bluuebunny/crossref_metadata_2025_split huggingface dataset:
1D Modelling of a Water-Steam Ejector as a Compression Step in High-Temperature Heat Pumps
Authors: Abu Khass Omar , Tran Anh Phong , Klöppel Steffen , Stathopoulos Panagiotis , Nicke Eberhard 
Published: August 2024

Abstract
High-temperature heat pumps (HTHPs) have emerged as a promising solution for decarbonizing process heat. With natural refrigerants like water, Rankine cycle-based HTHPs can deliver process heat up to 200°C, which covers a wide range of industrial processes. However, achieving these high temperatures necessitates advanced turbomachinery. Current designs processes for steam compressors are intricate and often tailored for specific applications. Furthermore, achieving the desired temperature typically requires multiple compressors, adding to the complexity of the system. To address this, ejectors can be utilized as a secondary steam compression mechanism within the heat pump architecture. By integrating an ejector, a portion of the heat pump condensate can be used and mixed with superheated steam from the compressor to simultaneously de-superheat the steam and raise its pressure. This approach can potentially reduce both compression power and the number of compression stages required. This paper presents a one-dimensional mathematical model of a water-steam two-phase ejector designed for HTHPs. Using thermodynamic 1D modelling, differential conservation equations and the IAPWS-IF97 equations of state are applied across the ejector’s components, accounting for flow compressibility and its two-phase nature. Closing equations are used in the mixing and diffuser sections to simulate the transfer of mass, momentum, and energy between the two streams, assuming homogeneous equilibrium. A specific use case for the ejector’s integration in a high-temperature heat pump cycle identified the boundary conditions for the simulations. The model enables the calculation of the 1D distribution of flow variables and key ejector performance indicators, such as the pressure ratio. This research offers advancements in two-phase water steam ejector modelling, shedding light on their potential as steam compression devices in HTHPs.
Large Axial Vibrations in Turbomachines: Non-Linear Behaviour of Double Sided Lubricated Thrust Bearing
Authors: Dassi Ludovico , Chatterton Steven , Gheller Edoardo , Pennacchi Paolo 
Published: August 2024

Abstract
Even if not a common phenomenon, large axial vibrations are a critical concern in turbomachinery, particularly when dealing with double-sided, oil-lubricated thrust bearings in compressors and gas turbines. This phenomenon, known as axial Sub-Synchronous Vibration (SSV), manifests as high-amplitude vibrations that can extend throughout the entire machine clearance. The high level of vibrations is a main concern for the structural integrity of the machines, and it can lead to the onset of a trip condition. The development of the vibration is often unpredictable, marked by sudden jumps in vibration amplitude due to various operational parameters of the machine, such as active power, clearance adjustments, oil temperature, and flow rate. To understand the problem, the non-linear behaviour of the oil film of the thrust bearing is analysed by solving the well-known Reynolds equation. The integral force on the bearing collar is calculated and then used to create a simplified axial model of the machine. Harmonic Balance is used to study the non-linear dynamics of the system, the bifurcation region is found, and a sensitivity analysis is performed by changing the most important operational parameters of the bearing. This phenomenon usually amplifies the vibrations induced by the coupling between axial-lateral vibrations, related to the thrust collar. Numerical results are compared to experimental data available in the literature.
Manufacturing and Build Variations Modelling for Multi-Stage Axial Compressors: Forced Response Predictions
Authors: Bruni Giuseppe , Krishnababu Senthil K. , Jackson Simon 
Published: August 2024

Abstract
Modern multi-stage axial compressors for gas turbine applications continue to require the achievement of higher efficiency whilst at the same time meeting the mechanical integrity and life requirements that have established the gas turbines as a key asset in many industrial applications. To avoid potential aero-mechanical issues, the development and validation of computationally efficient and accurate numerical tools is of paramount importance. This paper demonstrates how highly automated forced response analyses are integrated in the design of a new multistage axial compressor for industrial gas turbine applications. In case of twin-shaft engines with wide operating range requirements, each design concept can require hundreds of analyses. The capability to perform rapid design iterations considering aero-mechanical stability, unlocks new regions of the design space excluded by traditional design criteria, with potential issues being identified and rectified at an early stage in the product development process. Moreover, the scope of the assessments can be extended to consider effects which would not traditionally be considered as part of the design process, such as mistuning due to manufacturing variations. The methodology is here applied to in-tolerance geometrical variations, modelling the associated uncertainty on forced response. Characterizing the sensitivity to manufacturing variations provides actionable data for the development of robust design concepts. The methodology used for the design of a new compressor and subsequent predictions are validated against tip timing data from a full-scale engine test, demonstrating the accuracy of both the analyses and design process.
CFD Simulation of an S-Bend Diffuser With Passive Full Surface Effusion Cooling: Novel Slot Method Approach
Authors: Moradi Hossein , Birk Albrecht Michael 
Published: August 2024

Abstract
There are different approaches for CFD simulation of effusion-cooled surfaces, such as the 1D Porous Jump Coefficient and periodic boundary conditions. These methods are used to minimize the cost of simulation; however, each model has its own drawbacks. A novel approach called the “Slot Method” has been introduced for the first time in this research. In this method, based on the porosity of the effusion patches, the effusion holes are replaced by a limited number of slots to reduce the cost and time of simulations. The slot method is simulated using the Reynolds-Averaged Navier-Stokes (RANS) methodology to predict the pressure recovery performance of the diffuser, pressure distributions on the walls, outflow velocity distributions, and outflow temperature distributions. The CFD simulations are compared to experimental data from a rectangular S-duct diffuser as well as CFD simulations with 1D Porous Jump Coefficient boundary conditions reported by NG [1]. Four different numbers of slots are simulated using RANS k-ε models to investigate the effect of the number of slots on the main and secondary flows. The simulations show that the higher number of slots has the potential to mimic the behavior of the effusion holes. The simulations exhibit significantly more accurate predictions compared to the 1D Porous Jump Coefficient in terms of pressure recovery performance in the diffuser. Some discrepancies between the experimental data and the Slot Method in the outflow velocity distribution can be attributed to imprecise boundary conditions in the reported experimental data.
Investigation of the Coupling Between the Dynamics of Vortical Structures and Flame Stability in Bluff-Body Premixed Combustion Using Extended Spectral Proper Orthogonal Decomposition
Authors: Khalifehei Morteza , Yalcinkaya Yagiz , Padilla-Montero Iván , Gungor Ayse Gul , Rodríguez Daniel 
Published: August 2024

Abstract
Large eddy simulation data of a bluff-body stabilized flame are analyzed using spectral proper orthogonal decomposition (SPOD) to investigate: (i) the role of flame-vortex interactions in the dominant flow dynamics, and (ii) how the proper choice of the cross-spectral density (CSD) defining SPOD can assist in identifying the underlying dynamics. Bluff-body flame holders aim to achieve stable flames under lean premixed conditions to minimize pollutant emissions. The recirculation region induced by the body promotes the mixing of hot combustion products with unburnt gases, preventing the global blowoff of the flame. However, the coupling between the shear layers and flame-induced vorticity sources can result in large-scale flow structures that either contribute to increased flame stability or exhibit features typical of the early stages of flame blowout and extinction. SPOD is a data-driven analysis technique that is remarkably powerful in identifying and extracting low-dimensional models in stationary processes. For each frequency, it computes a basis of orthogonal modes that maximize the content of a predefined CSD in the leading modes. By choosing physically relevant variables to construct the CSD, different physics can be explored. This study uses this aspect to investigate the coupled dynamics between the flame-induced baroclinic torque, vortical structures, and the temperature field. The SPOD results show that the vorticity and temperature fields exhibit low-dimensional dynamics characterized by large-scale structures with a well-defined narrowband frequency and its harmonics. The dominant dynamics consist of varicose oscillations of the wake/flame region, originated by the flame-induced baroclinic torque.
Effect of Cracking Pressure and Flow Split Ratio on the Atomization Performance of Dual-Orifice Injectors
Authors: Kılıçgedik Hıdır Yankı , Tuncer Refik Alper 
Published: August 2024

Abstract
In gas turbine engines, pressure-swirl atomizers function in tandem with integrated valves, leading to performance in dual operation modes that markedly differs from scenarios where the injector operates independently. This can result in a deterioration of atomization quality when the secondary fuel line operates at a sub-optimal pressure, particularly during its initial activation.
This study explores spray characteristics such as circumferential and radial non-uniformity, cone angle, combined flow number, and instability for a representative engine configuration across various cracking pressures. The aim was to identify the flow split ratio corresponding to the weakest atomization performance. The findings indicate that when the secondary line engages at higher cracking pressures, the negative impact on atomization is less pronounced, with this deterioration occurring later. Conversely, at lower activation pressures, a higher spray angle can be achieved. Dynamic characteristics were also investigated using a high-speed shadowgraphy technique for different cracking pressures to further comprehend the effect of the flow split ratio on part-load operations, using spray-angle fluctuations as a measure to assess spray instability. It was observed that the nozzle’s flow number ratio dictates the most unstable operation point, with amplitudes diminishing as the critical flow number ratio is surpassed. Dynamic behavior of the dual-orifice nozzle could play a significant role in combustion instability and should be carefully considered during the design process.
Unsteady Loss Mechanisms in Low-Pressure Turbines With Diverging End-Walls Studied via High-Fidelity Simulation
Authors: Rosenzweig Marco , Kozul Melissa , Sandberg Richard D. 
Published: August 2024

Abstract
High-fidelity simulations are used to conduct controlled numerical experiments to investigate the effect of periodically incoming wakes on profile and three-dimensional loss mechanisms. The present work considers the MTU-T161 cascade with spanwise-diverging end-walls, representative of a high-lift, low-pressure turbine blade. All simulations are carried out at engine-relevant conditions, with exit Reynolds number of 90,000 and exit Mach number of 0.6. Upstream moving bars are used to generate incoming wakes which impinge on the blade and potentially alter its aerodynamic performance. Unlike previous studies, the incoming wakes are subjected to an additional axial pressure gradient when convecting through the passage, due to the divergence of the spanwise end-walls. The evolving secondary vortex systems around the bars periodically disturb the free-stream end-wall boundary layer facing the blade leading edge. This ultimately influences the end-wall related losses downstream of the blade and governs the overall aerodynamic performance of the blade. Following validation against available experimental data, a systematic variation of flow coefficient and reduced frequency extends the parametric space studied to encompass engine-realistic operating conditions. The high-fidelity simulations reveal the impact of incoming wakes on blade boundary layer losses and wake-induced losses both at the mid-span and within the end-wall regions. Furthermore, by decomposing the total loss generation, the data-rich results shed light on the underlying physical mechanisms driving unsteady losses when applied to phase- and time-averaged flow fields. Secondary losses incurred in the end-wall region show little sensitivity towards unsteadiness associated with incoming wakes and are rather prone to the turbulence levels in the passage. On the other hand, profile losses show high dependency on bar wakes in the absence of wake fogging. Whilst profile losses can be minimized by certain combinations of flow coefficients and reduced frequencies, they remain the dominant source of unsteady loss generation.
Quantification of Combustion Inhomogeneity Based on Sparsely Arranged Thermal Couples at the Outlet of Multi-Stage Turbines
Authors: He Qingfu , Huang Jingwei , Chi Zhongran , Xia Shuocheng , Zang Shusheng 
Published: August 2024

Abstract
The localized temperature anomalies induced by combustion manifested as circumferential or radial temperature inhomogeneity, are detrimental to the performance and reliability of the turbine cascades. Temperature inhomogeneities within the gas turbine are typically monitored by thermocouples installed at the turbine outlet, which cannot directly reflect the operating conditions of the combustion chambers and high-pressure turbines because of the migration and mixing of temperature inhomogeneities. Based on the effective prediction method for the azimuthal migration of temperature inhomogeneity, the temperature reconstruction using multi-Gaussian function approximation is developed. Dual-objective optimization is adopted for solving the system of nonlinear equations in reconstruction. Reconstruction is applied to data from cold streak migration experiments on a multistage turbine. Equal-span temperature profiles in different streamwise planes within the turbine are reconstructed based on sparsely arranged thermocouples at the turbine outlet. In addition, the azimuthal migration of the hot/cold streaks and the variation of the temperature profiles with the streamwise direction are reproduced. Comparison of the reconstruction with full-annulus unsteady-state numerical simulations shows that the temperature inhomogeneities and asymmetries in the circumferential and radial directions are correctly captured. The robustness tests show that the reconstruction is sensitive to the parameter characterizing the azimuthal migration of the combustion inhomogeneities, while is relatively insensitive to the thermocouple mounting positions and the parameters characterizing the temperature distributions.
Dynamic Prediction of Elastic-Supported Rotor With Friction Damper Based on 3D Contact Model
Authors: Fan Yu , Wang Shengshuo , Wu Yaguang , Zhang Shanzi , Shen Yiwen , Chen Mingmin 
Published: August 2024

Abstract
The elastic support with adjustable dry friction damper has prospects for vibration reduction of aero-engine rotors under variable working conditions. In this work, we propose a harmonic balance method for predicting the unbalanced response of the elastic supported rotor damped by a frictional damping structure. Distributed 3D contact models are used to describe the nonlinear constitutive relationship of the contact interface. Thus, both the time-varying normal force induced by the coupling of normal/tangential vibration and the curvilinear in-plane relative motion trajectory driven by the rotor whirl can be captured. A multi-step ROM technique is realized and used to reduce the model dimension. The analytical Jacobian matrix is derived to enhance the convergence. The in-house codes work well for predicting the unbalanced response of large-scaled rotor systems containing non-smooth local nonlinearities. Taking a finite element model of a frictionally damped rotor as an example, the accuracy of the proposed method is verified against the Newmark-β integration. The reduced model retains 12 DOFs from the original 172,158 nodes, with an average simulation time of 1.01 seconds per frequency point. Results also indicate that the distribution of contact state on the elastic support friction surface is not uniform, and there are fluctuations in normal force. This proves the necessity of discretizing the friction interface and adopting 3D contact models.
Compact Heat Exchangers With Curved Fins for Hydrogen Turbofan Intercooling
Authors: Capitao Patrao Alexandre , Jonsson Isak , Xisto Carlos 
Published: August 2024

Abstract
Hydrogen is being considered as a possible path towards carbon-neutral aviation. There are additional advantages besides its main benefit of CO2-free combustion. One application is to use it for aero engine heat management due to its cryogenic temperature and high heat capacity, including intercooling and exhaust heat recuperation. The focus of this paper is on the design of a compact heat exchanger integrated into an intermediate compressor duct (ICD), which could decrease compression work and specific fuel consumption (SFC). This compact heat exchanger features curved fins to promote flow turning and decrease pressure losses compared to more conventional straight fin heat exchangers. Conceptual design and duct shape optimization has been carried out which produced integrated ICD heat exchanger designs with significantly lower air-side total pressure losses compared to their conventional straight fin counterparts, which could improve system level integration and engine performance. A direct outcome of this study is a pressure loss correlation which can be used in future engine system level trade studies.
Impact of Blowing and Density Ratio on the Film Cooling and Heat Transfer in an Aggressive Turbine Center Frame
Authors: Jagerhofer Patrick R. , Glasenapp Tobias , Patzer Bastian , Göttlich Emil 
Published: August 2024

Abstract
It was shown in the previous study that the aft purge flows from the last stage of the high-pressure turbine (HPT) have a significant film cooling potential in the downstream turbine center frame (TCF) [1]. The TCF is a stationary duct that guides the flow from the high-pressure turbine (HPT) outlet to the low-pressure turbine (LPT) inlet and is the third most thermally loaded engine component after the combustion chamber and HPT. This paper investigates the impact of different purge-to-mainstream blowing ratios and density ratios on the film cooling effectiveness and the heat transfer coefficient in the TCF. The experiments were conducted in a product-representative 1.5-stage HPT-TCF-LPT vane configuration under Mach-similarity in the transonic test turbine facility (TTTF) at Graz University of Technology.
The blowing ratio has been demonstrated to be the dominant parameter for purge film cooling in TCFs since HPT purge flows typically have very low momentum. Even at twice the nominal blowing ratio, no cooling film detachment was observed on the TCF hub or shroud surface. Varying the density ratio in the experimentally possible range delivered no significant differences in the results. With increasing purge blowing ratios, the film cooling effectiveness in the TCF increases as expected, but the heat transfer also intensifies due to the purge injection. The gain in film cooling effectiveness, however, outweighed the heat transfer intensification as the heat transfer reduction on the hub monotonically increases with the blowing ratio. The circumferentially averaged film cooling on the hub scales relatively well with an offset version of the well-known Hartnett correlation [2] that takes into account the ingress-induced premixing of the purge flow in the cavities.
The Impact of Manufacturing Variations on the Aerothermal Performance of High-Pressure Turbine Blade Shrouds
Authors: Hulhoven Bram , Coull John D. , Jackson Dougal , Atkins Nicholas R. 
Published: August 2024

Abstract
High pressure turbine blade (HPTB) shrouds suffer manufacturing variations in both platform alignment and inter-platform gap width. Compared to hub endwalls, the aerothermal effects of shroud platform steps and gaps has had little attention, which introduces uncertainty in the sentencing of such manufacturing variations. This paper presents a shroud step sentencing correlation developed using a quasi-2D (Q2D) model of a shroud endwall step. The use of a Q2D model follows from the study of a 3D steady RANS simulation matrix of engine-representative platform steps and gap widths, based on a sample of scanned HPTB castings and finished parts. This study showed that the aftchord shroud step flow is Q2D and resembles canonical step flow with enhanced heat transfer at the reattachment point. The shroud step sentencing correlation is tested on the platform steps in the simulation matrix giving prediction errors below 20% for the vast majority of cases. Finally, the correlation is tuned using experimental data to mitigate the uncertainty associated with RANS simulations of separated flows.
Numerical Simulations and Sensitivity Analysis of Ice Formation on Fan Blades
Authors: Müller Katja , Flassig Peter , Flassig Robert 
Published: August 2024

Abstract
In-flight icing, the formation of ice during flight, poses risks to the safety and reliability of aircraft. Due to environmental conditions, ice accumulation occurs on the low-pressure compressor blades of an engine, diminishing aerodynamic performance and potentially causing damage to the engine. Numerical simulations of ice accretion are conducted on the blades of the NASA Rotor 67 utilizing the Computational Fluid Dynamics (CFD) software ANSYS CFX and the in-flight icing software FENSAP-ICE. One-dimensional and two-dimensional sensitivity studies aim to analyze the influences of temperature, droplet diameter and liquid water content (LWC) on the resulting ice build-up on the blade. The analyses reveal that ice accumulates predominantly at the leading edge of the blade, where collection efficiency is maximal. Additionally, an ice layer forms at the blade root on the pressure side. While LWC and temperature exerts a significant influence on the ice mass, only a marginal impact on droplet diameter is observed.