Airflow Speed Research Articles

Motion behavior of droplets on curved leaf surfaces driven by airflow.

In air-assisted spraying, pesticide droplet retention on crop leaves is key to evaluating spray effectiveness. However, airflow can deform leaves, reducing droplet retention and affecting spray performance. This study used wind tunnels and high-speed cameras to capture leaf deformation at different airflow speeds and the motion of droplets on curved leaf surfaces. The results showed that leaf curvature during bending deformation is generally less than 0.05 mm-1. Critical wind speed for droplet movement is negatively correlated with droplet size and leaf curvature, with a 24.8% difference between different leaf curvatures and a 17.5% difference between droplet sizes. The droplet's dimensionless shape variable is positively correlated with both droplet size and leaf curvature. The maximum shape variable on curved leaves reaches 0.24, with acceleration differences of about 30%, while droplets of different sizes show a maximum shape variable of 0.18 and an acceleration difference of up to 68%. These findings enhance understanding of droplet-leaf interactions and provide insights for improving pesticide efficiency.

Resonant Forcing by Solar Declination of Rossby Waves at the Tropopause and Implications in Extreme Precipitation Events and Heat Waves—Part 2: Case Studies, Projections in the Context of Climate Change

Based on the properties of Rossby waves at the tropopause resonantly forced by solar declination in harmonic modes, which was the subject of a first article, case studies of heatwaves and extreme precipitation events are presented. They clearly demonstrate that extreme events only form under specific patterns of the amplitude of the speed of modulated airflows of Rossby waves at the tropopause, in particular period ranges. This remains true even if extreme events appear as compound events where chaos and timing are crucial. Extreme events are favored when modulated cold and warm airflows result in a dual cyclone-anticyclone system, i.e., the association of two joint vortices of opposite signs. They reverse over a period of the dominant harmonic mode in spatial and temporal coherence with the modulated airflow speed pattern. This key role could result from a transfer of humid/dry air between the two vortices during the inversion of the dual system. Finally, focusing on the two period ranges 17.1–34.2 and 8.56–17.1 days corresponding to 1/16- and 1/32-year period harmonic modes, projections of the amplitude of wind speed at 250 mb, geopotential height at 500 mb, ground air temperature, and precipitation rate are performed by extrapolating their amplitude observed from January 1979 to March 2024. Projected amplitudes are regionalized on a global scale for warmest and coldest half-years, referring to extratropical latitudes. Causal relationships are established between the projected amplitudes of modulated airflow speed and those of ground air temperature and precipitation rate, whether they increase or decrease. The increase in the amplitude of modulated airflow speed of polar vortices induces their latitudinal extension. This produces a tightening of Rossby waves embedded in the polar and subtropical jet streams. In the context of climate change, this has the effect of increasing the efficiency of the resonant forcing of Rossby waves from the solar declination, the optimum of which is located at mid-latitudes. Hence the increased or decreased vulnerability to heatwaves or extreme precipitation events of some regions. Europe and western Asia are particularly affected, which is due to increased activity of the Arctic polar vortex between longitudes 20° W and 40° E. This is likely a consequence of melting ice and changing albedo, which appears to amplify the amplitude of variation in the period range 17.1–34.2 days of poleward circulation at the tropopause of the Arctic polar cell.

Spent lithium-ion battery recycling: Process optimization and carbon footprint analysis based on thermal mechanical force

ABSTRACT With the increasing number of spent lithium-ion batteries, the development of efficient and environmentally friendly recycling technologies has become a key research focus. This study aims to establish a physical recycling method that integrates thermal treatment and mechanical separation to enhance the recovery rate of LiFePO4 materials while minimizing environmental impact. The process combines thermal treatment, mechanical separation, and air separation, with key factors influencing material separation and recovery efficiency analyzed through single-factor and variance analyses. Additionally, the carbon footprint of the recycling process was assessed using SimaPro software. The experimental results indicate that within a temperature range of 270°C–300°C, thermal treatment effectively separates LiFePO4 from aluminum foil, achieving a recovery rate of 96.88%. The air separation experiments further demonstrate that at an airflow speed of 20 m/s, the cathode material and current collector can be efficiently separated. Moreover, the carbon footprint analysis shows that this method significantly reduces carbon emissions.

Structural build-up of 3D printed earth by drying

In recent years, the potential of earth materials in construction has emerged as a sustainable pathway, offering environmental benefits compared to traditional methods. When used in raw form, earth materials can be recycled at the end of a building life, reducing construction waste. In parallel, integrating additive manufacturing into the architecture, engineering, and construction (AEC) sector has brought about a shift in construction dynamics, combining efficiency with precision. This paper bridges the study of 3D printing with earth-based fresh mortars, emphasising the capabilities of the “Forced Layer Drying” (FLD) technique in the additive manufacturing process to increase the mechanical performance of the printing mortar.This paper begins by defining the requisite rheological properties for successful 3D printing. A chosen material for this paper is speswhite kaolin. An instrumental aspect of our research is exploring an established model for the drying rate of saturated porous media, such as earth and concrete, and its application to predict the evaporation rate of saturated earth-based mortar in 3D printing with forced drying conditions. The Wind-Tunnel experiment was conducted to validate this model, examining the interplay of airflow speed and temperature on the evaporation rate. Further deepening this study, the soil water content and undrained shear strength are correlated, specifically based on models derived from oedometer geotechnical standard tests. This facilitated a comprehensive understanding of porous earth-based materials in various moisture scenarios. Our findings confirm that airflow, temperature, and the geometry of the printed object play instrumental roles in affecting evaporation rate, consequent mechanical performance, and structural build-up of the material. The paper wraps up by offering insights into the practical application of 3D printing using earth-based mortars, with a special focus on FLD technique.

Dynamic diffusion characteristics of airflow and coal dust during the mining process based on MRF: A numerical simulation study

Turbulence generated by rotation of shearer has a great impact on the distribution of dust. The MRF method of multiple reference frame was employed to simulate airflow and dust distribution during mining process. The distribution of cutting dust under different airflow velocities, cutting speeds, and cutting direction (against or follow the direction of airflow) were compared and analyzed. Results show that the generated cutting dust using MRF method tends to move horizontally and vertically. As the speed of airflow increases, vertical characteristics diminish. Simultaneously, horizontal dissipation rises with the deviation of airflow speed. The increase of rotational speed augments the distance covered by cutting airflow, including vertical offset and windward motion. Moreover, the elevated drum speed amplifies airflow speed in the sidewalk and the primary influence range is approximately 80 m. When cutting in the downwind direction, the airflow exhibits a pronounced vertical and horizontal offset behind the drum. Conversely, when cutting in the upwind direction, these characteristics are less evident, resulting in a more uniform spatial distribution of cutting dust in the downwind direction. The majority of dust generated when cutting against the airflow tends to move in the low-altitude area, contributing to a more disordered pattern.

Numerical Study of Flow Field and Particle Motion Characteristics on Raw Coal Vertical Roller Mill Circuits

In order to improve the motion characteristics of particles in vertical roller mills (VRMs), the assumption that different structures of helical guide blades affect the internal flow field of the VRMs was put forward. The distributions of fluid velocity and vorticity in VRMs were analyzed, and the mechanism affecting the motion of particles and the separation performance was studied. The study took the MMLM2550 (supplied by Jiangsu Dahuan Group, China; grinding table diameter of 2550 mm) VRM as the research object, whose structure was improved by adding helical guide blades. The results showed that, with the increase in the width of blade, the air flow trajectory and the distribution of vorticity improved, which was conducive to the transport of particles. However, changing the thickness of the blade had little effect on the internal physical field of the VRM and particle motion characteristics. Therefore, the influence of blade’s thickness on these factors was ignored. With the increase in the number of helical guide blade turns, the direction of the helical guide blade remained consistent with the trajectory of the movement of particles, making it more conducive to the discharge of particles from the VRM. The height of the helical guide blade had a great influence on the flow field and the particle motion characteristics. The smaller the blade height, the greater the reflux in the primary separation zone, and stronger the irregular circulatory motion of particles, thus increasing the movement time and the distance of particles. With the increase in the number of blades, the airflow speed increased in the flow channel, so that the particles moved with the airflow at high speed, while the movement time was effectively shortened. The study provides valuable guidance for the improvement of VRM structures, and serves as a reference for characterizing the motion of particles and enhancing the internal flow field in VRMs.

Pulse power supply for plasma aerodynamic actuators

The reduction of local heat load on the structural elements of aircraft or spacecraft vehicles due to the shock wave/boundary layer interaction can be successfully controlled in the future using a system of plasma actuators. The efficiency of plasma aerodynamic actuators operation is directly related to a power source. It determines a covered plasma area, an air flow speed and a thrust the actuator creates. The paper deals with the operation of a high-voltage source of sawtooth pulses with high efficiency for controlling plasma actuators. The pulse power source can be easily scaled for different nonlinear capacitive loads.

Investigation of temperature field variations induced by the air thermodynamic behavior when trains pass through a high-speed railway tunnel in cold regions

High-speed railway tunnels in the cold region, whose numbers are increasing, are widely exposed to the threat of frost damage caused by extremely negative temperatures. The operation of high-speed trains has made this problem even more pronounced. But there are fewer studies focusing on the dynamic changes in temperature during train operation. In this paper, the air thermodynamic behavior of trains passing through a tunnel and its consequences were investigated with the help of the CFD method. In numerical simulations, conditions of different natural airflows, different train speeds, different blockage ratios, as well as two trains intersecting in the tunnel were involved. The following valuable results were obtained. In cold environments, train-induced pressure wave effects will affect the air thermodynamic behavior, but the overall trend in air temperature is mainly influenced by the heat transfer between cold and warm air. The high-speed train will lead to massive cold air being carried into the tunnel and some warm air inside being pushed out. Heat transfer between cold and warm air will cause a significant decrease in tunnel air temperature. This air thermodynamic behavior is particularly prominent in the case of large blockage ratios. When there are same-direction natural airflows, they will be coupled with train-induced airflows, causing a greater decrease in tunnel air temperature. In contrast, opposite-direction natural airflows can reduce the negative effects of the train. Taking the case of opposite-direction natural airflow velocity of 5 m/s as an example, the temperature changes of the three cross-sections are only 16.7 %, 14.8 %, and 42.1 % of those in the case of no natural airflow. Whatever the direction of natural airflows, coupling effects between them and train-induced airflows will be more significant as the natural airflow speed increases. Greater train speed means more cold air entering the tunnel and stronger heat transfer between cold and warm air, causing a more significant temperature decrease. When two trains intersect through the tunnel, airflows caused by them will be coupled. As a result, only a little air enters the tunnel from the entrance and exit, and the heat transfer between air with different temperatures is weak. In this case, the air temperature doesn't decrease but slightly increases as the air is compressed.

Bioaerosol sampling and bioanalysis: Applicability of the next generation impactor for quantifying Legionella pneumophila in droplet aerosols by flow cytometry

Bioaerosol generation, sampling, and cultivation-independent quantification of pathogenic bacteria play a crucial role in studying dose-response effects of Legionella pneumophila. Here, the Next Generation Impactor (NGI), initially created for pharmaceutical inhaling studies, was assessed for its potential to sample airborne bioaerosols and to separate size-dependent wet droplets by incrementally increasing the airflow speed. This stainless-steel sampler was shown in this study to be suitable for sampling prior to cultivation-independent analysis of pathogen-containing bioaerosols using washable cups. The applicability was studied by quantifying the total and intact cell count of L. pneumophila by flow cytometry after being dispersed into a droplet aerosol. Our results demonstrate a high total sampling efficiency of 95.5% ± 11.8% despite a lower biological sampling efficiency of 59.7% ± 16.5% for dry aerosols. However, by elevating the relative humidity (RH) to 100% in a liquid aerosolization unit, the biological sampling efficiency increased to over 90% for L. pneumophila. More than 50% of the cells were found in stage 1 using the liquid aerosolization unit. In comparison, 80% of the cells were sampled in stages 4–6 at 30% RH. Specifically, while at 100% RH, the droplet size mattered, at 30% RH, the size distribution of dry particles, in this case L. pneumophila, was relevant due to evaporation processes, which explains the size differences. These findings indicate the potential of the NGI for further exploration and application in studying other aerosol-borne pathogens, especially concerning the size distribution of wet droplets, viability, or effect-based bioanalysis.

Research on flow field characteristics of curved pipe in bulk grain cyclone conveying based on gas solid coupling

AbstractIn the transportation of grain particles, elbow wear is a pressing concern. A novel approach to mitigate this involves introducing a lateral air supplement rotation mechanism that enables swirling transportation. We assessed the integration of this device at angles of 45°, 55°, and 65° to the central axis of the main pipeline. While the multiphase flow velocity within the main conduit was held constant at 20 m/s, the lateral device's airflow velocities were tested at 20, 30, and 40 m/s. Utilizing the CFD–DEM simulation for grain particle transportation around bends, our findings indicated that an optimal arrangement was with the lateral device at 55° relative to the main pipeline, with an airflow speed of 30 m/s. This setup fostered a forward particle spiral, drastically diminishing wear on the pipe wall. Experimental evaluations corroborated the simulation's outcomes.

Synthesis of NO by rotating sliding arc discharge reactor with conical-spiral electrodes

The present work investigates the potential applications of nitrogen oxides (NO x ), particularly nitric oxide (NO) and nitrogen dioxide (NO2), generated through discharge plasma in diverse sectors such as medicine, nitrogen fixation, energy, and environmental protection. In this study, a rotating sliding arc discharge reactor was initially employed to produce high concentrations of gaseous NO x , followed by the utilization of a molybdenum wire redox reactor for NO2-to-NO conversion. The outcomes reveal that the discharge states and generations of NO x are affected by varying parameters, including the applied energies, frequencies and airflow states (1.3–2.6 m/s are the laminar flow, 2.6–5.2 m/s are the transition state, 5.2–6.5 m/s are the turbulent flow), and the concentrations of NO x within the arc discharge are higher than that in the spark discharge. Moreover, the concentrations of NO, NO2 and NO x gradually increased, and the concentration ratios of NO/NO2 and NO x /NO2 decreased with increasing the applied energy for one cycle from 14.8 mJ to 24.3 mJ. Meanwhile, the concentrations of NO, NO2 and NO x gradually decreased, and the concentration ratios of NO/NO2 and NO x /NO2 first decreased and then increased with increasing the applied frequencies from 5.0 kHz to 9.0 kHz. Further, the concentrations of NO, NO2 and NO x gradually decreased, and the concentration ratios of NO/NO2 and NO x /NO2 first increased and then decreased with increasing the air flow speeds from 1.3 m/s to 6.5 m/s. Lastly, the concentrations of NO increased and NO2 decreased with increasing temperature from 25 °C to 400 °C using molybdenum converted. These findings provide experimental support for the application of plasma in the fields of medicine, nitrogen fixation, energy and environmental protection.

Personalized air curtain optimized to reduce fine particle exposure in industrial environments with different indoor airflow conditions

Recently, personalized air curtains combined with safety helmets have shown great potential in reducing particle inhalation exposure of workers in industrial settings. In this study, the helmet of the basic air curtain (BA) was optimized. One optimization method was to add a mask to the helmet of the basic air curtain (BAF), and the other optimization method was to add a face shield and sealing cloth to the helmet of the basic air curtain (BAFS). Computational fluid dynamics (CFD) method was used to compare the protective effect (PE) of the air curtain helmets with BA, BAF, and BAFS configurations. The impacts of the air supply velocity (0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 m/s) of the air curtain in a static wind environment, and the direction and speed of the indoor airflow (0.1, 0.3, 0.5, 0.7 and 1 m/s) on the PE of the helmets were also investigated. Results showed that the BAFS helmet had the best respiratory protection, followed by the BAF and the BA helmet, regardless of indoor airflow conditions. The directional diversion effect of the face shield and the bidirectional blocking effect of the sealing cloth strengthened the PE. In the static indoor airflow environment, air supply velocity and helmet configurations had a remarkable impact on the PE. With the increase of the air supply velocity, the PE of the BA and optimized helmets showed S-shape and C-shape trends. When the air supply velocity reached 0.5 m/s, the PE of the BA, BAF, and BAFS helmets were close to 0.844, 0.985, and 1, respectively. In the uniform indoor airflow environments, the PE of the BAFS helmet was close to 1 and was almost undisturbed by the indoor airflow. This work may help inspire the development of respiratory protective equipment to reduce particulate exposure in industrial settings.

Effect of Hopf-Hopf bifurcation on the post-flutter behavior of a three-degree-of-freedom airfoil

The post-flutter dynamics of a three-degree-of-freedom nonlinear airfoil with unsteady aerodynamics are investigated based on the Hopf-Hopf bifurcation theory. Many prior works have relied on Hopf bifurcation theory to predict flutter behavior in airfoil systems. Although this approach facilitates flutter prediction and characterization of post-flutter behavior in numerous scenarios, it may be invalid in specific instances, such as when the Hopf bifurcation of the system degenerates. Therefore, this study focuses on a classical degenerate case of Hopf bifurcation in airfoil systems, specifically the Hopf-Hopf bifurcation. We show that the system undergoes various Hopf-Hopf bifurcations under specific parameter conditions as the center of gravity shifts. The local dynamics near the Hopf-Hopf bifurcation points are represented, including quasiperiodic oscillations on a three-dimensional torus. The airfoil begins to oscillate quasiperiodically after the airflow speed crosses specific Hopf-Hopf bifurcation points. The study also uncovers complex quasiperiodic crises and quasiperiodic hysteresis loops, which have not been reported in previous studies of aeroelastic systems. Then, many singularities and bifurcation curves are obtained near the Hopf-Hopf bifurcation point by semiglobal unfolding. Furthermore, the influence of stall effects on the bifurcation structure of the system is represented. It is shown that the types of Hopf-Hopf bifurcations may vary with the changes of stall effects, influencing the system's semiglobal bifurcation structures consequently. For all Hopf-Hopf bifurcation scenarios, stall effects affect one of the Neimark-Sacker bifurcation curve structures unfolded from the Hopf-Hopf bifurcation point significantly, while the other Neimark-Sacker bifurcation curve experiences minimal impact from stall effects. Moreover, a large nonlinear stall coefficient will postpone the onset of quasiperiodic/chaotic oscillations.

Experimental study on the impact of indoor unit airflow velocity on the performance of an automotive heat pump system with a suction line heat exchanger

This study aimed to investigate the effect of changing the indoor unit air flow rate on the performance of an automobile heat pump with a suction line heat exchanger. Using a four-way valve, the automotive heat pump system was developed by reversing the refrigerant direction in the automobile air conditioning system, excluding the compressor. A suction line heat exchanger was added to the test system to enhance heat transfer between the liquid and suction lines of the automotive heat pump system. Performance comparisons were first performed for R134a and R1234yf by disabling the suction line heat exchanger. Then, the suction line heat exchanger was activated for R1234yf, and the tests were repeated. Performance comparisons were made for two different compressor speeds and three different indoor unit airflow speeds. It was found that using the heat exchanger in R1234yf operations improved the heating capacity, compressor discharge temperature and coefficient of performance by approximately 1.8 %, 5.1 % and 5.9 %, respectively. The heating capacity of the heat pump system using R134a, R1234yf, and R1234yf with the suction line heat exchanger was determined to be in the range of 2.46–3.29 kW, 2.35–3.04 kW, and 2.39–3.11 kW, respectively. An increase in the airflow speed of the indoor unit from 1.4 m s−1 to 3.2 m s−1 resulted in an average decrease of approximately 12.3 % in the compressor discharge temperature. In contrast, the heating capacity and coefficient of performance increased by approximately 11.8 % and 14.4 % on average, respectively, for R1234yf operations with the heat exchanger. This study revealed that by optimizing the air flow rate in the R1234yf heat pump system with a suction line heat exchanger, improvements in the heating capacity and coefficient of performance can be achieved, thus providing better thermal comfort in the passenger compartment.

Research on UAV Downwash Airflow and Wind-Induced Response Characteristics of Rapeseed Seedling Stage Based on Computational Fluid Dynamics Simulation

Multi-rotor unmanned aerial vehicles (UAVs) are increasingly prevalent due to technological advancements. During rapeseed’s seedling stage, UAV-generated airflow, known as wind-induced response, affects leaf movement, tied to airflow speed and distribution. Understanding wind-induced response aids early rapeseed lodging prediction. Determining airflow distribution at various UAV heights is crucial for wind-induced response study, yet lacks theoretical guidance. In this study, Computational Fluid Dynamics (CFD) was employed to analyze airflow distribution at different UAV heights. Fluid–solid coupling simulation assessed 3D rapeseed model motion and surface pressure distribution in UAV downwash airflow. Validation occurred via wind speed experiments. Optimal uniform airflow distribution was observed at 2 m UAV height, with a wind speed variation coefficient of 0.258. The simulation showed greater vertical than horizontal leaf displacement, with elastic modulus inversely affecting displacement and leaf area directly. Discrepancies within 10.5% in the 0.5–0.8 m height range above the rapeseed canopy validated simulation accuracy. This study guides UAV height selection, leaf point determination, and wind-induced response parameter identification for rapeseed seedling stage wind-induced response research.

Design of an innovative flow isolation device (FID) as an air flow barrier to control the temperature of large storage areas in cold room applications

The virus transmission chain of Covid-19 has a resulted in a significant, global impact on social and working life. Covid-19 vaccines require protective refrigerated conditions during delivery and storage. Warehousing and transportation of these vaccines need to be properly controlled to maintain the product quality and efficacy. Logistics companies developed large-scale refrigerated warehouses as storage relay stations. The heat convection between two rooms of the large-scale, low-temperature warehouses with different temperatures for example (5 °C, -15 °C) should be prevented to improve efficiency. In this study, an innovative flow isolation device (FID) was designed in Taipei Tech to block the storage areas, preventing heat convection. This device can maintain a constant low-temperature in warehouses used for vaccine storage. The axial flow fan draws air from the protected zones (5 °C, -15 °C) into the device. A perforated plate stabilizes the flow rate and maintains a uniform flow direction, creating a flow barrier created between two rooms. This flow can significantly block the heat convection induced by two warehouses with different temperatures. The computational fluid dynamics (CFD) software Ansys Fluent is used to simulate the effect of the FID on the prevention of the heat convection between two rooms. Different case studies were simulated at different machine sizes and supply air flow speeds. The simulated flow patterns and velocity fields are used to evaluate the highest isolation efficiency. The findings show that the FID device can effectively maintain the low temperature of the warehouse. Moreover, the FID helps to avoid heat loss and maintain thermal comfort in working areas, reducing the risk of hypothermia.

Spray characteristics of elliptical orifice spray in diesel engine under air movement conditions

The development of high-quality mixture is a critical requirement for achieving high-efficiency and low-emission diesel engines, and fuel injection system performance improvement and in-cylinder airflow organization are crucial ways for achieving high-quality mixture. The elliptical nozzle is used as the research object in this research, and numerical simulation is utilized to investigate the effect of different airflow speeds and directions on the atomization characteristics of the elliptical nozzle jet, in order to provide a theoretical basis for the engineering application of the elliptical nozzle in diesel engines. The results show that under the same airflow conditions, the vertical penetration distance of the spray decreases while the horizontal penetration distance increases with the use of elliptical orifices, the surface wave perturbation on the windward side is more violent, and reduce spray field the Sauter Mean Diameter (SMD). The spray projected area grew by 13.5%, the spray SMD dropped by 14.8%, and the vertical penetration distance of the spray with elliptical orifices fell by 18% with an increase in airflow velocity from 0 to 20 m/s. When the airflow direction and the spray direction were at a 90° angle and the SMD was lower than that of the circular orifice by 12.9%. The angle between the airflow direction and the short axis of the elliptical orifice was 30°when the spray projection area was larger, the perturbation of the spray body was more intense, and the surface wave amplitude was larger.

Thermal influence in the design of DC to AC converters due to climatic change for photovoltaic solar plants

This research article discusses the impact of climatic changes in South America, with a case study in a tropical zone, particularly the rise in temperature by 1.15 °C from 1998 to 2022, reaching a maximum of 45.85 °C in 2023. Focusing on the Electronic Conversion Unit, especially IGBT efficiency during El Niño-Southern Oscillation phenomenon in 2023. The case study employs finite element analysis using Navier Stockes-Boussinesq equations, it evaluates the heat dissipation, airflow modeling, and temperature effects, the research proposes enhancements like redesigned air flow grids, centralized air filters, and wind fans. Implementing these improvements reduces the temperature by 5.6 °C, enhances airflow speed, and mitigates the climatic impact on electronic devices over the next two decades.

Prediction and comparison of burning rate of n-heptane pool fire in open space based on BPNN and XGBoost

Pool fires pose a threat to the safety and environmental protection of industrial production. The burning rate is one of the most important burning parameters that determines the behavior of pool fires. Back Propagation Neural Network (BPNN) and Extreme Gradient Boosting Tree (XGBoost) were used to predict the burning rate of n-heptane pool fire with the effect of fuel depth, ullage depth, area and perimeter of pool pans, atmospheric pressure and speed of cross air flow in open spaces. The results show that after optimizing the model parameters using RandomizedSearchCV, both models yielded higher precision evaluation results. Compared with BPNN, the proposed XGBoost model demonstrates better prediction performance, achieving a R2 of 0.9744, RMSE of 4.1068, and MAE of 2.5036 in test set. The impact of different hyperparameters and data normalization on model prediction accuracy was explored. The impact of fuel depth, ullage depth, atmospheric pressure, speed of cross air flow, area, and perimeter on burning rate was determined using SHapley Additive exPlanations (SHAP) sensitivity analysis. This analysis aids in conducting risk analysis for pool fires, and offers early warning and feasible reference for fire safety hazards.

Wind tunnel bench test of a pitch-and-plunge aeroelastic model undergoing nonlinear post-flutter oscillations

The nonlinear post-flutter aeroelastic behavior of a classical pitch-and-plunge airfoil model in low-speed wind tunnel bench tests is reported in this study for a range of airflow speeds where stable oscillations are observed. An experimental airfoil prototype is designed, characterized and evaluated. Time domain data of the airfoil motion as well as other pertinent frequency and bifurcation characteristics are presented for different values of airflow speed, starting at the critical linear flutter speed of the airfoil model and increasing up to the sudden manifestation of violent unstable oscillations (when the test is interrupted for the safety of the structural apparatus). Stable post-flutter nonlinear oscillations, mainly attributed to the dynamic stall phenomenon and in a lesser degree to hardening structural effects, are observed for a range of airflow speeds starting at the neutral stability boundary of the aeroelastic system. The amplitudes of oscillation increase with increasing airflow speed and settle onto a limit-cycle. The coupled frequency of oscillation is dominated by the plunge degree-of-freedom and also increases with increasing airflow speed. The observed critical airfoil cut-in speed of limit-cycle onset is about 8.1 m/s (reduced speed of 5.1), and the observed cut-out speed of unstable response is about 9.5 m/s (reduced speed of 6.0). This work contributes with the literature of Aeroelasticity by presenting the realization, evaluation, and wind tunnel test data of a pitch-and-plunge airfoil model undergoing nonlinear post-flutter oscillations that may be useful to support other studies for verification purposes of eventual numerical simulations of similar aeroelastic systems.