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Air-core vortices occurring at intakes cause efficiency losses, vibrations, operational difficulties, and erosion at affiliated water-conveying structures. Air-core vortices are in the forms of non-air entraining vortex (air-core vortex in suspension) and air-entraining vortex. The profile of an air-core vortex is considered to be one of the main characteristics of the vortex. There are available semi-empirical formulas for the profile of a vertical non-air entraining vortex (air-core vortex in suspension) occurring at a vertically-flowing downward intake. However, there is no available developed formula relating to the profile of a vertical air-entraining vortex occurring at a vertically-flowing downward intake because the height, radii, and other physical quantities of the imaginary section of the air-entraining vortex downstream of the intake entrance are not measurable. Therefore, the profile of a vertical air-entraining vortex needs to be predicted. In the present study, by modifying the available formula relating to the profile of a non-air-entraining vortex and incorporating available test data, a practical methodology is developed for predicting the profile of a vertical air-entraining vortex. This study provides a practical formula and a chart to determine the necessary parameters to predict the profile of a vertical air-entraining vortex. The validation of the proposed methodology is examined and checked with available test data relating to the profile of a vertical air-entraining vortex occurring at a vertically-flowing downward intake. The results of the present study are in good agreement with available test data relating to the profile of vertical air-entraining vortices (the coefficient of determination is between 0.976 and 0.995).

The characterization of flame and temperature characteristics is a crucial foundation in the study of fire dynamics within enclosures, including detectors, sprinklers, and smoke control. Despite its importance, there is a notable lack of analytical studies, with the only established equation addressing the temperature profile generated by a centerline fire. No research has been conducted on sidewall fires, even though they are more common in corridor-like enclosures with lateral openings. In this study, experimental analysis and modeling of sidewall fire characteristics in a corridor-like enclosure with lateral openings were conducted. The results show that flame length is constrained by the sidewall, and the flame length produced by a centerline fire is significantly shorter than that of a sidewall fire. The maximum ceiling excess temperature is higher in sidewall fires compared to centerline fires. New models for flame length and maximum temperature rise are proposed. It was also verified that the dimensionless temperature attenuation is greater in enclosures with lateral openings than in those with both ends open. In a corridor-like enclosure with lateral openings, the air entrainment into the plume from a sidewall fire is only 33% of that from a centerline fire. Additionally, the smoke layer thickness under various fire scenarios is analyzed. Finally, a normalized vertical temperature rise is introduced to propose the new correlations for the dimensionless vertical height at different distances from the fire source. These contributions significantly enhance the understanding of fire behavior in similar structures, providing valuable insights for improving fire protection strategies.

LED polymer multilayer films offer clear advantages over single-layer coatings, such as minimized particle settling, finer control over particle distribution, and more precise spectral tuning. However, the standard “coat–dry–coat” process for these multilayer systems often traps air bubbles, degrading film quality and uniformity. This study investigates the air entrainment mechanism in multilayer film formation. Bubbles form when the cured bottom layer exhibits a low contact angle, which destabilizes the advancing liquid front. High-speed microscopy captured these interfacial dynamics, and contact-angle measurements quantified the wetting behavior. Numerical simulations further demonstrated that reduced wettability and vortex formation drive air entrainment. To mitigate air entrainment, a semi-cured slot die coating approach was proposed to modify the surface wettability and suppress the flow instabilities. Incorporating temperature-dependent viscosity into the simulation model improved its predictive accuracy, cutting the error in predicted coating-gap limits from 11.49% to 4.99%. This combined strategy delivers reliable, bubble-free multilayer films and paves the way for more consistent, high-quality LED polymer applications.

The paper presents the evaluation of the influence of calcium sulfate on the air void microstructure in concrete and its action mechanism depending on the character of the air-entraining agent. Gypsum dehydration has been previously proven to negatively influence the air void structure of air-entrained concrete. Ettringite, nucleating from tricalcium aluminate and calcium sulfate, influences the adsorption and mode of action of anionic-based polycarboxylate ether admixtures. The authors suspected the admixture’s air-entraining mechanism was also affected by these characteristics. Gypsum dehydration was confirmed to influence the air void structure. In the case of the anionic surfactant, the content of air bubbles smaller than 300 µm was lower compared to cement with gypsum and hemihydrate. On the other hand, the content of air voids with a diameter up to 60 µm, which are the most favorable, was higher. The results obtained led to the conclusion that the mechanism of air entrainment was twofold, and in most cases occurred through the lowering of surface tension and/or through the adsorption of surfactant on cement grains. The adsorptive mechanism was proved to be more effective in terms of the total air content and the structure of the air void system. The results and conclusions of the study provide guidelines to determine the proper surfactant type to reduce the risk of improper air entrainment of concrete, and emphasize the importance of gypsum dehydration of cement in the process of air entrainment.

The generation of persistent foam in the cooling water discharge of coastal power plants poses significant environmental and operational challenges. This phenomenon is fundamentally driven by a \"hydro-chemical coupling\" mechanism, where hydraulic air entrainment generates bubbles that are subsequently stabilized by surfactants in the seawater. While chemical defoaming is costly and potentially polluting, existing physical solutions often fail to address the complex, transient flow regimes found in tidal discharge systems. To address this, this study proposes an integrated \"source control\" strategy to eliminate hydraulic air entrainment. Using a comprehensive 1:20 scale physical model, we analyzed the air entrainment mechanisms in a complex discharge system comprising siphon wells, a long culvert, and a steep terminal drop. We designed and validated a combined abatement solution featuring a flow-limiting orifice plate in the siphon well and a novel three-stage de-aeration well at the outlet. Experimental results demonstrate that this configuration effectively eliminates air entrainment for over 95% of the operational period. Furthermore, the hydraulic impact is minimal, with the upstream backwater rise remaining below 0.5m even under extreme high-tide conditions. This study establishes a robust, environmentally friendly engineering methodology for managing foam in complex hydraulic systems dominated by large tidal variations.

This study presents a new experimental approach to investigate the effect of density on the water entry of solid cylinders made of identical material. The cylinders have identical surface coating, diameter, and length. So, their critical dimensionless variables (related to a water entry problem) like Reynolds, Weber, Bond, Froude, and Capillary numbers are the same at a specified impact velocity except for the density ratio. The impact velocity is set by changing the released height of cylinders0.5 cm–95 cm, which varies from 0.31 to 4.32 ms −1 The study focuses on characterizing cylinders kinetics (trajectory/velocity/acceleration) and the influence of density ratio on the air-entrainment cavity dynamics (cavity sealing patterns, cavity dimensions, pinch-off time/depth, Worthington water jets, cavity shedding, etc.). A \"pco.dimax S\" high-speed camera is used to record the cylinders' pathway to obtain such information. Investigations reveal that even though the impact velocity remains the same, changing the effective density varies the time and depth of cavity pinching or the sealing regime. Also, the effective density has a significant role in the kinetics behavior of the projectiles' motion. Graphical abstract

We discuss the reasons for the growing need in India for the manufacture of prosthetic implants such as implants for total or partial knee replacement. Complex prostheses such as knee replacement implants are highly complex in shape; therefore, they are preferably manufactured using shaped casting. It is now well established that castings made using traditional filling systems suffer from unreliable mechanical properties, particularly the ultimate tensile strength and ductility. Reliability, however, is a critical requirement for prostheses. The present article describes the latest filling system for gravity casting of critical cobalt alloy implants for use in knee prostheses. The novelty of the proposed filling system for casting knee implants lies in the combination of a flush filter and a spin trap, sited appropriately within a bottom-gated naturally pressurized filling system, aimed at reducing entrainment defects, viz. air bubbles and oxide bifilms. An uprunner that serves to both fill and feed the castings and narrow slot gates connecting the uprunner to the casting cavities are the other important elements of the present filling system. Casting simulations of knee implants using the proposed filling system technology indicate reduced surface turbulence of the melt during the early stages of filling, followed by priming of the initial melt to separate entrained defect content, with clean melt eventually entering the casting mold cavities at a sub-critical velocity for surface turbulence (below 0.5 m/s). Thus, for the first time in the production of cast prostheses using gravity casting, reducing entrainment defects to a low and reproducible level to raise reliability appears possible. This indicates a positive forecast for the production of high-quality medical implant castings of extremely low defect content and therefore enjoying high reliability compared to castings made by traditional gravity running and gating methods.

Air entrainment during mold filling is a major source of oxide inclusion formation in metal casting. A model was recently developed by the authors to predict the volumetric air entrainment during pouring of metal castings. In the course of validating the model with experimental data for plunging liquid jets, it was shown that the air entrainment rate during mold filling depends fundamentally on the velocity and diameter of the jet formed by the pouring stream. In this study, the effect of more complex pouring conditions and gating system design on air entrainment is examined. Simulations are performed investigating the air entrainment characteristics of castings filled without a gating system, and with bottom-gated and side-gated filling systems. Results indicate that reducing the head height and pouring time, and the addition of a nozzle extension significantly reduces the air entrainment. In addition, using an offset pouring basin with a stopper and pressurizing the gating system further reduces the volume of entrained air. Simulation results also show that the generation of vortex flows inside the filling system is beneficial in reducing free surface turbulence, which results in less air entrainment and oxide inclusion formation during mold filling.

Numerical studies regarding the influence of entrapped air on the hydraulic performance of gullies are nonexistent. This is due to the lack of a model that simulates the air-entrainment phenomena and consequently the entrapped air. In this work, we used experimental data to validate an air-entrainment model that uses a Volume-of-Fluid based method to detect the interface and the Shear-stress transport k-ω turbulence model. The air is detected in a sub-grid scale, generated by a source term and transported using a slip velocity formulation. Results are shown in terms of free-surface elevation, velocity profiles, turbulent kinetic energy and discharge coefficients. The air-entrainment model allied to the turbulence model showed a good accuracy in the prediction of the zones of the gully where the air is more concentrated.

Purpose While many stepped spillways geometry design guidelines were developed for flat steps, designing pooled steps might be an appropriate alternative to spillways working more efficiency. This paper aims to deal with the inception point of air-entrainment and void fraction in the different height of the pools. Following that, pressure distribution was evaluated in aerated and non-aerated regions under the effect of different heights of the pools and slopes through the use of the FLOW-3D software. Comparison of obtained numerical results with experimental ones was in good agreement for all discharges used in this study. Pools height had the insignificant effect on the inception point location. The value of void fraction was more affected in lower discharges in comparison with higher ones. Negative pressure was not seen over the crest of spillway (non-aerated region), and the maximum pressure values were obtained for pools with 15 cm height along the crest in each discharge. In all slopes, negative pressure was not formed near the step bed in the pooled and flat stepped spillways. However, negative pressure was formed in more area near the vertical face in the flat stepped spillway compared with the pooled stepped spillway which increases the probability of cavitation phenomenon in the flat stepped chute. Design/methodology/approach A pooled stepped spillway was used in order to evaluate pressure, void fraction, and inception point. Also, different height of the pools was used. Numerical simulation of this study was fulfilled through Flow-3D software. The obtained results indicated that pools can affect two-phase flow characteristics including pressure, void fraction and inception point. Findings Over the crest, negative pressure was not seen. Pressure values were different for all used heights and the maximum ones obtained for 15 cm height. Also, pooled stepped played a more effective role in reducing the negative pressure points compared with flat cases. Inception point location was more affected in nappe and transition flow regimes in comparison with skimming flow regime particularly for 9 and 15 cm heights. Originality/value The research results of Felder et al. (2012a) from the University of Queensland were used to numerically simulate the flow over the pooled stepped spillway.