Gap Region Research Articles

Negative Dielectric Constant of Water at a Metal Interface.

Water polarizability at a metal interface plays an essential role in electrochemistry. We devise a classical molecular dynamics approach with an efficient description of metal polarization and a novel ac field method to measure the local dielectric response of interfacial water. Water adlayers next to the metal surface exhibit higher-than-bulk in-plane and negative out-of-plane dielectric constants, the latter corresponding physically to overscreening of the applied field. If we account for the gap region at the interface, the average out-of-plane dielectric constant is quite low (ε_{⊥}≈2), in agreement with reported measurements on confined thin films.

Data analysis on the three defect wavelengths of a MoS2-based defective photonic crystal using machine learning

To reduce the dimension of optoelectronic devices, recently, Molybdenum disulfide (MoS2) monolayers with direct bandgap in the visible range are widely used in designing a variety of photonic devices. In these applications, adjustability of the working wavelength and bandwidth with optimum absorption value plays an important role. This work proposes a symmetric defective photonic crystal with three defects containing MoS2 monolayer to achieve triple narrowband defect modes with wavelength adjustability throughout the Photonic Band Gap (PBG) region, 560 to 680 nm. Within one of our designs remarkable FWHM approximately equal to 5 nm with absorption values higher than 90% for the first and third defect modes are achieved. The impacts of varying structural parameters on absorption value and wavelength of defect modes are investigated. Due to the multiplicity of structural parameters which results in data plurality, the optical properties of the structure are also predicted by machine learning techniques to assort the achieved data. Multiple Linear Regression (MLR) modeling is used to predict the absorption and wavelength of defect modes for four datasets based on various permutations of structural variables. The machine learning modeling results are highly accurate due to the obtained R2-score and cross-validation score values higher than 90%.

Magnetic field effect on tunneling through triple barrier in AB bilayer graphene

We investigate electron tunneling in AB bilayer graphene through a triple electrostatic barrier of heights Ui(i=2,3,4) subjected to a perpendicular magnetic field. By way of the transfer matrix method and using the continuity conditions at the different interfaces, the transmission probability is determined. Additional resonances appear for two-band tunneling at normal incidence, and their number is proportional to the value of U4 in in the case of U2<U4. However, when U2>U4, anti-Klein tunneling increases with U2. The transmission probability exhibits an interesting oscillatory behavior when U3>U2=U4 and U3<U2=U4. For fixed energy E=0.39γ1, increasing barrier widths increases the number of oscillations and decreases Klein tunneling. The interlayer bias creates a gap for U2<U3<U4 and U3>U2=U4. In the four-band tunneling case, the transmission decreases in T++, T+− and T−− channels in comparison with the single barrier case. It does, however, increase for T−+ when compared to the single barrier case. Transmission is suppressed in the gap region when an interlayer bias is introduced. This is reflected in the total conductance Gtot in the region of zero conductance. Our results are relevant for electron confinement in AB bilayer graphene and for the development of graphene-based transistors.

EFFECT OF SOWING TIME IN COTTON (GOSSYPIUM HIRSUTUM L.) ON BOLL DISTRIBUTION, CELLULOSE RATIO AND FIBER QUALITY

The growth, flowering, square, and boll formation of the cotton plant are significantly affected by sowing time and fruiting distributions. This study was carried out in order to determine the effect of sowing time, varieties and boll distribution on fiber yield and fiber quality of cotton, under the GAP region ecological conditions of Türkiye during 2017 and 2018 cotton growing seasons. In this study, Candia and Lima cotton varieties were used as plant material. Cotton seeds were sown on 5 May (normal sowing) and 10 June (late sowing) using a pneumatic seeder in both years. In the study, the number of bolls (per plant-1), yield per plant (g plant-1), boll weight (g), ginning outturn (%), holocellulose, cellulose, scan viscosity, and polymerization degree were studied. According to the research, the number of bolls, boll weight, and fiber yield were higher in normal planting than in late planting. The low positional sympodial branch (1-5 fruit branches) boll position was better in the number of bolls, and the middle positional sympodial branch (6-10 fruit branches) was better in boll weight compared to other positions. The fiber yield obtained in a low positional sympodial branch (1-5 fruit branches) and middle positional sympodial branch (6-10 fruit branches) positions was higher than the upper positional sympodial branch position (11 and higher fruit branches). The effects of sowing times and cultivars on cellulose and holocellulose rations were statistically insignificant. The cellulose ratio (94.40) obtained in the upper positional sympodial branch position (11 and higher fruit branches) in the first year was higher than the other sympodial positions, while the effect of the boll position was statistically insignificant in the second year of the experiment. In conclusion, the planting time had a significant effect on boll positions and fiber quality of cotton. Late sowing had negative impact on boll maturation, cellulose synthesis, yield and fiber quality. Hence, the delay in cotton planting caused a decrease in yield; so, cotton should be sown as early as possible in the region. Keywords: Cotton, sowing date, boll position, boll weight, fiber quality

Imaging overpressurised fracture networks and geological barriers hindering fluid migrations across a slow-deformation seismic gap

There is an ongoing debate on the processes producing background seismicity and deformation transients across seismic gaps, i.e., regions that lack historical large-magnitude earthquakes. Essential missing elements are geophysical images that resolve sources of geophysical unrest. Here, we apply seismic scattering and absorption tomography to data recorded during the 2010–2014 seismic sequence within the Mt. Pollino seismic gap region (Southern Italy). The tomographic models show high sensitivity to fluid content, deformed fractured structures, and impermeable layers stopping fluid migrations. They bridge the gaps between geological and geophysical models and provide a highly-resolved image of the source of seismic and deformation unrest within this seismic gap. High absorption topping the western Pollino seismic volume appears pressurized between the low-Vp/Vs and low-scattering San Donato metamorphic core and a deep basement. Absorbing fluids can only migrate laterally to the east, blocked in the west and southwest by deep low-scattering barriers associated with east-dipping faults and to the north and southeast by saturated overpressurized low-scattering basins. This eastern migration is only partially effective, producing seismicity across the lowest boundary of the high-absorption volume. Our results showcase the potential of seismic scattering and absorption when imaging structures causing geophysical unrest processes across fault networks.

Optimizing thermoelectric performance of carbon-doped h-BN monolayers through tuning carrier concentrations and magnetic field

The thermoelectric properties of carbon-doped monolayer hexagonal boron nitride (h-BN) are studied using a tight-binding model employing Green function approach and the Kubo formalism. Accurate tight-binding parameters are obtained to achieve excellent fitting with Density Functional Theory results for doped h-BN structures with impurity type and concentration. The influence of carbon doping on the electronic properties, electrical conductivity, and heat capacity of h-BN is studied, especially under an applied magnetic field. Electronic properties are significantly altered by doping type, concentration, and magnetic field due to subband splitting, merging of adjacent subbands, and band gap reduction. These modifications influence the number, location, and magnitude of DOS peaks, generating extra peaks inside the band gap region. Heat capacity displays pronounced dependence on both magnetic field and impurity concentration, exhibiting higher intensity at lower dopant levels. Electrical conductivity is increased by double carbon doping compared to single doping, but is reduced at high magnetic fields because of high carrier scattering. The electronic figure of merit ZT increases with lower impurity concentration and is higher for CB versus CN doping at a given field strength. The power factor can be improved by increasing magnetic field and decreasing doping concentration. In summary, controlling doping and magnetic field demonstrates the ability to effectively engineer the thermoelectric properties of monolayer h-BN.

Bionic Design and Optimization of the Wear-Resistant Structure of Piston Rings in Internal Combustion Engines

Internal combustion engines, during their operation, subject the piston to high-temperature and high-pressure conditions, requiring it to endure intense, continuous reciprocating motion. This strenuous process leads to significant wear and tear. Among the engine’s crucial components, the piston ring plays a pivotal role but is particularly susceptible to wear. Therefore, extensive research has been devoted to investigating the wear of piston rings, a critical sealing component within internal combustion engines. To address the high cost of existing coating methods, which hinders widespread application, we propose a bionic design approach inspired by groove structures observed on earthworm bodies, aimed at enhancing the wear resistance of piston rings. Bionic piston rings featuring optimally designed groove structures inspired by the earthworm’s anatomy were designed. These rings exhibited varying groove depths (1 mm, 2 mm, and 3 mm), groove widths (0.1 mm, 0.3 mm, and 0.5 mm), and groove spacings (0.1 mm, 0.2 mm, and 0.3 mm). We conducted thermal–structural coupling analyses on both standard piston rings and these bionic counterparts. The results revealed that the maximum stress was concentrated at the first piston ring, precisely at the opposing region of the end gap. Thus, the initial piston ring endured the primary frictional losses. Moreover, a comparison of stress levels between bionic rings and the standard ring revealed that the bionic groove structure substantially reduced stress and minimized stress concentration, thus enhancing wear resistance. Groove width had the most notable influence on wear performance, followed by groove depth and groove spacing. Optimal wear resistance was achieved when the groove depth was 3 mm, groove width was 0.1 mm, and groove spacing was 0.1 mm. Subsequently, we constructed a piston ring friction test bench to validate the wear resistance of the most effective piston ring. The results indicated that the wear resistance of the bionic piston ring exceeded that of the standard piston ring by up to 19.627%. Therefore, incorporating a bionic groove structure within the piston ring can effectively reduce surface friction and enhance wear resistance. This, in turn, can enhance the operational lifespan of internal combustion engines under favorable working conditions.

Large‐Gap Quantum Spin Hall State in Double‐Transition‐Metal Homologous Compounds of WSi2N4: A First‐Principles Study

Recently, the MoSi2N4(MoN)4n homologous compounds have been synthesized, extending the MA2Z4 family materials to the superthick MA2Z4(MZ)n form. Herein, a first‐principles study on the double‐transition‐metal W2TiSi2N6 and related group VI–IV M2M′Si2N6 nanosheets is performed. Robust structural stability is affirmed in this W2TiSi2N6 nanosheet from the energetic, mechanical, dynamical, and thermal perspectives. Unlike the WSi2N4 and WSi2N4(WN)n systems, the W2TiSi2N6 nanosheet exhibits a semimetal behavior with the top valence and bottom conduction bands touching each other at the Fermi level. With the inclusion of spin–orbit coupling, a nontrivial band gap is opened in the W2TiSi2N6 nanosheet, which has a sizeable bulk gap of 0.11 eV. The Z2 invariant is 1 and a pair of topologically protected edge states emerges in the gap region, confirming that W2TiSi2N6 nanosheet is a quantum spin Hall (QSH) insulator. Through in‐plane strain engineering, the bulk gap can be further increased to 0.23 eV, which is sufficiently large for the room‐temperature QSH effect. Such a large‐gap QSH state is also present in other group VI–IV M2M′Si2N6 systems with the combinations of MM′ = WZr, MoZr, and MoHf. This study demonstrates that the double‐metal M2M′Si2N6 nanosheets are promising candidates to realize fascinating topological quantum states.

GRAF: Gap region aware framework for Al-Si alloy microscopic image segmentation

The shape of the primary silicon in Al-Si alloys is one of the main factors determining the properties of the alloy, which makes the microscopic image of Al-Si alloys become a crucial reference material in the study of the alloy. Accurate segmentation of silicon particles in Al-Si alloy micrographs is a necessary prerequisite for their quantitative analysis. The traditional manual annotation method requires high time and labor costs and will be affected by subjective factors of the annotator. Although automatic image segmentation methods can avoid these problems, there are silicon particles of different shapes and sizes in the Al-Si alloy microscopic image, and it is hard to separate adjacent silicon particles. These characteristics bring the automatic segmentation method severe challenge. Therefore, to address the issue of deviation in the annotation range when there is agglomeration of primary silicon particles in the microstructure images of Al-Si alloys, We propose a Residual Position-Aware Attention Network (RPAA-Net) for the segmentation of primary silicon particles. The RPAA-Net method enhances segmentation accuracy and robustness by incorporating a residual position-aware attention mechanism, enabling the network to better distinguish silicon particles from the surrounding non-silicon regions. To address the challenge of separating adjacent silicon particles in the image, we introduce a novel Gap Region Weighting Strategy (GRWS). GRWS enhances the model's focus on the gap regions between adjacent objects by applying additional weights during training. By combining RPAA-Net with GRWS, we construct a Gap Region Awareness Framework (GRAF) and experiment with different weights. We find that the weight with the most significant impact is 10, leading to the framework being named GRAF-10. Finally, we apply GRAF-10 to the Aluminum-Silicon Alloy Microstructure (ASAM) dataset. The results show that GRAF-10 outperforms the current state-of-the-art methods, improving the object-level Dice index(Dobj) by 1.56%. Additionally, it reduces the Merge Error (ME) metric by 6.74 and the Variation of Information (VI) metric by 5.43, effectively segmenting aluminum–silicon alloy microstructure images.

A first-principles and CALPHAD-assisted phase-field model for microstructure evolution: Application to Mo-V binary alloy systems

A multiscale computational framework combining the first-principles calculations and the CALPHAD approach with the phase-field method is presented to simulate the microstructure evolution in multicomponent steel alloys. We demonstrate the potential of the framework by predicting the microstructural evolution in elastically periodic arrays of the Mo-V binary sub-system. The framework utilizes the first-principles calculations using special quasi-random structures. Hitherto unavailable thermodynamic and material properties of the alloy are obtained by employing the first-principles calculations and the CALPHAD approach and fed into the phase-field model to predict the microstructure evolution at different temperatures within the miscibility gap region. In addition to the temperature and cooling rates, the model incorporates the role of mechanical fields in decomposition kinetics in the Mo-V binary alloy system. Regimes for temperatures and cooling rates at which spinodal decomposition occurs are identified. Applying external loading leads to directional phase separation in the Mo-V binary system. The elastic inhomogeneity in terms of material properties between the two phases initiates the directional alignment while eigenstrains and applied external loading control the degree of alignment. The framework developed is general and extendable to higher multicomponent sub-systems in steel alloys.

Analysis of electronic properties of hexagonal and triangular Bismuth quantum dot with different edges in the presence of magnetic field

We investigate energy spectra of Bi honeycomb quantum dots (BiQDs) considering buckled hexagonal and triangular structures with zigzag and armchair edges. We apply the four-orbital tight-binding approach. By using of the probability density of states, we distinguish some edge states in the regime of the band gap of Bi monolayer. We see that the number of edge states of zigzag (armchair) triangular BiQDs is more than the number of edge states of zigzag (armchair) hexagonal BiQDs. Also, we investigated energy spectra of hexagonal and triangular BiQDs with zigzag and armchair edges in the presence of the perpendicular magnetic fields. In the low and strong magnetic fields, there are relativistic Landau levels in the electronic spectra of BiQDs (in the hexagonal and triangular boundary conditions). Moreover, we show that edge atoms have more important roles in the formation of the line connectors between i and |i+1| Landau levels of hexagonal BiQDs than ones that are in the triangular BiQDs. In the middle numbers of the magnetic fields, more states collapse into Landau levels in which bulk atoms have a significant role to constitute them in both hexagonal and triangular BiQDs. Furthermore as the same as Bi nanoribbon spectrum, there are some helical edge modes in the band gap regions of Bi monolayer in which edge atoms are responsible to form them. These helical edge modes have topological properties.

Spin current for tuning the band gaps of spin waves

The paper reveals the mechanisms of interaction between the spin current in a conductor with strong spin–orbit coupling (Pt) and the spin wave in ferromagnetic media (YIG) with periodic thickness modulation under conditions of Bragg resonances and interlayer coupling. It is shown that in the structure the conditions for the formation of four Bragg resonances in the first Brillouin zone are satisfied. The effect of the spin current on spin waves with frequencies lying in the band gap region is much greater than the effect on spin waves at frequencies lying outside the band gaps. In particular, the spin current makes it possible to implement the frequency tuning of band gaps, changing the width and depth, as well as the number of band gaps. Moreover, the effect of the spin current on each of the band gaps is different. This feature allows us to talk about the frequency-selective control of band gaps in the spectrum of spin waves using the spin current.

Analysis of the effect of rigid vegetation patches on the hydraulics of an open channel flow with Realizable k-ε and Reynolds stress turbulence models

In this study, the effect of vegetation patches naturally located in the river and stream bed on flow characteristics was observed under laboratory conditions by using representative rigid vegetation. Then, the behavior of rigid vegetation was compared with two different (Realizable k-ε and Reynolds Stress) turbulence models using a CFD software (ANSYS-Fluent). Firstly, our use of models was validated. Then, they were used for numerical simulation. The velocity distributions energy dissipation, and turbulent intensities, at the determined points for the patches located in the downstream part, were analyzed with graphics and simulations. The vertical distribution of the average velocities was calculated at typical locations downstream. The magnitude of flow velocities was observed to decrease within the vegetation patch zone. The minimum values of the velocity magnitude were observed just behind the vegetation structures. Higher velocities were simulated in the vegetation patch regions compared with the gap regions. This identifies that the gap areas are appropriate for the deposition of sediments and advantageous for aquatic living beings in terms of physical atmosphere and nutriment. A maximum of 7 % energy dissipation difference occurred between the highest and lowest SVF values. For equal SVF values, a 1 % energy dissipation difference was obtained. This situation can be associated with the number of rods, and rod spacing being equal to the rod diameter. The 3-D turbulence intensity was only numerically measured and compared. Between the Realizable k-ε model and the RES model, the maximum 0.05 %turbulence density difference was observed (for SC1 and SC3 scenarios). We can associate this situation with the vortex and complex turbulent flow, which is formed from the channel bottom to the water surface, depending on the diameter of the rigid vegetation and the rod sequence. It was observed that there are effective methods to predict the flow model within both models.

Tailoring optical properties of hydrothermally synthesized SnMnSe nanocubes for optoelectronic and dielectric applications

In the current paper, we investigate the optical and dielectric properties of the SnMnSe nanocubes. The Sn0.5+xMn0.5−xSe (x = 0.375, 0.250, 0.125, 0) samples are prepared by simple hydrothermal method with the variation of the Sn and Mn concentration. The X-ray diffraction study shows that all the prepared samples are polycrystalline in nature. The average crystallite size increases along with the dislocation density and the average strain value with the increase in the Mn concentration. The morphology shows the formation of nanocubes. The average size of the cubes increases with the increase of Mn content. The reflectance data demonstrate the decreasing order of absorption edges with the increase of Mn content in the sample. The variation of the absorption edges with Mn content tends to decrease the optical bandgap by creating more disorder and defects between the gap region. Broad orange-red photoluminescence emission is observed for all the samples with 532 nm excitation. The electrical study of the sample shows high resistance values. The dielectric behavior as a function of frequency and temperature is investigated, and parameters like dielectric constant, AC conductivity, impedance spectroscopy, and electric modulus are deeply analyzed. The dielectric properties are useful for energy storage applications. All the above optical and dielectric properties of the SnMnSe matrix have potential use in the field of optoelectronics and dielectric applications.

Active band gap control of magnetorheological meta-plate using frequency feedback control law

An innovative special class of magnetorheological metamaterial is proposed to achieve a tunable band gap using a new frequency feedback control law. By using the frequency feedback control law, the active band gap can intelligently track the external excitation frequency. The active control function of the band gap is realized using an intelligent local resonator embedded in the plate. Such a local resonator consists of a mass and a magnetorheological elastomer (MRE) driven by an external magnetic field. The local resonator and metamaterial plate are modeled analytically, and an analytical expression is derived to predict the band gap region. The effect of the external magnetic field on vibration attenuations is analyzed by the Galerkin method. Subsequently, a closed-loop frequency feedback control strategy is used to actively adjust the band gap according to the excitation frequency. Based on this frequency feedback control strategy, the effective band gap range of the metamaterial plate can be largely widened. The effect of damping of the MRE on broadband vibration reduction is also investigated, and the results show that the damping of the MRE plays an important role in the control of the band gap of the magnetorheological metamaterial.

B-230 Monitoring SARS-CoV-2 Subvariants for Evaluation of the Diagnostic Kit’s Annealing Site Using Nanopore Sequencing

Abstract Background Currently, various diagnostic kits are being developed to aid in the rapid diagnosis or detection of SARS-CoV-2, but viruses continue to evolve through mutations resulting in phenotypic changes such as increased infectivity and pathogenicity, or vaccine evasion. Over time, such alterations in sequence may also occur at the annealing sites of the primers and probes in the diagnostic kit, leading to false-negative results. To prevent this, a continuous mutation monitoring is required. The authors performed SARS-CoV-2 Whole Genome Sequencing (WGS) and then compared and monitored the difference between actual experimental and public data from the National Center for Biotechnology Information (NCBI) datasets for each mutant strain. Methods WGS was performed by using GridION (Oxford Nanopore Technologies, UK) on 1500 nasopharyngeal swab SARS-CoV-2 positive samples requested for testing at SCL from January 2020 to December 2022. Experimental data were aligned through epi2me and analyzed using the Nextclade platform (Fig. 1A). For public data, 119 sequences reported in Korea (Fig. 1B) were retrieved from the NCBI database, reanalyzed using Nextclade platform, and compared. Results In numerous samples tested, mutation, insertion, and deletion were found to occur over time. In particular, in the case of Omicron subvariants, a common Gap (region 1; Gap: 11288–11296, region 2; Gap: 28362–28370) were identified in orf1ab (RdRP), the target gene for the majority of existing diagnostic kits, and in N gene (Fig. 1). Therefore, while designing a diagnostic kit, this region should not be included in the annealing site. Conclusion In order to maintain an effective diagnosis and quarantine system for COVID-19, mutations affecting the annealing site of primers and probes must be identified through a continuous genome monitoring. The results obtained from the continuous genome monitoring can be utilized to upgrade the existing commercially available kits as well as to develop new kits.

The enhanced mechanism of microwave-induced discharge between millimeter activated coke

Microwave heating has attracted extensive attention due to its advantages of low energy consumption and rapid heating. Due to its kinetic and thermal effects, microwave-induced activated coke discharge has been widely used in material preparation and reaction enhancement. However, the mechanism of microwave discharge for millimeter activated coke has not been clarified. In this work, we have investigated the mechanism of microwave discharge between millimeter activated cokes by experiments and simulations. Experimental results presented that the increase in particle size caused the inter-particle discharge transferred from weak sparks to large-scale violent discharge. Simulation results indicated that the increase in particle size led to enhanced microwave field resonance between particles, thereby promoting the inter-particle electric field, electron temperature and active species density. Finally, the particle size of cokes affected the deposition of microwave energy in discharge regions between particles. The influence of particle size on microwave-induced activated coke discharge was reflected in two mechanisms, namely, the microwave resonance enhanced mechanism that promoted the microwave energy deposition between particles and the focused microwave energy mechanism that dominated the inter-particle microwave energy deposition distribution concentrated in the center regions of the particle gap.

A feasibility study transplanting macrophages to a segmental nerve injury.

Promoting regeneration after segmental nerve injury repair is a challenge, but improving angiogenesis could be beneficial. Macrophages facilitate regeneration after injury by promoting angiogenesis. Our aim in this study was to evaluate the feasibility and effects of transplanting exogenous macrophages to a segmental nerve injury. Bone marrow-derived cells were harvested from donor mice and differentiated to macrophages (BMDM), then suspended within fibrin hydrogels to facilitate BMDM transplantation. BMDM survival was characterized in vitro. The effect of this BMDM fibrin hydrogel construct at a nerve injury site was assessed using a mouse sciatic nerve gap injury. Mice were equally distributed to "fibrin+Mφ" (fibrin hydrogels containing culture medium and BMDM) or "fibrin" hydrogel control (fibrin hydrogels containing culture medium alone) groups. Flow cytometry (n = 3/group/endpoint) and immunohistochemical analysis (n = 5/group/endpoint) of the nerve gap region were performed at days 3, 5, and 7 after repair. Incorporating macrophage colony-stimulating factor (M-CSF) improved BMDM survival and expansion. Transplanted BMDM survived for at least 7 days in a nerve gap (~40% retained at day 3 and ~15% retained at day 7). From transplantation, macrophage quantities within the nerve gap were elevated when comparing fibrin+Mφ with fibrin control (~25% vs. 3% at day 3 and ~14% vs. 6% at day 7). Endothelial cells increased by about fivefold within the nerve gap, and axonal extension into the nerve gap increased almost twofold for fibrin+Mφ compared with fibrin control. BMDM suspended within fibrin hydrogels at a nerve gap do not impair regeneration.

Multi-scale reconstruction of turbulent rotating flows with proper orthogonal decomposition and generative adversarial networks

Data reconstruction of rotating turbulent snapshots is investigated utilizing data-driven tools. This problem is crucial for numerous geophysical applications and fundamental aspects, given the concurrent effects of direct and inverse energy cascades. Additionally, benchmarking of various reconstruction techniques is essential to assess the trade-off between quantitative supremacy, implementation complexity and explicability. In this study, we use linear and nonlinear tools based on the proper orthogonal decomposition (POD) and generative adversarial network (GAN) for reconstructing rotating turbulence snapshots with spatial damages (inpainting). We focus on accurately reproducing both statistical properties and instantaneous velocity fields. Different gap sizes and gap geometries are investigated in order to assess the importance of coherency and multi-scale properties of the missing information. Surprisingly enough, concerning point-wise reconstruction, the nonlinear GAN does not outperform one of the linear POD techniques. On the other hand, the supremacy of the GAN approach is shown when the statistical multi-scale properties are compared. Similarly, extreme events in the gap region are better predicted when using GAN. The balance between point-wise error and statistical properties is controlled by the adversarial ratio, which determines the relative importance of the generator and the discriminator in the GAN training.

Effect of Tip Gap Size on the Performance of an Axial Compressor Stage with and without Active Flow Control

The tip gap region of an axial compressor rotor is a source of complex flows, inducing losses and stability issues. Recent works have proven the ability of blowing high-speed jets in the tip region to improve the surge margin of an axial compressor stage with a narrow tip gap configuration. However, the tip gap size can evolve during the compressor lifetime, possibly affecting its performance and operability. The objective is to evaluate the performance of an active flow control system on a compressor with different tip gap sizes. The present work is based on the single-stage compressor CME2 located at the Laboratory of Fluid Mechanics of Lille and equipped with actuators blowing at the rotor tip leading edge. Configurations with two different values of the tip gap to chord ratio (0.6% and 2.4%) are experimentally tested. RANS simulations are also performed. The effect of tip gap sizes and tip blowing on the flow topology and compressor performance is evaluated (surge margin improvement of the order of 200% for the larger tip gap size).