bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conjugate Modelling of a Fully Film Cooled Vane at Transonic Conditions
Authors: Swartz Jacob , Lynch Stephen , Krull Matthew , Gayoso Isabella 
Published: August 2024

Abstract
Internal and film hole cooling is widely used as a means to allow for higher turbine inlet temperatures while keeping blade metal temperatures within a tolerable range of the material. Appropriate modelling of the internal and external heat transfer is needed to understand and identify localized high temperature zones on the blade surface that could lead to premature failure. In order to accurately predict this, conjugate heat transfer modelling is used to solve for the coupled temperature fields of the solid and fluid. The modes of heat transfer include convection outside the vane surface, conduction through the vane material, and convection of the cooling flow inside the vane channels. The purpose of this study is to evaluate conjugate heat transfer predictions using commercially available computational fluid dynamics (CFD) software to model the internal and film cooling of a turbine vane operating from transonic to supersonic conditions. The boundary conditions of the conjugate models are based on recently obtained experimental data and the surface temperature predictions are compared to the experiments. Both Mach number and Reynolds number effects on surface temperature were evaluated at different blowing ratios in this study. The results from this work show that overall cooling effectiveness near the cooling holes increased with increasing blowing ratio despite the film cooling flow reaching blow-off conditions. Furthermore, the overall cooling effectiveness near the cooling holes increased slightly near the pressure side cooling holes with a higher exit Reynolds number in the mainstream flow, but not significantly elsewhere on the vane surface. However, a supersonic exit Mach number condition, which results in a fishtail shock that impinges on the suction side of the vane, yielded a sharp increase followed by a decrease in cooling effectiveness around the shock impingement.
Experimental Research on the Lubrication Cooling Performance and Durability of High-Speed Bearings Under Axial Overload Conditions
Authors: Han Yujie , Liu Binbin , Zhao Wei , Hao Long , Ma Yingqun , Zhao Qingjun 
Published: August 2024

Abstract
Aero-engine spindle bearings operate under extreme operating conditions, including high temperatures, high speeds, and heavy loads. Thus, the reliability of the design is critical to ensuring optimum engine performance. In order to assess the reliability and safety of high-speed angular contact ball bearings for an aero-engine spindle subjected to axial force overload, tests are conducted using a certain type of aero-engine spindle bearing test rig. The spindle bearings are tested at the design operation speed of 17,000 rpm and an axial force of 25,000 N, as well as overload conditions with a reduced speed of 14,000 rpm and a maximum axial force of 58,000 N. The study analyzes the effects of different bearing inner race speeds, axial loads and lubricant temperatures and flow rates on bearing temperature control and vibration. The results indicate that an increase in inner ring rotation speed has a significant impact on the temperature rise rate of the bearing. Under the same lubricant temperature and flow rate conditions, an increase in axial load has a considerable effect on the temperature rise of the bearing. Increasing the flow rate of the lubricant can effectively reduce the temperature rise of the bearing and suppress its vibration to a certain extent under the same operating conditions. Furthermore, the durability of the bearing under a load spectrum that includes both design conditions and overload conditions is evaluated and the bearing damage is briefly analyzed, which provides a research idea for improving the service life of the bearing. The results indicate that appropriate lubricant temperature and flow conditions can effectively avoid the excessive temperature rise of the bearing under high contact stress and extend the operating duration of the bearing. This study can provide guidance and reference for the structural safety design and overload use of high-speed angular contact ball bearings.
Cooling Injection Effect on the Suction Side Near-Tip Region of Turbine Blade With High-Speed Relative Casing Motion
Authors: Peng Xu , Jiang Hongmei , Lu Shaopeng 
Published: August 2024

Abstract
The high-speed relative casing motion between the casing and the turbine blade tip introduces significant complexities to the flow field near the tip, resulting in alterations to the heat transfer distribution on the suction surface of the blade near the tip, and further influence the arrangement of film cooling arrangements. However, due to the challenges associated with measuring heat transfer, the influence of cooling injection on the near-tip region of the suction side under high-speed relative casing motion still remains uncertain. This study aims to address this knowledge gap by conducting experiments on a high-speed disk rotor experimental rig. The heat transfer coefficient and cooling effectiveness are investigated for different cooling hole arrangements. Additionally, based on Computational Fluid Dynamic (CFD) method, the interaction mechanism of cooling injections under high-speed relative casing movement is comprehensively discussed. It is observed that the cooling effect, which would be effective under stationary conditions, is greatly diminished or even rendered ineffective when subjected to highspeed relative casing conditions. Furthermore, arranging the cooling holes at the location where the interaction between the Over-Tip-Leakage flow and the passage flow occurs would be an effective approach to enhance the cooling performance on blade near-tip suction side. The effect of different relative casing speed on suction side near-tip region cooling injection performances are also numerically investigated. These findings contribute to a better understanding of the considerations involved in the film cooling design of turbine blades.
Temperature Dependence of Aerated Turbine Lubricating Oil Degradation From a Lab-Scale Test Rig
Authors: Juárez Raquel , Creighton Barry , Petersen Eric L. 
Published: August 2024

Abstract
Operational, efficiency, safety, and economic issues may arise from the formation and accumulation of sludge, varnish, and coke deposits that result from the degradation of engine lubricants through oxidation or thermal breakdown processes. Having a good understanding of the limits of lubricant performance may be useful in determining the best way to protect the engines. To this end, experiments were conducted using Mobil DTE 732, a turbine lubricant, that is aerated using a coarse gas dispersion tube. The oil then flows through a heated test section with a known axial temperature distribution. The inlet and outlet bulk oil temperature measurements are collected and used to determine the amount of time required for deposit formation and buildup. The induction times were determined for various surface temperatures, up to 236°C. It was found that increased temperatures shortened induction times, and exposure to oxygen increased the rate at which deposits accumulate, but the nature of the deposits, soft and easily removed, was different from those formed during higher-temperature experiments completed in an inert environment in previous studies. Oil samples collected during the test were analyzed with FTIR spectroscopy with no significant changes detected.
Framework for Machine Learning-Based Turbulence Modeling to Accurately Predict the Complex Flows in Gas Turbines
Authors: Blumenthal Robert F. , Siorek Michal , Patil Sunil 
Published: August 2024

Abstract
Flow in turbomachinery such as industrial gas turbines is highly complex and exhibits different characteristics for different operating conditions within a duty cycle or performance range. This poses a challenge to predict the performance of the machine accurately and efficiently. Computational Fluid Dynamics (CFD) has been successfully used for aerothermal analysis of turbomachinery successfully. An important aspect of CFD analysis is setting best practice for turbulence models for a given range of the machine especially in a RANS (Reynolds Averaged Navier-Stokes) framework. This is usually a manual process and can be very time consuming based on the complexity of the flow. The ability in many of these turbulence models to adapt the model coefficients to a specific application, such as a gas turbine, is limited.
A novel approach is presented in this paper that uses a unique turbulence modeling paradigm and machine learning to accurately and efficiently predict complex flows over a wide range. The new Generalized k-ω (GEKO) turbulence model is unique in that it exposes key and selective coefficients that control the behavior of different flows that may be encountered in gas turbines, such as free shear flow and near-wall flow. This paper provides a generic framework to optimize these key coefficients via neural network-based machine learning algorithm while leveraging available experimental or benchmark data. This approach is applied to an industrial gas turbine exhaust diffuser. Comparisons of the flow predictions using this approach are done against the experimental data for design/off-design conditions.
Assessment of a Simplified Conjugate Heat Transfer Perforated Wall Model for the Effusion Cooling by LES Method
Authors: Wang Mengming , Ji Chenzhen , Lu Shikang , Shi Wentao , Zhu Tong 
Published: August 2024

Abstract
A simplified conjugate heat transfer model, named Advanced Perforated Wall Model (A-PWM), is proposed to simulate the process of effusion cooling and predict cooling effectiveness. The A-PWM performs conjugate coupling simulation without modeling the cooling hole geometry and considers all the impacts of heat convection and conduction during the effusion cooling process. In this paper, Large Eddy Simulation (LES) is used to evaluate the efficiency of the A-PWM model in predicting film cooling effectiveness. A comparative analysis of the cooling effectiveness obtained by A-PWM, conjugate heat transfer (CHT), and experimental data (EXP) is performed. The results show that the predicted cooling effectiveness of the LES-A-PWM can match with the EXP and LES-CHT in general. The total meshes for LES-CHT are 8.41 million, with a computational time of 174.7 core hours, while LES-A-PWM has a total mesh of 2.27 million and a total computational time of 65.43 core hours, resulting in a 62.55% improvement in computational efficiency. However, the local cooling effectiveness of LES-A-PWM at the hole exit (ranging from X/D of 0 to 2) is much higher than the results of EXP and LES-CHT. Comparative analysis of the vortex-field indicates that LES-A-PWM does not form a counter-rotating vortex pairs (CRVPs) at the hole outlet where X/D is equal to 0.
Research on the Aerodynamic Noise Performance of a Novel Structure of Cooling Fans in Series
Authors: Zheng Yuhang , Li Zhaoyin , Sun Zonghan , Lu Fang , Tian Jie , Ouyang Hua 
Published: August 2024

Abstract
In systems with high downstream flow resistance, a single fan is prone to operating in an unstable range and generating backflow downstream of the hub. Conventional fans in series could overcome system resistance by increasing the pressure rise capacity. However, conventional fans in series do not improve the flow deterioration in the hub area of a single fan but instead posed a serious challenge to the system’s noise reduction effect due to its complex structure. A novel structure of cooling fans in series using two different-sized fans is designed and manufactured, and the aerodynamic and acoustic performance of a series structure with a smaller-sized fan installed downstream of a larger-sized fan is investigated. The downstream small fan aims to reduce the flow deterioration such as backflow in the hub area of the upstream large fan, thereby achieving performance improvement. Experiments have confirmed that there is an optimal matching range between the speed of the large fan and the speed of the small fan under free-field conditions. The measured results of outlet wind speed indicate that the downstream flow field of the novel structure of fans in series is more uniform within this matching speed range. Noise and aerodynamic performance tests have shown that in the presence of system resistance and backflow conditions, the novel structure of fans in series can achieve higher aerodynamic performance at a total sound pressure level close to the prototype structure, achieving a maximum flow rate increase of 1.4% with only a 0.02 dB increase in noise. However, there is no severe backflow in the hub area under the free flow condition, and the new structure cannot fully play its role, resulting in a decrease in aerodynamic performance. The proposal of the novel structure of cooling fans in series can provide more options for the design of heat dissipation modules in different impedance systems.
Experimental Study of the Dynamics of Lean Premixed Hydrogen Flames in a Multi Jet Combustor
Authors: Beuth Jan Paul , Reumschüssel Johann Moritz , von Saldern Jakob G. R. , Ćosić Bernhard , Paschereit Christian Oliver , Oberleithner Kilian 
Published: August 2024

Abstract
In this study, the flame dynamics of lean premixed hydrogen jet flames are experimentally investigated. Acoustic and optical measurement devices are used to capture the response of a bundle of jet flames to acoustic forcing. Using helium as a fuel surrogate, we simulate the change in acoustic properties in the burner during the determination of cold burner transfer matrix measurements in order to avoid dangerous experiments. We investigate the influence of the equivalence ratio and the addition of methane as well as the interaction of the individual flames to evaluate the scalability of the results to systems with more flames. It is shown that the changes in the dynamic flame response can primarily be explained by the flame length, which changes both with the methane share and with the equivalence ratio. It can be observed that with small changes in the equivalence ratio, the flame length and the flame transfer function (FTF) change in the same way as with a small change in the gas composition. To assess the scalability of these results, we deactivate some of the jet flames and analyze how the overall response to acoustic forcing changes. We find that the FTF phase is not affected by the number of active flames. Analyzing the respective gain values, significantly stronger responses are measured for a few flames, but only small difference can be measured above a certain number of neighboring flames so that the lab scale results can also be expected to be valid for industrial configurations with a high number of flames.
Humidification Impact on the Performance Improvement of a Novel Two-Shaft Micro Gas Turbine: Thermodynamic Cycle Performance Assessment
Authors: Baghernejad Ali , Rehman Danish , Delanaye Michel , De Paepe Ward 
Published: August 2024

Abstract
Despite appearing as a promising technology for small-scale decentralized Combined Heat and Power (CHP), the relatively low electrical efficiency of micro Gas Turbines (mGTs) prevents them from being attractive to users with variable heat demand. Transforming the cycle into a micro Humid Air Turbine (mHAT) by adding a saturation tower in the cycle allows for an increase in the electrical efficiency of these units in moments of low heat demand. Although humidification is well studied and proven effective on the simple recuperated Brayton cycle mGTs, its potential for cycle performance improvement when applied on more advanced mGT cycles is currently unknown. Therefore, the numerical study presented in this paper aims to assess the impact of humidification on the performance of a novel two-shaft mGT from MITIS, exploiting the intercooled regenerative reheat gas turbine cycle concept. The benefits of water injection mostly rely on the increased heat capacity of the air-vapor mixture, and the more significant amount of heat recovered in the recuperator, both resulting a the lower fuel consumption. Simulation results show indeed that by introducing a saturation tower in this two-shaft turbogenerator system, waste heat is recovered, leading to increased electrical efficiency from 35.12% for the mGT cycle to 36.31% for the mHAT cycle while providing a flexible heat and power output. This rise in the efficiency is maybe small, but could be increased further by going towards more advanced cycle configuration (aftercooling) as well as by less limiting the TIT.
NOx Emissions Assessment of a Multi Jet Burner Operated With Premixed High Hydrogen Natural Gas Blends
Authors: Jaeschke Alexander , Ćosić Bernhard , Wassmer Dominik , Paschereit Christian Oliver 
Published: August 2024

Abstract
Decarbonization of gas turbine combustion creates a pressing demand for new technical solutions for the combustion process. While switching to hydrogen fuels may solve the problem of carbon emissions and associated pollutants it can also lead to stability issues for swirl-stabilized combustors due to its increased reactivity. However, with jet flame burner systems, the required flashback safety can be achieved with high axial flow velocities even for premixed combustion of 100% hydrogen fuel. The development of such an engineering solution, however, requires significant effort to reach the maturity of today’s swirl burners. This study examines the capacity of a premixed multi-tube jet burner to manage the chemical reactivity change over a range of volumetric blends from pure natural gas to pure hydrogen fuel. NOx emissions are measured and analyzed for atmospheric tests. The changes in emissions originate not only from altered combustion chemistry but also from changes inflame shape and turbulence intensity. To get a deeper understanding of the NOx formation process, a low-order model is designed and compared to the experimental data of technically and perfectly premixed combustion tests. Parameter variations of the low-order model are conducted to assess the influences on the NOx emission production of the multi jet burner. The information on the combustion process required for the model is obtained computationally and experimentally. Therefore, flame images are recorded and analyzed.
Intrinsic Thermoacoustic Feedback in Auto-Ignition Flames Stabilized in a Converging-Diverging Nozzle
Authors: Biagioli Fernando , Syed Khawar J. 
Published: August 2024

Abstract
Intrinsic thermoacoustic modes are studied in the case of self-igniting flames stabilised in the diverging section of a converging-diverging nozzle with Mach number in the range M = 0.6. Since auto-ignition is largely influenced by the pressure and static temperature conditions in the entire region upstream of the flame, the subject of intrinsic thermoacoustic modes, i.e. modes due to the closed-loop feedback between the flame behaviour and the upstream acoustic field in the absence of reflection from the upstream and downstream boundaries, is particularly interesting and relevant. These types of modes, which are very different in nature from those due to the closed-loop reflection of acoustic waves from the inlet and outlet boundaries, have been studied by several authors mostly in the case of conventional propagating premixed flames. In this work, the flame response to incident acoustic waves is determined analytically based on the linearised Rankine-Hugoniot relations applied to the instantaneous infinitesimally thin auto-ignition boundary. Acoustic wave propagation in the flow upstream and downstream of the flame is resolved by the Magnus expansion. Intrinsic thermo-acoustic modes are found by two different methods: a) as solutions of the closed-loop stability problem when the reflection coefficients at the inlet and outlet boundaries tend to zero, b) as poles of the flame scattering matrix. It is shown that the intrinsic modes obtained in this way coincide in the case of self-ignition in a straight duct, but differ in the case of a flame stabilised in a converging-diverging duct. This apparent discrepancy is discussed and explained.
Acoustic Excitation As a Flow Control Technique in a High-Speed Compressor Cascade
Authors: Coskun Seyfettin , Rajendran David John , Pachidis Vassilios , Bacic Marko 
Published: August 2024

Abstract
A numerical investigation of the effectiveness of acoustic excitation is carried out to control flow separation in a NACA65-K48 linear compressor cascade (LCC) in the absence of cascade endwalls. The operating conditions for the LCC are Ma = 0.67 and Rec = 560 × 103, which are representative of an aeroengine. For the numerical investigations, Improved Delayed Detached Eddy Simulation (IDDES) is used due to its capability to capture flow separation and unsteady flow characteristics with reasonable computational requirements among the high fidelity approaches. The flow through the cascade passage does not experience any separation at the aerodynamic design point (ADP) of the cascade. Therefore, an incidence angle of i = 8° is used in this study where flow separation is observed over blade the suction surface at x/c ≈ 0.6. For acoustic excitation, both external and internal acoustic excitation techniques are investigated. In external acoustic excitation, the sound source is distributed at the inlet boundary of the computational domain whereas in internal excitation, sound waves are introduced into the computational domain from a thin slot located at the onset of flow separation on the blade suction surface. Sound waves are introduced in the flow field at the modal frequencies in the uncontrolled flow, which are Stc = 0.187, 0.409, and 0.618 in terms of Strouhal number based on the blade chord length at a constant excitation amplitude of SPL = 151dB. The results have indicated that external acoustic excitation has no major effect in controlling flow separation in the LCC. Internal acoustic excitation, on the other hand, has a strong effect in modulating the flow separation in the LCC passage such that a reduction of Δζmax ≈ 16% is observed in the total pressure loss coefficient on the measurement plane located 0.4Cax downstream of the cascade exit. Further investigations are also carried out for the effect of sound amplitude on the effectiveness of internal acoustic excitation. In overall, acoustic excitation can serve as a means of flow control in aeroengine compressor cascades.