bluuebunny/crossref_metadata_2025 huggingface dataset:
Effusion Cooling With Backside Crossflow Cooling and the Backside Coolant Mass Flow Rate Greater Than the Effusion Cooling Mass Flow
Authors: Andrews G. E. , Khalifa I. M.
Published: November 2013

Full coverage effusion cooling was studied for a square array of 90° effusion cooling holes with backside cooling using a 5 mm depth duct air supply to the coolant holes, with the duct air mass flow rate being greater than the effusion cooling flow. This geometry represents combustor primary zone wall cooling with the dilution air or main combustion air comprising the excess backside flow rate. Active cooling was used with metal walls and 300K effusion cooling into a 27 m/s mean velocity duct flow at 770K crossflow temperature. The aim was to provide conjugate heat transfer experimental data to validate conjugate heat transfer CFD prediction procedures. The 152 mm square test section had 15 rows of holes The X/D value studied was 11.0, which gives a 3% effusion wall pressure loss at a relatively low effusion coolant mass flow rate. The duct air feed to the holes enhanced the backside cooling of the wall. These results were compared with previous work using a plenum chamber air feed and with a crossflow duct, but with equal cross flow air to effusion air. The increased duct air feed velocity relative to the plenum low velocity air feed resulted in an increase in the overall cooling effectiveness due to the additional heat transfer by the duct crossflow velocity. This effect was across the whole duct length when there was surplus cross flow air relative to effusion air, without this the enhanced heat transfer was small and confined to the leading edge area.
Unsteady Aerodynamics of Low-Pressure Steam Turbines Operating Under Low Volume Flow
Authors: Megerle Benjamin , Rice Timothy Stephen , McBean Ivan , Ott Peter
Published: November 2013

Non-synchronous excitation under low volume operation is a major risk to the mechanical integrity of last stage moving blades (LSMBs) in low-pressure (LP) steam turbines. These vibrations are often induced by a rotating aerodynamic instability similar to rotating stall in compressors. Currently extensive validation of new blade designs is required to clarify whether they are subjected to the risk of not admissible blade vibration. Such tests are usually performed at the end of a blade development project. If resonance occurs a costly redesign is required, which may also lead to a reduction of performance. It is therefore of great interest to be able to predict correctly the unsteady flow phenomena and their effects.

Detailed unsteady pressure measurements have been performed in a single stage model steam turbine operated with air under ventilation conditions. 3D CFD has been applied to simulate the unsteady flow in the air model turbine. It has been shown that the simulation reproduces well the characteristics of the phenomena observed in the tests. This methodology has been transferred to more realistic steam turbine multi stage environment. The numerical results have been validated with measurement data from a multi stage model LP steam turbine operated with steam. Measurement and numerical simulation show agreement with respect to the global flow field, the number of stall cells and the intensity of the rotating excitation mechanism. Furthermore, the air model turbine and model steam turbine numerical and measurement results are compared. It is demonstrated that the air model turbine is a suitable vehicle to investigate the unsteady effects found in a steam turbine.
Effect of Confinement on Combustion Characteristics in Lean Direct Injection Combustion System
Authors: Zeng Qinghua , Kong Wenjun , Sui Chunjie
Published: November 2013

Confinement has direct influence on the dome reference velocity and indirect influence on the combustor’s performance, emissions, operability, liner and dome temperature levels and gradients. Understanding the effects of the confinement is crucial to conventional combustor design.

Recently, lean direct injection (LDI) combustor has been popularly employed to reduce nitrogen oxides (NOx) emissions from gas turbine. Compared to conventional combustor, LDI combustor has a much larger amount of air entering into the dome. Therefore, combustion characteristics and confinement effects in LDI combustor are quantitatively or even qualitatively different from those in conventional combustor. As a result, some design criteria for conventional combustor are no longer applicable for LDI combustor and it is essential to investigate the effects of confinement level in LDI combustor.

In the literature, several studies have been conducted to understand how the confinement levels affect the characters of swirling non-reactive flow. However, there are few studies on the reactive flow and thereby the effects of confinement on combustion characteristics are not well understood. Due to its important role in combustor design, the confinement effect on spray combustion in LDI mode is systematically investigated in the present study.

The experimental setup is established to study the confinement effects. Experimental data on flame characteristics, centerline temperature distribution, and pollutant emissions are obtained. Experiments at five different confinement ratios, 2.8, 6.8, 10.6, 19.5, and 28.5, are conducted. The results show that the confinement level has an important impact on the flame characteristics, centerline temperature, and pollution emissions. The optimal confinement ratio is determined, at which the pollution emissions become the lowest.
Mechanical Design of Large Steam Turbine Components for Part Load Conditions
Authors: Lückemeyer N. , Qin F.
Published: November 2013

Recent developments like the significant introduction of renewable energy sources to the electricity networks worldwide have led to more frequent and extended operation of fossil power plants in part load conditions. As a result the typical load spectrum of large steam turbines used for electricity generation has changed over the last years and will continue to do so.

A number of papers has already been published on how to optimize the water-steam cycle and the steam turbine from a thermodynamical and aero-dynamical point of view for this new load regime in order to improve the average efficiency. But the changed load regime also poses a challenge for the mechanical design and structural integrity assessment of steam turbines.

Reason for this is that the rated conditions are not necessarily the most challenging boundary conditions and therefore not necessarily a suitable, conservative envelope for all other load cases for mechanical design. Pressures decrease, but steam temperatures in part loads can increase and heat transfer coefficients and the influence of radiation on the component temperatures change.

With an increasing demand for and a wider range of part load operation it for this reason becomes more important than ever to consider these load cases in the mechanical design.

This paper uses a large, double-flow intermediate pressure steam turbine as an example to investigate the impact of extended part load operation on the design. Both an analytical model and finite element calculations are used to compare from a structural integrity point of view a low part-load load case and the rated load case and to evaluate the significance of heat radiation.
A Study of a Modern Transonic Fan Rotor in a Low Reynolds Number Regime for a Small Turbofan Engine
Authors: Sonoda Toyotaka , Schnell Rainer , Arima Toshiyuki , Endicott Giles , Nicke Eberhard
Published: November 2013

In this paper, Reynolds effects on a modern transonic low-aspect-ratio fan rotor (Baseline) and the re-designed (optimized) rotor performance are presented with application to a small turbofan engine. The re-design has been done using an in-house numerical optimization system in Honda and the confirmation of the performance was carried out using DLR’s TRACE RANS stage code, assessed with respect to experimental data obtained from a small scale compressor rig in Honda. The baseline rotor performance is evaluated at two Reynolds number conditions, a high Reynolds condition (corresponding to a full engine scale size) and a low Reynolds number condition (corresponding to the small scale compressor rig size), using standard ISA conditions. The performance of the optimized rotor was evaluated at the low Reynolds number condition. The CFD results show significant discrepancies in the rotor efficiency (about 1% at cruise) between these two points due to the different Reynolds numbers. The optimized rotor’s efficiency is increased compared to the baseline. A unique negative curvature region close to the leading edge on the pressure surface of the optimized rotor is one of the reasons why the optimized rotor is superior to the baseline.
Numerical Evaluation of Influence of Internal Ribs on Heat Transfer in Flat Plate Film Cooling
Authors: Agata Yukiko , Takahashi Toshihiko , Sakai Eiji , Nishino Koichi
Published: November 2013

To augment the thermal efficiency of combined power generation plants, the turbine inlet temperature of an industrial gas turbine has been increased. Cooling technology plays a vital role in the durability of gas turbine blades in situations in which the turbine inlet temperature exceeds the allowable temperature of the blade material. Cooling air is also directly associated with the reduction in thermal efficiency because bleed air from the compressor is used for turbine cooling. Thus, improvement in cooling performance has a marked impact on the further augmentation of thermal efficiency by increasing turbine inlet temperature. To evaluate film cooling performance on the basis of heat flux reduction, it is necessary to accurately estimate both heat transfer coefficient and adiabatic film cooling effectiveness. Most studies of film cooling, however, have focused on improving adiabatic film cooling effectiveness. In contrast, there are few studies focusing on heat transfer coefficient. One of the reasons for this is that adiabatic film cooling effectiveness is a performance parameter unique to film cooling. To preliminarily estimate the heat flux through a blade, heat transfer coefficient without film cooling can still be used as substitute. Moreover, the accurate CFD prediction of heat transfer coefficient with film cooling is difficult, compared with the evaluation of adiabatic film cooling effectiveness. Therefore, in this study, we addressed the CFD prediction of heat transfer coefficient with film cooling on a flat plate, and discussed its feasibility. Recent gas turbine blades operated at a turbine inlet temperature of over 1300 degree Celsius employ internal convection cooling with ribbed passages and external film cooling. These cooling technologies have been studied extensively, particularly regarding their individual effects. On the other hand, there are few investigations on the interaction between internal convection cooling and the film cooling. Although most of such film-cooling studies employed stagnant plenums to bleed cooling air, some researchers including the present authors have shown the marked impact of the conditions for supplying coolant air on film cooling performance. In this study, we focus particularly on the influence of internal rib orientation on external film cooling performance along the blade outer surface. CFD analysis is used to resolve the flow fields of the flat plate film cooling and to clarify the influence of rib orientation on heat-transfer.
Life Assessment Technology of Steam Turbine Rotor
Authors: Chen Rong , He A Ping , Yang Yan Lei , Ye Xing Zhu , Jiang Pu Ning , Hua Wen Xiang
Published: November 2013

Turbine Rotor is one of the most important components of the Turbine-generator unit which is related closely with the safety and economy of the Power Plant’s Operation. In this paper the rotor design & analysis process for the Shanghai Turbine Plant’s super critical 600MW power station is introduced. Large thermal stresses maybe developed in the turbine rotors of the power plant during start-up, shutdown and load changes. The integrity of the turbine rotor is threatened by the material deterioration caused by fatigue and creep damage of the rotor at some critical locations. Rotor stress analysis using FEA is used to evaluate the strength and the temperature distribution of the turbine rotor. The life loss mechanisms of the turbine rotor are described. Key factors that influence fracture mechanisms are discussed. Rotor damage due to low-cycle fatigue, high-cycle fatigue and creep damage are discussed as the main elements to evaluate the life time of the turbine rotor.
Influence of Working Fluid on Gas Turbine Cooling Modeling
Authors: Sammak Majed , Thern Marcus , Genrup Magnus
Published: November 2013

Cooling is essential in all modern high-temperature gas turbines. Turbine cooling is mainly a function of gas entry temperature, which plays the key role in overall gas turbine performance. High turbine entry temperatures can be achieved through appropriate selection of blade cooling method and blade material. The semi-closed oxy-fuel combustion combined cycle (SCOC-CC) operates at the same high entry gas temperature, hence blade cooling is necessary. The aim of this paper was to calculate the required turbine cooling in oxy-fuel gas turbines and compare it to the required turbine cooling in conventional gas turbines. The approach of the paper was to evaluate the thermodynamic and aerodynamic factors affecting turbine cooling with using the m*-model. The results presented in the paper concerned a single turbine stage at a reference diameter. The study showed greater cooling effectiveness in conventional gas turbines, but a greater total cooled area in oxy-fuel gas turbines. Consequently, the calculated total required cooling mass flow was close in the both single stage turbines. The cooling requirement and cooled area for a conventional and oxy-fuel twin-shaft gas turbine was also examined. The gas turbine was designed with five turbine stages. The analysis involved various turbine power and combustion outlet temperatures (COT). The results showed that the total required cooling mass flow was proportional to turbine power because of increasing gas turbine inlet mass flow. The required cooling mass flow was proportional to COT as the blade metal temperature is maintained at acceptable limit. The analysis revealed that required cooling for oxy-fuel gas turbines was higher than for conventional gas turbines at a specific power or specific COT. This is due to the greater cooled area in oxy-fuel gas turbines. The cooling effectiveness of conventional gas turbines was greater, which indicated higher required cooling. However, the difference in cooling effectiveness between conventional and oxy-fuel gas turbines was less in rear stages. The cooling mass flow as percentage of gas turbine inlet mass was slightly higher in conventional gas turbines than in oxy-fuel gas turbines. The required cooling per square meter of cooled area was used as a parameter to compare the required cooling for oxy-fuel and conventional gas turbines. The study showed that the required cooling per cooled area was close in both studied turbines.
Evaluation of Electricity Cost in a Growing Market
Authors: Mohamed W. , Sethi V. , Pilidis P. , Abu A. O. , Nasir A. , Lotfi O.
Published: November 2013

Operating gas turbines at higher firing temperatures has been shown to be more thermally efficient with more power obtained from relatively less fuel. There is, however, an associated slight increase in operating and maintenance costs at higher power settings. This paper studies the relationship between gas turbine power setting, the hot gas-path components’ life consumption, operating and maintenance cost and how these parameters can affect the cost of electricity. A 165 MW gas turbine power plant is modelled and investigated with a comparative turbine blade lifing model that performs stress and thermal analysis, and creep life estimation using the parametric Larson Miller method. The outcomes of this analysis are then linked to an economic model to calculate the cost of generating electricity. The results shows that the optimum cost of electricity does not coincide with the lowest TET or power setting as would be expected when taking into account the creep life of the blade. This is because although lower TET results in improved component life, it will also result in lower thermal efficiency which is found to have a more significant impact on the overall electricity cost. In other words, the cost of electricity will increase at low TETs due to reduced thermal efficiency. On the other hand the cost of electricity will also increase at high TETs due to reduced turbine blade life that leads to increase in maintenance cost.
Combined Experimental/Numerical Method Using Infrared Thermography and Finite Element Analysis for Estimation of Local Heat Transfer Distribution in an Internal Cooling System
Authors: Egger Christian , von Wolfersdorf Jens , Schnieder Martin
Published: November 2013

In the present study a method for estimating local heat transfer distributions of internal cooling systems is described. Experimental data and finite element analysis are applied for this method. The investigations considered in this paper are based on experiments performed on a two-pass cooling channel connected by a 180° bend with internal rib arrangements. The solid walls of the cooling channels are made of a metallic material. During the experiment the temperature response of the outer surface induced by heated internal flow is recorded by infrared thermography. The internal heat transfer distribution is obtained using an optimization routine. For each loop of the optimization a transient thermal simulation of the solid body is performed applying the boundary and inlet conditions of the experiment. The temperature of the outer surface calculated by the finite element simulation is compared to the measured temperature recorded by infrared thermography. The difference of these temperature distributions is minimized by adapting the distribution of the internal heat transfer coefficients. The adaptation is conducted on single elements of the inner surface and will be presented in detail in the paper. This approach allows to achieve a high resolution in heat transfer while minimizing the required iterations. The combination of experimental data and finite element analysis allows to consider three dimensional conduction effects in the solid and the streamwise fluid temperature development. Results are compared to literature data.
Evaluation of Lean Axially Staged Combustion by Multi-Sector Combustor Tests Under LTO Cycle Conditions of a Small Aircraft Engine
Authors: Yamamoto Takeshi , Shimodaira Kazuo , Kurosawa Yoji , Yoshida Seiji
Published: November 2013

JAXA is conducting research and development on aircraft engine technologies to reduce environmental impact in the Technology Development Project for Clean Engines (TechCLEAN). As a part of the project, combustion technologies have been developed with an aggressive target that is an 80% reduction over the NOx threshold of the fourth Committee on Aviation Environmental Protection (CAEP/4) of the International Civil Aviation Organization (ICAO). Lean staged fuel nozzles have been developed and tested using a single-sector combustor under Landing and Take-off (LTO) cycle conditions of the target engine with a rated output of 40 kN and an overall pressure ratio of 25.8. A reduction of 82.2% in LTO NOx emissions relative to the ICAO CAEP/4 standard and drastic reductions in smoke and carbon monoxide (CO) emissions were resulted by single-sector combustor tests of a lean staged combustor with an additional premixed fuel nozzle (ECF: Emission Control Fuel nozzle). After the test, the pilot mixer of the single-sector combustor was improved and an additional 2.5% NOx reduction was achieved by combustion tests. As a next step, a multi-sector combustor with ECF was developed and tested. The test results show that the combustor enables a reduction of 82.2% in LTO NOx emissions relative to the ICAO CAEP/4 standard, though unburnt hydrocarbons (HC) and CO emissions are increased. Temperature distributions in the combustor exit plane were also evaluated.
Why Non-Uniform Density Suppresses the Precessing Vortex Core
Authors: Oberleithner Kilian , Terhaar Steffen , Rukes Lothar , Paschereit Christian Oliver
Published: November 2013

Isothermal swirling jets undergoing vortex breakdown are known to be susceptible to self-excited flow oscillations. They manifest in a precessing vortex core and synchronized growth of large-scale vortical structures. Recent theoretical studies associate these dynamics with the onset of a global hydrodynamic instability mode. These global modes also emerge in reacting flows, thereby crucially affecting the mixing characteristics and the flame dynamics. It is, however, observed that these self-excited flow oscillations are often suppressed in the reacting flow, while they are clearly present at isothermal conditions. This study provides strong evidence that the suppression of the precessing vortex core is caused by density stratification created by the flame. This mechanism is revealed by considering two reacting flow configurations: The first configuration represents a detached steam-diluted natural gas swirl-stabilized flame featuring a strong precessing vortex core. The second represents a natural gas swirl-stabilized flame anchoring near the combustor inlet, which does not exhibit self-excited oscillations. Experiments are conducted in a generic combustor test rig and the flow dynamics are captured using PIV and LDA. The corresponding density fields are approximated from the seeding density using a quantitative light sheet technique. The experimental results are compared to the global instability properties derived from hydrodynamic linear stability theory. Excellent agreement between the theoretically derived global mode frequency and measured precession frequency provide sufficient evidence to conclude that the self-excited oscillations are, indeed, driven by a global hydrodynamic instability. The effect of the density field on the global instability is studied explicitly by performing the analysis with and without density stratification. It turns out that the significant change on instability is caused by the radial density gradients in the inner recirculation zone and not by the change of the mean velocity field. The present work provides a theoretical framework to analyze the global hydrodynamic instability of realistic combustion configurations. It allows relating the flame position and the resulting density field to the emergence of a precessing vortex core.
Effects of Shape and Arrangement of Dimples on Film Cooling Performance Over Cutback Surface at Airfoil Trailing Edge
Authors: Nishida Satomi , Murata Akira , Saito Hiroshi , Okita Yoji , Nakamata Chiyuki , Iwamoto Kaoru
Published: November 2013

Trailing edge of a gas turbine blade is under very high thermal load because both sides are exposed to hot mainstream. The cooling film ejected from slots has to protect the cutback surface from the hot mainstream, and remove the heat from the surface. In this study, the film cooling performance of cutback surfaces with two types of dimples, spherical and teardrop-shaped dimples, were experimentally investigated with a transient infrared thermography method. Also, to examine the effects of arrangements, two different arrangements of the teardrop-shaped dimples, which are parallel and inclined to mainstream, were investigated. The dimples were arranged in two rows on the cutback surfaces. The Reynolds number of mainstream defined by the mean velocity and hydraulic diameter was 20,000, and profiles of local heat transfer coefficient and film cooling effectiveness on the cutback surface were measured for blowing ratios of 0.5–2.0. With the parallel teardrop-shaped dimples, reduction of the heat transfer in the upstream portion was less than that of the spherical dimples, and the heat transfer at downstream rims was higher. In the case of the inclined teardrop-shaped dimples, heat transfer enhancement at the downstream rims was higher than that of parallel one, and overall heat transfer coefficient was also higher. The film cooling effectiveness of all cases are almost equal values, namely, the dimpled surfaces could enhance heat transfer without reduction of the film cooling effectiveness; consequently significant cooling performance improvement was obtained for the teardrop-shaped dimple cases, especially with the introduction of inclined arrangement.
Aerodynamic Design of Abradable Liners With Integrated Endwall Treatments for Axial Compressor Rotors
Authors: Mayenberger Tobias , Kau Hans-Peter , Brignole Giovanni
Published: November 2013

In this study endwall treatments, which are integrated into an abradable liner, are used to reduce the liner solidity, defined by the volumetric proportion between endwall treatments and solid casing. Consequently the milled off amount of liner material during the rubbing process is decreased. The mechanical stresses in the rotor blades are thus supposed to be reduced, so that liner materials with higher strength can be used or additional blade tip coatings are dispensable. Accordingly, the purpose of the present study was to develop geometries of endwall treatments, which reduce the liner solidity as much as possible without degrading the stage performance of the test compressor. The focus of the work lies exclusively on the aerodynamics. Investigations were made by steady and unsteady computational fluid dynamics on a transonic single stage axial compressor with two different tip clearance sizes (0.64%/1.28% span). The developed configurations resemble casing treatments, comparable to axial slots and circumferential grooves, which are adapted to the specific tasks of liners. Solidity could be reduced by as much as 29% with negligible efficiency degradation for small tip gaps and increased efficiencies for large tip clearances.
Residence Time Distribution in a Swirling Flow at Non-Reacting, Reacting, and Steam-Diluted Conditions
Authors: Göckeler Katharina , Terhaar Steffen , Paschereit Christian Oliver
Published: November 2013

Residence time distributions in a swirling, premixed combustor flow are determined by means of tracer experiments and a reactor network model. The measurements were conducted at non-reacting, reacting, and steam-diluted reacting conditions for steam contents of up to 30% of the air mass flow.

The tracer distribution was obtained from the light scattering of seeding particles employing the quantitative light sheet technique (QLS). At steady operating conditions, a positive step of particle feed was applied, yielding cumulative distribution functions (CDF) for the tracer response. The shape of the curve is characteristic for the local degree of mixedness. Fresh and recirculating gases were found to mix rapidly at non-reacting and highly steam diluted conditions, whereas mixing was more gradual at dry reacting conditions. The instantaneous mixing near the burner outlet is related to the presence of a large scale helical structure, which was suppressed at dry reacting conditions.

Zones of similar mixing time scales, such as the recirculation zones, are identified. The CDF curves in these zones are reproduced by a network model of plug flow and perfectly mixed flow reactors. Reactor residence times and inlet volume flow fractions obtained in this way provide data for kinetic network models.
Optimization of Forcing Parameters of Film Cooling Effectiveness
Authors: Babaee Hessam , Acharya Sumanta , Wan Xiaoliang
Published: November 2013

An optimization strategy is described that combines high-fidelity simulations with response surface construction, and is applied to pulsed film cooling for turbine blades. The response surface is constructed for the film cooling effectiveness as a function of duty cycle, in the range of DC between 0.05 and 1, and pulsation frequency St in the range of 0.2–2, using a pseudo-spectral projection method. The jet is fully modulated and the blowing ratio, when the jet is on, is 1.5 in all cases. Overall 73 direct numerical simulations (DNS) using spectral element method were performed to sample the film cooling effectiveness on a Clenshaw-Curtis grid in the design space. The geometry includes a 35-degree delivery tube and a plenum. It is observed that in the parameter space explored a global optimum exists, and in the present study, the best film cooling effectiveness is found at DC = 0.14 and St = 1.03. In the same range of DC and St, four other local optimums were found. The physical mechanisms leading to the forcing parameters of the global optimum are explored and ingestion of the crossflow into the delivery tube is observed to play an important role in this process. The gradient-based optimization algorithms are argued to be unsuitable for the current problem due to the non-convexity of the objective function.
Rotorcraft Engine Cycle Optimization at Mission Level
Authors: Goulos Ioannis , Hempert Fabian , Sethi Vishal , Pachidis Vassilios , d’Ippolito Roberto , d’Auria Massimo
Published: November 2013

This work investigates the potential to reduce fuel consumption associated with civil rotorcraft operations at mission level, through optimization of the engine design point cycle parameters. An integrated simulation framework, comprising models applicable to rotorcraft flight dynamics, rotor blade aeroelasticity and gas turbine performance, has been deployed. A comprehensive and computationally efficient optimization strategy, utilizing a novel particle-swarm method, has been structured. The developed methodology has been applied on a twin-engine light and a twin-engine medium rotorcraft configuration. The potential reduction in fuel consumption has been evaluated in the context of designated missions, representative of modern rotorcraft operations. Optimal engine design point cycle parameters, in terms of total mission fuel consumption, have been obtained. Pareto front models have been structured, describing the optimum inter-relationship between maximum shaft power and mission fuel consumption. The acquired results suggest that, with respect to technological limitations, mission fuel economy can be improved with the deployment of design specifications leading to increased thermal efficiency, whilst simultaneously catering for sufficient performance to satisfy airworthiness certification requirements. The developed methodology enables the identification of optimum engine design specifications using a single design criterion; the respective trade-off between fuel economy and payload–range capacity, through maximum contingency shaft power, that the designer is prepared to accept.
Robust Methods for Creep Fatigue Analysis of Power Plant Components Under Cyclic Transient Thermal Loading
Authors: Kostenko Yevgen , Almstedt Henning , Naumenko Konstantin , Linn Stefan , Scholz Alfred
Published: November 2013

The aim of this paper is to apply robust mechanisms-based material laws to the analysis of typical high-temperature power plant components during an idealized start-up, hold time and shut-down sequence under a moderate temperature gradient. Among others a robust constitutive model is discussed, which is able to reflect inelastic deformation, hardening/recovery, softening and damage processes at high temperature. The model is applied for a creep analysis of advanced 9–12%CrMoV heat resistant steels and calibrated in particular case against experimental data for 10%CrMoV steel type. For a steam temperature profile transient heat transfer analysis of an idealized steam turbine component is performed providing the temperature field. From the subsequent structural analysis with the inelastic constitutive model local stress and strain state variations are obtained. As an outcome a multi-axial thermo-mechanical fatigue (TMF) loading loop for one or several loading cycles can be generated. They serve as input for a fatigue life assessment based on the generalized damage accumulation rule, whose results come close to reality. In addition, the accuracy of a simplified method which allows a rapid estimation of notch stresses and strains using a notch assessment rule (NAR) [1] based on Neuber approach is examined.
Modelling of Deposit Mechanisms Around the Stator of a Gas Turbine
Authors: Birello Fabio , Borello Domenico , Venturini Paolo , Rispoli Franco
Published: November 2013

The analysis of particle laden flow in turbines stages is a very actual topic as deposit can alter the blade cooling due to a partial or total blockage of film cooling holes and the modification of heat transfer coefficient between the internal cooling fluid and the blade surface.

A computational tool for predicting particle deposition on a solid surface, developed by the authors, is here applied and validated against literature data. The computational model is based on an Euler-Lagrangian approach with a one-way coupling for the description of the fluid-particles interaction. The deposit model used is based on the paper of Walsh et al., 1990.

The prediction of the fluid phase is carried out by using a URANS (Unsteady Reynolds Averaged Navier Stokes) approach on the well-validate open-source code OpenFOAM widely tested and validated by the authors and many other researchers worldwide in a number of turbomachinery relevant cases.

The numerical campaign was firstly focused on the analysis of the details of the flow field in order to identify the eventual presence and position of shocks as well as to put in evidence the shock/boundary layer interaction.

Then, the trajectories of two class of particles are analyzed in order to determine the influence of drag, pressure and velocity gradient on the particle pattern.

Finally, the adhesion on the blade surface and the influence of flow temperature is discussed.
A Hybrid Immersed Boundary CFD Approach to Oil and Gas Applications
Authors: Mulas Marco , Talice Marco , Grozescu Annabella N.
Published: November 2013

In the past decade a large degree of advancement has been made in CFD labs worldwide, towards the development of Immersed Boundary (IB) CFD methods. The IB method belongs to a new class of numerical methods sometime called mesh-less methods, as no standard meshes that conform to the geometry (or body) need to be generated. The discrete points where the calculation is performed can be freely distributed in the computational domain without great concern for the position of the geometry. The geometry is immersed into a Cartesian grid and the methodology accounts for the effects of the presence of the body in the flow field. The IB method therefore frees up the user from the time consuming and often complicated need for meshing. Plenty of proofs of accuracy and validations are presented yearly at the most prestigious CFD conferences and are available on the internet. Oil and Gas CFD applications are concerned with a variety of internal flow problems. Most of those problems present geometrical complexities, valves for instance, that make a standard body-fitted generation of good quality meshes almost an impossible task. And bad inputs, such as low quality meshes, always determine bad outputs, low quality results. In this paper the KARALIT CFD code based on a class of IB methodology akin to ghost cell methods, is applied to a class of applications encountered often in oil and gas plants, namely a pipeline connecting an arbitrary number of valves, or other devices. While complex valves and devices do make the standard body-fitted approach extremely tedious and difficult, on the other side pipelines are naturally and easily modeled using standard body-fitted cylindrical meshes. The hybrid CFD approach presented will show an automatic implementation of mixed type domain: pipes cylindrical body-fitted meshes are automatically generated by the method and automatically connected to the devices which are treated with the IB method. Examples of lines with arbitrary number of devices will be shown. Result and key performance parameters are provided from the IB CFD calculations and key conclusions about the line characteristic are drawn.
CFD Analysis of an Annular Micro Gas Turbine Combustion Chamber Fuelled With Liquid Biofuels: Preliminary Results With Bioethanol
Authors: Laranci Paolo , Bidini Gianni , Desideri Umberto , Fantozzi Francesco
Published: November 2013

Liquid biofuels, such as bioethanol, biodiesel and vegetal oils, can effectively be used in internal combustion engines blended with liquid fuels of fossil origin or in their substitution, allowing a reduction of CO2 and pollutant emissions in the atmosphere. This work is supported by a CFD analysis to study the feasibility of using these fuels derived from biomass in a 80 kWel micro gas turbine, originally designed for operation with natural gas. In this paper preliminary results about the behavior of bioethanol in the MGT combustion chamber are presented. The complete investigation however includes biodiesel and also glycerin, a byproduct of biodiesel production. To carry out the computational simulations, combustion models included in a commercial software and oxidation mechanism of ethanol taken from the literature were used. The geometry of the NG injector was modified to optimize the liquid inlet into the combustor. Simulation results in terms of temperatures, pressures, and emissions were compared with data available for natural gas combustion in the original combustion chamber.
Finger Seal Design Based on Fluid-Solid Interaction Model
Authors: Temis Joury M. , Selivanov Alexey V. , Dzeva Ivan J.
Published: November 2013

Multidisciplinary mathematical simulation technique is developed for static and dynamic analyses of a high-efficient finger seal. It comprises gas flow simulation and stress-deformed analysis of compliant fingers based on simplified models and seal performance evaluation by two-way fluid-solid interaction coupling. Computation time for developed fast models is significantly less than for time-consuming traditional numerical 3D approaches meanwhile the accuracy of the simplified models is sufficient for preliminary investigation of finger seal design features. The developed models allow to introduce the simple iterative algorithm to solve the inverse problem of mathematical simulation and to design the finger seal, satisfying the specified requirements for the radial displacements of the fingers. Initial dynamic analysis is performed on the basis of equivalent one-mass model allowing to estimate finger response to the rotor deflections.
A Numerical Investigation on Counterflow Flames of Biodiesel/Diesel Surrogate Blends
Authors: Han X. , Aggarwal S. K.
Published: November 2013

There is significant interest in increasing the use of biodiesel fuels especially by blending them with petroleum diesel. Biodiesels typically consist of long-chain saturated and unsaturated hydrocarbons along with an alkyl (methyl, ethyl or butyl) ester functional group. Previous studies have demonstrated that the combustion and emission characteristics of biodiesel fuels are mostly determined by the hydrocarbon chain length and the number and location of unsaturated bonds in their molecular structure. The present study aims to characterize the combustion and emission behavior of biodiesel/diesel surrogate blends by simulating PPFs burning blends of n-heptane, methyl decanoate and methyl-9-decenoate. A recently developed reduced mechanism for these blends is employed, and the effects of the blend composition on NOx and PAH emissions from these flames are examined. Results indicate that NOx emissions are only slightly reduced by the addition of C10 methyl esters. However, the formation of PAH precursors is noticeably affected by the surrogate blend. Results also indicate the need for further improving the reduced mechanism, especially with regards to some key reactions and species, which are important for accurately predicting the intermediate hydrocarbon species including PAH precursors.
Impact of Shear Flow Instabilities on the Magnitude and Saturation of the Flame Response
Authors: Terhaar Steffen , Ćosić Bernhard , Paschereit Christian Oliver , Oberleithner Kilian
Published: November 2013

Amplitude-dependent flame transfer functions, also denoted as flame describing functions, are valuable tools for the prediction of limit-cycle amplitudes of thermoacoustic instabilities. However, the effects that govern the transfer function magnitude at low and high amplitudes are not yet fully understood. It is shown in the present work that the flame response at perfectly premixed conditions is dominated by the growth rate of vortical structures in the shear layers. An experimental study in a generic swirl-stabilized combustor was conducted in order to measure the amplitude-dependent flame transfer function and the corresponding flow fields subjected to acoustic forcing. The applied measurement techniques included the Multi-Microphone-Method, high-speed OH*-chemiluminescence measurements, and high-speed Particle Image Velocimetry. The flame response and the corresponding flow fields are assessed for three different swirl numbers at 196 Hz forcing frequency. The results show that forcing leads to significant changes in the time-averaged reacting flow fields and flame shapes. A triple decomposition is applied to the time-resolved data, which reveals that coherent velocity fluctuations at the forcing frequency are amplified considerably stronger in the shear layers at low forcing amplitudes than at high amplitudes, an indicator for a nonlinear saturation process. The strongest saturation is found for the lowest swirl number, where the forcing additionally detached the flame. For the highest swirl number, the saturation of the vortex amplitude is weaker. Overall, the amplitude-dependent vortex amplification resembles the characteristics of the flame response very well. An application of linear stability analysis to the time-averaged flow fields at increasing forcing amplitudes yields decreasing growth rates of shear flow instabilities at the forcing frequency. It therefore successfully predicts a saturation at high forcing amplitudes and demonstrates that the mean flow field and its modifications are of utmost importance for the growth of vortices in the shear layers. Moreover, the results clearly show that the amplification of vortices in the shear layers is a dominant driver for heat release fluctuations and their saturation.
Combustion Instability in a Swirl Flow Combustor With Transverse Extensions
Authors: Saurabh Aditya , Paschereit C. O.
Published: November 2013

The present investigation is an analysis of self-excited combustion instability in a swirl flame-based combustor with transverse extensions. Transverse extensions create the possibility of studying flame interaction with transverse acoustic oscillations. Such investigation important for understanding the phenomenon of thermoacoustic instability in annular combustors, where during thermoacoustic instability, azimuthal acoustic modes of the combustor couple with the multiple flames of the combustor. Flame and flow field dynamics during self-excited thermoacoustic instability in the single burner test-rig is presented here. These results are then compared to the dynamics of the isothermal and reacting flows in response to axial and transverse acoustic forcing. Both axial and transverse forcing led to the formation of axisymmetric shear layer vortices. Adding to the insight gained from previous investigations, these results suggest that that swirl flow dynamics in response to transverse acoustics consists of a non-trivial, direct effect of transverse acoustics on the flow field, in addition to its response to longitudinal fluctuations induced by transverse forcing.
An Integrated Assessment of an Organic Rankine Cycle Concept for Use in Onboard Aircraft Power Generation
Authors: Perullo Christopher A. , Mavris Dimitri N. , Fonseca Eduardo
Published: November 2013

It is well established that there are advantages in moving towards non-pneumatic engine secondary systems. Such systems are used primarily to provide pressurization, cabin climate control, and de-icing; however, as bypass ratios continue to grow and engine cores become more efficient, the engine fan diameter is increased and core size is diminished. As a consequence, pneumatic off-takes require a larger percentage of the core flow leading to larger performance penalties. One current solution is to drive the aircraft environmental control systems (ECS) with large engine driven electric compressors rather than to use high pressure air from the core. Since cores are generally less sensitive to electrical power off-takes than to pneumatic off-takes this results in a smaller performance penalty. [F1] Using electrical air compressors also ensures fresh, clean air is delivered to the ECS thereby eliminating the risk of engine bleed contaminated cabin air.

This research uses the Environmental Design Space (EDS) to examine the feasibility of recovering engine core exhaust heat to perform useful work within the aircraft. EDS serves to capture interdependencies at the conceptual design level of fuel burn, emissions, and noise for conventional and advanced engine and airframe architectures [F2]. Recovering exhaust heat is accomplished through a novel concept that makes use of an organic Rankine cycle (ORC).The concept is similar in principle to heat recovery steam generators used in power plant applications to improve combined cycle efficiency [3]. The main difference is the ORC system is relatively lightweight and appropriate for use onboard an aircraft. The waste heat in this application is used to generate electricity to drive external air compressors to supply flow to the ECS. As a result pneumatic bleeds within the engine can be eliminated, thereby eliminating growing performance penalties associated with shrinking core size and increased fan diameters. An ORC is considered because ORC cycles are ideal for extracting low grade heat. As an additional benefit the ORC vapor cycle can use the fan inlet and wing leading edge anti-ice devices as a condensation heat transfer mechanism that could also allow the system to provide anti-icing capabilities, further reducing engine pneumatic off-takes. The current research focuses on the system as applied the ORC concept to a CFM56 sized engine and has analytically demonstrated from a 0.9% to a 2.5% benefit in vehicle fuel burn relative to a conventional, pneumatically driven ECS. Actual fuel burn savings are dependent on the net installation weight of the ORC cycle.
Spray Characteristics of Fischer-Tropsch Alternate Jet Fuels
Authors: Kannaiyan Kumaran , Sadr Reza
Published: November 2013

Increase in energy demand and stringent emission norms drive the need for clean, alternative energy source. Recently, gas-to-liquid (GTL), a synthetic jet fuel produced from natural gas using Fischer-Tropsch synthesis has grabbed global attention due to its cleaner combustion aspects when compared to the conventional jet fuel. The chemical and physical properties of GTL fuels are different from the conventional fuels which could potentially affect the atomization and in turn the combustion characteristics and pollutant formation. In this work the spray characteristics of two GTL blends and conventional Jet A-1 fuels are investigated downstream of a pressure swirl nozzle exit at two injection pressures and the results are then compared. Microscopic spray characteristics, droplet size and velocity distributions are obtained at global as well as local levels of the spray using global sizing velocimetry and phase Doppler anemometry measurement techniques, respectively. Results clearly show that although the GTL fuels have different physical properties, such as viscosity, density, and surface tension the spray characteristics of the GTL fuels are found to be similar to those of Jet A-1 fuel.