bluuebunny/crossref_metadata_2025_split huggingface dataset:
Part Load Strategy Definition and Annual Simulation for Small Size sCO2 Based Pulverized Coal Power Plant
Authors: Alfani Dario , Astolfi Marco , Binotti Marco , Silva Paolo 
Published: January 2021

Abstract
In the near future, due to the growing share of variable renewable energy (VRE) in the electricity mix and the lack of large-scale electricity storage, coal power plants will have to gradually shift their role from base-load operation to providing fluctuating back-up power to meet unpredictable and short-noticed load variations, in order to improve the stability of the electrical grid. However, current coal power plants have been designed to operate at base-load and are not optimized for flexible part-load operation, resulting in an intrinsic inadequacy for fast load variations. The founding idea of the H2020 sCO2-Flex project is to improve the flexibility of pulverized coal power plants by adopting supercritical carbon dioxide (sCO2) Brayton power cycles instead of common steam Rankine cycles. Despite the extensive available literature about the design of sCO2 power systems for different applications (concentrating solar power, waste heat recovery, 4th generation nuclear), there is still limited knowledge about part-load strategies that should be implemented in order to maximize system efficiency during real plant operation. This paper aims to provide a deeper insight about the potential of sCO2 power plants for small modular coal power plants (25–100 MWel) highlighting the difficulties that must be faced during part-load operation in order to ensure high system performances still guaranteeing a safe operation of the cycle components. The selected configuration is a recompressed cycle with high temperature recuperator bypass which is modelled in a MATLAB+REFPROP numerical tool specifically developed to optimize the plant nominal performance, to provide a preliminary sizing of each component and to evaluate and compare different off-design operating strategies. In particular, the off-design behavior and the operational constraints of each component will be implemented based on referenced numerical models, adopting reliable correlations and exploiting ad hoc codes for the performance evaluation.
Experimental and Computational Investigation of Shaped Film Cooling Holes Designed to Minimize Inlet Separation
Authors: Jones Fraser B. , Fox Dale W. , Bogard David G. 
Published: January 2021

Abstract
Film cooling is used to protect turbine components from the extreme temperatures by ejecting coolant through arrays of holes to create an air buffer from the hot combustion gases. Limitations in traditional machining meant film cooling holes universally have sharp inlets which create separation regions at the hole entrance. The present study uses experimental and computational data to show that these inlet separation are a major cause of performance variation in crossflow fed film cooling holes. Three hole designs were experimentally tested by independently varying the coolant velocity ratio (VR) and the coolant channel velocitty ratio (VRc) to isolate the effects of crossflow on hole performance. Leveraging additive manufacturing technologies, the addition of a 0.25D radius fillet to the inlet of a 7-7-7 shaped hole is shown to significantly improve diffuser usage and significantly reduce variation in performance with VRc. A second AM design used a very large radius of curvature inlet to reduce biasing caused by the inlet crossflow. Experiments showed that this “swept” hole design did minimize biasing of coolant flow to one side of the shaped hole and it significantly reduced variations due to varying VRc. RANS simulations at six VR and three VRc conditions were made for each geometry to better understand how the new geometries changed the velocity field within the hole. The sharp and rounded inlets were seen to have very similar tangential velocity fields and jet biasing. Both AM inlets created more uniform, slower velocity fields entering the diffuser. The results of this paper indicate large improvements in film cooling performance can be found by leveraging AM technology.
Effect of Struts Downstream of Low Pressure Turbine on Tone Noise Generation
Authors: Nigmatullin Ravil , Terenteva Larisa 
Published: January 2021

Abstract
In the present work a numerical study of tone noise generated by the last stage of the Low Pressure Turbine (LPT) of an aircraft engine designed for a medium-haul civilian aircraft has been conducted. The impact of struts on the tone noise characteristics is estimated. The method for turbine noise calculation is based on numerical integration of the three-dimensional unsteady Reynolds averaged Navier-Stokes equations using an in-house code for multi-stage simulations. To obtain the tonal characteristics of the generated noise, the pressure pulsation field is processed using the methods of radial mode analysis. The calculated pressure fluctuations contain all possible components of the frequency-modal spectrum, which allows us to determine profile of the generated tone noise and find propagating modes with maximum amplitude. The calculations showed that the presence of struts leads to a scattering effect, which manifests as an increase in the number of generated circumferential modes. These circumferential modes propagate both downstream and upstream and increase the total level of tone noise. The amplitudes of circumferential modes related to two different types of the interaction, rotor-stator and rotor-struts, are compared.
Active Flow Control Utilizing an Adaptive Blade Geometry and an Extremum Seeking Algorithm at Periodically Transient Boundary Conditions
Authors: Werder Tobias , Liebich Robert , Neuhäuser Karl , Behnsen Clara , King Rudibert 
Published: January 2021

Abstract
As a consequence of constant volume combustion in gas turbines pressure waves propagating upstream the main flow into the compressor system are generated leading to incidence variations. Numerical and experimental investigations of stator vanes have shown that Active Flow Control (AFC) by means of adaptive blade geometries is beneficial when such periodic incidence variations occur. A significant risk reduction in a compressor facing disturbances can thereby be achieved concerning stall or choke. Experimental investigations on such an AFC method with simultaneous application of a closed-loop control are missing in order to demonstrate its potential.
This work investigates a linear compressor cascade that is equipped with a 3D-manufactured piezo adaptive blade structure. The utilized actuators are piezoelectric Macro-Fiber-Composites. A throttling device is positioned downstream the trailing edge plane to emulate an unsteady combustion process. Periodic transient throttling events with a frequency of up to 20 Hz cause incidence changes to the blade’s leading edge. Consequently, pressure fluctuations on the blade’s surface occur, having a significant impact on the pressure recovery downstream of the stator cascade. Experimental results of harmonically actuating the piezo adaptive blade with the corresponding disturbance frequency show that the impact of disturbances can be reduced to approx. 50 %. However, this is only effective if the phase shift of the harmonic actuation is adjusted correctly. Using an inadequate phase shift reverses the positive effects, causing the aforementioned stall, choke, or significant losses. In order to find the optimum phase shift, even under varying, possibly unpredictable operating conditions, an Extremum Seeking Controller is presented. This gradient-based approach is minimizing the pressure variance over time by carefully adjusting the phase shift of the harmonic actuation of the AFC system.
Evaluation and Validation of Two-Phase Flow Numerical Simulations Applied to an Aeronautical Injector Using a Lagrangian Approach
Authors: Tillou Julien , Leparoux Julien , Dombard Jérome , Riber Eleonore , Cuenot Bénédicte 
Published: January 2021

Abstract
Non-reactive Lagrangian two-phase flow Large-Eddy Simulations (LES) of an industrial aeronautical injector are carried out with the compressible AVBP code and compared with an experimental database in an industrial context. While most of the papers are focused on simplex atomiser with only one fuel passage, we propose to account for specific industrial configurations based on duplex atomiser where both the primary and the secondary passages operate. For the second passage, the fuel spray angle is wider, leading to spray / wall interactions and airblast atomization.
The computation domain consists in the experimental mock-up without the fuel atomizer part. The liquid-injection boundary condition is applied through the phenomenological FIM-UR model, which prescribes droplet velocities and diameter distribution at the atomizer tip based on both the atomizer characteristics and the liquid mass flow rate. No specific models are used for spray / wall interaction, and droplets are assumed to slip on the walls. The numerical results are compared with the experimental database for Jet-A1 fuel, built through Phase Doppler Anemometry instrumentation, allowing access to local information regarding the droplets velocity components.
Three LES are performed for pressure loss ranging from 1 to 3%, covering an important part of the engine operating conditions, from high altitude relight to cruise operating point. Mean and fluctuating velocity profiles show a relatively good agreement with measurements, for all the operating points. It confirms that the spray/wall interactions, airblast and secondary breakup models may be neglected as a first approximation for configurations where only a relatively small amount of fuel impacts the wall.
Numerical Predictions of Turbine Cascade Secondary Flows and Heat Transfer With Inflow Turbulence
Authors: Kanani Yousef , Acharya Sumanta , Ames Forrest 
Published: January 2021

Abstract
Turbine passage secondary flows are studied for a large rounded leading edge airfoil geometry considered in the experimental investigation of Varty et al. (J. Turbomach. 140(2):021010) using high resolution Large Eddy Simulation (LES). The complex nature of secondary flow formation and evolution are affected by the approach boundary layer characteristics, components of pressure gradients tangent and normal to the passage flow, surface curvature, and inflow turbulence. This paper presents a detailed description of the secondary flows and heat transfer in a linear vane cascade at exit chord Reynolds number of 5 × 105 at low and high inflow turbulence. Initial flow turning at the leading edge of the inlet boundary layer leads to a pair of counter-rotating flow circulation in each half of the cross-plane that drive the evolution of the pressure-side and suction side of the near-wall vortices such as the horseshoe and leading edge corner vortex. The passage vortex for the current large leading-edge vane is formed by the amplification of the initially formed circulation closer to the pressure side (PPC) which strengthens and merges with other vortex systems while moving toward the suction side. The predicted suction surface heat transfer shows good agreement with the measurements and properly captures the augmented heat transfer due to the formation and lateral spreading of the secondary flows towards the vane midspan downstream of the vane passage. Effects of various components of the secondary flows on the endwall and vane heat transfer are discussed in detail.
Transient Aero-Thermo-Mechanical Multidimensional Analysis of a High Pressure Turbine Assembly Through a Square Cycle
Authors: Ganine Vlad , Chew John W. , Hills Nicholas J. , Mohamed Sulfi N. , Miller Matthew M. 
Published: January 2021

Abstract
Better understanding and more accurate prediction of heat transfer and cooling flows in aero engine components in steady and transient operating regimes are essential to modern engine designs aiming at reduced cooling air consumption and improved engine efficiencies. This paper presents a simplified coupled transient analysis methodology that allows assessment of the aerothermal and thermomechanical responses of engine components together with cooling air mass flow, pressure and temperature distributions in an automatic fully integrated way. This is achieved by assembling a fluid network with contribution of components of different geometrical dimensions coupled to each other through dimensionally heterogeneous interfaces. More accurate local flow conditions, heat transfer and structural displacement are resolved on a smaller area of interest with multidimensional surface coupled CFD/FE codes. Contributions of the whole engine air-system are predicted with a faster mono dimensional flow network code. Matching conditions at the common interfaces are enforced at each time step exactly by employing an efficient iterative scheme. The coupled simulation is performed on an industrial high pressure turbine disk component run through a square cycle. Predictions are compared against the available experimental data. The paper proves the reliability and performance of the multidimensional coupling technique in a realistic industrial setting. The results underline the importance of including more physical details into transient thermal modelling of turbine engine components.
Application of Digital Twin Concept for Supercritical CO2 Off-Design Performance and Operation Analyses
Authors: Moroz Leonid , Burlaka Maksym , Zhang Tishun , Altukhova Olga 
Published: January 2021

Abstract
To date variety of supercritical CO2 cycles were proposed by numerous authors. Multiple small-scale tests performed, and a lot of supercritical CO cycle aspects studied. Currently, 3-10 MW-scale test facilities are being built. However, there are still several pieces of SCO2 technology with the Technology Readiness Level (TRL) 3-5 and system modeling is one of them. The system modeling approach shall be sufficiently accurate and flexible, to be able to precisely predict the off-design and part-load operation of the cycle at both supercritical and condensing modes with diverse control strategies. System modeling itself implies the utilization of component models which are often idealized and may not provide a sufficient level of fidelity. Especially for prediction of off-design and part load supercritical CO2 cycle performance with near-critical compressor and transition to condensing modes with lower ambient temperatures, and other aspects of cycle operation under alternating grid demands and ambient conditions.
In this study, the concept of a digital twin to predict off-design supercritical CO2 cycle performance is utilized. In particular, with the intent to have sufficient cycle simulation accuracy and flexibility the cycle simulation system with physics-based methods/modules were created for the bottoming 15.5 MW Power Generation Unit (PGU). The heat source for PGU is GE LM6000-PH DLE gas turbine. The PGU is a composite (merged) supercritical CO2 cycle with a high heat recovery rate, its design and the overall scheme are described in detail. The calculation methods utilized at cycle level and components’ level, including loss models with an indication of prediction accuracy, are described. The flowchart of the process of off-design performance estimation and data transfer between the modules as well. The comparison of the results obtained utilizing PGU digital twin with other simplified approaches is performed. The results of the developed digital twin utilization to optimize cycle control strategies and parameters to improve off-design cycle performance are discussed in detail.
Effects of Endwall Film Coolant Flow Rate on Secondary Flows and Coolant Mixing in a First Stage Nozzle Guide Vane
Authors: Alqefl Mahmood H. , Nawathe Kedar P. , Chen Pingting , Zhu Rui , Kim Yong W. , Simon Terrence W. 
Published: January 2021

Abstract
Modern gas turbines are subjected to very high thermal loading. This leads to a need for aggressive cooling to protect components from damage. Endwalls are particularly challenging to cool due to a complex system of secondary flows near them that wash and disrupt the protective coolant films. This highly three-dimensional flow not only affects but is also affected by the momentum of film cooling flows, whether injected just upstream of the passage to intentionally cool the endwall, or as combustor cooling flows injected further upstream in the engine. This complex interaction between the different cooling flows and passage aerodynamics has been recently studied in a first stage nozzle guide vane. The present paper presents a detailed study on the sensitivity of aero-thermal interactions to endwall film cooling MFR (cooling mass flow to mainstream flow ratio). The test section represents a first stage nozzle guide vane with a contoured endwall and endwall film cooling injected just upstream of it. The test section also includes an engine-representative combustor-turbine interface geometry with combustor cooling flows injected at a constant rate. The approach flow conditions represent flow exiting a low-NOx combustor. Adiabatic surface thermal measurements and in-passage velocity and thermal field measurements are presented and discussed. The results show the dynamics of passage vortex suppression and the increase of impingement vortex strength as MFR changes. The effects of these changes of secondary flows on coolant distribution are presented.
Experimental Investigation on the Rubbing Process of Labyrinth Seals Against Honeycomb Liners
Authors: Munz Oliver , Hühn Lisa , Schwitzke Corina , Bauer Hans-Jörg , Fischer Tim , Ulan kyzy Sonun 
Published: January 2021

Abstract
Sealing systems contribute significantly to the efficiency of turbomachinery. Small gap widths, which are important for low leakage mass flows in labyrinth seals, combined with thermal and mechanical expansion of the rotor can lead to contact with the stator. During these so-called rubbing processes, it is necessary to make an accurate prediction with respect to the performance and service life of the seal. For this purpose, the influence of relative velocity in the contact (up to 165ms−1) and incursion rate (up to 0.5 mms−1) on the resulting thermal and mechanical loads as well as wear mechanisms are studied for the rubbing process between an inclined labyrinth seal fin and a honeycomb segment. Furthermore, different axial configurations of the seal fin with respect to the honeycomb structure are considered. The system reacts very sensitively to a change of the seal fin position relative to the honeycomb structure. The incursion per revolution reflects a change of the wear mechanism from abrasive to plastic for a certain value. The results of this study contribute to the optimization of labyrinth seals and the development of new types of liner materials as well as geometries.
Methods to Have Tighter Clearance in Gas Turbine: Turbine Section
Authors: Babu Santhana G. , Ramesh Kammalapalli , Tognarelli Leonardo 
Published: January 2021

Abstract
Typically, Gas turbine clearance between stator and rotor parts are governed by radial clearance which determines performance, cooling flow requirements, part performance etc. These clearances must be optimized to meet product requirements. Clearance which are kept too tight at assembly condition causes excessive rubbing during starting or shutdown of gas turbine which results in excessive heat generation and damage to rotating and statoric parts. In some cases, rubbing could cause tip liberations and damages to flow path which results in aero dynamic losses. Similarly, if rotor tip clearance is large at assembly condition results in aerodynamic losses. While designing component design at interface locations, tip clearance should be kept as minimum as possible to have proper balance between tip rubs at low speed and aero dynamic loss. In this paper describes the experience of Baker Hughes, wherein different design options which are considered to arrive at optimized clearance in low pressure turbine section of Gas turbine have been discussed. Typically, in low pressure turbine wherein the turbine airfoils were provided with tip rails and shrouds are brazed with honeycombs. These were allowed to rub during startup of Gas turbine engine and provide a tighter clearance at steady state operating condition. In this paper, to have tighter clearance in operating condition few methods of incorporating axial clearance in addition to radial tip clearance are discussed. By incorporating tighter axial clearance, it was found to be evident that performance estimated has improved compared to having only radial tip clearance. This paper also describes design considerations for honeycomb pertaining to axial clearance control and the methods for rubbing tip shroud with honeycomb. This paper highlights worm chart developed for a rotor blade and stator shroud configuration and highlight benefit of axial clearance control mechanism. This paper also covers different designs of heat dissipation methods in tip rails of a bucket while it is rubbing with honeycomb. In this paper, based analytical case study proves that, when axial clearance was made tighter, it reduces leakage flows and improves Low pressure turbine stage efficiency significantly.
Low-Order Modeling to Investigate Clusters of ITA Modes in Annular Combustors
Authors: Fournier Guillaume J. J. , Haeringer Matthias , Silva Camilo F. , Polifke Wolfgang 
Published: January 2021

Abstract
The intrinsic thermoacoustic (ITA) feedbackloop constitutes a coupling between flow, flame and acoustics that does not involve the natural acoustic modes of the system. One recent study showed that ITA modes in annular combustors come in significant number and with the peculiar behavior of clusters, i.e. several modes with close frequencies. In the present work an analytical model of a typical annular combustor is derived via Riemann invariants and Bloch theory. The resulting formulation describes the full annular system as a longitudinal combustor with an outlet reflection coefficient that depends on frequency and the azimuthal mode order. The model explains the underlying mechanism of the clustering phenomena and the structure of the clusters associated with ITA modes of different azimuthal orders. In addition, a phasor analysis is proposed, which enclose the conditions for which the 1D model remains valid when describing the thermoacoustic behavior of an annular combustor.