bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi-Aeroelastic Phenomena Modelling Part I: the Development of Whole LPC Model for Civil Turbofan Engine
Authors: Kulkarni Davendu Y. , Lad Bharat , di Mare Luca
Published: August 2024

Aeroelastic phenomena in the low-pressure compression (LPC) system of civil turbofan engines can cause a significant high-cycle fatigue (HCF) risk to the LPC components. Currently, the mechanical integrity risk to the LPC components is assessed by performing multiple, discrete aeromechanical simulations, which require large resources and incur high time-cost. Therefore, the development of a comprehensive modellingsimulation approach is necessary to assess multiple phenomena and components simultaneously that can provide accurate results within design timescales.

This paper presents the methodology for generating a common, system-level model for investigating multiple aeroelastic phenomena in fan and outlet guide vanes (OGVs). The development of a high fidelity, full-annulus CFD model of the whole low-pressure compression system is described. Time accurate unsteady CFD simulations are then conducted at multiple flight conditions. These information-rich simulations are interrogated to extract various parameters of interest to assess multiple aeroelastic phenomena.

The aeroelastic parameters are used to investigate 1EO fan forced response, fan alternating passage divergence (APD) response, OGV buffet, and OGV resonant forced response etc. In the second part of this paper, the application of this modelling methodology is demonstrated to evaluate and to better understand the efficacy of OGV asymmetric cyclic patterns.
The Unsteady Shock-Boundary Layer Interaction in a Compressor Cascade – Part 3: Mechanisms of Shock Oscillation
Authors: Munoz Lopez Edwin Joseph , Hergt Alexander , Klinner Joachim , Klose Bjoern F. , Willert Chris , Gümmer Volker
Published: August 2024

The shock-boundary layer interaction in transonic flows is known to cause strong unsteady flow effects that negatively affect the performance and operability of blade and cascade designs. Despite decades of research on the subject, little is still known about the physical mechanisms that drive the different oscillation frequencies observed with different designs. In the conclusion of this three-part series, the experimental and numerical data obtained with the Transonic Cascade TEAMAero are analyzed together in detail in order to test the main theories of continuous shock oscillation. This analysis exposes a main mechanism of shock oscillation, where pressure waves generated inside the passage of the cascade propagate upstream and interact strongly with the main shock when the latter is also in the passage. The interaction of these features causes a breakdown of the flow that is shown to propagate upstream, inevitably causing strong variations in the inflow angle and therefore on the operating conditions of the cascade. The high frequency content of these pressure waves is also shown to be responsible for weaker high-frequency variations of the shock movement throughout the cycle. Parallels are also drawn with previous experimental campaigns in order to search for a global understanding of the different observations made. Although various parts of the described interaction are not fully understood yet, and the dataset of experimental measurements compiled is still rather small, a good basis is provided on which to further study the underlying mechanisms of unsteady flows in transonic cascades.
Experimental Characterization of Darcy Friction Factors of Bump Channel Flows and Application to Cooling Flow Path Design
Authors: Kim Daejong
Published: August 2024

Foil bearings are considered the most promising oil-free bearing technology for small high-speed turbomachines. Among many different underlying supporting structures, corrugated bump foils are the most popular. Due to the geometry of corrugation, the bump foils have gas flow passages through the bump channels, and cooling gas is introduced through these bump channels. The flow resistance through these bump channels is a function of bump geometry, ambient conditions, and type of gases. When multiple foil bearings are installed within a system, cooling gas flow passage design through the bearings requires proper understanding of bump channel flow resistances. Inadequate cavity pressures arising from the cooling gas flow passage design can create undesirable axial force to the thrust bearings. This paper presents experimentally measured Darcy friction factors of typical bump channels in both laminar and turbulent flow conditions, as a function of flow Reynolds number and hydraulic diameter determined from the bump channel geometry. This paper also presents experimentally measured flow characteristics of radial and thrust foil bearings, and measured results are compared with the prediction using the experimentally extracted Darcy friction factors.
Design of a Scroll-Centrifugal Compressor for Supercritical Carbon Dioxide Power Cycles
Authors: Yang Zimu , Lu Zhenbo , Jiang Hongsheng , Zhuge Weilin , Song Panpan , Qian Yuping , Zhang Yangjun
Published: August 2024

Supercritical carbon dioxide (S-CO2) Brayton cycle is a promising power cycle in the field of energy conversion applications. When the cycle is applied for waste heat recovery of gas turbine power system, the operating state will change more drastically compared to other power generation applications, and it is more likely to operate near the critical point, where the thermophysical properties of CO2 vary largely.

To meet the requirements of S-CO2 Brayton power cycle for gas turbine power system, a new type of S-CO2 compressor, named scroll-centrifugal compressor, was proposed in this paper. This new compressor consists of two stages. The low pressure stage is scroll compression and the high pressure stage is centrifugal compression. It can operate at two modes, scroll compression mode and scroll-centrifugal compression mode, to adapt the drastic operating state change of the cycle.

In this paper, the preliminary design considerations of this new compressor were introduced. The design progress of the scroll stage and centrifugal stage was illustrated, respectively. The computational fluid dynamics (CFD) simulation was carried out to analysis the aerodynamic performance of this new compressor. The simulation results shows that this new type compressor can achieve the pressure ratio 1.97 as the inlet state near the critical point.
Coupled Vibration of a Centrifugal Compressor Blade Excited by Macro Fiber Composite Actuator
Authors: Nie Mingjie , Chen Yong , Tang Xu
Published: August 2024

The centrifugal compressor blade will be excited by unsteady flow and mechanical vibration such as distorted flow, turbulence and rotor vibration, etc. Coupled vibration of the blade will occur with several high-order modes, which may lead to complex high cycle fatigue failure. Traditional excitation methods such as hammer testing and shaker testing are inadequate for high-frequency excitation. In order to study the coupled vibration characteristics of a single centrifugal compressor blade, a dynamic response measurement method using Macro Fiber Composite (MFC) is carried out, which can generate complex excitation forces with different high-order natural frequencies and peak values combinations. The excitation system of MFC actuators was designed and built, consisting of a signal generator, MFC actuator and high voltage power amplifier. The excitation position of MFC is determined based on the measured strain magnitude in the MFC polarization direction of this order mode to ensure that sufficient energy can transfer to the blade. Using this system, three typical excitation methods were implemented to conduct high-order modal measurement experiments on the centrifugal impeller blades. These results were compared with impact hammer testing experiments. The findings indicate that MFC actuators offer advantages in modal testing, including ease of operation, excellent repeatability, high signal-to-noise ratio, and the ability to excite high-order modes. To evaluate the effect of external added mass and stiffness on the natural characteristics of the blade, impact experiments were performed using reflective paper and MFC actuators at different locations. The coupled vibration response of the blade is measured by using a scanning laser vibrometer. The measured high-order mode shapes, natural frequencies and coupled vibration response of the blade are compared with the finite element simulation results. The high cycle fatigue weak link location of the blade is studied under the coupled vibration conditions. The results show that the coupled excitation will cause the change of the HCF weak link location compared to the single mode excitation. The ratio of the peak value of the excitation level plays an important role.
Study on the Casing Recess Design Method for a Supercritical Carbon Dioxide Axial Turbine
Authors: Hu Zhuo , Jiang Hongsheng , Zhuge Weilin , Qian Yuping , Zhang Yangjun
Published: August 2024

Supercritical carbon dioxide (S-CO2) closed Brayton cycles have recently received extensive attention for their potential applications in various fields such as power generation and mobile propulsion. Due to the high density of CO2, S-CO2 turbines have much smaller sizes compared to gas turbines at the same level, making tip leakage flow a critical factor affecting turbine performance. In this study, the flow field of a small-scale S-CO2 axial turbine was analyzed through CFD simulations. The effects of blade tip clearance and casing recess design on turbine performance were investigated. The results indicate that the tip leakage flow in the blade passage hinders the mainstream flow and serves as a significant source of losses. As the tip clearance ratio increases, the intensity of leakage flow increases, leading to a noticeable decrease in turbine efficiency. With an increase in the depth of the casing recess, the turbine efficiency initially increases and then decreases. When the clearance size is larger, the corresponding optimal recess depth for the highest turbine efficiency shows an increasing trend. The impact of recess position on efficiency is not significant in this study. The recessed casing increases the intensity of the tip passage vortex, which develops along the pressure surface and involves the nearby fluid, suppressing the intensity of the tip leakage flow. A suitable combination of casing recess parameters can help improve turbine efficiency.
Detailed Characterization of Turbulence Intensity and Dissipation As Boundary Condition for 3D RANS Simulations
Authors: Bologna Virginia , Paliotta Pietro , Petronio Daniele , Satta Francesca , Simoni Daniele , Giovannini Matteo , Paccati Simone , De Vincentiis Luca , Gily Monica
Published: August 2024

In the present work, an Hot-Wire Anemometer and a five-hole pressure probe have been used to characterize the incoming flow of a large-scale turbine cascade. Measurements have been carried out to sample the flow in both spanwise and pitchwise directions, hence allowing a complete characterization of total pressure, mean velocity, turbulence intensity, and integral length scale, or dissipation function, of the flow. Distributions here obtained provide a fine characterization of the whole inlet plane. This kind of data will be especially important for properly setting up the boundary conditions of both low (i.e., RANS) and high-fidelity (i.e., LES or DNS) simulations aimed at solving the whole 3D flow field. To further highlight the significance of the present velocity and turbulent profiles, different RANS simulations have been carried out. The first simulation has been carried out with uniform inlet conditions while the second one with measured quantities at a flow Reynolds number equal to 400000. Two additional simulations have been conducted at a lower Reynolds number and turbulence intensity, adopting the typical assumption of uniform turbulence intensity and length scale along the span-wise direction or the more appropriate re-scaled experimental spanwise distributions. The results presented here demonstrate the improved accuracy obtained once the 3D simulations consider the proper distribution along the span, especially at low Reynolds number conditions. To further extend the present results to other simulations, the turbulence spanwise profiles have been normalized with their midspan value and their formulations are here available to the readers. CFD results obtained at the lowest Reynolds number condition show the effectiveness in adopting such re-scaled boundary conditions.
Sensitivity Analysis for Flow Stability of Axial Compressor Based on Meridional Flow
Authors: Ni Haoyu , Fang Yibo , Xu Dengke , Zhu Hengyi , Sun Dakun , Sun Xiaofeng
Published: August 2024

A sensitivity analysis method for flow stability of axial compressors based on meridional flow is proposed and employed to reveal the sensitive region of stability in the present paper. The meridional stability model which transforms the stability problem into an eigenvalue problem enables flow stability to be quantitatively expressed by system eigenvalues. By using the eigenvalue representing the developing characteristics of the perturbations as the targeted parameter and incorporating the adjoint method and the induced boundary conditions, the sensitivity analysis method for stability problem of the compressor based on meridional flow is established to identify sensitive regions in the flow field. In this study, a low-speed compressor stage in Beihang University, named TA36, is analyzed. The stability prediction model accurately predicts the stall margin, and the sensitivity analysis of the base flow parameters reveals that the onset of the rotating stall is particularly sensitive to the blade tip region of the rotor. Meanwhile, the sensitivity analysis of the external source terms shows that, applying specific control to the flow field near the tip of the blade can benefit the stall margin of the compressor. The theoretical method proposed in this work effectively identifies the positions of stability sensitivity, which provides valuable insights in understanding the unstable regions and mechanisms of stall inception in axial compressors. The sensitivity analysis to the external source term can guide the design of the flow control methods.
Thermodynamic Potential of Aluminum Oxide Ceramic Matrix Composite Application in the 1st Stage Vanes of Industrial Gas Turbines
Authors: Bohn Dieter , Götte Johannes , Kusterer Karsten , Liu Yiou
Published: August 2024

Ceramic matrix composites (CMC) for application in gas turbine hot sections have been a topic of research for the last three decades. Until now, CMCs have found only limited use due to their mechanical limitations, economic factors and availability of the base material Silicon Carbide. Currently, a new manufacturing process combining 3D braiding technology with slurry die casting based on aluminum oxide is being developed within a collaborative research project. It aims to create CMCs that can withstand the thermal and mechanical stresses while having a longer life cycle than conventional nickel-based super alloys used in industrial gas turbines. One task within the collaborative research project is to derive the impact of the application of the new type CMC on the gas turbine thermal cycle behavior. Thus, the objective of this paper is to show the potential of the 1st stage vane made of the new 3D braided Al2O3-CMC in terms of thermodynamic efficiency enhancement by cooling air reduction. The first stage vane of a generic 30 MW industrial gas turbine is analyzed as reference case by means of aero- (CFD), heat transfer (CHT) and mechanical (FEA) simulations at different cooling air mass flows in case of conventional vane material and the new type CMC in comparison. A thermodynamic model of the gas turbine is then used to show the implications on the cycle and its efficiency in case the material of the first stage vanes is changed to the new type CMC. The results show that the positive potential in thermal efficiency depends significantly on the further usage of the cooling passing through the hollow CMC vane.
Reconstruction of Two-Dimensional to Three-Dimensional Flow Transition Fields Using Neural Network-Based Generative Adversarial Networks
Authors: Xu Ruiling , Gao Song , Wang Zhiheng , Xi Guang
Published: August 2024

Flow transition is a common phenomenon in fluid dynamics, widely observed, particularly in scientific and technological fields such as turbomachine. However, accurately measuring and predicting flow transition poses a significant challenge due to its inherent complexity, and acquiring comprehensive data for the entire fluid domain is often a daunting task. Artificial intelligence (AI) emerges as a promising avenue for conveniently and efficiently obtaining typical information about flow transition, thereby assisting conventional experimental and computational methods. In this study, the Generative Adversarial Network (GAN) was extensively used in the fundamental neural network training model for reconstructing the three-dimensional flow fields in a compressor cascade. Through the joint training of the generator (G) and discriminator (D) based on GAN, the velocity distribution was constructed. The training dataset comprised 200 consecutive snapshots, with an additional 200 consecutive snapshots reserved for testing. To ensure a high degree of accuracy, the data for the compressor cascade flow was obtained through Direct Numerical Simulation (DNS). The trained generator model in this study successfully reconstructed three-dimensional flow field data, capturing the flow transition in smooth blade passages as well as the bypass transition induced by roughness elements. In-depth analysis of the data resulted in accurate predictions and reconstructions of the transition location, range, and structure. This study has achieved the reconstruction of information from two-dimensional to three-dimensional flow fields for time instances not included in the training data using the 2D3DGAN model. The implementation of this aspect implies that the 2D3DGAN model can be utilized to infer the flow field status at unknown time instances by leveraging partial information. This capability opens up greater potential applications in the engineering domain, thereby reducing experimental costs and enhancing engineering efficiency.
CFD Modelling and Experimental Validation of Temperature Profile at Pad Leading Edge of Tilting Pad Journal Bearings
Authors: Riva Andrea , Gheller Edoardo , Chatterton Steven , Pennacchi Paolo Emilio Lino Maria
Published: August 2024

An oil-film bearing is a mechanical component that exploits the hydrodynamic lubrication principle to support a rotating shaft. In tilting-pad journal bearings, the pad ability to tilt allows the bearings to support the load, theoretically eliminating the cross-coupling forces that compromise the system stability, as occur in fixed geometry bearings. The temperature of the oil at the leading edge of the pad results from the oil-mixing process that occurs in the between-pad region. A correct prediction of this temperature is fundamental for the estimation of the static and dynamic properties of Tilting Pad Journal Bearings (TPJBs). The most common approach used for the estimation of the leading-edge temperature adopts the so-called mixing-coefficients approach. A hot oil carry-over coefficient is used to describe the fraction of hot oil coming from the upstream pad. A constant leading-edge temperature is obtained as a result. In general, the value selected for the hot oil carry-over factor strongly affects the results and needs to be accurately selected. In this study, a three-dimensional Computational Fluid Dynamic (CFD) model is introduced to simulate the mixing of the oil in the groove and to extract the temperature distribution at the leading edge of downstream pads. The CFD model is then linked to a thermo-hydrodynamic (THD) model for the oil-films that solves both the Reynolds and the energy equations. To validate the integrated model, an experimental campaign was carried out by introducing an array of temperature probes in the groove. Finally, the numerically estimated temperature distribution at the leading edge of the downstream pad is compared with the experimental results.
An Improved Experimental Validation of Nonlinear Forced Response Simulation of Shrouded Blades
Authors: Ahmed Rizwan , Ferhatoglu Erhan , Tamatam Lakshminarayana Reddy , Firrone Christian Maria , Zucca Stefano
Published: August 2024

Friction damping devices like tip shrouds are usually employed in Low Pressure Turbine (LPT) blades to reduce their large vibration amplitudes. From an engineering point of view, experimental validation of the numerically predicted dynamic behavior of the blade is essential to demonstrate the damping performance of shrouds in LPTs. In accordance with this purpose, this study presents the comparison of experimental and numerical results for the detailed investigation of the dynamic behavior of shrouded turbine blades. A brief overview of the experimental test rig, which has been previously developed to measure both the nonlinear forced response and contact forces simultaneously, is first presented. The experimental results show the effect of different normal preloads and excitation force levels on the measured parameters. To compute the nonlinear forced response of the blade and the shroud contact forces, the test rig is modeled in a commercial finite element software, and the system matrices are extracted in a reduced order form. The Harmonic Balance Method is applied in a nonlinear solver developed dedicatedly with the implementation of a 3D contact model. The comparison of the experimental and numerical results is presented in particular cases where lower normal preload to excitation force ratio results in alternate stick and slip transitions. The results show that experimental dynamic behavior of shrouded blade is computationally captured in most of the cases. The non-matching results are also highlighted for some cases in which the non-unique contact forces introduce the response variability. For these cases, response boundaries are numerically estimated by utilizing an optimization algorithm.

The outcomes of this paper consequently exhibit a detailed validation procedure for the simulation tools and an understanding of the numerical concerns like convergence.
Understanding the Aerodynamic Damping Behavior of an Industrial Axial Compressor Rotor With Multi-Row Effects
Authors: Pinelli Lorenzo , Vienni Dario , Tapinassi Libero , Michelassi Vittorio , Burberi Corrado , Lorusso Salvatore , Ignesti Mirko , Marconcini Michele
Published: August 2024

The evaluation of aerodynamic damping in compressor rotor airfoils is key to predict forced response amplitudes, since the fluid flow effects generate the most important contribution to the overall damping. The experimental and numerical assessment of aerodynamic damping has been studied from a long time and different methodologies have been proposed and validated in the Literature: the first objectives of such studies were the evaluations of the flutter occurrence to design flutter resistant or tolerant configurations. Yet, the study of damping can be extended to stable configuration in order to distinguish between mechanical and aerodynamic contributions. The experimental campaigns are usually intended to measure the mechanical damping through in vacuum test campaign, or the overall damping with in-situ measurements (with strain-gauges or tip timing techniques). On the other hand, classical flutter method can be also applied to predict the positive damping from a numerical point of view. In this context, the paper presents an in-depth numerical investigation of aerodynamic damping of an industrial axial compressor transonic stage. The effect of multi row interaction is assessed in and out of resonance conditions. For a specific mode, the numerical predictions are compared with overall damping measured by processing the related frequency response.
Experimental Study on Stability Enhancement of a Natural Gas GT Burner With Hydrogen Flame Piloting Operated With Simulated Exhaust Gas Recirculation
Authors: Galeotti Sofia , Picchi Alessio , Becchi Riccardo , Lemmi Gianmarco , Meloni Roberto , Babazzi Giulia , Giannini Nicola , Facchini Bruno , Andreini Antonio
Published: August 2024

Efficient coupling between gas turbine power plants fuelled with natural gas and Carbon Capture and Storage (CCS) units can be achieved by taking advantage of turbine Exhaust Gas Recirculation (EGR), since CCS efficiency increases with the CO2 content of the incoming flow. On the other hand, the combustion process has to endure the reduction of overall flame reactivity caused by EGR, with a potential increase of CO and UHC emissions, and modifications in the flame dynamic behaviour. In order to extend the combustor operability window, non-conventional pilot flames can be exploited to improve overall flame stabilization: in the current study the use of local hydrogen pilots was investigated. A lean-premixed burner for heavy-duty Gas Turbines was studied at ambient pressure in a reactive single-cup test rig at the THT Lab of the University of Florence, replicating EGR with the addition of CO2 to the combustion air. Reactive PIV measurements revealed a jet flame flowfield, not significantly affected by simulated EGR, which instead alters substantially the flame structure. Hydrogen addition has been found beneficial in widening the burner operating window, allowing higher premix splits to be achieved and reducing pressure oscillations also in EGR conditions. A modest decrease in CO emissions with high EGR levels was observed, and the flame structure detected with OH* chemiluminescence suggests that an optimization of the pilot injection geometry for dual fuel configuration could remarkably improve burner performance with EGR by enhancing the interaction between hydrogen pilot jets and natural gas flame.
Aerodynamic Characterization of LPBF Manufactured Honeycomb Like Sealing Designs Within a Labyrinth Sealing
Authors: Heitmann Timo , Göbel Fabian , Bardenhagen Andreas
Published: August 2024

Laser Powder Bed Fusion (LPBF) is an enabling technology to manufacture complex and thin-walled geometries. Former publications have successfully proven the application of the LPBF pulse wave approach to produce additive manufactured (AM) sealing segments, meeting the general geometrical requirement of 0.1 mm wall thickness. The objective of this paper is the continuative characterization of LPBF sealing structures regarding their aerodynamic behavior. An analytic optimization, based on the geometric leakage coefficient with a new approach of calculation, is chosen to define the optimal cell design for small clearance. Four different LPBF designs including hexagon and rhombus shapes are accompanied by a conventional honeycomb and a smooth liner for comparison. In order to characterize the leakage behaviors all samples are tested at a pre-established test rig of the KIT (Karlsruhe Institure of Technology). The experimental test plan includes the variation of the gap distance between 0.2 and 1.2 mm and an equal increase of the pressure ratio (PR) from 1.1 to 2.0. The performance is determined by measuring the mass flow rate and static pressure conditions within the chambers of a labyrinth sealing plate by means of nine pressure tubes. The results indicate a higher sealing efficiency for AM design at low sealing gaps. An increase of the gap distance to 1.2 mm favors the conventional honeycomb. The expected grading of the sealing performance according to the geometric increase factor could not be demonstrated. The consideration of the discharge coefficient (CD) shows the qualitative application of the new effective gap distance. For three liner structures the discharge coefficient appear to be constant at varying sealing gaps. The higher sealing performance of two LPBF designs in comparison to the standard honeycombs at small gap widths shows the potential for future investigations.
CFD Study of Journal Bearing Flow Physics and the Influence of Oil Feed Condition Within a Planetary Gearbox
Authors: Martin Ivo , Kurz-Hardjosoekatmo Wolfram , Schrewe Sebastian
Published: August 2024

Increasingly strict emission regulations and continuous pressure on cost-per-flying-hour require further reductions in fuel consumption of modern gas-turbines in the aviation industry. One promising technology is the geared turbofan, enabling for a larger bypass ratio for better thrust efficiency. The required gearbox may be a planetary gear box including journal bearing for the planet gears to cope with the high torques and centrifugal forces. The flow physics in such bearings is usually described as a Taylor-Couette flow, a two-dimensional simplification of the Navier-Stokes equations. However, during testing it has been observed that the feed condition, w.r.t. the positioning of oil feed bores and the flow split among these, has significant three-dimensional influence on measurements. Within the scope of this paper, the journal-bearing-flow physics is assessed based on a journal bearing which has a static inner, and a rotating outer cylinder, as well as its axis rotating around a centre axis. A full three-dimensional CFD is performed which includes centrifugal force, thermal conduction to the metal parts, two-phase flow (air/oil), cavitation from oil to oil-vapor, as well as evaporation of dissolved air within the oil phase. This assessment shows how the feed condition and feed temperature affect the three-dimensional gap flow along the circumference of a journal bearing. Furthermore, contour plots of flow variables within the lubrication gap show the presence of a recirculation zone just before the smallest gap which is not described by the traditionally applied Reynolds equation.
Negative CO2 Emission Gas Power Plant As Technology for Utilization of Sewage Sludge, Production of Electrical Energy, and CO2 Capture - Case of Chamber Under Transpiration Cooling
Authors: Ziółkowski Paweł , Stasiak Kamil , Ditaranto Mario , Wiseman Samuel , Mikielewicz Dariusz
Published: August 2024

This work focuses on the concept developed in the nCO2PP project, which aims to demonstrate a technology that allows to achieve negative CO2 emissions through Carbon Capture and Storage (CCS) applied to sewage sludge. A feedstock is first gasified, then the resulting syngas is burned in a semi-closed oxy-fuel gas turbine with pure oxygen and water, using the advantages of oxy-combustion, to ease the capture of CO2 in the resulting exhaust gases. High-temperature combustion later takes place in a dedicated wet combustion chamber before expansion in a turbine which produces electricity. Given that in Polish law sewage sludge is treated as biomass, a negative CO2 emission factor is achieved. Works in the project are performed both in experimental and design terms. The concept of transpiration cooling will be considered in terms of different methods. Additionally, previously unpublished computational flow dynamics (CFD) simulations related to transpiration cooling were compared with measurement and design analyses. Experimental efforts include a demonstration of water transpiration through a porous structure.
A Real Time AI-Based Strategy for the Design of a Low-Pressure Turbine Profile
Authors: Bellucci Juri , Granata Angelo Alberto , Silei Mattia , Giovannini Matteo , Spano Ennio , Notaristefano Andrea , Lengani Davide
Published: August 2024

This paper focuses on the implementation of a data-driven, AI-powered design strategy for Low Pressure turbine (LPT) profiles.

The objective is to develop an effective LPT profile optimization environment, capable of rapidly generating a CFD calculation database to feed AI-based tools for subsequent phases of design space exploration. To achieve this purpose, an automatic workflow has been developed to create profile geometries, computational meshes, and perform URANS calculations. CFD results are then collected both in terms of overall performance (losses) and detailed flow field. AI-models are then trained over this large database, resulting in an accurate metamodel that can be effectively explored looking for specific design solutions. The paper will present and discuss the AI-based tool, showing how in addition to suggesting optimal geometries, it offers additional outputs to inform the designer. Indeed, the tool can provide optimal geometries that match mechanical and geometrical constraints providing performance at varying Reynolds number. Moreover, the blade-loading and the entire 2D flow field are predicted in real-time for the optimal geometry at a given operating condition.
Innovative Cavity Modeling for Centrifugal Compressors Aeromechanical Analysis
Authors: Batisti Marco , Pinelli Lorenzo , Toni Lorenzo , Guglielmo Alberto , Marconcini Michele , Arnone Andrea
Published: August 2024

Centrifugal compressor aeromechanics is playing an increasingly important role in the energy transition scenario, especially when operating with low molecular weight gases, such as hydrogen. For these machines, maximum impeller tip speeds are limited by structural requirements and so aeromechanical assessment must be included from the preliminary design stages. When performing forced response analysis of centrifugal impellers, it is mandatory to consider the contribution of the unsteady forces acting within front and rear cavities. The flow field inside the cavities has different time and length scales compared with the main flow field, and from a modeling standpoint seal regions have to be included in the computational domain: this means that a comprehensive Computational Fluid Dynamics (CFD) simulation may require substantial efforts for the setup and high computational time and resources. In this context, the paper presents an acoustic analytical model for predicting pressure perturbation within centrifugal compressor cavities without solving them with unsteady CFD approaches. The model is fed with appropriate boundary conditions to be applied at the entrance of the cavities and analytically solves the pressure perturbation distribution in an annular environment. To validate the presented analytical model, unsteady calculations were performed on impeller-vaned diffuser domains with cavities at different operating conditions, and the unsteady pressure field in the cavities was used as target solution. The comparison between the analytical model results and the CFD solution shows a very good agreement for all the different blade passing frequencies under investigation, paving the way for accurate aeromechanical evaluations in the preliminary design phase when complete unsteady CFD simulations are not compatible with design timing.
Aerothermal Optimization and Sensitivity Analysis of a Turbine Rotor Tip With a Circumferential Casing Groove Configuration
Authors: Li Weiqi , Tao Zhi , Song Liming , Li Jun , Feng Zhenping
Published: August 2024

The design of rotor tips is facing increasing challenges due to higher turbine inlet temperatures and blade loads. To tackle these issues, this study proposes a novel solution that integrates a circumferential casing groove (CG) configuration with a squealer tip. The CG is parameterized and integrated with an efficient global optimization algorithm, establishing an aerothermal optimization framework for the turbine rotor tip. Taking the stage efficiency and tip heat transfer coefficient as the optimization objectives, multiple representative optimized solutions for the CG configuration are obtained. The results demonstrate that the optimal solution aimed at maximizing stage efficiency achieves a superior trade-off in aerothermal improvement. Quantitatively, it increases the stage efficiency by 0.41% and decreases the tip and casing heat transfer coefficients by 7.06% and 7.75% respectively, while only slightly increasing the blade heat transfer coefficient. This improvement in aerothermal performance can be attributed to the CG’s ability to control tip leakage flow and regulate the topology of the tip vortex system. Besides, a global sensitivity analysis is employed to identify the key geometric parameters of CG. The starting point of the CG is found to be the most crucial parameter and its influence laws are investigated through a variable-controlling methodology. In summary, the proposed CG configuration and optimization strategy offer a promising solution to diminish tip leakage losses and enhance the thermal performance of turbine rotor tips.
Advancements in Sustainable Aviation Fuels: Impact of Nano-Additives and Ammonia-Based Strategies on Emissions
Authors: Di Gloria Pasquale , De Giorgi Maria Grazia , Strafella Luciano , Ciccarella Giuseppe , Castelluzzo Gregorio Grazio , Baldassarre Francesca , Ficarella Antonio
Published: August 2024

The increasing commitment to sustainable practices has intensified research into innovative methods to diminish the release of harmful pollutants and greenhouse gases, such as CO2, CO, and NOx, into our environment. A promising avenue of exploration lies in the adoption of fuel emulsions enriched with nano-additives aimed at curtailing NOx emissions.

In this context, our study delves into the impact of nano-particulate additives — specifically those based on ammonia and water — on the combustion characteristics of Jet-A1 aviation fuel. Utilizing a 300-kW liquid swirl combustor, we conducted a series of experiments across two global equivalence ratios (Φ = 0.24 and Φ = 0.40). Our investigation encompassed the analysis of laminar flame speed (LFS) and an in-depth examination of flame properties through advanced chemiluminescence imaging and modal analysis techniques.

The primary objective was to unravel the complexities of how these nano-additives modulate flame dynamics and the intricate web of internal chemical reactions, alongside evaluating the broader environmental ramifications resulting from alterations in the combustion process.

The experimental outcomes revealed that the integration of urea and water additives into the fuel matrix distinctly affected LFS, with observed enhancements at the lower global equivalence ratio and detrimental impacts when the ratio was increased. Through modal analysis, we discerned a notable stabilizing influence on the flame’s behavior, which was particularly pronounced at leaner fuel conditions.

From the study of the spray, the addition of water and urea appears to influence combustion chemistry, and more uniform sprays facilitate more complete combustion.

Chemiluminescence imaging further illuminated these effects, demonstrating a higher emission intensity of NH2* radicals compared to NH* radicals, a variance contingent on the global equivalence ratio. Notably, the experimental data indicated a substantial abatement in NOx emissions, predominantly at the lower equivalence ratios. This reduction was accompanied by a marginal uptick in CO2 and CO emissions — a trade-off that warrants consideration.
The Hybrid Pathway to Flexible Power Turbines: Part C, Enabling Live Thermal Boundary Prediction Using Real-Time Plant Measurements and LSTM Neural Networks
Authors: Baker Mark , Rosic Budimir
Published: August 2024

The global drive towards renewable energy is imposing challenging operating requirements on power turbines. Flexible load-leveling applications must accept more frequent and demanding start-stop cycles. Full transient analyses are too computationally expensive for real-time simulation across all operating regimes so monitoring relies on sparse physical measurements. Alone, these sparse data lack the fidelity for real-time prediction of a complex thermal field. A new hybrid methodology is proposed, coupling data across a range of fidelities to bridge the limitations in the individual analyses. Combining several fidelity methods in parallel: low-order models, corrected by real-time physical measurements, are calibrated with high-fidelity simulations. The multi-faceted hybrid approach enables the real-time speed of low-order analysis at high resolution. This paper series develops the critical enabling features of the hybrid method. Real-time definition of the simulation thermal boundary condition is fundamental to the methodology. A novel Long-Short-Term-Memory (LSTM) neural network is presented, enabling time series prediction of the turbine thermal profile. The remote sensing method utilizes standard plant measurements to reconstruct the turbine temperature history, allowing reliable thermal prediction whilst removing the need for direct monitoring of the casing temperature. Calculations within the training region demonstrated high accuracy, achieving a mean square error of 3.1 K and maximum instantaneous peak error of 7.6 K. Combining a reduced feature space and efficient two-step predictor-corrector structure, the LSTM method offers high-speed temperature calculation, successfully predicting one month of operating data in under a minute.
Topology Optimization of Centrifugal Compressor Exhaust Volute With Discrete Adjoint Method
Authors: Zhang Huiying , Wan Siyuan , Jiang Mindi , Xi Xi , Xu Shengli
Published: August 2024

The exhaust volute, an important component of a centrifugal compressor, plays a crucial role in improving overall compressor efficiency. Traditional design methods rely heavily on designer’s experience and often result in low design efficiency. In this study, a topology optimization design method for the exhaust volute flow channel is proposed to address this issue. The optimization objective focuses on minimizing flow energy dissipation within the design domain while considering flow compressibility. The sensitivity of the objective function to design variables is calculated using the discrete adjoint method. In the open-source platform OpenFOAM, the finite volume method is utilized to solve governing equations with darcy source term and adjoint equations, and the Method of Moving Asymptotes (MMA) algorithm is applied to solve the optimization problem. Numerical examples of different volute types in two and three dimensionals are used to demonstrate the effectiveness of the proposed method. The results show that the topology optimization method proposed in the present work can quickly obtain the optimal volute configuration.
Pulsations and Vibrations in the Discharge Piping of a Throttled Supercritical CO2 Turbine
Authors: Wilkes Jason , Patil Abhay , Bygrave Jon
Published: August 2024

Choke nozzles present an economical option to control the expander downstream conditions in high-pressure, high-temperature supercritical CO2 loops; however, the expansion and high fluid momentum exiting the choke may induce instability, causing pulsating behavior and vibration of the loop due to fluid-structure interaction. The current study investigates the performance of a conventional choke design utilizing CFD simulations to provide detailed insight into jet behavior and interaction with the wall. The analysis uses constant boundary conditions and doesn’t account for any flow instability due to fluctuations and swirl velocities at the expander outlet. The CFD outcomes reveal the whirling motion of the jet after exiting the choke sticking to the pipe wall during the initial phase of jet formation. This whirling jet interacts with the downstream pipe and was shown during testing to create large pressure pulsations in the downstream piping. The study concludes with the design, analysis, and testing of a flow conditioner-type choke that redistributes and homogenizes flow downstream of the choke, which reduces the undesirable excitations and consequently eliminates the pipe vibrations.
Fluidic Thrust Vectoring on an Altitude-Adaptive Double-Divergent Nozzle Using a Bypass Passage
Authors: Das Arnab Kumar , Mankodi Tapan K. , Saha Ujjwal K.
Published: August 2024

Shock vector control (SVC) is one of the most researched topics in the field of fluidic thrust vectoring (FTV). In SVC, a secondary fluid flows through an injector to deflect the primary flow through the nozzle. However, the losses associated with the secondary injection is significantly high due to engine bleed. Modern research on SVC focuses on the use of bypass passage in order to mitigate this loss. The present study deals with this so-called bypass-SVC on altitude-adaptive double-divergent nozzles (DDNs), which have two diverging sections separated by an inflection point. The inflection Mach number is set to be 1.5. Three different DDN configurations have been studied in this work by varying the lengths of the diverging sections. The steady-state flow-field has been numerically solved using ANSYS Fluent software over a range of nozzle pressure ratios (NPRs), and results have been compared to a single-divergent nozzle (SDN) of the same nozzle area expansion ratio (ε). The results indicate higher pitch thrust vector angle (δp) for the DDNs as compared to the SDN at certain NPRs. Also, the thrust losses (ω) have been observed to be less for the DDNs as compared to the SDN at higher NPRs. In the non-vectored state, the coefficient of thrust (CF) of the DDNs is comparable with that of the SDN.
On the Relationship Between Swirl and Unsteadiness Within Turbine Rim Seals
Authors: Vella Simon , Tang Hui , Carnevale Mauro , Scobie James A. , Lock Gary D. , Salvatori Francesco , Sangan Carl M.
Published: August 2024

Unravelling the flow physics pertaining to hot gas ingress in turbines is crucial in enabling designers to realise global decarbonisation targets in aerospace. A turbine rim seal is fitted at the periphery of the rotor-stator cavity to minimise the ingress of annulus gas, which detrimentally affects cycle efficiency. The inherent unsteadiness in rim seal flows, arising from shear gradients between contiguous flow paths, introduces a consequential, yet presently unestablished, influence on sealing characteristics.

A single-stage axial turbine facility in conjunction with an aeroengine architecture is employed to assess the steady and unsteady sealing characteristics of a range of industrially-relevant rim seals. Time-averaged measurements of gas concentration and swirl, acquired over a range of flow coefficients (CF), exhibited an inverse relationship between sealing performance and the purge-mainstream swirl difference (Δβ). Spectral analysis of unsteady pressure signals revealed an associated unsteadiness, induced by the strength of the annulus-cavity interaction. Across all CF, a low-frequency harmonic range consistently displayed proportionality between spectral activity and Δβ. Thus, a relationship between steady and unsteady characteristics was established.

Examining a series of rim seal configurations with varying radial clearances signified that sealing performance was predominantly influenced by the radially outermost clearance. The configurations exhibiting superior performance presented heightened spectral activity, ascribed to an increased radial purge mass flux and establishing a definite relationship with concurrent steady measurements.