bluuebunny/crossref_metadata_2025 huggingface dataset:
Centrifugal Compressor Casing Treatment Design for a Turbocharged Hydrogen Combustion Engine
Authors: Gibson Lee , Leonard Thomas , Iosifidis Georgios , Di Modica Dario-Vincenzo , Ratz Johannes , Ueno Takahiro
Published: August 2024

Rapid decarbonisation of energy-intensive industries such as heavy-duty transport and stationary power generation is essential to meet the emissions targets set by legislative authorities around the globe. Emission-free battery technologies are promising but they do not yet achieve the energy density needed for larger machines and the suitability of fuel cells to operate in harsh environments remains uncertain. Hence, Hydrogen internal combustion engines (ICEs) emerge as an attractive solution. Existing Diesel and Gasoline ICEs can be readily adapted to Port Fuel Injection (PFI) Hydrogen ICEs using lean-burn combustion or Exhaust Gas Recirculation (EGR) to achieve high efficiency and low emissions. Such engine configurations typically demand turbocharger compressors with high pressure ratio and efficiency. However, compressor map width tends to decrease with increasing pressure ratio and this can sometimes limit the engine operating range. The literature review identified the ported shroud (or bleed slot) casing treatment as an effective add-on technology to improve compressor map width, particularly at high pressure ratios. This paper details the design of a ported shroud casing treatment for a highly loaded centrifugal compressor equipped with a vaneless diffuser. A parametric study was conducted using a validated Computational Fluid Dynamics (CFD) model to determine the sensitivity of compressor pressure ratio, efficiency, and recirculation ratio to the downstream slit position, width and meridional angle. The angle of the struts necessary for structural support of the ported shroud inside the compressor housing was also considered. The findings of the parametric study were subsequently used to inform a design optimisation with the goal of maximising the potential stability enhancement offered by a ported shroud casing treatment.
Unsteady Investigation of Side Loading Effect on Single-Stage Centrifugal Compressors
Authors: Bicchi Marco , Lottini Fabrizio , Biliotti Davide , Ortiz Neri Massimiliano , Querini Lorenzo , Bianchini Cosimo
Published: August 2024

Single-stage centrifugal compressors have historically found usage in several industrial and civil applications thanks to their high efficiency, robustness, and wide operating range. However, despite the simplicity in the architecture, the overhung configuration represents a challenging arrangement for the design of these types of machines. In particular, the presence of a discharge volute with variable cross-sectional area around circumference further exacerbates such task due to its intrinsic asymmetric shape. Indeed, focusing on the volute-impeller interaction, static pressure distortions could introduce non-negligible forces that act on journal bearings. Against this backdrop, a good prediction of static pressure fields is pivotal. In this perspective, a methodological framework leveraging unsteady and steady CFD analyses is proposed and validated using on-site measurements of a real working machine by exploiting the built-in instrumentation of the active magnetic bearing system. The main goal of the present work is to provide and validate a numerical methodology useful for the prediction of the magnitude and the angular position of the induced side force on single-stage centrifugal compressors. Specifically, the theoretical contribution of the research is to investigate the limits of steady computations against unsteady modelling for the evaluation of volute-impeller interactions in single-stage centrifugal compressors with vaneless diffuser. On a practical level, a criticality analysis on the importance of several modelling aspects on the calculations of side load prediction is provided. The proposed approach is verified on a centrifugal compressor stage for expander-compressor applications. Results show good agreement between CFD results and field data. The present research lays the foundations for future studies aiming to predict volute-impeller interaction in single-stage centrifugal compressors.
Design-Point Techno-Economics of Brayton Cycle PTES for Combined Heat and Power
Authors: Neises Ty , McTigue Joshua
Published: August 2024

Pumped thermal energy storage (PTES) systems are grid batteries that use heat pumps to create both hot and cold thermal energy stores when there is excess electricity and then use a power cycle to convert the thermal energy into electricity when there is demand for electricity. In normal operation, Joule-Brayton PTES discharges low-grade heat at temperatures useful for thermal energy consumers like district and industrial heating. Furthermore, PTES designs, like conventional combined heat and power (CHP) technology, can be modified to sacrifice some round-trip efficiency RTE to increase the temperature of heat rejection.

This paper uses design-point performance and cost models that provide a detailed understanding of the efficiency and cost trade-offs of rejecting heat at various temperatures in ideal-gas Brayton PTES configurations. First, we keep the heat rejection in its nominal location in the PTES system: in the discharge cycle after the low-pressure exit of the recuperator before the cold-storage heat exchanger. Next, we move the heat rejection to the discharge turbine exit. We define design-point metrics that isolate both the cost and performance penalty associated with the hotter heat rejection and attribute it exclusively to the heat economic metrics. Finally, we estimate the performance of electric heater technology to generate heat at equivalent temperatures. We find that the levelized cost of heat, including the cost of thermal energy storage (TES) buffering the PTES and heat off-taker, compares favorable versus electric technologies and is less than the cost of natural gas for low temperature scenarios and competitive with the cost of natural gas in some regions of the contiguous United States in high temperature scenarios.
Multistage Turbomachinery Optimization for High Temperature Heat Pumps With the Reverse Rankine Cycle
Authors: Schaffrath Robert , Stathopoulos Panagiotis , Schmitz Andreas , Nicke Eberhard
Published: August 2024

The electrification of process heat generation will be a key to achieving carbon neutrality in the coming decades. One of the most promising approaches is to replace conventional heat supply systems with high-temperature heat pumps (HTHPs). A promising heat pump concept is based on the reverse Rankine cycle that uses water as its working fluid. By using turbomachinery for the compression process in this cycle, the performance of the HTHP can be increased compared to volumetric displacement systems, like screw or piston compressors. Although the design of the compressor geometry can be done sequentially in relation to the HTHP cycle design, better results can be obtained by an approach that integrates turbomachinery and the thermodynamic cycle design. Against this background, an automated optimisation method for a reverse Rankine HTHP with two radial turbocompressors in series is presented. In contrast to the current state of the art, the presented novel optimization approach uses 3D CFD data to calculate compressor performance. Furthermore, the integration of low fidelity compressor specific reduced order models are used to accelerate the gradient-free optimization process by a CO-Kriging surrogate model. The advantages of the novel approach are justified by comparing the numerical effort and the final values of the optimization objectives.
A Study of Loss Model Parameter Sensitivity in Compressor Unsteady Flow Simulations
Authors: Jing Zhenhao , Neumeier Yedidia , Prasad J. V. R. , James Darrell K.
Published: August 2024

This paper presents results from a comprehensive sensitivity analysis focused on loss models used in a recently developed compressor unsteady mean line flow model for a transonic axial-centrifugal compressor. The mean line flow model treats flow through rotors and stators in their respective reference frames (rotating or stationary), and the compressor performance is determined by the kinetic energy addition and various physics-based loss models in relative frames. In this paper, we describe the modeling approach of the compressor flow model, as well as the loss models that are used to obtain a relatively good match against test data. Sensitivity studies of selected loss model parameters are presented to show the effect of individual loss model parameters on the overall compressor characteristics in the entire speed range. The effects of losses on unsteady flow transients are assessed by comparing the transient responses when a step reduction of throttle area is applied. The comparisons show that the change in loss magnitude has weak effects on transient response if the change of loss does not significantly change the system stability.
Investigating the Performance of Multi Element Wind Lens
Authors: Elsafty Kareem , Elbaz Ahmed
Published: August 2024

A major limitation for the full utilization of wind turbines as the main power source is the large variation of wind availability from one area to another, especially at locations with low average wind speeds. Harnessing energy from the wind using diffuser augmented wind turbines or wind concentrators (commonly called wind lens) is one of the trending topics in the field of wind energy where low wind speed is encountered. The main objective of the present work is to investigate the performance of a new type of wind concentrator composed of multi element airfoil sections. Comparison of the new design is made with common design of wind lens to find the optimum configuration that outperforms a conventional wind lens. The proposed design also allows for extra air flow to pass into the lens between the two elements. This allows the application of dual rotor wind turbine with the wind lens where a second rotor is placed at the exit section of the lens. The performance of the new design was examined using CFD technique via the commercial software ANSYS FLUENT. The study investigated the tilt angle of the front piece, the tilt angle of the back piece as well as the gap between the two sections on the mass flow rate through the lens throat and exit sections. The results of the mass flow rate and wind velocities as well as the drag coefficient are compared with conventional wind lens results. The results show that it is possible to increase the mass flow rate through the throat section by 48.3% in comparison with freestream mass flow rate. The results indicated the possibility of enhancing the mass flow rate through the exit section by 14% higher than that at lens throat. The drag coefficient of the multi element wind lens is 17% lower than that of the conventional wind lens with brim.
Conjugate Modelling of a Fully Film Cooled Vane at Transonic Conditions
Authors: Swartz Jacob , Lynch Stephen , Krull Matthew , Gayoso Isabella
Published: August 2024

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

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

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

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

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

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

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

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

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

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

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

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.
Detailed Sliding-Mesh Computation of Turbulent Jet Ignition and Combustion in a Wave Rotor Combustor With Stationary Pre-Chamber
Authors: Yinusa Rasheed K. , Nalim Mohamed Razi
Published: August 2024

Computational fluid dynamic and chemical simulation is used to investigate the ignition and combustion processes in a pior experimental wave rotor combustor that used a stationary pre-combustion chamber to produce a traversing hot reactive jet or torch for rapid ignition in the wave rotor. The traversing jet delivers reactive hot gas into a premixed ethylene-air mixture in a constant volume combustor from a continuous-flow prechamber torch igniter positioned at a fixed location adjacent to one end of the wave rotor with a clearance gap. This finite-volume fluid dynamics and combustion simulation consider three channels of the wave rotor, with combustion simulated fully in one channel, to optimize computational cost while closely mimicking the traversing jet motion and subsequent ignition and combustion processes using a transient Reynolds Averaged Navier-Stokes two-equation eddy-viscosity turbulence model with detailed chemistry mechanism with 81 species and 573 reactions. The simulation begins at a point in the wave rotor cycle when the channel contains an unburnt uniform mixture with substantial and varied residual turbulence. The pressure rise, flame travel, and heat release rates predicted are compared with experimental data previously collected from a highly instrumented wave rotor constant volume combustor rig. Experimental conditions that had not been measured, but which may affect its combustion processes include turbulent kinetic energy and turbulence scales of the mixture prior to ignition, and the level of active radicals in the traversing hot jet. The pre-chamber combustion model is manipulated to understand how dosing of free radical species enhances localized ignition initiation and affects overall fuel burn. The initial turbulent properties were varied to understand the sensitivity of combustion to turbulence as the flame propagates away from the initial ignition jet zone. These findings advance the understanding of a demonstrated wave rotor combustor with potential to revolutionize gas turbine engine technology.
Effect of Transverse Acoustic Excitation Over a Partially-Premixed Swirling Flame
Authors: Gupta Ravi , Bohrey Aayushi , Panda Pratikash
Published: August 2024

In this work, we investigate the effect of transverse acoustic excitation on a partially premixed swirling flame. Azimuthal instabilities in annular gas turbine combustors are one of the major challenges. Thermoacoustic instabilities are driven by azimuthal acoustic modes. We have designed and fabricated a multi-nozzle linear array combustor to simulate the flow conditions of an annular combustor. The nozzle features an axial swirler with a centerbody acting as a fuel injector. Simultaneous high-speed chemiluminescence (OH*) and high-frequency pressure measurements are conducted to measure the time-averaged flame shape and the chamber acoustics respectively. These measurements are taken at multiple forcing frequencies and amplitude under in-phase (IP) and out-of-phase (OP) conditions. It is observed that, at one of the combustor modes (580Hz), during OP forcing, the flame transitions from a V-shape to an M-shape as the forcing amplitude is increased. However, with IP forcing the flame continues to remain in V-shape with the increase in forcing amplitude. Spectral proper orthogonal decomposition (SPOD) analysis of OH* images show that for OP forcing dominant mode shapes are present mostly at 0.5D away from the center-line, but for IP forcing the dominant mode shapes indicate combined axial and radial oscillations in the OH* intensity field. Furthermore, cross-wavelet transform (XWT) analysis shows a strong correlation between pressure fluctuations and OH* fluctuations around the forcing frequency for IP forcing, and a weak or intermittent correlation for OP forcing. Based on the acoustic simulation, instantaneous time snapshots of OH* chemiluminescence and existing literature, we hypothesize that the transition from V-shape to M-shape can be due to acoustically induced velocity and vortical fluctuations near burner lip during OP forcing. This causes the V-flame to stretch, roll outward, and stabilize in the outer recirculation zone (ORZ).
Rotor Design of Heavy-Duty Gas Turbines for Power Generation: A Comparative Analysis for Transition to Net Zero Emission Target
Authors: Ugel Diego , Olmes Sven , Cassinelli Claudio , Goerzer Michael , Ivkovic Sinisa , Winge Torsten , Bordo Luca
Published: August 2024

Current scenarios towards net zero emission assume an increasing demand for peaking operation of installed and new heavy-duty gas turbines for power generation, resulting in raising targets for transient behaviors of gas turbine rotors.

During the design development process cyclic damaging mechanisms related to centrifugal and thermal loads, as well as rotordynamic effects leading to high vibration and associated high-cycle fatigue mechanisms are mandatorily considered, accounting for potential aging effects taking place during the engine life. Additionally, rotor deformation due centrifugal and thermal loads are analyzed in detail to achieve the best rotor-casing clearance conditions, aiming to maximize engine performance and availability.

To satisfy the same set of functions and requirements different OEMs offer since decades alternative architectural layouts, stemming from both identified technical solutions and historical heritage. These existing layouts are compared in some publications, mostly focusing on baseload steady-state stress and idealized warm-up and cool-down considerations.

In this paper the two main families of existing rotor designs, namely bolted and welded, are analyzed and compared, on the basis of two F-Class engines in the portfolio of Ansaldo Energia. With a specific attention to transient effects from real operating cycles relevant for flexibility demand, the paper shows insights about design, clearance, lifetime management and extension.

The performed analysis highlights the key differentiators of the two fundamental rotor architectures that Ansaldo Energia is maintaining in its technology portfolio.
Numerical vs Experimental Investigation on Fuel Gas Leak Dispersion in a Real Scale GT Enclosure
Authors: Lucherini Gabriele , De Leo Elena , Minotti Stefano , Presotto Valentina , Singh Rajnish Kumar , Raju Susila Jegan Vishnu
Published: August 2024

Fuel gas leak is a possible scenario that could occur inside a gas turbine (GT) enclosure due to the large number of connections in the fuel gas supply line. Forced ventilation and gas detection systems are used as main mitigations to guarantee an acceptable level of safety. While the ventilation air promotes the dilution below the flammable range of any fuel gas release, the gas detectors monitor the concentrations levels and trigger corrective actions anticipating hazard scenarios. The combined design of these two systems is based on the use of CFD analyses as predictive tool according to guidelines given by ISO 21789.

The introduction of hydrogen as fuel for gas turbines makes this design more critical for all its characteristics such as reactiveness and large range of flammability. This leads to an intrinsic higher risk of ignition in case of leakage respect to other conventional fuels like natural gas.

In this context, it is fundamental to build reliable and robust computational models for the prediction of fuel gas dispersion inside a complex geometry with forced ventilation flow like a gas turbine package. For this purpose, experimental data of a fuel gas leakage inside a real scale GT enclosure would be needed to tune and validate such numerical models. Since up to now this kind of data is not available in literature, an experimental campaign on NovaLT16 100% H2 package was executed to create a real reference for CFD simulations. Hydrogen is rarely utilized in full scale tests for obvious safety concerns, thus methane was chosen to be released reproducing a real operating scenario. The same set up was replicated with CFD analyses and the results were finally compared.
SCADA-Based Long-Term Wind Turbine Performance Degradation Analysis Based on Deep Learning Techniques
Authors: Peng Dandan , Terzi Ludovico , Desmet Wim , Gryllias Konstantinos
Published: August 2024

In the context of the rapid development of wind energy as a renewable resource, ensuring effective monitoring and maintenance of wind turbines is increasingly important. Despite the large volume of data collected by Supervisory Control and Data Acquisition (SCADA) systems, extracting key feature information to construct successful condition monitoring models remains a complex and challenging task. This study introduces a deep learning approach, called Convolutional Neural Network-based Support Vector Data Description (CNN-SVDD), aiming at effectively monitoring the long-term health status of wind turbines and providing timely warning for potential faults. The method employs Convolutional Neural Network (CNN) to deeply analyze time-series features and the correlations between sensors from SCADA data, capable of overcoming the challenges posed by environmental noise and changes in operational conditions. Subsequently, within the deep feature space learned by CNN, the SVDD classifier constructs a soft-boundary hypersphere. It allows for some samples to reside outside the hypersphere, thereby enhancing robustness against potential outliers in the SCADA data. Notably, the optimization processes of CNN and SVDD are linked, forming together an end-to-end process. The anomaly score generated by SVDD may act as an intelligent health indicator for assessing long-term performance degradation in wind turbines. Additionally, the radius of the hypersphere serves as a threshold for potential fault warnings. Extensive experiments on SCADA data acquired from multiple wind turbines over an 11-year period demonstrate the effectiveness of this method in early fault warning and long-term wind turbine performance degradation monitoring.
Optimization of Low-Pressure Turbine Blade by Means of Fine Inspection of Loss Production Mechanisms
Authors: Russo Matteo , Carlucci Andrea , Dellacasagrande Matteo , Petronio Daniele , Lengani Davide , Simoni Daniele , Bellucci Juri , Giovannini Matteo , Granata Angelo Alberto , Gily Monica , Manca Carlotta
Published: August 2024

In the present work, Proper Orthogonal Decomposition (POD) has been applied to Large Eddy Simulations (LES) of two high-loaded low-pressure turbine cascade operating under unsteady inflow for the detailed investigation of the entropy production in the different part of the blade passage. To this end, the Turbulent Kinetic Energy (TKE) production, diffusion and dissipation terms appearing into the stagnation pressure transport equation have been integrated all over the computational domain. The POD-based procedure allows splitting the contribution due to different coherent flow dynamics to the turbulent kinetic energy production and dissipation, due to the migration, bowing, tilting and reorientation of the incoming wake filaments, as well as to the breakup of streaky structures into the blade boundary layer and/or to the formation of Von Karman vortices into the wake of the blade. This enables a designer to identify the dominant POD modes (i.e., turbulent flow structures) responsible for loss generation mechanisms, their dynamics and the spatial locations where they mainly act, thus providing a deep view on the physical phenomena to be controlled. Following this optimization strategy, a new low pressure turbine profile has been designed. After running a LES calculation on the new optimized geometry, POD results showed that it is possible to design a higher-loaded profile which operate with a lower global loss coefficient. Thanks to stronger acceleration imposed to the bulk flow in the former part of the blade passage, the new loading distribution is shown to be responsible for lower upstream wake migration losses, as well as for a smaller amount of TKE production in the trailing edge wake zone, as a result of the early suction side boundary layer transition.
Modeling and Predicting Deflagration Phenomena in Hydrogen-Enriched Gas Turbine Exhausts: A CFD Approach
Authors: Lemmi Gianmarco , Nassini Pier Carlo , Cerutti Matteo , Andreini Antonio
Published: August 2024

The adoption of hydrogen-enriched fuels in gas turbine power plants is gaining prominence as an effective strategy for decarbonization. However, this transition presents unique challenges, particularly in relation to hydrogen’s wider flammability range compared to natural gas when mixed with air. Under certain operating conditions, this can lead to the undesired formation of flammable mixtures within the gas turbine exhaust channel, which, if ignited, can result in structural damage due to pressure increases caused by the deflagration process. An effective and robust way of assessing the related safety risk is to rely on high-fidelity Computational Fluid Dynamics (CFD) models, capable of accurately predicting the overpressure generated by the ignition of flammable mixtures.

In this study, a CFD model has been developed to perform three-dimensional and unsteady simulations of the deflagration of hydrogen-air mixtures within large partially confined volumes, representative of an industrial gas turbine exhaust. A high-fidelity Large Eddy Simulation (LES) approach coupled with the Renormalization Group Theory (RNG) subgrid-scale model was employed for turbulence modelling, while the Flamelet Generated Manifold (FGM) tabulated chemistry approach with the Turbulent Flame Speed Closure (TFSC) was adopted as the combustion model. Computational results have then been compared to experimental data from the literature to validate the presented model in terms of numerical domain discretization, turbulence modelling, and combustion modelling. The analysis is aimed at replicating the main overpressure peaks as measured by the British Gas Midlands Research Station. While exhibiting a satisfactory alignment with the experimental pressure distribution in the test case, the proposed setup was able to capture the primary dynamics of the deflagration process, demonstrating its readiness for application to real gas turbine exhaust geometries.

The setup has been then used to simulate the deflagration process of a hydrogen-air mixture at the exhaust of an industrial gas turbine manufactured by Baker Hughes. A discussion on this latter case has been reported as well in this paper.