Search Results (5,680)

As a core component of large marine engines, the compressor delivers robust and efficient power for propulsion. This study focuses on assessing and quantifying the uncertainty in the aerodynamic performance of a transonic rotor under various operating conditions, with the aim of investigating the impact of blade manufacturing variability on performance. Monte Carlo simulation (MCS) and sensitivity analysis were initially employed to identify parameters that significantly influence airfoil performance. Subsequently, a non-intrusive polynomial chaos (NIPC) uncertainty quantification model was developed to compare the effects of tip clearance deviation and surface geometry deviation on rotor performance. The study then analyzes how the geometric deviation at the different spanwise sections affects aerodynamic performance. The results reveal that geometric deviations have a more profound influence on aerodynamic performance than blade tip clearance. The impact of geometric deviations on average pressure ratio and efficiency of the transonic compressor rotor intensifies as the air mass flow rate approaches the near-stall point, while it decreases near the choking point. Interestingly, fluctuations in pressure ratio exhibit the opposite trend. Regarding spatial distribution, deviations in the upper half of the blade span (near the tip) exert a more dramatic influence on mass flow rate and pressure ratio fluctuation. A conceivable reason is that the inlet airflow velocity increases along the radial direction of the blade, and manufacturing variations in the same magnitude produce more notable relative geometric deviations in the upper half of the blade span. Centered on the machining tolerance guidelines for transonic compressor rotors, this work recommends stricter profile tolerance requirements for the upper half of the blade span. Full article

The optimal control of cooling water systems is of great significance for energy saving inchiller plants. Previously optimal control methods optimize the flow rate, temperature or temperature difference setpoints but cannot control pumps and cooling tower fans directly. This study proposes a direct optimal control method for pumps and fans based on derivativecontrol strategyby decoupling water flow rate optimization and airflow rate optimization, which can make the total power of chillers, pumps and fans approach a minimum. Simulations for different conditions were performed for the validation and performance analysis of the optimal control strategy. The optimization algorithms and implementation methods of direct optimal control were developed and validated by experiment. The simulation results indicate that total power approaches a minimum when the derivative of total power with respect to water/air flow rate approaches zero. The power-saving rate of the studied chiller plant is 13.2% at a plant part-load ratio of 20% compared to the constant-speed pump/fan mode. The experimental results show that the direct control method, taking power frequency as a controlled variable, can make variable frequency drives regulate their output frequencies to be equal to the optimized power frequencies of pumps and fansin a timely manner. Full article

In this study, the nonlinear forced vibration response of fiber-reinforced laminated composite beams coated with functionally graded materials (FGMs) is investigated under the combined action of aero-thermoelastic loads and a concentrated harmonic excitation. The mathematical formulation is established using the Euler–Bernoulli beam theory, where von Kármán geometric nonlinearities are taken into account, along with the modified third-order piston theory to represent aerodynamic effects. By neglecting axial inertia, the resulting set of nonlinear governing equations is simplified into a single equation. This equation is discretized through the Galerkin procedure, yielding a nonlinear ordinary differential equation. An analytical solution is, then, obtained by applying the method of multiple time scales (MTS). Furthermore, a comprehensive parametric analysis is carried out to evaluate how factors such as the power-law index, stacking sequence, temperature field, load amplitude and position, free-stream velocity, and Mach number influence both the lateral dynamic deflection and the frequency response characteristics (FRCs) of the beams, offering useful guidelines for structural design optimization. Full article

This study investigates the combustion behavior of H₂–CH₄ mixtures with oxygen-enriched air, achieved through injecting ozone (O₃) into the air intake of the burner fan. The motivation for this approach lies in the high reactivity of hydrogen compared to methane, with the aim of promoting a more favorable oxidizing environment for overall combustion. The research combines theoretical analysis with experimental validation using a diffusion-type burner operating at a fuel flow rate of 1.2 Nm³/h. For this flow rate, the ozone injection led to an equivalent O₂ concentration of approximately 21.7%. At this enrichment level, flame temperature was calculated to increase by 70–90 °C. The burner was specifically designed for the diffusion combustion of H₂–CH₄ mixtures and features three fuel injection nozzles, each surrounded by five air inlets. Experiments employed premixed H₂-CH₄ gas cylinders (Linde) with hydrogen concentrations of 20% and 30%, respectively. The results confirmed slight combustion intensification due to elevated oxygen concentration, with no issues related to flame stability or pulsations observed. Core flame temperature and flue gas emissions, including CO₂, were measured. The results support the further development of this combustion technology by increasing the allowable oxygen concentration limit. Full article

This study explores the combustion behavior of three biomass pellet types—wood (W), sunflower husk (SH), and a mixture of wood and sunflower husks (W/SH)—in a residential hot water boiler. Experiments were carried out under two air supply regimes (40%/60% and 60%/40% primary to secondary air) to measure flue gas concentrations of oxygen (O₂), carbon monoxide (CO), and nitrogen oxides (NO_x). The results indicate that SH pellets generate the highest emissions (CO: 1095.3 mg/m³, NO_x: 679.3 mg/m³), while W pellets achieve the lowest (CO: 0.3 mg/m³, NO_x: 194.1 mg/m³). The mixed W/SH pellets produce intermediate values (CO: 148.7 mg/m³, NO_x: 201.8 mg/m³). Overall boiler efficiency for all tested fuels ranged from 90.3% to 91.4%. Numerical simulations using ANSYS CFX (2024 R2 (24.2)) were performed to analyze temperature distribution, flue gas composition, and flow fields, showing good agreement with experimental outlet temperature and emission trends. These findings emphasize that both pellet composition and air distribution significantly influence efficiency and emissions, offering guidance for optimizing small-scale biomass boiler operation. Full article

This study presents an integrated assessment of anchorage-related emissions and air quality impacts in the Panama Canal region through Automatic Identification System (AIS) data, bottom-up emission estimation, and atmospheric dispersion modeling. One year of terrestrial AIS observations (July 2024–June 2025) captured 4641 vessels with highly variable waiting times: mean 15.0 h, median 4.9 h, with maximum episodes exceeding 1000 h. Annual emissions totaled 1,390,000 tons of CO₂, 20,500 tons of NO_x, 4250 tons of SO₂, 656 tons of PM₁₀, and 603 tons of PM_2.5, with anchorage activities contributing 497,000 tons of CO₂, 7010 tons of NO_x, 1520 tons of SO₂, 232 tons of PM₁₀, and 214 tons of PM_2.5. Despite the main engines being shut down during anchorage, these activities consistently accounted for 34–36% of the total emissions across all pollutants. High-resolution emission mapping revealed hotspots concentrated in anchorage zones, port berths, and canal approaches. Dispersion simulations revealed strong meteorological control: northwesterly flows transported emissions offshore, sea–land breezes produced afternoon fumigation peaks affecting Panama City, and southerly winds generated widespread onshore impacts. These findings demonstrate that anchorage operations constitute a major source of shipping-related pollution, highlighting the need for operational efficiency improvements and meteorologically informed mitigation strategies. Full article

The reverse circulation drill bit is the key component for the efficient and smooth implementation of the pneumatic hollow-through down-the-hole (DTH) hammer reverse circulation continuous coring (sampling) technology. To obtain the structural form of a reverse circulation drill bit with better reverse circulation performance, revealing its local flow fields by computational fluid dynamics (CFD) simulation is an effective approach. Taking the inner jet holes-type reverse circulation drill bit as the research object, three kinds of symmetrical and asymmetrical structures of inner jet holes were proposed. The CFD simulation results show that increasing the air volume supply and the number of inner jet holes leads to an increase in the velocity of air flow jet within the inner jet holes, an increase in the negative pressure formed in the central through channel below the inner jet holes, an enhancement of the reverse circulation performance and suction capacity formed by the reverse circulation drill bit, and an acceleration of the upward flow velocity of the rock cores (samples) located at the bottom of the borehole. Additionally, the reverse circulation performance formed by the reverse circulation drill bit with staggered arranged inner jet holes is superior to that of the reverse circulation drill bit with uniformly distributed inner jet holes. Under the same simulation conditions, the static pressure (i.e., negative pressure) and the upward flow velocity formed by the JB6 model are 2.34 kPa and 30.778 m/s higher than those formed by the JB3-3 model, while these two values formed by the JC6 model are 0.197 kPa and 3.689 m/s higher than those formed by the JB6 model, respectively. In conclusion, an asymmetric structural design would be more reasonable for the design of the inner jet holes-type reverse circulation drill bit. Full article

The growing demand for micro-launchers capable of placing payloads between 1 and 100 kg into low Earth orbit stems from rapid advances in electronics and the resulting increase in nanosatellite capabilities. Simultaneously, space programs are prioritizing the use of alternative propellants, those that are more sustainable, cost-effective, and readily available. As a result, modern launcher development emphasizes versatility, reliability, reusability, and adaptability to various working fluids. This paper presents the experimental validation of a supersonic turbine design methodology tailored for such adaptable systems. The focus is on a turbine class intended for a turbopump in micro-launchers with payload capacities around 100 kg. The experimental campaign employed two working fluids (air and methane) to assess the method’s robustness. The validation was performed on a stator only planar model, and the experimental data was compared with the analytical result obtained through the Mach number similarity criterion. The results confirm that the approach accurately identifies flow similarity through Mach number matching, even when the working fluid changes. Comparative analysis between experimental data and predictions demonstrates the method’s reliability, with measurement uncertainties also addressed. These findings support the methodology’s applicability in practical engine design and adaptation. Future work will explore enhancements to improve predictive capability and flexibility. The method may be extended to other systems where fluid substitution offers design or operational advantages. Full article

Cold-air pooling (CAP) and frost risk represent significant climate-related hazards in karstic and agricultural environments, where local topography and surface cover strongly modulate microclimatic conditions. This study focuses on the Mohos sinkhole, Hungary’s cold pole, situated on the Bükk Plateau, to investigate the formation, structure, and persistence of CAPs in a Central European karst depression. High-resolution terrain-based modeling was conducted using UAV-derived digital surface models combined with multiple GIS tools (Sky-View Factor, Wind Exposition Index, Cold Air Flow, and Diurnal Anisotropic Heat). These models were validated and enriched by multi-level temperature measurements and thermal imaging under various synoptic conditions. Results reveal that temperature inversions frequently form during clear, calm nights, leading to extreme near-surface cold accumulation within the sinkhole. Inversions may persist into the day due to topographic shading and density stratification. Vegetation and basin geometry influence radiative and turbulent fluxes, shaping the spatial extent and intensity of cold-air layers. The CAP is interpreted as part of a broader interconnected multi-sinkhole system. This integrated approach offers a transferable, cost-effective framework for terrain-driven frost hazard assessment, with direct relevance to precision agriculture, mesoscale model refinement, and site-specific climate adaptation in mountainous or frost-sensitive regions. Full article

The escalating global demand for primary energy—still predominantly met by conventional carbon-based fuels—has led to increased atmospheric pollution. This underscores the urgent need for alternative energy strategies capable of reducing carbon emissions while meeting global energy requirements. Hydrogen, as a clean combustible fuel, offers a promising alternative to hydrocarbons, producing neither soot, CO₂, nor unburned hydrocarbons. Although nitrogen oxides (NO_x) are the primary combustion by-products, their formation can be mitigated by controlling flame temperature. This study investigates the viability of hydrogen as a clean energy vector by simulating an unsteady, turbulent, non-premixed hydrogen jet flame interacting with an air co-flow. The numerical simulations employ the Unsteady Reynolds-Averaged Navier–Stokes (URANS) framework for efficient and accurate prediction of transient flow behavior. Turbulence is modeled using the Shear Stress Transport (SST k-ω) model, which enhances accuracy in high Reynolds number reactive flows. The combustion process is described using a presumed Probability Density Function (PDF) model, allowing for a statistical representation of turbulent mixing and chemical reaction. The simulation results are validated by comparison with experimental temperature and mixture fraction data, demonstrating the reliability and predictive capability of the proposed numerical approach. Full article

Surge is a typical aerodynamic instability phenomenon in the compressors of aeroengines. The surge can lead to severe performance degradation and even structural damage to the engine and the air vehicle, making it a longstanding critical concern in the industry. Analyzing and understanding the surge process contributes to enhancing the aerodynamic stability of designed compressors. Previous research in this field often focuses solely on the compressor itself while neglecting the mutual interaction between the compressor and other components in the entire engine system. This study investigates the compressor surge process within an integrated engine environment using a full-engine three-dimensional Unsteady Reynolds-averaged Navier–Stokes (URANS) simulation method for the entire engine system, validated through variable geometry turbine experiments on a small turbojet engine. The result demonstrates that the integrated three-dimensional simulation approach can capture the primary flow characteristics of the compression system during surge within an integrated engine environment. Under the influence of the variable geometry turbine, the studied small turbojet engine enters a state of mild surge. This paper also investigates the changes in aerodynamic forces during surge and reveals the two-regime surge phenomenon that exists during the engine surge. Full article

Gas monitoring and dust control in coal mine goafs are critical for ensuring safe and efficient production. To address the challenges posed by dust accumulation from mechanized mining and ventilation systems, this study designs a spiral-driven gas purification pipeline robot integrating a wet dust removal mechanism. The robot features a modular structure, including a spiral drive, a plugging and extraction system, and a wet dust removal unit, to enhance pipeline adaptability and dust removal performance. Dynamic modeling reveals that the robot’s speed increases with the deflection angle of the driving wheel, with optimal performance observed at a 45° angle. The analysis of the rolling friction, medium resistance, and deflection angle indicates that reducing the angle improves the obstacle-crossing ability. Numerical simulations of gas migration in the goaf identify a high dust concentration at the air outlet and show that flow velocity significantly affects dust removal efficiency. Simulation and prototype testing confirm stable robot operation at deflection angles of between 30° and 90° and effective crossing of 5 mm barriers. Optimal dust removal is achieved with a 5 m/s flow velocity, 0.6 MPa water mist pressure, and 400 mm chord grid spacing, providing both theoretical and practical guidance for gas monitoring and dust control in coal mine goafs. Full article

Using Excel and its Solver feature, a novel method of analyzing the component reactions of an overall reaction is outlined. As an example, autothermal reforming (300–700 °C) of acetic acid (AA), a significant component of pyrolysis oil, was considered. The overall reaction can be viewed as comprising five individual reactions: reforming, oxidation, water–gas shift, reverse Boudouard, and methanation. A laboratory apparatus was set up in which acetic acid, air, and water were continuously fed to a BASF dual-layer catalytic reactor in plug flow at 1 atm. For this setup, it is easy to construct a material balance in Excel in which five factors, f_i, are defined which represent the fraction of reactant going to each of the individual five reactions. Using the Solver feature of Excel, it can readily be determined which of the five factors f_i produce the best match of the calculated exit gas composition with the measured gas concentrations for CO, CO₂, H₂, CH₄, and O₂. Furthermore, a program such as GasEq or Aspen can then be used to calculate the theoretical equilibrium gas composition at a given condition. Using this equilibrium gas composition and Solver, the individual (f_i)_equilb can be calculated. Thus, the ratio f_i/(f_i)_equilb is an indication of how close each component reaction is to equilibrium. In this way, an idea is gained of which of the individual component reactions need to be improved or inhibited or if operating parameters should be adjusted. For the specific case of autothermal reforming of acetic acid, the steam reforming reaction requires at least 600 °C to approach equilibrium. In contrast, the oxidation reaction goes to equilibrium throughout the temperature range, completely consuming oxygen. The water–gas shift reaction appears to approach equilibrium to the extent of 71–90% throughout the temperature range. The reverse Boudouard reaction is favored at lower temperatures; in fact, coking was predicted and found at the low temperature of 300 °C. Full article

Microplastics released from synthetic garments pose a complex challenge to society and the environment. Textiles contribute to microplastic pollution throughout their entire lifecycle—from design and production to washing and use to their disposal—and can enter the environment through wastewater, soil, and air. The detachment of fibre fragments and their fate in the environment has received attention in the recent literature but lacks a harmonised research methodology and a holistic approach to the topic. This work presents a model to estimate the flows of microplastic fibres and synthetic garments in geographical Europe, expressed in tonnes per year. It was developed through a search of the literature to provide an estimate of synthetic fibres entering the environment and to identify the connections between the stakeholders involved. A first-level multicriteria decision analysis was conducted to recognise relevant pollution flows: the study revealed significant but poorly understood pathways, such as the flow of microplastics in the indoor and outdoor air during garment wear. Also, the flow of microplastics from the combined sewer overflow of untreated water during heavy precipitation and the flow to the agricultural land from the application of sewage sludge result in relevant pathways to water and soil, respectively. By fostering collaboration across multiple actors, the transition toward sustainable textile practices can significantly reduce fibre pollution. Full article

Confinement with a rectangular cross-section is commonly used to simulate the role of a swirl combustor, yet its effect on swirling flows remains poorly understood. This study investigates the influence of confinement on the isothermal flow field of a counter-rotating swirler. A particle image velocimetry (PIV) system was employed to measure the swirling flow field under varying confinement ratios at an air pressure drop equivalent to 3% of atmospheric pressure. The results reveal two distinct flow patterns, delineated by a critical confinement ratio of approximately 8.92. Detailed analyses of the velocity components, contour distributions, and Reynolds shear stresses were conducted. The two flow patterns are attributed to the wall attachment effect and swirling intensity, respectively. Furthermore, the results confirm that the swirling flow field is primarily governed by the confinement ratio. Full article