bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Heat Transfer and Pressure Field of Jet Impingement on the Side of a Dimpled Surface
Authors: Cheng Li-Jian , Xu Wei-Jiang , Zhu Hui-Ren , Jiang Ru
Published: August 2017

An efficient way to improve the efficiency of the aero engine is to increase the temperature of the turbine inlet, which requires more advanced turbine cooling techniques. The dimple heat transfer enhancement is a technique that can enhance the convective heat transfer of the surfaces by processing a certain arrangement of jet holes and dimples on the surfaces. The objective of this paper is to investigate the characteristics of heat transfer and pressure loss for an inline array of round jets impinging on the side of dimpled surface. Meanwhile, the results are compared to those of the impingement directly over the dimples and the flat surface. The investigated parameters are Reynolds number (Re) of 5000, 8000 and 11500, the ratio of jet-to-plate spacing to jet diameter (H/Dj) of 2, 4, 6 and 8, the ratio of dimple depth to dimple diameter (d/Dd) of 0.15, 0.25 and 0.29. Results show that increasing the Reynolds number can improve the heat transfer. The shallower dimples enhance higher heat transfer than the deeper ones. For the target surface, the side impingement conducts the highest improvement at H/Dj = 8, d/Dd = 0.15 and Re = 11500. The improvement is about 16% higher than that of the frontal impingement while this value is 7% when compared to the flat surface. However, for the jet surface at the same operating condition, the side impingement leads to the worst heat transfer performance by 25% and 15% lower than that of the frontal impingement and the flat surface, respectively. The higher Reynolds number causes higher total pressure loss. But the pressure loss coefficient of the side impingement is not significantly different from that of the frontal impingement and the flat surface.
Oral Assessments of Student Learning in Undergraduate Aerospace Propulsion and Power Courses
Authors: Rouser Kurt P.
Published: August 2017

A purposeful approach has been taken to match teaching pedagogies (techniques), learning experiences and assessment methods to various types of student learning in undergraduate aerospace propulsion courses at junior-level at the United States Air Force Academy and at the senior-level at Oklahoma State University. Prior studies in the scholarship of teaching and learning have shown the benefits of matching assessment methods, as well as teaching pedagogies and learning experiences, to the types of student learning associated with desired educational outcomes. Literature suggests that the best method for teaching and assessing student cognitive learning is through explanation and presentation. Oral assessments have been implemented at the Air Force Academy and Oklahoma State University to evaluate student cognitive learning in undergraduate aerospace propulsion and power courses. An oral midterm exam was developed to assess student acquisition of subject matter knowledge and understanding of fundamental concepts, the type of learning occurring early in course lesson sequences. End-of-semester design project poster sessions and presentations were used as summative oral assessments of student creative thinking, decision making, and professional judgement. Conversely, two written midterm exams and a final exam primarily focused on assessing student problem solving skills and less on comprehensive knowledge. Oral assessments also served as reflective thinking experiences that reinforced student learning. Student feedback on oral assessment methods was collected through surveys conducted after each assessment. Survey results not only revealed the effectiveness of using oral assessments but also how to improve their design and implementation, including the use of information technology and broader curricular employment.
Experimental Study of Thermo-Acoustic Instability Triggering in a Staged Liquid Fuel Combustor Using High-Speed OH-PLIF
Authors: Renaud Antoine , Tachibana Shigeru , Arase Shuta , Yokomori Takeshi
Published: August 2017

A staged injector developed by JAXA and fueled with kerosene is studied in a high-pressure combustion experiment. With a stable pilot fuel flow rate, the fuel flow rate in the main stage is progressively increased. A high-speed OH-PLIF system is used to record the flame motion at 10,000 fps. In the beginning of the recording, POD modes shows that the flame behavior is dominated by relatively low-frequency rotation due to the swirling motion of the flow. These rotational motions then coexist with a thermo-acoustic instability around 475 Hz which increases the amplitude of the pressure fluctuations inside the chamber. DMD analyses indicate that this instability is associated with a widening of the flame occurring when the pressure fluctuations are the highest, giving the instability a positive feedback. The instability frequency then abruptly switches to 500 Hz while retaining the same driving mechanisms. Potential candidates for this frequency change are proposed.
Frequency Analysis Performed on Compressor Blades of Two Types of Gas Turbines Using Campbell and SAFE Diagrams
Authors: Bab Saeed , Behzadi Mohsen , Ahmadi Ahmad , Ramesh Ali , Shahrabi Ali Reza , Fathi Sola Jalal
Published: August 2017

This paper investigates the results of a frequency analysis performed on the blades of the last three compressor stages of two different gas turbines (Case A and B). The axial compressors in A and B have ten and eleven stages, respectively. The studied stages have identical number of blades in both compressors. However turbine B has higher number of upstream vanes before each rotating stage. Turbine B is actually a modified version of A with higher power output. The manufacturer provides acceptable ranges for several natural frequencies of blades of stage No.8 to 10 in case A. One of the purposes of this study is to figure out the logic behind the abovementioned ranges.

FEM has been used in order to determine the natural frequencies of a single blade (for Campbell diagram) and bladed disk (for SAFE diagram). By surveying the results of the Campbell diagrams for blades of case A’s mentioned stages, it is concluded that the manufacturer has obtained the acceptable ranges by considering a 10% difference (at least) between single blade natural frequencies and excitation frequencies (upstream vane passage frequencies (VPF)).

On the other hand, according to Campbell diagram, there is no resonance for these blades within the operational speed while SAFE diagrams show the existence of one resonance mode within the same range. The reason of this contradiction is found to be ignoring the disk stiffness effect on the blades frequencies. A same procedure was also followed to study the critical frequencies of the blades of the last three stages of turbine B’s compressor by SAFE diagrams.

By checking the critical modes, it is concluded that these modes in case B are transferred to one or two modes higher in comparison to A which results in a much better vibrational behavior. This has been acquired by increasing the number of the upstream vanes.

In addition, in case A’s compressor, the blades of the stage No.10 have been designed with far thicker airfoils (approximately 50%) when compared to stage No.8 and 9, even though their other dimensions are almost identical. But, this fault has been corrected in turbine B and the airfoils of all three stages almost have the same thickness. To sum up, although the design of mentioned blades in turbine B looks better and more logical than A, still a more precise look at its stages bladed disk SAFE diagrams reveals another issue. In some references there are some hints that low number of critical nodal diameter (veering region) might cause high level of blade vibration due to mistuning and this means that even in turbine B the design might not be optimal. A cure could be an increase or decrease in the number of upstream vanes in order to have a higher critical nodal diameter.
Study of Experimental and Calculated Flame Speed of Methane/Oxygen-Enriched Flame in Gas Turbine Conditions As a Function of Water Dilution: Application to CO2 Capture by Membrane Processes
Authors: Cabot G. , Chica Cano J. P. , de Persis S. , Foucher F.
Published: August 2017

A solution for CCS (Carbon Dioxide Capture and Sequestration of CO2) is oxycombustion. Due to the high cost of pure O2 production, however, other approaches recently emerged such as post-combustion coupled with Oxygen Enhanced Air (OEA). This is the solution studied in this paper, which presents an innovative gas turbine cycle, the Oxygen Enriched Air Steam Injection Gas Turbine Cycle (OEASTIG). The OEASTIG cycle is composed of Methane combustion with OEA (Oxygen Enhanced Air), EGR (Exhaust Gas Recirculation) and H2O coming from a STIG (Steam Injection Gas Turbine). CO2 capture is achieved by a membrane separator. The final aim of this work is to predict NO and CO emissions in the gas turbine by experimental and numerical approaches. Before carrying out this study, the validation of a reaction mechanism is mandatory. Moreover, this new gas turbine cycle impacts on the combustion zone and it is therefore necessary to understand the consequences of H2O and CO2 dilution on combustion parameters. While a large number of papers deal with CO2 dilution, only a few papers have investigated the impact of water dilution on methane combustion. A study of the influence of H2O dilution on the combustion parameters by experimental and numerical approaches was therefore carried out and is reported in the present paper. The paper is divided in three parts: i) description of the innovative gas turbine (OEASTIG) cycle and determination of the reactive mixtures compatible with its operation; ii) validation of the reaction mechanism by comparing laminar methane flame velocity measurements performed in a stainless steel spherical combustion chamber with calculations carried out in a freely propagating flame using the Chemical Workbench v.4.1. Package in conjunction with the GRIMech3.0 reaction mechanism; iii) Extrapolation to gas turbine conditions by prediction of flame velocities and determination of the feasible conditions from a gas turbine point of view (flame stability). In particular, mixtures (composed of CH4/O2/N2/H2O or CO2) leading to the same adiabatic temperature were investigated. Lastly, the influence of oxygen enrichment and H2O dilution (compared to CO2 dilution) were investigated.
An Experimentally Derived Model to Predict the Water Film in a Compressor Cascade With Droplet Laden Flow
Authors: Neupert Niklas , Harbeck Janneck Christoph , Joos Franz
Published: August 2017

In recent years overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Despite the positive thermodynamic effect on the cycle droplets entering the compressor increase the risk of water droplet erosion and deposition of water on the blades leading to an increase of required torque and profile loss. Due to this detailed information about the structure and the amount of water on the surface is key for compressor performance.

Experiments were conducted with a droplet laden flow in a transonic compressor cascade focusing on the film formed by the deposited water. Two approaches were taken. In the first approach the film thickness on the blade was directly measured using white light interferometry. Due to significant distortion of the flow caused by the measurement system a transfer of the measured film thickness to the undisturbed case is not possible. Therefore, a film model is adapted to describe the film flow in terms of height averaged film parameters.

In the second approach experiments were conducted in an undisturbed cascade setup and the water film pattern was measured using a non-intrusive quantitative image processing tool. Utilizing the measured flow pattern in combination with findings from literature the rivulet flow structure is resolved. From continuity of the water flow a film thickness is derived showing good agreement with the previously calculated results. Using both approaches a 3D reconstruction of the water film pattern is created giving first experimental results of the film forming on stationary compressor blades under overspray fogging conditions.
Experimental Investigation on the Tip Vortex of a Wind Turbine With and Without a Slotted Tip
Authors: Liu Pengyin , Chen Jinge , Xin Shen , Zhu Xiaocheng , Du Zhaohui
Published: August 2017

In this paper, a slotted tip structure is experimentally analyzed. A wind turbine with three blades, of which the radius is 301.74mm, is investigated by the PIV method. Each wind turbine blade is formed with a slots system comprising four internal tube members embedded in the blade. The inlets of the internal tube member are located at the leading edge of the blade and form an inlet array. The outlets are located at the blade tip face and form an outlet array. The near wake flow field of the wind turbine with slotted tip and without slotted tip are both measured. Velocity field of near wake region and clear images of the tip vortex are captured under different wake ages.

The experimental results show that the radius of the tip vortex core is enlarged by the slotted tip at any wake age compared with that of original wind turbine. Moreover, the diffusion process of the tip vortex is accelerated by the slotted tip which lead to the disappearance of the tip vortex occurs at smaller wake age. The strength of the tip vortex is also reduced indicating that the flow field in the near wake of wind turbine is improved. The experimental data are further analyzed with the vortex core model to reveal the flow mechanism of this kind of flow control method. The turbulence coefficient of the vortex core model for wind turbine is obtained from the experimental data of the wind turbine with and without slotted tip. It shows that the slotted tip increases the turbulence strength in the tip vortex core by importing airflow into the tip vortex core during its initial generation stage, which leads to the reduction of the tip vortex strength.

Therefore, it is promising that the slotted tip can be used to weaken the vorticity and accelerate the diffusion of the tip vortex which would improve the problem caused by the tip vortex.
Analytical Study of Low-Frequency Helmholtz Mode Oscillation in a Model Combustor
Authors: Zhang Man , Lin Yuzhen , Tao Wenjie
Published: August 2017

The “growl” mode combustion instability is one of the most destructive phenomenon occurring in the lean burn aeroengine combustor at low power condition. This topic is widely investigated these years focusing on the mechanism of flame structures, oscillation modes and the development of prediction methods. Recently, an analytical prediction method which based on the linear solution of Helmholtz equation was successfully used to predict the inception of the growl instability. In this model, the flame tube and the inflow duct are modeled as individual cavities and connected through a swirler acting as the neck of Helmholtz resonators. However, in many applications, the inflow duct has more complex geometry and thus complex acoustic boundary condition. So there is the need to extend this approach in a more universal form. This is the motivation of the current work.

This paper firstly presents the measured dynamic pressure and the flame motions in a single sector combustor. By changing the cross section area of the inflow duct, self-excited combustion instability was observed. This combustion instability mainly occurred at the frequency of 350HZ∼400Hz. The test results showed that flame front moves with the bulk flow in the axial direction while the pressure fluctuations in the inflow duct show a harmonic feature. It confirms that the combustion instability corresponds to the Helmholtz mode. This phenomenon was next analyzed with a new low-order linear acoustic method developed in this paper. The method integrates the model of Helmholtz resonator within harmonic oscillation (also called IM2H), and is validated by comparing with experimental data. By considering Helmholtz oscillation in the flame tube, the predicted frequency and mode agree well with experiments. The results show that the stability of the system is more sensitive to the geometry design parameter than the aerodynamics parameters.
Identification of Torsional Natural Frequencies and Damping As Well As Prediction of Stress Amplitudes at a Nuclear Power Train
Authors: Grein Roland , Ehehalt Ulrich , Balkowski Ingo
Published: August 2017

As the landscape of energy production in Europe and other developed countries undergoes a rapid shift towards renewable energies, such as offshore wind, the use of HVDC (High-Voltage Direct Current) technology is increasing. HVDC converter stations have been reported to potentially cause sub-synchronous torsional interaction (SSTI) with turbo-generators in the grid. This phenomenon implies a negative electrical damping at the turbo-generator which may result in non-attenuating torsional vibrations. This is especially an issue in power grids where the close proximity of the power stations to the HVDC converter stations cannot be avoided. Therefore, in order to ensure safe and stable operation, monitoring of torsional vibrations is required.

In this article, a proof-of-concept study of touchless torque sensing at a nuclear power train in Gösgen, Switzerland, is presented. All three sub-synchronous natural frequencies were detected by the torque sensor during a load rejection test and show very good agreement with theoretical predictions based on finite element calculations. Possibilities to devise monitoring and eventually protection systems for torsional vibrations based on this technology are also discussed.
Optimization of Coupled System Components Using Approximations of Interface Quantities
Authors: Lockan Michael , Bestle Dieter , Janke Christian , Meyer Marcus
Published: August 2017

Optimization of complex systems like jet engines is a process where discipline experts from several departments or even different companies have to work together. Thus, a complete system analysis code usually does not exist preventing an overall system optimization. Therefore, the system is typically split into components, and interface parameters between components are decided and fixed in early design stages based on low-fidelity information. Finally the components are optimized separately according to these fixed settings which, however, may prohibit an overall optimal system behavior even if sophisticated subsystem optimization is performed. Consequently, interface parameters should be varied in an overall coupled system optimization process and adapted to subsystem needs.

This may be supported by utilizing collaborative optimization strategies. Basically there are two types of such optimization approaches: global strategies with nested optimization loops and local subsystem optimization strategies supported by sensitivity-based approximations of other subsystems. The multidisciplinary optimization approach presented here combines the benefits of both strategies: efficient global optimization and approximations of subsystem quantities without the need of sensitivity information. It starts with an initial design of experiments for each component by varying all input parameters and evaluating the associated outputs. Due to the fact that these quantities consist of shared design parameters and outputs of other components, not all of the used input parameter combinations are feasible for the coupled system. In order to enforce consistency for the entire system, the interface regions are characterized by feasibility criteria acting as approximated constraints for further component optimizations. Beside that an approximation of the overall system objective is provided to all components to drive component design towards an overall optimal system performance.

The developed approach is demonstrated by an application to a jet engine turbine consisting of a high and low pressure part where the goal is to maximize the overall turbine efficiency. On the one hand the turbine is optimized with the proposed approach by splitting it into two coupled components; on the other hand the turbine is optimized as a complete system. It turns out that the proposed approach yields equally good results in much shorter time than overall optimization.
Numerical Investigation and Shape Design Improvement of a Turbine Inlet Combined Valve
Authors: Ye Dongting , Ma Jiaobin , Xie Yonghui , Zhang Di , Xu Sihua
Published: August 2017

Nowadays, the development of turbines tends to enlarge the capacity and increase the corresponding parameters. Turbine inlet valve is an important part of turbine governing system. Consequently, the high pressure turbine requires good performance of the inlet valve. In this paper, the aerodynamic performance of a real ultra-supercritical power unit turbine inlet combined valve is analyzed in detail via numerical method. At the same time, the shape design of valve plug is improved by means of specific effective methods, including geometrical analysis and quick selection of the angles. A porous medium model is adopted to deal with the strainer structure and it has a good effect on the numerical simulation. The SST turbulence model is finally selected for calculation to obtain reliable results. The results show that the flow in the combined valve presents obvious flow separation nearby the valve plug and downstream of the throat. According to the analysis of pressure and static entropy, it can be concluded that the main pressure loss is concentrated in the strainer and control valve chamber, and an obvious vortex appears in control valve chamber with energy dissipation. Suitable optimization theory plays an effective role in the research. In this process, much attention has been paid to the decrease of pressure loss. Parabola and quick opening shapes are adopted to improve the shape of valve plug and a series of shapes with different angles are tested. The two best optimization models are selected and their results are analyzed. The results show good performance and the pressure loss coefficient reduces from 2.0% to 1.7%.
Experimental Study on Pressure Losses in Circular Orifices With Inlet Cross Flow
Authors: Feseker Daniel , Kinell Mats , Neef Matthias
Published: August 2017

The cooling air in the secondary air system of gas turbines is controlled and metered by numerous restrictors, mainly in the shape of orifices. The ability to understand and predict the associated pressure losses are important in order to improve the air flow in the secondary air system. This experimental study investigates the behavior of the discharge coefficient for circular orifices with inlet cross flow which is a common flow case in gas turbines. Examples of this are at the inlet of a film cooling hole or the feeding of air to a blade through an orifice in a rotor disc.

Measurements were conducted for a total number of 38 orifices, covering a wide range of length-to-diameter ratios, including short and long orifices with varying inlet geometries. Up to five different chamfer-to-diameter and radius-to-diameter ratios were tested per orifice length. Furthermore, the static pressure ratio across the orifice was varied between 1.05 and 1.6 for all examined orifices.

The results of this comprehensive investigation demonstrate the beneficial influence of rounded inlet geometries and the ability to decrease pressure losses, which is especially true for higher cross flow ratios where the reduction of the pressure loss in comparison to sharp edged holes can be as high as 54%. With some exceptions, the chamfered orifices show a similar behavior as the rounded ones but with generally lower discharge coefficients. Nevertheless, a chamfered inlet yields lower pressure losses than a sharp edged inlet. The obtained experimental data was used to develop two correlations for the discharge coefficient as a function of geometrical as well as flow properties.
Investigation of Advanced Lifetime Calculation Procedure for Steam Turbines in Flexible Operation
Authors: Jarmowski Dennis , Capozzi Paolo , Vogt Jan , Helbig Klaus
Published: August 2017

At high intermittent renewable energy share, plants are forced to operate more flexible beyond their original design intent. Many plants are older than 30 years with only limited residual lifetime. Decreasing energy prices and capacity factors will further enforce older plants to more transient operation with steeper gradients. Steam Turbine (ST) protections systems on site often are not designed for such flexible operation and therefore do not properly supervise the resulting impact on lifetime consumption.

Therefore precise lifetime management concepts are required to increase plant reliability and flexibility, mitigate risks for new implemented operation modes like faster start-ups and extended turn down.

The prerequisite for properly managing a plants lifetime is the accurate knowledge of the current state of consumed lifetime, which is evaluated in a lifetime assessment (LTA). This includes a standardized process for the calculation of creep and fatigue damage. For this long-term field operation data is used as input. The current LTA procedure typically limits the analysis to transient operation during start-up and shut-down. Other types of transient operation such as improved turn-down also need to be considered in order to take all relevant operation modes into account.

Therefore dedicated, new advanced methods are required for the precise estimation of the lifetime impact due to new operation modes with higher requirements compared to an assessment based on known current procedure. These methods will allow optimizing asset lifetime. In order to maintain power plant competitiveness, operation and maintenance cost must be reduced despite the demand for improved turn-down and more frequent start-up procedures.

This paper presents results of ST lifetime studies combining long-term operation data (including improved turn-down operation), FEM calculations and simplified and advanced constitutive material models.

In a first investigation, the rotor is modelled with FEM and thermal boundary conditions during isolated transient operation are derived from measurement data combined with generically elaborated new turn-down profiles.

The impact of the start-stop (enclosing cycle) and turndown cycle (sub-cycle) on the lifetime consumption is evaluated. For this, sub-cycles are considered in combination with the enclosing cycle and as isolated cycle.

In a second investigation, the above described calculation model is fed with 2 years of continuous operation data. Postprocessing is performed with common rain-flow methods and compared to an accumulative start-stop cycle assessment.

Based on the input of the calculation with the advanced constitutive material model further fracture mechanic investigations are performed.

The paper closes with an outlook on opportunities arising from digitalization of power generation equipment.
Numerical Study of Cage Dynamics Focused on Hydrodynamic Effects of Guidance Land Clearances for Different Ball-Pocket Clearances in Cryogenic Environments
Authors: Choe Bok Seong , Lee Jeon Kook , Jeon Doyoung , Lee Yongbok
Published: August 2017

This study presents the dynamic motion of a ball bearing cage submerged in a cryogenic fluid under high-speed conditions. The dynamic motion of the cage has been studied as a function of the race land–cage and ball–cage pocket clearances for different inner race rotation speeds under light load conditions. In addition, this study conducted computational fluid dynamics (CFD) analysis using commercial software to analyze the fluid dynamic forces on the cage. The hydraulic force obtained from the CFD analysis was coded in commercial ball bearing analysis software as a function of the eccentricity ratio and rotation speed of the cage. Finally, the dynamic motion of the ball bearing cage considering the effects of fluid dynamic forces has been studied. The results include the cage whirling amplitude, fluctuation of cage whirling speed, and cage wear for various cage clearances and rotation speeds. The cage outer guidance clearances studied were 1.14, 1.04, 0.94, 0.84, and 0.74 mm and the ball–pocket clearances were 0.62, 0.92, 1.22, 1.52, and 1.82 mm. The rotation speeds of the inner race were 5,000, 8,000, and 11,000 rpm. The cage whirling amplitude decreases as the outer guidance clearance decreases, and it decreases as the rotation speed increases up to 11,000 rpm because of the increasing hydrodynamic force of the liquid nitrogen (LN2). However, the probability density function (PDF) curves indicate that an increase in the rotor speed increases the standard deviation in the cage whirling frequency. The wear loss of the cage was greatest for the largest race land–cage and the smallest ball–cage pocket clearances, owing to the increased number of intermittent collisions between the cage and the ball bearings (ball–race). Consequently, the analysis results for various operating conditions (inner race rotation speeds, cage clearances, traction coefficients, etc.) are in good agreement with the reference results.
Application of a RANS-Informed Analytical Model for Fast Noise Prediction of Contra Rotating Open Rotors
Authors: Tormen Damiano , Giannattasio Pietro , Zanon Alessandro , Kühnelt Helmut , De Gennaro Michele
Published: August 2017

The present work focuses on the fast prediction of the interaction noise (IN) components of a Contra Rotating Open Rotor (CROR) engine at take-off. The flow field past the CROR is computed using a steady RANS approach coupled with the concept of mixing plane between the rotors to remove the flow unsteadiness due to the propeller interaction. The effects of such interaction are then recovered applying the analytical model of Jaron et al. (2014), balanced with data extracted from the RANS solution, to extrapolate the information about the wake of the front rotor and the potential flow fields through the mixing plane. This RANS-informed approximation allows recovering the unsteadiness of the flow-blades interaction in terms of unsteady blade response. The tonal noise at the blade passing frequency and the interaction noise are then estimated using the analytical frequency domain model proposed by Hanson (1985). The present method for the fast prediction of CROR noise has been validated by comparison with the results of URANS simulations and noise measurements. CROR geometry UDF F7/A7 with both 8 × 8 and 11 × 9 blade counts has been considered. The flow velocity profiles extrapolated through the mixing plane agree well with the URANS results, except in the vicinity of the blade tip, where the analytical extrapolation method is not able to deal properly with the strongly 3D tip vortex flow. The comparison of the predicted interaction noise with acoustic measurements shows that the present fast RANS-informed approach is capable of estimating the directivity of the CROR noise with reasonable accuracy.
Variable Geometry Compressors for Heavy Duty Truck Engine Turbochargers
Authors: Wöhr Michael , Müller Markus , Leweux Johannes
Published: August 2017

This paper presents the development approach, design and evaluation of three turbocharger compressors with variable geometry for heavy duty engines. The main goal is the improvement of fuel economy without sacrifices regarding any other performance criteria. In a first step, a vaned diffuser parameter study shows that efficiency improvements in the relevant operating areas are possible at the cost of reduced map width. Concluding from the results three variable geometries with varying complexity based on vaned diffusers are designed. Results from the hot gas test stand and engine test rig show that all systems are capable of increasing compressor efficiency and thus improving fuel economy in the main driving range of heavy duty engines. The most significant differences can be seen regarding the engine brake performance. Only one system meets all engine demands while improving fuel economy.
Surface Roughness Impact on Low-Pressure Turbine Performance due to Operational Deterioration
Authors: Kellersmann Andreas , Weiler Sarah , Bode Christoph , Friedrichs Jens , Städing Jörn , Ramm Günter
Published: August 2017

The overall efficiency and operational behavior of aircraft engines are influenced by the surface finish of the airfoils. During operation, the surface roughness significantly increases due to erosion and deposition processes. The aim of this study is to analyze the influence of roughness on the aerodynamics of the low-pressure turbine of a mid-sized high bypass turbofan. In order to gain a better insight into the operational roughness structures, a sample of new, used, cleaned and reworked turbine blades and vanes are measured using the confocal laser scanning microscopy technique. The measurement results show local inhomogeneities. The roughness distributions measured are then converted into their equivalent sand grain roughness ks,eq to permit an evaluation of the impact on aerodynamic losses. The numerical study is performed using the CFD-solver TRACE which was validated before with existing data from Rig experiments. It is observed that the influence of the surface roughness on the turbine efficiency is significant at take-off but negligible at cruise. A detailed analysis on the aerodynamics at take-off shows that very rough airfoils lead to higher profile and secondary loss. Due to the higher disturbances present in flows circulating over rough walls, the transition occurs earlier and the momentum thickness increases in the turbulent boundary layer. The service-induced roughness structures cause an efficiency drop in the low pressure turbine of ηT = −0.16% compared to new parts. A gas path analysis showed that this results in an increased fuel flow of Δṁf = +0.06% and an exhaust gas temperature rise of ΔEGT = +1.2K for fixed engine pressure ratio which is equivalent to roughly 4 percent of the typical EGT margin of a fully refurbished engine. This result stresses the importance of roughness induced loss in low pressure turbines.
Commissioning of Off-Shore Gas Compressor With 9-Axes Magnetic Bearing System: Commissioning Tools
Authors: Aeschlimann B. , Hubatka M. , Stettler R. , Housseini R.
Published: August 2017

This paper addresses the commissioning of an industrial 9-axes oil-free integrated motor-compressor that is installed on an off-shore oil rig. The magnetic bearing system and advanced software tools are shown to support the machine mechanical assembly, testing, and long term operation protection. The magnetic bearings are used as measurement devices to reduce commissioning time and, because of the high hard- and software integration level of machine and measurement, to improved commissioning quality and reliable long term operation. Measurement data from the commissioning of the machine are presented.
3-D Computational Loss Analysis of an Asymmetric Volute Twin-Scroll Turbocharger
Authors: Palenschat Torsten , Newton Peter , Martinez-Botas Ricardo F. , Müller Markus , Leweux Johannes
Published: August 2017

In times of stringent emission standards for automotive and truck applications, exhaust gas recirculation (EGR) is used in IC engines to reduce NOx emissions by recirculating a portion of an engine’s exhaust gas. The amount of exhaust gas determined for EGR is withdrawn from the exhaust gas route and routed back into the combustion chamber. The recirculated exhaust gas acts as an inert gas and, when mixed with the pre-combustion mixture, helps to decrease the combustion temperature and thus NOx emissions.

Designed for a diesel engine within a truck application, the turbine in this particular research project is fed by two cylinder groups, however, only the exhaust gas of one group is recirculated. The reduced mass flow in the small turbine scroll (EGR-scroll) through EGR withdrawal, along with the increased pressure required for EGR transport, leads to a massive reduction in the mass flow parameter of the EGR-scroll.

The common turbocharger design process has been based on steady admission rather than unsteady admission given through the pulsating nature of multi-cylinder admission. This has lead to diverging results of turbochargers performing well on steady hot gas test rigs compared to performing badly in the final tests on the engine itself.

In this paper however, unequal admission resulting from pulsating admission is taken into account. Based on unsteady admission, a methodology is proposed for steady computations with unequal admissions, and a thorough 3D CFD loss analysis is to be presented to understand the turbine behaviour, reveal the regions for improvements, and provide a framework for further development.
Advanced Control for Clusters of SOFC/GT Hybrid Systems
Authors: Rossi Iacopo , Zaccaria Valentina , Traverso Alberto
Published: August 2017

The use of model predictive control (MPC) in advanced power systems can be advantageous in controlling highly coupled variables and optimizing system operations. Solid oxide fuel cell/ gas turbine (SOFC/GT) hybrids are an example where advanced control techniques can be effectively applied. For example, to manage load distribution among several identical generation units characterized by different temperature distributions due to different degradation paths of the fuel cell stacks. When implementing a MPC, a critical aspect is the trade-off between model accuracy and simplicity, the latter related to a fast computational time. In this work, a hybrid physical and numerical approach was used to reduce the number of states necessary to describe such complex target system. The reduced number of states in the model and the simple framework allow real-time performance and potential extension to a wide range of power plants for industrial application, at the expense of accuracy losses, discussed in the paper.
Reduction of Soot Emitted by Gas Turbines Fired on Gasoil
Authors: Galantine Bernard , Lepante Philippe , Angebert Alex , Vierling Matthieu , Aboujaib Maher , Sokolov Dmitry , Plouhinec Mickael , Moliere Michel
Published: August 2017

Particulate matter (PM) emitted by the combustion of liquid fuels consist of both ash and soot particles. For installations fired on heavy fuel oil, ash particles represent a substantial fraction of the PM emitted. However, when one burns distillate oil, soot accounts for more than 95% of the PM emission. There is currently a marked move towards the reduction of particles emitted by combustion installations. This includes gas turbines operated in cogeneration or in simple/combined cycle. This trend is driven namely by the EU BREF (Best Available Techniques Reference Document) and IED (Industrial Emission Directive), which recommend more stringent PM limitations for the combustion of gaseous and liquid fuels. Due to the proposed regulations GE has performed testing to evaluate the efficiency of catalysts mobilized in the form of fuel additives on soot emissions of heavy duty gas turbines (“GT”) fired on # 2 diesel oil (#2 DO) also known as gasoil.

In the framework of a collaboration between EDF and GE, a full-scale test has been performed at the Jarry Sud power plant in Guadeloupe (West Indies), involving a Frame 6B, with three types of benign oxidation catalyst additives: cerium (IV), cerium (III) and iron (III). The results of this trial proved successful with a PM abatement level up to 80% attained at full load.

The paper summarizes the preparation and execution of this field test with emphasis placed on the activity of cerium that appeared efficient at concentrations as low as a few ppm. The performances of iron and cerium are also compared.
A Review of the Experience Achieved at the Yugadanavi 300 MW CCGT in Sri Lanka: Increasing the Firing Temperature of Gas Turbines Using a Novel Vanadium Inhibitor
Authors: Marikkar Nuhuman , Jayath Tharindu , Egodawatta Kithsiri , Vierling Matthieu , Aboujaib Maher , Sokolov Dmitry , Meskers Donald , Russell Robert , Moliere Michel
Published: August 2017

In regions developing rapidly but deprived of natural gas, gas turbines (GT) in combined cycles (CC) fired on Heavy Fuel Oil (HFO) can represent effective and environmentally viable power generation options.

The 300 MW Yugadanavi plant in Sri Lanka, which features two 9E GTs burning low-sulfur HFO, best exemplifies this specific situation. This project was fast-tracked in 2006, when the country started its fast development and the national grid needed fast power additions and frequency stability. Since 2008, it has been supplying 200 MWe to the Ceylonese grid, in simple cycle. Then in 2010, its capacity rose up to 300 MWe without any extra fuel consumption, after its conversion to a combined cycle.

In November 2016, Yugadanavi has completed 55,000 hours of successful operation, has generated 6,000 TWh and burned 1 million tons of HFO achieving on average efficiency and reliability performances as high as 44% and 96% respectively.

Starting 2010, LTL and GE joined their efforts in plant upgrade initiatives. In 2014 they demonstrated an efficient method to reduce the smoke emissions, using benign combustion catalysts. Within a next upgrade step, a new vanadium inhibition technology has been field-tested in 2015–2016, which enables improving the availability and energy performances of the plant by namely increasing the firing temperature of the gas turbines.

After recalling the key milestones of this significant HFO project, the joint paper will outline the operation experience and positive environmental outcomes of the developments carried out within an LTL-GE collaboration, with a special emphasis on the most recent results obtained with the new inhibition technology.
An Acceleration Method for Numerical Studies of Conjugate Heat Transfer With a Self-Adaptive Coupling Time Step Method: Application to a Wall-Impinging Flame
Authors: Koren Chai , Vicquelin Ronan , Gicquel Olivier
Published: August 2017

The application of large-eddy simulations to conjugate heat transfer problems can promisingly provide accurate results, including fluctuating heat loads which are critical for thermal fatigue. Such simulations rely on separate solvers and a coupling methodology which must be accurate and robust. In this context, the Hybrid-Cell Neumann-Dirichlet (HCND) coupling approach can adapt dynamically the coupling frequency given a desired accuracy. However, in order to determine statistics (mean, RMS, . . .) in a permanent regime, this approach must benefit from an acceleration technique which is here first derived and validated. Two configurations of a wall-impinging flame are then simulated: a quasi-steady case and a pulsated case. The former enables to validate the ability of the accelerated HCND method to predict a steady state wall temperature, while the latter highlights the retained acceleration which does not alter the fluctuations in wall temperature and wall heat flux. Both cases benefit from the self-adaptation of the coupling period provided by the method.
Exhaust Gas Recirculation at Elevated Pressure Using a FLOX® Combustor
Authors: Kutne Peter , Richter Judith , Gounder James D. , Naumann Clemens , Meier Wolfgang
Published: August 2017

To reduce CO2 emissions from the combustion of fossil and alternative fuels, carbon capture technologies present a promising approach. But the efficiency of the capture process depends on the CO2 concentration in the exhaust gas which is relatively low for gas turbine power plants. Exhaust gas recirculation (EGR) is a promising approach to increase the CO2 concentration in the exhaust gas stream and thus reduce the energy losses. In this study a FLOX® combustor was used to investigate the influence of EGR on the combustion process of natural gas at elevated pressure. The combustor stabilizes the flame without use of swirl, by creating a strong recirculation through high momentum injection of the fresh gas into the combustion chamber. This enables the establishment of a distributed combustion zone, which promises advantages for the use of gas mixtures with low reactivity like those occurring in EGR processes. At a pressure of 5 bar it was possible to increase the CO2 concentration in the exhaust gas up to 7 vol%, which is already enough to realize an efficient CO2 capture process. At 10 bar the CO2 concentration could be increased to 9 vol%. The changes in flame stabilization due to pressure increase and different EGR rates are investigated by OH*-chemiluminescence imaging and discussed. The contribution of auto-ignition and flame propagation to flame stabilization is estimated by a kinetic model calculation.
Analysis of the Transfer Function of Large and Small Premixed Laminar Conical Flames
Authors: Gaudron R. , Gatti M. , Mirat C. , Schuller T.
Published: August 2017

The Flame Transfer Function (FTF) of premixed laminar conical flames submitted to flowrate modulations is a configuration of fundamental and practical interest for improving the design of thermo-acoustically stable low power burners. Many theoretical models were developed for relatively large single flames based on labscale experiments, while most domestic and industrial burners operate with a collection of small injectors. Measurements of the FTF of laminar premixed methane/air conical flames are compared with analytical expressions deduced from kinematic descriptions of flame wrinkling when the burner size is reduced. The flame aspect ratio is kept constant corresponding to a flame tip half-angle α = 14.47° and the radius of the injector is reduced from R = 11 mm to R = 1.5 mm. Three different velocity perturbation models are tested, with and without an additional model accounting for the dynamics of the flame anchoring point. For the largest flames R = 11 mm and 7 mm, the best agreement is found for a FTF model with an incompressible velocity disturbance in the fresh reactants stream. The anchoring point dynamics has only a weak influence on the FTF gain and phase-lag plots of these flames. For the smallest flames (R = 1.5 mm), a FTF model based on a uniform flow perturbation yields the best match with experiments for the phase-lag plot, but none of the three velocity perturbation models reproduce the FTF gain evolution as measured in experiments. Including the contribution of the anchoring point dynamics to the FTF significantly changes the FTF gain predictions, but it does not allow to reproduce the main features observed in the measured gain curves and the phase-lag predictions worsen. It is concluded that an additional modeling effort is needed to adequatedly reproduce the FTF of small premixed laminar conical flames.