bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of Nonlinear Systems Under Narrow Band Excitation Using Equivalent Linearization and Path Continuation
Authors: Förster Alwin , Panning-von Scheidt Lars 
Published: September 2021

Abstract
Turbomachines experience a wide range of different types of excitation during operation. On the structural mechanics side, periodic or even harmonic excitations are usually assumed. For this type of excitation there are a variety of methods, both for linear and nonlinear systems. Stochastic excitation, whether in the form of Gaussian white noise or narrow band excitation, is rarely considered. As in the deterministic case, the calculations of the vibrational behavior due to stochastic excitations are even more complicated by nonlinearities, which can either be unintentionally present in the system or can be used intentionally for vibration mitigation. Regardless the origin of the nonlinearity, there are some methods in the literature, which are suitable for the calculation of the vibration response of nonlinear systems under random excitation. In this paper, the method of equivalent linearization is used to determine a linear equivalent system, whose response can be calculated instead of the one of the nonlinear system. The method is applied to different multi-degree of freedom nonlinear systems that experience narrow band random excitation, including an academic turbine blade model. In order to identify multiple and possibly ambiguous solutions, an efficient procedure is shown to integrate the mentioned method into a path continuation scheme. With this approach, it is possible to track jump phenomena or the influence of parameter variations even in case of narrow band excitation. The results of the performed calculations are the stochastic moments, i.e. mean value and variance.
Amplitude-Dependent Damping and Driving Rates of High-Frequency Thermoacoustic Oscillations in a Lab-Scale Lean-Premixed Gas Turbine Combustor
Authors: Hofmeister Thomas , Sattelmayer Thomas 
Published: September 2021

Abstract
This paper presents the numerical investigations of amplitude-dependent stability behavior of thermoacoustic oscillations at screech level frequencies in a lean-premixed, atmospheric, swirl-stabilized, lab-scale gas turbine combustor. A hybrid Computational Fluid Dynamics / Computational AeroAcoustics (CFD / CAA) approach is applied to individually compute thermoacoustic damping and driving rates for various acoustic amplitude levels at the combustors’ first transversal (T1) eigenfrequency. Harmonically forced CFD simulations with the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations mimic the real combustor’s rotating T1 eigenmode. A slow and monotonous increase of the forcing amplitude over time allows observation of the amplitude-dependent flow field and flame evolution. In accordance with measured OH*-chemiluminescence images, a pulsation amplitude-dependent flame contraction is reproduced in the CFD simulations, where acoustically induced backflow at the combustion chamber inlet is identified as the root-cause of this phenomenon. At several amplitude levels, period-averaged flow fields are then denoted as reference states, which serve as inputs for the CAA part. There, eigenfrequency simulations with linearized flow equations are performed with the Finite Element Method (FEM). The outcomes are damping and driving rates as a response to the amplitude dependency of the mean flow field, which combined give the net thermoacoustic growth rate. It is found that driving due to flame-acoustics interactions only governs a weak amplitude dependency, which agrees with prior, experimentally based studies at the authors’ institute. This disqualifies the perception of heat release saturation as the root-cause for limit-cycle oscillations — at least in this high-frequency thermoacoustic system. Instead, significantly increased dissipation due to the interaction of acoustically induced vorticity perturbations with the mean flow is identified, which may explain the formation of a limit-cycle.
Discrete Element Method Simulations of Additively Manufactured Components With Integrated Particle Dampers
Authors: Kiracofe Daniel , Postell Matthew , Scott-Emuakpor Onome , Runyon Brian , George Tommy 
Published: September 2021

Abstract
One major benefit of Additive Manufacturing is parts counts reduction. Several formerly distinct parts can be printed as one unit, reducing cost and weight. However, the interface between parts is often a major source of vibration damping, so eliminating interfaces can lead to fatigue failures. To alleviate this, researchers have been exploring the integration of damping features inside parts. Leaving a small pocket of unfused powder creates a particle damper. Particle dampers have long been known to suppress unwanted vibration. However they are highly complex and predicting their behavior is difficult. The particle damper literature often has contradictory claims, as what works best for one application does not work for another. Because the additive feedstock powder is much smaller (5–50 μm) than particles in typical particle dampers, it is difficult to draw conclusions from the existing literature to develop design guidelines. This papers reports on a Discrete Element Method (DEM) numerical simulation of additively manufactured cantilever beams with a small pocket of unfused powder. DEM explicitly simulates the motion of each particle and their interactions. Previously reported experiments with varying beam geometry showed nearly an order of magnitude difference in damping ratio depending on the location of the pocket along the beam. The simulation was able to accurately predict the damping ratio based on the input geometry. As a result, the correlated simulation tool can be used to optimize future designs. From the simulations, it was observed that particle-wall momentum exchange and particle-particle inelastic collisions appeared to be key contributors to the damping ratio. Additionally, a non-linear subharmonic motion of particles was observed, which suggests additional ways to improve performance.
The Influence of Condensation on the Performance Map of a Fuel Cell Turbocharger Turbine
Authors: Wittmann Tim , Lück Sebastian , Hertwig Tim , Bode Christoph , Friedrichs Jens 
Published: September 2021

Abstract
Exhaust gas of an automotive fuel cell is enriched with water vapour and has a pressure potential which can be utilized by a turbine. The gas expansion in the turbine leads to droplet nucleation and condensation. This results in a release of latent heat and a decrease of the gaseous mass flow which has a considerable influence on the turbine performance. This study aims to numerically investigate the influence of these phenomena on the performance map of the radial turbine of an automotive fuel cell turbocharger. For this purpose, the classical nucleation theory and Young’s droplet growth law are integrated into an Euler-Lagrange approach. The results show an almost linear relation between the pressure ratio and the condensation while the specific aerodynamics of an operating point has only a minor influence. At 80 % relative humidity of the inflow, the investigated turbine showed condensation above a total-to-static pressure ratio of 1.8. Condensation leads to thermal throttling of the turbine and to a temperature increase of the rotor outflow of up to 50 K. Increasing humidity of the inflow increases the power output, but condensation losses reduce the efficiency.
Micromechanical Modeling Tension-Compression Fatigue Hysteresis Loops Model of Fiber-Reinforced Ceramic-Matrix Composites Considering Fibers Failure
Authors: Li Longbiao 
Published: September 2021

Abstract
In this paper, a micromechanical tension-compression fatigue hysteresis loops model of fiber-reinforced ceramic-matrix composite (CMC) was developed considering fibers failure. Multiple fatigue damage mechanisms of fibers failure, interface debonding, slip and wear, and matrix fragmentation were considered and incorporated in the micromechanical fatigue hysteresis loops model. Upon unloading, the unloading stress-strain relationship was divided into three stages, including, (1) Unloading Stage I: the unloading interface counter slip stage and the unloading stress is between the tensile peak stress and the matrix crack closure stress; (2) Unloading Stage II: the unloading partial compressive stage and the unloading stress is between the matrix crack closure stress and the unloading complete compressive stress; and (3) Unloading Stage III: the unloading complete compressive stage and the unloading stress is between the unloading complete compressive stress and the compressive valley stress. Multiple micromechanical damage parameters of fibers failure probability, unloading/reloading transition stress, closure stress of the matrix cracking, compressive transition stress, complete compressive stress, unloading/reloading inverse tangent modulus (ITM), and interface counter slip/new slip ratio (ICSR/INSR) were adopted to characterize the tension-compression stress-strain hysteresis loops. Experimental tension-compression fatigue stress-strain hysteresis loops of unidirectional CMCs were predicted using the developed micromechanical models. The characteristics of the tension-compression fatigue hysteresis loops of unidirectional CMC are analyzed for different material properties, damage state, and tensile fatigue peak stress.
A Novel Vibration-Based Fault Detection Approach of Bolted Engineering Structures Without Reference
Authors: Li Quankun , Shao Zengde , Liao Mingfu 
Published: September 2021

Abstract
Because of some advantages such as low cost, detachability and reusability, bolted joints are widely applied in various open beam-like engineering structures like steel beams and train rails and closed ring-type engineering structures like steel frames and oil pipelines to keep different structural components together. However, bolted engineering structures often encounter vibration-induced joint faults like self-loosening, crack, leakage and corrosion since they are generally subjected to external dynamic loads caused by vibration environments. Joint damages would seriously affect structures’ reliability and durability, and increase maintenance costs. Therefore, fault detection of bolted engineering structures is very important and necessary. For beam-like and ring-type engineering structures with single excitation and multiple damaged bolted joints, various methods monitoring changes in nonlinear structural features have been developed. To avoid the use of structural features from benchmark structures for reference during the derivation of damage indicators, a novel vibration-based fault detection approach utilizing features from damaged structures only is proposed in this study. In the new method, the dynamic model of bolted engineering structures is simplified as a general MDOF model with nonlinear elements simulating nonlinear bolt loosening faults. By changing the value of related mass, three similar equations from the damaged structure are used to form one matrix, and then the singularity of matrix is used to detect the existence and position of faults. Results from simulations on the beam-like and ring-type models with multiple damages demonstrate that the proposed approach could be an effective tool to estimate the state of bolted engineering structures.
A Novel Test Rig Using Air for Investigation of Vibration and Interaction of Two Steam Turbine Control Valves
Authors: Wallat Stefan , Preibisch Stefan , Strauch Matthias , Brillert Dieter 
Published: September 2021

Abstract
The governing of steam turbines is often realised by a set of two or more valves, which control the amount of steam entering the turbine. During part-load operation forces caused by pressure fluctuations, turbulence etc. are acting on the throttling valve and lead to spindle vibrations. Besides these mechanisms, it is assumed that there is also an interaction between the control valves, which leads to another source of vibration.
In this paper, the design of a new test rig using air with two parallel control valves is presented. One aspect of the design is the chosen scaling method, which includes material selection for the valve spindle, and ensures comparability and transferability of the vibrational behaviour to the full scale with steam. Another aspect is the selection of measurement equipment.
The results show that the reasons for valve vibrations can be located both upstream and downstream of the valve seat. Forces caused by pressure fluctuations in and behind the valve gap lead to similar oscillations at both valves. In addition, the upstream valve causes disturbances that lead to partly differing behaviour of the second valve.
Simulation of Passing Wakes Inducing Unsteady Boundary Layer Transition Around Low-Pressure Turbine Blade
Authors: Dufau Antoine , Marty Julien , Man Daniel , Piot Estelle 
Published: September 2021

Abstract
The present study focuses on the very high-lift T106C cascade with passing wakes and aims to validate the γ - Re θ ¯ model of Menter-Langtry used to predict laminar-turbulent transition based on unsteady Reynolds-Averaged Navier-Stokes simulations. The comparison to experimental data provided by Von Karman Institute, shows that the transition model is able to capture the influence of passing wakes on transition phenomenon. Like the experiments, the simulations show a reduction of the time-averaged separation bubble length and of the overall losses in the presence of passing wakes. For this numerical study, four other wakes have been generated in order to study the influence of wake parameters on the transition onset, on the laminar separation bubble formation and on the turbine cascade performances. For a given averaged turbulence intensity and total pressure deficit, thinner wakes seem to have a more positive effect on boundary layer, reducing the separation and the overall losses.
Improved Rotor Design With Combined 3D-2D Probabilistic Approach
Authors: Schuchard Lukas , Voigt Matthias , Mailach Ronald , Dumstorff Peter , de Lazzer Armin , Almstedt Henning 
Published: September 2021

Abstract
Availability and flexibility, largely in terms of start-up times, are becoming paramount for today’s steam turbine operation. Thus, precise knowledge of the stresses components experience and their lifetime consumption in transient regimes is vital for safe turbine operation. A typical lifetime-driving feature is low cycle fatigue in rotor grooves that is caused by rotor-blade root interaction and thermo-mechanical stresses.
In the course of a previous project at Technische Universität Dresden [1, 2] a 2D axisymmetric, transient thermo-mechanical model of an intermediate pressure steam turbine rotor had been developed for probabilistic analysis. Thereby, the blade root compound’s stiffness and the twisting of rhomboid blade roots in circumferential grooves, both of which cannot be modelled directly in 2D, were found to be key drivers for uncertainties in lifetime calculation.
To overcome these limitations, a 3D four-stage, fifteen-blade mechanical model for further analysis was created. The present work introduces this 3D model. It is then employed in a probabilistic sensitivity study to further refine the understanding of the influence of unknown or uncertain boundary conditions on the stresses that drive lifetime consumption. These results for stationary and exemplary transient operation are fed back into fine-tuning the existing 2D model in order to match the 3D calculated stresses. With its far lower computational effort the improved 2D model is well-suited for efficient future probabilistic analysis for robustness estimation and design space exploration.
Synergistic Effect of Soot Formation in Ethylene/Propane Co-Flow Diffusion Flames at Elevated Pressures
Authors: Zheng Dongsheng , Hui Xin , Xue Xin , Liu Weitao 
Published: September 2021

Abstract
The synergistic effect of soot formation refers to the interaction between different fuels during soot forming processes, which results in higher soot formation than any individual fuels. The present study experimentally investigates the synergistic effect of soot formation in co-flow diffusion flames of propane/ethylene fuel mixtures. The total carbon mass flow rate of the propane/ethylene mixture was kept constant at 0.5 mg/s, and the propane carbon ratio (RC) was defined as the ratio of carbon mass flow rate of propane to the total carbon mass flow rate. The laser-induced incandescence (LII) and light extinction (LE) techniques were applied to measure the soot volume fractions (SVF) at pressures of 0.1–0.5 MPa. The results showed strong synergistic effect in propane/ethylene mixtures at atmospheric conditions; however, increasing pressure weakens the synergistic effect. The LII intensity contours showed that the soot formation zone extends when synergistic effect occurs at RC = 0.1 and 0.2 for 0.1 and 0.3 Mpa. The normalized peak SVF showed that synergistic effect monotonically becomes weak with increasing pressure from 0.1 to 0.3 Mpa; meanwhile, the it still stayed strong at 0.2 Mpa when using normalized maximum soot yield, and then turned to be weaker as pressure increases. Further comparison analysis of the SVF profiles between RC = 0 and 0.1 revealed that the synergistic effect occurs at the two-wing area of the sooty flame at low axial flame height, and then gradually becomes stronger with increasing axial flame height in the soot zone for 0.1–0.3 Mpa. To illustrate the pressure effects on synergistic soot formation, numerical analysis in homogeneous closed reactor was conducted and it was found that The PAHs formation competition between C3H3 pathway and HACA mechanism results in the different soot formation phenomenon of ethylene/propane flames.
The Development Problems of Two-Fuel Burner for the Gas Turbine Combustion Chamber
Authors: Vasilyev A. Yu , Chelebyan O. G. , Maiorova A. I. , Tarasenko A. N. , Tarasov D. S. , Zakharov V. M. 
Published: September 2021

Abstract
The work is devoted to the design of a spraying device for the combustion chamber GTE-65.1 on liquid fuel.
The paper presents the following results:
1) The 3D calculations of the air channels characteristics for two burners types — pilot and main — were carried out. Data were obtained on the flow and pressure fields inside and at the burners outlet, and also the volumes of the reverse flow zones.
2) The main and pilot nozzles have been designed for the two spraying devices types. The values of droplet dispersity and spray angle were obtained, depending on the fuel injection pressure.
3) Based on the calculations carried out, the models of two spraying liquid fuel devices were designed and manufactured, the design of which is based on the design of the single-fuel combustion chamber (CC) on natural gas burners for GTE-65.1.
At the next stage of the work, it is planned to carry out experimental studies of the two devices models aimed at obtaining an aerosol mixture with the desired properties to ensure uninterrupted operation of the GTE-65.1 on liquid fuel. Some preliminary experimental data are presented in this paper.
Inlet Distortion Simulations of a Transonic Fan With CFD and Low-Order Methods
Authors: Favaron Carlo , Magrini Andrea , Visentin Alessandro , Menegozzo Luca , Benini Ernesto 
Published: September 2021

Abstract
Future aircraft are expected to have a high level of fuselage-engine integration, exposing the propulsor to non-uniform inflow conditions, in which the performance and stability of the engine fan can be severly affected. This paper proposes a study of a transonic fan subject to inlet distortion by employing steady RANS simulations and mean line calculations. The steady CFD results, although insufficient to correctly measure the interaction of the distortion across the cascade passages, are used as a benchmark to compare the prediction of a leaner low-order tool, adopting a superposition of several 1D calculations in the discretised compressor approach. A continuous total pressure deficit is imposed at the inlet and the distorted operating points are compared to the clean inflow case. The performance drop at the peak efficiency point is similar for the two models, altough the mean-line 1D method fails in closely matching the distribution in the upper span of the blade. The qualitatively similar response of the low-order approach to the distorted inflow should allow for its use in preliminary blade design exploration once improved for high-speed flow prediction.
Experimental Investigation of Dual-Swirl Spray Flame in a Fuel Staged Optical Model Combustor With Laser Diagnostics
Authors: Yang Siheng , Wang Jianchen , Wang Zhichao , Han Meng , Lin Yuzhen , Wang Yexin 
Published: September 2021

Abstract
Lean premixed prevaporized combustors often feature staged combustion with a premixed main flame anchored by the nonpremixed pilot flame to obtain a wide operating range. Interaction between pilot flame and main flame is complex. The present article investigates the flame topologies and flame-fuel interactions in separated stratified swirl flames under various operating conditions (fuel to air ratio FAR and fuel stage ratio α) and injector designs (main stage swirl number Sm and fuel injection angle JA). Experiments are carried out in the centrally staged optical model combustor at inlet pressure P3 = 0.49–0.7 MPa and inlet temperature T3 = 539 K. At first, the flame structures obtained from OH-PLIF are investigated and discussed for the baseline injector (Sm = 0.9, JA = −50°). The V-shaped flame is stabilized in the inner shear layer (ISL) with the flame attachment point located at the lip for the pilot flame mode (α = 1). Dual flame is observed in the combustor for the fuel staged combustion (α &lt; 1): the main flame stabilized in the outer shear layer (OSL) and the pilot flame stabilized in the inner shear layer (ISL). For increasing α from 0.15 to 0.25, gaps between the main flame and pilot flame are decreased, indicating a stronger interaction between the two flames. The flame structure for different injector geometries is then investigated. It is found that the higher main stage swirl number induces a larger flame opening angle, decreasing the interaction between two flames. Fuel injected into crossflow (JA = −50°) is found to generated a more separated flame, decreasing the flame interactions. Finally, fuel distribution measured by kerosene-PLIF is analyzed with the correlation to flame structure. Results show that the existence of a good mixing of fuel and fresh air in ISL and OSL provide favorable conditions for chemical reaction with high heat release. The OH distribution is highly correlated to fuel distribution. The fuel zone is located at the inner side of high OH region, indicating the reaction and heat release take place after the mixing of preheating of fuel-air mixture.
Effect of Tip Vortex Reduction on Air-Cooled Condenser Axial Flow Fan Performance: An Experimental Investigation
Authors: Pretorius J. P. , Erasmus J. A. 
Published: September 2021

Abstract
Large diameter axial flow fans are used in Air-cooled Condenser (ACC) systems of modern power stations. Efficiency improvements on these fans can significantly reduce the ACC power consumption and increase the net sent-out power to the grid. This study targets fan performance enhancement through blade tip vortex reduction. Experimental investigations are performed on a representative ACC scale fan, where tests consider the effects of tip clearance and two new tip endplate designs on fan performance. Test results confirm the findings of previous studies, showing the negative effect of increasing tip clearance on performance. Despite testing limitations, results from tests incorporating endplates show fan static pressure coefficient and efficiency increases over large ranges of flow coefficient compared to the datum fan. These outcomes agree with observations from literature and warrants further exploration. Future work is recommended to provide confirmation on the presented trends.