bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of Compressed Sensing Method With ℓ1/2-Norm in Fan/Compressor Mode Detection
Authors: Li Zhaoyin , Yang Zeyuan , Chai Pengfei , Sun Zonghan , Tian Jie , Ouyang Hua 
Published: September 2023

Abstract
In this paper, ℓ1/2-norm method is used to replace the traditional ℓ1-norm to improve the compressed sensing technique. Numerical experiments and fan/compressor tests were performed to validate the applicability and robustness of the CS method based on ℓ1/2-norm. Numerical experiments show that ℓ1/2-norm method can effectually eliminate the spurious mode peaks generated by failed recovery of ℓ1-norm method. Further study with random sensor failure shows the stronger robustness and applicability of ℓ1/2-norm method. In the low-order acoustic mode detection experiment on cooling fan, 24 sensors were used to conduct a mode decomposition at blade passing frequency (BPF). The recovered signal using ℓ1/2-norm method was sparser than that using ℓ1-norm method. In the case two sensors were randomly selected and removed as failed sensors, the deviation between results of ℓ1/2-norm method and original signal was also found smaller. In the condition that more sensors failed and ℓ1-norm method did not work properly, ℓ1/2-norm method could still detect the main mode. For further validation, the data from a high-order aerodynamic pressure mode detection experiment on axial compressor with two sensors damaged was processed through ℓ1/2-norm method. The mode decomposition results at both BPF and the rotating instability frequency (RIF) agreed with the conclusion of the first experiment. Numerical experiments and fan/compressor tests show that using ℓ1/2-norm instead of ℓ1-norm can significantly improve the application and robustness of compressed sensing in mode detection.
Numerical Investigation Into the Impact of Operating Boundary Conditions on NOx Formation in Hydrogen Micromix Combustion System
Authors: Singh Gaurav , Zghal Malika , Sun Xiaoxiao , Gauthier Pierre , Sethi Vishal 
Published: September 2023

Abstract
Hydrogen micromix combustion is a promising technology for achieving zero mission-level carbon emissions with ultra-low NOx potential. A reduced-order NOx emissions prediction model is essential for preliminary hydrogen engine cycle design space exploration and optimization studies.
Hence, this paper investigates the influence of key operating conditions, including equivalence ratio (ϕ), combustor inlet temperature (T3) and pressure (P3) on NOx emissions in a hydrogen micromix combustion. The assessments were performed using steady Reynolds-Averaged Navier-Stokes (RANS) simulations with thermal NOx model at various power conditions representative of the aircraft mission. The RANS model constants were calibrated against Large Eddy Simulations (LES) conducted previously by the group. The comprehensive numerical database was developed from these assessments to derive a NOx emissions correlation as a function of the operating conditions defined above.
The study demonstrates that the LES-calibrated RANS models can predict NOx emissions trends, which agrees with the known physics of NOx formation. When experimental data is not yet available, the resulting correlation can be used at the preliminary stage of the design process to identify low NOx engine cycles that merit (more resource-intensive) higher fidelity numerical simulations or experiments. The methodology is flexible and extensible and may be applied to future low-emissions hydrogen combustion technologies.
Numerical Investigation of a Hydrogen-Air Flame for NOx Prediction
Authors: Leparoux Julien , Mercier Renaud , Puggelli Stefano , Cailler Mélody , Moureau Vincent 
Published: September 2023

Abstract
Sustainable Aviation Fuels (SAF) are a major candidate to reduce pollutant emissions in future aeronautical engines. Recently, the use of hydrogen as a fuel has gained a high interest partly because its combustion is free from carbon dioxide, a greenhouse gas, and produces few pollutants, mainly nitrogen oxides (NOx). Over the last decades, efforts on numerical methods for combustion simulation in aero-engines have largely been focused on kerosene-air combustion. However, the current transition may have a significant impact on the computational methodologies for combustor design. Hydrogen defines novel modeling issues and challenges the current state of art on numerical methodologies. The current study presents a numerical investigation of a hydrogen-air burner using Large-Eddy Simulations (LES) with a focus on NOx prediction. The considered configuration is a two-staged combustor, similar to the well-known RQL (Rich-Quench-Lean) technology, supplied by a single coaxial injector characterized experimentally. Two combustion models are investigated: i) tabulated chemistry based on premixed flamelets ii) transported chemistry description by using a 21-species chemical scheme. Numerical results are compared with experimental data (NOx concentrations, temperature distributions, pressure losses). A focus on models predictions is carried out.
Results show a good agreement to predict the main flow characteristics and the premixed flame position over different operating points and geometries for both frameworks. In contrast, NOx emissions are more sensitive: while the overall trend is well captured, the quantification is more scattered. Finally, an in-depth analysis is proposed to link NOx production with the non-premixed flame size.
Integrated Hybrid Engine Cycle Design and Power Management Optimization
Authors: Ghelani Raj , Roumeliotis Ioannis , Saias Chana Anna , Mourouzidis Christos , Pachidis Vassilios , Bacic Marko , Norman Justin 
Published: September 2023

Abstract
A novel integrated gas turbine cycle design and power management optimization methodology for parallel hybrid electric propulsion architectures is presented in this paper. The gas turbine multi-point cycle design method is extended to turboprop and turbofan architectures, and several trade studies are performed initially at the cycle level. It is shown that the maximum degree of electrification is limited by the surge margin levels of the booster in the turbofan configuration.
An aircraft mission-level assessment is then performed using the integrated optimization method initially for an A320 Neo style aircraft case. The results indicate that the optimal cycle redesigned hybrid electric propulsion system (HEPS) favors take-off and climb power on-takes while optimal retrofit HEPS favor cruise power on-takes. It is shown that for current battery energy density (250 Wh/Kg), there is no fuel burn benefit. Furthermore, even for optimistic energy density values (750 Wh/kg) the maximum fuel burn benefit for a 500 nm mission is 5.5% and 4% for redesigned and retrofit HEPS, respectively. The power management strategies for HEPS configurations also differ based on gas turbine technology with improvement in gas turbine technology showing greater scope for electrification.
The method is then extended to ATR 72 style aircraft case, showing greater fuel burn benefits across the flight mission envelope. The power management strategies also change depending on the objective function, and optimum strategies are reported for direct operating cost or fuel burn. The retrofit case studies show a benefit in direct operating cost compared to redesigned case studies for ATR 72. Finally, a novel multimission approach is shown to highlight the overall fuel burn and direct operating cost benefit across the aircraft mission cluster.
Mitigation of Start-Up Coupled Lateral-Torsional Vibration of a Synchronous Motor Driven Integrally Geared Centrifugal Compressor
Authors: Luo Zhusan , Schwarz Carl L. 
Published: September 2023

Abstract
This paper presents a study on the enhancement of the coupled lateral-torsional rotordynamic performance of a synchronous motor driven main air compressor. This is a four-stage integrally geared centrifugal compressor with two pinions. In compressor commissioning, the low speed pinion experienced excessive lateral vibration during start. This pinion was intensely excited when the motor speed passed through the first torsional natural frequency of the compressor drive train. A coupled lateral-torsional vibration analysis is performed to predict the oscillating torques in different shafts, gear mesh forces and lateral vibrations of the pinions. To understand the mechanisms for the high pinion start-up vibration, main design variables and operating conditions that may affect the pinion vibration are examined. The results show that the pinion start-up vibration is sensitive to the coupling torsional stiffness, the pinion bearing design, the impeller mass properties, and the gear mesh direction (upmesh or downmesh). It has been found from the frequency response functions that the vibration is strongly associated with the first backward mode frequency and logarithmic decrement, whose importance has not been realized in this sense. To effectively mitigate the excessive lateral vibration, rotordynamic design considerations are briefly discussed in this paper.
On the Development of High Lift, High Work Low-Pressure Turbines
Authors: Clark John P. , Paniagua Guillermo , Cukurel Beni 
Published: September 2023

Abstract
Here we describe a combined design, numerical, and experimental program intended substantially to increase the lift and work of low-pressure turbine stages. This exercise is critically dependent upon the appropriate modeling of boundary-layer transition over airfoil surfaces. The effort proceeds through the design of turbine stages consistent with future unmanned air vehicle engine cycles. Then, a series of experiments are described that increase in complexity while driving the technology to more realistic embodiments. Representative experimental data are compared to pre-test predictions of the flow field, and it is shown that acceptable Reynolds lapse behavior is achievable even for turbines with significantly increased lift and work over state-of-the-art systems. Additionally, it is shown that through the judicious use of appropriate flow control technologies, it is possible to improve further the lapse characteristics of very high-lift airfoils. Finally, the benefits of applying such high lift, high work low-pressure turbine components are outlined with respect to a notional aircraft system, and future experiments are proposed.
Non-Destructive Inspection of Hot Corrosion Damage on Internal Surfaces of Turbine Blades
Authors: Kuipers Justin , Wiens Kevin 
Published: September 2023

Abstract
Two non-destructive techniques for the identification of hot corrosion damage on internal surfaces were investigated: magnetic permeability measurements and x-ray computed tomography (CT). A group of sixty-one Solar Titan 130 stage 1 blades which were known to have hot corrosion damage on the internal surfaces at a specific location were used for the investigation. X-ray CT was able to accurately identify the presence of hot corrosion as well as the extent to which it had progressed through the wall at the location of interest. The magnetic permeability technique was found to accurately identify whether hot corrosion damage had occurred at the location of interest, but could not as accurately determine the extent to which the damage had progressed through the wall. The results of the non-destructive testing were validated by destructive examination of some blades. The non-destructive testing methods evaluated through the study were able to determine the presence and extent of localized hot corrosion damage on internal surfaces, allowing for higher repair yields.
One Dimensional Model to Predict the Total Pressure Loss of Volute for Inward Flow Radial Supercritical CO2 Turbines
Authors: Hoque Syed Jiaul , Kumar Pramod , Gopi Pramod Chandra 
Published: September 2023

Abstract
Inward flow radial sCO2 turbines operate at considerably higher speeds than conventional gas or steam turbines making only the low specific speed designs practically realizable. Low specific speed designs suffer from significantly high viscous losses in the volute due to long and narrow flow passages. The volute loss in low specific speed designs causes an 8–12% efficiency drop, approximately 50% of the total loss. The paper proposes a quasi-one-dimensional model to estimate the total pressure loss of a volute with acceptable accuracy while consuming negligible computational power compared to a three-dimensional CFD simulation. The model converts the three-dimensional flow of a volute into an equivalent quasi-1D flow. Boundary layer-based momentum integral method is used on the quasi-1D flow path to calculate the total pressure loss. A computer program is developed to implement the proposed model. The accuracy of the model is tested with three-dimensional CFD results in the kW to MW power scale for different boundary conditions. The validation study is conducted for two volute cross-sections – circular and trapezoidal, to check the universality of the model. The model estimates the total pressure loss with less than 10% error for all test conditions. For the same conditions, a fully developed pipe flow model shows a considerably high error (∼50%) in total pressure loss prediction. The model can also accurately calculate losses under off-design operations and volute with surface roughness.
Mistuning Sensitivity of a Fan Bladed-Disk With Geometrical Nonlinearities
Authors: Quaegebeur Samuel , Thouverez Fabrice 
Published: September 2023

Abstract
In order to decrease their environmental impact, turboengine manufacturers tend to increase the span of fan blades while maintaining a slender profile. This design leads to more pronounced geometrical nonlinear effects. Computing the frequency response function of such structures is complicated due to the size of their associated finite element model. Classical substructuring approaches are no longer efficient to reduce the size of the problem as all the nodes of the system must be kept since they experience nonlinear behaviors. Different reduction methodologies have been defined in the past decades to tackle such nonlinear systems. Among these strategies, the Direct Normal Form extends the theory of normal form to finite element models. This methodology is here applied to a single blade model. Based on the assumption of a fairly rigid disk and of the cyclic symmetric properties, a full cyclic symmetric reduced-order model is computed. In this work, this methodology is extended to account for random mistuning. Such a strategy allows to perform, for instance, fast parametric studies. This paper studies the sensitivity of the random mistuning on a nonlinear Open Rotor system in order to help turboengineers in their design phase. Three ranges of the excitation level are studied. At low level of excitation, the system is close to the linear case. For higher forcing amplitude, a high amplification factor due to the merge of an isolated branch is observed, which is detrimental for the structure. For the last range (contains the highest forcing amplitudes), the nonlinearities are highly activated and low values of the amplification factor are obtained due to the spread of the vibrational energy over the frequency range.
Data-Driven Surrogate Modeling of Microturbine Combustors Burning Hydrogen Blends
Authors: Bhattacharya Chandrachur , Christopher Joshua , Thierry David , Biruduganti Munidhar , Supekar Sarang , Dasgupta Debolina 
Published: September 2023

Abstract
Hydrogen is a good candidate as an alternative fuel for power generation, due to the absence of carbon. Retrofitting available combustion systems to run hydrogen or its blends with natural gas is an effective option to decarbonize this sector. This demands a reassessment of the system response for the entire range of operation. Experimentation can be expensive and prohibitive from safety standpoints, and though computational models can provide data to fill the gaps, they come with their own sets of challenges. Data-driven surrogates use machine learning methods to learn from the sparse available data and can fill this knowledge gap by learning statistical correlations that describe the system. In this paper, a data-driven surrogate model is developed for a Capstone C65 microturbine combustor that is modified to burn pure natural gas and blends with up to 60% hydrogen for various power demands. Gaussian process (GP) regression modeling is used to learn from this dataset to emulate the system characteristics. Active learning is also invoked to learn a good model using as few data points as possible. Additional data is, then, generated using Reynolds-averaged Navier-Stokes (RANS) simulations of the same combustor geometry across a wider range of operating conditions i.e., 0–100% hydrogen for 0–65kW power loads. This provides low-fidelity information that can be included in a multi-fidelity learning setting which shows distinct improvements over the single-fidelity model. The novel multi-input-multi-output multi-fidelity GP surrogate modeling framework used in this work, is developed in-house using GPyTorch, which runs on a PyTorch backend, and is capable of superior scaling compared to traditional GP approaches.
Effect of Reduced Oil Flow Rate on the Performance of a Load on Pad Journal Bearing: Flooded vs. Evacuated Conditions
Authors: San Andrés Luis , Ouyang Zihan , Qin Yudi 
Published: September 2023

Abstract
Means to decrease the energy consumption of tilting pad journal bearings (TPJBs) without affecting their performance and structural integrity are mandatory in a cost efficient operation. Reducing the lubricant flow supplied to a bearing is a distinct method to diminish drag power losses along with savings in oil storage and pump equipment. However, a too low flow remains questionable in industrial practice. Starved flow conditions produce hot pad surfaces that could lead to Babbitt failure; and under certain loads, generate subsynchronous vibrations (SSV). This paper aims to resolve some of the issues above via measurements of the load performance conducted with a four-pad TPJB configured as load-on-pad (LOP) and having its ends sealed or open to make flooded and evacuated conditions. Prior measurements were conducted with the same bearing under load-between-pads (LBP); see Refs. [1,2]. The nominal supplied flow (Q) of ISO VG 46 oil at 60 °C is proportional to shaft speed (max. 12 krpm: 62.8 m/s surface speed). In the tests, the flow Qs ranges from 1.5 Q to just ¼ Q, and the applied units load reaches 2.07 MPa. Compared to the flooded bearing, the evacuated bearing produces a slightly larger eccentricity across the range of flow rates. For a unit load = 2.07 MPa and shaft speed of 6 or 12 krpm, the highest pad subsurface temperature reaches ∼ 130° C for Qs below 50% nominal. For both bearings, flooded or evacuated, drag power losses decrease ∼30% as the oil flow drops from 100% to 50% Q. As the oil flow increases to 1.5 Q, the drag power increases ∼10% for both bearing types at 6 krpm and for the flooded one at 12 krpm, while the evacuated bearing shows a reduction of ∼7%. The drag power grows as the static load increases; the evacuated bearing producing up to ∼ 40% lesser power loss than the flooded bearing. Both bearings produce similar size direct stiffnesses though largely orthotropic, Kyy &gt;&gt; Kxx. Direct damping coefficients Cxx ∼ Cyy increase with shaft speed and unit load but dramatically decrease as Qs drops, in particular for the evacuated bearing. The current measurements and those in Refs. [1,2] demonstrate that LOP and LBP bearings can safely operate with 50% of nominal flow thus saving drag power and without too large pad temperature rises. Alas, too low Qs produce a significant reduction in the damping coefficient orthogonal to the applied load direction. The effect is most evident in the LOP evacuated bearing which is most prone to show SSV Hash.
Impact of Fuel Type on Aircraft Range: An Initial Optimization Study
Authors: de Nercy - Maingard Hugo , Palies Paul 
Published: September 2023

Abstract
Aviation decarbonization is an essential step to contribute to reduce the CO2 footprint and the impact on climate. Among the various possible avenues to fulfill this requirement, thermal-powered aircraft fueled with liquid hydrogen is considered in this paper. Considering the several challenges at stake, one central question that subsists in deploying such aircraft is the impact of the fuel on the Breguet range. For example, for hydrogen, the density either as a gas or as a liquid is very low compared to other in-use or being considered fuels, yet its specific energy (MJ/kg) is the highest. These two major differences, fluid density and energy density, need to be coupled to the aircraft range to assess accurately what type of flights mission can be covered with hydrogen or other fuel. In this paper, a model is developed and applied to three different fuels to determine the corresponding aircraft range, volume of tank, and engine fuel mass flow rate for two mission profiles and two aircraft class. The mission profiles considered are both short and long haul. The aircraft studied are narrow-body and wide-body aircraft class. The two main fuels considered in this paper are SAF and hydrogen. The model development is presented as well as the iterative procedure to calculate key quantities. It is shown that for a narrow-body aircraft and a range of 1322 km, it would require nearly one ton of liquid hydrogen, which represents an estimated corresponding tank volume of 15 m3. This result is of major importance because as of today narrow-body aircraft are responsible for nearly 50% of the aviation CO2 footprint worldwide and are used on average over distances of 1322 km.
Rotordynamics of a Rotor Supported by Foil Bearings Under Various Housing Excitation
Authors: Lee Woongeon , Kim Daejong 
Published: September 2023

Abstract
Proton Exchange Membrane (PEM) Fuel cell Systems (FCS) are rapidly growing technology in the field of electric cars, buses, and trucks. In such applications, a motor-driven oil-free air compressor is one of the most critical auxiliary subsystems for the FCSs. Foil bearings are the perfect choice as oil-free bearings for FCS compressors due to high rotordynamics stability and shock-resistance. The platform of a motor-driven oil-free compressor can also be used as an electric turbocharger for traditional internal combustion engines. All electromechanical subsystems for electric vehicles must satisfy vibration endurance requirements following ISO 16750-3:2012, characterized by certain g-loading at specific frequencies. FCS air compressors also follow the same ISO 16750 standard. For the compressor to satisfy ISO 16750 requirement, detailed rotordynamics simulations with externally excited compressor housing under certain g-loading are essential to design the foil bearings considering the static and dynamic loads to the bearing and rotordynamics stability. The main objectives of the current research are 1) to develop a six degree of freedom (6-DOF) dynamic model of the rotor supported by foil bearings under external excitation to the compressor housing, 2) to simulate linear and non-linear rotordynamics of the compressor rotor supported by two radial foil bearings, and 3) to provide appropriate design guideline such as bump stiffness and axial length of the foil bearings. The simulations show that the rotor is stable for both under single frequency excitation and simultaneous excitations of all the frequencies in ISO 17650 standard. 4-DOF modal analyses were applied to identify natural mode of the system under the housing excitation.