bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Alignment Monitoring Device for the Output Shafting of Marine Gas Turbine
Authors: Xue-You Wen , Dong-ming Xiao , Bin Dong , Zi-gang Song , Dan Kou 
Published: September 2016

When a marine gas turbine is installed on the ship, the alignment among the power turbine, the output shaft and the reduction gearbox needs to be examined and adjusted precisely. After a long period of gas turbine operation, the alignment of the shafting needs be reviewed and adjusted regularly according to relevant regulations as well.
The paper introduces an alignment monitoring device, by which the alignment of the shafting under static and dynamic conditions can be acquired at any time. The device has been verified by real shipboard tests and the on-condition maintenance can be realized. The device can reduce significantly the workload of scheduled maintenance and can be used as a recorder for the responds of gas turbine against various dynamic shocks.
Performance Optimization and Economic Analysis of Geothermal Power Generation by Subcritical and Supercritical Organic Rankine Cycles
Authors: Liu Changwei , Gao Tieyu , Zhu Jiangnan , Xu Jiamin 
Published: September 2016

In a sustainability context, using renewable energy sources to hedge against increasing consumption of fossil fuels and reduce greenhouse gas emissions becomes increasingly important. The geothermal resource has a great application prospect due to its rich reserves and convenient utilization, and Organic Rankine Cycle (ORC) is a effective method to convert the low-grade geothermal to electricity. To improve the performance of geothermal ORC system, working fluid selection, system parameter optimization and the cycle design are the main approaches. Zeotropic mixtures may show superiority as ORC working fluids due to the temperature glides during the phase transitions, which leads to better temperature matches between the working fluid and the heat source/sink. Moreover, owing to the changing temperature during the transition from liquid to vapor in the vapor generator, supercritical ORC provides a great potential in geothermal utilization and irreversibility reduction.
This paper displays an investigation on the performance optimization and economic analysis of various working fluids under subcritical and supercritical conditions. To avoid the silica oversaturation, the geothermal water reinjection temperature should not be less than 70 °C. Turbine inlet temperature, condenser outlet temperature as well as turbine inlet pressure (for supercritical ORC) are optimized to maximize the net power output. Moreover, economic analysis is conducted by taking heat exchanger area per unit power output (APR) and the specific investment cost (SIC) as indicators under the optimal net power output condition. The results shows that working fluid with a medium critical temperature yields greater net power output in supercritical ORC and mixture produces larger net power output compared with its pure components in subcritical ORC. Compared with isobutane (R600a) under subcritical condition, isobutane/isopentane (R600a/R601a) and isobutane/pentane (R600a/R601) under subcritical condition, R134a and R1234ze(E) under supercritical condition yield 3.9%, 3.8%, 8.5% and 8.8% more net power outputs, respectively. In addition, R600a/R601a and R600a/R601 under subcritical condition own higher APR and SIC while R134a and R1234ze(E) under supercritical condition possess lower APR and SIC.
Influence of Reynolds Number on the Performance of Process Centrifugal Compressors
Authors: Liu Yan , Tao Li-hua , Wang Jian , Wang Yang , Wang Xue-jun , Wang Wei 
Published: September 2016

Over the past 60 years, effects of changes in Reynolds number on performance of centrifugal compressors have been widely investigated. However most of cases deal with those compressors with small or medium flow coefficients. Studies on the influence of Reynolds number on centrifugal compressors with large flow coefficients and high machine Mach number are rarely seen in the literature.
This paper deals with two types of centrifugal compressors. One type of compressor (Model 1) has a relatively large capacity with high machine Mach number. The flow coefficient and machine Mach number are 0.16 and 1.05 respectively at the design condition. Those design parameters for the other type of compressor (Model 2) are 0.11 and 0.7 respectively. Both experimental and numerical results show that with increase in Re, aerodynamic performance of centrifugal compressors is improved. However, to what extent that improvement is gained depends on properties of the baseline compressor. When Reynolds number of Model 1 becomes about 5 times large due to increase in the inlet pressure, its polytropic efficiency is only improved 0.7% at the design point in experiment. Flow field inside the impeller is similar to its prototype. For Model 2, when Reynolds number becomes 1.78 times large due to scaling up, the polytropic efficiency of the enlarged one is improved about 2% at the design point. These results demonstrate that for a compressor with large flow coefficient and high machine Mach number, i.e. originally high Reynolds number, the influence of Reynolds number on its performance is limited.
In addition to experiment and CFD, two empirical formulas are applied to work out performance correction due to a change in Reynolds number for Model 1 and Model 2. Although CFD results are more accurate than the empirical results, empirical formula is still useful to get relatively reliable performance correction.
Numerical Study of the Effect of Honeycomb Tip on Tip Leakage Flow in Turbine Cascade
Authors: Fu Yunfeng , Chen Fu , Chen Cong , Song Yanping 
Published: September 2016

A novel leakage flow control strategy with honeycomb seal applied on the tip of the rotor blades in a highly-loaded turbine cascade is proposed. The numerical method is used to study the tip leakage flow in a highly-loaded turbine cascades with flat tip and with honeycomb seal structure, the mechanism of honeycomb tip on inhibiting leakage flow is analyzed, the influence of various relative gap heights is also been investigated. The discussions of the action of the honeycomb-tip structure in reducing leakage flow and improving the turbine efficiency provide the according for control methods of tip leakage flow.
Through the comparative study among three different tip structures of honeycomb tip, honeycomb casing and flat tip, the results show that both honeycomb tip and honeycomb casing inhibit the leakage flow effectively, but honeycomb tip has positive effect on reducing the flow loss in cascade. For the cascade with honeycomb tip, on one hand, the vortices rolled up in the regular hexagon honeycomb cavities dissipate the energy of the tip leakage flow, and the range of influence of the vortices is nearly one third of the tip clearance height. On the other hand, the radial jets caused by the honeycomb obstruct the tip leakage flow like a “pneumatic fence”, resulting in weaker leakage flow and less leakage flow rate. Besides, the honeycomb tip reduces the scale of the leakage vortex, thus the leakage loss also decreases. Compared with the flat tip cascade at the clearance height of 1%H, the honeycomb tip cascade with the same clearance height obtains decrease of the leakage flow rate and leakage flow speed in circumference by 10.16% and 20%. As a result, the leakage vortex in honeycomb tip cascade is undermined, the loss is reduced by nearly 4.43%.
Considering the abradable property of the honeycomb seal that can protect the blade tips from damage, the cascade with honeycomb tip structure can obtain a smaller clearance height and achieve better sealing effect. Compared to cascade with the flat tip at the clearance height of 2%H, the amount of leakage flow using inlet flow in the honeycomb tip cascades decreases by 17.33%, 36.63% and 54.79% at the clearance heights of 2%H, 1.5%H and 1%H, the losses related to the leakage flow is reduced by nearly 5.71%, 14.33% and 25.24%, respectively.
Influence of Nonlinear Flame Models on Thermoacoustic Instabilities in Combustion Chambers
Authors: Campa Giovanni , Cademartori Roberto 
Published: September 2016

Thermoacoustic phenomena observed in gas turbine combustion chambers are usually related to a dependence of the heat release fluctuations to the velocity fluctuations at the injection point. Linear models for this dependence give information about stability, while nonlinear models can predict also limit cycles amplitude and frequency. This nonlinear dependence can be obtained by means of experiments or numerical tools by measuring the flame describing function (FDF). Analytical expressions have been proposed in the years to obtain nonlinear flame models to be introduced into simplified tools. Through these nonlinearities, information about limit cycle amplitudes, bifurcation diagrams and hysteresis can be achieved. The importance of this information is related to the possibility of managing the variation of certain operating parameters to keep the combustor in a safe operating zone. Additionally, from the bistable zone information about the operational margin can be obtained in order to stay far from the unstable condition.
The aim of this work is to describe a simplified procedure to track combustors bifurcation diagrams using nonlinear flame models implemented in a 3D thermoacoustic tool based on the finite element methods (FEM) in the frequency domain. First flame describing functions (FDF) for not swirled and swirled burners from the literature are considered and applied to simplified configurations. Then, FDFs are introduced into an industrial configuration and the bifurcation diagrams are tracked. For both cases, the paper describes the influence of various FDFs parameters and shapes on the predictions of combustors stability boundaries.
Thermo-Fluid Dynamic Analysis on the Compression Process of Liquid-Gas Two-Phase
Authors: Mohan Abhay , Chidambaram Palani Kumar , Suryan Abhilash , Kim Heuy Dong 
Published: September 2016

In a typical compressor - turbine cycle, the majority of the output power from the turbine is consumed for the operation of the compressor. In order to obtain higher output from turbines, certain techniques are employed to reduce compressor work. It is known that the compressor work increases continually with the increase in temperature of the operating fluid. One of the techniques to achieve reduction of temperature of the fluid is through the inter-cooling between the compressor stages. But this may lead to the decrease in the overall efficiency of the cycle. Another concept is to utilize the high enthalpy of vaporization of water. One of these techniques is known as wet compression. Here water droplets are introduced into the compressor and the fluid mixture is compressed. The droplets absorb the heat from the surroundings and evaporate, and thus reduces the temperature of the operating fluid. This in turn decreases the compression work. Also in order to maintain the O/F ratio of gas turbine, the mass flow rate of the fuel will also increase. All the above mentioned factors thus increase the net power output of the turbine engine.
For the current study, a cylinder-piston system containing air involving fine droplets of water is modeled as a simple representation of the wet compression process. The compression process is achieved by the movement of the piston. Thermodynamic properties such as pressure and temperature are investigated in detail for different parameters such as rates of compression, droplet mass and sizes. Analytical equations are derived and validated using the classical D-square law. These equations are used in order to track the change in fluid properties during the compression process and its deviation from dry air compression. The results thus obtained are discussed in terms of the rates of compression, absolute and relative humidities. Corresponding thermodynamic curves are generated which are seen to deviate significantly from the dry isentropic curves. It is observed that smaller diameter droplets, slower speeds of compression and higher amount of overspray percentages lead to lower compressor work.
Exhaust Gas Recirculation on Humidified Flexible Micro Gas Turbines for Carbon Capture Applications
Authors: De Paepe Ward , Montero Carrero Marina , Giorgetti Simone , Parente Alessandro , Bram Svend , Contino Francesco 
Published: September 2016

From all fossil fuels, natural gas has the lowest carbon to hydrogen ratio, which enables Gas Turbines (GTs) running on natural gas to produce electricity with the lowest CO2 emissions per produced kWh. These lower emissions have pushed power production towards natural gas. However, if we want to move towards a carbon clean power production, the carbon in the exhaust must be captured. This leads to a major challenge since the low CO2 concentration in the exhaust of a GT makes carbon capture much more expensive compared to coal fired power production.
The CO2 concentration can be increased by performing Exhaust Gas Recirculation (EGR). However, EGR on GT cycles negatively affects the efficiency. Using the concept of Humid Air Turbine (HAT), we investigate whether the efficiency losses can be compensated by introducing water in the cycle. This paper presents this novel approach by showing the impact of EGR on a flexible humidified micro Gas Turbine (mGT). It is based on results of simulations performed in Aspen® using the Turbec T100 mGT as reference case. Both the dry and wet operation of the Turbec T100 were simulated and validated with experimental results. For improved carbon capture, EGR was simulated in both the dry and the humidified mGT cycle. Simulation results indicate that EGR has no effect on the thermodynamic performance of the mGT and its components (compressor, turbine and recuperator), however efficiency is reduced significantly (up to 3.8% relative at nominal power output) because of additional losses to the fan blower installed to ensure the EGR. Additionally, the cycle performance strongly depends on the degree of cooling of the EGR stream before injection in the compressor inlet. Nevertheless, the simulation results also reveal that mGT humidification increases the total cycle efficiency, entirely compensating the EGR induced losses. Humidifying the mGT with EGR even leads to a higher electric efficiency than the standard mGT cycle, unlocking the idea of carbon capture in mGTs.
FLOvane: A New Approach for HP Vane Design
Authors: Wang Dingxi , Ornano Francesco , Li Yan Sheng , Wells Roger , Hjalmarsson Christer , Hedlund Lars , Povey Thomas 
Published: September 2016

The University of Oxford has been working for a number of years on a conceptually new philosophy for HP vane design [1].
The desired function of the HP vane is to accept flow from a — generally — annular intake, and turn and accelerate it with minimum loss and heat transfer, and with due consideration to mechanical, manufacturing and integration issues. The conventional design process is well-defined: annulus line definition; through-flow analysis; 2D airfoil section definition; vane stack definition; lean/sweep treatments; secondary flow contouring and fillet design; vane and platform cooling system design; integrated aero/thermal/capacity optimization. The process is based on optimizing 2D airfoil stacks to control secondary flows. More recent research (last 20 years) has led to better understanding of airfoil lean, airfoil sweep, leading edge treatments and end-wall profiling. There may be some iterative optimization in which the airfoil sections themselves are modified, but these treatments (as implied by the terminology) are essentially modifications to a 2D airfoil stack which interrupts the upstream annular (most aero-engines) or can-partitioned (most land-based gas turbines) duct.
It is proposed that a more natural design starting point for admitting and accelerating flow with minimum loss (etc.) is a trumpet-shaped flow-path which gradually turns to the desired angle. This approach rejects many traditional concepts in aerodynamics (the sacrosanct nature of the airfoil, concepts of good and bad lift distributions, concepts of vane and platform, etc.), and focuses our attention on the design of a highly-lofted flow-path.
The purpose of this paper is to show that there may be merit in reappraising the starting point for HP vane design, and in investigating Fully Lofted Oval vane (FLOvane) forms of the type described. The corresponding author has not yet heard a good argument against the proposed design philosophy. Despite significantly diverging from conventional wisdom in terms of both process and final geometric form, the following advantages are claimed: improved aerodynamic loss characteristics, reduced heat load, improved cooling performance, improved thermal-mechanical life, improved stage/engine efficiency.
The claimed advantages are justified with detailed numerical analyses of two current industrial gas turbines, compared back-to-back with modified turbines incorporating unoptimised FLOvane designs. Significant performance improvements were observed when FLOvane designs were used.
Endwall Loss in Turbine Cascades
Authors: Coull John D. 
Published: September 2016

Prior to the detailed design of components, turbomachinery engineers must guide a mean-line or throughflow design towards an optimum configuration. This process requires a combination of informed judgement and low-order correlations for the principle sources of loss. With these requirements in mind, this paper examines the impact of key design parameters on endwall loss in turbines, a problem which remains poorly understood.
The analysis focuses on parametric computational studies of linear cascades, which represent a simplified model of real-engine flow. The designs are nominally representative of the Low Pressure Turbine blades of an aero engine. The paper examines the variations across the design space in a quantitative manner, examining the impact of flow angles, blade thickness and suction surface aerodynamics.
Efficient Multi-Objective Optimization of Labyrinth Seal Leakage in Steam Turbines Based on Hybrid Surrogate Models
Authors: Cremanns Kevin , Roos Dirk , Hecker Simon , Dumstorff Peter , Almstedt Henning , Musch Christian 
Published: September 2016

The demand for energy is increasingly covered through renewable energy sources. As a consequence, conventional power plants need to respond to power fluctuations in the grid much more frequently than in the past. Additionally, steam turbine components are expected to deal with high loads due to this new kind of energy management. Changes in steam temperature caused by rapid load changes or fast starts lead to high levels of thermal stress in the turbine components. Therefore, todays energy market requires highly efficient power plants which can be operated under flexible conditions. In order to meet the current and future market requirements, turbine components are optimized with respect to multi-dimensional target functions. The development of steam turbine components is a complex process involving different engineering disciplines and time-consuming calculations. Currently, optimization is used most frequently for subtasks within the individual discipline. For a holistic approach, highly efficient calculation methods, which are able to deal with high dimensional and multidisciplinary systems, are needed. One approach to solve this problem is the usage of surrogate models using mathematical methods e.g. polynomial regression or the more sophisticated Kriging. With proper training, these methods can deliver results which are nearly as accurate as the full model calculations themselves in a fraction of time.
Surrogate models have to face different requirements: the underlying outputs can be, for example, highly non-linear, noisy or discontinuous. In addition, the surrogate models need to be constructed out of a large number of variables, where often only a few parameters are important. In order to achieve good prognosis quality only the most important parameters should be used to create the surrogate models. Unimportant parameters do not improve the prognosis quality but generate additional noise to the approximation result. Another challenge is to achieve good results with as little design information as possible. This is important because in practice the necessary information is usually only obtained by very time-consuming simulations.
This paper presents an efficient optimization procedure using a self-developed hybrid surrogate model consisting of moving least squares and anisotropic Kriging. With its maximized prognosis quality, it is capable of handling the challenges mentioned above. This enables time-efficient optimization. Additionally, a preceding sensitivity analysis identifies the most important parameters regarding the objectives. This leads to a fast convergence of the optimization and a more accurate surrogate model. An example of this method is shown for the optimization of a labyrinth shaft seal used in steam turbines. Within the optimization the opposed objectives of minimizing leakage mass flow and decreasing total enthalpy increase due to friction are considered.
Nonlinear Hydrodynamics of a Bluff-Body Stabilized Turbulent Premixed Flame
Authors: Lee C. Y. , Cant R. S. 
Published: September 2016

Bluff-body stabilized turbulent premixed flames can experience hydrodynamic instability caused by the interaction of the flame with small-scale vortices in the separated shear layer around the recirculation region, as well as with the large-scale coherent structures in the far-wake. A globally hydrodynamically unstable system, for example one which involves vortex shedding, can exhibit limit-cycle behaviour due to the coupling between pressure oscillation and velocity fluctuations. In this work, the hydrodynamic behaviour of a bluff-body stabilized turbulent premixed propane/air flame in a model jet-engine afterburner is investigated using Computational Fluid Dynamics (CFD). A URANS approach was found to be appropriate for the range of frequencies considered in this study. Combustion is modelled using a modified flame surface density (FSD) approach. The observed self-excited hydrodynamic oscillations are analyzed using a nonlinear dynamical framework which is capable of capturing elaborate nonlinear behaviour including quasiperiodicity and chaos. The results from the CFD are first validated using available experimental data. The velocity at the inlet is gradually increased from 14 m/s to 33 m/s and the global flame structure is observed. With increasing inlet velocity, the flame first transitions from steady state to an oscillating state with a symmetrical flame structure, and eventually to an asymmetrical flame structure at higher velocities. The flame is essentially steady in the lower range of velocities considered before transitioning to a limit cycle oscillation after a critical velocity is exceeded.
A doubling in the frequency of the hydrodynamic oscillation is also observed at intermediate values of inlet velocity. This investigation demonstrates that turbulent premixed reacting flows can exhibit strong hydrodynamic oscillation. An understanding of such behaviour can assist in developing methods to control flow instabilities and therefore help in suppressing thermoacoustic oscillation.