bluuebunny/crossref_metadata_2025_split huggingface dataset:
Loss Predictions in the High-Pressure Film-Cooled Turbine Vane of the FACTOR Project by Mean of Wall-Modeled Large Eddy Simulation
Authors: Harnieh Mael , Odier Nicolas , Dombard Jérôme , Duchaine Florent , Gicquel Laurent 
Published: January 2021

Abstract
The use of numerical simulations to design and optimize turbine vane cooling requires precise prediction of the fluid mechanics and film cooling effectiveness. This results in the need to numerically identify and assess the various origins of the losses taking place in such systems and if possible in engine representative conditions. Large-Eddy Simulation (LES) has shown recently its ability to predict turbomachinery flows in well mastered academic cases such as compressor or turbine cascades. When it comes to industrial representative configurations, the geometrical complexities, high Reynolds and Mach numbers as well as boundary condition setup lead to an important increase of CPU cost of the simulations. To evaluate the capacity of LES to predict film cooling effectiveness as well as to investigate the loss generation mechanisms in a turbine vane in engine representative conditions, a wall-modeled LES of the FACTOR film-cooled nozzle is performed. After the comparison of integrated values to validate the operating point of the vanes, the mean flow structure is investigated. In the coolant film, a strong turbulent mixing process between coolant and hot flows is observed. As a result, the spatial distribution of time-averaged vane surface temperature is highly heterogeneous. Comparisons with the experiment show that the LES prediction fairly reproduces the spatial distribution of the adiabatic film effectiveness. The loss generation in the configuration is then investigated. To do so, two methodologies, i.e, performing balance of total pressure in the vanes wakes as mainly used in the literature and Second Law Analysis (SLA) are evaluated. Balance of total pressure without the contribution of thermal effects only highlights the losses generated by the wakes and secondary flows. To overcome this limitation, SLA is adopted by investigating loss maps. Thanks to this approach, mixing losses are shown to dominate in the coolant film while aerodynamic losses dominate in the coolant pipe region.
Application of Scale Adaptive Simulation Model to Studying Cooling Characteristics of a High Pressure Turbine Blade Cutback Trailing Edge With Different Cooling Configurations
Authors: Li Yuefeng , Xu Huazhao , Wang Jianhua , Song Wei , Wang Ming , Liu Taiqiu , Wang Xu 
Published: January 2021

Abstract
Effective cooling structure design in the trailing edge (TE) of a high pressure turbine (HPT) blade is essential to increase turbine efficiency and maintain structural integrity. To obtain efficient cooling structures and understand clearly cooling mechanism, this paper adopted numerical simulation methods to investigate fluid flow and cooling characteristics in detail downstream of a HPT blade TE cutback region. The effects of typical TE configurations on cutback cooling performance are investigated including three types of internal turbulators (cylindrical pin fins and elliptic pin fins arranged in streamwise and spanwise orientations), the cutback with/without land extensions and three kinds of ejection lip profiles (one straight lip shape marked as “A” and two rounded lip shapes marked as “B” and “C”, respectively). The Scale Adaptive Simulation (SAS) is implemented to study the complex unsteady mixing process downstream of the cutback under operating condition of blowing ratio M = 0.65. The results from the Shear Stress Transport (SST) k-ω model are compared as well.
SAS is capable to reproduce the periodical vortex shedding phenomena and resolve the vortices coherent structures. Compared with the experimental data, SAS provides more accurate predictions in terms of laterally averaged adiabatic cooling effectiveness ηaw and discharge coefficient Cd than the SST k-ω model. On the rear part of the cutback surface, large deterioration in ηaw is predicted by SAS for all configurations, but ηaw is considerably over-predicted by the SST k-ω model except for the case of elliptic pin fins with spanwise orientation. The elliptic pin fins with streamwise orientation significantly improve ηaw at the rear part of the cutback surface over the baseline model with cylindrical pin fins and slightly increase Cd. However, the elliptic pin fins with spanwise orientation drastically reduce the ηaw and Cd. Downstream of the cutback, the coherent structures are strongly disturbed and become chaotic compared to the TE with cylindrical and streamwise oriented elliptic pin fins. The application of land extensions only causes an evident change to the coherent structure immediate downstream of the lip, and slightly improves ηaw and reduces Cd over the baseline model on the rear part of the cutback surface. Rounded lip shapes B and C also show an obvious increase in ηaw on the rear part of the cutback surface but only a minor increase in Cd compared to the straight lip shape A. The rounded lip helps the coolant diffuse into the TE cutback and reduce the intensity of mixing. Due to larger rounding radius of shape B, the cooling effectiveness predicted by shape B is slightly better than shape C.
Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner With Central Bluff Body
Authors: Biagioli Fernando , Innocenti Alessandro , Terhaar Steffen , Marchione Teresa 
Published: January 2021

Abstract
Lean premixed gas turbulent flames stabilized in the flow generated by an industrial swirl burner with a central bluff body are experimentally found to behave bi-stable. This bi-stable behaviour, which can be triggered via a small change in some of the controlling parameters, for example the bulk equivalence ratio, consists in a rather sudden transition of the flame from completely lifted to well attached to the bluff body. This has impact on combustion dynamics, emissions and pressure losses. While several experimental investigations exist on this topic, numerical analysis is limited. The present work is therefore also of numerical nature, with a two-fold scope: a) simulation and validation with experiments of the bi-stable flame behaviour via Computational Fluid Dynamics (CFD) in the form of Large Eddy Simulation (LES) and b) analysis of CFD results to shed light on the flame stabilization properties. LES results, in case of the lifted flame, show that the vortex core is sharply precessing at a given frequency. Phase averaging these results at the frequency of precession clearly indicates a counter-intuitive and unexpected presence of reverse flow going all the way through the flame apex and the bluff body tip. The counter-intuitive presence of a lifted flame is explained here in terms of the phase averaged data which show that the flame apex is not placed at the centre of the spinning reverse flow region. It is instead slightly shifted radially outward where the axial velocity recovers to low positive values of the order of the turbulent burning rate. A simple one-dimensional flame stabilization model is applied to explain this peculiar flame behaviour. This model provides first an estimation of the flame radius of curvature in terms of axial velocity and turbulence quantities. This radius is therefore used to determine the total flux of reactants into the flame, given by an axial convection and a radial diffusion contributions. Subsequently the possibility of the flame positioned at the centre of the vortex is excluded based on the balance between this flux and the turbulent burning rate. A clear explanation of the mechanism leading to the sudden flame jump has instead not been identified and only some hypotheses are provided.
Equivalent Linearization of Bladed Disk Assemblies With Friction Nonlinearities Under Random Excitation
Authors: Förster Alwin , Panning-von Scheidt Lars , Wallaschek Jörg 
Published: January 2021

Abstract
The present article addresses the vibrational behavior of bladed disk assemblies with nonlinear shroud coupling under random excitation. In order to increase the service life and safety of turbine blades, intense calculations are carried out to predict the vibrational behavior. The use of friction dampers for energy dissipation and suppression of large amplitudes adds a nonlinearity to the mechanical system, which complicates the calculations. Depending on the stage, different types of excitation can occur in a turbine, from stationary to transient, synchronous to asynchronous as well as deterministic to random excitation. Random excitation in combination with the presence of nonlinearities makes the calculation of the vibrational behavior even more complex. So far, this problem has only been dealt with to a limited extent in the literature on turbomachinery. Nevertheless, there are in general different approaches and methods to address this problem most of which are strongly restricted with regard to the number of degrees of freedom. The focus of this paper is the application of an equivalent linearization method to calculate the stochastic response of an academic model of a bladed disk assembly under random excitation. The fundamental idea of the method is to linearize a nonlinear system in such a way that the most suitable equivalent linear system is found taking into account the approximated distribution of the response amplitude. To apply this method to a system with a friction nonlinearity, the linear part of the system is considered in state space and extended with additional nonlinear equations. The nonlinear contact is modelled with a Bouc-Wen formulation to reproduce the hysteretic character of a nonlinearity occurring in the presence of a friction damper. The classical Bouc-Wen formulation is standardized in such a way that the usual parameters can be replaced by physical ones such as the normal force or contact stiffness. The nonlinear force of the friction nonlinearity is linearized regarding the stochastic distribution of the system response. Both the excitation and the response are limited to mean-free, stationary stochastic processes, which means that the stochastic moments do not change over time. However, the spectrum of the excitation is not limited to being constant, as it is the case with Gaussian white noise. The equivalent linearization method could also deal with a narrowband or broadband excitation spectrum. Unlike previous papers on this topic, the calculations are performed on a full bladed disk assembly in which each sector is represented by a reduced order model with several degrees of freedom.
Conjugate Heat Transfer Characteristics of Double Wall Cooling on a Film Plate With Gradient Thickness
Authors: He Juan , Deng Qinghua , Zhou Weilun , He Wei , Gao Tieyu , Feng Zhenping 
Published: January 2021

Abstract
Double wall cooling, consisting of internal impingement cooling and external film cooling, is an advanced cooling method of gas turbines. In this paper, the flow and conjugate heat transfer characteristics of double wall cooling which has a film plate with gradient thickness are analyzed numerically. The detailed overall cooling effectiveness distributions are obtained by solving steady three dimensional Reynolds-averaged Navier-Stokes equations.
In the double wall cooling scheme, seven vertical film holes and six impingement holes are staggered with same diameter (D), and the hole pitch of them are both set to 6D in flow direction and lateral direction. The gradient thickness along the flow direction is realized by setting the angle (α) between the lower surface of the film plate and the horizontal plane at −1.5 deg and 1.5 deg respectively. By comparing the results of four broadly used turbulence models with experimental data, SST k-ω is selected as the optimal turbulence model for double wall cooling analysis in this paper. In addition, the number of grids are finally determined to be 5.2 million by grid sensitivity calculation. The influence of the thickness gradient on the overall cooling effectiveness is revealed by comparing with the constant thickness film plate (Baseline 1 and 2), and all the cases are performed under four various coolant mass flow rates, which correspond to blowing ratios ranging from 0.25 to 1.5.
The calculated results show that the thickening of the film plate downstream is beneficial to improve overall cooling effectiveness at low blowing ratio, which is benefit from two aspects. One is the thicken film plate weakens the flow separation in film hole and velocity of film hole outlet, another is the thicken film plate makes the impingement channels convergence, and impingement cooling is strengthened to some extent. However, with the increase of blowing ratio, the increasing trend gradually weakens due to the jet-off and limited impinge ability. For thickening film plate, the variations of the double wall cooling configurations are considered at initial film plate thickness tf of 2D and 3D, it is found that the ability to improve the overall cooling effectiveness by thickening the film plate downstream decrease as the initial film plate thickness increases, which is due to the increase of heat transfer resistance, and another finding is the cooling effectiveness of downstream thickening film plate with initial thickness of 2D is higher than that of 3D, which will provide a theoretical foundation both for improving cooling performance and reducing turbine blade weight at the same time. The influence of initial impingement gap H is also observed, and the study come to the fact that the best cooling performance occurred in H = 2D.
Axisymmetric Tip Gap Profiling in a Shroudless Axial Turbine
Authors: Abda M. , Rose M. G. 
Published: January 2021

Abstract
The inevitable gap between the rotor tips and the casing promotes flow leakage driven by the pressure difference between the pressure side and suction side of the blade. Axisymmetric tip gap profiling was applied at the blade tip and the casing endwall to reduce the tip leakage maintaining the same gap clearance. The investigation was held on a shroudless single stage axial turbine designed in ETH Zurich University named LISA D. The numerical calculation showed that axisymmetric tip gap profiling reduced the tip leakage flow and improved the efficiency by 0.65% and 0.1% respectively. However, the stage mass flow increased and as a result so did the rotor capacity. When the stage mass flow was reduced to the design value to maintain the design capacity, the effect of the axisymmetric tip gap profiling further improved, due to a reduction in the entropy generation rate of the tip leakage and passage vortices. The tip mass flow reduced by 2.39% and the efficiency improved significantly by 0.6%. It was observed that the tip profiling increased the size of the separation bubble in the PS/tip junction, which increased blockage effect in the gap. Hence, reduced the leaking flow to the SS, which results in weaker tip leakage vortex and its associated losses.
Behavior of a Variable Geometry Turbine Wheel to High Cycle Fatigue
Authors: Avola Calogero , Racca Alberto , Montanino Angelo , Williams Carnell E. , Renella Alfonso , Belluscio Michele 
Published: January 2021

Abstract
Maximization of the turbocharger efficiency is fundamental to the reduction of the internal combustion engine back-pressure. Specifically, in turbochargers with a variable geometry turbine (VGT), energy losses can be induced by the aerodynamic profile of both the nozzle vanes and the turbine blades. Although appropriate considerations on material limits and structural performance of the turbine wheel are monitored in the design and aero-mechanical optimization phases, in these stages, fatigue phenomena might be ignored. Fatigue occurrence in VGT wheels can be categorized into low and high cycle behaviors. The former would be induced by the change in turbine rotational speed in time, while the latter would be caused by the interaction between the aerodynamic excitation and blades resonating modes.
In this paper, an optimized turbine stage, including unique nozzle vanes design and turbine blades profile, has been assessed for high cycle fatigue (HCF) behavior. To estimate the robustness of the turbine wheel under several powertrain operations, a procedure to evaluate HCF behavior has been developed. Specifically, the HCF procedure tries to identify the possible resonances between the turbine blades frequency of vibrations and the excitation order induced by the number of variable vanes. Moreover, the method evaluates the turbine design robustness by checking the stress levels in the component against the limits imposed by the Goodman law of the material selected for the turbine wheel. In conclusion, both the VGT design and the HCF approach are experimentally assessed.
Volumetric Velocimetry Measurements of Purge-Mainstream Interaction in a 1-Stage Turbine
Authors: Carvalho Figueiredo A. J. , Schreiner B. D. J. , Mesny A. W. , Pountney O. J. , Scobie J. A. , Li Y. S. , Cleaver D. J. , Sangan C. M. 
Published: January 2021

Abstract
Air-cooled gas turbines employ bleed air from the compressor to cool vulnerable components in the turbine. The cooling flow, commonly known as purge air, is introduced at low radius, before exiting through the rim-seal at the periphery of the turbine discs. The purge flow interacts with the mainstream gas path, creating an unsteady and complex flow-field. Of particular interest to the designer is the effect of purge on the secondary flow structures within the blade passage, the extent of which directly affects the aerodynamic loss in the stage.
This paper presents a combined experimental and Computational Fluid Dynamics (CFD) investigation into the effect of purge flow on the secondary flows in the blade passage of an optically-accessible 1-stage turbine rig. The experimental campaign was conducted using Volumetric Velocimetry (VV) measurements to assess the three-dimensional inter-blade velocity field; the complementary CFD campaign was carried out using URANS computations. The implementation of VV within a rotating environment is a world first and offers an unparalleled level of experimental detail.
The baseline flow-field, in the absence of purge flow, demonstrated a classical secondary flow-field: the roll-up of a horseshoe-vortex, with subsequent downstream convection of a pressure-side and suction-side leg, the former transitioning in to the passage vortex. The introduction of purge, at 1.7% of the mainstream flow-rate, was shown to modify the secondary flow field by enhancing the passage vortex, both in strength and span-wise migration. The computational predictions were in agreement with the enhancement revealed by the experiments.
The STEP 10 MWe sCO2 Pilot Demonstration Status Update
Authors: Marion John , Lariviere Brian , McClung Aaron , Mortzheim Jason , Ames Robin 
Published: January 2021

Abstract
A team led by Gas Technology Institute (GTI®), Southwest Research Institute® (SwRI®) and General Electric Global Research (GE-GR), along with the University of Wisconsin and Natural Resources Canada (NRCan), is actively executing a project called “STEP” [Supercritical Transformational Electric Power project], to design, construct, commission, and operate an integrated and reconfigurable 10 MWe sCO2 [supercritical CO2] Pilot Plant Test Facility. The $122* million project is funded $84 million by the US DOE’s National Energy Technology Laboratory (NETL Award Number DE-FE0028979) and $38* million by the team members, component suppliers and others interested in sCO2 technology. The facility is currently under construction and is located at SwRI’s San Antonio, Texas, USA campus. This project is a significant step toward sCO2 cycle based power generation commercialization and is informing the performance, operability, and scale-up to commercial plants.
Significant progress has been made. The design phase is complete (Phase 1) and included procurements of long-lead time deliver components. Now well into Phase 2, most major equipment is in fabrication and several completed and delivered. These efforts have already provided valuable project learnings for technology commercialization. A ground-breaking was held in October of 2018 and now civil work and the construction of a dedicated 25,000 ft2 building has progressed and is largely completed at the San Antonio, TX, USA project site.
Supercritical CO2 (sCO2) power cycles are Brayton cycles that utilize supercritical CO2 working fluid to convert heat to power. They offer the potential for higher system efficiencies than other energy conversion technologies such as steam Rankine or Organic Rankine cycles this especially when operating at elevated temperatures. sCO2 power cycles are being considered for a wide range of applications including fossil-fired systems, waste heat recovery, concentrated solar power, and nuclear power generation.
By the end of this 6-year STEP pilot demo project, the operability of the sCO2 power cycle will be demonstrated and documented starting with facility commissioning as a simple closed recuperated cycle configuration initially operating at a 500°C (932°F) turbine inlet temperature and progressing to a recompression closed Brayton cycle technology (RCBC) configuration operating at 715°C (1319 °F).
Flow Physics During Surge and Recovery of a Multi-Stage High-Speed Compressor
Authors: Zhao Fanzhou , Dodds John , Vahdati Mehdi 
Published: January 2021

Abstract
Stall followed by surge in a high-speed compressor can lead to violent disruption of the flow, damage to the blade structures and eventually engine shutdown. Knowledge of unsteady blade loading during surge is crucial for compressor design such as axial gap optimisation. The aim of this paper is to demonstrate the feasibility of using 3D full assembly URANS CFD for modelling surge cycles of an 8-stage high-speed compressor rig.
Results from this work show stalling of the mid-stages is the surge trigger. During the flow reversal, a strong acoustic reflection occurs when the convected entropy perturbations reach the intake opening, which increase the blade loading significantly. During recovery, a hysteresis loop was recorded due to hot air reingestion, which led to a strong shear at mid-span of the IGV/R1 domain and the formation of rotating helical flow structures. The final phase of recovery was accompanied by a 4-cell multi-row tip rotating stall, which was cleared as the compressor recovered to the forward flow characteristic. It was also shown that the single passage model, despite its limitations and shortcomings in modelling recovery, can provide reasonably accurate transient flow features during surge and thus considerable insight to the flow behaviour, which can be used to obtain a first approximation of casing and blade loading.