Search Results (484)

A vortex reducer is employed to reduce the pressure drop during the radially inward air bleeding process in aero-engines. The vortex reducer with deswirl nozzles (DVR) has the advantage of structural robustness; however, its complex, non-monotonic flow rate–pressure drop characteristic limits its widespread application. In an effort to resolve this issue, the current study employs both experimental and numerical methodologies to investigate the effects of nozzle geometric parameters on the flow characteristics of the DVRs, which are currently deficient. The findings indicate that, irrespective of variations in nozzle radial position or flow area, an elevation in the design point flow rate invariably results in an augmented pressure drop, and this coupling effect cannot be circumvented by modifying the geometric parameters. When the nozzle radial position is lowered to below b₁ = 130 mm or the flow area is reduced to below d₂ = 1.19 mm, the flow characteristic of the DVRs becomes monotonic; nevertheless, due to the severely limited flow capacity, such a monotonic characteristic lacks practical engineering significance. Therefore, both the nozzle radial position and the flow area should be regarded as separate independent variables in optimization calculations during the design process, necessitating the development of a rapid and accurate low-dimensional model. Full article

In this work, Direct Numerical Simulation (DNS) investigates the combustion behaviour of a reactive transverse lean premixed jet of an ammonia blend (10% NH₃, 11% H₂, 16% O₂ and 63% N₂ by volume) injected through a rectangular nozzle in a pre-heated non-vitiated air crossflow at a pressure of 5 bar. The configuration has been chosen from a Reynolds-Averaged Navier–Stokes (RANS) test campaign to ensure low NO and low unburned fuel, while maintaining a high temperature profile at the turbine inlet. The DNS shows that the flame stabilises on the leeward side of the rectangular jet, within and downstream of the recirculation region, while high scalar dissipation and short residence times prevent persistent anchoring on the windward side. Joint statistics reveal that the reaction does not follow a constant equivalence ratio path, since intermediate progress states are shifted towards leaner mixtures by entrainment, dilution and differential diffusion. The strongest heat-release and displacement-speed events occur in localised regions where mixture state, stretch and flame-front geometry act jointly. The displacement-speed budget is mainly controlled by the chemical source term, with diffusion reducing the net propagation speed and stratification-induced cross terms remaining small. Under intense stretch, positively curved flame elements exhibit larger displacement speeds, indicating a coupled effect of curvature, preferential diffusion and local radical transport. NO formation is dominated by fuel-nitrogen chemistry: HNO and NH₂ are the main NO-producing routes, whereas N₂ and N₂O provide the dominant NO-sink channels. The DNS predicts an outlet-averaged NO level of 400 dppm, while extended-domain RANS calculations indicate that longer residence times could reduce it below 100 dppm. Full article

The transition toward carbon-neutral energy systems has accelerated interest in hydrogen-fueled combustion technologies, where efficient fuel–air mixing is essential for stable and clean combustion. In the present study, the mixing characteristics of under-expanded supersonic jets injected into a pressurized environment are numerically investigated using validated computational fluid dynamics simulations. Two nozzle configurations are examined: a straight nozzle and sudden-expansion nozzles with different expansion ratios and expansion locations. The governing compressible flow equations are solved using the rhoCentralFoam solver with the SST k–ω turbulence model. The numerical framework is validated against Sod’s shock tube solution and experimental data for under-expanded supersonic free jets. The results show that sudden-expansion nozzles significantly modify the shock-wave structure, jet penetration, and lateral spreading compared with the straight nozzle. Among the investigated configurations, nozzles with intermediate expansion-section lengths exhibited pronounced Mach-disk oscillations with a dominant frequency of approximately 10 kHz. The normalized supersonic core length decreased from 17.79 for the straight nozzle to 5.50 for the best-performing sudden-expansion configuration, while the normalized jet half-width increased from 0.82 to 1.70, indicating substantially enhanced mixing performance. The findings demonstrate that nozzle geometry strongly governs the trade-off between flow stability and mixing enhancement in high-pressure supersonic jets. Full article

Exhaust piping in diesel engines is subject to severe thermal stress arising from high-temperature, high-pressure gas flows, and spray cooling with atomizing nozzles has become a widely adopted method to safeguard structural reliability. However, at present, the understanding of the spray fragmentation mechanism of two-phase flow under low inlet pressure is still not comprehensive. This study establishes a three-dimensional model of a gas–liquid impinging-jet nozzle and applies a coupled Volume-of-Fluid to Discrete-Phase-Model (VOF–DPM) approach to resolve the liquid breakup process in detail. High-speed imaging experiments were carried out to validate the numerical results. Orthogonal tests were conducted at five pressure levels for both gas and water—0.28, 0.24, 0.20, 0.16, and 0.12 MPa—producing 25 data pairs of spray cone angle and Sauter Mean Diameter (SMD). Within the 0–0.3 MPa air inlet pressure range explored here, raising the pressure consistently reduced the SMD and widened the cone angle, although both trends weakened as the pressure increased. Water inlet pressure exhibited a nonlinear influence, with local extrema appearing in the higher-pressure region. The overall SMD reached a minimum of 34.12 μm and a maximum of 149.04 μm. Using these 25 data points, a genetic algorithm was employed to optimize the pressure ratio under the constraint of total hydraulic power, yielding optimization strategies for different power budgets. An additional outcome of the simulation was the identification of a structural weakness: by reshaping the original flat impingement surface into a full conical surface, atomization quality improved by 29.36% under identical boundary conditions. These findings clarify the atomization mechanism of gas–liquid impinging jets under low inlet pressure and offer practical guidance for nozzle optimization. Full article

Sediment management represents a key challenge for hydropower plants, as it requires balancing river continuity preservation with the mitigation of erosion-related damage. To identify admissible sediment loads that ensure acceptable wear levels, reliable numerical tools are required for the prediction of multiphase flow behavior under different sediment transport conditions. In this framework, the present study applies a steady-state inhomogeneous Eulerian approach to investigate the three-phase flow (water–air–sediment) inside a Pelton nozzle under different needle-opening conditions and high sediment volume fractions. The CFD model is first validated under clear water–air conditions by comparing the predicted discharge coefficient with the literature data for the same nozzle geometry. Subsequently, the validated framework is extended to sediment-laden configurations, and the resulting injector performance and jet characteristics are compared with the corresponding clear-water case. The results highlight that the presence of sediments leads to increased pressure losses and modifications of the jet structure, which may adversely affect the hydraulic performance of the downstream Pelton runner. Full article

Efficient capture of respirable dust remains difficult in fully mechanized excavation roadways because fine particles readily migrate with airflow beyond the effective spray region. Here, a wind-assisted negative-pressure dust suppression device was developed by integrating annular Venturi entrainment with a mechanical air duct, enabling coupled airflow induction and droplet transport. The device was optimized using nozzle atomization tests, CFD-based orthogonal simulations, and laboratory-scale validation. The results show that an SK508 solid-cone nozzle provides suitable atomization for Venturi-induced suction. Using induced air inlet velocity and diffuser-inlet static pressure as evaluation indicators, the optimal Venturi unit was obtained at 0.1 MPa water pressure, 0.4 MPa air pressure, a 15° diffuser angle, and a throat-center nozzle position. For the integrated device, the best configuration was ten Venturi tubes, an impeller rotational speed of 2400 r/min, and an impeller position of 300 mm from the air duct inlet. In laboratory-scale tests, the complete wind-assisted negative-pressure mode outperformed fan-only, spray-only, wind-assisted spray, and negative-pressure secondary dust suppression modes, achieving maximum total and respirable dust suppression efficiencies of 87.39% and 86.68%. The results demonstrate the feasibility of coupling mechanical airflow with Venturi entrainment and support subsequent field-scale validation. Full article

Adequate spray deposition and penetration of pesticides into the lower part of the soybean canopy can increase the chances of successfully protecting plants from diseases and insects. Only a small number of comprehensive studies have examined how spray application parameters (nozzle types, travel speed, droplet size, application rate, application equipment) affect droplet penetration into the inner and lower parts of the soybean canopy. However, the data obtained from replicated plots in these field experiments showed significant variability due to uneven soybean canopy characteristics and unpredictable wind speed and direction. To minimize variability in field studies, this study used a new methodology: conducting the experiment under controlled conditions in a wind tunnel. This research was conducted to evaluate the effect of increasing the distance between soybean rows on the spray coverage and deposition of different droplet size classes from various nozzles, delivering spray to the lower canopy in a wind tunnel. Four commercially available spray nozzles with droplet size classification from medium to extremely coarse were mounted on a spray boom with a spray controller to spray an application rate of 150 L ha⁻¹ under laminar wind speeds of 0, 2.4, and 5.1 m s⁻¹. Rectangular pots containing fully grown soybeans were placed in the test section of the tunnel at center-to-center distances of 0.38 and 0.76 m to replicate narrow and wide row spacings, respectively, commonly used by soybean growers. Eight points in each soybean row were selected to collect spray deposition and coverage with water-sensitive papers (WSPs) and acrylic plates (APs), respectively, at the top, middle, and lower layers of the canopy. Results showed that the top of the soybean canopy consistently received the highest amount of spray, regardless of application conditions, as expected, while the middle and lower layers of the canopy did not receive much spray. Nozzle types and wind speeds were not significant factors in increasing spray penetration into the middle to lower layers of soybean plants. Although wider row spacing improved the spray deposition in the lower part of the canopy, this improvement was not statistically significant. The main conclusions derived from this study indicate that even using wider row spacing configurations, spray penetration into the lower parts of the soybean canopy was limited due to denser canopy conditions and the effects of high wind speeds. Therefore, other advanced spray techniques, such as air-assisted spraying or using other mechanisms to expose lower parts of the canopy to the nozzles, may be needed to effectively overcome these limitations. Full article

In long-haul flights, cold non-insulated structural zones within aircraft cabins can lead to discomfort for passengers and crew, particularly during cruise phases. Moreover, during ground operations in cold weather, maintaining the thermal conditioning of the cabin becomes challenging, especially with open doors. This article presents the development of an active air curtain designed to address these issues by isolating significant cold zones and enhancing cabin comfort. The conceptual design is based on redirecting conditioned air to form a controlled barrier, which reduces thermal gradients and air mixing. The cold stream infiltrating from non-insulated structures was characterized under typical cruise scenarios using flight test data, while the open-door scenario on the ground was characterized analytically. A CFD analysis was performed to optimize nozzle geometry, airflow rate, and placement. Based on simulation results, a prototype was manufactured and tested in a controlled laboratory environment. The experimental validation confirmed the effectiveness of the air curtain in minimizing heat loss and improving thermal comfort. This paper discusses design trade-offs, thermal performance, and integration considerations, highlighting the potential of air curtains as a lightweight and low-impact solution for environmental control systems in modern transport cargo aircraft. Full article

The interaction between crossflows from sprinkler nozzles and airflow is crucial for engineering applications, particularly affecting the efficiency of sprayed areas. This study investigates the deformation of a continuously injected conical water spray subjected to horizontal airflow, using a planar laser imaging method as a visualisation technique. Experiments were conducted in a wind tunnel at a constant water pressure of 0.2 MPa and four airflow rates (0.1, 0.2, 0.4, and 0.6 m³·s⁻¹) to systematically vary the air-to-water momentum ratio. A grayscale-based analysis method was developed using a per-pixel Look-Up Table (LUT), enabling indirect assessment of droplet concentrations and spray structure. This approach allowed for a detailed examination of changes in the spray cone shape under flowing air. By assessing the water spray across three vertical planes intersecting the spray cone, it became possible to calculate lateral area and cone volume at different air-to-water mass flow ratios. The spray formation region exposed to airflow exhibited larger cone volumes than those with minimal airflow. The changes in apparent spray angles for the tested nozzles were determined to characterize the cone shape. The apparent spray angle varies systematically with the air-to-water mass flow ratio, confirming the dominant role of aerodynamic forces. These findings improve the understanding of spray behavior under crossflow and provide a basis for validating numerical models of air–water interactions. Full article

The demand for materials that can operate reliably in extreme environments, including rocket nozzles, re-entry heat shields, sharp leading edges, high-velocity impact, and high-temperature energy systems, continue to drive advances in thermal–structural materials. Carbon/Carbon composites remain a leading baseline because of their low density, high-temperature mechanical retention in inert atmospheres, and excellent thermal-shock tolerance. However, long-term durability is constrained by rapid oxidation in air at elevated temperatures, limited fracture toughness and elastic modulus in many architectures, and high manufacturing cost driven by multi-cycle densification and stringent quality assurance. Consequently, contemporary strategies increasingly rely on modifying Carbon/Carbon composites with ultra-high-temperature ceramics and adopting accelerated or simplified manufacturing routes. This review synthesizes recent progress in the design, manufacture, and application of high-performance modified Carbon/Carbon composite systems for extreme aerospace environments, emphasizing composition/architecture selection, oxidation, and ablation protection, toughening concepts, and cost-aware densification. Because extreme environments performance is governed by coupled aerothermal loading, gas–surface chemistry, internal transport, recession, and thermomechanical response, the review also consolidates the multiscale modeling and software toolchains increasingly used to size thermal-protection systems, interpret experiments, and guide down-selection. Key challenges and future directions are further discussed for reusable materials and validated performances beyond ~2000 °C. Full article

In view of the practical engineering demand and performance optimization of compressed air-driven fire-extinguishing projectile launchers, a two-dimensional axisymmetric compressible flow numerical model is established based on ANSYS Fluent 2023. Numerical verification is conducted by comparing with classical zero-dimensional theoretical results and reference data from the published literature to guarantee simulation accuracy. Combined with the internal ballistic motion characteristics, the present study systematically investigates the effects of initial pressure, flow passage structure, loading position and projectile mass on launch dynamic behavior and the energy utilization mechanism. The results reveal that the initial high-pressure chamber pressure dominates the total energy output of the system. Appropriately increasing the valve gap and nozzle diameter can improve flow characteristics and energy transfer efficiency. Adjusting the loading position and barrel length effectively balances the internal ballistic response, while larger projectile mass brings higher inertial resistance and obvious efficiency attenuation. This work clarifies the quantitative influence of key structural and operating parameters, and provides theoretical support and engineering reference for the design, parameter matching and performance improvement of similar fire-extinguishing launching equipment. Full article

Upper Northern Thailand continues to face a protracted structural crisis from fine-particulate matter (PM_2.5), primarily driven by biomass burning and wildfires. Conventional mechanical capture systems, such as cyclones, often suffer a drastic efficiency drop when treating sub-micron particles. This study introduces an innovative Evaporative Condensation Growth Scrubber (ECGS) designed to bridge this technological gap by promoting the growth of fine particles through heterogeneous nucleation. Experimental testing across 10 different nozzle configurations was conducted to optimize the system’s performance. The results revealed that the ECGS system significantly outperformed the dry cyclone (Baseline) across all nine testing configurations. While the Baseline showed inherent limitations in capturing sub-micron particles, the ECGS demonstrated relative efficiency improvements ranging from 39.53% to 83.23% for PM_2.5, and 26.10% to 61.50% for PM₁₀ compared to the baseline. Optimal performance was achieved using a 90-degree injection angle and a 10 cm distance, which created a complete spray curtain and maximized collision probability. Under these conditions, the outlet PM_2.5 concentration stabilized at 11.81 µg/m³ within 180 s of water injection. Crucially, despite sensor interference caused by high relative humidity, the system’s effectiveness was confirmed by a significant difference in performance in PM₁₀ and PM_2.5 removal. The PM₁₀ collection efficiency outperformed that of PM_2.5 by 28.82%, providing empirical evidence that PM_2.5 particles successfully acted as nuclei for condensation and grew into the larger PM₁₀ size range. This particle growth enabled more effective centrifugal separation, demonstrating that the ECGS system offers a viable and efficient solution for fine particle removal in highly polluted environments. Full article

Laminar co-flow in microchannels typically results in stratified streams with diffusion-limited mixing. This work presents an additively manufactured microfluidic platform that integrates a pulse tank and a transverse injection nozzle into an otherwise straight channel, enabling pulse-driven mixing and droplet generation using air-pressure actuation alone. In Device A, transverse pulsed injection disrupted the stratified interface and significantly enhanced mixing compared with the no-pulse case, as confirmed by an entropy-based mixing index. In Device B, pulsed injection into a continuous oil phase enabled stable droplet-on-demand generation with pressure-tunable droplet diameter in a straight circular channel. The devices operated in a laminar regime, with representative Reynolds, Péclet, and capillary numbers confirming diffusion-limited baseline mixing and stable dripping-type droplet formation. The results demonstrate that pulse-driven injections in a simple, additively manufactured geometry provide an effective, low-complexity approach to mixing enhancement and droplet generation without external fields or complex channel designs. Full article

The foaming of hydrogels presents a promising strategy for tailoring mechanical and radiological properties to replicate biological soft tissues for biomedical phantom applications. A computational fluid dynamics (CFD) framework is developed to predict void fraction distribution in alginate hydrogel precursor solutions aerated by air injection through a bottom nozzle. The objective is to use the framework for the design of the foaming system to match the desired gas-fraction distribution and radiological property. Seven parametric cases are investigated, varying inlet air velocity, alginate concentration, and surface tension. Results show that higher inlet velocities promote stronger jet penetration and greater gas accumulation, while increasing alginate concentration confines the bubble plume, with quasi-steady gas fractions displaying a non-monotonic trend with concentration. Elevated surface tension yields broader plume coverage and improved gas distribution uniformity at the expense of peak void fraction. The predicted void fractions map to Hounsfield Unit (HU) values of −34 to −103, corresponding to adipose and fatty breast tissue attenuation (−50 to −150 HU). The peak gas fraction at 5.0 wt% alginate yields −307 HU, approaching published experimental CT measurements for the same formulation (−460 to −233 HU). Full article

With the increasing demand for higher efficiency in semiconductor machining, air spindles with compensation systems have attracted growing attention. The pneumatic nozzle–cylindrical flapper is a promising sensing approach due to its high precision and suitability for displacement measurement of high-speed rotating bodies. However, its complex three-dimensional flow behavior leads to significant deviations from conventional nozzle–flat flapper models, limiting its practical application. This study aims to clarify the flow mechanisms governing the nozzle–cylindrical flapper system and to establish a reliable framework for predicting its static characteristics. A computational fluid dynamics model is developed to analyze gas flow within the micron-scale clearance under varying gap sizes and angular orientations, and the results are validated against experimental measurements. The analysis shows that curvature plays a dominant role in the flow behavior. Increasing curvature enhances inertia-driven acceleration and weakens viscous effects while simultaneously inducing strong recirculation due to flow wrapping around the cylindrical surface. These competing mechanisms explain the observed deviations from conventional models and cannot be captured by two-dimensional approaches. Based on the numerical results, a mass flow rate compensation coefficient is introduced and correlated with the momentum compensation coefficient. A quadratic relationship between the two coefficients is identified, indicating a common recirculation-driven mechanism. These findings support previous semi-empirical assumptions and provide a basis for predicting static characteristics with reduced reliance on experimental calibration. Full article