bluuebunny/crossref_metadata_2025 huggingface dataset:
Mission Performance Simulation of Integrated Helicopter–Engine Systems Using an Aeroelastic Rotor Model
Authors: Goulos Ioannis , Giannakakis Panos , Pachidis Vassilios , Pilidis Pericles
Published: November 2013

This paper presents an integrated approach, targeting the comprehensive assessment of combined helicopter–engine designs, within designated operations. The developed methodology comprises a series of individual modeling theories, each applicable to a different aspect of helicopter flight dynamics and performance. These relate to rotor blade modal analysis, three-dimensional flight path definition, flight dynamics trim solution, aeroelasticity and engine performance. The individual mathematical models are elaborately integrated within a numerical procedure, solving for the total mission fuel consumption. The overall simulation framework is applied to the performance analysis of the Aérospatiale SA330 helicopter within two generic, twin-engine medium helicopter missions. An extensive comparison with flight test data on main rotor trim controls, power requirements and unsteady blade structural loads is presented. It is shown that, for the typical range of operating conditions encountered by modern twin-engine medium civil helicopters, the effect of operational altitude on fuel consumption is predominantly influenced by the corresponding effects induced on the engine, rather than on airframe–rotor performance. The implications associated with the implicit coupling between aircraft and engine performance, are discussed in the context of mission analysis. The potential to comprehensively evaluate integrated helicopter–engine systems within complete three-dimensional operations, using modeling fidelity designated for main rotor design applications, is demonstrated. The proposed method essentially constitutes an enabler in terms of focusing the rotorcraft design process on designated operation types, rather than on specific sets of flight conditions.
Equivalence Ratio Startup Control of a Fuel Cell Turbine Hybrid System
Authors: Tucker David , Pezzini Paolo , Banta Larry
Published: November 2013

Initial startup of a direct-fired fuel cell turbine power system with equivalence ratio control using cathode air bypass valves to minimize thermal shock to the fuel cell was evaluated using the Hybrid Performance (Hyper) project hardware-based simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory. The turbine in the system was started with the minimum possible airflow through the fuel cell cathode from a cold condition using two bypass valves to mitigate thermal shock failure in the fuel cell. The limitation of bypass flow was set by air requirements to maintain a combustor equivalence ratio below 0.6 during turbine windup. A 1D distributed fuel cell model operating in real time was used to produce individual cell transient temperature profiles during the course of the turbine start. The results provide insight into the procedural requirements of starting a fully coupled hybrid system.
Comparative Experimental Investigation on Aerodynamic Performance of Steam Turbine Cascades: Part I — Rotor Blades
Authors: Gao Lei , Zheng Qun , Chen Hang
Published: November 2013

In this paper, the static aerodynamic performance of the second to last stage rotor blades of a marine steam turbine is experimentally investigated. The experiments have been carried out for both original blade (ORI R1) and modified blade (MOD R1) annular cascades. The experimental results indicate that the straight original blade is aft-loaded type, and there is a large degree of diffusion at the tip end wall. The improvement methods include adopting twist blades, adjusting the blade profile to reach the aft-loaded as much as possible at both end walls as well as combining with the cylindrical meridian lines. It has been found in the experiment that the transverse pressure gradient of the modified decreases at both end walls, so does the loss of the flow, especially it weakens the secondary flow at the tip end wall. The aerodynamic loss coefficient of improved blades has reduced by about 25%.
Influence of Local Surface Roughness of Rotor Blade on Performance of an Axial Compressor Stage
Authors: Chen Shaowen , Sun Shijun , Xu Hao , Zhang Longxin , Wang Songtao , Zhang Tian
Published: November 2013

The influence of local surface roughness of rotor blades on the performance of axial compressor stages were investigated through numerical simulation with local surface roughness added on the suction and pressure surfaces of rotor blades of realistic compressor stage NASA Stage35. First of all, the reliability of a commercial computational fluid dynamic code was validated and the computed performance maps showed a good agreement with experimental data from literatures. Numerical results indicated that the increase in surface roughness in most of the local positions may cause the deterioration of compressor stage performance. The amplitude of decrease in compressor performance due to the addition of surface roughness in outer and inner portions of the span and the area near the leading edge of the rotor blades would be much greater than that in the region near the trailing edge. The roughness added to the pressure surface near the leading edge had less impact on the stage characteristics, including the mass flow rate at the choked point. Thus the compressor characteristic got close to that under normal conditions and showed a wider stable operating range. The mass flow in the choked region and the adiabatic efficiency were less affected by the roughness added to the region near the trailing edge of pressure surface from rotor blades. However, this scheme mentioned before would increase the total pressure ratio to some extent, with the adverse effect of adding roughness on the corresponding suction surface.
Numerical Investigation of the Plane-Wave Reflection Coefficient of an Exhaust Pipe at Elevated Temperatures Using Linearized Navier-Stokes Equations
Authors: Jörg Christoph , Gikadi Jannis , Sattelmayer Thomas
Published: November 2013

When modeling gas turbine sound emissions an important boundary condition is the acoustic reflection coefficient at the engine exhaust. Here, the flow discharges into atmosphere at elevated temperature and high flow velocity. The exit reflection coefficient governs the proportion of engine core noise that is radiated into the far-field as well as the acoustic energy contained inside the engine. In addition to pure jet noise, the core noise transmitted through the exit boundary contributes to the overall acoustic emission of an engine, particularly in the audible low frequency regime. In this paper we investigate the plane-wave reflection coefficient at the jet exhaust for a series of different jet Mach numbers and temperatures by solving the linearized Navier-Stokes equations (LNSEs) in frequency space using a finite element method. This approach accounts for effects of mean flow, i.e. scattering and refraction in shear layers, as well as acoustic interaction with unstable shear layers and entropy fluctuations. Their combined effect may cause amplification or attenuation of incident acoustic waves. Applicability and accuracy of the LNSE approach are validated for a set of ambient flow cases at different Mach numbers where a broad base of experimental data and theoretical models is available from literature. Consecutively, the numerical experiment is extended to significantly higher flow temperatures for which few publications exist. The results for elevated flow temperatures show a considerable decrease in the reflection coefficient magnitude with increasing flow temperature. These computations are compared to results obtained from the theory derived by Munt [1,2] and differences are assessed.
Adaptive Flow Field Thermal Modeling Techniques for Turbine Rotor-Stator Cavities
Authors: Rey Villazón Jose Maria , Berthold Martin , Kühhorn Arnold
Published: November 2013

At preliminary design stages of the turbine discs design process, reducing uncertainty in the thermal prediction of critical parts models is decisive to bid a competitive technology in the aerospace industry. This paper describes a novel approach to develop adaptive thermal modeling methods for non-gaspath turbine components. The proposed techniques allow automated scaling of disc cavities during preliminary design assessment of turbine architectures.

The research undertaken in this work begins with an overview of the past investigations on the flow field in cavities of the air system surrounding the turbine discs. A theoretical approach is followed to identify the impact of the design geometry and operation parameters of a simplistic rotor-stator cavity, with special focus on swirl and windage effects. Then, a parametric CFD process is set up to conduct sensitivity analysis of the flow field properties. The CFD sensitivity analysis confirmed the parameter influences concluded from the theoretical study.

The findings from the CFD automated studies are used to enhance the boundary conditions of a thermal FE-model of an actual high pressure turbine. The new set of thermal boundary conditions adapts the flow field to changes in the cavity parameters. It was found that the deviation to experimental data of the traditional preliminary modeling technique is about 4 times higher as the deviation of the CFD-enhanced technique. When running the FE-model through a transient cycle, the results from the CFD-enhanced method are significantly closer to the test data than those from the traditional method, which suggests there is high potential for using these adaptive thermal techniques during turbine preliminary design stages.
Influence of the Inflow Confinement on the Flashback Limits of a Premixed Swirl Burner
Authors: Seidel V. , Marosky A. , Hirsch C. , Sattelmayer T. , Geng W. , Magni F.
Published: November 2013

This work presents a study of the effect of the inflow condition on the flame flashback performance of a gas turbine burner. A generic swirl burner for basic combustion research on engine scale is investigated both under atmospheric conditions in a combustion test rig and numerically to reveal the impact of inflow conditions on the burner stability. Flashback resistance is examined with highly reactive hydrogen fuel and numerical studies with isothermal large eddy simulations (LES) are performed to investigate transient flow field data. Earlier publications showed excellent flashback resistance of a down scaled burner version of similar design, which was tested in a rig with strongly restricted cross sectional inflow area. An influence of the test rig setup on the flashback limits was not expected. However, the results presented in the paper reveal that the inflow conditions at the swirler and the distribution of axial velocity inside the swirler are crucial for flame stability. The inflow conditions upstream of the swirler were modified to redistribute the axial velocity field inside the swirler. Velocity fluctuations both inside the swirler and downstream of the burner outlet were reduced and consequently the susceptibility to perturbations in the flow field. This measure prevents the formation and propagation of local zones of negative axial velocity upstream of the flame position and increases the robustness of the flow field. After modification of the inflow condition the excellent flashback limit data of the down scaled burner was fully reproduced.
Thermoacoustic Analysis of a Full Annular Lean Burn Aero-Engine Combustor
Authors: Andreini Antonio , Facchini Bruno , Giusti Andrea , Vitale Ignazio , Turrini Fabio
Published: November 2013

In order to reduce NOx emissions, modern gas turbines are often equipped with lean burn combustion systems, where the engine operates near the lean blow-out limits. One of the most critical issues of lean combustion technology is the onset of combustion instabilities related to a coupling between pressure oscillations and thermal fluctuations excited by the unsteady heat release. In this work a thermoacoustic analysis of a full annular combustor developed by AVIO is discussed. The system is equipped with an advanced PERM (Partially Evaporating and Rapid Mixing) injection system based on a piloted lean burn spray flame generated by a pre-filming atomizer. Combustor walls are based on multi-perforated liners to control metal temperature: these devices are also recognized as very effective sound absorbers, thus in innovative lean combustors they could represent a good means both for wall cooling and damping combustion instabilities. The performed analysis is based on the resolution of the eigenvalue problem related to an inhomogeneous wave equation which includes a source term representing heat release fluctuations (the so called Flame Transfer Function, FTF) in the flame region using a three-dimensional FEM code. A model representing the entire combustor was assembled including all the acoustically relevant geometrical features. In particular, the acoustic effect of multi-perforated liners was introduced by modeling the corresponding surfaces with an equivalent internal impedance. Different simulations with and without the presence of the flame were performed analyzing the influence of the multi-perforated liners. Furthermore, different modeling approaches for the FTF were examined and compared with each other. Comparisons with available experimental data showed a good agreement in terms of resonant frequencies in the case of passive simulations. On the other hand, when the presence of the flame is considered, comparisons with experiments showed the inadequacy of FTFs commonly used for premixed combustion and thus the necessity of an improved FTF, more suitable for liquid fueled gas turbines where the evaporation process could play an important role in the flame heat release fluctuations.
Design and Numerical Flow Analysis of a LNG Power Recovery Turbine
Authors: Li Kaiqiang , Sun Jinju , Fu Juntao , Song Peng
Published: November 2013

The liquefaction process of natural gas often operates at high pressure level, thus the LNG product is of very high pressure and must be reduced to satisfy the technical requirement for storage and transportation. Traditionally, the high-pressure LNG is expanded isenthalpically by means of J-T valves but this introduces an unexpected temperature rise, leading to vaporization of LNG product and subsequently a reduced delivery. An efficient alternative is using the LNG expanders to replace the J-T valves and achieve a near-isentropic expansion and subsequently suppress the cavitation. In the present study, a single stage LNG turbine expander is developed as a replacement of J-T valve for the purpose of cavitation suppression. The cavitating flow behavior is investigated by using a multiphase cavitation model. The effect of impeller geometric parameters on the turbine flow and performance has been identified through sensitivity studies. The following are demonstrated: (1) The predicted turbine overall efficiency is 91.34%, shaft power delivery is 81.16kW, temperature drop is 0.84 K; and the overall vaporization rate is less than a percentage. (2) Cavitation is encountered in the impeller leading edge region and half stream-wise region, resulting respectively from the viscous dissipation and flow separation. (3) At larger than design flow rates, the predicted turbine overall efficiency decreases nonlinearly with the flow rate due to cavitation zone growth in the leading edge region; at lower than design flow rates, the overall efficiency increases with the flow rate, due to cavitation zone decrease in the half streamwise region. (4) Cavitating flow behavior is sensitive to impeller geometry tuning. Variation of the impeller inducer twist angle reduces the trialing edge cavitation and subsequently improves the turbine overall performance. (5) Cavitation flow behavior is also sensitive to the radial gap size of the nozzle and impeller.
Effect of Boundary Layer Suction on Aerodynamic Performance of High-Turning Compressor Cascade
Authors: Zhang Longxin , Chen Shaowen , Xu Hao , Ding Jun , Wang Songtao
Published: November 2013

Compared with suction slots, suction holes are (1) flexible in distribution; (2) alterable in size; (3) easy to fabricate and (4) high in strength. In this paper, the numerical and experimental studies for a high turning compressor cascade with suction air removed by using suction holes in the end-wall at a low Mach numbers are carried out. The main objective of the investigation is to study the influence of different suction distributions on the aerodynamic performance of the compressor cascade and to find a better compound suction scheme. A numerical model was first made and validated by comparing with the experimental results. The computed flow visualization and exit parameter distribution showed a good agreement with experimental data. Second, the model was then used to simulate the influence of different suction distributions on the aerodynamic performance of the compressor cascade. A better compound suction scheme was obtained by summarizing numerical results and tested in a low speed wind tunnel. As a result, the compound suction scheme can be used to significantly improve the performance of the compressor cascade because the corner separation gets further suppressed.
Validation of Surface Pressure Predictions for Nozzle Airfoil and Endwall Film Cooling Design Using Transonic Cascade Measurements
Authors: Dees Jason E. , Tallman James A. , Heminger Michael A. , Wilde Daniel
Published: November 2013

This study compares surface pressure measurements and predictions for a high pressure turbine first-stage nozzle vane. The surface pressure measurements were taken in a 3D annular cascade, consisting of four airfoils and five passages. The cascade was uncooled, axisymmetric at both inner and outer endwalls, and reproduced the design intent Reynolds and Mach numbers of the real engine component. Static pressure measurements were taken along the airfoil profile at 15, 50, and 85% span, with duplicate midspan measurements across the four airfoils for assessing the tangential periodicity of the flow. Static pressure measurements were also taken on the inner and outer endwall surfaces of the center airfoil passage, with 40 measurement points uniformly distributed over each endwall. Three methods of surface pressure prediction were compared with the data: (1) a 2D inviscid CFD solution of a single airfoil passage at fixed spanwise locations, (2) a 3D RANS CFD solution of a single airfoil passage, and (3) a 3D RANS CFD solution of the full five-passage cascade domain. Both of the single-passage solutions assumed flowfield periodicity in the tangential direction and compared favorably to the center passage airfoil data. This finding suggested that the cascade center passage was sufficiently representative of the full-annulus turbomachine environment and validated the cascade for further experimental studies. The adjacent airfoil pressure measurements quantified the passage-to-passage variation in the cascade flowfield, and the 3D full-cascade CFD compared favorably with the peripheral airfoil data. The full-cascade CFD also compared favorably with the data on both endwalls: with an average and maximum deviation of 0.5 and 2%, respectively. These findings provide confidence in the 3D CFD methods for use in determining local flow rates from cooling/leakage geometry, and serve as an important first step toward validating the methods for real-engine blockage effects like coolant and endwall contouring.
Evaluation of NiCrAl Foil for a Concentrated Solar Power Application
Authors: Pint Bruce A. , Anderson Bruce N. , Matthews Wendy J. , Waldhelm Chris M. , Treece William
Published: November 2013

A NiCrAl-type foil (alloy 214) was selected for evaluation for heat exchanger applications for a concentrated solar power (CSP) system. Due to the formation of a protective alumina surface oxide, this class of alloys can operate at higher temperatures than conventional stainless steels or even Ni-base alloys, such as alloy 625. Laboratory testing is being conducted at 1000° and 1050°C in dry air using 10 h thermal cycles in order to simulate the CSP duty cycle at a high temperature to accelerate the degradation process. Mass change data showed indications of degradation of the foils with exposures up to 8,000 h. Foil specimens also were stopped after 2,400 h to measure the loss of Al in the foil as a method to predict lifetime. Previous lifetime modeling results for 1h cycles in air with 10%H2O provided an initial basis to predict lifetime for this material to >100,000 h operating times as a function of foil thickness and exposure temperature for this application.
Simulation of Static Performance of Air Foil Bearings Using Coupled FEM and CFD Techniques
Authors: Paouris Leonidas I. , Bompos Dimitrios A. , Nikolakopoulos Pantelis G.
Published: November 2013

The main objective of the current work is to determine a relationship between the top and bump foil’s geometry and load carrying capacity in a journal compliant air foil bearing. Static and steady state operation is assumed throughout the analysis. A finite element model is adopted in order to investigate the operational characteristics of the specific bearing. Bump foil’s elastic behavior is modeled using two node linear spring elements. During fluid analysis, compressible viscous steady state Navier-Stokes equations are numerically solved. The material used during the structural analysis is Inconel X750 and it is assumed that it has linear and elastic behavior. Thermal effects are not taken under consideration. Constant ambient pressure is applied at the free faces of the fluid as well as no slip condition at the surface of the fluid that faces the top foil. CFD and structural models are solved separately. At the beginning of the analysis CFD problem is solved with the assumption that the top foil has not yet been deformed. After the solution of the CFD problem, the pressure distribution at the surface of the fluid that faces the top foil is applied at the top foil and then the structural problem is solved. Consequently the deflections of the top foil are applied on the corresponding surface of the CFD model and the algorithm continues until convergence is obtained. As soon as the converged solution for the pressure distribution is obtained, numerical integration is performed along the surface of the bearing in order to calculate its load carrying capacity. The same procedure is repeated for different values of bump foil thickness, height and pitch in order to define a pattern that describes the bearing’s load carrying capacity as a function of the geometric parameters of the structural problem. Static bearing performance characteristics, such as pressure distribution, bump foil deflection and load capacity are calculated and presented. Furthermore fluid film thickness, top foil deflection and fluid pressure are investigated as functions of the bearing angle as well as load carrying capacity as a function of the bump and top foil stiffness. Finally, a simple thermal analysis is incorporated in order to estimate the temperature rise in the CFD domain due to viscous heat.
Basic Research of Wetness Effects in a Steam Turbine: Experimental Investigations Using Turbine Cascade Tests
Authors: Watanabe Eiichiro , Ooyama Hiroharu , Tsutsumi Masanori , Tanaka Yoshinori , Satsuki Hiroshi , Tabata Soichiro
Published: November 2013

Detailed understanding and evaluation of the wetness effects have become important with high pressure wet steam applications in nuclear power plant and developments with longer last stage blades. In order to simplify the phenomena and to understand the basic behavior of the water droplets in the blade passages, air cascade tests with water sprays have been conducted. The water droplet motion in turbine cascade and the effects of wetness and droplet size on the wetness loss have been experimentally investigated. Total energy loss has been measured using a three-hole pressure tube and water droplets size and velocity has been measured using phase Doppler particle analyzer in a linear cascade.
Modeling Unsteady Flow of a Lean Partially Premixed Flame on a Dry Low NOx Combustion System
Authors: Matarazzo Salvatore , Laget Hannes , Vanderhaegen Evert , Kok Jim B. W.
Published: November 2013

The phenomenon of combustion dynamics (CD) is one of the most important operational challenges facing the gas turbine (GT) industry today. The Limousine project, a Marie Curie Initial Training network funded by the European Commission, focuses on the understanding of the limit cycle behavior of unstable pressure oscillations in gas turbines, and on the resulting mechanical vibrations and materials fatigue. In the framework of this project, a full transient CFD analysis for a Dry Low NOx combustor in a heavy duty gas turbine has been performed. The goal is to gain insight on the thermo-acoustic instability development mechanisms and limit cycle oscillations. The possibility to use numerical codes for complex industrial cases involving fuel staging, fluid-structure interaction, fuel quality variation and flexible operations has been also addressed. The unsteady U-RANS approach used to describe the high-swirled lean partially premixed flame is presented and the results on the flow characteristics as vortex core generation, vortex shedding, flame pulsation are commented on with respect to monitored parameters during operations of the GT units at Electrabel/GDF-SUEZ sites.

The time domain pressure oscillations show limit cycle behavior. By means of Fourier analysis, the coupling frequencies caused by the thermo-acoustic feedback between the acoustic resonances of the chamber and the flame heat release has been detected. The possibility to reduce the computational domain to speed up computations, as done in other works in literature, has been investigated.
Comparative Study of Solar Thermal Brayton Cycles Operated With Helium or Argon
Authors: Kusterer Karsten , Braun René , Moritz Norbert , Sugimoto Takao , Tanimura Kazuhiko , Bohn Dieter
Published: November 2013

Concentrating Solar Power (CSP) plants often use Rankine cycles operated with water/steam as energy conversion cycles. Since the solar central receiver technology could provide receiver fluid outlet temperatures higher than 900°C, open and closed gas turbine technologies become a promising alternative. Closed solar Brayton cycles operating with appropriate fluids can reach similar or higher thermal efficiencies than water/steam Rankine cycles but have the advantage of less consumption of fresh water.

This paper presents the results of a comparative thermodynamic and process study of closed solar thermal Brayton cycles operated with Helium or Argon as working fluids. The main components of the cycles are two axial compressors with an intercooler, a recuperator and one axial turbine. The solar heat is fed in by a central receiver technology. It is assumed that the transferred heat to the cycles is constant and the turbine inlet temperature is 900°C.

A first one-dimensional design approach for both cycles is performed based on the results of the thermodynamic considerations. The major parameters like stage types, number of stages, rotational speed, etc. are determined and discussed.

The thermodynamic and process investigation results for the described closed Brayton cycles show that thermal efficiencies over 46% can be established for both fluids. The design considerations show that both cycles are feasible, but with respect to design dimensions the Argon based cycle can be built up with fewer stages and more compact, if compared to the Helium cycle.
Large Eddy Simulations of Turbofan Engine Exhaust Plume Dispersion on Take-Off Runway
Authors: Spanelis Apostolos , Garry Kevin , Savill Mark
Published: November 2013

The pollution generated by the aircraft engines at the start of the take-off run is an important contributor to the local air quality in proximity to airports. The installation of an array of baffles in the runway strip behind the start of the runway, a configuration aiming to accelerate the lift-off of the exhaust plume, is numerically investigated. Validation tests are carried out in an effort to limit the computational cost. In this way, experimental data, including mean and RMS velocity profiles, as well as passive scalar concentrations, have been referenced. Additionally, a Dynamic Response Algebraic Model for Baffle Imitation (DRAMBI) has been devised. The numerical model is presented and tested. Experimental data obtained in the Atmospheric Boundary Layer Wind Tunnel (ABLWT) of Cranfield University, including drag force measurements and passive scalar concentrations, are used for the validation of the model. The predictions of DRAMBI are also compared to the results of conventional simulations including the baffle geometries. In this way, two-dimensional volume sections of mean and RMS contours of velocity and passive scalar, are presented and analysed. Finally, the axial momentum reduction required so that buoyancy becomes dominant and the plume naturally lifts-off, is investigated.
Highest-Efficient Film Cooling by Improved NEKOMIMI Film Cooling Holes: Part 1 — Ambient Air Flow Conditions
Authors: Kusterer Karsten , Tekin Nurettin , Reiners Frederieke , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo , Kazari Masahide
Published: November 2013

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is a today common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for manufacturing even by advanced manufacturing processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations much easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under ambient air flow conditions similar to conditions for a wind tunnel test rig. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. A set of most promising configurations has been also investigated experimentally in the test rig. The best configuration outperforms the basic configuration by 17% regarding the overall averaged adiabatic film cooling effectiveness under the experimental conditions.
Alternative Microturbine Fuels Feasibility Study Through Thermal Stability, Material Compatibility and Engine Testing
Authors: Quintero S. Arias , Schmitt J. , Blair R. , Kapat J.
Published: November 2013

Historically, gas turbine fuels have been procured based on availability and low cost criteria. But in the last few decades, with the growing concern over the negative environmental impacts produced by emissions, alternative fuels have been developed and tested with the objective to reduce such negative effects. Physical properties and the broad chemical composition, including trace elements, may result in engine performance issues found only after extensive operation. This, in turn, results in higher maintenance and operation costs. This paper studies the feasibility for microturbine application of several renewable fuels, identifying key relationships between physical and chemical properties, thermal stability, materials compatibility, and turbine performance.
Design and Operating Experience on the Recent Application of the Fuel Staging Technology for AE94.3A Gas Turbine
Authors: Alecci Marco , Bulli Alessia , Gottardo Enrico , Mori Giulio , Piana Carlo , Rio Roberto , Rizzo Sergio , Zito Domenico
Published: November 2013

The paper describes the experience made on the first, recent application of the fuel staging technology on AE94.3A gas turbine engine. The experience started in the frame of combustion upgrade projects by the beginning of 2011 when some conceptual ideas rose.

The most effective solution was found in the application of radial fuel staging through the modification of an existing, dual fuel, diagonal swirler. CFD calculation was carried out in order to evaluate numerically the differences that the introduction of the radial fuel staging would have brought in comparison with the standard, reference configuration. After that one promising solution was selected and applied to a prototype, the test phase started. The experimental test was initially performed at the engine conditions on a high pressure test rig. The rig architecture was designed to be as representative as possible of the GT annular combustion chamber. The rig was equipped with the most advanced instrumentation in order to monitor and store all the main parameters of the burner during the test. High pressure tests showed a good agreement with the CFD calculation and an effective capability of the prototype to stage the fuel by generating a “co-pilot” flame. The word “co-pilot” was coined for the behaviour of the resulting flame to act as a second pilot in supporting and stabilizing the main premix flame. The on site validation was carried out on Enel La Casella GT1 power plant, downstream the upgrade of the gas turbine with the last recent AE94.3A model. The validation phase was performed according to two separate sessions: the first one using the standard, reference burner solution and the second one with the radial staged configuration.

The advantage of the fuel staging technique was twofold. The first one was concerning the minimum environmental load: the contribution of the fuel staging was approximately 7 MW. The second one was concerning the global performance of the whole combined cycle power plant at the base load. It was possible to increase turbine inlet temperature of about 30 °C and the GT power output of about +7% in comparison with the standard, reference burner solution.
Comparison of Thermal Stability Characteristics of Fischer-Tropsch and Hydroprocessed Alternative Jet Fuels in a Fixed Bed Reactor
Authors: Quintero S. Arias , Schmitt J. , Blair R. , Nash D. , Kapat J.
Published: November 2013

The recent volatility in oil prices has fueled uncertainty about the world’s ability to meet future demands. Furthermore, the growing concern over the negative environmental impacts produced by emissions has resulted in worldwide efforts for developing renewable jet-fuel alternatives. This has led current military and civilian fuel specifications to allow the use of Fischer-Tropsch (FT) and Hydroprocessed fuels (HEFA) in blends up to 50% in volume with regular Jet-A/JP-8. On the other hand, physical properties, and the broad chemical composition, including trace elements in those fuels, may result in engine performance issues found only after extensive operation. This may result in higher maintenance and operation costs. This study presents the coking depositions of several renewable fuels after being stressed in a fixed bed reactor. This was done in an effort to assess the effects (if any) on the thermal stability of renewable fuels interacting with materials representative of state of the art aircraft systems (steel, aluminum, titanium tubing) and to determine whether the use of renewable fuels enhances thermal stability when blended, up to 50%, with oil-derived fuels.
Autoignition Properties of Fossil- and GTL-Kerosene and its Model Fuel
Authors: Eigenbrod Christian , Giese Frank , Reimert Manfredo , Rickmers Peter , Klinkov Konstantin
Published: November 2013

The autoignition properties of GTL-kerosene sprays have been examined in a hot blow-down wind-tunnel. The results are compared to those of fossil kerosene and the model fuel for GTL-kerosene. A total of more than 1100 experiments were carried out in the pressure range between 4.5 and 6 bar and at temperatures between 740 and 840 K. The sprays were injected in a jet-in-crossflow configuration into hot air of about 30 m/s velocity. It can be shown that the induction times of GTL-kerosene are essentially longer (between 10 and 30%) than those from fossil Jet A1 and its pressure and temperature dependency compares favorably to those of n-decane sprays. This indicates that GTL-kerosene has very good properties if a lean prevaporized premixed combustion with low NOx-emissions is desired. N-decane as the well matching model fuel for GTL-kerosene was found through single droplet ignition experiments performed in microgravity in the Bremen drop tower. These experiments were comparing various mono- and bi-component fuel’s ignition properties to those of GTL-kerosene droplets.
Parametric Optimization of Unsteady Endwall Blowing on a Highly Loaded LPT
Authors: Benton Stuart I. , Bernardini Chiara , Bons Jeffrey P. , Sondergaard Rolf
Published: November 2013

Efforts to reduce blade count and avoid boundary layer separation have led to low-pressure turbine airfoils with significant increases in loading as well as front-loaded pressure distributions. These features have been independently shown to increase losses within the secondary flow field at the endwall. Compound angle blowing from discrete jets on the blade suction surface near the endwall has been shown to be effective in reducing these increased losses and enabling the efficient use of highly loaded blade designs. In this study, experiments are performed on the front loaded L2F low-pressure turbine airfoil in a linear cascade. The required mass flow is reduced by decreasing hole count from previous configurations and from the introduction of unsteady blowing. The effects of pulsing frequency and duty cycle are investigated using phase-locked stereo particle image velocimetry to demonstrate the large scale movement and hysteresis behavior of the passage vortex interacting with the pulsed jets. Total pressure loss contours at the cascade outlet demonstrate that the efficiency benefit is maintained with the use of unsteady forcing.
Integrated Tools for Future Distributed Engine Control Technologies
Authors: Culley Dennis , Thomas Randy , Saus Joseph
Published: November 2013

Turbine engines are highly complex mechanical systems that are becoming increasingly dependent on control technologies to achieve system performance and safety metrics. However, the contribution of controls to these measurable system objectives is difficult to quantify due to a lack of tools capable of informing the decision makers. This shortcoming hinders technology insertion in the engine design process. NASA Glenn Research Center is developing a Hardware-in-the-Loop (HIL) platform and analysis tool set that will serve as a focal point for new control technologies, especially those related to the hardware development and integration of distributed engine control. The HIL platform is intended to enable rapid and detailed evaluation of new engine control applications, from conceptual design through hardware development, in order to quantify their impact on engine systems. This paper discusses the complex interactions of the control system, within the context of the larger engine system, and how new control technologies are changing that paradigm. The conceptual design of the new HIL platform is then described as a primary tool to address those interactions and how it will help feed the insertion of new technologies into future engine systems.
Experimental Investigation of Flow Instability in a Turbocharger Ported Shroud Compressor
Authors: Gancedo Matthieu , Guillou Erwann , Gutmark Ephraim
Published: November 2013

Turbocharger centrifugal compressors are equipped with a “ported shroud” to reduce flow instabilities at low mass flow rate. This passive stability control device using flow recirculation has been demonstrated to extend the surge margin of a compressor, without substantially sacrificing performance. However, the actual working mechanisms of the system remain not well understood.

In this paper, the relationship between inlet flow recirculation and instability control is studied using stereoscopic particle image velocimetry (PIV) in conjunction with dynamic pressure transducers at the inlet of a turbocharger compressor with and without a ported shroud. Both stable and unstable operational points are analyzed with use of phase-locked PIV measurements in surge.

Detailed description of unstable flow in a centrifugal compressor is presented with the reconstruction of the complex flow structure evolution at the compressor inlet during surge. Rather than one-dimensional, the surge flow is described by a three-dimensional axisymmetric structure of combined entering and exiting swirling flows, alternating in magnitude during the self-excited pressure cycle. The correlation between pressure and velocity measurements shows that the development of compressor unsteadiness is accompanied with swirling reversed flow at the impeller tip. The influence of the ported shroud on the inlet velocity flowfield is seen with the presence of localized flow recirculation. Stability improvement with a ported shroud is thus explained by removing swirling backflow at the impeller inducer tip and recirculating it to the impeller inlet to increase the near shroud inlet blade loading and incidence angle.
Mathematical Model of MCFC (Molten Carbonate Fuel Cell) for Power Plant Simulations
Authors: Milewski Jarosław , Wołowicz Marcin , Miller Andrzej
Published: November 2013

An MCFC model concept is presented. The MCFC model was built in HYSYS.Plant environment is based on its standard libraries. The main elements of the MCFC model and chemical reactions are presented. Selected performance characteristics at the design point of MCFC are presented.

A new equation is given to define MCFC voltage, which was obtained based on new assumptions and which can be used instead of the classical approach.
On Kinematic Relaxation and Deposition of Water Droplets in the Last Stages of Low Pressure Steam Turbines
Authors: Starzmann J. , Kaluza P. , Casey M. V. , Sieverding Frank
Published: November 2013

In the first part of the paper steady two-phase flow predictions have been performed for the last stage of a model steam turbine to examine the influence of drag between condensed fog droplets and the continuous vapour phase. In general, droplets due to homogeneous condensation are small and thus kinematic relaxation provides only a minor contribution to the wetness losses. Different droplet size distributions have been investigated to estimate at which size inter-phase friction becomes more important.

The second part of the paper deals with the deposition of fog droplets on stator blades. Results from several references are repeated to introduce the two main deposition mechanisms which are inertia and turbulent diffusion. Extensive post-processing routines have been programmed to calculate droplet deposition due to these effects for a last stage stator blade in three-dimensions. In principle the method to determine droplet deposition by turbulent diffusion equates to that of Yau and Young [1] and the advantages and disadvantages of this relatively simple method are discussed.

The investigation includes the influence of different droplet sizes on droplet deposition rates and shows that for small fog droplets turbulent diffusion is the main deposition mechanism. If the droplets size is increased inertial effects become more and more important and for droplets around 1 μm inertial deposition dominates. Assuming realistic droplet sizes the overall deposition equates to about 1% to 3% of the incoming wetness for the investigated guide vane at normal operating conditions.
Optimum Design of a Double Reheat Steam System in an Ultra Supercritical Unit
Authors: Zhou Luyao , Xu Gang , Xu Cheng , Yang Yongping , Li Yuanyuan , Deng Jianling
Published: November 2013

Ultra supercritical power generation technology is entering a fast developmental stage. Thus, using the double reheat system is necessary to improve the thermal performance of ultra supercritical units. In this paper, steam system designs were optimized and exergy analysis research on ultra supercritical double reheat units is carried out. The double reheat steam system based on the traditional eight extractions regenerative system is presented. In addition, the regenerative system setting with an outside steam cooler and two additional extractions is put forward. The quantitative energy saving effect of main optimization measures after various systems are analyzed and compared is also given. The present study proved that the setting with outside steam coolers could obviously decrease the superheat degree of extractions for ultra supercritical double reheat units. Moreover, two additional extractions are helpful in optimizing the distribution of the increase in water enthalpy in the regenerative system. Both optimization measures are conducive in improving the unit efficiency and in decreasing the coal consumption rate. The current paper also presents case studies and exergy analysis based on the aforementioned cases. The results show that the coal consumption rate of the optimized double reheat unit is reduced by 2.36 g/kWh compared with the double reheat unit based on the traditional regenerative system with the same initial parameters. The total exergy loss of the regenerative system is reduced by approximately 10% for the setting with outside steam coolers. The total exergy loss of the regenerative system with ten extractions can be further reduced by nearly 18%. Therefore, setting with outside steam coolers and additional appropriate extractions are both conducive in improving the performance of ultra supercritical double reheat units. Thus, a remarkable energy saving effect is observed. The current paper provides a theoretical basis for performance evaluation and design optimization of ultra supercritical double reheat units.