bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Evaluation of Forward and Backward Swept Axial Fan Design for Automotive Applications With Identical Aerodynamic Performance
Authors: Sivaramakrishnan Anand , Bleiziffer Mihai , Girmscheid Felix
Published: August 2024

This paper introduces a pioneering approach to address a notable research gap in the realm of axial fan design for automotive application. Through a collaborative effort between Hanon Systems and Advanced Design Technology (ADT), advanced design techniques employing inverse design methodology were harnessed to develop axial fans with identical aerodynamic performance while minimizing acoustic emissions. The primary focus was on a comprehensive exploration and comparison of the acoustic behavior exhibited by forward and backward swept blade designs, set within a distinctive context.

The methodology encompassed the application of advanced turbomachinery design methods and inverse design principles. This innovative approach aimed to create fans that not only achieved identical airflow performance but also exhibited superior acoustic characteristics, all within the constraints of identical blade dimensions. The initial step involved a meticulous identification of key factors influencing fan performance and acoustics. A detailed design specification was then established, and advanced design optimization techniques were deployed to precisely adjust the blade geometry. This precision engineering ensured that the fans met desired specifications while maintaining similar aerodynamic performance.

Subsequent to the design phase, comprehensive simulations and experimental testing were executed to validate the designs. The focus was on comparing the aerodynamic and acoustic performance of forward and backward swept cooling fans, both designed to achieve identical aerodynamic performance. The results from these tests provided valuable insights into the acoustic aspects of axial fans, particularly in the context of automotive applications.

This research project stands as a substantial contribution to the field of acoustics in the automotive industry. It not only showcases the feasibility of designing axial fans with identical aerodynamic performance characteristics irrespective of blade sweep but also underscores the efficacy of advanced turbo design and inverse design techniques in achieving this outcome.
Numerical Analysis of the Boundary Layer Behavior of Low-Speed Linear Cascade Compressor Airfoils With Single and Tandem Configurations
Authors: Reisinger Lukas , Bieli Philippe , Gümmer Volker
Published: August 2024

A numerical design space study investigates the boundary layer behavior of highly loaded compressor airfoils featuring single and tandem configurations in a low-speed linear cascade with contracting endwalls. The study considers various Reynolds numbers, turbulence intensities, and blade loads. DLR’s CFD solver TRACE is used for the numerical simulations with a rotation-corrected k-ω turbulence model, Low-Mach preconditioning, and the γReΘ transition model. A robust method for evaluating boundary layer parameters is introduced, based on which representative reference airfoils are designed. Laminar flow dominates around the blade for small Reynolds numbers, turbulence intensities, and low boundary layer loading. As Reynolds numbers increase and turbulence levels rise, the transition progresses into the accelerated front portion of the blade’s suction side. The transition behavior and boundary layer development of the rear vane in a tandem configuration depends on the front vane’s boundary layer behavior. Lower Reynolds numbers correspond to increased boundary layer loading, and the presence of a maximum shape factor at the trailing edge varies with turbulence intensity and transition onset, influenced by the blade design. High turbulence intensities and small Reynolds numbers increase boundary layer thickness, affecting the interaction between front and rear vanes in tandem configurations. The entropy production per chord length in the boundary layer rises with decreasing Reynolds numbers and increasing turbulence intensity. The findings emphasize the need for distinct design guidelines for single and tandem configurations, considering the varying Reynolds numbers and boundary layer behaviors.
An Experimental Case Study in Combining Topology Optimization and Additive Manufacturing Techniques to Generate Novel and High-Performance Compact Heat Exchanger Designs
Authors: Rees Thomas W. , Azam Abdullah , Casari Nicola , Banks Polly , Jiranek Lukas , Furino Stefano , Muley Arun
Published: August 2024

The recent industrialization of additive manufacturing processes has led to research interest in alternative, more complex two-fluid heat exchanger designs, such as those constructed from repeating triply periodic unit cell geometries like gyroids, Schwarz minimal surfaces or other complex geometries. These types of designs are particularly convenient because their performance can be scaled up or down by including more or fewer periodic unit cells in the final heat exchanger lattice. Despite their complexity, repeating periodic unit cell-based heat exchanger designs have not been shown to have performance advantages over more traditional designs and therefore have yet to find widespread industrial application. This failure is partially due to the fact that the periodic unit cells used to build these heat exchangers are not optimized for thermo-fluid efficiency, as well as the fact that accurate simulation of a heat exchanger containing thousands of complex unit cells is extremely challenging, making the design of the overall heat exchanger difficult.

This paper presents the results of a project to develop a heat exchanger design method which can overcome these deficiencies. In particular, we design, build, and test a crossflow two-fluid heat exchanger based on a periodic unit cell designed using a proprietary topology optimization algorithm. The heat exchanger is manufactured using additive manufacturing. Analysis of the unit cell design showed that it generated secondary flows to increase the effectiveness of the heat transfer while also minimizing unnecessary loss-generating flow structures. The performance of the entire heat exchanger was simulated computationally using RANS-based CFD simulations on a single unit cell. The results of this simulation were used to build a reduced-order model to predict the heat transfer and pressure drop across the entire heat exchanger at two representative operating conditions.

After numerical simulation, the final design was manufactured from stainless steel using a Renishaw 500Q machine and its performance was measured experimentally. The experimental results are favorably compared against the numerical predictions to validate both the CFD simulations on the periodic unit cell as well as the reduced order model of the entire heat exchanger. This indicates that the topology optimization design process can be confidently applied to design scalable heat exchangers.
Artificial Intelligence-Based Performance Maps for Expander-Compressor Analysis in Energy Transition Applications
Authors: Lottini Fabrizio , Bicchi Marco , Agnolucci Andrea , Marconcini Michele , Arnone Andrea
Published: August 2024

Limiting the global warming impact requires a drastic reduction of greenhouse gas emissions (GHG) to reach a zero-carbon growth by 2050. Against this backdrop, turbomachinery designers are asked to develop more compact, efficient, and reliable machines. The research focuses on developing machines able to reduce energy losses and overall footprint, thus improving power plants efficiency and operability. To this end, expander-compressors (EC) seem to play a key role in the energy transition and appear a promising technology for high-density plants, especially together with hydrogen (H2) or supercritical carbon dioxide (sCO2) as working fluid. However, when operating conditions changes, a reduction in machine efficiency may be expected, with a consequent degradation of the overall system performance. In order to optimize the operation of the power plant, it is crucial to understand how the variation of the expander-compressor behavior affects the working conditions of the other components of the plant. In this perspective, a fast and reliable way to estimate the EC performance at different operating conditions is necessary. Although the scientific literature shows several studies on mean-line approaches for expanders and centrifugal compressors, the joint use of 1D models with artificial neural networks (ANN) for ECs combined machine is still overlooked. To fill this gap, the prediction of artificial intelligence (AI)-based performance maps is proposed in this work. The tool has been tested in a case study based on a real EC. Results showed a rapid evaluation of EC efficiency while varying the operating conditions.
Liquid Cooling of Fuel Cell Powered Aircraft: The Effect of Coolants on Thermal Management
Authors: Frey Adam C. , Bosak David , Stonham Joseph , Sangan Carl M. , Pountney Oliver J.
Published: August 2024

Electric propulsors powered by Proton Exchange Membrane Fuel Cells (PEMFCs) offer a net zero solution to aircraft propulsion provided that the hydrogen reactant is produced renewably. Heat generated by the PEMFCs can be transferred to atmospheric air via a liquid cooling system; however, the cooling system results in parasitic power and adds mass to the propulsion system, thereby affecting system specific power. The design of the cooling system is sensitive to the choice of liquid coolant and so informed coolant selection is required if associated parasitic power and mass are to be minimized.

Two approaches to selection of coolants for PEMFC-powered aircraft are presented in this paper for operating temperatures in the range 80–200°C (this covers low, intermediate, and high temperature PEMFCs). The first approach uses a Figure of Merit (FoM) alongside minimum and maximum operating temperature requirements. The FoM supports the selection of coolants that minimize pumping power and mass while maximizing heat transfer rate. The second approach uses a cooling system model to select “Pareto efficient” coolants. A hybrid-electric aircraft using a PEMFC stack is used as a representative case study for the two approaches.

Hydrocarbon-based coolants are shown to be favorable for the case study considered here (aromatics for PEMFCs operating at < 130°C and aliphatics for PEMFCs operating at > 130°C). As the PEMFC operating temperature increases, the parasitic power and mass of the TMS decreases. Operating at elevated temperatures is therefore beneficial for liquid cooled PEMFC-powered aircraft. Nevertheless, there are diminishing gains in performance at higher operating temperatures.

The two approaches outlined in this paper are useful to PEMFC TMS designers. The FoM enables expedient coolant screening in preliminary TMS design, and the model provides a high-fidelity method for optimal coolant selection.
Combustion Optimization and Burnout of Ammonia-Based Gaseous Fuels in the Constant Pressure Sequential Combustion System Operated in Rich-Quench-Lean Mode
Authors: Heggset Tarjei , Meyer Ole H. H. , Gruber Andrea , Tay-Wo-Chong Luis , Ciani Andrea
Published: August 2024

In the context of fuel-flexible operation of gas turbines, providing on-demand large-scale electric power without incurring in emissions of carbon dioxide, a convenient feature of Ansaldo Energia’s Constant Pressure Sequential Combustion (CPSC) system is the possibility of controlling the amount of fuel independently fed to the two combustion stages depending on the reactivity and combustion characteristics of the fuel itself. Crucially, in the case of ammonia-based fuels, this includes the capability of switching the CPSC operating mode from a conventional Lean Pre-Mixed (LPM) combustion to a Rich-Quench-Lean (RQL) staging strategy that mitigates undesired emissions of atmospheric pollutants (NOx) and greenhouse gases (N2O) emerging from the oxidation of fuel-bound nitrogen. Building upon an earlier numerical-modelling assessment of the CPSC system capability to operate in RQL mode (GT2023-103835) [1], the present work extends the scope of the initial preliminary study with a comprehensive set of additional calculations, based on massively parallel Large Eddy Simulation (LES) performed in conjunction with detailed chemical kinetics. Firstly, it is reported that, according to the numerical modelling predictions, a transition to stable, low-emission combustion of pure (non-decomposed) ammonia in the Multi-Burner First Stage (MBFS) can be achieved following an initial ignition and flame stabilization of a more reactive, partially decomposed ammonia blend. Secondly, it is shown that, at the equivalence ratio investigated, the unburnt fuel fractions emerging from the fuel-rich MBFS flames are completely oxidated by secondary air injected within the Dilution-Air Mixer (DAM) section of the CPSC. Furthermore, it is found that this burnout process occurring in the DAM section of the CPSC does not lead to significant increase of NOx and N2O emissions, thereby confirming the excellent potential of the CPSC to operate cleanly and efficiently with ammonia-based fuels.
Comparative Analysis of the Effect of Two Tower Geometries on Offshore Wind Turbine Wake Aerodynamics
Authors: Simone Albanese , Barnabei Valerio Francesco , Morici Vincenzo , Corsini Alessandro , Castorrini Alessio
Published: August 2024

Rotor-wake interaction and the corresponding power loss are a significant aspect to account for in the development and design of new offshore wind farms. As the wake shed by upstream turbines can induce a substantial reduction in the power generated by the downstream turbines, turbines are located at considerable relative distances, allowing the downstream flows to have a larger space to recover kinetic energy from the freestream flow field. The mechanism of wake recovery is an interesting area of study for wind engineering, being affected by various factors such as mixing with atmospheric and ground turbulence, interaction of the wake flow and tip vortices with fixed structures and obstacles. In this paper, we examine the impact of support structures on downstream turbulent flow and wake recovery for a utility-scale wind turbine operating in an offshore environment. We use the actuator line method to model the rotor, a common approach to simulating wind farms with CFD solvers, while the support structures geometry given by the tower and nacelle is directly resolved by the CFD mesh. The CFD simulation is based on the incompressible k-ω SST-IDDES model, which is a hybrid LES/RANS turbulence model with enhanced wall-modeling capabilities. The numerical modeling is implemented in Open-FOAM and in a dedicated library for the actuator line model to simulate the blade’s aerodynamics. This is further augmented with a finite element model to account for blade elasticity. In the presented investigation, we use the IEA-15MW turbine model. The rotor is mounted on two distinct types of towers: a standard mono-pylon tower and a tripod-style tower.
Investigating the Influence of Non-Uniform Radial Inlet Distortion on the Performance of Counterflow Model Combustor
Authors: Shi Yunjiao , Luo Shaowen , Zhao Ningbo , Yang Ren , Zheng Hongtao
Published: August 2024

As gas turbine technology, design capabilities, and numerical simulation capabilities continue to advance, the boundary conditions at the inlet of the combustion chamber are no longer set as simple uniform inflow. Instead, the impact of upstream compressor exit flow distortion on combustion chamber performance is fully considered. Therefore, this study employs numerical simulation to analyze in-depth the variation patterns of radial distortion at the inlet of a swirl combustor. The research results indicate that radial distortion simultaneously increases the total pressure loss in both cold and hot flow fields. As the distortion peak shifts upward, the total pressure loss increases (by 0.54%), but it has little impact on combustion efficiency and thermal resistance loss. Changes in the distortion peak velocity position affect the separation vortex location in the diffuser section and the penetration depth of dilution holes, thereby influencing flame morphology and outlet temperature distribution. The increase in total pressure loss along the path becomes more pronounced as the flow turns from the diffuser to the combustor, especially under upper peak conditions. The diffuser exhibits the strongest suppression effect on the velocity peaks of the lower peak and middle peak conditions. This study provides valuable insights for establishing accurate boundary condition models that describe the inlet effects of combustion chambers in numerical simulations of gas turbine combustors.
Ammonia and Ammonia/Hydrogen Mixtures Ignition Delay Times and Chemical Kinetic Model Validation at Gas Turbine Relevant Conditions
Authors: Pierro Michael , Dennis Christopher W. , Pothen Alex-Abraham , Hulliger Nikolas , Kelly Tyler , Fraze Matthew , Urso Justin J. , Rahman Ramees K. , Kinney Cory , Winquist Mark , Vega John , Subbaraman Ganesan , Steele Robert , Vasu Subith S.
Published: August 2024

Undiluted mixtures of ammonia/hydrogen (NH3/H2) were auto-ignited inside the University of Central Florida’s high-pressure shock tube, allowing for lower temperature ignition data and realistic fuel concentrations to be experimentally tested and compared to chemical kinetic models. Ignition delay time (IDT) measurements were collected at the conditions relevant to power generation gas turbines (5–20 bar, 1000–1700 K) and across a range of equivalence ratios (0.5–1.5). The data was compared against the 2018 Glarborg et al. model, which contains nitrogen-based chemistry and was previously validated at lower pressures and dilute conditions. The 20 bar experimental IDT data is predicted well by the model, but large deviations were shown for 5 and 10 bar with hydrogen addition. Experimental 5 bar IDTs were measured to be faster than the 10 and 20 bar data, highlighting the unique combustion chemistry of the hydrogen explosion limits. The model failed to capture explosion limit properties at intermediate pressures, where hydrogen pressure-dependence reaction chemistry is prominent. A sensitive analysis was performed to investigate the top reaction pathways predicted by the model and the chain branching reactions H + O2(+M) → HO2(+M) and HO2 + H → 2OH are suggested as key reactions to reinvestigate to improve the 2018 Glarborg et al. model predictions of the hydrogen explosion limits. Furthermore, an improved chemical kinetic model is shown built upon the experimental data. By improving chemical kinetic models, air-breathing hydrogen/ammonia turbine combustor efficiencies can be improved, and nitrogen oxide (NOx) emissions can be lowered to ultimately reduce greenhouse emissions.
A Reactor-Network Framework to Model Performance and Emissions of a Longitudinally-Staged Combustion System for Carbon-Free Fuels
Authors: Gopalakrishnan Harish S. , Maddipati Raj , Gruber Andrea , Bothien Mirko R. , Aditya Konduri
Published: August 2024

Hydrogen and ammonia are considered crucial carbon-free energy carriers optimally suited for seasonal chemical storage and balancing of the energy system. In this context, longitudinally-staged combustion systems represent an attractive technology in power generation for their capability of achieving low NOx emissions while conserving high load and, crucially, fuel flexibility at high thermal efficiency. Such two-stage combustion systems have been successfully implemented for natural gas firing of gas turbines and, more recently, have shown significant potential for clean and efficient hydrogen-firing operation. However, optimal operation with ammonia-based fuel mixtures is yet to be established. In a recent numerical modelling study (GT2023-103835), a novel Rich-Quench Lean (RQL) operational concept was proposed to burn a fuel-rich mixture of partially-decomposed ammonia and air (for equivalence ratios ϕ ∼ 1.1–1.2) in the first stage of a longitudinally-staged combustion system. Complete oxidation of the remaining (hydrogen) fuel is theoretically ensured by dilution-air addition downstream of the first stage combustor and it is confirmed by predictions from ongoing LES calculations (GT2024-128946). However, any operational concept based on these near-stoichiometric combustion conditions, while minimizing undesired prompt NOx and N2O formation by ammonia oxidation, can potentially result in significant, and certainly unpractical, thermal load on the first stage combustor liner that needs to be mitigated. In the present study, we exploit a newly developed reactors-network model to efficiently investigate the NOx-emissions performance of a longitudinally-staged combustion system fired with natural gas, hydrogen or ammonia. Firstly, the reactors network framework is validated with experimental, computational and other similar reactor network results in the literature. Secondly, the optimal air distribution within the longitudinally-staged combustion system is found for clean (low emissions) and efficient (complete fuel conversion) ammonia-firing operation. Thirdly, the consequences of such “ammonia-optimized” air distribution on flame stabilization and NOx emissions in more conventional natural gas- and hydrogen-firing operation are considered. Finally, an optimal air and fuel distribution is suggested for the longitudinally-staged combustion system on the basis that, while still ensuring robust flame stabilization and high turbine inlet temperature, it minimizes NOx emissions for all three fuels considered.
Numerical Analysis of Convective Heat Transfer Processes and Performance Assessment of Lattice and Triply Periodic Minimal Surface Geometries
Authors: Casini Niccolò , Mazzei Lorenzo , Da Soghe Riccardo
Published: August 2024

The increasing relevance of additive manufacturing has sparked interest in lattice and triply periodic minimal surfaces (TPMS) for lightweight, high-performance components. These structures have recently gained attention in thermo-fluid applications for enhanced heat transfer capabilities. Despite their potential, gaps remain in understanding how design affects convective heat transfer. Previous studies show higher friction factors in lattice and TPMS compared to smooth pipes, which nevertheless achieve greater efficiency index due to increased surface area and Nusselt number. This study examines various lattice and TPMS structures, like Gyroid, Diamond, and BCC, alongside conventional channels and pin fins. Using steady-state CFD, it analyses pressure drop and heat transfer covering Reynolds numbers from 10,000 to 40,000, representative of gas turbine cooling applications. Numerical simulations are validated against literature experimental data, confirming good agreement. Results identify the gyroid structure as the most efficient, emphasizing the role of increased wetted area in heat transfer enhancement despite the low fin efficiency provided by Inconel and the small wall thickness.
Effect of Flare Angle in a Counter-Rotating Dual Radial Swirler on the Stability of a Swirl-Stabilized Flame
Authors: Rathod Darshan D. , S. K. Thirumalaikumaran , Kumar Sonu , Panda Pratikash , Basu Saptarshi
Published: August 2024

A novel high-shear injector developed at the National Centre for Combustion Research and Development (NCCRD) is further investigated in the current study. The effect of flare angle on reacting and non-reacting flow field and stabilization of the flame is explored using high-speed OH* chemiluminescence, high-speed stereo particle image velocimetry and simultaneous pressure fluctuation measurements. Flare is the diverging part attached at the end of the injector and the angle of the diverging section is called the flare angle (β). The flare angle is varied in three steps, 0°, 30°, 50°. For each case of flare, 4 cases of inlet Reynolds’s number (Re) and 8 cases of equivalence ratio (ϕ) totalling 32 cases are explored to elucidate the effect of β on flame size and rich and lean blow-off limits. Central recirculation zone (CRZ) which plays a pivotal role in the stabilization of the flame is found to be altered with a change in β. With an increase in β, the CRZ size increases in non-reacting and reacting cases. For β = 0°, the effect of heat addition and the effect of increasing ϕ on CRZ size is very minimal. There is a slight change noticed in CRZ size with increasing ϕ for β = 30° case. The effect of increasing ϕ on CRZ size is found to be very pronounced for the β = 50° case. Non-reacting flow field provides insights into the CRZ formation mechanism, which also changes for different β. Due to the counter-rotating nature of the primary and secondary swirling air, it is possible to qualitatively distinguish among them using the azimuthal velocity component. This distinction provides insights into the mixing distance and its variation with β. Lean blow-off limit deteriorates with an increase in β, and this is delineated using non-reacting flow field data. Reacting flow-field provides valuable insights into the effect of heat addition and the effect of ϕ on flow field at various β. Rich blow-off limit improves with an increase in β, which can be explained using reacting flow field data. Further, the dynamics of the flame and pressure data are reported indicating the presence of thermo-acoustic instability.
Integrated System Modal and Mistuning Identification for Integrally Bladed Rotors
Authors: Beck Joseph A. , Brown Jeffrey M. , Gillaugh Daniel L.
Published: August 2024

The safety of Integrally Bladed Rotors (IBRs) is often assessed through bench-level vibration tests to measure amplification factors and back-out sector frequency deviations via mistuning identification (ID) algorithms. This process is usually composed of two separate steps. First, a system ID step is completed to identify system modal data. Then, this data is input into mistuning ID algorithms. Errors in identified modal data will then propagate to produce errors in the system’s predicted mistuning. Obtaining robust mistuning estimates then requires larger quantities of accurate modal data. This effort seeks to attain accurate mistuning data by coupling the system and mistuning ID steps into a more parallel, versus serial, process that is capable of identifying many system modes. An iterative Polyreference-Least Squares Complex Frequency-domain (P-LSCF) algorithm finds modal data, and a mistuning ID algorithm obtains mistuning data at each iteration. An outlier detection method is proposed to remove spurious modes that cause erroneous mistuning results. Then, a weighted, least-squares regression approach is employed to remove the impact of sector-specific outlier data. This method reduces errors in identified mistuning parameters from the Fundamental Mistuning Model (FMM) ID algorithm. Furthermore, the approaches eliminate the need for users to determine true versus spurious system modes in each iteration of the P-LSCF algorithm, thus removing ambiguity. The developed approaches are first tested on simulated data from industrial IBRs that provide challenging test cases. Finally, real bench-top Traveling Wave Excitation (TWE) data is obtained, and results are compared across different Engine Order (EO) excitations. Results show the efficacy of the developed approaches and their ability to account for and reduce uncertainty in identified mistuning parameters.
Development of a Reduced Order Model for Double Wall Liner Cooling Schemes
Authors: Karasu Zeki Tuğberk , Kıyıcı Fırat , Erdem Erinc
Published: August 2024

Double wall cooling scheme combines the impingement and effusion cooling schemes and efficient way to deal with higher temperature values. However, its complex structure makes the simulations and experiments more expensive. The present study aims to develop a correlation-based one-dimensional low order model to predict wall temperature values for double wall structures before conducting numerical analysis and experiments. The effusion cooling is modeled by using single hole film cooling correlations, that includes effect of the lateral hole displacements, hole angle and blowing ratio, are combined with a superposition method to represent staggered hole arrays in the axial direction. On the other hand, the effect of impingement cooling is added as a source term. Several experimental data is used for validating the one-dimensional solver. In addition, conjugate heat transfer analysis is conducted for better understanding of the heat transfer mechanism, and comparing the computational time. One-dimensional model and conjugate heat transfer analysis are in a good agreement with experimental data for different double wall cooling configurations. Also, the low order model provides highly accurate results in a remarkably shorter time than the conjugate heat transfer analysis. The low order model proves itself as a promising tool that the industry could quickly adopt to evaluate innovative cooling geometries.
Effect of Gerlach Cross-Section on S-Duct Inlet Performance in High Subsonic Flow
Authors: Frosst Benjamin D. , Asghar Asad , Allan William D. E. , Stowe Robert A. , Pimentel Rogerio , Ingram Grant , Orchard Timothy
Published: August 2024

It was hypothesized in literature that Gerlach re-shaping of the cross-section of S-duct inlet bends may reduce the transverse pressure gradient and mitigate or eliminate flow separation. This paper presents an internal performance evaluation of an S-duct diffuser with Gerlach cross-sectional area compared to a baseline S-duct. The generic baseline test article was a rectangular-entrance S-duct transitioning to a circular exit, a configuration typical of single-engine air vehicles. The important geometric parameters were exit-to-entrance area ratio of 1.57 and an offset-to-length ratio of 0.37. The performance of the intake was evaluated at Ma = 0.80 by measuring the axial static pressure distribution, exit total pressure and three-dimensional velocity at the aerodynamic interface plane. The measurements were used to evaluate and compare the aerodynamic performance of the S-duct variants. The geometries and flow conditions were also simulated numerically and validated using experimental performance metrics. The static pressure recovery decreased for the Gerlach S-duct; however, total pressure recovery improved. This work will contribute to the development of improved performance for S-duct inlets and for predicting the performance of aero-engines and air vehicles at high-subsonic flight conditions.
Thermodynamic Design and Analysis of Steam Rankine Cycle for Nuclear Fusion Application
Authors: Thanganadar Dhinesh , Acres Jack
Published: August 2024

Generating electricity from nuclear fusion is a promising renewable energy source in the medium to long term. The UK Atomic Energy Authority (UKAEA) is developing a commercial fusion reactor, namely Spherical Tokamak for Energy Production (STEP), with the ambition of building a prototype power plant able to deliver a target 100 MW net electricity to the grid by 2040. This infers that the power cycle has to produce > 700 MW electricity to meet the in-house parasitic load. The magnetically confined fusion reactor delivers heat which will be carried by the coolant to the power cycle, where the heat is converted to electricity. Designing a power cycle for a fusion application has its own challenges owing to the requirement of 1) accepting heat at multiple temperature levels, 2) able to cope with fast transient operation, 3) efficiently integrate low grade-heat received from high heat flux plasma facing in-vessel components, and 4) offer high thermodynamic conversion efficiency to overcome the high parasitic load of fusion reactor. Different closed-loop power cycle options are possible including Rankine or Brayton cycles and this paper describes a potential steam Rankine cycle design meeting the steady-state requirements of the fusion reactor.
Design and Simulation of a Blowdown Facility for Supercritical Carbon Dioxide
Authors: Ghavami Mohsen , White Martin T. , Chibli Hicham , Sayma Abdulnaser I.
Published: August 2024

This paper describes an experimental blowdown facility designed to characterise the expansion of supercritical CO2 near the critical point. Specifically, the test rig aims at replicating the expansion process at the leading edge of a CO2 compressor with the goal of studying the role of real-gas effects, and possible condensation. The test rig consists of two pressure vessels (high and low pressure), a reciprocating compressor used for charging, a temperature-controlled water circuit to adjust the temperature of the high-pressure tank and a test section comprised of a convergent-divergent nozzle.

The specification of the pressure vessels and the recharging compressor is described which are selected to allow for reasonable charging and blowdown times. The design of a thermal management system is also described that keeps the conditions within the high-pressure vessel temperature within the desired range, whilst avoiding over pressurisation. The optimisation of the test rig layout is also discussed which includes identifying an economically and technically viable solution for the positioning of pressure relief valves and the ventilation system. Furthermore, the range of anticipated test conditions that can be achieved and the expected expansion process within the nozzle have been explored using transient lumped mass models of pressure vessels that are coupled with a quasi-steady nozzle model to determine the expected conditions within the nozzle. The nozzle model assumes a homogeneous mixture under thermal equilibrium at any point where the working fluid enters the saturation dome.

For the defined test rig specifications (high pressure tank = 0.1 m3; low pressure tank = 0.185 m3; CO2 charge = 100 kg; nozzle throat = 100 mm2) it is predicated that constant inlet pressure conditions can be sustained for between 0.4 and 5.5 seconds for test section inlet conditions ranging between 27 and 45 °C, and 70 and 90 bar.
Performance Characterization of a Radial Rotating Detonation Combustor With Axial Exhaust
Authors: Langner Dalton , Gupta Apurav , James Ashley , Agrawal Ajay K.
Published: August 2024

This experimental study characterizes the performance of a radial rotating detonation combustor (RDC). An aerospike nozzle for rocket propulsion has been integrated into the center of the combustor, although the same combustor could also be coupled with turbomachinery. The radial RDC utilized a rapid to gradual (RTG) area change in the flow direction to effectively confine the detonation region close to the inlet plane and to improve the uniformity of the flow exiting the RDC. Three test cases were analyzed, (a) a baseline case at a total reactant mass flow rate, ṁ = 0.136 kg/s and equivalence ratio, ϕ = 0.6, (b) a higher reactant flow rate, ṁ = 0.318 kg/s and ϕ = 0.6, and (c) a higher ϕ = 0.8 at ṁ = 0.318 kg/s. All tests were conducted using methane and a 67% oxygen and 33% nitrogen (by mole) oxidizer mixture. Measurements were acquired using CTAP probes inside the combustion channel and along the aerospike to characterize the performance, PCB and ion probes near the detonation region to identify wave modes and their variations during the test, and thrust measurements using a six-axis force sensor. Results show highly complex wave modes with multiple co-rotating and/or counter-rotating waves depending upon the reactant flow rate. The pressure and thrust measurements are consistent with the wave mode analysis. In general, a positive (combustor only) pressure gain was inferred when losses associated with the injection system were excluded. The study highlights the challenges associated with fuel-air mixing and integrating the RDC with downstream hardware.
Cracking Behavior of Environmental Barrier Coatings/CMC System Using Acoustic Emission and Digital Image Correlation
Authors: Panakarajupally Ragavendra Prasad , Morscher Gregory N. , Shi Jun
Published: August 2024

An investigation into the cracking behavior of advanced environmental barrier coating / woven SiC/SiC ceramic matrix composite (CMC) system under uniaxial tension testing was performed in this study. The effect of substrate (CMC) condition on the coating behavior was also studied. Acoustic emission (AE) and digital image correlation (DIC) were implemented as health monitoring techniques to gain detailed insights into the fracture process of the coating and to identify the origin and location of the fracture events. Fluorescent penetrant inspection was used in-situ in some cases to help identify cracks. Post-test microscopy was performed to correlate the results with DIC and AE. It was evident that for the as-produced woven substrate, the EBC coating cracked prior to substrate cracking; however, for the altered surface substrate, the CMC substrate formed matrix cracks prior to the EBC coating.
Unsteady Flow Mechanism of Corner Separation Control Using Blade End Slots in a Highly Loaded Compressor Cascade
Authors: Liu Yangwei , Zhong Weibo , Tang Yumeng
Published: August 2024

Blade end slots has been proved to be an effective method to suppress the corner separation, thereby improving the aerodynamic performance of compressor. The unsteady effects of blade end slots affiliated with a highly-loaded compressor cascade on corner separation control are investigated based on delayed detached eddy simulation under the Mach number of 0.59. The corner separation vortex structures between the datum blade and the end slotted blade are compared. The vortex topologies are markedly reorganized and suppressed by the blade end slots. Unsteady flow behaviors of separation vortex and the corresponding dynamic mechanisms are analyzed in both time and frequency domains. The interaction of the self-adaptive jet flow from the blade end slots to the corner separation flow results in smaller-scale vortices in the blade end region with a higher characteristic frequency. Consequently, the unsteady effects caused by corner separation vortices are significantly reduced in range and intensity through the enhancement of flow mixing and the rapid dissipation of corner separation vortices into larger-scale lower-frequency features. Furthermore, spatiotemporal features and dynamics of corner separation flow with blade end slot control are investigated using the enhanced dynamic mode decomposition method. Results show that the dominant unsteady flow behavior develops with better stability, and the intermittency of low-frequency and large-scale behavior is reduced via the blade end slot control.
Thermohydraulic Performance Analysis in Square Duct Featuring Novel High-Performance Broken Ribs and Ribs With Fins for High Reynolds Number Gas Turbine Blade Internal Cooling
Authors: Pandya Naimish , Ekkad Srinath V.
Published: August 2024

This study investigates the thermal-hydraulic performance of novel rib configurations, specifically novel V-shaped broken ribs, and V-shaped ribs with fins, within a square channel for significantly high Reynolds number conditions. The Reynolds-averaged Navier-Stokes (RANS) equations are solved utilizing the ANSYS Fluent 2022 R2 solver with the realizable version of the k-ε RNG turbulence model. Computational simulations cover a Reynolds number range from 100,000 to 500,000 while maintaining various dimensions for ribs and fins relative to the channel hydraulic diameter (Dh). The conventional V-shaped rib configuration data from the previous experiment has been used to validate the numerical model for this study. The V-shaped ribs with fins exhibit higher heat transfer enhancement surpassing V-shaped broken ribs by 13% at Reynolds of 300,000. More importantly novel V-shaped ribs with fins and V-shaped broken ribs geometry do not show significant heat transfer degradation when the Reynolds number increases from 100,000 to 500,000. This study offers valuable insights for optimizing rib geometry concurrently to enhance hydraulic and thermal performance for extremely high Reynolds number conditions (> 90,000).
Magnetically Coupled Oscillators and a Smartphone
Authors: Pathak Praveen , Patel Yogita , Raj Rishi
Published: August 2024

10.1119_5.0150809.1 10.1119_5.0150809.1
Janus nanoparticles as efficient interface compatibilizer in blends of polylactide and elastomers: Importance of interfacial relaxation on toughening
Authors: Qiao Huawei , Yang Bingrui , Zheng Botuo , Chen Mingfeng , Cardinaels Ruth , Moldenaers Paula , Lamnawar Khalid , Maazouz Abderrahim , Zhang Huagui
Published: August 2024

For blending immiscible polymers, such as in the toughening modification of polylactide (PLA) via blending with rubbery materials, interfacial compatibilization is of great significance while the mechanism, especially the role of interfacial rheology, remains elusive. In this study, styrene-butadiene block copolymer elastomer (SBC) was employed to toughen PLA and a dumbbell-shaped Janus nanoparticle (JNP) consisting of polymethyl methacrylate and polystyrene spheres with equal size (∼80 nm) was used as the compatibilizer. Located at the interface, JNPs exhibited a great compatibilization efficiency in PLA/SBC blends, as demonstrated by the good morphology stabilization against droplet coalescence under static annealing and low shear flow conditions, as well as by the resistance against droplet breakup under high shear flow conditions. Moreover, as revealed from the linear viscoelasticity of JNP compatibilized blends, when JNP loading is more than 2 phr, aside from shape relaxation, an interfacial relaxation dominated by Marangoni stress was observed, indicating the possibility of particle redistribution on droplet surfaces. However, when loading is more than 4 phr, relaxations in the terminal zone no longer exist, implying the possible formation of a particle network on the droplet surface. This is consistent with the mechanical properties. The blend shows the greatest toughness at JNP loading around 3 phr, while the toughness is very poor when JNP loading is either too low or too high. This suggests interfacial relaxation to be crucial to guarantee a good toughening effect of SBC in PLA.
Stress-controlled medium-amplitude oscillatory shear (MAOStress) of PVA–Borax
Authors: Ramlawi Nabil , Hossain Mohammad Tanver , Shetty Abhishek , Ewoldt Randy H.
Published: August 2024

We report the first-ever complete measurement of MAOStress material functions, which reveal that stress can be more fundamental than strain or strain rate for understanding linearity limits as a function of Deborah number. The material used is a canonical viscoelastic liquid with a single dominant relaxation time: polyvinyl alcohol (PVA) polymer solution cross-linked with tetrahydroborate (Borax) solution. We outline experimental limit lines and their dependence on geometry and test conditions. These MAOStress measurements enable us to observe the frequency dependence of the weakly nonlinear deviation as a function of stress amplitude. The observed features of MAOStress material functions are distinctly simpler than MAOStrain, where the frequency dependence is much more dramatic. The strain-stiffening transient network model was used to derive a model-informed normalization of the nonlinear material functions that accounts for their scaling with linear material properties. Moreover, we compare the frequency dependence of the critical stress, strain, and strain-rate for the linearity limit, which are rigorously computed from the MAOStress and MAOStrain material functions. While critical strain and strain-rate change by orders of magnitude throughout the Deborah number range, critical stress changes by a factor of about 2, showing that stress is a more fundamental measure of nonlinearity strength. This work extends the experimental accessibility of the weakly nonlinear regime to stress-controlled instruments and deformations, which reveal material physics beyond linear viscoelasticity but at conditions that are accessible to theory and detailed simulation.
Tourism Touché: USA Fencing’s Delicate Dance With Tournament Site Selection
Authors: Baker Bradley J. , Gardner Ashley
Published: August 2024

This case explores the complex process of developing a national calendar of marquee events for the Olympic sport of fencing. USA Fencing, the national governing body, must meet diverse stakeholders’ needs while balancing competing priorities. Chief among the tensions is maximizing organizational revenues to fund operations versus minimizing costs and barriers to event access for participants. Suitable venues are scarce and clustered in major metropolitan areas with restrictive calendars. The limited number of potential locations impedes USA Fencing’s ability to extract concessions from host cities and negotiate hotel room rebates and venue rental fees. This also limits USA Fencing’s ability to accommodate other stakeholder preferences, such as attractive locations and adhering to a recently adopted policy to give preference to locations in states with inclusive laws regulating women’s reproductive health and LGBTQIA+ issues. With no perfect solutions, navigating these constraints requires judicious analysis of alternatives and artful negotiation between attendee demands and organizational imperatives to develop event schedules aligning with USA Fencing’s mission. By wrestling with this multidimensional resource allocation dilemma, students sharpen analytic skills and strategic decision-making competencies, grappling with the same complex questions event directors face in real-world scheduling environments marked by inadequacy and compromise.
Are There Sex Differences in Anaerobic Performance Following a Dynamic Warm-Up? A Randomized, Counterbalanced, and Crossover Design Study
Authors: Fulawka Kara , Schleper Alexander , Forsyth Lucas , Scribbans Trisha , Anzalone Robert , Villar Rodrigo
Published: August 2024

The increasing trend of females participating in elite and historically male-dominated sports has also resulted in a rise in females performing dynamic warm-ups (DWs). DW is a widely used practice in hockey. However, there is scarce evidence describing how DWs impact subsequent anaerobic performance and whether this response differs between sexes. This study aimed to determine sex differences in anaerobic performance when preceded by a DW. Twenty National Collegiate Athletics Association Division-II hockey players (n = 20, 10 female) completed a Wingate Anaerobic Test (WAnT) preceded by a DW or no warm-up in a randomized, counterbalanced order and followed a crossover design. The DW was ∼8 min long and consisted of 13 movements that targeted prime muscles and joints involved in ice skating. The WAnT consisted of a 30-s, maximal effort sprint against 7.5% of the participant’s body mass performed on a cycle ergometer. Peak power output (PPO), relative peak power (RPP), mean anaerobic power (MP), and fatigue index (FI) evaluated anaerobic performance during the WAnT. There were no significant differences between male and female scores following DW. MP was significantly higher in males and females, but PPO, RPP, and FI were not when a DW preceded the WAnT. In both conditions, males had higher PPO and MP than females, while there were no sex differences in RPP and FI. In conclusion, performing a DW before a WAnT improved MP for females and males with no adverse effects on PPO, RPP, and FI. This study suggests that DW might benefit hockey players independently of sex.