bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Damping Behavior of Strongly Coupled Structure and Acoustic Modes of a Rotating Disk With Side Cavities
Authors: Barabas Botond , Benra Friedrich-Karl , Petry Nico , Brillert Dieter 
Published: September 2021

Abstract
High cycle fatigue is a continuous research topic within the turbomachine community. One field of the investigations is the fluid-structure interaction of 2-D impellers, which can be simplified as disks with their surrounding side cavities. In modern machines the pressure ratios tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the disk structure play an important role in machine design. However, they are not fully understood, yet. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at higher pressure levels. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood.
This paper summarizes the test rig setup and focuses on one of the main findings of an extensive experimental research project, which investigated the fluid-structure interaction of a disk with side cavities, at the University of Duisburg-Essen. The focus lays on the damping behavior of strongly coupled acoustic and structure modes.
Measurement results gathered at the aeroacoustic test rig are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the half-width method. Compared to the weakly coupled structure mode, the damping of the strongly coupled structure mode is some orders higher at atmospheric pressure conditions. The damping ratio decreases with an increasing pressure level, however still remains some orders higher, than the damping of weakly coupled structure modes.
Supercritical Pseudo Boiling in Cubic Equations of State
Authors: Banuti Daniel T. 
Published: September 2021

Abstract
Today, modern combustion systems and advanced cycles often reach operating pressures exceeding the working fluid’s or fuel’s critical pressure. While the liquid-gas coexistence line is the dominant feature in the fluid state space at low pressures, a supercritical analog to boiling, pseudo boiling, exists at supercritical pressures. Pseudo boiling is the transcritical state transition between supercritical liquid states and supercritical gaseous states, associated with peaks in heat capacity and thermal expansion. This transition occurs across a finite temperature interval. So far, the relation between the pseudo boiling line of tabulated hi-fi p-v-T data and the behavior of efficient engineering cubic equations of state (EOS) is unclear. In the present paper, we calculate the slope of the pseudo boiling line analytically from cubic equations of state. The Redlich-Kwong EOS leads to a constant value for all species, Peng-Robinson and Soave-Redlich-Kwong EOS yield a cubic dependency of the slope on the acentric factor. For more than twenty compounds with acentric factors ranging from −0.38 to 0.57 calculated slopes are compared with NIST data and vapor pressure correlations. Particularly the Peng-Robinson EOS matches reference data very well. Classical empirical values of Guggenheim or Plank & Riedel are obtained analytically. Then, pseudo boiling predictions of the Peng Robinson EOS are compared to NIST data. Deviations in transition temperature interval, and nondimensional parameters of the distributed latent heat are compared. Especially the different caloric behavior of tabulated fluid data for H2, N2, CO2, and H2O cannot be reproduced by the Peng Robinson EOS. These results may open the way towards new EOS with specific emphasis on Widom line and supercritical transition behavior.
Effects of Rotation on the Flow Structure in a Compressor Cascade
Authors: Ventosa-Molina Jordi , Koppe Björn , Lange Martin , Mailach Ronald , Fröhlich Jochen 
Published: September 2021

Abstract
In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration, one with the Coriolis force removed, without any other change. This setup allows very clean assessment of the influence of rotation. The turbulence-resolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region the Tip Leakage Vortex is enlarged and destabilised. Inside the tip gap the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly.
Rotordynamic Evaluation of a Large High-Speed Rotor Equipped With Flexure Pivot Journal Bearings and Integral Squeeze Film Damper
Authors: Vannini Giuseppe , Innocenti Alice , Cangioli Filippo , Jongsoo Kim 
Published: September 2021

Abstract
The current oil and gas market trends lead the compressor OEMs to increase the rotational speed and maximize the efficiency given a target power output. Especially when applied to large process gas centrifugal compressors, characterized by high-flexibility ratio, the achievement of these targets pushes the rotordynamic design towards its limit in terms of API requirements.
Tiling pad journal bearings (TPJBs) are commonly adopted in high-speed applications for their inherent stability characteristics that permit to ensure the rotordynamic stability and eliminate self-induced sub-synchronous vibrations.
The experimental activities subject of this paper aim to assess, for the first time, the rotordynamic behaviour of a large dummy rotor (6 meter long and total weight of 8 tons) equipped with Flexure Pivot tilting-pad journal bearing and Integral squeeze film damper (ISFD). This system level testing program has been performed in the Authors’ high-speed balancing bunker properly equipped with special instrumentation such as: flow meters and pad temperature probes to monitor journal bearing behaviour, displacement probes to measure rotor vibrations relative to the bearings.
The main objective of the experimental activity is the full assessment of the rotordynamic response and the selection of the best configuration to target the design requirements (e.g. FPJB and “Active ISFD” vs. FPJB and “Inactive ISFD”).
On the Performance of Wave-Like Dry Friction and Piezoelectric Hybrid Flexible Dampers
Authors: Wu Y. G. , Fan Y. , Li L. , Zhao Z. M. 
Published: September 2021

Abstract
This paper proposes a flexible dry friction plate to mitigate the vibration of thin-walled structures for one resonance crossing. Based on a cantilever beam-friction damper finite element model, the geometry and material parameters of the friction plate are optimized numerically through steady-state response analyses by the widely-used Multi-Harmonic Balance Method (MHB-M). In order to further improve the damping effect, piezoelectric material is distributed to the flexible damper, and two types of dry friction and piezoelectric hybrid dampers are explored, namely semi-active and passive, respectively. For semi-active hybrid dampers, piezoelectric material is used as an actuator to adjust the normal load applied to the friction interface in real time, so that the friction damping is improved. For passive ones, piezoelectric material is used as a transducer, which dissipates the strain energy stored in the wave-like plate by the shunting circuit, additional shunted piezoelectric damping contributes to the total output damping accordingly. Better damping effect compared with the friction baseline is realized for the two types ideally. This damping module has a simple structure and avoids the problem of installation and maintenance of piezoelectric material which is generally bonded to the host structure. Technical challenges are: the semi-active type requires excessive voltage applied to the piezoelectric actuator, while the passive one needs to connect a programmable synthetic circuit.
Mechanism Analysis of the Influence of Blade Thickness Deviation on The Performance of Axial Flow Compressor
Authors: Ji Tianyuan , Chu Wuli , Guo Zhengtao , Yang Jibo 
Published: September 2021

Abstract
The deviation between the actual processed blade and the designed blade shape inevitably occurs in the process of compressor blade manufacturing. Rotor37 was used as the research object and a three-dimensional steady Reynolds averaged Navier-Stokes simulation method was adopted in order to study the influence mechanism of blade thickness deviation on blade performance. The blade was parameterized and the blade thicknesses were increased or decreased uniformly, with changes of 0.06mm and 0.1mm respectively. Results illustrate that the blade thickness deviation affects the total pressure ratio, isentropic efficiency and stability margin of the single-stage rotor. Increasing the blade thickness will inhibit the transport of low speed airflow from blade root area to blade tip area along the radial direction. In the peak efficiency condition, this inhibit will cause low speed airflow to converge in the middle of the blade and increase the flow separation loss; while in the reference near stall condition, the inhibition of low speed airflow transport will weaken the accumulation of low energy airflow in the tip area, reduce the loss in the corner area, and expand the stable working range of the blade. Further, increasing the blade thickness causes the shock wave position to move backward and the shock wave intensity will decrease.
Overview of Unsteady Phenomena Emerging in a Stalled 1.5-Stage Transonic Compressor
Authors: Mütschard Silas , Werner Jan , Karl Maximilian , Kunkel Christian , Schiffer Heinz-Peter , Biela Christoph , Robens Sebastian 
Published: September 2021

Abstract
A new transonic compressor test rig for gas turbine front stages was commissioned at the Technical University of Darmstadt in 2018. In the first measurement campaign numerous transient stall maneuvers were conducted by throttling the compressor beyond its stability limit. Several distinct phenomena can be observed during in-stall operation.
This work gives an overview of those different manifestations of stall with focus on classification and characterization. For this purpose, detailed post-processing and unsteady data analysis are conducted providing information in terms of operating points, propagation speeds of disturbances, structural behavior of the rotor as well as unsteady wall pressure fields.
The authors propose explanations for the different phenomena and possible influences of the rig on the in-stall behavior are discussed. Finally, an overview of the occurrence of the detected phenomena is given.
Effective Clearance And Differential Gapping Impact on Seal Flutter Modelling and Validation
Authors: Corral Roque , Greco Michele , Vega Almudena 
Published: September 2021

Abstract
This paper presents an update of the model derived by Corral and Vega (2018, “Conceptual Flutter Analysis of Labyrinth Seal Using Analytical Models. Part I - Theoretical Support”, ASME J. of Turbomach., 140 (12), pp. 121006) for labyrinth seal flutter stability, providing a method of accounting for the effect of dissimilar gaps. The original CV model was intended as a conceptual model for understanding the effect of different geometric parameters on the seal stability comprehensively, providing qualitative trends for seal flutter stability. However, the quantitative evaluation of seal flutter, and the comparison of the CV model with detailed unsteady numerical simulations or experimental data, require including additional physics. The kinetic energy generated in the inlet gap is not dissipated entirely in the inter-fin cavity of straight-through labyrinth seals, and part is recovered in the downstream knife. This mechanism needs to be retained in the seal flutter model. It is concluded that when the theoretical gaps are identical, the impact of the recovery factor on the seal stability can be high. The sensitivity of the seal stability to large changes in the outlet to inlet gap ratio is high as well. It is concluded that fin variations due to rubbing or wearing inducing inlet gaps more open than the exit gaps lead to an additional loss of stability concerning the case of identical gaps. The agreement between the updated model and 3D linearized Navier-Stokes simulations is excellent when the model is informed with data coming from steady RANS simulations of the seal.
Weldability and Properties of Newly Developed LW4280 High Gamma Prime Nickel Based Superalloy for 3D AM and Repair of Turbine Engine Components
Authors: Gontcharov Alexandre B. , Lowden Paul , Jena Ashutosh , Kwon Sunyong , Brochu Mathieu 
Published: September 2021

Abstract
Chemical composition, structure, mechanical and oxidation properties of welds produced utilizing laser direct energy deposition process of a newly developed LW4280 welding powder will be presented. Crack-free and high-density specimens were fabricated for manufacturing standard and subsized tensile test samples as per ASTM E-8. Optical and scanning electron microscopy revealed the formation of epitaxial grain growth during solidification of the welding pool followed by precipitation of fine gamma prime phase during the reheating from the subsequent weld layers. A sub-solvus primary aging temperature determined using Thermo-Calc software followed by secondary aging resulted in precipitation of above 49% of cuboidal γ′ phase. Excellent ultimate tensile strength of 1310 MPa (190 ksi), 0.2% yield strength of 855 MPa (124 ksi), and elongation of 18.7% were measured at ambient temperature. At 926°C (1700°F), the tensile testing yielded of 579 MPa (84 ksi), 0.2% yield strength of 462 MPa (67 ksi), and elongation of 18.8%. Cyclic oxidation resistance of the LW4280 weld material at 1120°C (2048°F) was superior to Rene 80 and Mar M247 while slightly below Rene 142.
Numerical Investigations of a High Pressure Compressor Exposed to Unsteady Pressure Gain Combustion Employing Data-Driven Methods
Authors: Bicalho Civinelli de Almeida Victor , Peitsch Dieter 
Published: September 2021

Abstract
Pressure gain combustion (PGC) should substantially improve the thermodynamic efficiency of gas turbines by increasing the fluid total pressure as it traverses the combustion chamber. However, PGC introduces additional unsteadiness to the intrinsically complex turbomachinery flow. A high pressure compressor, located right upstream of the PGC section, is therefore constantly exposed to flow fluctuations, experiencing drop in efficiency, increase in pressure loss as well as higher stalling and structural failure risks. This numerical work analyzes how one stage of a well-established engine, namely the NASA EEE core compressor, reacts to the disturbances induced by the potential implementation of PGC. Unsteady computational fluid dynamics are employed with boundary conditions simulating the combustion unsteadiness.
The main focus of the current paper is the application of data-driven methods, including the proper orthogonal decomposition (POD) and the dynamic mode decomposition (DMD), when comparing the high pressure compressor baseline operation with the PGC-disturbed case. Representative flow features and their frequency content, not identifiable with typical methods such as phase-averaging, are easily extracted from snapshots sequences. The results not only allow the identification of the most relevant coherent structures present in the unsteady flow, but also show how they change in the presence of PGC. This contribution sheds light on how novel PGC technology can be integrated with turbomachinery components, identifying modifications in the main flow features with the use of advanced decomposition techniques.
Proof-Of-Concept of a Thermal Barrier Coated Titanium Cooling Layer for an Inside-Out Ceramic Turbine
Authors: Gauvin-Verville Antoine , Dubois Patrick K. , Picard Benoit , Landry-Blais Alexandre , Plante Jean-Sébastien , Picard Mathieu 
Published: September 2021

Abstract
Increasing turbine inlet temperature (TIT) of recuperated gas turbines would lead to simultaneously high efficiency and power density, making them prime candidates for low-emission aeronautics applications, such as hybrid-electric aircraft. The Inside-out Ceramic Turbine (ICT) architecture achieves high TIT by using compression-loaded monolithic ceramics. To resist inertial forces due to blade tip speed exceeding 450 m/s, the shroud of the ICT is made of carbon-polymer composite, wound around a metallic cooling ring. This paper demonstrates that it is beneficial to use a titanium alloy cooling ring with a thermal barrier coating (TBC), rather than nickel superalloys, for the interstitial cooling ring protecting the carbon-polymer from the hot combustion gases. A numerical Design of Experiments (DOE) analysis shows the design trade-offs between the minimum safety factor and the required cooling power for multiple geometries. An optimized high-pressure first turbine stage of a 500 kW microturbine concept using ceramic blades and a titanium cooling ring in an ICT configuration is presented. Its structural performance (minimum safety factor of 1.4) as well as its cooling losses (2% of turbine stage power) are evaluated. Finally, a 20 kW-scale prototype is tested at 300 m/s and a TIT of 1375 K during 4hrs to demonstrate the viability of the concept. Experiments show that the polymer composite was kept below its maximum safe operating temperature and components show no early signs of degradation.
Prediction and Validation of the Transient Pressure Field in a Centrifugal Compressor With Vaned Diffuser for the Application in High Cycle Fatigue Stress Estimations
Authors: Bacakci Gökay , Fröhlig Friedrich , Stuhldreier Lukas , Deutsch Johannes , Jeschke Peter 
Published: September 2021

Abstract
In this paper, the transient pressure field in a centrifugal compressor is predicted by the Nonlinear Harmonic (NLH) method, as well as the unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations and validated by transient pressure measurements. The accurate prediction of these pressure fluctuations is crucial, because they have a significant influence on the High-Cycle-Fatigue (HCF) behavior in turbomachinery applications. As the first step, excited and non-excited rotational speeds, caused by rotor-stator interactions, are identified by modal analysis performed on a single segment impeller assembly. In order to eliminate any additional pressure fluctuations caused by blade vibrations, three non-excited operating points at different rotational speed levels are selected for the transient flow simulations. The transient pressure fields predicted by these methods are validated by transient pressure measurements at three circumferentially different locations on the impeller shroud. A study of the modeling of these fast-response pressure probes in numerical calculations also falls within the scope of this work in order to identify its effect on the transient pressure amplitudes. The results of the numerical calculations and measurements are compared in the frequency domain by performing Fast-Fourier Transformations (FFT) and Short-Time Fourier Transformations (STFT) on the numerical and experimental data respectively. It is shown that the transient pressure field in a single staged centrifugal compressor is calculated accurately by both of the numerical methods in comparison to the transient flow measurements. This paper demonstrates that the numerical modeling of the fast-response pressure sensors has a significant impact on the unsteady pressure amplitudes, which needs to be taken into account for a reliable experimental validation process.
Heat Transfer Enhancement in a Double Sequential Impingement Channel
Authors: Gaffuri Michele , Ott Peter , Naik Shailendra , Henze Marc 
Published: September 2021

Abstract
Sequential impingement channels can reduce the adverse effect of crossflow in narrow impingement channels, as well as increase the cooling efficiency. In this work, sequential impingement channels are experimentally investigated using the transient liquid crystal technique to assess their thermal performances. A low heat transfer region is identified in the downstream part of the first channel where the flow is discharged into the second plenum. Various means of increasing the heat transfer at this location are investigated. Ribs on the target plate allow for an increase of the average heat transfer coefficient with small losses in pressure. Reducing the channel cross-section increases the mean flow velocity and, combined with the ribs, allows for a further increase of the heat transfer. Additionally, the geometrical changes of the channel caused by the addition of a ramp with a rounded corner, allow to decrease the pressure losses associated with the discharge into the second plenum, which is not optimal in the baseline configuration due to the sharp corner of the purge hole. Further reducing the cross-section to increase the heat transfer, however, increases the pressure losses due to the small open area in the transition zone.
Design and Tests of a New Damper for a Gas Turbine Thin-Shell Duct
Authors: Gabriele Serena , Di Sisto Paolo , Del Vescovo Giuseppe , Simone Conti 
Published: September 2021

Abstract
Gas turbine (GT) liners, transition ducts and exhaust diffusers are large thin-shell ducts bounded by two barrels, typically characterized by multiple natural frequencies inside the operating speed range of the engine rotor.
In most applications, GT ducts are supported on one side only and they are free to expand inside the gas turbine so to avoid thermal distresses.
The GT ducts are typically damped structures able to prevent high cycles fatigue failures. Damping is provided by sliding features as insulation or bolted joints.
This paper describes the redesign of a transition duct (TD) after it was discovered that in some operating conditions, duct could crack for high cycle fatigue (HCF).
The TD connects the flow path of the gas generator turbine with the flow path of the power turbine.
The new TD has been made more robust, but it has also been equipped of dampers capable to operate at high temperature.
Starting from the analyses of field data, a predictive FEA model has been developed and validated. After a deep investigation of the TD modes that could be excited by flow path and/or by rotor vibrations, it was decided to add two dampers, one for each barrel of the TD.
Due to internal space limitations, a new type of damper has been designed for the external barrel.
Both dampers have been sized using FEA. Harmonic analyses rather than forced response transient analyses have been performed so to verify the effectiveness of the new design. In the simulations, dampers have been replaced by harmonic forces able to reproduce the friction force of the dampers.
Validation of the method and damper calibration has been done by performing lab tests and full-size TD tests.