bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas Turbine Rotor Damper Lift-Off Study
Authors: Manoharan S. , Abhimanyu S. , Babu S. , Tognarelli Leonardo , Peano Guido 
Published: October 2022

Abstract
Gas turbine rotor system is subjected to vibratory stresses due to excitations caused by various excitation sources at varying energy levels. To dissipate the energy that occurs in the rotating system, damping is induced internally or externally. Damping is achieved by having damper at the appropriate location in the rotor system. The damper needs to have a provision to assemble in the rotor assembly, which is typically a split, facilitating the damper to wind and unwind in circumferential direction. The damper used in the rotating system needs to be axisymmetric with a suitable cross-section, to achieve the required level of damping. As the damper is used at the interior location of the rotor system, it needs to build necessary preloading by itself in such a way that the damper rotates with the rotor system during operation. Damper design study is very vital in deciding the shape of the damper in such a way that it provides efficient damping and minimizing the vibratory stress. At some vibrating condition, damper tends to detach from its supporting feature which is referred to as damper lift-off. The magnitude of this lift-off is expected to be higher at the split regions compared to other circumferential location of the damper, which makes the damper design very complex. When the damper split region passes through the maximum lobe and minimum lobe position of any nodal diameter, the region near the split tends to lift-off from its support and behaves like a simply supported beam and cantilever beam respectively. A careful consideration of this damper lift-off phenomenon in damper design is key towards achieving a robust damper design. Various types of simulation techniques using finite element analysis are followed in performing necessary design assessments. This paper is intended to describe the steps followed in performing damper design study to help achieving design robustness.
Experimental Study on the Surface Geometry of Foam-Metal Casing Treatment
Authors: Wang Yuqing , Sun Dakun , Li Jia , Zhang Jinming , Dong Xu , Sun Xiaofeng 
Published: October 2022

Abstract
Foam-metal casing treatment (FMCT) installed over the rotor tip has been proved to affect the performance of compressors. To develop a design strategy for FMCTs, different parameters of surface geometries (SGs), including the shape, staggering, and denseness, based on a 2mm-depth groove were designed to model the FM surface morphology, which dominates the transverse flow resistance near the end wall region. Eight axial installation locations of the casing treatment were set on the tested low-speed compressor, among which the optimum stall margin improvement (SMI) up to 11.5% with 1% efficiency loss was achieved by a brush-type SG at a near mid-chord axial location. But the acoustic measurements of all the SGs showed nearly no benefit of broadband noise reduction. Accompanied by the investigations into the flow field and pressure unsteadiness, the mechanism of FMCT on compressor stability and noise attenuation were discussed and the design strategy was obtained.
Modeling the Convection of Entropy Waves in Strongly Non-Parallel Turbulent Flows Using a Linearized Framework
Authors: Kaiser Thomas Ludwig , Noiray Nicolas , Male Quentin , Oberleithner Kilian 
Published: October 2022

Abstract
The study investigates two effects, which can lead to a mitigation of entropy waves in a gas turbine combustor: Mean flow shear dispersion and turbulent mixing. Using a transport equation for coherent fluctuations of a passive scalar in combination with a k-ε turbulence model, the advection and turbulent diffusion of entropy waves is modeled. The method is applied to a flow in a duct of rectangular cross section, previously investigated with experimental and numerical means by Weilenmann et al. [1]. We analyze the impact of a steady jet in crossflow (JIC) in the rectangular duct on the mitigation of entropy waves by the mean flow shear dispersion mechanism. First, a comparison to Large Eddy Simulation (LES) results demonstrates the capability of the linearized approach to quantify the decay due to turbulent mixing and mean flow shear dispersion. The results further indicate that the inhomogeneous highly three dimensional flow profile and increased turbulence caused by the JIC significantly mitigates entropy waves due to the enhancement of the mean flow shear dispersion and turbulent mixing in comparison to a base line configuration without the JIC. Second, we investigate in a parameter study the effect of turbulent mixing on the mitigation of the entropy waves. It is shown that the results are highly case dependent. While in some situations an increase in turbulent mixing — as expected — leads to a mitigation of entropy waves, in other situations it may have the opposite effect. We demonstrate that this is the case if turbulent mixing annihilates entropy fluctuations selectively in those regions, which contribute significantly to mean flow shear dispersion.
Three-Dimensional Multi-Objective Design Optimization of a 6.5-Stage Axial Flow Compressor Blades With Lean and Twist
Authors: Lei Fan , Zhang Xiawen , Ju Yaping , Zhang Chuhua 
Published: October 2022

Abstract
With great development in numerical optimization and wide application of computational fluid dynamic methods, the three-dimensional design optimization of multi-stage axial flow compressor will become a routine practice in the future. The common critical issue arisen from the practice is how to carry out the three-dimensional design optimization of multi-stage axial flow compressor at an affordable design cost. To tackle this problem, a three-dimensional design optimization method is developed, in which reference vector guided evolutionary algorithm, the ensemble of surrogate models, adaptive sampling method and computational fluid dynamics (CFD) simulation are integrated, to improve the adiabatic efficiency and broaden the stability margin. The ensemble of surrogate model consists of linear regression model, support vector regression model, Kriging model and radial basis function. The blade lean and twist are set as design variables for all the stators while for the rotors only the blade twist is considered. By taking advantage of these advanced methods, a 6.5-stage axial flow compressor with totally 60 design variables is optimized at design speed-line. CFD calculations show that the adiabatic efficiency at design point is increased by 0.88%. The stall margin is increased from 12.72% to 14.08%, and the choke margin is increased from 20.41% to 21.35%. Flow analysis of the optimal compressor indicates that the blade lean is mainly responsible for suppressing the endwall flow separation while the blade twist for the stage match between adjacent blade rows. This work is of great significance for three-dimensional multi-objective design optimization of multi-stage axial flow compressor.
Influence of Gas-To-Wall Temperature Ratio on the Leakage Flow And Cooling Performance of a Turbine Squealer Tip
Authors: Yan Dongjie , Li Jieling , Xie Wenbo , Wang Zhaoguang , Lu Shaopeng , Jiang Hongmei , Zhang Qiang 
Published: October 2022

Abstract
In high-pressure turbines, there is a large difference in temperature between the mainstream and the turbine blade surface. Most of the turbine blade tip heat transfer researches were conducted under the assumption that the Over-Tip-Leakage (OTL) flow field is independent of the wall thermal condition. Recent numerical and experimental studies have revealed that two-way coupling effect between aerodynamics and heat transfer should not be neglected. The heat transfer coefficient obtained by conventional method is not able to match realistic engine condition accurately. This study investigates the impact of wall thermal boundary condition on tip cooling performance of squealer turbine blades. The RANS CFD result was validated against experimental tip heat transfer data obtained from a highspeed test rig with the effect of high-speed relative casing motion. The aerothermal performance for both uncooled and cooled squealer tips were studied at two different gas-to-wall temperature ratios 1.7 and 1.1, with the mainstream gas temperature held constant at 340 K. It was found that the location and strength of cavity vortices varied with different wall thermal boundary conditions, leading to different signatures in tip heat transfer and cooling performance. It is recommended that experimental heat transfer data and film cooling effectiveness obtained at near adiabatic wall boundary condition should be corrected before their application to the tip cooling design process. It would be more reliable to match the wall-to-gas temperature ratio during tip experimental study.
An Upgraded Chemical Kinetic Mechanism for ISO-Octane Oxidation: Prediction of Polyaromatics Formation in Laminar Counterflow Diffusion Flames
Authors: Ramirez Hernandez Astrid , Kathrotia Trupti , Methling Torsten , Braun-Unkhoff Marina , Riedel Uwe 
Published: October 2022

Abstract
Iso-octane is widely recognized as a prominent candidate to represent the oxidation of iso-alkanes within jet fuel and gasoline surrogates. This work evaluated a chemical kinetic mechanism for iso-octane focusing on the model’s capability to predict the formation of polycyclic aromatic hydrocarbons (PAHs). As the model is intended to be further coupled with soot models, the chemical kinetic mechanism must supply good predictability of the formation and consumption of PAHs considered as major soot precursors. A first validation of the iso-octane sub-model as incorporated within ESTiMatE-Mech, using experimental data from literature, reveals the need to improve the sub-model. Considerable deviations were observed in the prediction of the PAHs, although concentration profiles of major species and fundamental combustion properties such as ignition delay time and laminar flame speed were accurately predicted. Through rate of production and sensitivity analyses of the mechanism, nine reactions were identified to have a strong influence in the (over)prediction of the PAHs. These reactions have been modified based on information gathered from literature resulting in an updated version of the mechanism called ESTiMatE-Mech_mod. Simulation results with this modified mechanism showed that this updated mechanism is now capable of predicting well the targeted PAHs, while retaining the good initial prediction of the major species concentration profiles as well as of laminar flame speeds and ignition delay times.
Experimental Assessment of a Reverse Brayton Cycle Based on Automotive Turbochargers and E-Chargers for Cryogenic Applications
Authors: Serrano José R. , Dolz Vicente , Ponce-Mora Alberto , López-Carrillo Juan A. 
Published: October 2022

Abstract
The utilization of automotive engine components for the development of a reverse Brayton cycle is shown in this study. The well-known characteristics of turbochargers and electrical centrifugal compressors commonly used in the automotive industry is a starting point for developing an experimental cycle configuration of a reverse Brayton refrigeration cycle with the ability to achieve up to 115K after a multi-stage compression with intermediate cooling and a single-stage expansion in a radial turbine using air (R-729) as working fluid. The use of a variable nozzle turbine allows to evaluate the optimum rack position for each operating point, as well as having control over refrigeration capacity. Studies over the minimum cycle pressure at the inlet of the first stage of compression have been performed to assess the possible benefit of creating vacuum or pressurize the working fluid. A 1m3 cooling chamber was attached to the installation to test the ability of cooling different thermal loads working under different operation ways, open or closed cycle, this is, letting the working fluid to interact with the thermal load or cooling it through a heat exchanger. The evaluation of thermodynamic parameters allows to obtain the coefficient of performance (COP) of the installation as well as the efficiency of each component. The analysis of turbomachinery performance will allow identifying weak points to improve cycle performance, and to improve the coupling model between the rotatory machines as well as to adapt the size of the installation to the refrigeration capacity required for different applications.
Experimental Investigation Into the Effect of a Ceramic Matrix Composite Surface on Film Cooling
Authors: Wilkins Peter H. , Lynch Stephen P. , Thole Karen A. , Vincent Tyler , Quach San , Kaufman Eleanor 
Published: October 2022

Abstract
Ceramic matrix composite (CMC) components enable high turbine entry temperatures, which can lead to improved efficiencies in gas turbines. Implementing film cooling over CMC components, similar to how it is employed for conventional metal components, can extend part life and push operating temperatures beyond the temperature capabilities of CMCs alone. However, CMCs have unique surface topology that can influence film cooling performance. Often this topology takes the form of an irregular wavy pattern due to the weave of the fibers that make up the strengthening component of the composite. In this study, shaped 7-7-7 film cooling holes are embedded in a 5 Harness Satin weave pattern representative of a CMC, at two orientations of the pattern. Detailed adiabatic film effectiveness measurements are obtained in a wind tunnel using an infrared camera while near-wall flowfield measurements are obtained with a high-speed particle image velocimetry system. A range of blowing ratios between one and three are investigated at a density ratio of 1.5 and freestream turbulence intensities of 0.5% and 13%. Across the majority of the tested conditions, the CMC surfaces result in lower film cooling performance than a smooth surface. At a freestream turbulence intensity of 0.5%, the adiabatic film effectiveness is moderately insensitive to blowing ratio for both weave orientations. The boundary layer over the CMC surfaces increases the mixing between the coolant and the mainstream through a combination of increased turbulence, reduced near wall velocities, and a thicker boundary layer.
Aero-Thermal Analysis of Non-Axisymmetric and Flat Endwalls Under the Operational and Geometrical Uncertainties
Authors: Tao Zhi , Wang Jie , Song Liming , Li Jun 
Published: October 2022

Abstract
Given the rapidly increasing turbine inlet temperature and aerodynamic loads, turbine endwalls are bearing exceptionally harsh flow and thermal conditions. Therefore, the turbine endwalls must be meticulously and efficiently designed, with special attention to the influences of geometric and operational uncertainties. This is of vital importance to the efficient and reliable operation of gas turbines. In this paper, a generic uncertainty analysis framework was established for different endwall schemes. Operational fluctuations of the mainstream and geometrical tolerances of the purge slot were taken as input uncertainties. The aero-thermal performance of a benchmark flat endwall and a non-axisymmetric endwall contouring (NEC) was statistically analyzed and compared under the propagation of the input uncertainties. Results showed that, despite the impact of the input uncertainties, the NEC endwall remained effective in enhancing the statistical performance of all three criteria. It was noteworthy that the NEC endwall also greatly reduced the sensitivity of the areas dominated by secondary vortices to the input uncertainties. However, its profiled regions were found to be highly sensitive to the input uncertainties. Furthermore, the influential uncertain parameters were also identified and compared for the flat and NEC endwalls. The inlet flow angle was the most significant parameter for the three performance criteria of the flat endwall. However, for the NEC endwall, the importance of the inlet flow angle was significantly reduced. Instead, the mainstream turbulence intensity became the most influential parameter for the aerodynamic and heat transfer performance, and the slot width became the most influential parameter for the film cooling performance. The underlying flow physics was well explained by CFD results.
Experimental Force Coefficients for a Fully-Partitioned Pocket Damper Seal and Comparison to Other Two Seal Types
Authors: Delgado Adolfo , San Andrés Luis , Yang Jing , Thiele Jonathan 
Published: October 2022

Abstract
Labyrinth seals (LS), honeycomb seals (HCS) and hole-pattern seals, pocket damper seals (PDS) and fully-partitioned damper seals (FPDS) serve as balance pistons on the discharge side of barrel type centrifugal compressors. These seals, facing large pressure differentials along with significant changes in gas density, produce sizeable lateral forces that impact compressor stability and its rotordynamic performance. There is extensive archival data on the dynamic forced performance of LS and textured surface seals. However, the experimental database for a FPDS is insufficient, thus a comprehensive comparison of their dynamic force performance against that of textured surface seals is missing. The paper presents experimentally derived rotordynamic force coefficients for a FPDS along with a direct comparison to published data for an HCS and a LS, both similar in size and in operating conditions. The dynamic load tests with the FPDS include operation at a shaft speed (Ω) of 10 krpm (rotor surface speed of 60 m/s) while supplied with air at Pin = 70 bar and Tin =10 °C, and a discharge at Pout = 0.25, 0.5, and 0.65 of Pin. The pre-swirl circumferential velocity at the seal inlet is low, approximately 6% of rotor surface speed. The FPDS having eight pockets × eight axial blades produces a direct stiffness (K) increasing with excitation frequency (ω), though K &lt; 0 for the lowest pressure ratio PR = (Pout/Pin) = 0.25. The cross-coupled stiffness (k) is invariant to frequency whereas the direct damping (C) steadily decreases as ω/Ω → 1, and then increases for larger frequencies. Hence, the effective damping coefficient (Ceff = C – k/ω) is approximately constant for ω &lt; Ω, while increasing for higher frequencies. For the three PRs, the FPDS leakage is roughly up to 26% larger than the HCS leakage, while the 20-blade LS leaks in between both. The comparison of results shows the LS has insignificant forces compared to those from the HCS and FPDS, both producing a comparable Ceff and similar crossover frequencies (Ceff &gt; 0). The HCS produces a large direct stiffness (K), three to four times that from the FPDS. Comparison of CFD predictions for the FPDS against the experimental force coefficients shows significant differences, in particular an over estimation of direct stiffness as the frequency grows along with a lower direct damping for frequencies equal and above the shaft speed. Besides manufacturing considerations, a FPDS is a better alternative to an HCS whose large centering stiffness (K) may affect the compressor critical speed, hence shortening the separation margin with respect to the operating speed.
Investigation on Strain and Stress Principal Axes in Unsteady DNS Turbine Data
Authors: Lengani D. , Simoni D. , De Vincentiis L. , Ðurović K. , Pralits J. , Henningson D. S. , Hanifi A. 
Published: October 2022

Abstract
In the present work, high-fidelity direct numerical simulation (DNS) data has been adopted in conjunction with an extensive post-processing to provide a detailed description of the turbulence characteristics and its production within a low pressure turbine (LPT) cascade blade passage operating with unsteady inflow. Proper orthogonal decomposition is used at first to provide the statistical representation of the flow structures that occur in the blade passage. Different inlet turbulent scales are isolated and a representation of the turbulence produced in the passage is also provided. Principal axes of the Reynolds stress and the strain tensors have been analyzed to provide further insight on the turbulence production. Since each spatial POD mode captures a quota of the Reynolds stress tensor, the POD modes are well suited to provide reduced order models (ROMs) that represent the different scales of turbulence. Namely, four different scales are defined, and the eigenvectors of the stress tensor for each reduced model are discussed. The discussion includes the comparison with the principal axis of the strain rate tensor.
It is shown that the spatial locations where the eigenvectors of the strain and stress tensors are aligned lead to the largest production of turbulent kinetic energy. The deterministic periodic perturbations induced at the inlet by the unsteady incoming wakes lead to the largest production of turbulence in the passage region where the highest strain is detected and where the eigenvectors of the two tensors are aligned. In the suction side boundary layers, the highest production is related to the local maximum of the Reynolds shear stress due to the stochastic perturbations. The deterministic perturbations do not contribute to the production of turbulence in the suction side boundary layer, even though their induced stress is not negligible, because the eigenvector directions have a maximum misalignment.
Techno-Economic Comparison of Several Technologies for the Waste Heat Recovery From Gas Turbine Exhausts
Authors: Ghilardi Alessandra , Frate Guido Francesco , Baccioli Andrea , Ulivieri Dario , Ferrari Lorenzo , Desideri Umberto , Cosi Lorenzo , Amidei Simone , Michelassi Vittorio 
Published: October 2022

Abstract
The waste heat recovery from the gas turbine (GT) exhaust is typical for increasing performance and reducing CO2 emissions in industrial facilities. Nowadays, numerous already operating GT gas turbine plants could be retrofitted and upgraded with a bottoming cycle powered by the GT exhaust gasses. In this case, the standard solution would be to use a water Steam Rankine Cycle (SRC). However, even if this technology the SRC usually yields the best efficiency, other technologies alternatives are often preferred on the lower size scale. Organic Rankine Cycles (ORCs) are the commercial alternatives to SRC Steam Rankine Cycles, but many other alternative cycles exist or can be developed, with potential benefits from safety, technical or economic points of view. This study compares several alternative technologies suited to recover GT gas turbine waste heat, and a detailed cost analysis for each is presented. On this basis, a guideline is proposed for the technology choice considering a wide range of application sizes and temperature levels typical for waste heat recovery from GTs gas turbines. The compared technologies are ORCs, Rankine Cycles (RCs) with water and ammonia mixtures at constant composition, supercritical CO2 cycles (sCO2), sCO2 cycles with mixtures of CO2, and other gasses. As it resulted, ORCs can achieve the lowest levelized cost of energy (32 $/MWh – 46 $/MWh) if flammable fluids can be employed. Otherwise, RCs Rankine cycles with a constant composition mixture of water and ammonia are a promising alternative, reaching a Levelised Cost Of Energy (LCOE) of 36–58 $/MWh.