a lower and higher cut-off frequency of 30 and 60 Hz, respectively.
A Predictive Model for Preliminary Gas Turbine Blade Cooling Analysis
Authors: Chowdhury Nafiz H. K. , Zirakzadeh Hootan , Han Je-Chin
Published: August 2015

The growing trend to achieve a higher Turbine Inlet Temperature (TIT) in the modern gas turbine industry requires, in return, a more efficient and advanced cooling system design. Therefore, a complete study of heat transfer is necessary to predict the thermal loadings in the turbine vane/blade. To estimate the metal temperatures, it is important to simulate the external hot gas flow condition, the conduction in the blade material, and the internal coolant flow characteristics accurately and simultaneously. As a result, proposing novel, quicker, and more convenient ways to study the heat transfer behavior of gas turbine blades is of absolute necessity. In the current work, a predictive model for the gas turbine blade cooling analysis in the form of a computer program has been developed to answer this need. The program is capable of estimating distribution of coolant mass flow rate, internal pressure and metal temperature of a turbine blade based on external and internal boundary conditions. The simultaneous solutions result from the coupled equations of mass and energy balance. The model is validated by showing its accuracy to predict the temperature distributions of a NASA E3 blade with an uncertainty of less than +/−10%. Later, this paper documents the overall analysis for a set of different boundary conditions with the same blade model (E3) and demonstrates the capability of the program to extend for other cases as well.
Pressure Measurements on the Blade Surface in the Rotating System of a Side Channel Blower
Authors: Münsterjohann Sven , Becker Stefan
Published: August 2015

Side channel blowers are used in a wide range of applications like the paper and printing industry, dental vacuum, industrial vacuum cleaners or road sweepers. As all these applications occur in the neighborhood of human beings, a low noise emission of the side channel blowers is necessary. To obtain an closer insight to the flow field and the noise produced, this paper is dealing with pressure measurements in the rotating impeller of a double flow side channel blower. Seven thin line pressure sensors are integrated into two opposing blade surfaces to measure the pressure distribution within one blade segment. The necessary modifications to the impeller as well as the housing and the mounting of the telemetric system are demonstrated. A pressure correction will be applied to correct the pressure offset due to the used measurement technique. The results show the exemplary time trend of the pressure, the phase averaged pressure generation for different working points and rotational speeds of 50Hz and 60Hz. Especially, the pressure distribution during the passage of the interrupter region is analyzed. Additionally, the results are presented in the frequency domain. The pressure measurements are linked to the acoustic noise emission by the application of an acoustic analogy and its source definition by the second time derivative of the measured, hydrodynamic pressure.