bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Development of a Synchronized Harmonic Balance Method for Multiple Frequencies and its Application to LPT Flows
Authors: Crespo Javier , Contreras Jesús 
Published: January 2021

Abstract
The aim of this paper is to describe the development and application of a multi-frequency harmonic balance solver for GPUs, particularly suitable for the simulation of periodic unsteadiness in nonlinear turbomachinery flows comprised of a few dominant frequencies, with an unsteady multistage coupling that bolsters the flow continuity across the rotor/stator interface.
The formulation is addressed with the time-domain reinterpretation, where several non-equidistant time instants conveniently selected are solved simultaneously. The set of required frequencies in each row is driven into the governing equations with the help of almost-periodic Fourier transforms for time derivatives and time shifted boundary conditions. The spatial repetitiveness inside each row can be exploited to perform single-passage simulations and the relative circumferential positioning of the rotors or stators and the different blade or vane counts is tackled by means of adding fictitious frequencies referring to non-adjacent rows therefore taking into account clocking and indexing effects.
Existing multistage row coupling techniques of harmonic methods rely on the use of non-reflecting boundary conditions, based on linearizations, or time interpolation, which may lead to Runge phenomenon with the resulting numerical instabilities and non-preserving flux exchange. Different sets of time instants might be selected in each row but the interpolation in space and time across their interfaces gives rise to robustness issues due to this phenomenon. The so-called synchronized approach, developed in this work, consist of having the same time instances among the whole ensemble of rows, ensuring that flux transfer at sliding planes is applied more robustly. The combination of a set of shared non-equidistant time instances plus the use of unequal frequencies (real and fictitious) may spoil the Fourier transforms conditioning but this can be dramatically improved with the help of oversampling and instants selection optimization. The resulting multistage coupling naturally addresses typical numerical issues such as flow that might reverse locally across the row interfaces by means of not using boundary conditions but a local flux conservation scheme in the sliding planes.
Some examples will be given to illustrate the ability of this new approach to preserve accuracy and robustness while resolving them. A brief analysis of results for a fan stage and a LPT multi-row case is presented to demonstrate the correctness of the method, assessing the impact in the modeling accuracy of the present approach compared with a time-domain conventional analysis. Regarding the computational performance, the speedup compared to a full annulus time-domain unsteady simulation is a factor of order 30 combining the use of single-passage rows and time spectral accuracy.
Assessment of MULTALL As CFD Code for the Analysis of Tube-Axial Fans
Authors: Danieli Piero , Masi Massimo , Delibra Giovanni , Corsini Alessandro , Lazzaretto Andrea 
Published: January 2021

Abstract
This work deals with the application of the open source CFD code MULTALL to the analysis of tube-axial-fans. The code has been widely validated in the literature for high-speed turbomachine flows but not applied yet to low speed tutbomachines. The aim of this work is to assess the degree of reliability of MULTALL as a tool for simulating the internal flow in industrial axial-flow fan rotors. To this end, the predictions of the steady-state air flow field in the annular sector of a 315mm tube-axial fan obtained by MULTALL 18.3 are compared with those obtained by two state-of-the-art CFD codes and experimental data of the global aerodynamic performance of the fan and the pitch-wise averaged velocity distribution downstream of the rotor. All the steady-state RANS calculations were performed on either fully structured hexahedron or hexa-dominant grids using classical formulations of algebraic turbulence models. The pressure curve and the trend of the aeraulic efficiency in the stable operation range of the fan predicted by MULTALL show very good agreement with both the experimental data and the other CFD results. Although the estimation of the fan efficiency predicted by MULTALL can be noticeably improved by the more sophisticated state-of-the-art CFD codes, the analysis of the velocity distribution at the rotor exit supports the use of MULTALL as a reliable CFD analysis tool for designers of low-speed axial fans.
Load Influence on Hydrostatic Oil Film Journal Bearing Stiffness Characteristics
Authors: Moroz Leonid , Romanenko Leonid , Kochurov Roman , Kashtanov Evgen 
Published: January 2021

Abstract
Hydrostatic bearings are widely used in industry, including aerospace and energy sectors. Hydrodynamic lubrication mechanism has been well studied analytically and experimentally and various types of bearings were developed to provide increasing operating speed, load capacity, stability and efficiency for modern rotating machines. Hydrostatically lubricated bearings have principal difference (in comparison with hydrodynamic bearings) and their characteristics have been an area of continued research.
The goal of this work is to develop a robust algorithm, which can predict hydrodynamical characteristics and dynamic stiffness and damping coefficients of hybrid and hydrostatic bearings with increased accuracy and which can be used for engineering/design purposes. The developed approach is based on Reynold’s equations, where the unknown parameters are the rotor position and fluid pressure in recess pockets. Finite difference method in combination with the successive over-relaxation algorithm is used for a numerical solution of Reynold’s equations. Newton’s method is applied to solve the generated system of equations.
Applying the developed approach, the effect of load influence on the hydrodynamical and the dynamic stiffness characteristics has been studied. Several hydrostatic bearing designs which are based on the published data were considered to compare the results calculated applying the approach with the experimental and theoretical data given in the literature. Performed study shows when journal eccentricity can’t be neglected while simulating hydrostatic bearing characteristics. Simulations also allow for analysis of how different design/geometrical parameters and initial conditions (supply pressure) influence bearing performance characteristics.
The developed approach can be utilized as a practical tool which allows for the prediction of performance characteristics of hydrostatic bearing with increased accuracy.
Multiphase Rotating Detonation Engine
Authors: Dunn Ian , Ahmed Kareem 
Published: January 2021

Abstract
The first experimental evidence of a solid-gas multiphase rotating detonation engine. Coal particles, carbon black with a volatility of 1% and a carbon concentration of 99%, were detonated successfully over many operational parameters. These operational parameters surrounding the various points of investigation are shown in multiple 2-D slices as well as plotted in one 3-D graph to show the effects of varying carbon concentrations. These parameters include: variation in total mass flux injected into the annulus ranging from (≅120–270 kg/(s*m2), variation in hydrogen-air equivalence ratio (0.65–1.0), and finally variation in total concentrations of carbon (0–42.5%). High-speed backend imaging allowed for the analysis of the detonation wave dynamics, where detonation velocities were deduced using Discrete Fourier Transforms. By varying the parameters mentioned above, detonation velocities experienced in the detonation channel allowed for an introduction of an optimal operational point. When carbon was injected into very lean hydrogen-air conditions, the detonation was over-driven, causing fluctuations in the detonation velocities upwards of ∼100 m/s. As carbon concentrations increased further, detonation wave velocities relative to Chapman-Jouguet detonation velocities decreased.
Improvements of Experimental Research of Wet Steam in Turbines Using CFD Simulations
Authors: Kolovratnik Michal , Jun Gukchol 
Published: January 2021

Abstract
The Czech Technical University in Prague (CTU) has been conducting both theoretical and experimental research on wet steam for over 50 years. Part of this research has focused on the development of an instrument for measuring the structure of the liquid phase of wet steam — an optical extinction probe. The measurements of the wet steam structure using our optical extinction probe take place in operative steam turbines. Due to the non-negligible interaction of the probe with the flow field in its vicinity, the wet steam parameters within the probe measuring space change. This probe-flow field interaction (PFFI) negatively affects the accuracy of the measurement of the liquid phase structure.
This paper presents partial results of our research into the interaction between the optical probe and the surrounding flow field. Particularly, it is the result of CFD simulations of wet steam (WS) flow in the low-pressure section of a 1000 MW nuclear plant steam turbine, in which the probe has been used repeatedly. In the simulations we consider, non-equilibrium condensation allows for the observation of the formation and development of the liquid phase within the turbine. The influence of PFFI on the liquid phase structure is evaluated by a coefficient called the Probe Influence Factor (PIF). In this work, the PIF values are presented for 3 varying traversing positions of the probe along the L-1 stage turbine blade. The use of the PIF to analyse the experimental measurement results is also discussed.
The second part of the paper deals with the possibility of modifying the shape of the probe measuring head. Based on detailed analysis of the CFD simulations of PFFI, modifying the shape of the probe is proposed to reduce this interaction. The benefit of this change is evaluated using CFD simulations. Comparisons between the PIF coefficients of the original and modified optical probes indicate that modifying the shape may reduce the PFFI influence on experimental measurements.
Parametric Study on Micro-Roughness Shapes for Enhanced Jet Impingement Heat Transfer
Authors: Devakottai Ramaswamy , Madhavan Srivatsan , Singh Prashant , Ekkad Srinath V. 
Published: January 2021

Abstract
Development of efficient cooling technologies are imperative to support the constant push for higher turbine inlet temperatures to achieve increased overall turbine efficiency. High-pressure stage turbine blades are subjected to hostile environment involving high temperature turbulent flow exiting from the combustor section. The blade leading edge is subjected to flow stagnation and hence requires special attention in terms of both, internal and external cooling. This study is focused on improving the internal side heat transfer coefficient by installing novel micro-roughness elements on the target wall. The study is based on Singh, Prashant, et al. “Effect of micro-roughness shapes on jet impingement heat transfer and fin-effectiveness.” International Journal of Heat and Mass Transfer 132 (2019): 80–95, where different micro-roughness shapes were investigated experimentally and numerically. The authors proposed that the novel concentric-cylinder shaped roughened geometry exhibited highest fin-effectiveness. Present study reports the effect of three micro-roughness shapes, viz. cylindrical, cubic and concentric cylinder. Conjugate heat transfer study was performed, and the heat transfer performance was reported in the form of local Nusselt number and globally averaged fin-effectiveness. An array jet configuration of 5 × 5 jets with a jet-to-jet spacing of X/Djet = Y/Djet = 3 and jet-to-target plate spacing of Z/Djet = 1 was maintained for jet-diameter based Reynolds number (ReDjet) ranging from 3,000 to 12,000. Investigation on the effect of pin-fin shapes shows that the concentric-shaped micro pin-fin element had the highest fin-effectiveness of 2.45 at ReDjet = 12,000. Further, pin-fin optimization studies were performed for the concentric cylinder pin-fin shape, where the effect of pin-fin height and the effect of internal to external diameter ratio was studied. The pin-fin effectiveness increased with increase in height and diameter ratio, and a maximum fin effectiveness was observed for maximum pin-fin height.
An Additively Manufactured Four Sensor Fast Response Aerodynamic Probe
Authors: Chasoglou Alexandros , Tsirikoglou Panagiotis , Kalfas Anestis , Abhari Reza 
Published: January 2021

Abstract
The current work describes the design, development and testing of a miniature fast response aerodynamic probe (FRAP) with 4 sensors (4S), able to perform measurements in unsteady three-dimensional flow field. Moreover, the calibration and first results with the newly developed probe is also provided. The miniature FRAP-4S demonstrates a 3 mm tip diameter, which represents a 25% reduction in diameter size, in comparison to a first generation FRAP-4S, without any loss in terms of measurement bandwidth. The 3 mm outer casing of the probe is additively manufactured with a high-precision binder jetting technique. In terms of aerodynamic performance, the probe demonstrates high angular sensitivity up to at least ± 18° incidence angle in both directions.
To evaluate the measurement accuracy of the newly developed FRAP-4S, measurements are performed at the Laboratory for Energy Conversion (LEC) in both a round axisymmetric jet and an one-and-a-half stage, unshrouded and highly-loaded axial turbine configuration. Turbulence measurements performed with the miniature FRAP-4S are compared against hot-wire studies in round free-jets found in the literature. Good agreement in both trends but also absolute values is demonstrated. Moreover, the performance of the probe is compared against traditional instrumentation developed at LEC, namely miniature pneumatic and FRAP-2S probes. The results indicate that the FRAP-4S, despite its larger size in comparison to the other probes tested, can resolve the main flow patterns, while the highest deviations occur in the presence of highly skewed and sheared flows. Furthermore, the additively manufactured probe was proven to be robust after more than 50 hours of testing in representative turbine environment configuration. Finally, it should be highlighted that the newly developed FRAP reduces measurement time by a factor of three in comparison to FRAP-2S, which directly translates to reduced development time and thus cost, during turbomachinery development phase.
Experimental Evaluation of Dynamic Characteristics of Circular Arc Spring Dampers for Rotating Machinery
Authors: Takeuchi Ryota , Ishimaru Hidetsugu , Yamashita Hideaki , Yabui Shota , Inoue Tsuyoshi 
Published: January 2021

Abstract
This study presents an experimental evaluation of the dynamic characteristics of the circular arc spring damper (CASD), which attenuates the vibration of rotating machinery. The CASD is a novel type of fluid film damper that has two or more arc-shaped beams and dual slits (radial clearances) formed by wire electric discharge machining (WEDM). A major advantage of CASDs over conventional Squeeze Film Dampers (SFDs) with squirrel-cage springs is their compactness and low weight. The concept of CASDs was originally proposed by Kanki et al. in 2005. However, the basic characteristics of this type of damper, including the influence of the geometries, added mass coefficients, and cross-coupled terms of dynamic coefficients have not been investigated. To clarify these characteristics, a series of excitation tests was conducted on three types of CASDs to identify their dynamic coefficients. The features of the newly developed test rig and experimental results are presented in this study. Tested dampers have the same outer diameter (160 [mm]) and damper width (44 [mm]) but different arc patterns (2-arc or 4-arc) and radial clearances (about 0.3 or 1.2 [mm]). All dampers were tested in both open-end and end-sealed configuration. The influence of the end-seal clearances (about 0.1 to 0.4 [mm]) was also examined. The following results were obtained: (1) 4-arc type CASDs have greater damping than that of 2-arc types; (2) CASDs have a considerable amount of added mass coefficients, especially in the end-sealed condition; (3) Smaller end-seal clearances make the damping and added-mass coefficients significantly larger; (4) A large level of damping can be produced with dashpot configuration (large radial clearances and small end-seal clearances), though the added-mass effect becomes more prominent; (5) Cross-coupled terms are very small in centered / small amplitude motion. These new findings can be utilized for the design and application of CASDs to real rotating machineries.
Optimization of Turbine Squealer Tip Cooling Design by Combining Shaping and Flow Injection
Authors: Duan P. H. , He L. 
Published: January 2021

Abstract
In this study, a turbine squealer tip is optimized by a multi-objective genetic algorithm (MOGA) with varying the squealer heights and the tip cooling configurations. The three objectives selected are the aerodynamic efficiency, the film cooling effectiveness and the surface fluid temperature variance. The multi-scale methodology is implemented to reduce the computational cost and to skip the meshing of cooling holes. Two optimization approaches are compared: a) a conventional method that optimizes an uncooled shape first and then the cooling configuration sequentially, and b) a method that optimize shaping and cooling concurrently. The concurrent method is found to obtain a heat transfer performance that is not achieved by the conventional optimization. Moreover, by adding the cooling, the performance ranking of the uncooled blades in terms of the aerodynamic efficiency is changed. These observations are due to the strong interaction between the coolant and the tip leakage flow. They indicate that the coolant injected at the tip is not passive as expected in the conventional film cooling designs. By altering the tip leakage flow structure, the coolant can reduce the tip leakage loss, which contradicts the conventional wisdom that the added coolant should always lead to extra losses due to the extra mixing. More detailed observations of the flow field indicate that the influence of the squealer height towards the aerodynamic efficiency is caused by two competing effects: the blockage effect to reduce the tip leakage mass flow rate and the sudden expansion loss effect to generate additional losses. The heat transfer performance can be significantly influenced by increasing the squealer height because of the trapped coolant in the cavity.
A Novel Modular Tool for the Simulation of Gas Turbine-Based Cogeneration Systems
Authors: Carcasci Carlo , Lubello Pietro , Brogelli Riccardo , Snickars Carlo , Vettori Gregorio 
Published: January 2021

Abstract
The effort in the adoption of energy efficient technologies and the attempt at reducing CO2 emissions has brought a new wave in the diffusion of distributed generation and a renewed interested in CHP systems, especially in the case of industrial cogeneration applications. It is therefore of primary importance for prime movers ‘producers — as Baker Hughes — to develop fast and reliable simulation methods that are able to estimate the overall performances of the proposed plants in order to help the customer assessing the feasibility of the investment.
The aim of this paper is to introduce a newly developed tool for the simulation of design and off-design conditions of gas turbine-based cogeneration systems, where heat is recovered through a Heat Recovery Steam Generator. The tool is meant to be driven by a small amount of inputs, making it possible to define sharp strategies for the design of such plants since the early phases of interaction with customers.
Design points have been varied to assess their influence on the off-design working points of the plant and on the overall performances, which have been considered through the parameters of global efficiency and Primary Energy Saving.
Results have highlighted the importance of considering the off-design effects in the simulation of CHP systems, both from a correct evaluation of plant’s critical operating parameters and from a correct estimation of plant’s performances.
Experimental Study on Thermal Efficiency of a Multi-Jet Anti-Icing System With Piccolo Tube
Authors: Bu Xueqin , Huang Ping , Sun Haoyang , Lin Guiping 
Published: January 2021

Abstract
An experimental study was conducted to investigate the jet impingement thermal efficiency of a typical model for a multijet anti-icing system under different experimental conditions such as air mass flow rate at the jet exit, piccolo tube position and circumferential angle of jet holes. The experimental results showed that jet mass flow rate, velocity at the jet exits (whether choking conditions were established at the jet exits or not) and piccolo tube-to-leading edge distance within the cavity had significant influence on thermal efficiency of the anti-icing system. The heat flux on the external surface of leading edge, diameter of jet holes and circumferential angle of jet holes had a measurable but small effect on thermal efficiency of the anti-icing system.
Accuracy and Sensitivity Analysis of Aerodynamic Performance Prediction Models for Transonic Axial-Flow Compressors
Authors: Zhang Xiawen , Ju Yaping , Zhang Chuhua 
Published: January 2021

Abstract
The mean-line method, as the corner stone of preliminary aerodynamic design of axial-flow compressors, is heavily dependent on the accuracy and robustness of empirical prediction models, mainly the deviation models and loss models. A large number of such models have been developed, however, a comprehensive evaluation of their prediction capabilities was lacked yet. To carry out the accuracy and sensitivity analysis of these prediction models developed in the both academic and industry communities, we here developed a one-dimensional mean-line method which implements several widely used deviation and loss models. Then, the developed mean-line method was applied to predict the speed-lines of aerodynamic performance for three representative transonic axial-flow compressors, i.e., NASA Rotor 35, NASA Stage 35 and NASA 74A first front three-stage. The parallel coordinates method was particularly adopted to effectively perform the sensitivity analysis of totally 2448 combinations of deviation and loss models through a heuristic comparison of the model predictions with the available experimental data. The accuracy analysis indicates that, by using the best model combinations, the prediction error of peak efficiency point is generally kept below 2% whereas that of surge margin varies significantly from 3.03% to 18.93%. However, the most accurate model combination is dependent on the compressor type and rotational speed. The sensitivity analysis shows that the prediction robustness is remarkably influenced by the deviation model accounting for axial velocity ratio effect, the design shock loss model and the off-design total loss model. This work provides the design engineers with prediction model selection, and the model developers with prediction improvement direction for axial-flow compressors.