Tip Surface Research Articles

Investigation of burnout effect in turbine blade tip leakage at transonic conditions – a numerical study

Abstract In the aviation industry, turbine blade tip leakage significantly impacts the economy due to aerodynamic losses in the turbine. The tip leakage flow increases when the tip surface is exposed to high heat loads from the burnout effect, contributing to nearly 30% of the total loss in the turbine stage. This study numerically investigates two-dimensional flat tip and burnt-out tip models under different flow accelerations at transonic conditions. Variations in the discharge coefficient are examined for different pressure ratios across the tip gap. Flow and shockwave patterns for various blade tip geometries are obtained and analyzed. The burnt-out tip notably increases tip leakage, and a significant decrease in turbine efficiency is observed beyond a critical burnout limit. The quantified losses at different stages of blade tip burnout are used to predict the effective operational life of the blade. A correlation is developed to relate the non-dimensional tip-leakage flow parameters to the normalized blade-tip geometry.

Does the Scenario of Connection Between the Positive Leader Tip and the Lateral Surface of the Negative Leader Exist?

AbstractBased on the high‐speed video observations obtained at the Tall‐Object Lightning Observatory in Guangzhou (TOLOG), the attachment processes of three lightning flashes seem to belong to the connections between “the lateral surface of negative leader and positive leader tip” which had never been reported before were investigated. The leader connection processes of these flashes were examined in detail, and a mechanism behind connecting behavior between the lateral surface of negative leader and positive leader tip was discussed. Observation shows that negative leaders usually have abundant branches. Although some may extinguish, they still maintain a certain conductivity. When the positive leader tip comes close to the lateral surface of the negative leader (usually a few tens of meters), the previously disappeared short branch can be reactivated. It is easier for the positive leader tip to connect the tips of these branches (whether they have been extinguished or not).

Numerical simulation of multiphase flow and prediction of sediment wear in a large Pelton turbine

AbstractThe problem of sediment wear presents a significant challenge for hydraulic turbines operating in sediment‐rich rivers, particularly for high‐head Pelton turbines. In this study, the VOF model, SST k–ω model, and DPM model were employed to simulate the gas–liquid–solid three‐phase flow within a large Pelton turbine, which operates under a rated water head of 671 m and has a single capacity of 500 MW, at a hydropower station situated on a sediment‐laden river. The sediment wear prediction model, derived from the sediment wear test of the model turbine, was utilized to forecast the sediment wear on the flow components of the Pelton turbine at the hydropower station. The results show that there are obvious pressure and velocity gradients near the nozzle outlet of the Pelton turbine in the power station, and the wear of the nozzle surface is gradually increasing, and the wear in the downstream area of the nozzle is more serious. The wear rate at the needle tip surface reached 1.372 μm/h, while the socket ring surface exhibited a wear rate of 3.175 μm/h. he highest wear rate recorded for the water bucket is 0.940 μm/h. After a year of continuous operation, the maximum erosion observed was 5.62 mm on the runner bucket made of stainless steel and wear‐resistant metal, 8.23 mm on the spray needle, and 19.05 mm on the nozzle mouth ring, highlighting the severity of sediment wear on the Pelton turbine. It is recommended that surface treatment technology be applied to the flow‐through components of the Pelton turbine at this hydropower station to enhance the wear resistance of the turbine and extend the operational life of the unit.

Scanning Electron Microscopic Evaluation of Surface Defects of Remover Retreatment File After Single and Multiple Uses.

This study aimed to evaluate surface defects of Remover rotary Nickel-Titanium (NiTi) files after single and multiple uses in conventional endodontic retreatment procedures using scanning electron microscopy (SEM). Eighty acrylic blocks, simulating root canals with a 1.5 mm internal diameter, a 5 mm radius of curvature, and a 55° curvature, were utilized. After chemomechanical preparation and obturation, 24 new Remover files (N30, 7%, L23) were randomly assigned to three groups: single use, triple use, and six uses. The files were operated at 600 rpm with a torque of 2.5 Ncm, cleaned, and sterilized after each use. SEM analysis at magnifications of 100x, 250x, and 500x revealed surface defects, including tip deformation, microcracks, fracture, unwinding, surface pitting, and blade disruption. Deformation was observed in 75% of the files after a single use and in 100% of the files after three and six uses. Microcracks were absent after single use but appeared in 25% and 87.5% of files after three and six uses, respectively, showing a statistically significant increase (p < 0.001). Surface pitting also significantly increased among groups (p = 0.004). No fractures were observed in any group. The most common defects were tip deformation (91.7%) and surface pitting (70.8%). The findings suggest that repeated use of NiTi files significantly increases surface defects, elevating the risk of fatigue fractures. Thus, the results recommend limiting the reuse of Remover files to a maximum of 3x. Further research is needed to correlate defect types with anatomical factors and to assess file effectiveness in retreatment scenarios.

Change in root morphology, growth, and P transfer: Does foliar P application restrain root P-foraging behavior of Cunninghamia lanceolata seedlings in P-deficient environments?

Although foliar phosphorus application (FPA) is a fertilization method that can rapidly supplement nutrient elements in plants, it remains unclear whether it significantly affects the response strategy of roots under environmental stress. In this study, changes in plant growth, biomass allocation, and P use efficiency (PUE) of Chinese fir in different P environments were analyzed by FPA and root P application (RPA) treatments. The effects of FPA on P-foraging behavior of Chinese fir root system in P-deficient environment were then discussed. The root biomass with RPA was more significant at 0.03-0.25mmol·L-1 P concentrations than that with FPA; however, the PUE was significantly reduced by 28.89–29.41%. With an increase in the P application concentration, under the effect of FPA, the Chinese fir roots mainly reduced root proliferation by decreasing the tip number, surface area and volume but increasing in diameter, as well as the PUE of root, aboveground. As a result, the entire plant was improved. However, the degree of morphological adjustment of the root system was lower than that under RPA. In summary, both FPA and RPA can alleviate P starvation in Chinese fir to a certain extent, thereby improving PUE. Compared with RPA, FPA had a more significant impact on the behavior of Chinese fir roots in sensing and responding to soil P content, and the roots could more quickly sense changes in P content in the body. This mechanism provides valuable insights into the root response strategies of plants in P-deficient environments.

Morphological Characterization of Tissue Destruction According to the Distance Between Holmium:YAG Laser Tip and Tissue Surface.

Little is known about the soft tissue destruction by holmium laser clinically used for holmium laser enucleation of the prostate (HoLEP), subject to the distance between the laser fiber tip and the tissue surface. We aimed to investigate the impact of the distance between the laser fiber tip and the phantom surface (DLP) on a soft tissue phantom (STP) in relation to the surgical modes of HoLEP. STP responses to the laser pulses produced by a commercial holmium:yttrium aluminum garnet (Holmium:YAG) laser at an output setting 2 J were observed at different values of the DLP (0, 1, 2, 3, and 4 mm) to look at (1) the single laser pulse-induced cavitation bubble and its penetration into the STP, (2) the STP destruction by a single pulse, (3) the STP destruction by 60 pulses repeated at 12 Hz, and (4) the thermal effect by the multiple pulses visualized on a thermosensitive bovine serum albumin (BSA) STP. We observed that the laser pulse produced a heated gas bubble in water centered at the laser fiber tip. The bubble shape depended on the DLP. The bubble completely penetrated into the STP at the DLP of 0 mm and the penetration decreased with the DLP. The size of the destruction of the STP by the laser pulses was shown to decrease as the DLP increased. Test with the BSA STP showed that, at the DLP of 3 mm, the destruction became insignificant while the thermal effects were still effective. We illustrated that soft tissue destruction by the Holmium:YAG laser is associated with cavitation effects. We provide for the first time experimental evidence for various surgical modes in HoLEP such as incision and hemostasis in relation to the DLP.

Investigation on two-dimensional ultrasonic vibration plane turning method based on elliptical plane swinging strategy along short axis

In the ultrasonic elliptical vibration cutting (UEVC) process, the surface morphology suffers from the large fluctuation of ridge height and residual height, which has restricted the development of UEVC technology. Therefore, on the basis of the elliptical plane swinging strategy along a short axis, a surface topography improvement method (i.e., swing ultrasonic elliptical vibration turning (SUEVT)) for two-dimensional ultrasonic vibration plane turning is proposed in this study. The core idea of the method is to swing the ultrasonic elliptical vibration plane along the short axis to form a machining inclination angle, which reduces the ridge height of the machined morphology to a certain extent, thereby optimizing the surface microstructure and reducing the surface roughness. First, this study establishes a mathematical model of the tool tip trajectory of ultrasonic elliptical vibration under different swing angles, theoretically analyzes the influence of swing angles on the tool tip trajectory and surface topography, and provides a theoretical basis for revealing the surface topography formation mechanism of SUEVT. Second, an engineering practice scheme of SUEVT is proposed, and a processing experiment platform is built. Finally, cutting experiments of SUEVT for TC4 titanium alloy were conducted, studying the influence of swing angles on surface topography and roughness and assessing the feasibility of the method. Results showed that compared with ultrasonic elliptical vibration turning (UEVT), SUEVT has certain advantages in improving surface morphology. When the swing angle of SUEVT is 15°, the surface roughness decreases the most, reaching 19.00 %. Under the condition of SUEVT θ = 15°, the surface roughness decreases first and then increases with the increase in spindle speed, while it is proportional to the feed speed and ultrasonic power. The method proposed in this study can provide new methods and new ideas for ultrasonic elliptical vibration high surface quality machining.

Characterization of field emission from oxidized copper emitters

In this work, the field electron emission from oxidized copper emitters was studied by aging with radii in the range of 80–300 nm. The samples were prepared by an electrochemical etching method using an H3PO4 solution. The samples were exposed to air for 30 d to form an oxide film owing to aging. Measurements were carried out under high vacuum conditions in the range of 10−6 mbar. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM- EDS) was used to calculate the emitter radius, study the purity of the samples, and detect the oxide layers. Current–voltage (I-V) characteristics were studied and analyzed using Murphy-Goode (MG) plots and rectification tests. Furthermore, the spatial distribution of the electron emission and current stability were recorded and used to analyze the electron emission behavior of the tip surface. The trap density was also studied when the oxide layer was 3 layers thick. The results show that the emitters passed the orthodoxy test at low voltages. It was found that traps play an important role in increasing the switch-on current as the area of the oxide layer increases. It was found that the emitter acts as a point capacitor based on the charging and discharging processes of the electrons in the traps. The emission pattern showed great stability, which opens up prospects for this type of emitter in industry.

Self-Driven Graphene Photodetector Arrays Enabled by Plasmon-Induced Asymmetric Electric Field.

Gap surface plasmon (GSP) modes enhance graphene photodetectors (GPDs)' performance by confining the incident light within nanogaps, giving rise to strong light absorption. Here, we propose an asymmetric plasmonic nanostructure array on planar graphene comprising stripe- and triangle-shaped sharp tip arrays. Upon light excitation, the noncentrosymmetric metallic nanostructures show strong light-matter interactions with localized field close to the surface of tips, causing an asymmetric electric field. These features can accelerate the hot electron generation in graphene, forming a directional diffusion current. Accordingly, the artificial GPDs exhibit a wavelength-dependence behavior covering the wavelength range from 0.8 to 1.6 μm, with three photoresponse maxima corresponding to the nanostructures' resonances. Additionally, the polarization-dependent GPDs can realize a responsivity of ∼25 mA/W and a noise equivalent power of ∼0.44 nW/Hz1/2 at zero bias when excited at the resonance of 1.4 μm. Overall, our study offers a new strategy for preparing compact and multifrequency infrared GPDs.

Determining the angle of the frontal working surface of the soil-piercing head asymmetrical tip for static soil-piercing

Problem. From the analysis of the technical literature, it was established that among the trenchless technologies for laying underground engineering communications and service pipelines, the technology with the possibility of forming a horizontally directed communication cavity in the soil using soil-piercing installations of static action is the most common. Goal. This method consists in forcefully pressing a soil-piercing working body, which has the form of a conical-cylindrical projectile, into the soil. At the same time, the well is formed by radial extrusion of the soil around the formed well. However, the use of such equipment does not provide high accuracy, which limits its practical application within 20 m. It is not sufficient for modern requirements of creating transitions during the laying of communications. Methodology. One of the ways to improve the efficiency of laying underground networks is to extend this method over a longer distance by correcting the trajectory of the working body. This is achieved by using a soil-piercing head with an asymmetric tip. Due to this, in addition to the axial resistance of the soil, a transverse component force appears, which deflects the head during its advancement in the soil. The question of determining the angle of displacement of such a tip is important in terms of the process control. Results. In the paper, a calculated dependence is proposed for determining the rational value of the angle of inclination of an asymmetric tip working surface, which is a flat plane cut at the angle of a cylinder. An analysis of the dependence of the angle of the working surface inclination on the physical and mechanical properties of the soil is also given. Originality. It was determined that the maximum angle of inclination of the frontal surface is determined by the conditions of soil descent from it. Its maximum value, for example when working in loam, should not exceed 55o-67o for a tip made of steel. Practical value. The obtained calculated dependence can be useful for determining the angle of inclination of the flat frontal surface of the tip of the soil piercing working tool for controlled static soil piercing at the stage of designing networks and choosing an effective method for drilling a well under roads or other obstacles.

Estimating the Depths of Normal Surface Notches Using Mode-Conversion Waves at the Bottom Tip.

In this work, a two-parameter inversion problem is analyzed, related to surface crack widths for measuring depths of normal surface notches, based on a laser-based ultrasonic measurement method in the time domain. In determining the depth measurement formulas, the main technique is the time delay between reflected and scattered waves. Scattered waves are generated by two reflections along the bottom and three mode transformations at the surface of the crack tips. Moreover, the scattering angle of the mode-conversion waves is 30°. These two key factors lead to corrected item "2wβ" in the depth measurement formula. A laser-based ultrasonic experimental platform is built to generate and receive surface waves in a non-contact manner on aluminum and steel specimens with surface cracks. The depth measurement method proposed in this paper has been validated through theoretical, simulation, and experimental methods. Finally, in this paper, an effective approach for quantitatively measuring crack depths, based on laser ultrasound, using the time-domain properties of surface wave propagation is provided.

Turbine blade tip aerothermal characteristics considering the influences of cavity tip shaping

The presence of turbine blade tip clearance can cause tip leakage losses and enhance the thermal load on the tip region. The continuously increasing inlet temperature of the turbine poses a tremendous challenge for turbine blade tip design. Reasonable turbine blade tip configurations can effectively reduce the thermal load on the tip region and enhance aerodynamic characteristics. Here, surface Nu distributions of flat, cavity, and five modified tip configurations are obtained through transient liquid crystal measurement technology. Furthermore, a numerical study combined with experimental results is conducted to investigate the aerothermal characteristics of the tip regions for each configuration. The results indicate that the flat tip (FT) has the highest tip surface thermal load and maximum aerodynamic loss, and the cavity structure can effectively reduce the average Nu on the tip surface. Among the five modified configurations, the SS ribbed configuration (SRT) and the lateral ribs configuration (SLCT) exhibit relatively optimal aerothermal performance. Specifically, compared to FT, the SRT tip configuration shows an average Nu reduction of 27.4 % on the tip surface and a 16.3 % decrease in tip clearance leakage compared to FT; the average Nu on the SLCT tip surface and the tip clearance leakage relative to the FT are reduced by 27.2 and 17.3 %, respectively.

Visible light enhanced selective benzene response of hexagonal atomic structured CuS microcloves

We have reported CuS microcloves (MCs) for highly selective detection of benzene using scanning kelvin probe (SKP) technique. The electron microscopy investigations revealed the formation of clove shaped CuS with a size of about 1–2 µm at 180 °C and 6 h. The time of reaction significantly affected the crystallinity as well as the morphology of resulting CuS materials. The investigations on adsorption behavior of different types of common volatile organic compounds (VOCs) with varying charge and nature revealed an outstanding selectivity towards benzene when compared to other VOCs. The difference in work function between gold tip and sensor surface modified with CuS MCs was decreased under the exposure of light, most likely caused by transfer of electrons to conduction band of CuS under illumination of light. As a result, the CuS MCs showed enhanced photo response in visible light exposure in the presence of benzene. A chemiresistive type sensor device was fabricated using CuS MCs and exposed to benzene vapor in a concentration ranging from 2.8 to 11.2 ppm. The sensitivity was found to be 1.63 × 10-3 ppm−1. Notably, a rapid response time of ∼6 s and recovery time of ∼ 16 s was achieved for the sensor at a benzene concentration of 5.6 ppm at room temperature. Also, considerable and repeatable sensor response was observed for 560 ppb of benzene vapor at 70 °C. Hence, these results suggested that the CuS MCs have huge potential as novel material for selective benzene detection in gas phase towards breath analysis and other environmental monitoring.

The investigation on the flow characteristics during the continuous development of the tip leakage vortex cavitation in an axial pump-jet propulsion

The continuous deterioration and development of tip leakage vortex (TLV) cavitation in the pump-jet propulsion significantly affect propulsion performance and operational stability. Larger eddy simulation and cavitation tunnel experiment are utilized to investigate the temporal and spatial evolution characteristics of TLV cavitation under varying cavitation conditions. The results reveal that the continuous development of TLV cavitation prompts the TLV to gradually move away from the blade suction surface due to increasing pressure difference at the blade tip surface. Furthermore, the development of TLV cavitation amplifies the effect of the radial outward Coriolis force and makes the TLV even more unstable. Under the influence of the tip leakage flow, primary generation of turbulent kinetic energy (TKE) persistently migrates to the TLV core center and subsequently travels downstream. Despite the large magnitude of TKE that occurs at the TLV core center, the TKE generation remains low. With the inception of TLV cavitation, the transport of TKE between the TLV core center and the surrounding flow gradually intensifies, followed by a subsequent weakening of this transport effect. It increases again as the breakdown of TLV becomes more severe.

Deformation and retentive forces variations of the additively manufactured cobalt-chromium and titanium alloys dental clasps

This in vitro study aimed to evaluate the additive manufacturing (AM) of cobalt chromium Co-Cr and titanium Ti alloy clasps for clinical use. After scanning the Ni-Cr die of the first molar, Akers' clasps were designed using computer-aided design/ computer-aided manufacturing (CAD/CAM). The clasps were manufactured from Co-Cr-W dental alloy and Ti-6Al-4V alloy powder using AM machines. Then, they were divided into two groups. The initial retentive force of the clasps was measured using a universal testing machine. Cyclic loading of the clasps was carried out by a specially designed insertion-removal testing apparatus in wet condition up to 5000 cycles. Retentive force was measured at 1000, 2000, 3000, 4000, and 5000 cycles. Moreover, the intaglio surface of each clasp was scanned using the scanner; and superimposition between the pre- and post-cycling clasp files was performed to evaluate deformation after cyclic loading. The fitting surfaces of retentive clasp tips were examined with a scanning electron microscope (SEM). Finally, it has been found that the initial retentive force for the Co-Cr group was 10.81 ± 0.37 N, and for the Ti group was 5.41 ± 0.18 N. Additionally, during the testing periods, both Co-Cr and Ti clasps continued to lose retentive force within the cycles of placement and removal. This effect was more prominent in the Co-Cr than in the Ti clasps. The distances between pre- and post-cycling in the retentive arm were −0.290 ± 0.11 mm and −0.004 ± 0.01 mm in Co-Cr and Ti alloys, respectively, and in the reciprocal arm were −0.072 ± 0.04 mm and −0.032 ± 0.04 mm in Co-Cr and Ti alloys, respectively. The retentive force required to remove the Ti clasps was found to be significantly lower than those required to dislodge the Co-Cr clasps. Co-Cr and Ti clasps lost significant amounts of retentive force from the initial use to the 3.5-year periods of simulated clinical use.

Drag reduction design and experiments for the chisel-shaped shovel tip

To address the issue of high resistance encountered by traditional chisel-shaped shovel tips during tillage, this study drew inspiration from the micro V-shaped structures found in shark skin. Using laser cladding technology, a V-shaped wear-resistant coating was applied to the front surface of the shovel, with different drag-reducing V-shaped structures achieved by controlling the coating overlap ratio H (including 20%, 40%, and 60%). Additionally, the rear surface of the shovel tip was designed to mimic the V-shaped morphology of shark skin, proportionally amplified, and given a certain backward tilt angle θ to further reduce resistance. Through the discrete element simulation experiments while maintaining θ at 0°, it was found that the shovel tip achieved the best drag reduction effect when H was 40%. Based on this, the study varied the values of θ (including 0°, 1°, 3°, and 5°) while keeping H at 40%. Discrete element simulation experiments were conducted at depths of 250mm, 275mm, and 300mm to analyze the disturbance effect, fragmentation effect, and resistance of the shovel tip. Considering all factors, the shovel tip with θ of 5° was selected as the optimal choice. Finally, a soil trench experiment was conducted to verify the performance of the V-shaped shovel tip with H of 40% and θ of 5°, as well as the chisel-shaped shovel tip, in tillage operations. The experimental results showed good agreement with the simulation results, and the designed V-shaped shovel tip achieved a maximum drag reduction of 12.87%. This design provides valuable references for the structural optimization of subsoiler, contributing to the improvement of their performance and efficiency.

Numerical study of porous tip treatment in suppressing tip clearance vortices in cavitating flow

Tip clearance cavitation (TCC) is a type of vortex cavitation. It widely exists in axial flow hydraulic machinery and has significant negative influence on the mechanical service life and the operating stability. It is necessary to suppress the tip clearance vortices (TCV) to control the TCC in engineering applications. Based on the analysis of the advantages and disadvantages of the present various suppression strategies, a new coupling method is proposed in this study by combining the damping approach and the diversion approach. Porous medium material is used to realize the coupling effect. A 2 mm span length porous tip is installed on the solid tip surface of a hydrofoil under two gap sizes conditions (representing two types of gap flow pattern), and excellent suppression results of the TCV and TCC are obtained. The characteristics and mechanism of the clearance flow are analyzed by numerical simulation. The numerical accuracy is verified by experimental qualitative observations. The simulation results show that the temporal and spatial stability of the clearance flow field is enhanced, and the leakage velocity and the TCV strength are weakened via the combined action of damping and diversion effects. There is a difference in the damping mechanism between the two gap flow patterns. It is a comprehensive result of viscous dissipation and momentum loss in the jet pattern represented by the small gap size, and primarily, the result of momentum loss in the rolling pattern represented by the large gap size.

Effect of Si doping on elastic-plastic fracture toughness (JIC) of T91 ferritic/martensitic steel in liquid lead-bismuth eutectic

This work was devoted to understanding the effect of Si doping (1.27 wt%) on elastic-plastic fracture toughness (JIC) of T91 ferritic/martensitic (F/M) steel in liquid lead-bismuth eutectic (LBE, Pb44.5Bi55.5, wt%) under various parameters. The results showed that Si doping significantly promoted occurrence of liquid metal embrittlement (LME) and led to more severe degradation of fracture toughness at 350 °C, especially in oxygen-poor LBE. The LME susceptibility of T91-Si steel was found to be nearly independent on the loading speeds, while T91 F/M steel exhibited a stronger LME effect when the loading speed was decreased from 0.02 mm/min to 0.002 mm/min. Oxygen concentration had a mild effect. Detailed microstructural analyses showed that the fracture behavior of the T91-Si steel in LBE environment at 350 °C was analogous to cleavage fracture and the crack propagation was mainly transgranular. The crack wall was quite rough and locally faceted to low-index crystallographic planes of {110}. Numerous dislocations were also present in the vicinity of the crack tip. No solid evidence of diffusion of Pb and Bi into the steel bulk was discovered even at the atomic scale, which strongly suggests a crack tip surface adsorption-based LME mechanism.

Effects of the circumferential casing groove configuration on aerothermal performance of a transonic turbine stage

In order to control tip leakage flow and improve the tip aerothermal performance, a circumferential casing groove (CG) configuration is proposed. Taking the typical transonic turbine stage TTM (Thermal Turbomachinery and Machine Dynamics) as the research object, the effects of CG with different heights (b), initial locations (IL) and widths (w) on the aerodynamic loss of the turbine stage and heat transfer characteristics of the tip region are investigated numerically. Results indicate that due to the introduction of CG, the vortex system topology in the tip region changes remarkably. Tip leakage vortex (TLV) is separated into two parts, with TLV-1 being entrained and dissipated by upper passage vortex (UPV) and TLV-2 rebuilding behind the groove and extending to the trailing edge. The interaction between TLV and UPV changes with the development of both. Also, complicated flow-thermal interplays lead to the change of thermal load in the tip region, which attributes to the difference of local turbulence mixing intensity. More quantitatively, a CG with the groove of b = 3.0 g, IL = 0.20 Cax and w = 0.05 Cax can increase ηTS by 0.38%, and reduce the area-averaged heat transfer coefficient (HTC) by 5.28% and 1.49% for the tip and casing surface, respectively, with a slight increase of area-averaged HTC on the blade by 0.29%. Overall, CG with appropriate geometrical parameters can improve aerothermal performance of the turbine tip significantly, without any serious increase of thermal load on the blade.

Autonomous convergence of STM control parameters using Bayesian optimization

Scanning tunneling microscopy (STM) is a widely used tool for atomic imaging of novel materials and their surface energetics. However, the optimization of the imaging conditions is a tedious process due to the extremely sensitive tip–surface interaction, thus limiting the throughput efficiency. In this paper, we deploy a machine learning (ML)-based framework to achieve optimal atomically resolved imaging conditions in real time. The experimental workflow leverages the Bayesian optimization (BO) method to rapidly improve the image quality, defined by the peak intensity in the Fourier space. The outcome of the BO prediction is incorporated into the microscope controls, i.e., the current setpoint and the tip bias, to dynamically improve the STM scan conditions. We present strategies to either selectively explore or exploit across the parameter space. As a result, suitable policies are developed for autonomous convergence of the control parameters. The ML-based framework serves as a general workflow methodology across a wide range of materials.