bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vortex Structures Analysis and Loss Mechanisms in Axial Compressor Cascade With and Without Bleeding Slot Using Large Eddy Simulation
Authors: Gong Yun , Chen Shaowen , Zheng Haipeng , Wang Songtao 
Published: January 2021

Abstract
Tip leakage flow is one of the main sources of flow losses in an axial compressor, and the understanding of the tip leakage flow helps to explore better flow control methods and design more advanced compressors. Therefore, the vortex structures and loss mechanisms were analyzed in a compressor cascade with tip clearance in the present paper. Large eddy simulation was used to better resolve the vortices with more accurate numerical results. The iso-surface of Q criterion in the compressor cascade is captured for recognizing and analyzing the vortex structures. The horse shoe vortices, tip leakage vortex, induced vortex, tip separation vortex and passage vortex were well captured and their interactions were interpreted. Fast Fourier Transformation was also applied to analyze the frequency signal in the flow field. Afterwards, the case with an upstream bleeding slot was also calculated and compared with the original case without a bleeding slot. The bleeding rate is 2.8% of the mass flow rate at inlet. The removal of the inlet boundary layer resulting from the bleeding leads a 42.4% reduction of the total pressure loss coefficient compared with that of the case without the bleeding slot. In the case with the bleeding slot, the size of the passage vortex is greatly reduced, and the mixing between the tip leakage vortex and passage vortex is postponed. Better performance is achieved with the bleeding slot accordingly.
Injection of Kerosene Into a High-Temperature and High-Speed Air Crossflow
Authors: Yulan Wang , Yong Mu , Xiongjie Fan , Qianpeng Zhao , Gang Xu 
Published: January 2021

Abstract
The jet of kerosene into high-temperature and high-speed air crossflow was studied experimentally, to study the characteristics of penetration and evaporation in afterburner. A fuel injection bar with a 0.6 mm diameter plain orifice was used in the experiment. The angle between jet and air flow was 90°. The tests were conducted at atmospheric pressure. The air temperature was between 400 °C to 800 °C, and the air velocity increased from 100 m/s to 250 m/s, which was close to the working condition of the afterburner. The jet flow rate also increased from 5 kg/h to 40 kg/h. Fuel-PLIF was used to visualize the trajectory and structure of the jet trajectory. It was observed that the core region of the jet (the largest volume flow) was close to the windward side, and the leeward side of the jet had a relatively wide peripheral area due to the shear of the high-speed airflow. The jet trajectory is affected by viscosity force, inertia force and surface tension in different proportion under high-temperature and high-speed airflow. The jet penetration is related to the momentum ratio (q), air flow Weber number (We0), and aerodynamic Weber number (Wea). In experiment, q ranged from 2 to 236, We0 ranged from 72 to 735, and Wea ranged from 0.36–41. The relationship between penetration to these variables was established. The plume width and evaporation distance under different test conditions were compared. The results show that the plume width varied within a narrow range in high-temperature and high-speed air crossflow, and the fuel evaporation distance was much more affected by the fuel flow than the airflow condition, basically in a linear correlation with fuel flow. The results are of great significance to the size design and arrangement of the stabilizers in afterburners.
Nonlinear Response and Stability of an Experimental Overhung Compressor Mounted With a Squeeze Film Damper
Authors: Gooding William J. , Meier Matthew A. , Gunter Edgar J. , Key Nicole L. 
Published: January 2021

Abstract
This paper presents rotordynamic data obtained within a test facility studying the aerodynamics of a high-speed centrifugal compressor for aero-engine applications. The experimental overhung compressor is supported by two rolling element bearings. The compressor-end ball bearing is supported by an oil-fed squeeze film damper.
After some period of operation, the compressor began to exhibit a unique nonlinear increase in the rotordynamic response followed by an unexpected subsynchronous whirl instability as the speed continued to increase. Finally, as the rotor speed was increased further, the rotor re-stabilized.
A numerical model of the compressor system was created using a commercially available software suite. This model indicates the effective weight of the damper support has a significant effect on the frequency of the second critical speed. Increasing this weight causes the second critical speed, originally predicted at 35,200 RPM, to shift down to 15,650 RPM. This increase in the support weight is due to inertial interaction between the damper support and the surrounding static structure. The increased shaft deflection that occurs as the rotor passes through this shifted critical speed causes the damper to lockup, resulting in the increased response observed experimentally. At a slightly higher speed, Alford-type aerodynamic cross-coupling forces excite the two subsynchronous critical speeds. Finally, as the rotor departs from the second critical speed, the damper unlocks and is able to effectively suppress the Alford-type instabilities, allowing the rotor to return to stable operation.
The Effect of Reaction on Compressor Performance
Authors: Chana Krishan S. , Miller Robert J. 
Published: January 2021

Abstract
Reaction is the fundamental parameter by which the asymmetry of the velocity triangle of a stage is set. Little is understood about the effect that reaction has on either the efficiency or the operating range of a compressor. A particular difficulty in understanding the effect of reaction is that the rotor and stator have a natural asymmetry caused by the centrifugal effects in the rotor boundary layer being much larger than that in the stator boundary layer. In this paper a novel approach has been taken: McKenzie’s ‘linear repeating stage’ concept is used to remove the centrifugal effects. The centrifugal effects are then reintroduced as a body force. This allows the velocity triangle effect and centrifugal force effect to be decoupled. The paper shows the surprising result that, depending on how the solidity is set, a 50% reaction stage can either result in the maximum, or the minimum, profile loss. When the centrifugal effects are removed, 50% reaction is shown to minimise endwall loss, maximise stage efficiency and maximise operating range. When the centrifugal effects are reintroduced, the compressor with the maximum design efficiency is found to rise in reaction by 5% (from 50% reaction to 55% reaction) and the compressor with the maximum operating range is found to rise in reaction by 15% (from 50% reaction to 65% reaction).
LES of the Ignition of a Two-Phase Staged Swirling Burner: Influence of Ignition Location and Operating Conditions on the Flame Shape
Authors: Mesquita Léo C. C. , Vié Aymeric , Ducruix Sébastien 
Published: January 2021

Abstract
Staged multipoint injection has been developped as an interesting technology to control flow and flame dynamics in Lean Premixed Prevaporized (LPP) swirled gas turbine burners. The BIMER combustor, a two-staged swirling burner composed of a pilot stage and a multipoint stage, has been operated for many years to shed light on the complex phenomena related to such kinds of burners, as well as to build an experimental database for the validation of numerical developments. During the experimental campaigns, several flame archetypes have been encountered, flame shape transitions and a consequent hysteresis cycle were observed depending on the liquid fuel splitting between the stages. As each flame archetype presents different combustion characteristics and thermoacoustic behavior, it is highly relevant to understand how to stabilize such archetypes. In this optics, the objective of the present paper is to investigate ignition as a way to control the final flame archetype. By means of Large Eddy Simulations, we explore different operating conditions and have a direct insight into the flame propagation process. Two operating conditions are simulated: a low and a high flow rate condition. Two simulations are performed for each operating point, one where the ignition kernel is initiated in the Outer Recirculation Zone (ORZ) and the other one where it is initiated in the Central Recirculation Zone (CRZ). In all cases the fuel is injected only through the pilot injector, as in the ignition process during experiments. For the low power point, both ORZ and CRZ ignitions lead to the stabilization of a V-flame. When igniting on the high power operating point, the ORZ ignition results in a M-shaped flame, while the CRZ one results in a tulip shape. These different behavior are analyzed and discussed in the final part of the paper.
Prediction of Gas Turbine Performance Using Machine Learning Methods
Authors: Goyal Vipul , Xu Mengyu , Kapat Jayanta , Vesely Ladislav 
Published: January 2021

Abstract
The current study is based on multiple machine learning algorithms to predict the normal behavior of operational parameters including power generated and blade path temperature spread. The predictions can be used to identify anomalies and probable failures in the gas turbine performance. The data used in the study is taken from multiple heavy-duty gas turbine units of combined cycled utility power plants which are known to contain operational failures. The predictors include operational parameters such as fuel flow, various thermodynamic variables, etc.
In the first step, we cluster the observations into different working modes, because of the heterogeneous behavior of the gas turbine parameters under various modes. Then we consider predicting the operational parameters under each mode respectively, via algorithms including random forest, generalized additive model, and neural networks. The models are trained and parameters are selected based on the overall prediction performance on the validation set.
The comparative advantage based on prediction accuracy and applicability of the algorithms is discussed for real-time use and post processing. The advantage of our method is that they achieve high predictive power and provide insight into the behavior of specific gas turbine variables, e.g.- turbine blade path temperature spread, which are not explicitly known to have any correlation with other thermodynamic variables.
Film Cooling Superposition Theory for Multiple Rows of Cooling Holes With Multiple Coolant Temperatures
Authors: Fuqua Matthew N. , Rutledge James L. 
Published: January 2021

Abstract
The classical method of superposition has been used for several decades to provide an estimate of the adiabatic effectiveness for multiple sets of already well-characterized film cooling hole rows. In this way, design work is aided by classical superposition theory prior to higher fidelity experiments or simulations that would account for fluid dynamic interaction for which superposition cannot account. In the present work, we consider the additive effects of multiple rows of coolant holes, but now also with coolant issuing at different temperatures. There are a number of ways that coolant may issue from different cooling hole rows at different temperatures, one of which is simply the necessarily different internal channels through which the coolant must pass.
The film cooling effectiveness is investigated for double rows of cooling holes wherein the two rows have different coolant temperatures. A double row consisting of an upstream slot and a downstream row of 7-7-7 cooling holes were first evaluated with a single coolant temperature to demonstrate that classical superposition theory applies well to the present configuration. Superposition theory is then extended to the context of multiple coolant temperatures and a new non-dimensional parameter is identified, which governs cooling performance. The theory is experimentally evaluated by independently varying the coolant temperatures of the two rows. Circumstances are identified in which a second row of cooling holes may be detrimental to cooling performance.
Design and Optimization of Turbomachinery Components for Parabolic Dish Solar Hybrid Micro Gas Turbine
Authors: Arifin Maulana , Schatz Markus , Vogt Damian M. 
Published: January 2021

Abstract
The application of power plants based on renewable energy sources is attractive from an ecological viewpoint. Micro Gas Turbine (MGT) combined with solar energy is a highly promising technology for small-scale electric power generations in remote areas. In MGT state-of-the-art development, the necessity of the numerical optimization in turbomachinery components becomes increasingly important due to its direct impact on the MGT cycle performance.
The present paper provides the multidisciplinary design optimization (MDO) of a radial turbine and radial compressor for a 40 kW Solar Hybrid Micro Gas Turbine (SHGT) with a 15m diameter parabolic dish concentrator. The objectives of MDO are to maximize the stage efficiency, to minimize the maximum stress and the inertia, and to enhance the operational flexibility. Preliminary design and performance map prediction using one-dimensional (1D) analysis are performed for both turbine and compressor at various speed lines followed by full three-dimensional (3D) Computational Fluid Dynamics (CFD), Finite Element (FE) analyses and 3D parameterization in the MDO simulations. The purpose of 1D analysis is to set the primary parameters for initial geometry such as rotor dimensions, passage areas, diffuser and volute size.
The MDO has been performed using fully coupled multi-stream tube (MST), 3D CFD and FE simulations. MST is used for calculating the load on the blade and the flow distribution from hub to shroud and linearized blade-to-blade calculations based on quasi-three dimensional flow. Thereafter, 3D CFD simulations are performed to calculate efficiencies while the structural stresses are simulated by means of FE analyses. In the current studies, Numeca Fine/Turbo is used as a CFD solver and Ansys Mechanical as a FEA solver, together with Axcent™ as an interface to Fine/Design 3D for geometry parameterization.
Furthermore, the cycle analysis for SHGT has been performed to evaluate the effect of the new turbomachinery components from the MDO on the SHGT system performance. It is found that using the MST fully coupled with CFD and FE analysis can significantly reduce the computational cost and time on the design and development process.
Comparison of Blind Diagnostic Indicators for Condition Monitoring of Wind Turbine Gearbox Bearings
Authors: Qi Junyu , Mauricio Alexandre , Gryllias Konstantinos 
Published: January 2021

Abstract
Under the pressure of climate change, renewable energy gradually replaces fossil fuels and plays nowadays a significant role in energy production. Among different types of energy sources, wind power covered 14% of the EU’s electricity demand in 2018. The Operations and Maintenance (O&M) costs of wind turbines may easily reach up to 20–25% of the total leverised cost per kWh produced over the lifetime of the turbine for a new unit. According to Wood Mackenzie Power & Renewables (WMPR) onshore wind farm operators are expected to spend nearly $15 billion on O&M services in 2019. Manufacturers and operators try to reduce O&M on one hand by developing new turbine designs and on the other hand by adopting condition monitoring approaches. One of the most critical and rather complex assembly of wind turbines is the gearbox. Gearboxes are designed to last till the end of asset’s lifetime, according to the IEC 61400-4 standards. On the other hand, a recent study over approximately 350 offshore wind turbines indicated that gearboxes might have to be replaced as early as 6.5 years. Therefore a plethora of sensor types and signal processing methodologies have been proposed in order to accurately detect and diagnose the presence of a fault. Among others, Envelope Analysis is one of the most important methodologies, where an envelope of the vibration signal is estimated, usually after filtering around a selected frequency band excited by impacts due to the fault. Sometimes the gearbox is equipped with many acceleration sensors and its kinematics is clearly known. In these cases Cyclostationary Analysis and the corresponding methodologies, i.e. the Cyclic Spectral Correlation and the Cyclic Spectral Coherence, have been proposed as powerful tools. On the other hand often the gearbox is equipped with a limited number of sensors and a simple global diagnostic indicator is demanded, being capable to detect globally various faults of different components. The scope of this paper is the application and comparison of a number of blind global diagnostic indicators which are based on Entropy (Permutation entropy, Approximate entropy, Samples entropy, Fuzzy entropy, Conditional entropy and Wiener entropy), on Negentropy (Infogram), on Sparsity (Sparse-L2/L1, Sparse-L1/L0, Sparse-Gini index) and on Statistics (Mean, Standard deviation, Kurtosis, etc.). The performance of the indicators is evaluated and compared on a wind turbine data set, consisted of vibration data captured by one accelerometer mounted on six 2.5 MW wind turbines, located in a wind park in northern Sweden, where two different bearing faults have been filed, for one wind turbine, during a period of 46 months. Among the different diagnostic indicators Permutation entropy, Approximate entropy, Samples entropy, Fuzzy entropy, Conditional entropy and Wiener entropy achieve the best results detecting blindly the two failure events.
Influence of Labyrinth Clearance on the Flow of Rotating Orifices in a Parallel Labyrinth-Orifice System
Authors: Wang Jie , Ding Shuiting , Qiu Tian , Gao Ziqiang 
Published: January 2021

Abstract
Orifices, especially rotating orifices, are an important flow element of the secondary air system in a modern aero-engine, and their discharge coefficient depends on the geometry, the operating point and the surrounding environment. The influence of Reynolds number, pressure ratio, rotational speed, inlet chamfer, inclination angle, length-to-diameter ratio, etc. on the discharge coefficient of rotating orifices under the assumption of room temperature and adiabatic has been reported in many literatures. However, the rotating speed, the temperature of the gas in the front and rear chambers of rotating orifices and the temperature of the chamber wall change continuously during the actual operation of the engine, especially during the acceleration and deceleration of the engine, which will cause deformation of the chamber wall and the rotating components, resulting in a large change in the labyrinth seal clearance on the periphery of the rotating orifice disk. Although the change of the seal clearance can be evaluated by some methods, it still has a crucial influence on the fluid flow in the front cavity of rotating orifices, which may affect the discharge coefficient of rotating orifices, thereby affecting the amount of cooling air flowing through rotating holes. Therefore, the knowledge of the influence of labyrinth seal clearance should be considered into the discharge coefficient of rotating orifices, which is essential for a reasonable distribution of the cooling air in the second air system under various working conditions and ensures the safety and reliability of the aero-engine in all-inclusive line.
This paper presents the relationship between the discharge coefficient of rotating orifices and theoretical velocity ratio in the relative frame of reference (U/Wax) under different labyrinth seal clearance conditions, which is based on the study of the flow state in the front chamber of rotating orifices under different seal clearances, rotating speeds and pressure ratios. The results indicate that with the increase of the labyrinth seal clearance on the periphery of the rotating orifices disk, the discharge coefficient of rotating orifices decrease under the condition of small velocity ratio, while the discharge coefficient is almost unchanged under the large velocity ratio. Comparing the flow field structure and velocity field under the condition of different labyrinth seal clearances, the same pressure ratio and the same velocity ratio, the reasons for the influence of labyrinth seal clearance on the discharge coefficient of rotating orifices are analyzed.
Investigating Boundary Layer Flashback of a High Turbulence Intensity Jet Flame at Gas Turbine Conditions
Authors: Auwaijan Nicolas , McDonell Vincent 
Published: January 2021

Abstract
Hydrogen derived from non-fossil sources is an attractive candidate to replace carbon based fuels in gas turbines, as it is inherently carbon free. Yet the unusual combustion properties of hydrogen requires some care to successfully use it in gas turbines. To attain the lowest NOx emissions, uniformly low reaction temperatures must be assured thus the reactants must be well mixed. This is accomplished in low emission gas turbines by mixing the reactants within a pre-mixer section prior to entry into the combustor. With the addition of hydrogen into the fuel, certain issues arise such as higher flame speeds compared to carbon based fuels. Flashback is a phenomena that occurs when the flame no longer propagates beyond the exit of the premixer/injector but instead retracts and propagates upstream towards, and ultimately into the pre-mixer, causing significant damage due to such high temperatures. Flashback occurs when the flame speed exceeds either the local or bulk flow velocity. In practice, the question arises regarding the impact of turbulence levels. While an increase in turbulence intensity may help improve mixing, it also known to increase turbulent burning velocity. In the present work, the influence of bulk turbulence intensity of the flow on boundary layer flashback is investigated. Data are acquired for a different turbulence intensities at pressures from 3 to 8 bar with preheated reactants up to 750 deg. K. Various mixtures of hydrogen and methane are evaluated. The results show that even with significantly different bulk flow turbulence intensities (based on the ratio of flow centerline turbulence to centerline axial velocity) boundary layer flashback is not strongly affected. This is attributed to the role of the quenching distance in connection with damping within the boundary layer. It is noted that core flow flashback or other flashback mechanisms may be affected differently.