bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance Prediction of a Multi-Stage Ammonia-Water Turbine Under Variable Nozzle Operation via Machine Learning
Authors: Du Yang , Liu Tingting , Dai Yiping , Fan Gang , Wang Jiangfeng , Zhao Pan 
Published: September 2021

Abstract
This study proposes machine learning models to predict the performance of a multi-stage ammonia-water radial turbine using variable nozzle operation under different operating conditions. A 1.2 MW four-stage ammonia-water radial turbine is firstly designed. Then, the one-dimensional off-design simulation model is developed based on the geometric parameters to mainly evaluate the effects of different nozzle outlet angles and turbine inlet temperatures on the turbine performance. A set of data, which consists of 10,000 training points based on one-dimensional model, is used to train the proposed two high-dimensional model representation (HDMR) methods. The forward HDMR model predicts the mass flow rate, turbine outlet temperature, turbine power and turbine efficiency for any combination of turbine nozzle outlet angle and turbine inlet temperature, while the reverse HDMR model predicts the mass flow rate, turbine outlet temperature, turbine efficiency and turbine nozzle outlet angle for any combination of turbine power and turbine inlet temperature. The two HDMR models are validated using 238 sets of separated test data. The results show that the minimum coefficients of determination (R2) of forward HDMR model and reverse HDMR model are 0.9837 and 0.9953, respectively. The maximum relative errors of two HDMR models are below 1.6822%, so the quality of the proposed machine learning methods is high. The overall performance maps of multi-stage ammonia-water radial turbine under the variable nozzle operation method are constructed based on the reverse HDMR model. The reverse HDMR model is helpful in monitoring the healthy operation state of turbine.
Investigating Gas Turbine Internal Cooling Using Supercritical CO2 at High Reynolds Numbers for Direct Fired Cycle Applications
Authors: Searle Matthew , Roy Arnab , Black James , Straub Doug , Ramesh Sridharan 
Published: September 2021

Abstract
In this paper, experimental and numerical investigations of three variants of internal cooling configurations — dimples only, ribs only and ribs with dimples have been explored at process conditions (96°C and 207bar) with sCO2 as the coolant. The designs were chosen based on a review of advanced internal cooling features typically used for air-breathing gas turbines. The experimental study described in this paper utilizes additively manufactured square channels with the cooling features over a range of Reynolds number from 80,000 to 250,000. Nusselt number is calculated in the experiments utilizing the Wilson Plot method and three heat transfer characteristics — augmentation in Nusselt number, friction factor and overall Thermal Performance Factor (TPF) are reported. To explore the effect of surface roughness introduced due to additive manufacturing, two baseline channel flow cases are considered — a conventional smooth tube and an additively manufactured square tube. A companion computational fluid dynamics (CFD) simulation is also performed for the corresponding cooling configurations reported in the experiments using the Reynolds Averaged Navier Stokes (RANS) based turbulence model. Both experimental and computational results show increasing Nusselt number augmentation as higher Reynolds numbers are approached, whereas prior work on internal cooling of air-breathing gas turbines predict a decay in the heat transfer enhancement as Reynolds number increases. Comparing cooling features, it is observed that the “ribs only” and “ribs with dimples” configurations exhibit higher Nusselt number augmentation at all Reynolds numbers compared to the “dimples only” and the “no features” configurations. However, the frictional losses are almost an order of magnitude higher in presence of ribs.
Development and Application of a Concentration Probe for Mixing Flows Tracking in Turbomachinery Applications
Authors: Babazzi G. , Bacci T. , Picchi A. , Fondelli T. , Lenzi T. , Facchini B. , Cubeda S. 
Published: September 2021

Abstract
Modern gas turbines present important temperature distortions in the core-engine flowpath, mainly in the form of hot and cold streaks imputed to combustor burners and components cooling systems. As they highly influence turbines performance and lifetime, the precise knowledge of the thermal field evolution through the combustor and the high-pressure turbine is fundamental. The majority of past studies investigated streaks migrations directly examining the thermal field, while a limited amount of experimental work employed approaches based on the detection of tracer gases. The latter approach provides a more detailed evaluation of the evolution and mixing of the different flows. However, the slow time response due to the employment of sampling probes and gas analysers make the investigation of a whole measurement plane extremely time consuming. To tackle this issue, in this study a commercial oxygen sensor element and its excitation/detection unit were integrated into a newly developed probe to carry out local tracer gas concentration measurements exploiting the fluorescence behaviour. The probe was provided with a Kiel-like shield, a pressure port and a thermocouple, in order to correct the readings in case of 3D flows with pressure, temperature and velocity gradients. The paper summarizes the probe development and calibration activities, with the characterization of its accuracy for different flow conditions. Finally, two probe applications are described: firstly the probe was used to detect tracer gas concentrations on a jet flow; afterwards it was traversed on the interface plane between a non-reactive, lean combustor simulator and the NGV cascade. The probe has proven to provide accurate and reliable measurements both from a quantitative and qualitative point of view even in highly 3D flow fields typical of gas turbines conditions.
Stator Blades Manufacturing Geometrical Variability in Axial Compressors and Impact on the Aeroelastic Excitation Forces
Authors: Gambitta Marco , Kühhorn Arnold , Beirow Bernd , Schrape Sven 
Published: September 2021

Abstract
The manufacturing geometrical variability is a source of uncertainty, which cannot be avoided in the realization of machinery components. Deviations of a part geometry from its nominal design are inevitably present due to the manufacturing process. In the case of the aeroelastic forced response problem within axial compressors, these uncertainties may affect the vibration characteristics. For this reason, the impact of geometrical uncertainties due to the manufacturing process onto the modal forcing of axial compressor blades is investigated in this study.
The research focuses on the vibrational behavior of an axial compressor rotor blisk. In particular the amplitude of the forces acting as source of excitation on the vibrating blades is studied. The geometrical variability of the upstream stator is investigated as input uncertainty. The variability is modeled starting from a series of optical surface scans. A stochastic model is created to represent the measured manufacturing geometrical deviations from the nominal model. A data reduction methodology is proposed in order to represent the uncertainty with a minimal set of variables.
The manufacturing geometrical variability model allows to represent the input uncertainty and probabilistically evaluate its impact on the aeroelastic problem. An uncertainty quantification is performed in order to evaluate the resulting variability on the modal forcing acting on the vibrating rotor blades. Of particular interest is the possible rise of low engine orders due to the mistuned flow field along the annulus. A reconstruction algorithm allows the representation of the variability during one rotor revolution. The uncertainty on low harmonics of the modal rotor forcing can be therefore identified and quantified.
Suppression of Non-Synchronous-Vibration Through Intentional Aerodynamic and Structural Mistuning
Authors: Stapelfeldt Sina , Brandstetter Christoph 
Published: September 2021

Abstract
Non-synchronous vibrations (NSV) arising near the stall boundary of compressors are a recurring and potentially safety-critical problem in modern axial compressors and fans. Recent research has improved predictive capabilities and physical understanding of NSV but prevention measures are still lacking. This paper addresses this by systematically studying the influence of aerodynamic and structural mistuning on NSV. This is achieved by incorporating mistuning effects in a validated linear model, in which individual blade modes are modelled as single-degree of freedom mass oscillators coupled by a convected aerodynamic disturbance term. The results demonstrate that both structural and aerodynamic mistuning are effective. While structural mistuning improves stability by preventing aero-structure lock-in, aerodynamic mistuning, which locally reduces the tip blockage, attenuates the aerodynamic disturbance causing NSV. In the latter case, the circumferentially-averaged conditions are shown to be most influential, while the pattern plays a minor role. A combination of moderate aerodynamic and structural mistuning (1%) was also found to be effective. These findings are relevant for design decisions, demonstrating that small blade-to-blade variations can suppress NSV.
Numerical Study of Droplet Erosion in the First-Stage Rotor of an Axial Flow Compressor
Authors: Agati Giuliano , Borello Domenico , Di Gruttola Francesca , Rispoli Franco , Venturini Paolo , Gabriele Serena , Simone Domenico 
Published: September 2021

Abstract
In the present paper, a procedure for the study of the water washing in axial flow compressors is presented. The study is part of an ongoing partnership between Baker Hughes and Sapienza University of Rome aiming at maximizing the washing of the compressor blades while maintaining the erosion under specific thresholds. A computational analysis in the first part of an axial flow compressor (i.e. up to the first rotor) was carried out by using Ansys Fluent for the solution of multi-phase flow, while the water droplet erosion mechanism was modeled by the authors by using a properly developed methodology implemented in Fluent though the use of User Defined Functions. The washing process efficiency as well as the erosion rate are evaluated by introducing appropriate indexes. A parametric analysis was carried out by varying the mass flow rate of injected water. Two different computational grids were considered aiming at simulating two different configurations. In the first one the rotor blades leading edge (LE) is placed in the wake released by IGVs trailing edge (TE). In the second configuration, the rotor blades LE is located in a circumferential position corresponding to the mid-pitch between two successive IGVs. These two configurations simulate the situations of minimum and maximum water impact on the rotor blade surfaces. For all the injection conditions here considered, the configuration where IGVs trailing edges were aligned with the rotor blades LEs resulted in higher impacts and erosion on the blade pressure sides. When rotating rotor blades LEs in the middle of the IGVs vanes, rotor LEs were found to be the mostly washed regions but also the most subject to erosion phenomena. The computed indexes show the not optimal distribution of the injectors from the washing efficiency point of view.
Improvement of Aerodynamic and Strength Characteristics of a Multi-Shaft Axial Turbine of a Turboshaft Engine
Authors: Popov Grigorii , Goriachkin Evgenii , Egorov Igor , Baturin Oleg , Salnikov Anton , Solovieva Anastasia , Zhurenkov Yurii 
Published: September 2021

Abstract
The article presents the results of solving the complex task of increasing the rotor wheel strength factor and the efficiency of the twin-shaft axial turbine of the small turboshaft engine using methods of multidisciplinary optimization. This turbine consists of a single-stage compressor turbine (CT) and a free turbine (FT).
An analysis of the original variant of the turbine revealed that the strength factor of their rotor wheels are significantly lower than the necessary structural requirement. To eliminate the occurring problem at the first step the initial task of estimation the rotor wheels only on the basis of structural requirements was performed without taking into account aerodynamic processes. As a result, variants of the turbine rotor wheels were obtained to provide the structural constraints. They were used as starting points for the complex task of optimization, taking into account aerodynamic and deformation processes.
The task of multi-disciplinary CT and FT optimization was solved step by step. As a first step, specific CT and FT models were built, which as a result of their optimization allowed to ensure acceptable strength factor of rotor wheel and slightly increased turbine efficiency.
In the next step, a joint model of both turbines was built and tested. Its analysis showed that mutual influence of these working processes of the turbines leads to a distortion of the flow temperature distribution in the flow path, which causes a reduction of the FT blades strength criteria to an unacceptable level.
Further optimization of the joint turbine model, taking into account aerodynamic and deformation processes, made it possible to increase the efficiency of both turbines by 0.4% (for each one), providing the necessary safety margins for the disks.
Convection in Scaled Turbine Internal Cooling Passages With Additive Manufacturing Roughness
Authors: Stafford Gabriel J. , McClain Stephen T. , Hanson David R. , Kunz Robert F. , Thole Karen A. 
Published: September 2021

Abstract
Additive manufacturing processes, such as direct metal laser sintering (DMLS), enable creation of novel turbine cooling internal passages and systems. However, the DMLS method produces a significant and unique surface roughness. Previous work in scaled passages analyzed pressure losses and friction factors associated with the rough surfaces, as well as investigated the velocity profiles and turbulent flow characteristics within the passage. In this study, the heat transfer characteristics of scaled additively manufactured surfaces were measured using infrared (IR) thermography. Roughness panels were CNC machined from plates of aluminum 6061 to create near isothermal roughness elements when heated. Fluid resistance differences between the aluminum roughness panels and roughness panels constructed from ABS plastic using the same roughness patterns from McClain et al. (2020) were investigated. Finally, the overall thermal performance enhancements and friction losses were assessed through calculation of surface averaged “global thermal performance” ratios. The global thermal performance characterizations indicate results in-line with those found for traditional commercial roughness and slightly below traditional internal passage convection enhancement methods such as swirl chambers, dimples, and ribs. The passages investigated in this study do not include compressibility effects or the long-wavelength artifacts and channel geometric deviations observed by Wildgoose et al. (2020). However, the results of this study indicate that, based on the roughness augmentation alone, artificial convective cooling enhancers such as turbulators or dimples may still be required for additively manufactured turbine component cooling.
Mathematical Modeling of the Polytropic Process Using the Sequential Cubic Polynomial Approximation
Authors: Taher Matt 
Published: September 2021

Abstract
The polytropic process is used to signify the effect of “energy degradation” associated with the equipment losses, which is as an inherent irreversibility in a compression process. The polytropic process is path dependent, which entails the irreversibility associated with the system. The change of gas composition and operating conditions affect the energy degradation. In this paper the polytropic process of real gas is explained and thermodynamics and mathematical model used in Taher-Evans Cubic Polynomial Method [1], [2] is presented. The elegance of Taher-Evans Cubic Polynomial Method is its rapid solution technique and high precision for calculating polytropic efficiency as required for compressor performance testing by the ASME PTC-10 [3].
Structurally Constrained Aerodynamic Adjoint Optimisation of Highly Loaded Compressor Blades
Authors: Cuciumita Cleopatra , John Alistair , Qin Ning , Shahpar Shahrokh 
Published: September 2021

Abstract
Adjoint aerodynamic optimisation has recently gained increased popularity for turbomachinery applications due to the large number of parameters that can be used without incurring additional major computational costs. This work presents an adjoint based aero-structural optimisation method having efficiency as the objective function and maximum von Mises stress set as a constraint. The full optimisation loop was set up with free-form deformation for geometry parametrisation. A response surface was created beforehand for computing the maximum von Mises stress using a meshless method. A discrete adjoint approach was used to obtain the gradients of the objective function with respect to each design parameter, while the constraint gradients were computed using finite differences. A sequential least squares programming algorithm was used as the optimizer. Tests carried out on a highly loaded compressor blade showed that the method successfully increases the efficiency by more than 3% while maintaining the maximum stress under the imposed value. The results also showed that the constrained optimisation loses about 1% in potential efficiency gain compared to the same optimisation process without stress constraint. Overall, the work provides a methodology for conducting structurally constrained adjoint aerodynamic optimisation that can be applied for large number of design parameters while maintaining low computational costs. It also provides reference for constructing and selecting a response surface to be used in the optimisation process.
Flow Response of an Industrial Gas Turbine Combustor To Acoustic Forcing Extracted From Unforced Data
Authors: Beuth Jan Paul , von Saldern Jakob G. R. , Kaiser Thomas Ludwig , Reichel Thoralf G. , Paschereit Christian Oliver , Ćosić Bernhard , Oberleithner Kilian 
Published: September 2021

Abstract
Gas turbine combustors are commonly operated with lean premix flames, allowing for high efficiencies and low emissions. These operating conditions are susceptible to thermoacoustic pulsations, originating from acoustic-flame coupling. To reveal this coupling, experiments or simulations of acoustically forced combustion systems are necessary, which are very challenging for real-scale applications. In this work we investigate the possibility to determine the flame response to acoustic forcing from snapshots of the unforced flow. This approach is based on three central hypothesis: first, the flame response is driven by flow fluctuations, second, these flow fluctuations are dominated by coherent structures driven by hydrodynamic instabilities, and third, these instabilities are driven by stochastic forcing of the background turbulence. As a consequence the dynamics in the natural flow should be low-rank and very similar to those of the acoustically forced system. In this work, the methodology is applied to experimental data of an industry-scale swirl combustor. A resolvent analysis is conducted based on the linearized Navier-Stokes equations to assure analytically the low-rank behavior of the flow dynamics. Then, these dynamics are extracted from flow snapshots using spectral proper orthogonal decomposition (SPOD). The extended SPOD is applied to determine the heat release rate fluctuations that are correlated with the flow dynamics. The low-rank flow and flame dynamics determined from the analytic and data-driven approach are then compared to the flow response determined from a classic phase average of the acoustically forced flow, which allow the research hypothesis to be evaluated. It is concluded that for the present combustor, the flow and flame dynamics are low-rank for a wider frequency range and the response to harmonic forcing can be determined quite accurately from unforced snapshots. The methodology further allows to isolate the frequency range where the flame response is predominantly driven by hydrodynamic instabilites.
Virtual Gas Turbines Part II: an Automated Whole-Engine Secondary Air System Model Generation
Authors: Kulkarni Davendu Y. , di Mare Luca 
Published: September 2021

Abstract
The design and analysis of the secondary air system (SAS) of gas turbine engine is a complex and time-consuming process because of its complicated geometry topology. The conventional SAS design-analysis model generation process is quite tedious, time consuming. It is still heavily dependent on human expertise and thus incurs high time-cost.
This paper presents an automated, whole-engine SAS flow network model generation methodology. During the SAS preprocessing step, the method accesses a pre-built whole-engine geometry model created using a novel, in-house, feature-based geometry modelling environment. It then transforms the engine geometry features into the features suitable for SAS flow network analysis. The proposed method not only extracts the geometric information from the computational geometry but also retrieves additional non-geometric attributes such as, rotational frames, boundary types, materials and boundary conditions etc. Apart from ensuring geometric consistency, this methodology also establishes a bi-directional information exchange protocol between engine geometry model and SAS flow network model, which enables making engine geometry modifications based on SAS analysis results.
The application of this feature mapping methodology is demonstrated by generating the secondary air system (SAS) flow network model of a modern three-shaft gas turbine engine. This capability is particularly useful for the integration of geometry modeler with the simulation framework. The present SAS model is generated within a few minutes, without any human intervention, which significantly reduces the SAS design-analysis time-cost. The proposed method allows performing a large number of whole-engine SAS simulations, design optimisations and fast re-design activities.
Bayesian Optimization for Multi-Objective High-Dimensional Turbine Aero Design
Authors: Zhang Yiming , Ghosh Sayan , Vandeputte Thomas , Wang Liping 
Published: September 2021

Abstract
Industrial design fundamentally relies on high-dimensional multi-objective optimization. Bayesian Optimization (BO) based on Gaussian Processes (GPs) has been shown to be effective for this practice where new designs are picked in each iteration for varying objectives including optimization and model refinement. This paper introduces two industrial applications of BO for turbine aero design. The first application is GE’s Aviation & Power DT4D Turbo Aero Design with 32 design variables. It has a single objective to maximize with 32 input/design variables and thus considered high-dimensional in terms of the input space. BO has significantly succeeded the traditional design schemes. It has been shown that finding the maximum-EI points (inner-loop optimization) could be critical and the influence of inner-loop optimization was evaluated. The second application is for multi-objective optimization. Each simulation run is the aggregate result from multiple CFD runs tuning geometry and took 24 hours to complete. BO has been capable to extend the existing Pareto front with a few additional runs. BO has been searching along the border of the design space and therefore motivate the open-up of design space exploration. For both applications, BO successfully guide the CFD run and allocate design variables more optimum than previous design approaches.