bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sparse Reconstruction Method of Non-Uniform Sampling and its Application in Blade Tip Timing System
Authors: Tian Jie , Zhang Xiaopu , Chen Yong , Russhard Peter , Ouyang Hua 
Published: January 2021

Abstract
Based on the blade vibration theory of turbomachinery and the basic principle of blade timing systems, a sparse reconstruction model is derived for the tip timing signal under an arbitrary sensor circumferential placement distribution. The proposed approach uses the sparsity of the tip timing signal in the frequency domain. The application of compressive sensing in reconstructing the blade tip timing signal and monitoring multi-mode blade vibrations is explored. To improve the reconstruction effect, a number of numerical experiments are conducted to examine the effects of various factors on synchronous and non-synchronous signals. This enables the specific steps involved in the compressive sensing reconstruction of tip timing signals to be determined. The proposed method is then applied to the tip timing data of a 27-blade rotor. The results show that the method accurately identifies the multi-mode blade vibrations at different rotation speeds. The proposed method has the advantages of low dependence on prior information, insensitivity to environmental noise, and simultaneous identification of synchronous and non-synchronous signals. The experimental results validate the effectiveness of the proposed approach in engineering applications.
Improved Life Assessment for Ni-Based Gas Turbine First Stage High Pressure Turbine Nozzles
Authors: Maggiani Gianluca , Roy Matthew J. , Colantoni Simone , Withers Philip J. 
Published: January 2021

Abstract
Industrial gas turbines (GTs) have advanced and numerous changes in both use, materials employed and design boundaries have occurred. The constraints aimed at lowering NOx emissions for improving the footprint, have driven designers to increase the firing temperatures and to look for improved cooling systems of GTs nozzles. These factors led to more severe operating conditions for hot gas path components and to the need for more accurate and comprehensive thermo-mechanical models for life assessment purposes. Within this context, a Lemaitre-Chaboche viscoplastic model has been coupled with a modified θ-projection creep model for MAR-M-247 material to account for steady-state creep effects in a finite element transient analysis (FEA). These material models have been applied on a cooled, first stage nozzle for a recently developed high-efficiency gas turbine. A verification assessment has been performed on a overfired, off-design transient analysis. The viscoplastic model developed showed the capability of predicting an accurate initiation zone of cracking. The FEA employing the captured inelastic behaviour predicted a high stress state in the location where an experimental crack nucleated. Furthermore, the model demonstrates the capability of using the Lemaitre-Chaboche plastic model coupled with the θ-projection creep model to predict reasonable inelastic strains for the entire lifetime of a gas turbine.
Design and Development of an Engine Nozzle Testing Facility
Authors: Sundararaj Ramraj H. , Sekar Chandra , Arora Rajat , Kushari Abhijit 
Published: January 2021

Abstract
An engine test facility, capable of being operated with different nozzles, has been developed. The shape of this component has evolved substantially, over the years, from seemingly simple circular geometries to very complex geometries designed to address different requirements. There are numerous test facilities that facilitate an extensive standalone component level testing of these components. However, such testing does not offer an insight into the effect these complex geometries will have on the performance of a gas turbine engine. This facility will serve as a demonstration for graduate and doctoral students, enhancing their understanding of engine performance.
The core of the test facility is a single spool turbojet engine from AMT, Netherlands. The engine is instrumented with pressure and temperature measurements at every inter-component location. A conventional intake duct is designed, for measurement of air flow rate. The entire engine is mounted on a 6-axis force measurement device, for measurement of thrust during engine operations. Towards the rear of the engine, a straight duct is attached after the jet pipe, on which any new nozzle can be retrofitted to the engine. To address changes in operating conditions when using different nozzles, the engine is equipped with a suitably designed bleed duct, which is attached onto the jet pipe.
The engine, successfully integrated with all the components, has been subjected to multiple tests at different power settings. The first test was done using the baseline engine, operated at various rotor speeds. The next test was done with a custom nozzle having an area ratio of 2, attached to the jet pipe. Owing to the successful design of the components, the engine performance was measured when operated with a smaller area nozzle.
Impact of Realistic Manufacturing Uncertainties on the Aerodynamic Performance of a Transonic Centrifugal Impeller
Authors: Liu Yiming , Qin Ruihong , Ju Yaping , Spence Stephen , Zhang Chuhua 
Published: January 2021

Abstract
Centrifugal impellers are inevitably subjected to manufacturing uncertainties during the machining process due to many factors. Such manufacturing uncertainties resulting in geometrical variations lead to impeller performance degradation. For a transonic impeller, the complexity of the flow field may amplify this deterioration. In view of this, it is important to have a clear understanding of the effect caused by manufacturing uncertainties. However, relevant studies are rare and lack consideration of realistic manufacturing uncertainties. Furthermore, the high dimensionality caused by high-fidelity uncertainty model makes the computational fluid dynamics (CFD) unaffordable, making the development of high-efficiency and high-fidelity method for high-dimensionality uncertainty quantification (UQ) problems become urgent.
To tackle these limitations, a group of 92 machined centrifugal impellers were scanned, and a statistical model of realistic manufacturing uncertainties was built. With the combination of the CFD simulations and Non–Intrusive Polynomial Chaos (NIPC) methods, the influence of manufacturing uncertainties on the polytropic efficiency and flow field of a transonic centrifugal impeller was quantified. To achieve a good trade-off between the computational efficiency and accuracy for the UQ, a Dual Dimensionality Reduction (DDR) method was proposed, by which the dimensionality of the spatially varying input, i.e., the manufacturing error field, was reduced to 3. The results showed that the manufacturing errors of machined impellers follow Gaussian distributions with a mean error of zero and a shape increased standard deviation near the blade leading edge. The polytropic efficiency of the examined impeller exhibited a negatively skewed distribution and the mean efficiency was reduced by 0.34%. The flow mechanisms behind the performance degradations mainly lay in the increased shock losses near the blade tip and separation losses near the hub. The present study provides a fundamental contribution to the uncertainty quantification of turbomachinery and establishes a theoretical foundation for the development of robust centrifugal impellers.
LES Informed Data-Driven Modelling of a Spatially Varying Turbulent Diffusivity Coefficient in Film Cooling Flows
Authors: Ellis Christopher D. , Xia Hao , Page Gary J. 
Published: January 2021

Abstract
A novel data-driven approach is used to describe a spatially varying turbulent diffusivity coefficient for the Higher Order Generalised Gradient Diffusion Hypothesis (HOGGDH) closure of the turbulent heat flux to improve upon RANS cooling predictions in film cooling flows. Machine learning algorithms are trained on two film cooling flows and tested on a case of a different density and blowing ratio. The Random Forests and Neural Network algorithms successfully reproduced the LES described coefficient and the magnitude of the turbulent heat flux vector. The Random Forests model was implemented in a steady RANS solver with a k-ω SST turbulence model and applied to four cases. All cases saw improvements in the predicted Adiabatic Cooling Effectiveness (ACE) over the cooled surface compared to the standard Gradient Diffusion Hypothesis (GDH) approach, but only minor improvements in the centreline and lateral spread are seen compared to a HOGGDH model with a constant cθ of 0.6. Further improvements to cooling predictions are highlighted by extending these data-driven approaches into turbulence modelling to improve flow field predictions.
Meanline Analysis and CFD Study of a Radial Inflow Turbine With Vaneless Distributor for Low Temperature Organic Rankine Cycle
Authors: Deligant M. , Braccio S. , Capurso T. , Fornarelli F. , Torresi M. , Sauret E. 
Published: January 2021

Abstract
The Organic Rankine Cycle (ORC) allows the conversion of low-grade heat sources into electricity. Although this technology is not new, the increase in energy demand and the need to reduce CO2 emissions create new opportunities to harvest low grade heat sources such as waste heat. Radial turbines have a simple construction, they are robust and they are not very sensitive to geometry inaccuracies. Most of the radial inflow turbines used for ORC application feature a vaned nozzle ensuring the appropriate distribution angle at the rotor inlet. In this work, no nozzle is considered but only the vaneless gap (distributor). This configuration, without any vaned nozzle, is supposed to be more flexible under varying operating conditions with respect to fixed vanes and to maintain a good efficiency at off-design. This paper presents a performance analysis carried out by means of two approaches: a combination of meanline loss models enhanced with real gas fluid properties and 3D CFD computations, taking into account the entire turbomachine including the scroll housing, the vaneless gap, the turbine wheel and the axial discharge pipe. A detailed analysis of the flow field through the turbomachine is carried out, both under design and off design conditions, with a particular focus on the entropy field in order to evaluate the loss distribution between the scroll housing, the vaneless gap and the turbine wheel.
Signal Processing Techniques to Detect Centrifugal Compressors Instabilities in Large Volume Power Plants
Authors: Niccolini Marmont Du Haut Champ Carlo Alberto , Ferrari Mario Luigi , Silvestri Paolo , Massardo Aristide Fausto 
Published: January 2021

Abstract
The present paper shows signal processing techniques applied to experimental data obtained from a T100 microturbine connected with different volume sizes.
This experimental activity was conducted by means of the test rig developed at the University of Genoa for hybrid systems emulation. However, these results can be extended to all advanced cycles in which a microturbine is connected with additional external components which lead to an increase of the plant volume size. Since in this case a 100 kW microturbine was used, the volume was located between the heat recovery unit outlet and the combustor inlet like in the typical cases related to small size plants. A modular vessel was used to perform and to compare the tests with different volume sizes.
The main results reported in this paper are related to rotating stall and surge operations. This analysis was carried out to extend the knowledge about these risk conditions: the systems equipped with large volume size connected to the machine present critical issues related to surge and stall prevention, especially during transient operations towards low mass flow rate working conditions.
Investigations conducted on acoustic and vibrational measurements can provide interesting diagnostic and predictive solutions by means of suitable instability quantifiers which are extracted from microphone and accelerometer data signals. Hence different possible tools for rotating stall and incipient surge identification were developed through the use of different signal processing techniques, such as Wavelet analysis and Higher Order Statistics Analysis (HOSA) methods. Indeed, these advanced techniques are necessary to maximize all the information conveyed by acquired signals, particularly in those environments in which measured physical quantities are hidden by strong noise, including both broadband background one (i.e. typical random noise) but also uninteresting components associated to the signal of interest. For instance, in complex coupled physical systems like the one it is meant to be studied, which do not satisfy the hypothesis of linear and Gaussian processes inside them, it is reasonable to exploit these kinds of tools, instead of the classical Fast Fourier Transform (FFT) technique by itself, which is mainly adapt for linear systems periodic analysis.
The proposed techniques led to the definition of a quantitative indicator, the sum of all auto-bispectrum components modulus in the subsynchronous range, which was proven to be reliable in predicting unstable operation. This can be used as an input for diagnostic systems for early surge detection. Furthermore, the presented methods will allow the definition of some new features complementary with the ones obtainable from conventional techniques, in order to improve control systems reliability and to avoid false positives.
Impact of Turbine-Strut Clocking on the Performance of a Turbine Center Frame
Authors: Sterzinger P. Z. , Merli F. , Peters A. , Behre S. , Heitmeir F. , Göttlich E. 
Published: January 2021

Abstract
Previous studies have indicated a potential for improving the performance of a Turbine Center Frame (TCF) duct by optimizing the clocking position between the high-pressure-turbine (HPT) vanes and TCF struts. To assess the impact of clocking on the performance, a new test vehicle with a clockable ratio of HPT vanes to TCF struts, consisting of an HPT stage (aero-dynamically representative of the second-stage HPT engine), a TCF duct with non-turning struts, and a first-stage low-pressure turbine vane, was designed and tested in the transonic test turbine facility (TTTF) at Graz University of Technology.
This paper quantifies the performance impact of clocking and describes the mechanisms causing TCF flow field changes, leveraging both experimental and numerical data. Other areas in the TCF duct impacted by the choice of the HPT vane circumferential position including the strength of unsteady HPT-TCF interaction modes, TCF strut incidence changes, and carry-over effects to the first LPT vane are additionally highlighted.
Five-hole-probe (5HP) area traverses and kielhead-rake traverses were used to asses the flow field at the TCF-exit and calculate the pressure loss. The flow field at the TCF exit shows significant differences depending on the circumferential position of the HPT vane. A relative performance benefit of 5% was achieved. A series of unsteady RANS simulations were performed to support the measured results, understand and characterize the relevant loss mechanisms. The observed performance improvement was related to interaction between the HPT secondary -flow structures and the TCF struts.
The impact of the HPT vane clocking on the unsteady flow field downstream of the TCF was investigated using Fast-Response Aerodynamic Pressure Probe (FRAPP) area traverses, analyzed by means of modal decomposition. In this way the individual azimuthal modes were ranked by their amplitude and a dependency of the clocking position was observed and quantified.
Metallurgical Evaluation of an Additively Manufactured Nickel-Base Superalloy for Gas Turbine Guide Vanes
Authors: Bridges Alex , Shingledecker John , Torkaman Alex , Houck Lonnie 
Published: January 2021

Abstract
In this paper, AM produced test samples of a IN939 derivative nickel-based alloy were tested for tensile, fatigue and creep properties at temperatures up to 871°C and compared to the traditional cast material. Initial results showed improved tensile and fatigue strength, but a reduction in both long-term creep rupture strength and creep ductility in the AM produced material compared to the cast baseline. Microstructural observations in the AM produced material showed a significant difference in the overall metallurgical characteristics beyond grain size compared to the castings. In addition to the laboratory studies and to provide a direct comparison between AM and traditional castings, both AM and cast components were tested in live engine trials exceeding 4,000 hours.
Detailed scanning electron microscopy techniques were used to evaluate the evolution of grain size, gamma-prime, MC carbide and secondary M23C6 carbide size and distribution throughout a 5-step heat treatment process. Post-test evaluations for creep rupture specimens of the AM material showed creep cavitation near grain boundaries. The results from the AM produced material are discussed in comparison to expected properties and characteristics from traditional casting methods. Results have shown that material production and short-term metallurgical properties are sufficient to produce quality high temperature stationary guide vanes, but additional research and development is needed to optimize the AM process to achieve high-temperature creep behavior comparable to castings.
Experimental Study of the Endwall Heat Transfer of a Transonic Nozzle Guide Vane With Upstream Jet Purge Cooling: Part 1 — Effect of Density Ratio
Authors: Mao Shuo , Sibold Ridge A. , Lash Stephen , Ng Wing F. , Xu Hongzhou , Fox Michael 
Published: January 2021

Abstract
Nozzle guide vane platforms often employ complex cooling schemes to mitigate ever-increasing thermal loads on endwall. Understanding the impact of advanced cooling schemes amid the highly complex three-dimensional secondary flow is vital to engine efficiency and durability. This study analyzes and describes the effect of coolant to mainstream blowing ratio, momentum ratio and density ratio for a typical axisymmetric converging nozzle guide vane platform with an upstream doublet staggered, steep-injection, cylindrical hole jet purge cooling scheme. Nominal flow conditions were engine representative and as follows: Maexit = 0.85, Reexit/Cax = 1.5 × 106 and an inlet large-scale freestream turbulence intensity of 16%. Two blowing ratios were investigated, each corresponding to upper and lower engine extrema at M = 3.5 and 2.5, respectively. For each blowing ratio, the coolant to mainstream density ratio was varied between DR = 1.2, representing typical experimental neglect of coolant density, and DR = 1.95, representative of typical engine conditions.
An optimal coolant momentum ratio between = 6.3 and 10.2 is identified for in-passage film effectiveness and net heat flux reduction, at which the coolant suppresses and overcomes secondary flows but imparts minimal turbulence and remains attached to endwall. Progression beyond this point leads to cooling effectiveness degradation and increased endwall heat flux. Endwall heat transfer does not scale well with one single parameter; increasing with increasing mass flux for the low density case but decreasing with increasing mass flux of high density coolant. From the results gathered, both coolant to mainstream density ratio and blowing ratio should be considered for accurate testing, analysis and prediction of purge jet cooling scheme performance.
CFD-CRN Study of NOx Formation in a High-Pressure Combustor Fired With Lean Premixed CH4 / H2 - Air Mixtures
Authors: Vashishtha Ashish , Yousefian Sajjad , Goldin Graham , Frojd Karin , Jella Sandeep , Bourque Gilles , Monaghan Rory F. D. 
Published: January 2021

Abstract
The main motivation of this study is to investigate detailed NOx and CO formation in high-pressure dump combustor fired with lean premixed methane-air mixture using CFD-CRN hybrid approach. Further, this study is extended to investigate the effect of H2 enrichment on emission formation in the same combustor. Three-dimensional steady RANS CFD simulations have been performed using a Flamelet Generated Manifold (FGM) model in Simcenter STAR-CCM+ 2019.2 with the DRM22 reduced mechanism. The CFD simulations have been modelled along with all three heat transfers modes: conduction, convection and radiation. The conjugate heat transfer (CHT) approach and participating media radiation modelling have been used here. Initially, CFD simulations are performed for five lean equivalence ratios (ϕ = 0.43–0.55, Tinlet = 673 K, Vinlet = 40 m/s) of pure methane-air mixture operating at 5 bar. The exit temperature and flame-length are compared with available experimental data. The automatic chemical reactor network has been constructed from CFD data and solved using the recently developed reactor network module of Simcenter STAR-CCM+ 2019.2 in a single framework for each cases. It is found out that the CRNs up to 10,000 PSRs can provide adequate accuracy in exit NOx predictions compared to experiments for pure methane cases. The contribution of NOx formation pathway, changes from N2O intermediate to thermal NO as equivalence ratio increases. Further studies are performed for two equivalence ratios (ϕ = 0.43 and 0.50 to simulate the impact of H2 addition (up to 40% by volume) on NOx formation pathways and CO emission. It is found out here that the contribution from NNH pathway increases for leaner equivalence ratio cases (ϕ = 0.43), while thermal pathway slightly increases for ϕ = 0.50 with increase in H2 content from 0% to 40%.
Investigation of Moisture Removal on Last Stage Stationary Blade in Actual Steam Turbine
Authors: Sato Hideaki , Tabata Soichiro , Tochitani Naoto , Sasao Yasuhiro , Takata Ryo , Osako Masaki 
Published: January 2021

Abstract
This paper presents an investigation for wet steam flow through the slit on the last stage hollow stationary blades of a steam turbine. The aim of this investigation is to evaluate the moisture removal performance by measuring the quantity of drain and “Motive steam” from some kinds of slit configurations under the actual turbine operating environment. Motive steam is effective steam sucked from the slit and removed together with drain.
The measurement was carried out on a 105 MW class steam turbine at “T-point”, a verification power plant owned by Mitsubishi Hitachi Power Systems, Ltd. [MHPS]. The measurement system was constructed right under the turbine. Even though both drain and steam were sucked from the slit on the stationary blade, drain was separated by the cyclone separator and measured by detecting the water level accumulated in the water level tank by the optical pulse sensor. For the measurement of the motive steam quantity, the choked flow rate measured by the critical nozzle was used to obtain the slit characteristic data of pressure ratio (ratio of blade surface static pressure to outer ring inner pressure). The critical nozzles were arranged in parallel, and the measurement was carried out by adopting a multi-valve switching system. And CFD slit analysis, in which the drain discharge path inside the last stage hollow stationary blade is modeled, was also carried out. The CFD slit analysis was compared with the measurement result to examine the internal flow. The corresponding CFD was calculated by ANSYS CFX. And the coarse water droplets analysis by the kinetic equation of the discrete droplet model was also carried out.
From the measurement result and the evaluation, it was confirmed that the slit with groove configuration is more effective than the normal slit under the actual turbine operating environment.