bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on Performance Degradation Prediction Method of Heavy-Duty Gas Turbine Based on Data-Physics Fusion Under Uncertainty
Authors: Liu Yiyang , Jiang Xiaomo , Wei Manman , Ge Xin
Published: August 2024

Heavy-duty gas turbines (HDGT) have been widely used for power generation, because of their unique characteristics of high efficiency, low-emission, and flexible in rapid startup and shutdown. However, their main components such as compressor, combustion chamber, and turbine are usually operating under harsh environments such as high temperature, high pressure and high corrosion for a long time. The resulting fatigue, leakage, corrosion, or fouling in various components often lead to their performance degradation over the operating time, lowering the productivity of the gas turbine. Performance prediction becomes a powerful approach to monitor the degradation degree so that maintenance recommendation is provided to effectively ensure the efficiency and productivity of the machine.

This paper presents a new data-physics intelligent fusion approach for performance degradation prediction of HDGT under uncertainty. A thermodynamic heat balance model is first established to simulate component characteristics. The actual operating data of a real-world gas turbine are then employed for physics-based model assessment and parameters correction. Next, The deviation between expected performance data and actual heat balance value under the current operating point is utilized to assess the performance degradation. Finally, in order to consider the uncertainties in both the sensor signals and the prediction model, an improved Bayesian-LSTM (long short-term memory) model is proposed to predict multiple performance indicators by seamlessly integrating Bayesian variational inference with LSTM model. This method models each of the weight and bias parameters as a continuous distribution, rather than a constant. About half a year of sensor data collected from a 180 MW real-world gas turbine is utilized in a comparison study with the traditional LSTM models to demonstrate the superiority of the proposed method in predicting the performance trend of gas turbines. The proposed methodology can not only produce the predicted curve, but also obtain the fluctuation range of the prediction output to effectively consider the uncertainty in both the data and model, thus improving the robustness of the proposed model.
Investigations on Effects of Inflow Turbulence on Vortex-Induced Vibrations of a Wind Turbine Airfoil With the Wake Oscillator Model
Authors: Lian Bo , Tong Xin , Zhu Xiaocheng , Du Zhaohui
Published: August 2024

Design load and vibration for parked conditions are of utmost importance for large-scale modern wind turbines with increasing flexibility, especially edgewise vibration when the blade is at a high angle of attack. In this study, effects of inflow turbulence on vortex-induced vibration (VIV) of a wind turbine airfoil at 90 degrees of attack angle is examined. The study is carried out using the wake oscillator model, which is identified from the fluid-structure interaction (FSI) simulations. The turbulence induced dynamics is observed to be significantly distinct from that under uniform inflow and is heavily dependent on the turbulence intensity and mean velocity. The vibration response under inflow turbulence represents intermittency and broadband frequency characteristics near natural frequency and vortex shedding frequency since the inflow fluctuation drives the system to alternately enter and exit the frequency lock-in regime. In addition, Gaussian process regression is used to obtain a surrogate from input inflow conditions to output VIV loads. The results show that the incoming turbulence increases the risk of high amplitude vibration in the original low amplitude velocity regime, especially for high turbulence intensities. The conclusions may provide a new perspective for VIV response evaluation of the wind turbine under inflow turbulence.
A Fitting Process for the Optimal Modelling of an Anion Exchange Membrane (AEM) Electrolyser
Authors: Mennilli Francesca , Jin Lingkang , Rossi Mosè , Comodi Gabriele
Published: August 2024

Empirical and semi-empirical numerical models of electrolysers and fuel cells are used to predict their behaviour and study rapidly how the performance of a technology changes. Both the polarisation and efficiency curves are mainly dependent on both pressure and temperature and, with a few experimental data, it is possible to forecast the cell behaviour at different operating conditions without performing any additional tests. However, numerical models do not always resemble the system’s performance properly due to the lack of information on crucial parameters like the kinetics ones; indeed, these parameters are difficult to retrieve from the scientific literature and the manufacturers of such technologies. Starting from a semi-empirical model of an Anion Exchange Membrane (AEM) electrolyser from the scientific literature, this paper aims to provide a methodology to assess these parameters with a fitting process. Results showed that the use of fitted coefficients led to a better prediction of the AEM electrolysers behaviour. The model showed a better fitting of the activation and Ohmic regions lowering the Root Mean Square Error (RMSE) by 3.5%, moving from 0.065 V in the original model to 0.03 V in the fitted one.
CFD Meshing and Simulation Best Practices for a Turbine Stage With Squealer Tips, Trailing-Edge Cooling and End-Wall Cooling Injection
Authors: Hansen Thorsten , Munktell Erik , Scheuerer Georg , Zhuang Qingyuan , Zwiener Kim
Published: August 2024

The present study discusses and verifies workflows for simulating the flow through turbine stages featuring complex geometry like cooling holes at the hub and shroud surfaces, cavities upstream and downstream of the rotor, and rotor blades with squealer tips. Linne et al. [3] investigated such a configuration experimentally. Their experiments served as the test case for the present simulations. The geometric complexities forbid using mapped hexahedral meshes, the mesh elements of choice for standard geometries. Therefore, the first part of the paper investigates the use and accuracy of unstructured polyhedral meshes by comparing their accuracy and computational efficiency to hexahedral meshes on a reduced geometry model. The second part applied unstructured polyhedral meshes to the complete geometry model. The simulations showed that adding trailing edge cooling and rotor cavities prevents convergent steady-state solutions on the finer meshes. Rotor cavities and trailing edge cooling had a perceptible influence on the calculated isentropic efficiencies.
Investigation on the Effect of Resolving Waves Motion in the Simulation of Offshore Wind Farms
Authors: De Girolamo Filippo , Castorrini Alessio , Morici Vincenzo , Tieghi Lorenzo , Rispoli Franco
Published: August 2024

Offshore Wind Turbines (WTs) are characterized by heights that fall within the Atmospheric Boundary Layer (ABL). In ABL the flow is characterized by specific turbulence scales and velocity profile. The motion of the sea surface can influence turbulence in the surface layer, thereby impacting wake dynamics and recovery. In this study, we explore the role of wave modeling in the wake interaction between two wind-oriented IEA 15 MW reference WTs, modeled using the Actuator Line Method (ALM). Two hybrid LES-RANS simulations are carried out, one with a flat sea and the other with swell wave motion, imposed by a dynamic computational grid. Turbulence modelling relies on k-ω SST IDDES model, enabling the resolution of the large-scale turbulence associated with wind fluctuations and turbine wakes. The Kaimal velocity spectrum is here applied to generate stochastic velocity fluctuations superimposed as a time-dependent boundary condition to a neutrally stratified ABL velocity profile. Results showed that wind-aligned waves can induce an alternating up- and down-wash effect up to 50 meters from the sea surfaces, behaving as a modification (reduction) of the aerodynamic roughness. This effect is more evident in the wake flow. Analysing the performance of the downwind rotor, a 0.5% difference in power production is observed for the case with resolved waves motion.
Simulation of Full Featured Compressor Using Massive Parallel Unsteady CFD
Authors: Suhrmann Jan , Adami Paolo , Ganine Vladislav , Falcao Do Couto Alves Rigel , Reutter Oliver
Published: August 2024

A major benefit of using CFD in compressor design is reduction of test runs, which speeds up the design process and minimizes costs. This work presents the next step in achieving such a goal. Unsteady simulations of a high-fidelity full annulus compressor rig model with more than 5 billion mesh nodes were performed at part-speed conditions on tens of thousands of cores. Simulated geometric features included among others full cavity geometries, blade clearances and VSV penny gaps. For these comprehensive simulations, a modernized CFD solver was used demonstrating a speedup of more than 3X compared to its original version. This was achieved mainly through several optimizations that improved inter- and intra-node performance as well as through reduction of I/O. For post processing, the in-situ technique has been used to output 1D, 2D and 3D flow data at affordable time and disk usage. The results of these simulations were compared to state-of-the-art steady-state simulations of the same model as well as to the actual rig test data.

This example of one of the largest industrial-grade unsteady simulations to date demonstrates significantly improved capability of a modernized CFD solver as well as the opportunities and potential of using high-fidelity CFD models to improve and accelerate the compressor design process.
Centrifugal Compressor Design and Surge Simulation for Active Inference Based Control
Authors: Sathish Sharath , Khader Mahmoud , Sayma Abdulnaser , Shah Sunil
Published: August 2024

Among myriad industrial applications, the centrifugal compressor is a critical equipment in both upstream and downstream oil and gas production and processing facilities. In upstream applications, the varying properties (temperature, pressure, mass flow) of crude oil during the life of a reservoir coupled with different modes of operation (crude composition) emphasize compressor surge as a crucial factor in its design and operation. The surge constrains design leading to oversizing and higher capital costs. It also narrows the safe operating range during service, resulting in suboptimal performance and higher operating costs.

With its origins in neuroscience, active inference (AIF) is gaining traction in industrial applications involving sequential decision making under uncertain and noisy conditions. This paper proposes a novel AIF based advanced process control methodology for robust surge control under uncertain and noisy conditions. AIF based control offers several advantages over traditional methods like Proportional-Integral-Derivative (PID) and Model Predictive Control (MPC). It inherently integrates perception and action, allowing for more adaptive and context-aware decision-making in uncertain environments.

As a prelude to building an AIF surge controller, a natural gas centrifugal compressor is designed for a set of input specifications using a through flow model to generate characteristic or performance maps. The maps are then embedded in an ASPEN HYSYS® dynamic model to simulate operational conditions that result in surge. The key contributions of this paper are designing a natural centrifugal compressor prone to surge conditions due to highly uncertain suction conditions, integrating the compressor maps into a dynamic system model and simulating surge scenarios, and developing a methodology for AIF based surge control.
Aerothermal Performance of Slashface Leakage With Double Surface Angle Under Realistic Swirling Inflow
Authors: Li Zhiyu , Zhang Kaiyuan , Li Zhigang , Li Jun
Published: August 2024

The turbine vanes being manufactured and assembled piece by piece leads to an unavoidable gap on the vane endwall called slashface. Usually, the coolant leakage introduced from the slashface with a single surface angle aims to prevent hot gas ingression and protect the vane endwall. However, the cooling effectiveness is greatly reduced when considering the swirling flow from the combustor. In the current work, against strong swirling inflow, a new solution to improve endwall film cooling performance through applying the slashface leakage with the double surface angle is carried out. Through numerical method, the effects of the location of the angle transition region (D/L = 0%, 25%, 50%, 75%, 100%) and mass flow ratio (MFR = 0.5%, 1.0%, 1.5%) of the leakage on the turbine vane endwall aerothermal and film cooling performance are investigated. The results indicated that the coverage area of the coolant on the endwall was obviously enlarged when the slashface leakage with the double surface angle was employed. The film cooling level on both the endwall and suction side surface of the vane increased with increasing MFR. Moreover, the endwall thermal load was reduced. The designs of D/L = 25% and 50% are recommended for their high endwall film cooling level and low endwall thermal load. This paper provides turbine designers with a new idea to increase endwall film cooling performance by the slashface leakage with the double surface angle when considering aggressive swirling inflow.
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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Aerodynamic Design Optimization of Centrifugal Compressor Blade Using Parameterized Free-Form Deformation
Authors: Xu Dongqiang , Yu Jianyang , Shen Jinsong , Li Ning , Song Yanping , Yang Xinlong
Published: August 2024

To address the challenges encountered during a multioperating-point optimization of centrifugal compressor blades, including a large design space, redundant search, limited flexibility, and low optimization efficiency, this paper presents an aerodynamic optimization approach for centrifugal compressor impeller blades based on parameterized free-form deformation (FFD) and deep learning. To realize the parametric control of a compressor blade, a three-dimensional FFD control body is arranged around a blade according to the geometric characteristics. The inverse distance weighting (IDW) mesh deformation algorithm is used to extrapolate the deformation of surface mesh points to volume mesh points. Using this method, the analysis mesh can be directly updated with high quality instead of regenerating the geometry model when design variables are changed during optimization. Based on this and convolutional neural networks, a design optimization framework is established by combining the optimal Latin hypercube sample method and the NSGA-II multi-objective genetic algorithm. An optimization of the centrifugal compressor blade of a micro gas turbine was carried out, and the results showed that the total pressure ratio and isentropic efficiency at the design point was increased by 4.03% and 1.21 percentage points, respectively. The optimization results demonstrate that the developed optimization framework can effectively improve the performance of centrifugal compressors and provide support for compressor design.
Investigation of the Sigma Approximation Technique for the Solution of the Time Spectral Equation System
Authors: Zhu Yuze , Zhang Yuxuan , Zhang Sen , Wang Dingxi
Published: August 2024

The time spectral method is commonly utilized to analyze periodic unsteady flows within turbomachines. However, the time spectral solutions in regions with large temporal and spatial gradients, such as wakes, shocks, and boundary layers, can be plagued with unphysical oscillations, known as the Gibbs phenomenon. This paper presents an investigation into the sigma approximation technique, which is capable of significantly attenuating the Gibbs phenomenon by dampening high-frequency nonlinear components in the time spectral solutions. Central to this technique are three sigma factors: the exponent, the cut-off number, and the number of harmonics, which collectively determine the damping effects for each frequency. However, the optimal combination of them remains to be ascertained considering the trade-off between the accuracy of solutions and the reduction of unphysical oscillations. In this study, numerical simulations are performed to evaluate the efficacy of this technique based on a two-row compressor configuration. It is found that the Gibbs-type unphysical oscillations can be effectively mitigated without notably compromising the solution accuracy through an optimal combination scheme of sigma factors. The NASA Stage 35 case study further verifies the effectiveness of the proposed optimal sigma factor combination in preserving the accuracy of time spectral solutions. Moreover, the von Neumann analysis reveals that the sigma approximation technique can enhance the numerical stability of the time spectral equation system, thereby allowing the use of aggressive numerical parameters to accelerate convergence. The stability analysis results are verified by a two-dimension bump under two different flow conditions and further assessed using a two-row compressor.
Industrial Applications of Transfer Learning Methods for Aircraft Propulsion Systems
Authors: Jacobs Ryan , Krishnan Sandipp , Bhaduri Anindya , Luan Lele , Pandita Piyush , Ghosh Sayan , Wang Liping
Published: August 2024

Sparse data problems challenge engineers throughout the lifecycle of aircraft propulsion systems. For instance, data from legacy systems may not be applicable to novel high-pressure turbine blade configurations, driving substantial computational and test efforts to design and validate the blade. Once the blade is fielded, some manufacturers implement predictive maintenance approaches to reduce downtime and associated costs of sustaining the fleet. However, after entry-into-service for a new design or re-design, limited field observations are available with which to construct prognostic models for the life of the blade. In this paper we explore transfer learning methods in machine learning to overcome these challenges. The goal is to borrow strength from one setting with abundant data — available for legacy systems that may have different configurations and/or operations — and transfer the embedded knowledge to model new systems in a different setting where fewer data are available. Transfer learning methods have been implemented for a broad range of machine learning approaches, and in this paper we highlight industrial propulsion applications from various phases of the propulsion system life-cycle where transfer learning is applied with three frameworks that GE has developed: Bayesian Hybrid Modeling, Probabilistic Deep Neural Networks, and Physics Discovery. The added benefit of leveraging data from similar contexts is examined for each framework.
Data-Driven Turbulence Modeling for Film Cooling Heat Transport, Part II: Modeling and Evaluation
Authors: Zhang Zhen , Zhang Weiran , Su Xinrong , Yuan Xin
Published: August 2024

In film cooling problems, the turbulent heat transport and the resultant cooling effectiveness distribution are difficult to predict for traditional Reynolds-averaged Navier-Stokes (RANS) methods. In this paper, a data-driven model of the turbulent Prandtl number is built based on the Physics Informed Neural Network (PINN), which trains the turbulence model based on flow data from RANS and temperature data from Large Eddy Simulation (LES). PINN is used as an efficient inverse solver to get turbulence information from the mean flow data such as velocity and temperature and also as a model trainer to train the algebraic turbulence model at the same time. Accelerated by modern GPUs, the PINN method has been a powerful competitor to the adjoint method and the ensemble Kalman filter to solve inverse problems. The obtained data-driven model can adjust the intensity of turbulent heat transport and thus reduce the error of the traditional RANS method. After validation, the model shows good generalization ability when the hole geometry and the blowing ratio vary.
Damping Phenomena in Rotating Machines: A Focus on Rotor Damping With Synchronous and Asynchronous Excitation
Authors: D’Alessandro Francesco , Garnier Florian , Guivarch Damien , Zutshi Amit , Kang Weize , Kunnil Manoj , Narayanan Payyoor , Robinson Mark , Kumar J. S. , Cao Jianming , Rose Ted
Published: August 2024

Accurate modeling of damping in rotors is critical for rotor dynamic analysis of turbo machinery such as aircraft engines. This paper documents the recent work of the ‘Rotordynamics consortium’ with the cooperation of Safran Aircraft Engines, General Electric Aerospace, Hexagon (MSC.Software) and Boeing demonstrating best practices for rotor damping across the solution disciplines of both frequency and transient response as well as complex eigenvalue analysis. Any rotating machine is subject to out of balance loading due to the imperfections associated with manufacturing processes. Out of balance or unbalance loading is always present and is known as a synchronous phenomenon as the frequency of the unbalance excitation is synchronous with the rotation speed of the rotor, leading to vibration causing noise and fatigue issues. In contrast, the frequencies of asynchronous vibrations are unrelated to the rotation speed of the rotor and are typically caused by external aerodynamic loads, bearing properties such as squeeze film dampers and other nonlinearities to name a few. Synchronous excitation tends only to excite forward whirl modes of rotating machines that are axisymmetric, whereas asynchronous excitation may excite any whirl modes of the structure, even those with a rotor that is axisymmetric. With the deep differences in these two families of excitation, it is essential to adapt the simulation procedure to the type of excitation and especially important to represent the frequency dependent damping affecting rotating parts in a faithful manner. Viscous and structural (hysteretic) damping are studied numerically in a rotating shaft under synchronous and asynchronous excitation using the MSC NASTRAN finite element software. A simplified dual-rotor finite element model is used to demonstrate the non-synchronous response of one rotor on the other one, representative of a whole aircraft engine. Credible values of stiffness, damping and mass properties are adopted to give integrity to the work and pave the way to an industrial scale problem.
A Thermal Model for a Hybrid Gas Bearing System in Oil-Free Turbochargers
Authors: Jung Wonbae , Delgado Adolfo , Dudlo Anthony , Kang Sang-Guk , Kweon Chol-Bum M.
Published: August 2024

With little drag friction, gas bearings operate at high rotor speed and high temperature and thus enable long operating life along with material damping for mechanical energy dissipation. However, most computational tools for modeling gas bearings are not accessible to bearing manufacturers or potential endusers, and the models are restricted to specific geometries and operating conditions or are missing important features, thus limiting their utility. This paper presents the thermal energy transport in a hybrid gas bearing for oil-free turbochargers with integrated heat and fluid flow models to produce a comprehensive thermo-hydrodynamic analysis predictive tool, and to design and evaluate air-lubricated gas bearings by predictions and experiments. An efficient algorithm couples the solution of the Reynolds equations and the thermal energy transport equations in the film between the rotor and a pad of the hybrid gas bearing, and updates the temperature-dependent viscosity and film thicknesses during the iterative process. The balance of the bulk-flow thermal energy transport is that the summation of drag power losses plus heat convection into the film equals to the thermal energy advected by the film. The predictions show the film temperature varies along circumferential and axial directions by following the balance of the energy flows, and shows high film temperatures corresponding to the small film thicknesses and thus large film pressures. The predicted result also shows the peak temperature of the film occurs at the exit side of the film near the trailing edge of each pad. Thermocouples installed axially at the leading and trailing edges of each pad measure temperature of the film to validate the thermal module. The test repeats and averaged for each rotor speed from 2 krpm to 22 krpm at intervals of 2 krpm, for supply pressure varying along 25 psi to 100 psi and predicted film temperature matches well with the measured one. The parameters of interest in this analysis include the gas supply condition, bearing configuration, and the gas properties at high altitudes and high rotation speeds. The parametric study results show the density and kinematic viscosity are the most dominant properties of the gas lubrication for the film temperature.