bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heat Transfer Enhancement in Pulsating Flows: A Bayesian Approach to Experimental Correlations
Authors: Ignuta-Ciuncanu Matei Cristian , Noon Chris , Martinez-Botas Ricardo F. 
Published: August 2024

Abstract
This research focuses on improving the modelling of heat transfer effects in pulsating exhaust flows. We address the challenges of understanding oscillating flow by employing the Metropolis-Hastings Markov Chain Monte Carlo sampling method for parameter estimation, accounting for measurement uncertainties.
The knowledge can be applied to waste heat from reciprocating devices, pulsating turbocharger performance, and flow fields with significant cyclic variations. We demonstrate the feasibility of characterising heat transfer capacity in pulsating flows using Bayesian inference and polynomial regression for experimental data correlation. This methodology is furthermore applied to identify heat transfer patterns in cold gas flow through a heated pipe across a range of mass flow rates and pulsating frequencies. To achieve this, the thermal performance variations across the length of the pipe through temperature and pressure changes are quantified. The model developed exhibits robust performance and high data efficiency (R2 ∈ [0.83, 0.89]) and notable extrapolation capacity in predicting mean heat transfer beahviour based on boundary measurements. The results address the lack of experimental insights on pulsating flows encountered in heavy-duty transport applications and can be extended for heat recovery in systems such as exhaust manifolds and Organic Rankine Cycle gas turbines.
A Parametric Study on NOx Emissions From Ammonia Containing Product Gas in Rich Quench Lean Combustion
Authors: Raslan Ahmed , Yang Silin , Durocher Antoine , Güthe Felix , Bergthorson Jeff 
Published: August 2024

Abstract
Due to climate change, there has been an increasing demand for fuels that can accelerate the transition away from fossil fuels to clean energy. Humidified product gas obtained from gasifying biomass is emerging as a promising candidate to replace natural gas, as it is composed of a gaseous mixture of hydrogen, steam, carbon monoxide and methane. However, the gasification process releases ammonia and other nitrogen bearing compounds into the product gas, resulting in substantial increases in nitric oxides, NOx, in the exhaust. As such, there has been a recent push to understand the underlying chemical kinetics that drive NOx formation in order to optimize gas turbines to mitigate emissions at the source. In this study, a simplified CRN model for a gas turbine Rich-Quench-Lean (RQL) type combustor was developed in Cantera. The following parameters were investigated in this study: equivalence ratio of the primary section (1.1 to 1.6), overall equivalence ratio (0.6 to 1.1), steam dilution (25% and 50% molar dilution), post flame residence time (0 to 75 ms) and recirculation from the post quench region to the primary section (0 and 40% by mass). Additionally, a benchmark CRN representing a Lean Burner (LB) as also developed. Results of the CRN model suggest that, when comparing to LB, a RQL type combustor delivers up to a 75% reduction in emissions. Additionally, it was found that, for both the LB and RQL combustors, an overall lean to stoichiometric equivalence ratio is well suited to reduce emissions in highly humidified fuels, while for moderately humidified fuels it is preferable to operate in an overall slightly rich equivalence ratio. The difference observed is mainly due to the fact that, at high humidification and lean conditions, the temperature is favourable for the conversion of ammonia to nitrogen. While, at moderate humidification and rich conditions, NO reacts with ammonia in the reburn process. Finally, it is suggested that the incorporation of recirculation from the secondary section to the primary section of the RQL burner results in a broader low emission region, due to more favourable conditions for ammonia conversion to nitrogen in the primary section.
The Unsteady Shock-Boundary Layer Interaction in a Compressor Cascade – Part 2: High-Fidelity Simulation
Authors: Klose Bjoern F. , Morsbach Christian , Bergmann Michael , Munoz Lopez Edwin J. , Hergt Alexander , Kügeler Edmund 
Published: August 2024

Abstract
In the second part of this three-paper series, high-fidelity simulations of the Transonic Cascade TEAMAero at the aerodynamic design point with Rein = 1.35 × 106 and Main = 1.21 are presented. A high-order discontinuous Galerkin spectral element method with finite-volume subcell shock capturing is employed to simulate the flow based on an implicit LES scheme and advanced over several buffeting cycles to reliably capture the shock unsteadiness. A study on the spanwise domain size shows that the shock oscillation amplitude decreases with increasing span, although its frequency and mean location remains fixed through the simulations. By comparing high- and low-resolution LES results, it is further presented that deviations from under-resolution are mostly limited to the separated region past the shock, where the high-fidelity results match experimental results more closely. In addition to the LES, low-fidelity URANS is shown to capture the shock unsteadiness correctly, but at a reduced amplitude and fails to match the force distributions on the blade surface. Through examination of instantaneous flow features, space-time relations and spectral proper orthogonal decomposition, a basic analysis of the shock-boundary layer interaction is presented and indicates that velocity perturbations travel upstream through the subsonic boundary layer and periodically cause oblique shock waves, transporting the information from the boundary layer into the passage.
Impact of High Freestream Turbulence on LPT Endwall Flow – Part II: Endwall Flow Dynamics
Authors: Donovan Molly H. , Marks Christopher R. , Fletcher Nathan , Rumpfkeil Markus P. 
Published: August 2024

Abstract
The flow field surrounding low-pressure turbine blades is associated with significant losses in the endwall region. The exact location and behavior of the endwall structures is tied to the incoming boundary layer state; therefore, the incoming freestream turbulence is expected to impact dynamic characteristics of these structures and the associated losses. As discussed in Part I, the incoming turbulence intensity was varied between &lt; 1% and 7% at three different Reynolds numbers within a linear cascade of high-lift high-work low-pressure turbine blades. The focus of this paper will be on the effect elevated freestream turbulence has on the unsteady dynamics of the endwall flow structures. Three planes of high-speed stereoscopic particle image velocimetry were collected within the passage of the turbine blades capturing cross-sectional slices of key endwall vortices. From a detailed flow analysis completed with SPIV measurements, it was established that elevating the turbulence levels had a direct impact on the locations and time-dependent characteristics of the endwall topology. Differences in temporal characteristics were observed in all planes with the introduction of elevated turbulence; however, the bimodal behavior documented by other researchers near the leading edge was still observed. The horseshoe vortex was found to intermittently lose coherence at the leading edge and in the passage. The frequency of the loss of coherence events as well as the vortex position was altered as the freestream turbulence was elevated.
A Practical Evaluation of Equations of State and the New PTC-10 Polytropic Calculations for Centrifugal Compressors
Authors: Srinivasan Anand , Kurz Rainer , David Timothy 
Published: August 2024

Abstract
The ASME Performance Test Code (PTC-10) stipulates the need for a unified polytropic calculation procedure on reporting out performance characteristics for centrifugal compressors. The accurate determination of enthalpy and entropy, in addition to the thermodynamic gas constants, plays a crucial role in predicting the performance of a compressor. The measured temperatures and pressures at the inlet and exit of the compressor are used to obtain the thermodynamic properties, which are in turn used to evaluate the compressor performance. These thermodynamic properties depend on the equation of state used for the calculations. In this paper, the influence of equation of state on the performance of centrifugal compressors on carbon dioxide and natural gas is investigated. Several commonly used equations of state including REFPROP, Redlich-Kwong, Lee-Kesler-Ploecker and Peng-Robinson are used for the comparison. The recently-released 2022 revision to the ASME PTC-10 code proposes the use of the Sandberg-Colby & Huntington’s methods to evaluate the polytropic performance of a centrifugal compressor. The use of these methods is investigated in this paper to evaluate the performance of gas compressors. A discussion on the use of these methods on natural gas as a function of discharge pressure is also presented in this paper.
Numerical Study on Separation Flows of a Compressor Transition Duct
Authors: Liu Zhenliang , Wu Yadong , Zhang Xinze , Ouyang Hua 
Published: August 2024

Abstract
The transition duct is a core part of aeroengines, connecting low and high-pressure compressors (LPC & HPC). Nowadays, the balance between the stability of airflow and the compactness of transition ducts has been the major concern of designers. Unstable flows growth at low mass flow rate operating point and may cause accidents. A detailed understanding of the flow field of the transition ducts is crucial for achieving an optimal and safe design. A URANS simulation is conducted based on a combined model of a strutted transition duct and the outlet guide vane (OGV) of LPC. Focusing on the dynamics of vortices inside OGV and strut passages, the development and evolution of vortices are carefully discussed. The separations within OGV passages are categorized into closed and open separation, with the latter significantly blocking the passage and migrating circumferentially. Trailing vortex pair and corner separation vortex around the struts are stable, showing no interaction between passages. Further, the Proper Orthogonal Decomposition (POD) method is utilized. The corresponding relationship between instantaneous features of the pressure field at OGV passages and POD modes is revealed. Equally spaced peaks in the frequency domain are presented by different modes. In lower span, more energy is preserved in low-frequency modes. In higher span, more energy is preserved in high-frequency modes.
Design, Analysis, and Testing of an Additively Manufactured Catalytic Combustor for a Micro-Wave Rotor Turbine
Authors: Tüchler Stefan , Adamou Adamos , Akbari Pejman , Copeland Colin D. 
Published: August 2024

Abstract
In this paper, an additively manufactured (AM) Inconel catalytic combustor was tested in combination with a micro-wave rotor turbine with non-axial channels designed for shaft power extraction. This was done in an open-loop configuration over a range of operating conditions in order to characterise the behaviour of the wave rotor and combustor separately. The catalytic combustor data yielded low pressure losses of approximately 1% and provided stable and continuous operation up to outlet temperatures of 900°C and combustion efficiencies of up to 99%. The data also revealed a high sensitivity to local over-fuelling and hot spots that severely reduced service life. This is attributed to the additive manufacturing process producing uneven fuel injector hole sizes that cause uneven fuel mixing upstream of the catalytic reactor. However, it showed that first, it is possible to manufacture and coat an additively manufactured catalytic core. Secondly, it showed that the design freedom of AM could be used to make catalytic combustors viable in commercial applications.
Experimental Evaluation of an Electric Powertrain Designed for a 180-kW Turboelectric Aircraft Ground Test Rig
Authors: Johnsen Joshua , Melvin Joshua , Drake Joshua , Jdiobe Muwanika , Rouser Kurt 
Published: August 2024

Abstract
This paper presents the experimental results of a representative aircraft turboelectric powertrain. The 180-kW hybrid gas-electric ground test rig was designed, fabricated, and experimentally evaluated. Hybrid turboelectric power systems are an enabler for future medium- to long-range electrified aircraft, offering higher energy density over current battery technologies. Previous studies have focused on analytical models of turboelectric power systems. However, as industry stakeholders continue to advance toward implementing turboelectric parallel hybrid aircraft, there is a lack of practical knowledge regarding their implementation. The objectives of this study are twofold. First, the study aims to evaluate the real-time transient performance of turboelectric aircraft. The second objective aims to characterize the real-world challenges of safely constructing and operating a hybrid turboelectric aircraft. To accomplish both objectives, a turboprop-powered ground test vehicle was designed and fabricated. The ground test vehicle was constructed from a modified Cessna-172 aircraft, a modified 180-kW PBS-TP100 turboprop, two wing-mounted electric motors, and a purpose-built hybrid-turboelectric powertrain. A portion of the turboprop shaft power is extracted to generate electricity for the battery system and wing-mounted electric motors. The test vehicle was successfully brought to full engine power and the wing-mounted electric motors were run through a series of operating points to experimentally evaluate transient electrical and mechanical performance. Observations are made regarding the interdependent time responses of the electro-mechanical systems. Results from the test run include engine performance metrics, current, voltage, and acoustic data. The generator peaked at 4-kW and was augmented by 13-kW of battery power to drive distributed propulsors, while the turboprop generated 142-kW of power for the variable pitch propeller. Practical recommendations for safe integration are identified, such as the need for a pre-charge circuit, crowbar circuit, and future short protection circuit. This study provides critical insight into the design and practical implementation of turboelectric power systems for future electrified aircraft.
Multidisciplinary Optimisation of Additive Manufactured Heat Exchangers for Aeronautical Applications
Authors: Chiodi Alessandro , Alaia Alessandro , Lombardi Edoardo , Cisternino Marco , Gkaragkounis Konstantinos , Shahpar Shahrokh 
Published: August 2024

Abstract
In this work, we investigate a new methodology for the multi-scale simulation and optimisation of Micro Channel Heat Exchangers with lattice-like topology based on homogenization theory. The lattice matrix is modelled as an equivalent porous medium and is simulated only at the macroscale using standard CFD tools. Micro and meso-scale effects are incorporated in terms of variable permeability tensor and heat transfer coefficients, which are assumed to be non-linear functions of the local flow conditions and lattice geometry. Scale bridging is achieved thanks to a Machine Learning (ML) model which is trained to infer the required closure relationships from a database of Direct Numerical Simulations (DNS). DNS are performed at the scale of a single lattice cells for several geometries at varying operating conditions. The proposed approach is used to solve a benchmark problem provided by Rolls-Royce plc. The test case involves the optimization of a heat exchanger employed in the cooling system of power electronic. In order to assess the soundness of the proposed methodology, numerical results for three different configurations are presented. The effect of under (over) fitting is also investigated in terms of quality and performances of the final optimal geometry.
Numerical Study on the Influence of Purge Slot Shapes on the Film Cooling Performance of Endwall With the Mainstream Swirl
Authors: Zhang Jinghan , Xie Gang , Lou Yuzhu , Li Haiwang 
Published: August 2024

Abstract
For modern gas turbine design, a slot exists between the first-stage nozzle guide vane and the combustion chamber flame tube due to assembly requirements. This structure’s cooling performance is often overlooked or oversimplified in design. However, this article will consider the real combustion chamber exit flow field and conduct a detailed study of the cooling effect under aggressive swirl flow in the slot. This study employs a boundary condition generation method to evaluate the influence of swirling flow under various inlet conditions through numerical methods. The fundamental model consists of a single-row 45-degree slot combination with C3X nozzle guide vane. On this basis, a novel laterally expanding slot is designed. To assess the influence of swirling flow, two cases under two swirling flow orientations were studied. The numerical findings indicate that, under the conventional slot structure, the positive inlet condition can diminish the cooling effectiveness of the purge slot, whereas the negative swirl flow enhances it. Under uniform inlet, the newly designed laterally expanding slot demonstrates an average adiabatic cooling effectiveness surpassing that of the conventional slot, reaching as high as 76%. This innovative design exhibits superior cooling performance under both positive and negative swirl flow inlet conditions, while also maintaining a high degree of robustness in the presence of swirl flows.
On the Optimum Distribution of Multiple Helmholtz Resonators for Annular Combustors
Authors: Chen Hongwei , Yin Liming , Liu Xiaopei , Chen Mingmin , Yang Dong 
Published: August 2024

Abstract
The combustors of many modern land-based gas turbines and aero-engines are annular. This kind of combustors often suffer from thermoacoustic oscillations, with the occurrence of mostly the circumferential first-order, second-order and third-order oscillation modes in the annular combustion chamber. This could cause severe pressure oscillations in the combustor, which may increase noise and NOx emissions, affect the safe operation of the engine and even cause irreversible damages to the structure. To solve this problem, passive control methods are widely used — adding passive acoustic dampers such as Helmholtz resonators (HRs). Depending on the type and number of HRs, and the possible positions over the circumference to install them, there could easily have millions, or even billions, of possible arrangement patterns. Finding a good design is the key to solve this problem. In this paper, we perform a theoretical and numerical study of an annular combustor installed with multiple types of HRs over the circumference. Firstly, a simple annular duct with arbitrary distributions of these HRs is studied analytically by solving the nonlinear eigenvalue problem of a 1D network model. Based on the results of the analytical method, the impact of the HRs on the acoustic modes of the combustion chamber is studied and the optimum arrangement of multiple resonators is obtained. This arrangement usually gives a null (or small) mode splitting strength and a good damping effect. Finally, we apply the optimum arrangement to damp the thermoacoustic modes that have been captured by numerical simulation for a real annular combustor. We use numerical simulations based on solving the 3D Helmholtz equation in COMSOL to verify the feasibility of the optimum arrangement.
A Deep Learning Based Model for Identifying Recirculation Zones From Experimental Images of Trapped Vortex Combustors
Authors: Dash Priyabrat , Mallik Tanaya , Verma Nikhil , Roy Choudhury Aritra , Ravikrishna R. V. , Aditya Konduri 
Published: August 2024

Abstract
Particle image velocimetry (PIV) is a standard method for studying primary recirculation zones in trapped vortex combustors (TVCs), which can operate in an RQL configuration. However, its intrusive nature can disrupt the flow, flame, and equipment in compact combustors, leading to inaccuracies. As an alternative, we use deep learning models based on generative adversarial networks (GAN, a widely used approach) and vision transformers (ViT, a recently devised promising architecture) to estimate the position and overall structure of large-scale vortices from a non-invasively measured quantity, such as the planar laser-induced fluorescence (PLIF) of a species. These models are trained using datasets from large-eddy simulations (LES) of TVCs with information regarding all scalars constituting the state variable, with the addition of noise to mimic experimental data. Quantitative metrics such as relative errors and PDFs of velocity components and their orientation have been used to demonstrate that the ViT exhibits better performance than the GAN. Sensitivity to the type of noise added to simulation data during training is studied as well. The trained model is then used to infer velocity vectors from noisy OH-PLIF data. In the absence of ground truth for that case, qualitative observations reinforce our earlier notion of the superiority of ViT. Such models will facilitate intelligent data fusion and the development of digital twins of combustors.
Investigation of Flame Response in a Swirling Micromix Hydrogen-Methane Combustor
Authors: Liu Dewen , Feng Zhenzhen , Tian Xiaojing , Xu Liangliang , Gu Mingming , Lin Yang , Xia Xi , Qi Fei 
Published: August 2024

Abstract
Hydrogen-enriched natural gas combustion is a hot topic in industrial and academic communities due to the need for carbon emission reduction. However, thermoacoustic instability poses a major challenge for lean combustion development, particularly the higher frequency combustion oscillations. This study investigates the flame response in micromix hydrogen/methane flames within a low to medium frequency range of 50 to 1200 Hz, revealing a critical mixing ratio. Above this threshold, the flame response is dominated by hydrogen combustion, whereas below it, methane combustion takes precedence. Overall speaking, the hydrogen addition significantly enlarges the low-pass filter limit of the flame transfer function. Simultaneous OH* chemiluminescence and PIV experiments demonstrate that the gain is associated with the flame size and the number of acoustic-induced vortices on the flame surface. Higher frequency acoustic forcing leads to flame responses out of phase at different longitudinal positions, resulting in a low global flame response. Hydrogen addition reduces the flame length and enhances the FTF gain at specific frequencies.
Thermodynamic Optimization of Load-Following Operation in a Decarbonized Combined Cycle Power Plant Under Net-Zero Scenarios
Authors: Ravelli Silvia 
Published: August 2024

Abstract
Post-combustion capture (PCC) by means of mono-ethanolamine (MEA) and hydrogen co-firing, combined with exhaust gas recirculation (EGR), were applied to a typical 2x1 combined cycle (CC) with the goal of reaching net-zero CO2 emissions. The novelty lies in integrating decarbonization solutions into the daily operation of the CC, when power generation is adjusted according to fluctuations in electricity demand, throughout two representative days in summer and winter.
More specifically, off-design thermodynamic modelling was adapted to incorporate a multivariable optimization problem to find the maximum power plant efficiency as a function of the following decision variables:
- load of each gas turbine (GT), spanning from minimum turndown to full load;
- EGR rate, in a range that depends on the fuel type: [0; 0.4] for 100% natural gas (NG) vs. [0; 0.55] when hydrogen is fed to the combustor;
with the constraint of net power output equal to electricity demand, for given environmental conditions.
Suggestions were made to mitigate the energy penalty due to decarbonization in the load-following operation mode, taking the integration of MEA CO2 capture into the NG-fired CC as a benchmark. The solution in which EGR combines optimally with hydrogen in the fuel mixture, with the addition of PCC to abate residual CO2 emissions, has proven to be the most efficient way to provide dispatchable clean energy, especially in cold climates.