bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement and Prediction of Centrifugal Compressor Axial Forces During Surge: Part 2 — Dynamic Surge Model
Authors: Munari Enrico , Morini Mirko , Pinelli Michele , Brun Klaus , Simons Sarah , Kurz Rainer 
Published: August 2017

The force acting on centrifugal compressors is an important parameter to be considered throughout the operating life of these turbomachines. When the compressor is operating in surge conditions these forces can become highly dangerous for the mechanical and aerodynamic structures. This instability is usually avoided in industrial applications but the anti-surge system may not react in time when emergency shutdowns or power failures take place. During these rapid transients, surge can develop, generating unsteady forces which can harm the close clearance components of the compressor. Therefore, the capability to predict the characteristics and the dynamics of these surge forces would allow the estimation of the off-design fatigue cycles produced on these components by surge. Currently, no validated method exists to predict the frequency and amplitude of the surge forces and determine the potential damage of these components.
In this paper a lumped parameter model, developed by using the bond graph approach to predict the dynamic surge fluid-dynamic oscillations, is presented. The model requires the geometry and the steady-state performance maps of the compressor as inputs, together with the piping system configuration characteristics.
The simulator, is provided with a supplementary tool to estimate the axial force frequency and amplitude, taking into consideration all the contributions to the axial fluid-dynamic thrust, the stiffness-damping of the thrust bearing and the mass of the rotor.
The model was tuned and validated using the test case axial force data from the Southwest Research Institute facility. The model has shown good agreement with the experimental results which implies that it can offer significant information about the severity of a surge event and the quantification of the machine performance losses together with possible damage to the close clearance components. This study is a first important step that can lead to schedule optimization for maintenance and repair activities.
Working Fluid and Parametric Optimization of a Two-Stage ORC Utilizing LNG Cold Energy and Low Grade Heat of Different Temperatures
Authors: Sun Zhixin , Wang Shujia , Xu Fuquan , Wang Tielong 
Published: August 2017

Natural gas is considered as a green fuel due to its low environmental impact. LNG contains a large amount of cold exergy and must be regasified before further utilization. ORC (Organic Rankine Cycle) has been proven to be a promising solution for both low grade heat utilization and LNG cold exergy recovery. Due to the great temperature difference between the heat source and LNG, the efficiency of one-stage ORC is relatively small. Hence, some researchers move forward to a two-stage Rankine cycle.
Working fluid plays a quite important role in the cycle performance. Working fluid selection of a two-stage ORC is much more challenging than that of a single-stage ORC. In this paper, a two-stage ORC is studied. Heat source temperatures of 100,150 and 200°C are investigated. 20 substances are selected as potential candidates for both the high and low Rankine cycles. The evaporating, condensing and turbine inlet temperatures of both Rankine cycles are optimized by PSO (Particle Swarm Optimization).
The results show that the best combination for heat source temperature of 100°C is R161/R218 with the maximum exergy efficiency of 35.27%. The best combination for 150°C is R161/RC318 with the maximum efficiency of 37.84% and ammonia/ammonia with the maximum efficiency of 39.15% for 200°C. Fluids with intermediate critical temperature, lower triple point temperature and lower normal boiling temperature are good candidates.
Development of Compression System Dynamic Simulation Code for Testing and Designing of Anti-Surge Control System
Authors: Mohajer Abbas , Abbasi Eshagh 
Published: August 2017

As cost of damages to the compression systems in oil and gas industry can lead to significant capital cost loss and plant downtime, these valuable assets must be carefully protected to achieve a high level of production and operational reliability. In recent years, several research activities have been conducted to develop knowledge in analysis, design and optimization of compressor anti surge control system. Since, the anti-surge control testing on a full scale compressor are limited for possible consequences of failure and also the experimental facility can be expensive to set up control strategies and logics, design process often involves analyses using compression system dynamic simulation. Such Simulator enables the designer to test the new control logic and see the results before implementing it on governor system. This would increase the reliability and prevents undesirable costs resulting from practical trial and error process. Taking into account its own requirements and market demand, a high fidelity compression system dynamic simulation environment has developed by MAPNA Turbine (TUGA) to verify the anti-surge control system design and test the control logic across the all operating range of the compressor performance. Typical control scenarios that have to be considered are process control, starting and stopping, and emergency shutdowns. Having such simulator is also deemed to be essential to serve other applications during all stages of system life cycle, including but not limited to the educational tool for operators training, Site Acceptance Test (SAT) and Factory Acceptance Test (FAT) and compression plant design optimization.
This research focuses on developing and validating a physics-based, modular, non-linear and one-dimensional dynamic model of a compression system: centrifugal compressor and its surrounding process equipment like scrubber, cooler, a recycle line with a control valve and check valve. The mathematical approach of the model is based on laws of conservation and the included ordinary differential equations (ODEs) which describe the system dynamics, is solved by using advanced computational method in an in-house FORTRAN code. Compressor characteristics maps generated from company compressor test bench are used to determine compressor pressure ratio and efficiency. All equipment and inlet/outlet accessories as well as test instructions follow the requirements of PTC10. The simulation within a wide range of operating conditions allows a parametric study to be performed and the optimal values of the control parameters to be selected. In order to check the validity of the model, the simulation results are then compared with experimental data taken on the company industrial compressor test facility and also with operational field measurement.
A New Temperature Based Method for Determination of Lifetime Consumption of Turbo-Machinery Components During Operation
Authors: Sistaninia M. , Ugel D. , Olmes S. 
Published: August 2017

In order to operate the turbo-machineries more flexibly, a lifetime counting method was developed which enables estimating lifetime consumption of high thermal-inertia components based on the temperature history of the components. It can account for consumed fatigue life at the locations of temperature measurement during the turbo-machine operation. By considering the operation history, the structural component can be operated closer to its lifetime limits, to increase the intervals between inspections, and therefore to extend the operational lifetime of the turbo-machine.
In this method the cold start (CS) to full load cycle, with the number of cycles to crack initiation Ncs, is defined as reference load cycle. The damage weighting factor Ni/NCS for cyclic event i is then calculated based on a semi-empirical correlation between Ni/NCS and the temperature history of the part. The semi-empirical correlation can be determined for each component or each location depending on the required precision. It is determined based on the Low Cycle Fatigue (LCF) life calculated for different Gas Turbine (GT) operation scenarios. The damage weighting factors are then employed to calculate the lifetime consumption using Miner’s rule.
The predictions of this method for the turbine housings of several Gas Turbines (GTs) were evaluated against finite element (FE) results. Multiple load cases were considered for each GT. It is shown that this approach can account for the lifetime consumption using the minimum required number of GT operation parameters.
CFD Analysis of the Combustion Chamber of a Commercial Aircraft Engine of Medium Thrust Class From a Maintenance Perspective
Authors: Kuntzagk Stefan , Kraft Jörn , Esemann Ina 
Published: August 2017

The combustion chamber of aircraft engines plays an important role in achieving the optimum performance during an engine overhaul. For long decades, it has been common understanding in the MRO business that a well overhauled compressor and turbine are required to get an engine with low SFC and high EGT margin. In recent work at Lufthansa Technik AG, a comprehensive CFD analysis of the combustion chamber showed that, in contrast to this, small geometrical features influence the mixing process in the combustion chamber and can have an effect on the exit temperature profile. This in turn can reduce the accuracy of the EGT measurement significantly and create measurement errors and misinterpretations of the real engine performance.
In order to get insight into the flow topology, a very detailed digital model has been created using scans of the hardware available in the shop. Important geometrical features such as the cooling provisions and swirl creating components have been included in a very detailed manner with an efficient hexahedral mesh. The model includes the HPT vanes and the cooling flow extraction from the secondary cold flow. CFD results have been generated using the flow solver Ansys CFX 17.1, which is able to predict all relevant physical effects such as injection of liquid fuel, evaporation, and combustion of Jet A1 fuel using the Burning-Velocity combustion model. The flow in the combustion chamber shows large natural fluctuations. Subsequently, for each case a transient calculation has been carried out in order to allow an evaluation of the time-averaged flow field. Different geometrical features are investigated to predict the effect of geometry deviations on the exit temperature profile, e.g. the shape and size of the dilution holes.
Finally along the example of two CFM56 engines it will be shown how the data obtained by the detailed CFD model is used to optimize work-scoping and maintenance procedures. On the two cases put forward the combination of extended test-cell instrumentation and detailed modeling enabled not only the identification but also the rectification of combustion chamber deviations. This in turn minimized the necessary work, whereas in the past combustion chamber issues often went unnoticed and consequently resulted in extensive additional work.
Influence of Carrier Air Preheating on Autoignition of Inline-Injected Hydrogen-Nitrogen Mixtures in Vitiated Air of High Temperature
Authors: Schmalhofer Christoph A. , Griebel Peter , Aigner Manfred 
Published: August 2017

Gas turbines will play a significant role in future power generation systems because they provide peak capacity due to their fast start-up capability and high operational flexibility. However, in order to meet the COP 21 goals, de-carbonization of as turbine fuels is required. Compared to natural gas operation, autoignition and flashback risks in gas turbines operated on hydrogen-rich fuels are higher which has to be taken into account for a proper gas turbine design. From investigations of these phenomena at relevant operating conditions with appropriate measurement techniques, e.g. high-speed imaging, the understanding of the non-stationary processes occurring during autoignition can be improved and design guidelines for a safe and reliable gas turbine operation can be derived.
The present study investigates the influences of elevated carrier-air preheating temperatures and hydrogen fuel volume fractions on autoignition at hot gas temperatures higher than 1100 K and pressures of 15 bar. An in-line co-flow injector is used to inject the hydrogen-nitrogen fuel mixtures. The formation, temporal and spatial development of autoignition kernels at high-temperature vitiated air conditions, e.g. relevant to reheat combustor operation, are studied. The experiments were conducted in an optically accessible mixing section of a generic reheat combustor. The hydrogen-nitrogen fuel mixtures of up to 70 vol. % hydrogen are injected in-line into the mixing section along with the carrier-air which was preheated to temperatures between 303 K and 703 K. High-speed imaging was used to detect the autoignition kernels and their temporal and spatial development from luminescence signals. Particle Image Velocimetry measurements were conducted to obtain the velocity distribution in the mixing section at autoignition conditions.
The influences of vitiated air temperatures and carrier preheating temperatures on autoignition and flame stabilisation limits are shown, alongside the spatial distribution of different types of autoignition kernels, developing at different stages of the autoignition process. The development of autoignition kernels could be linked to the shear layer development derived from global experimental conditions.
Influence of a Cylindrical Exhaust Hood Installation on the Last Stage Rotor Blades of a Low Pressure Model Steam Turbine
Authors: Müller Fabian F. , Schatz Markus , Vogt Damian M. , Aschenbruck Jens 
Published: August 2017

The influence of a cylindrical strut shortly downstream of the bladerow on the vibration behavior of the last stage rotor blades of a single stage LP model steam turbine was investigated in the present study. Steam turbine retrofits often result in an increase of turbine size, aiming for more power and higher efficiency. As the existing LP steam turbine exhaust hoods are generally not modified, the last stage rotor blades frequently move closer to installations within the exhaust hood. To capture the influence of such an installation on the flow field characteristics, extensive flow field measurements using pneumatic probes were conducted at the turbine outlet plane. In addition, time-resolved pressure measurements along the casing contour of the diffuser and on the surface of the cylinder were made, aiming for the identification of pressure fluctuations induced by the flow around the installation. Blade vibration behavior was measured at three different operating conditions by means of a tip timing system.
Despite the considerable changes in the flow field and its frequency content, no significant impact on blade vibration amplitudes were observed for the investigated case and considered operating conditions. Nevertheless, time-resolved pressure measurements suggest that notable pressure oscillations induced by the vortex shedding can reach the upstream bladerow.
Investigation of a Gas Turbine Process With Reheat Combustion at Flue Gas Recirculation and Oxyfuel-Conditions
Authors: Beenken Florian , Joos Franz 
Published: August 2017

In near future electrical power generation will still be supplied by fossil fuels. To reach the targets of the conference on climate change in Paris 2015 one method proposed is the CO2 sequestration and usage or alternatively storage.
Compared to coal-fired power station the amount of CO2 in the exhaust gas of gas turbine power station is much less and therefore more difficult to remove. To enhance the efficiency of the CO2-sequestration process enrichment of the CO2 in the exhaust gas could be a solution. This can be achieved by exhaust gas recirculation or by burning with pure O2 instead of air avoiding a lot of N2 in the exhaust gas, called Oxyfuel process.
The work concerns to investigations of a reheat gas turbine operating with flue gas recirculation as well as with Oxyfuel operation. The thermodynamic process has been modeled in detail considering the additional demand of cooling of the combustors and the turbines at Oxyfuel process. Additional combustion experiments have been carried out with flue gas recirculation as well as with Oxyfuel conditions burning Natural Gas with O2 in a CO2 environment to investigate the flame stability and extinction limit.
The thermophysical properties, like specific heat capacity and sound velocity, are strongly altered by the high content of CO2 and H2O in the fluid of the turbine as well as of the compressor. For example during Oxyfuel conditions the pressure ratio is expected to decrease to about 78% of air operation. The influence of flue gas recirculation and Oxyfuel process to the gas composition as well as to the heat transfer and exit conditions are discussed.
Experimental and Numerical Investigation of Transition Effects on a Low Reynolds Number Airfoil
Authors: Collison Michael J. , Harley Peter X. L. , di Cugno Domenico 
Published: August 2017

Low speed, small scale turbomachinery operates at low Reynolds number with transition phenomena occurring. In small consumer product applications, high efficiency and low noise are key performance metrics. Transition behaviour will partly determine the state of the boundary layer at the trailing edge; whether it is laminar, turbulent or separated impacts aerodynamic and acoustic performance. This study aimed to evaluate a commercially available CFD transition model on a low Reynolds number Eppler E387 airfoil and identify whether it was able to correctly model the boundary layer transition, and at what expense.
CFD was carried out utilising the ANSYS Shear Stress Transport (SST) k-ω γ-Reθ transition model. The CFD progressed from 2D in Fluent v150, through to single cell thickness 3D (pseudo 2D) in CFX v172. An Eppler E387 low Reynolds number airfoil, for which experimental data was readily available from literature at Re = 200,000 was used as the validation case for the CFD, with results computed at numerous incidence angles and mesh densities.
Additionally, experimental surface oil flow visualisation was undertaken in a wind tunnel using a scaled E387 airfoil for the zero incidence case at Re = 50,000. The flow visualisation exhibited the expected key features of transition in the breakdown of the boundary layer from laminar to turbulent, and was used as a validation case for the CFD transition model.
The comparison between the results from the CFD transition model and the experimental data from literature suggested varying levels of agreement based on the mesh density and CFD solver in the starting location of the laminar separation bubble, with higher disparity for the position of the reattachment point. Whether 2D or 3D, the prediction accuracy was seen to worsen at high incidence angles. Finally, the location of the laminar separation bubble between CFD and oil flow visualisation had good agreement and a set of guidelines on the mesh parameters which can be applied to low Reynolds number turbomachinery simulations was determined.
Experimental and Numerical Analysis of FLOX®-Based Combustor for a 3kW Micro Gas Turbine Under Atmospheric Conditions
Authors: Seliger Hannah , Stöhr Michael , Yin Zhiyao , Huber Andreas , Aigner Manfred 
Published: August 2017

This paper presents an experimental and numerical study of the flow field and heat release (HRL) zone of a six-nozzle FLOX®-based combustor at atmospheric pressure. The combustor is suitable for the use in a micro gas turbine (MGT) based combined heat and power (CHP) system with an electrical power output of 3 kW. The velocity field was measured using stereoscopic particle image velocimetry (PIV). The heat release zone was visualized by OH*-chemiluminescence (OH* CL) and the flame front by OH planar laser-induced fluorescence (OH PLIF). The results are compared with CFD simulations to evaluate the quality of the applied numerical turbulence and combustion models. The simulations were performed using Reynolds-averaged Navier-Stokes equations in combination with the k-ω-SST-turbulence model. Since the FLOX®-based combustion is dominated by chemical kinetics, a reaction mechanism with detailed chemistry, including 22 species and 104 reactions (DRM22), has been chosen. To cover the turbulence-chemistry interaction, an assumed probability density function (PDF) approach for species and temperature was used.
Except for minor discrapancies in the flow field, the results show that the applied models are suitable for the design process of the combustor. In terms of the location of the heat release zone, it is necessary to consider possible heat losses, especially at lean operating conditions with a distributed heat release zone.
A Study of s-CO2 Power Cycle for CSP Applications Using an Isothermal Compressor
Authors: Heo Jin Young , Ahn Yoonhan , Lee Jeong Ik 
Published: August 2017

For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including higher cycle efficiencies, reduced component sizing, and potential for the dry cooling option, in comparison to the conventional steam Rankine cycle. Increasing number of investigations and research projects are involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems.
In this conceptual study, an isothermal compressor, a turbomachine which undergoes the compression process at constant temperature to minimize compression work, is applied to the s-CO2 power cycle layout. To investigate the cycle performance changes of adopting the novel technology, a framework for defining the efficiency of the isothermal compressor is revised and suggested. This study demonstrates how the compression work for the isothermal compressor is reduced compared to that of the conventional compressor under varying compressor inlet conditions.
Furthermore, the recompression Brayton cycle layout using s-CO2 as a working fluid is evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the simple recuperated Brayton cycle with an isothermal compressor performs better than the given reference recompression cycle by 6–10% points in terms of cycle thermal efficiency. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency. Adopting an isothermal compressor in the s-CO2 layout, however, can imply larger heat exchange area for the compressor which requires further detailed design for realization in the future.