bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of the Stability and Surge Limit in an Industrial Centrifugal Compressor With Variable Inlet Guide Vanes
Authors: Stemmermann Julian , Reymond Loïc Marc , Geilich Marius , Jeschke Peter 
Published: September 2023

Abstract
The instability phenomena of an industrial centrifugal compressor are experimentally investigated under various pre-swirl settings and rotational speeds, ranging from subsonic to transonic inflow. The compressor under consideration was installed in an open-loop test rig and consists of variable inlet guide vanes (IGV), a non-splittered impeller, a vaneless diffuser and a volute. The IGV allows pre-swirl angles of −15° (counter-rotating pre-swirl) to +60° (co-rotating pre-swirl). The compressor map measurement in the off-design region at different IGV pre-swirl angles shows that co-rotating pre-swirl facilitates rotating stall. A nominal non-integer stall cell number of 2.4 to 4.6 and a rotational speed of 10 to 25% of the impeller rotational speed characterize the rotating stall phenomena observed. In contrast, mild surge is observed on speed lines without pre-swirl and with counter-rotating pre-swirl at a low rotational speed. At some operating points rotating stall occurs in addition to the mild surge, whereby the rotating stall shows a broadband signal rather than a distinct frequency. The surge limit mass flow rate of the speed lines without pre-swirl stagnates at an approximate isentropic relative Mach number at the leading edge of 0.69 and then rapidly increases at a Mach number of 0.78. As such, the operating range of the compressor stage significantly decreases and the stability and surge limit coincide. In summary, the results presented in this paper show that the IGV has a major impact on the type of instability preceding the deep surge of the compressor stage. The surge limit does not follow any obvious pattern and therefore its prediction during the pre-design remains challenging.
Development of a Chemical Looping Combustor Fed With Natural Gas and Its Integration With a Gas Turbine in ASPEN Plus
Authors: Bartocci Pietro , Abad Alberto , Cabello Arturo , de Las Obras Loscertales Margarita , Zampilli Mauro , Taiana Andrea , Serra Angela , Fantozzi Francesco 
Published: September 2023

Abstract
The lowest cost solution for carbon capture and storage in power plants at the moment is represented by chemical looping combustion. This technology nevertheless has not yet met the market due to scale up needs and also to the fact that to be coupled to a gas turbines a chemical looping combustor has to be operated at high pressure and high temperature. While high pressurization of the reactor can imply problems in the management of the circulation rate and the sealing between the air reactor and the fuel reactor; operation at high temperature can imply agglomeration, sintering and also attrition problems for the oxygen carriers. To analyze those problems a Mari Curie project has been funded under the Horizon2020 EU program. This paper presents the analysis of two configurations of the chemical looping combustor and of the coupled gas turbine. Both configurations are examples of possible bioenergy with carbon capture and storage (BECCS) technologies. The aim is to compare BECCS efficiency with that of combined cycles fed with natural gas and using post-combustion carbon capture and storage, which seem to be the competing technologies. A methodology for the dimensioning of the pressurized chemical looping combustor to be coupled to a gas turbine of the power of about 12 MW mechanical power, is presented and applied also based on the results of experimental campaigns previously performed at the Spanish National Research Council (CSIC), Instituto de Carboquimica of Zaragoza, Spain.
A Conceptual Model for the Flutter Mechanism in Interlocked Turbine Blades
Authors: Gallardo Juan Manuel , Pérez Escobar Óscar 
Published: September 2023

Abstract
Many turbine rotor blades adopt the interlock configuration; among its advantages, there is a large increase in the natural frequencies with respect to the simpler cantilever configuration. Most widespread assessment methods estimate that this frequency increase should lead to a large improvement to the flutter stability of the interlocked rotor rows; some well-known approaches, such as the Panovsky-Kielb stability maps, suggest that flutter should be very unlikely for interlock configurations. Nevertheless, both the experience and detailed simulations indicate that it is possible to find flutter in interlocked blades, even with moderate aspect ratio.
In this paper, the authors study the underlying physics behind flutter for interlocked blades, and present a very simplified model that is able to reproduce the main modal characteristics of interlocked blades, including the frequency increase and change in mode-shape as a function of the nodal diameter. This model also identifies a flutter mechanism, which is dependent on the aerodynamic interaction between the bending and torsion motion of the blade; even if both basic motions are individually stable, their interaction may lead to a coupled aeroelastic instability. The results from this simplified model are fully consistent with detailed 3D linearized unsteady CFD simulations of representative turbine rotor blades, and should be of application in many realistic cases of interlock flutter. Finally, the authors present a study on the influence of the main parameters of the simplified model on the flutter stability, and derive some conclusions about the implications on flutter-free interlock design.
Wind Turbine Drivetrain Fault Detection Using Multi-Variate Deep Learning Combined With Signal Processing
Authors: Jamil Faras , Jara Avila Francisco , Vratsinis Konstantinos , Peeters Cédric , Helsen Jan 
Published: September 2023

Abstract
The maintenance of wind turbines is essential to reduce wind energy levelized costs. Earlier detection of potential faults in the rotating subcomponents, such as the drivetrain, helps to plan maintenance actions. Several vibration processing methods, e.g., short-time Fourier analysis, are available in the literature to detect faults, however, they require domain expertise. Moreover, many researchers are focusing on machine learning methods to complement such techniques. This paper combines deep learning methods, more specifically auto-encoders, with more than 400 indicators based on advanced signal processing techniques. It is impractical to train a deep-learning model for each indicator, and significant manual effort is required to investigate all indicators. This paper focuses on a multivariate deep learning model to explore the potential to learn the underlying relationships among the signal processing indicators for healthy datasets and compress them into one health status. The reconstruction error of this model is then used to identify changes in the condition of the system. The output directly illustrates the high-level health state of the system for early fault detection. This proposed method is demonstrated on real-life offshore wind turbine data from several years. Further analysis can be done to pinpoint specific fault types using frequency spectrum analysis.
Optimization of an HPT Blade and Sector-Based Annular Rig Design for Supercritical CO2 Power Cycle Representative Testing
Authors: Tuite Logan , Braun James , Paniagua Guillermo 
Published: September 2023

Abstract
As part of the ongoing research into the design of hardware for zero emission cycles, a first stage high-pressure turbine (HPT) blade is optimized for a 350 MWe supercritical CO2 (sCO2) power cycle using the surrogate-assisted genetic algorithm optimizer in Numeca FINE/Design 3D with objectives of increasing efficiency and decreasing heat load to the blade. Supercritical CO2 property tables are constructed from NIST REFPROP data, and a bicubic interpolation is used to create polynomial expressions for the condensable gas simulation in FINE/Turbo. A detailed mesh sensitivity study is performed for a baseline design to identify the proper grid refinement and efficiently allocate resources for the optimization. Seventy design variables are selected for the initial population generation. Self-organizing maps are then used to reduce the number of design variables, focusing on the most important ones affecting the objective functions. The optimization results in approximately 3000 three-dimensional Reynolds Averaged Navier Stokes simulations of different blade shapes with increases in efficiency of up to 0.85 percentage points and decreases in heat load of 14%. Families of blade shapes are identified for experimental testing in an annular rig at the Purdue Experimental Turbine Aerothermal Laboratory. A design to adapt the Big Rig for Aerothermal Stationary Turbine Analysis test section for testing optimized geometries is introduced, which features eccentric radius sectors allowing for scaled-up geometries of sCO2 optimized blade profiles to be tested at design cycle representative conditions at high Reynolds numbers in dry air. Analysis into the effects of Reynolds number, working fluid, and geometric relations are presented to prove the efficacy of the test method.
Model Predictive Control Strategies for Turbine Electrified Energy Management
Authors: Hill Elyse D. , Amthor Aria E. , Soloway Donald I. , Simon Donald L. , Connolly Joseph W. 
Published: September 2023

Abstract
The increasing electrification of aircraft propulsion systems is leading to new control architectures being developed to address integration between electric machines and gas-based turbine engines. For hybrid-electric propulsion systems, current conceptual architectures often couple electric machines with the shafts of gas turbine engines and introduce energy storage. Leveraging the electrical power system of hybridized engines, Turbine Electrified Energy Management (TEEM) is a recent control approach that improves transient operability in an effort to enable more efficient and lighter weight turbomachinery. This study seeks to expand TEEM’s application beyond traditional proportional-integral (PI) control by presenting linear model predictive control (MPC) schemes to execute the TEEM concept. Through constraint selection and cost function design, transient operability goals for TEEM are considered with no external logic or saturation. Unique to the designs are the use of a washout filter, which simplifies transient detection and motor activation logic. The proposed architectures are implemented with both centralized MPC and distributed MPC approaches, and comparisons are drawn to a benchmark PI controller simulated on a nonlinear turbofan engine model at one ground condition and one cruise condition. Performance is evaluated using compressor maps, stall margin performance, and two novel metrics: transient stack usage and transient excursion integral. Results reveal the linear MPC scheme performs comparably to the baseline controller and can be implemented in at least two distinct configurations with potential for further modifications, thus establishing the groundwork for future investigations.
Pressure Characteristic Rollover of a Transonic Centrifugal Impeller
Authors: Cao Teng , Hayashi Yoshihiro , Tomita Isao 
Published: September 2023

Abstract
This paper presents a detailed numerical investigation of a transonic centrifugal compressor to understand the mechanism causing its pressure rise characteristic rollover, which fundamentally impacts compressor stability. Distinct characteristic rollover behaviors at different compressor speeds are predicted and studied. It is found that the impeller characteristic rollover occurs at high blade tip Mach number (&gt; 1) conditions. It is the result of a combination of the inducer and exducer performance. The inducer is found to stall early, while the exducer is mostly a stable part maintaining the overall impeller stability. The overall impeller characteristic rolls over when the exducer’s performance deteriorates significantly, which happens at higher flow conditions towards high speed. This is due to the flow compressibility effect (density change). It shows the flow density across the impeller increases with the blade tip Mach number. The increased density leads to a reduced exducer exit flow coefficient with higher workload and aerodynamic losses. Detailed analysis is carried out to understand the 1D and 3D flow mechanisms governing the inducer and exducer, hence the impeller characteristic.
Active Fluidic Control of a Nozzle Guide Vane Throat
Authors: Spens Alexander , Bons Jeffrey P. 
Published: September 2023

Abstract
Experiments were conducted to validate the building blocks of a fluidically controlled variable area turbine concept that uses injected high-pressure air to effectively reduce the choke area of the turbine inlet. Preliminary results from a simple quasi-1D converging-diverging nozzle, with an injection flow slot upstream of the throat, showed a 2.2:1 ratio between throttled mass flow rate and injected mass flow rate at a constant nozzle pressure ratio. The penetration of the injection flow and corresponding reduction in the primary flow streamtube were successfully visualized using a shadowgraph technique. Building on this success, a representative single passage nozzle guide vane transonic flowpath was constructed to demonstrate feasibility beyond the quasi-1D converging-diverging nozzle. Both secondary slot blowing from the vane pressure surface and vane suction surface just upstream of the passage throat again successfully reduced primary flow. In addition, fluidic vortex generators were used on the adjacent suction surface to reduce total pressure loss and further throttle the primary flow. Implications for application of this active flow control technology to a variable area turbine are considered.
Distortion Transfer in Multi-Stage Compressor and Modeling of Spool-Coupling Problem With Circumferentially Distorted Inflow
Authors: Okada Ryuichi , Murooka Takeshi , Kato Dai 
Published: September 2023

Abstract
Among various types of total pressure distortion, circumferential distortion is well known to reduce the operability range of the aero engine. The effect of the circumferential total pressure distortion on single-stage fans have been studied by various researchers. There are, however, few studies about the effect of the circumferential total pressure distortion on multistage compressors. It is also known that in the case of turbojet engines or low bypass ratio turbofan engines, not only the LPC (fan) but also the HPC is influenced by the circumferential distortion. This is called spool coupling effect. However, no method has been fully established to assess the effect of the circumferential distortion on each component and eventually on the whole engine.
In the first part of the present study, the flow field of a multistage research compressor, the front six stages of the Energy Efficient Engine, under circumferentially distorted inflow is analyzed using the Body Force Method, whose coefficients are tuned using the steady RANS solution of the compressor with clean inlet flow. The computed results show that, while the rear stage operates much like in the way described by the parallel compressor model, the front stage experiences circumferential aero loading fluctuations due to the static pressure field formed at the boundaries of the distortion. Consistency of the results is qualitatively confirmed based on comparisons with theory.
In the second part of the study, a new engine performance model including spool coupling effect is proposed. It is a so-called “Parallel Engine” model, in which all the components are divided into distorted and undistorted sectors. The spool coupling effect is represented by a single parameter, namely the normalized axial gap between LPC and HPC. Change in the performance of a notional turbojet engine with circumferential distortion due to the spool coupling effect is presented. Outlook to combine the two methods is briefly summarized at the end.
Impact of Tip Clearance Variation of Highly Loaded Tandem Blades in Axial Compressors
Authors: Konrath Liesbeth , Peitsch Dieter 
Published: September 2023

Abstract
Tandem blades are a means to achieve highly loaded compressor stages. The resulting secondary flow structures around tandem blades, however, are very complex and the source of unwanted losses reducing the potential of tandem blades. Especially for tandem blades with tip clearance, the complexity of the flow increases significantly due to the two imminent clearance vortices. Experimental campaigns were conducted to analyze the development of secondary flows in the tip region of tandem blades for different clearance sizes and incidence angles. For comparison, a conventional single airfoil blade of similar turning serves as reference. Furthermore, the tandem blades feature a highly enlarged pitch-to-chord ratio in comparison to the reference blade. By analyzing the flow topology around the tandem blades, the potential to reduce the blade count within the cascade can be assessed as well. Five-hole probe pressure measurements in the wake of the blades as well as oil flow visualizations of the blade surfaces and the tip clearance end wall have been carried out. Generally, the five-hole probe measurements show a similar development for both, tandem and reference blade, when increasing clearance height and incidence. Differences emerge, when the analysis of the measurements is split up into gap and non-gap side. Going deeper into the flow topology, oil flow visualizations show similar developments for the front blade tip clearance vortex and the reference blade with increased clearance heights and incidences. The tandem rear blade clearance vortex seems largely unaffected, confirming previous observations. The rear blade tip clearance vortex seems to have a stabilizing effect on the flow field.
A Numerical Test Rig for Turbomachinery Flows Based on Large Eddy Simulations With a High-Order Discontinuous Galerkin Scheme - Part 2: Shock-Capturing and Transonic Flows
Authors: Klose Björn F. , Morsbach Christian , Bergmann Michael , Hergt Alexander , Klinner Joachim , Grund Sebastian , Kügeler Edmund 
Published: September 2023

Abstract
In the second paper of this three part series, we focus on the simulation of transonic test cases for turbomachinery applications using a high-order discontinuous Galerkin spectral element method (DGSEM). High-fidelity simulations of transonic compressors and turbines are particularly challenging, as they typically occur at high Reynolds number and require additional treatment to reliably capture the shock waves characterizing such flows. A recently developed finite-volume subcell shock capturing scheme tailored for the DGSEM is applied and evaluated with regard to the shock sensor. To this end, we conduct implicit large-eddy simulations of a high-pressure turbine cascade from public literature and a transonic compressor cascade measured at the German Aerospace Center, both at a high Reynolds number above 106. Based on the results, we examine modal-energy and flow-feature based shock indicator functions, compare the simulation data to experimental and numerical studies and present an analysis of the unsteady features of the flows.
Development of a Reduced Order Model Based on Aerodynamic Influence Coefficients to Simulate Aeroelastic Phenomena in Axial Compressor Blades
Authors: Casoni Marco , Benini Ernesto , Magrini Andrea 
Published: September 2023

Abstract
A reduced order model (ROM) is proposed to simulate the aeroelasticity of compressor blades in both coupled and uncoupled mode at low computational cost. The ROM describes the structural dynamics of blades using the mode superposition technique, while effective aerodynamic forces are modeled using various system identification methods. The ROM takes advantage of the aerodynamic influence coefficients (AIC) to model the aerodynamic loads of vibrating blades. System identification of unsteady aerodynamic forces is performed using ARX polynomial models, nonlinear ARX polynomials, Hammerstein-Wiener models and recurrent neural networks. Two different training signals are tested, and their performance is compared. The uncoupled results are validated against traditional Fourier method, showing good agreement in estimated aerodynamic damping. The different formulations of the coupled ROM are then compared to the coupled full order model (FOM) of reference: consistent predictions for the damping ratio are achieved, with a substantial reduction of the computational cost with respect to full order models of reference.
Influence of Casting Defects on the Low Cycle Fatigue Performance of MAR-M247 – A Path Towards a Probabilistic Model
Authors: Radners Jan , Schweizer Christoph , Eckmann Stefan , Al-Ameri Malek , Amann Christian , Gumbsch Peter , Kadau Kai 
Published: September 2023

Abstract
Intermittent renewable energy sources are becoming increasingly important. This creates a demand for more flexible gas turbine operation conditions, to fill supply gaps and manage peak loads. As a result, the number of startup and shutdown cycles — the low cycle fatigue (LCF) loading of a gas turbine component — increases substantially. This work investigates the LCF performance of a common rotor blade material, to support the future transition towards more flexible power plant operation. One of the goals of this multi-year government funded project is the development of a probabilistic life model of cast material including defects such as porosity. The focus of this work is the investigation of the influence of casting defects on the LCF performance of cast MAR-M247. A comprehensive test program on defective and defect-free specimens at realistic engine conditions, i.e., temperature and stress was conducted. A first deterministic fatigue life model that accounts for material defects is proposed.
A Data-Centric Approach to Loss Mechanisms
Authors: Senior Alistair C. , Miller Robert J. 
Published: September 2023

Abstract
Breaking down the total loss in a turbomachine into a number of low order physical models is a powerful way of developing loss models. A problem, however, is that in complex flows it is often not clear how to put together these physical models in the correct way. An additional problem is that the designer often doesn’t know whether all of the underlying low order physical models are correct or whether a more general, and accurate, physical model is yet to be discovered. In practice this problem often leads to loss models of low accuracy, which only work in a limited part of the overall design space. This paper shows that machine learning can be used to augment a designer in the process of developing loss models for complex flows. It is shown that it helps both in understanding how to put together the underlying physical models in a more accurate way, and also in discovering new, and more general, underlying physical models. The paper illustrates the new method using the problem of compressor and turbine profile loss. This problem was chosen because it is well understood and therefore is a good way of validating the new method. However, surprisingly the new method is shown to be able to develop a new profile loss model which is more accurate than previous models. This is shown to have been achieved by the machine learning finding a new, more general, underlying model for trailing edge mixing loss.