Search Results (671)

This paper reviews numerical modeling approaches for Dielectric Barrier Discharge (DBD) plasma actuators in aircraft active flow control. While extensive experimental studies exist, a dedicated review of computational methodologies—covering macroscopic, microscopic, and empirical models—has been absent. This work systematically evaluates major models (Shyy, Suzen–Huang, Dorr–Kloker, Roth, Orlov–Corke, Massines), discussing their formulations, assumptions, computational cost, and applicability. It synthesizes simulation studies in aerodynamic applications such as separation control, drag reduction, transition delay, film cooling, and compressor stability. Key findings show that macroscopic models offer a practical balance between accuracy and cost for design-oriented studies, whereas microscopic models provide deeper physical insight at higher expense. The review highlights the effectiveness of DBD actuators in modifying boundary layers, delaying stall, and improving aerodynamic efficiency. Finally, persistent challenges are identified—including energy efficiency, scalability, and model calibration and future directions are suggested, such as hybrid modeling, multi-actuator arrays, and real-time control integration. Full article

For unshrouded turbine blades, the high-speed tip clearance leakage flow induced by the pressure gradient on the pressure and suction surface sides significantly increases the thermal load in the turbine blade tip regions. Film cooling technology is an effective measure for reducing the external heat transfer temperature at the blade tips. Novel cooling strategies for the turbine blade tip are introduced to reduce adiabatic wall temperature. Here, the spatial distribution of film cooling effectiveness and the associated flow physics of the rib-slot and trapezoidal-slot tip configurations are investigated numerically and experimentally under transonic conditions. Film cooling effectiveness on the tip is quantified using the pressure-sensitive paint technique. Density ratios of 1.5 and 2.0 are considered, with tip clearances set at 0.7% and 1.5% of the blade height and the cascade exit Mach number set at 1.05. Both the trapezoidal-slot and rib-slot tip cooling approaches are capable of establishing complete film coverage over the tip surface. The rib-slot configuration delivers markedly higher effectiveness values over the mid-chord and trailing-edge regions relative to the trapezoidal-slot design. Conversely, the trapezoidal-slot scheme improves tip aerodynamic performance compared with the rib-slot arrangement, with the benefit being most pronounced in the larger clearance setting. Full article

The thermal contact resistance between a clip-attached TO 247 package and heat sink is a very large contributor to the total thermal resistance. Therefore, it is important to investigate its reliability and lifetime behavior. The novelty of this investigation is the new, detailed lifetime behavior measurement results of thermal contact resistance between package and heat sink. We have carried out an accelerated lifetime test on 30 samples at 110 °C with acceleration factor of 35 for 18 weeks, corresponding to 12.1 years operating life in indoor environments. The samples were 7 without interlayer film, 12 with 12.5 µm thick silver film and 11 with 6 µm thick silver film. At the start of the test, the average of the thermal contact resistance of samples with 12.5 µm silver film was 20.7% lower, and with 6 µm silver film, the average of thermal contact resistance was 8.7% lower than the average of thermal contact resistance of samples without film. During the first operating month, thermal contact resistance decreased by an average of 5%. Then followed an additional 5% decrease for 12 years. All individual samples show lower thermal contact resistance after 12.1 years compared to the start. No failures were observed, not even among high outliers. By a visual inspection of heat sink surfaces, high outliers can be avoided from start. The thermal contact resistance variation is smaller for samples with silver films compared to samples without film. Samples show decreasing thermal contact resistance with increasing dissipated power. Several previously known stabilizing mechanisms can hypothetically explain the results. Not only the softness of silver, but also the high ductility and Poisson Ratio, which elongate a 12.5 µm thick film more than a 6 µm thick µm film, are hypothesized to better fill out microscopic voids. We observe silver film surface structure changes when comparing aged silver films to un-aged silver films, indicating material movements, but no exact mechanism could be proven. Therefore, the explanations studied are hypothetical. Since all measured thermal contact resistances were lower after 12.1 years, our conclusion is that stabilizing types of mechanisms are dominant during the operating lifetime for indoor environments. Full article

Optical inverse design faces a dilemma: neural surrogates enable fast, differentiable search but can yield physically unreliable pseudo-optima, whereas solver-in-the-loop optimization is reliable yet costly. Most surrogate methods also trust the surrogate throughout the search, train separate models for performance prediction and structure optimization, and remain largely black-box. We propose Physics-Verified Spectral Dreaming (PVSD), a unified framework for forward prediction, inverse design, and physical interpretability: a frozen differentiable spectral surrogate “dreams” structural mutations by input-gradient ascent to explore the design space, while a physical solver adjudicates every accepted update—the surrogate proposes, physics decides. We instantiate it as PVSD-TMM for one-dimensional multilayer radiative coolers. The forward predictor attains $R^2=0.9936/0.9964/0.9828$ for net cooling power, solar reflectance, and primary-window emissivity; neural dreaming lifts the population-mean net cooling power of 1000 random seeds from $-466.7$ to $65.8$ W m⁻² ($91.4\%$ reaching net cooling), and continuous-thickness refinement with 5 nm rounding yields a 14-layer manufacturable final design. Independent COMSOL finite-element and analytic TMM cross-validation converge to $P_{\mathrm{cool}}\approx 172$ W m⁻², $R_{\mathrm{solar}}\approx 0.970$, and ${\epsilon }_{\mathrm{win}}=0.9252$. This is a full-spectrum radiative-balance result for an idealized radiative-only case ($h_{\mathrm{conv}}=0$), not a window-emittance-only metric; PVSD thus achieves high simulated broadband radiative-cooling performance under the stated assumptions, without claiming global optimality. Full article

The phase transition of paraffin powder mixed in wellbore concrete is generated by baking it, so that the paraffin powder is melted. The influence of baking temperature and paraffin dosage on phase transition degree of paraffin powder and the carbonation resistance of wellbore concrete was studied. Combined with microscopic testing methods such as scanning electron microscopy, the microscopic morphology of phase-transited paraffin films within the cement matrix and the mechanism by which they enhance the carbonation resistance of cement-based materials were analyzed. The results indicate that when baking temperature reaches 80 °C, the paraffin particles in the cement-based material can melt into viscous droplets. Partially melted paraffin particles condense within the internal pores of the cement matrix upon cooling, sealing the transmission pathways of CO₂ gas into the cement-based material. Fully melted paraffin droplets flow within the internal pores of the cement matrix and, upon condensation, firmly adhere to the pore walls, forming a relatively dense and smooth film. This film isolates CO₂ gas contact with the cement matrix, significantly improving carbonation resistance of the cement-based material. When the paraffin dosage exceeds 3% and the baking temperature surpasses 100 °C, the phase transition of paraffin powder achieves a fully carbonation-resistant effect. Full article

To push the specific impulse and power output of the thrust-controlled solid rocket motor (TCSRM) even higher, the solid-propellant flame temperature is driven to 3000–3600 K. That level of thermal assault subjects the pintle to extreme heat flux and aggressive erosion, a combination that directly undercuts motor reliability. An effective cooling strategy for the pintle is therefore mandatory. Here, a film-cooling scheme is deployed for thermal protection of the pintle, and a comprehensive study on the transient aero-thermal characteristics of pintle film cooling is carried out to demonstrate how it outperforms the uncooled baseline in extending pintle survival and to reveal the effects of the blowing ratio and pintle moving speed on the performance. The results indicate that the film cooling contributes to improving the pintle cooling performance. As pintle velocity increases, the absolute velocity component of the coolant jet parallel to the mainstream velocity decreases. This causes the relative angle between the coolant jet and mainstream to increase, leading to a stronger interaction between the coolant jet and mainstream. Accordingly, except under low-blowing-ratio conditions, the time-averaged film-cooling effectiveness declines as the pintle velocity increases. Moreover, there is an optimum blowing ratio to achieve the highest time-averaged film-cooling effectiveness. Full article

Abrasive flow machining (AFM) is an effective finishing process for complex internal surfaces, particularly cavities, intersecting holes, and micro-channels that are difficult to access using conventional tools. However, when low-viscosity abrasive media is used (here defined, relative to conventional putty-like viscoelastic AFM carriers (with apparent viscosities of 10³–10⁵ mPa·s), as a water-based slurry with an apparent viscosity below 300 mPa·s over the operating shear-rate range), unfavorable flow conditions during the initial polishing stage can induce local over-polishing, erosion depressions, stepped patterns, and cavitation pits, resulting in non-uniform surface quality. The relationship between these flow behaviors and polishing defects remains insufficiently understood. To address this issue, this study investigates the AFM process applied to turbine blade film cooling holes through combined experimental and numerical approaches. The observed defects include erosion depressions, stepped surface patterns, and cavitation pits. The effects of abrasive injection pressure, flow velocity, hole geometry, abrasive viscosity, and particle size on defect formation are systematically examined. The results show that the initial abrasive filling level strongly affects defect distribution by altering the evolution of shear fields and void regions within the hole. Experimentally, at high Reynolds numbers (Re > 2 × 10⁴), intensified local shear and cavitation promote defect formation, while a moderate inclination angle (45–60°) and a higher aspect ratio (>8) are favorable for polishing uniformity. Complementary numerical simulations further indicate that smaller abrasive particles (<5 μm) and a moderate abrasive viscosity (~60 mPa·s) are predicted to improve polishing uniformity. This study clarifies the fluid-dynamic origin of polishing defects in film cooling holes and provides process guidance for suppressing local over-polishing, cavitation, and uneven material removal. Full article

The new technological solutions supporting hard machining processes are becoming an up-to-date research area. The enhancement of cooling lubrication efficiency in the cutting zone plays a crucial role in improving cutting performance. This paper investigates the effectiveness of Minimum Quantity Lubrication (MQL) using SiC nanoparticle-enhanced oil in the hard milling process of AISI D2 tool steel. The results are compared with dry and pure MQL modes based on criteria including cutting force components, surface roughness, tool wear, and tool life. The research results show that compared to dry and pure MQL, the SiC nanofluid MQL environment provides the best performance with reductions in feed force F_x (22.3–23.8%), thrust force F_y (20.5–55.3%), tangential force F_z (26.5–34%), surface roughness (37–62.3%), tool wear (46.1–73.3%), and increased tool life (80–200%). These findings demonstrate that the lubrication and cooling efficiency of the base oil is improved with the addition of SiC nanoparticles. The deep penetration of oil droplets into the cutting zone and the formation of the oil film significantly contributed to reducing friction and cutting heat. SiC nanoparticles not only improved the lubricating and cooling capabilities of the base cutting oil but also created secondary mechanisms within the cutting zone. Furthermore, monitoring cutting forces and surface roughness can be suggested as supplementary criteria for evaluating tool wear and tool life. This research will provide important technological guidance and a theoretical basis for the improvement of hard milling and application of the SiC nanofluid MQL technique. Full article

In this work, a post-annealing rapid cooling and aging treatment process is innovatively proposed to build high-performance zinc tin oxide (ZTO) thin-film transistors. The relaxation effect on the abundant oversaturated oxygen vacancy deep-level traps contributes to the shallow donor formation during the aging period. The TFTs aged in an air environment for 10 days possess significantly improved electrical performance, including a clearly increased on/off current ratio of 7 × 10⁶ from 2 × 10⁴ and a markedly increased saturation mobility of 5.9 from 2.2 cm²·V⁻¹·s⁻¹, verifying the facile method to improve the electrical property of polycrystalline TFTs, and the method has been investigated using the grain boundary defect relaxation model and energy band theory. It is worth mentioning that the TFTs aged under vacuum conditions realized more effective regulation and control on off-state current and demonstrated a wider aging time window. The distinctive illumination interface stability was studied in depth using a charge trapping model and electron–hole pair model, which embody the potential application in photoelectric detectors. Full article

Inconel 718 exhibits poor machinability due to its high strength and low thermal conductivity, which induce severe thermo-mechanical loads. Conventional cooling strategies struggle to concurrently regulate heat dissipation and interface lubrication. This paper proposes a machining method based on Active Thermal Conductive Media (ATCM), which simultaneously exerts the Rehbinder mechanochemical effect and solid-phase enhanced heat transfer effect by pre-coating a liquid graphene film on the workpiece surface. Orthogonal turning tests were conducted using a K313 carbide tool at a cutting speed of 30 m/min, cutting width of 2 mm, and undeformed chip thickness of 0.1 mm. The cutting force, cutting temperature, cutting power, and tool wear characteristics under six machining conditions—dry cutting, flood cutting, Minimum Quantity Lubrication (MQL), Cryogenic MQL (CMQL), Nanofluid MQL (NMQL), and ATCM-assisted cutting—are systematically compared. The results show that ATCM achieves a 21.6% reduction in cutting force, a 20% reduction in cutting temperature, and a 34.9% reduction in cutting power through the synergistic coupling effect of reduced heat generation and enhanced heat dissipation, with adhesive wear and diffusion wear of the cutting tool significantly suppressed. Full article

6061 aluminum alloy is lightweight and has good thermal conductivity, while 304 stainless steel possesses excellent mechanical properties and corrosion resistance; both have broad application prospects in cooling circuits. Propylene glycol coolant shows great potential in liquid cooling systems due to its low toxicity and good antifreeze properties. However, during operation, galvanic corrosion may occur when the two metals come into direct contact within the coolant, thereby threatening system safety and service life. This study focuses on 6061 aluminum alloy, 304 stainless steel, and their galvanic couples. Electrochemical testing, SEM, 3D confocal microscopy, and XPS were used to systematically investigate their self-corrosion and galvanic corrosion behavior in propylene glycol coolant at pH values of 4.8, 6.8, and 8.8. The results indicate that 6061 aluminum alloy is more sensitive to pH changes; its corrosion resistance first increases and then decreases as pH rises, with the least corrosion occurring at pH = 6.8 and the most severe at pH = 4.8. 304 stainless steel exhibited lower corrosion rates at pH 6.8 and 8.8, but corrosion significantly worsened at pH 4.8. For the 6061 aluminum alloy/304 stainless steel couple, the galvanic current first decreased and then increased with rising pH, while the galvanic potential first increased and then decreased. The 6061 aluminum alloy consistently acted as the anode, and the 304 stainless steel consistently acted as the cathode, with the highest sensitivity to galvanic corrosion observed at pH 4.8. XPS analysis shows that under different pH conditions, the corrosion products of 6061 aluminum alloy are Al(OH)₃ and Al₂O₃, while the main components of the passivation film on 304 stainless steel remain unchanged. Full article

This paper presents a novel decomposition method for split-film probes to improve pitch angle determination over a wide range of flow velocities. Conventional approaches often suffer from the velocity dependence of the directional response function, resulting in large angular errors. The proposed method introduces a new functional formulation based on effective cooling velocities and velocity-dependent reference parameters. These parameters are explicitly derived from calibration data and modeled using fourth-order polynomial regressions to suppress velocity-induced variance. Experimental verification conducted for velocities between 2.2 and 14.6 m/s demonstrates that the proposed method collapses the calibration data more effectively than previous models. The total angular estimation error does not exceed ±2° within the pitch angle range from −60° to 60°. The proposed approach is therefore suitable for reliable measurements in low-velocity regions of complex flows, such as wakes and recirculation zones. Full article

By itself or combining with other cooling technologies, the dew point indirect evaporative cooler (DIEC) will be the preferred solution for cooling buildings. However, there are still some gaps in the research on DIEC performance, one of which is that 3-D (3-dimensional) models and methods are not widely used to comprehensively indicate the cooling mechanism. Most of the available numerical methods adopted 1-D or 2-D models. Existing 3-D models and methods either ignore the water film and plate or are so complicated in the grid system and numerical calculation induced by huge size differences among calculation regions that their attractions are weak. A novel simplified numerical method for DIEC performance is first suggested in this paper, and then, its validity and more efficiency than an existing 3-D numerical method are verified with the help of experimental data and numerical results. Finally, the effects of structure and operating parameters on the performance of a plate DIEC are analyzed by this present method and COMSOL Multiphysics 6.3 software, especially η/η₀ (the reinforcement factor), which was innovatively introduced. Similar results to those of existing literature were obtained, which further indicated the practicability of this simplified method. In the conditions involved in this paper, a channel length of 1.5 m, a width of 4 mm, Re_in (the Reynolds number at the inlet) of 1483, and a (the air ratio) of 0.33 are recommended. In the condition suggested by this paper, η/η₀ is close to 1.2. In the same conditions, this proposed method reduces the number of mesh elements by approximately 58% and the wall-clock computational time by approximately 52% under the reported workstation conditions, and its value would be more obvious for more complicated problems. Full article

Thermal overload in internal combustion engines may progressively destabilize lubricant-film integrity and promote severe tribological deterioration within highly stressed contact interfaces. This study investigates the thermo-tribological degradation sequence of a high-mileage gasoline engine subjected to prolonged idle operation under impaired cooling conditions, ultimately resulting in engine seizure. The investigated engine had accumulated 356,724 km, while the lubricant had remained in service for approximately 26,724 km prior to the experiment. The post-failure investigation combined teardown inspection, geometrical camshaft assessment, reverse gravimetric reconstruction, hydraulic tappet surface profiling, XRF surface characterization, laboratory oil analysis, and SEM/EDS evaluation of wear debris. The results demonstrated strongly localized degradation concentrated primarily within the cam–tappet interfaces. Severe non-uniform camshaft wear was accompanied by pronounced hydraulic tappet surface damage and evidence of unstable boundary-lubrication conditions. Laboratory oil analysis revealed elevated wear-metal concentrations, depletion of the alkaline reserve, increased oxidation indicators, and a final Class D oil condition assessment. SEM/EDS characterization identified Fe-bearing wear debris associated with sustained material removal and debris recirculation during the final degradation stage. The combined evidence supports a coupled thermo-tribological degradation mechanism involving lubricant deterioration, boundary-lubrication instability, adhesive wear acceleration, oxidative surface degradation, and debris-assisted surface damage preceding final engine seizure. The present case study provides experimentally documented evidence of lubrication collapse under real-engine thermal runaway conditions and highlights the critical role of lubricant condition in maintaining tribological stability under severe thermal loading. Full article

Reliable temperature monitoring is essential for the thermal management and safe operation of modern telecommunication equipment. However, conventional temperature sensors are often relatively large and rigid, which limits their applicability for localized temperature measurement on compact electronic components. In this study, a flexible thin-film thermocouple based on NiCr–NiSi thermoelectric materials was developed for temperature monitoring of telecommunication equipment. The sensor adopts a multilayer structure consisting of a polyimide (PI) flexible substrate, an Al₂O₃ insulating layer, NiCr and NiSi thermoelectric films, and a SiO protective layer and was fabricated using magnetron sputtering. Static calibration experiments show that the fabricated sensor exhibits a thermoelectric sensitivity of approximately 40.45 µV/°C, which is close to the reference value of conventional K-type thermocouples, with a relative error of about 1.34%. Repeated heating–cooling cycles demonstrate good repeatability and stable thermoelectric characteristics. Dynamic tests under representative transient thermal conditions showed that the sensor could continuously capture temperature variations without signal interruption or abnormal fluctuations. To further quantify its dynamic behavior, a numerical step-response simulation was performed for the PI/Al₂O₃/NiCr–NiSi/SiO multilayer structure. The simulated thermal time constant and curve-extracted 90% response time were 0.0343 s and 0.0803 s, respectively, under the specified boundary conditions. Owing to its small thickness, low thermal mass, and good mechanical flexibility, the proposed thin-film thermocouple can be conformally attached to compact and curved electronic surfaces, indicating promising potential for real-time localized temperature monitoring of telecommunication equipment and other compact electronic systems. Full article