bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coupled Vibration of a Centrifugal Compressor Blade Excited by Macro Fiber Composite Actuator
Authors: Nie Mingjie , Chen Yong , Tang Xu 
Published: August 2024

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.