bluuebunny/crossref_metadata_2025_split huggingface dataset:
Validation of an Analytical Model for the Acoustic Impedance Eduction of Multi-Cavity Resonant Liners by a High-Fidelity LES Approach
Authors: Giaccherini Simone , Pinelli Lorenzo , Marconcini Michele , Pacciani Roberto , Arnone Andrea 
Published: October 2022

Abstract
The massive growth of the air traffic during the last years is leading to stricter limitations on the noise emission levels radiated from aircraft engines. To face this issue, the installation of acoustic liners on the intake duct and the exhaust nozzles is a common strategy adopted to properly abate noise emissions coming from the fan, the compressor, the turbine, and the jet.
In this context, the aim of the present paper is to use high-fidelity LES simulations to validate a MDOF (multi-degree of freedom) extension of the single- and double-degree of freedom (SDOF and DDOF) analytical model provided by Hersh for impedance eduction of acoustic liners.
Firstly, the results of the original Hersh model are compared with LES calculations performed with the OpenFOAM suite on a single-orifice and single-cavity layout (SDOF). Then the extension of the Hersh model to multi-cavity (MDOF) geometries by using a recursive formulation is presented. Finally, high fidelity simulations are carried out for single-orifice and multi-cavity (MDOF) configurations to validate the method extension and to understand how resonant coupling and acoustic impedance are affected by multi-cavity resonant elements.
The excellent agreement between the high-fidelity results and the analytical predictions for the single-cavity pattern confirms that the Hersh model is a useful formulation for a preliminary design of a SDOF acoustic liner. The model extension to MDOF configurations enables the designers to broaden the design space, and thus a validated analytical method is strictly necessary to perform sensitivity studies to the multi-cavity geometrical parameters (i.e., face-sheet thickness, cavities depth, porosity). Basically, a multi-cavity configuration makes the liner element resonate at different frequencies leading to multiple absorption peaks in the audible range. In this way, the acoustic performance of the liner is extended to a wider frequency range, overcoming the limitations of a traditional SDOF configuration.
A Model and Experimental Validation for a Piston Rings - Squeeze Film Damper: A Step Toward Quantifying Air Ingestion
Authors: Koo Bonjin , San Andrés Luis 
Published: October 2022

Abstract
Rotor-bearing systems often rely on squeeze film dampers (SFDs) to increase the dynamic stability and reduce rotor motion amplitudes while traversing critical speeds. In aircraft engines, to increase the damping capacity within a limited physical space, piston rings (PRs) seal the axial ends of a squeeze film land. However, lubricant still leaks through the slit in the PR abutted ends, and air enters into the film to make a bubbly oil mixture with a much reduced damping capability. This paper presents a volume of fluid (VOF) model for a PR sealed ends SFD facing ambient air (not submerged in lubricant and prone to air entrainment) and delivers predictions benchmarked against experimental results obtained in a dedicated test rig. A lubricant feed pressure and flow large enough to prevent air ingestion vary with the damper geometry, the lubricant inlet and outlet conditions, and the kinematics of the journal. A parametric study for a typical SFD shows the period-averaged gas volume fraction (GVF) increases as the journal squeeze film velocity (vs) increases and as the film clearance decreases. Most importantly, the location of the PR slit relative to the feedhole affects the amount of air drawn into the film. When the PR slit faces a feedhole, the film land is mostly filled with a pure lubricant. The GVF increases as the arc distance from the PR slit to the feedhole increases. The physical model, anchored by the test data, effectively addresses a fundamental challenge in SFD design and operation; namely, to quantify the amount of air ingested and its effect on the damper forced performance.
Numerical Predictions of Mean Performance and Dynamic Behavior of a 10 MWe sCO2 Compressor with Test Data Validation
Authors: Hosangadi Ashvin , Weathers Tim , Liu Zisen , Pelton Robert , Wygant Karl , Wilkes Jason 
Published: October 2022

Abstract
High-fidelity aerodynamic analysis has been demonstrated for mean performance and unsteady dynamics in a sCO2 compressor designed by Hanwha Power Systems Americas for a 10 MWe Concentrating Solar Power plant. Simulations were performed with CRUNCH CFD® software tool that was matured to accurately model near critical real fluid effects in sCO2. Pre-test predictions for mean performance were validated with test data collected later. Performance predictions were accurate and captured sensitivity of the efficiency to inlet temperature of CO2 as well as steep drop-off at high flow rates due to condensation in the inlet throat. Detailed analysis was performed to understand the source of these performance losses at near critical conditions. Unsteady dynamic effects in the compressor at off-design conditions were also identified and quantified. In particular a system wide “condensation surge” condition was detected at high flow coefficients that results in large amplitude pulsations with accompanying mass flow fluctuations at low frequencies and has potential to cause damage in closed loop systems.
Stratified and Buoyancy-Induced Flow in Closed Compressor Rotors
Authors: Lock Gary D. , Jackson Richard W. , Pernak Mikolaj , Pountney Oliver J. , Sangan Carl M. , Owen J. Michael , Tang Hui , Scobie James A. 
Published: October 2022

Abstract
The radial growth of compressor discs is strongly influenced by conjugate heat transfer between conduction in the co-rotating discs and buoyancy-driven convection in the rotating fluid core between the discs. An accurate prediction of metal temperatures of these discs is an important issue in thermo-mechanical design, where blade-tip clearances must be controlled carefully to ensure safety and efficiency under all operating conditions. This paper presents an experimental study of the fluid dynamics and heat transfer in a closed rotating cavity, comparing results with theoretical models and introducing a new compressibility parameter χ. At large values of χ, where compressibility effects are significant, the air temperature approaches that of the shroud; such conditions suppress buoyancy effects and the flow in the rotating cavity becomes stratified, with convection replaced by conduction inside the fluid core. There are important practical consequences of stratification with significant differences in temperature distributions and stresses inside compressor discs.
The influence of χ is also shown on the radial temperature distributions for the discs and on the shroud heat transfer correlations, which are compared qualitatively with previously published data collected where the effects of compressibility are relatively small. The experiments reveal that there is a critical value of χ where the convective heat flux to the shroud is zero. The radial distribution of disc temperature was that expected from pure conduction in a cylinder. A new heat transfer correlation based on measured shroud heat flux and the theoretical core temperature is presented.
The unsteady flow characteristics in the cavity were also investigated, identifying coherent rotating structures across a range of experimental conditions. These cyclonic / anti-cyclonic vortex pairs generate the non-dimensional circumferential pressure difference necessary for the radial outflow (of cold fluid) and inflow (of hot fluid) through the rotating core. The experiments show the magnitude of these pressure variations can be correlated against Grashof number and that at high values of χ the structures do not exist. The combined experimental and theoretical results will be of practical interest to engine designers and for the validation of computational models.
Simulating Stall Inception in a High-Performance Fan With Clean and Distorted Inlets
Authors: Bedke Andrew M. , Adams Tyler , Gorrell Steve E. 
Published: October 2022

Abstract
The effect of distorted inflow on jet engine fan stability is an important consideration in both commercial and high performance aircraft applications. Novel commercial aircraft configurations offer significant reductions in fuel burn, but require engine fans to continuously operate with severe amounts of inlet distortion. Complex inlet ducts in high performance aircraft also result in distorted flow at the fan inlet. This paper investigates and compares the mechanisms of stall inception for cases of both clean and distorted inlet flow. Unsteady RANS simulations of stall inception in a high performance transonic fan were obtained for both cases. In both instances, the mechanism for stall inception is shown to be interactions between the detached bow shock and the tip clearance vortex, which causes the formation of two vortices within the blade passage. The location and strength of these vortices both affect the LE spillage into the adjacent blade rows. When inlet distortion is present, mass redistribution upstream of the fan results in variations in rotor incidence. An area of high incidence is located outside the circumferential extent of the applied distorted sector. In the high incidence region, the shock is detached 3.9%–8.1% chord more than the clean inlet case, making LE spillage more likely. The same mechanisms of stall inception are observed when distortion is present. However, the severity of the stalling phenomena is more pronounced within the high incidence region of the annulus. A rotating stall cell grows out of the stalled passages present at the near-stall operating point and ultimately extends 59% chord upstream of the LE and 18.7% span radially. Understanding the effect of distortion on the mechanisms of stall inception will allow appropriate steps to be taken to extend the stable operating range of modern commercial and high performance fans.
Oxygen Storage Incorporated Into Net Power and the Allam-Fetvedt Oxy-Fuel sCO2 Power Cycle – Technoeconomic Analysis
Authors: Moore J. Jeffrey , Pryor Owen , Cormier Ian , Fetvedt Jeremy 
Published: October 2022

Abstract
With the planned future reliance on variable renewable energy, the ability to store energy for prolonged time periods will be required to reduce the disruption of market fluctuations. This paper presents a method to analyze a hybrid liquid-oxygen (LOx) storage / direct-fired sCO2 power cycle and optimize the economic performance over a diverse range of scenarios. The system utilizes a modified version of the NET Power process to produce energy when energy demand exceeds the supply while displacing much of the cost of the ASU energy requirements through cryogenic storage of oxygen. The model uses marginal cost of energy data to determine the optimal times to charge and discharge the system over a given scenario. The model then applies ramp rates and other time-dependent factors to generate an economic model for the system without storage considerations. The size of the storage system is then applied to create a realistic model of the plant operation. From the real plant operation model, the amount of energy charged and discharged, the CAPEX of each system, energy costs and revenue and other parameters can be calculated. The economic parameters are then combined to calculate the net present value (NPV) of the system for the given scenario. The model was then run through the SMPSO genetic algorithm in Python for a variety of geographic regions and large-scale scenarios (high solar penetration) to maximize the NPV based on multiple parameters for each subsystem. The LOx storage requirements will also be discussed.
Design of Annular Thermoelectric Generators System to Recover Waste Heat From Aircraft Jet Engine
Authors: Aljaghtham Mutabe 
Published: October 2022

Abstract
Thermoelectric (TE) materials were investigated in several applications due to their capability to convert waste heat into electrical power. The possibility of implementing thermoelectric generators (TEGs) onto exhaust pipe of turbojet engine to recover waste heat energy is introduced in this study using 3D finite element method. The annular TE configuration can be mounted on the exhaust pipe utilizing the temperature difference between hot gas flow and cool air bypass flow. Geometrical parameters of annular TEGs structure such, TE leg angle, and gap distance angle are also optimized to quantify the total amount of TE modules on the outer surface area of the exhaust pipe. Due to higher values of thermomechanical properties, silicon germanium which also performs better at higher temperature range with higher values of figure of merit (ZT) is selected as TE materials. However, due to high temperature gradient, the cascade annular thermoelectric systems are also included in this study by inserting skutterudite as another TE material at lower stage which is suitable at intermediate temperature range. The comparison of using annular single stage (silicon germanium) and two stages (silicon germanium & skutterudite) TE systems is investigated.
Numerical Modeling of Lean Spray Lifted Flames in Inclined Multi-Burner Arrangements
Authors: Langone Leonardo , Amerighi Matteo , Andreini Antonio 
Published: October 2022

Abstract
Modern combustors operate with lean mixtures to prevent Nitrogen oxides (NOx) formation by limiting the peaks of the temperature inside the combustion chamber. One of the main drawbacks of these technologies is the higher risk of Lean Blow-Off (LBO) compared to the state-of-art Rich Quench Lean combustors. To limit this possibility, combustor designers introduced pioneering concepts for this component. In this fashion, the CHAiRLIFT (Compact Helical Arranged combustoRs with lean LIFTed flames) concept founds its advantages in the structure of the combustion chamber. It combines two concepts: the tilting of the burner’s axis relative to the engine axis with a low-swirl lifted spray flame. Here, the combustion can be stabilized at very low equivalence ratios thanks to the interaction between consecutive burners. A numerical analysis was carried out to support the experimental campaign aiming to investigate the performance of the burner under different tilting angles for the burners. Two-phase simulations of the CHAiRLIFT full rig burner were performed in the commercial CFD suite ANSYS Fluent and the results were compared with the available experimental data. Furthermore, a deeper sensitivity to the tilting angle was conducted through the introduction of specific performance parameters to assess the performance and to seek the best promising setup. The outcomes have shown that tilt angles between 20° and 30° could lead to an improvement of the exhaust recirculation, regarding the considered operating conditions.
Free-Stream Turbulence Induced Boundary-Layer Transition in Low-Pressure Turbines
Authors: De Vincentiis Luca , Ðurović Kristina , Lengani Davide , Simoni Daniele , Pralits Jan , Henningson Dan S. , Hanifi Ardeshir 
Published: October 2022

Abstract
In the present work the evolution of the boundary layer over a low-pressure turbine blade is studied by means of direct numerical simulations. The set-up of the simulations follows the experiments by [1], aiming to investigate the unsteady flow field induced by the rotor-stator interaction. The free-stream flow is characterized by high level of free-stream turbulence and periodically impinging wakes. As in the experiments, the wakes are shed by moving bars modeling the rotor blades and placed upstream of the turbine blades. To include the presence of the wake without employing an ad-hoc model, we simulate both the moving bars and the stationary blades in their respective frames of reference and the coupling of the two domains is done through appropriate boundary conditions. The presence of the wake mainly affects the development of the boundary layer on the suction side of the blade. In particular, the flow separation in the rear part of the blade is suppressed. Moreover, the presence of the wake introduces alternating regions in the streamwise direction of high- and low-velocity fluctuations inside the boundary layer. These fluctuations are responsible for significant variations of the shear stress. The analysis of the velocity fields allows the characterization of the streaky structures forced in the boundary layer by turbulence carried by upstream wakes. The breakdown events are observed once positive streamwise velocity fluctuations reach the end of the blade. Both the fluctuations induced by the migration of the wake in the blade passage and the presence of the streaks contribute to high values of the disturbance velocity inside the boundary layer with respect to a steady inflow case. The amplification of the boundary layer disturbances associated with different spanwise wavenumbers has been computed. It was found that the migration of the wake in the blade passage stands for the most part of the perturbations with zero spanwise wavenumber. The non-zero wavenumbers are found to be amplified in the rear part of the blade at the boundary between the low and high speed regions associated with the wakes.
Canned Sealless Pumps for Hazardous Applications?
Authors: Alsultan Abdulrahman , Alharbi Shuja 
Published: October 2022

Abstract
Oil and Gas industry has many applications considered as toxic or hazardous, where process fluid leakage is not permitted and leads to health, safety and environmental impacts. Caustic/Acidic applications, High Benzene Concentrations, Hydrogen sulfide rich oil/gas as well as liquids operating above their auto-ignition temperatures are examples of such liquids that pose as a risk to the industry operation, and for those, special arrangements are in place to allow for the safe operation environment.
Pumps in the industry requires special attention, specifically in the interface between the fluid and the environment, where potential of leakages are foreseen. Mechanical Seals are used to contain the fluid within the equipment, but the prices are ever increasing for such seals, along with maintenance, design and operating requirements. Several alternatives to seals are being employed nowadays, such as Sealless systems, which is hermitically sealed from atmosphere, and does not require sealing. This technology is considered relatively new, and requires more studies to understand the limitations and factors associated, from an owner and design perspective. Things like financial factors, maintenance factors and design limitation should be studies further, in order to have a mature and reliable technical solution available to end users.
Experimental Investigation of the Effects of Thermal Barrier Coating on Twisted Blade Full Film Cooling
Authors: Yan Hao-nan , Liu Cun-liang , Zhang Li , Guo Yu-hang 
Published: October 2022

Abstract
Film cooling and thermal barrier coating technologies are often used in thermal protection of aero-engine turbine blades. But the film-hole structure can be often affected by thermal barrier coatings (TBC) spraying, resulting in the variations of aerodynamic and thermal performances of film cooling. In this paper, adiabatic film cooling effectiveness distribution contours of twisted vanes with multi-row film cooling holes in fan-shaped cascade tunnel were obtained by PSP technology. The effects of TBC on twisted vanes film cooling effectiveness were studied, which was sprayed by electron beam physical vapor deposition (EB-PVD). Three typical density ratio (DR) of 1.0, 1.5 and 2.0 and three mass flow ratio (MFR) of 8.92%, 10.45% and 12.21% were test. The air was selected as the mainstream, nitrogen, carbon dioxide and 15% sulfur hexafluoride mixd with 85% argon were independently selected as secondary flow to produce three density ratios of 1.0, 1.5 and 2.0.
The results indicate that TBC improves film cooling effectiveness on suction surface by 6.2%–16.67%, and significantly reduces the film cooling effectiveness on the leading edge (37.7%–52.7%) and gill areas of the pressure surface (28.8%–32%). In these three regions, the difference between vanes with and without TBC is slightly affected by the change of MFR, and gradually decreased with the increase of density ratio. The film cooling effectiveness of the pressure surface near the trailing edge is less weakened by the TBC, where the maximum reduction is 8.92%. Compared with the cylindrical hole rows, TBC has less impacts on film cooling effectiveness at fan-shaped hole rows.
Numerical Study of Combustor-Turbine Interaction by Using Hybrid RANS-LES Approach
Authors: Tomasello Stella Grazia , Andreini Antonio , Meloni Roberto , Cubeda Simone , Andrei Luca , Michelassi Vittorio 
Published: October 2022

Abstract
The complex flow field of gas turbine lean combustors is meant to reduce NOx emissions and maintain a stable flame by controlling the local temperature and promoting high turbulent mixing. Still, this may produce large flow and temperature unsteady distortions capable of disrupting the aerodynamics and heat transfer of the first high-pressure-turbine cooled nozzle. Therefore, the interaction between the combustion chamber and the turbine nozzle is analyzed first with the help of scale-resolving simulations that notably also include a realistic turbine nozzle cooling system. To determine the nature and severity of the interaction, and the risks associated to performing decoupled simulation, the results of the coupled computer simulation are analyzed and compared with those of decoupled simulations. In this case, the combustor is computed by replacing the turbine nozzle with a discharge convergent with the same throat area, and the conditions at the interface plane are used as inlet boundary conditions for a conventional RANS of the nozzle. The analyses of the coupled and decoupled simulation reveal that the combustion chamber is weakly affected by the presence of the nozzle, whereas the two thermal fields of the nozzle surface differ considerably, as well as the disruption of the film cooling by the incoming flow distortions.
Turbine Endwall Contouring Through Advanced Optimization Techniques
Authors: Burigana Matteo , Verstraete Tom , Lavagnoli Sergio 
Published: October 2022

Abstract
Non-axisymmetric endwall profiling offers features to simultaneously mitigate aerodynamic losses and hot gas ingestion in axial turbines. The current paper presents an optimization methodology to generate a contoured surface integrated with real geometrical effects such as blade fillets and a rim seal channel with the aim of achieving higher efficiencies while reducing the hot gas ingestion.
The contoured rotor platform is constructed using a B-spline surface clamped in the axial direction. On the azimuthal direction the surface is unclamped to allow geometrical continuity across the periodic boundaries. The endwall parametrization is used to optimize a rotor hub platform of a high-pressure turbine stage.
A differential evolution optimizer is used to rank individuals in terms of efficiency. The single-objective optimization is set to maximize the aerodynamic efficiency and it is defined such that it accounts for the flow non-uniformity trough a mixed out averaging procedure. Engine representative conditions typical of a two-stage high pressure turbine are used as boundary conditions. Geometrical and aerodynamic constraints are set to guarantee a fair comparison among individuals and to meet engine requirements. Two surface parameterizations, which use a different number of design variables but share the same construction strategy, are presented to show the trade-off between the number of degrees of freedom and the aerodynamic improvement. Different purge flow conditions are considered to assess the robustness of the optimization results at off-design condition for relevant geometries.
The aim of the paper is to show the advanced shape flexibility of the implemented parametrization for contoured platforms featuring technological effects such as blade fillet and rim seal channel. The work provides design guidelines to set-up engine-realistic constraints for endwall contour optimization of turbine stages.