bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation of the Overall Transient Operation of Gas Turbines
Authors: Petkovic Djordje , Banjac Milan B. , Milic Srdjan , Madzar Teodora , Petrovic Milan V. , Wiedermann Alexander 
Published: October 2022

Abstract
Reduction of the start-up time and flexible operation require comprehensive testing and modification of a gas turbine. The cost of this testing can be significantly reduced by using reliable dynamic models to simulate critical regimes without the possibility of damage. This paper describes a dynamic model, called GTDyn, for simulation of the complete transient operation of gas turbines, from start-up to shutdown. In addition to basic transient phenomena, volume packing, and heat soakage, the effects of the tip clearance change on the performance are also included. The performance of the compressor and the turbine are described using steady-state characteristics, while component dynamics are modeled with the conversation laws in the form of ordinary differential equations. The applied component characteristics are calculated using through-flow solvers. A large number of compressor maps are implemented to include adjustments of stator blades and changes in tip clearances. The model is paired with a control system for the regulation of speed/load and turbine exit temperature. For the start-up sequence, a mode with starter assistance is implemented. The developed model was applied for simulating multiple start-ups to analyze the influence of thermal states on machine performance. The numerical results are compared with experimental data for an industrial single-shaft, air-cooled gas turbine. The comparison includes temperatures and pressures at inlet and outlet stations of each component, inlet mass flow, IGV adjustment, fuel mass flow, gas turbine speed, and power. The numerical results for starter power and compressor tip clearance are also presented.
Effects of the Surge Motion on the Performance of Floating Wind Turbine Considering Blade Structural Flexibility
Authors: Zhou Le , Shen Xin , Chen Jiajia , Yin Fanfu , Du Zhaohui 
Published: October 2022

Abstract
The flexible deformation of the slender blade has non-negligible effects on the performance of modern megawatt wind turbines, especially under marine environments where additional six degrees of motion is introduced by floating platform. In this research, an aeroelastic coupling model is established based on the lifting surface free vortex wake (LS-FVW) method and geometrically exact beam theory (GEBT) method. By adopting the model developed, the effects of the surge motion on the unsteady aeroelastic performance of floating offshore wind turbines (FOWTs) are investigated with the NREL 5 MW wind turbine. The results show that, the surge motion will increase the average power and thrust of FOWT, while the blade deformation has the opposite effect. The increase of the amplitude and frequency of the surge motion will increase the fluctuation amplitude and frequency of the power, thrust and structural deformation of the wind turbine. Besides, the smaller the amplitude or frequency of the surge, the stronger the ability of the wind turbine-floating platform system to restore stability.
Impact of Post-Stall Extrapolation and Rotational-Augmentation Models on the Performance of Stall-Controlled Wind Turbines
Authors: Papi Francesco , Nocentini Alberto , Melani Pier Francesco , Bianchini Alessandro 
Published: October 2022

Abstract
While most wind energy comes today from utility-scale machines, small wind turbines SWTs can still play a role in off-grid installations or in the context of distributed production and smart energy systems. Due to cost reasons, SWTs (especially up to 100kW) are usually controlled via progressive stall of the blades. Accurate airfoils polars are therefore key in engineering simulation models, not only to ensure predictive blade performance, but are also pivotal for proper controller tuning and an effective evaluation of loads. This study presents an analysis on the impact of post-stall extrapolation methods for airfoil polars, combined with the rotational-augmentation correction, on the aero-servo-elastic simulation of a stall-controlled wind turbine. The selected test case is the UNIFI 50kW RWT, a 50kW reference turbine recently developed by Università degli Studi di Firenze. Aero-servo-elastic simulations are carried out with the open-source code OpenFAST by NREL considering typical turbine Design Situations. Several post-stall extrapolation methods are tested on the same set of polars, also including the 3D correction. Results prove that the performance of turbines like the one studied here is strongly dependent on these methods, especially after the needed correction for rotational-augmentation is applied. In this view, dedicated studies and experimental validations in the next future could help increase the predictivity of low-order numerical models, establish new engineering best-practices, and finally increase the economic feasibility of small wind turbines.
Application of an Automatic Mesh Convergence Procedure for the Large Eddy Simulation of a Multipoint Injection System
Authors: Puggelli Stefano , Leparoux Julien , Brunet Clément , Mercier Renaud , Liberatori Luce , Zurbach Stephan , Cabot Gilles , Grisch Frédéric 
Published: October 2022

Abstract
Lean combustion is an attractive alternative to limit pollutants levels in order to meet the imposed limitations for the next generation of civil aero-engines. However, its implementation involves important technological questions related to the augmentation of the air dedicated to the combustion process. An effort on the injection system design is required and Large Eddy Simulation (LES) can be a useful tool in order to explore the design of novel concepts. At the state of the art, the validation of LES in high-pressure reactive conditions and in presence of the liquid phase is still limited. This shrinks the understanding and optimization of lean devices. The industrial project PERCEVAL, between Safran Tech and the CORIA laboratory, aims at extending the actual knowhow on lean combustion. Novel optical experimental techniques have been developed at CORIA to gain detailed information on industrial injection systems at high-pressure conditions. Within PERCEVAL, Safran Tech is in charge of the assessment of LES by using the experimental data-set collected at CORIA. In this framework, a novel Automatic Mesh Convergence (AMC) procedure, based on adaptive mesh refinement, has been developed in the YALES2 platform to speedup the calculation process. In the present paper, the AMC framework is described and then applied on the lean injection system designed at Safran Tech and tested during PERCEVAL. An analysis is carried out to evaluate the interest and gains offered by the AMC framework.
A Stepped Shaft Labyrinth Seal vs. a Pocket Damper Seal: Leakage and Dynamic Force Coefficients Under Wet Gas Operation
Authors: Torres José , San Andrés Luis , Yang Jing 
Published: October 2022

Abstract
Centrifugal compressors use annular gap seals, typically labyrinth type, to restrict process gas leakage from high-pressure regions to low-pressure regions. Modern machinery favors pocket damper seals (PDS) which produce significantly more effective damping than labyrinth seals (LS) do. Presently, liquid tolerant compressors enable efficient deep sea oil and gas (O&G) production facilities; and seals supplied with a two-phase flow mixture, liquid in gas, can have a large impact on the dynamic stability and leakage performance of O&G turbomachinery. The paper details experimental results for the leakage and force coefficients procured in a wet gas test rig hosting both a stepped shaft PDS and LS. The two seals have similar geometry and operate with shaft speeds up to 5,250 rpm (surface speed = 35 m/s) and pressure ratios (inlet/exit) = 2.5 to 4.2. The seals are supplied a light oil in air mixture whose liquid volume fraction (LVF) reaches up to 10% (liquid mass fraction &gt; 90%). Both seals feature the same shaft diameter D = 127 mm, axial length L = 0.38D, four blades (and eight 45° pockets). The LS has a 15% larger clearance than the PDS, hence it leaks more. For a pure gas condition (LVF = 0), the PDS is 25% more effective to restrict leakage than is the LS. Supplied with a wet gas, the mass flow through the seals grows since the mixture density increases. The effective clearance (Cr.e) of the PDS tends to decrease as LVF increases whereas that for the LS increases. The direct stiffness (K) for both seals is small and becomes negative as the liquid content increases. The cross-coupled stiffnesses are too small for accurate identification. The PDS produces a greater direct damping (C) than the LS when operating with a wet gas of identical LVF. The PDS C significantly grows as the LVF increases from 0% to 0.7%. Derived from a computational fluid dynamics model, predictions of leakage agree well with the measurements, whereas force coefficients are roughly ½ of the experimental ones. Changes in the LVF produced broadband subsynchronous vibrations (SSV) in the PDS, not so in the LS. The experimental results are a reference for the engineered design of LSs and PDSs operating with two-phase flow.
Field Testing and Operation of a 300 kW Active Magnetic Bearing Supported Turboexpander-Generator for Natural Gas Pressure Letdown
Authors: Khatri Rasish , Hawkins Larry , Liu Jeremy , Ortiz Neri Massimiliano , Cangioli Francesco , Biliotti Davide 
Published: October 2022

Abstract
A 300 kW turboexpander-generator was developed by Baker Hughes, in conjunction with Calnetix Technologies, for use in a natural gas pressure letdown application. A prior technical publication [1] describes the synchronous permanent magnet generator design and presented some preliminary test data from the prototype unit. In this paper, the machine design, including rotordynamics and active magnetic bearing (AMB) system design, are reviewed. Unbalance response measurements made during a standard mechanical running test at the manufacturer’s facility are shown, including comparisons to predictions made using API 617 guidelines. Turboexpander and generator operating data collected from the initial field installation in Bologna, Italy are then covered in detail. Field data presented includes aerodynamic performance data, closed-loop AMB transfer functions, and plant transfer functions at various power levels, vibration data from spin testing, backup bearing clearance measurements made using the magnetic bearings, thrust load vs. power curves, and generator efficiency at various power levels. The measurements made in the field confirm that the turboexpander-generator meets all customer requirements. Additionally, important case studies are presented, which demonstrate the magnetic bearings diagnosing real field problems. As of 2020, the machine is operating in parallel with a legacy Joule-Thomson valve. A future technical paper will discuss comparisons of predictions and measurements related to a series of shutdown tests performed on the machine under various shutdown scenarios.
Multi-Parameters Sensitivity Analysis of Overall Cooling Effectiveness on Turbine Blade and Numerical Investigation of Internal Cooling Structures on Heat Transfer
Authors: Liu Runzhou , Li Haiwang , You Ruquan , Tao Zhi 
Published: October 2022

Abstract
Turbine blade overall cooling effectiveness is a conjugate result under the influence of various parameters. In order to analyze the overall cooling effectiveness more accurately, we have to categorize all the influencing parameters. This paper builds a one-dimensional conjugate heat transfer model with four parameters which are adiabatic film cooling effectiveness, heat transfer coefficient ratio between blade external surface (hg) and internal surface (hi), internal coolant warming factor (Tg−Tw,iTg−Tc), Biot number. The effects of different internal cooling structures, film hole inclined angle and blowing ratio on flow and heat transfer characteristic were numerically investigated based on flat-plate film hole model and impingement-effusion model, where 3-D steady RANS method with SST k-ω model was used. V-rib, 45° inclined rib, 90° rib and dimple were adopted to compare with smooth internal channel. The results show that four dimensionless parameters (adiabatic film cooling effectiveness, heat transfer coefficient ratio, warming factor, Biot number) are positively correlated with overall cooling effectiveness. The overall cooling effectiveness is the most sensitive to adiabatic film cooling effectiveness, followed by warming factor. This indicates that the adiabatic film cooling effectiveness is the worthiest to improve. The numerical results show that the ribs and dimple structures have little influence on the distribution of adiabatic film cooling effectiveness and Biot number on the mainstream side. The 45° rib presents higher overall cooling effectiveness.
Experimental Analysis of an Axial Compressor Operating Under Flow Distortion
Authors: Baretter Alberto , Joseph Pierric , Roussette Olivier , Romanó Francesco , Dazin Antoine 
Published: October 2022

Abstract
In aircraft engines, compressor stages can encounter situations in which the flow is distorted at rotor inlet, for example during particular flight maneuvers, or due to the shape of the inlet of the airframe. The main objective of this paper is to investigate experimentally the effect of an inlet flow distortion on the internal flow dynamic and its consequences on the performance and operability of these machines. The distortion was generated by a porous plate grid installed upstream of the compressor. Eight total pressure rakes placed downstream of the grid were used to evaluate the distortion. Unsteady pressure measurements were performed on the casing at different axial and azimuthal positions to investigate the dynamic flow behavior at nominal conditions, at an operating point close to stall and during the transition to stall. 2D-2C PIV maps, synchronized with the runner position, were obtained on rotor blade-to-blade planes at three different spanwise positions (79%, 51%, 18% of the blade span). Three relative angular positions of the grid to the laser sheet were investigated at two different flow rates, namely the nominal flow rate and a flow rate close to stall. These three positions are corresponding to the laser sheet cutting through i/ the center of the grid’s wake and ii/ the two edges of the grid. The impact of the distortion on the performance of the compressor is analyzed and compared to existing models. The impact of the flow dynamic will also be considered, especially in operations close to the stall limit.
LES of Turbulent Premixed CH4/H2/Air Flames With Stretch and Heat Loss for Flame Characteristics and Dynamics
Authors: Kutkan Halit , Amato Alberto , Campa Giovanni , Tay-Wo-Chong Luis , Æsøy Eirik 
Published: October 2022

Abstract
This paper presents large eddy simulation (LES) turbulent combustion models for premixed methane/hydrogen/air mixtures which account for stretch, heat loss and Lewis number effects by means of a previously proposed turbulent flame speed expression [1]. In this expression stretch and heat loss effects are introduced by means of strained non-adiabatic laminar consumption speed calculations in fresh-to-burnt counter flow configurations with detailed chemistry, and preferential diffusion of hydrogen is accounted for by calculating an effective Lewis number of the reactants.
To validate and analyze the performance of the models, large eddy simulations of fully premixed atmospheric bluff body stabilized methane/hydrogen/air flames are compared against experimental measurements [2, 3]. Heat release distributions and mean flame shapes are compared against OH* chemiluminescence data. Flame dynamics are investigated by extracting flame transfer functions (FTFs) with system identification (SI) methods and comparing them with measured FTFs from experiments.
The Influence of Combustor Hot Streaks on the Aerodynamic Performance of a Turbine Center Frame
Authors: Badžek Ena , Patinios Marios , Farisco Federica , Heitmeir Franz , Göttlich Emil 
Published: October 2022

Abstract
This paper investigates the influence of combustor temperature non-uniformities on modern engine turbine center frames (TCFs). Due to their position in an engine, coupled with the trends of more aggressive designs, increased turbine inlet temperatures (TIT), and utilization of lean-burn combustors, turbine center frames are exposed to even higher temperatures and non-uniform temperature flow fields. These temperature non-uniformities, or hot streaks, were previously studied at the combustor - high-pressure turbine (HPT) interface, but there is no available research in the open literature that clarifies their influence on the TCF performance. A new test bench, designed specifically for fundamental research on hot streaks, was set up at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz University of Technology. The test bench features a 90° sector-cascade of an engine representative TCF geometry, equipped with a hot streak generator and a flow conditioning grid. Experimental data was gathered by means of five-hole-probe area traverses at the TCF inlet and outlet planes. Two individual clocking positions of hot streaks in respect to the leading edges of the struts were investigated, as well as three different radial positions for each of the clocking scenarios. Hot streaks were injected upstream of the flow conditioning grid, generating a representative temperature ratio at the TCF inlet plane. Results show that the hot streaks have migrated radially outwards and are characterized by different temperature distributions, depending on the injection position. An increase in pressure loss and thermal loading of the strut and of the shroud is observed.
Numerical Investigation of Potential Flow Induced Vibrations of Steam Turbine Last Stage Rotor at Low Load Operation – Part 1: Sensitivity to Flutter Occurrence
Authors: Pinelli Lorenzo , Mariotti Filippo , Arnone Andrea , Marconcini Michele , Arcangeli Lorenzo , Ciuchicchi Lorenzo , Maceli Nicola 
Published: October 2022

Abstract
The present paper is part of a two-part publication that aims to numerically investigate the occurrence of flow induced vibrations in a steam turbine last stage rotor at low load operations. Experimental and numerical investigations at low load operations are gaining interest in the design of steam turbine blades due to the effort required to achieve carbon free objectives, which lead to higher flexibility of steam power plants. Reliable machines able to work safely at low load conditions are required for coupling with renewable energy sources and high output power plants. In this part 1 paper, the last rotor of a low-pressure steam turbine module installed in concentrated solar plants has been numerically evaluated to assess the flutter stability at different low load conditions, while the companion part 2 deals with the investigation of unsteady aerodynamic instabilities which might arise in the last stage rotor.
In the present work, aerodynamic and flutter simulations were performed at different load conditions, from the design point to very low mass flows to achieve a real sensitivity of flutter behavior to the mass flow rate. By means of steady state multistage results, aerodynamic performance and flow structures were evaluated. The decreasing mass flow and blade load reveal the formation of wide separation areas both on the last rotor pressure side and in the exhaust duct, bringing the stage up to ventilating conditions. The flutter analyses were performed with an uncoupled non-linear method in order to estimate the aerodynamic damping for a selection of mode-shape families. From aerodamping results it was possible to observe the trend in the flutter response at different load conditions and it is evident how the shock wave system near the tip plays a major role in energy exchange between flow field and the vibrating profile. The results show an overall flutter stability of the blade up to very low load conditions. This means that for these type of rotor profiles and corresponding applications, flutter occurrence is not the main issue, and further vibration causes like rotating instabilities have to be investigated as demonstrated in the companion part 2 paper.
A Numerical Study on the Effects of Circumferential Positions of Combustor Hot Streaks on a TCF Configuration
Authors: Benauer Richard , Schreck Stefan , Leitl Peter , Badzek Ena , Patinios Marios , Farisco Federica 
Published: October 2022

Abstract
This work presents the results of numerical investigations conducted within the framework of a project focused on studying the influence of combustor hot streaks onto the aerodynamic performance of a TCF representative geometry. Different circumferential positions of the hot streaks, in respect to the leading edges of the high pressure turbine (HPT) stator vanes, were examined in order to determine changes in the flow field and its influence on the downstream components. Numerical investigations were carried out at Bionic Surface Technologies GmbH using the commercial tool ANSYS CFX. Transient simulations were performed to obtain the flow-field and capture the propagation of the hot streaks through the HPT stage into the TCF. Time averaged five-hole-probe measurements, taken from the TU Graz transonic test turbine facility (TTTF), were used as the initial boundary conditions for the simulations. Results are showing that the circumferential position of the hot streaks influences the temperature distribution at the TCF outlet since the hot streaks follow the fluid migration in the TCF, and are therefore affected by secondary flow structures originating from the fluid interaction with the HPT and TCF struts. Results also present an increase of pressure loss below 1%, for the hot streaks simulations.
Design of an Air-Cooled Condenser for CO2-Based Mixtures: Model Development, Validation and Heat Exchange Gain with Internal Microfins
Authors: Illyés Viktoria , Morosini Ettore , Doninelli Michele , David Pierre-Luc , Guerif Xavier , Werner Andreas , Di Marcoberardino Gioele , Manzolini Giampaolo 
Published: October 2022

Abstract
CO2 blends provide tremendous advantages when used as a working fluid in transcritical power cycles with respect to pure CO2. The benefits become especially apparent if coupled with concentrated solar power since increasing the critical temperature of the blend with respect to pure CO2 allows dry condensing at high ambient temperatures in locations of high solar radiation. One key cycle component is the cooler, which in this work is designed as an air-cooled condenser with a MATLAB in-house code. The internal, condensation heat transfer model used in this paper relies on a correlation developed by Cavallini (2006). The model itself is validated against experimental data from a test rig for heat transfer measurements on a CO2 + R1234ze(E) mixture. The resulting design of the condenser is compared with the commercial software HTRI for a specific case study which is representative of the condenser of a recuperated cycle working with a CO2 + C6F6 blend. The authors also present an upgraded heat exchanger design with microfinned tubes, the DIESTA tubes, and groovy fins on the air side. The design of the heat exchanger adopting the mixture is compared to a case with pure CO2 as the working fluid.