Airflow Field Research Articles

Numerical Simulation of Icing Characteristics on the Surface of an Aero-engine Guide Blade

This paper takes the guiding blade of a type of aero-engine needle as the research object for the icing problem of the guiding blade and uses the numerical simulation method to simulate the airflow field, supercooled water droplet impact and icing situation on the surface of the guiding blade under different flight conditions, to analyze the influence of flight speed on the icing situation of the guiding blade. It is found that the incoming flow velocity has a significant effect on the icing of the guide vanes, with the flight velocity increasing from 34m/s to 102m/s, the icing of the leading edge of the vanes increases by 98.1%; meanwhile, the icing range of the guide vanes is significantly related to the incoming flow velocity, with the flight velocity increasing, the icing range expands significantly; in addition, the icing range gradually expands from the root to the outermost end of the vanes, with the flow velocity The maximum icing range at 102m/s was extended from 17% to 20% of the chord length.

Droplet Penetration Model Based on Canopy Porosity for Spraying Applications

Analysing the penetration and droplet deposition characteristics in the canopy of fruit trees is critical for optimising the operational parameters of air-assisted spraying equipment, achieving precise application of chemicals, and improving the effectiveness of fruit tree pest and disease control. We used a mobile LIDAR system to detect the tree canopy characteristics and optical porosity and conduct wind tunnel experiments to investigate the interaction between the tree canopy, the airflow field, and the droplet penetration ratio in the canopy of fruit trees. The results show that the relative wind velocity decreases rapidly during canopy penetration, and that the minimum value occurs at the back of the canopy. The smaller the optical porosity, the greater the reduction in wind velocity is. The quadratic exponential regression model had the highest coefficient of determination (R2) (0.9672) and the lowest root mean square error (RMSE) (5.56%). This paper provides information on optimising the spraying parameters, improving the pesticide utilisation rate, and selecting the optimum spraying conditions and application parameters.

Numerical simulation of the spatial and temporal distributions of the downwash airflow and spray field of a co-axial eight-rotor plant protection UAV in hover

The downwash airflow of a multi-rotor unmanned aerial vehicle (UAV) in hover can improve the penetration rate of droplets in the canopy of fruit trees, but the uncertain distribution of the downwash airflow can also lead to the generation of uneven distribution of droplets. With a co-axial eight-rotor plant protection UAV as the research object, the computational fluid dynamics (CFD) method is adopted in this study to establish the coupled flow field model of the downwash airflow and the two-phase flow model of airflow-droplets in hover. The spatial and temporal distribution law of the downwash airflow is analyzed, and the impact of the motion law of the droplets in the spray field is investigated. The results show that the downwash airflow shifts from an unsteady state to a steady state over time. Various wind vortices such as wake vortex, ground diffusion airflow, and vortex ring are generated during the evolution process, with a “negative velocity channel” of downwash airflow velocity identified in the central region under the rotors. The farther the airflow is from the rotor, the larger the area field of wake vortex airflow. Consequently, there is a gradual coupling of the left and right adjacent wake vortices from mutual independence, with the “spiral effect” of the downwash wind field offset by the mutual coupling of the upper and lower rotors of the UAV. When the installation position of the nozzle falls within the below-rotor region, the distribution of droplet deposition becomes more penetrative than the central axis installation position of the nozzle. It indicates that the below-rotor installation position of the nozzle can prevent droplets from entering into the coupling region of the trailing vortex, which reduces droplet drift. According to the field test, the measurement and simulation results of the downwash air velocity are consistent, with the minimum and maximum relative error reaching 4% and 29%.

Study on the Influence of the Cage Lifting Piston Effect in Main Intake Shafts on Air Flow in Transportation Lanes

The main intake shaft in the mine serves as the main intake and return air shaft and also serves as a lifting shaft. The piston wind effect caused by the frequent operation of large and efficient hoisting cages in the shaft will disturb the normal flow of airflow in the transport lane connected to the shaft and affect the underground ventilation effect. Therefore, based on the SST k-ω turbulence model, this paper uses the dynamic mesh to simulate the air-fluid in the cage running in the shaft and verifies the simulation data through field measurement to study the influence of piston effect on the airflow field in the transport lane. The results show that the piston effect caused by cage operation in the shaft will disturb the flow of normal airflow in the transportation lane and affect the ventilation effect in the mine. The 1765.0 m transport lane is closest to the position of the shaft inlet, which is most significantly affected by the piston wind effect. The low-speed eddy current zone generated at the tail of the cage in the upwind operation has a large area and strong adsorption force, which causes the gas at the local position in the transportation lane to generate eddy current and reverse flow, hindering the flow of fresh air in the lane. The influence distance and strength of the piston effect on each measuring point in the transportation lane are limited. When the measuring point distance increases from 21.7 m to 71.7 m, the differential pressure of measuring points in 1414.0 m, 1584.0 m and 1765.0 m transport lanes decreases by 11.08 Pa, 9.62 Pa and 8.58 Pa, respectively.

Nozzle arrangement study for pre-cooling the inlet air of natural draft dry cooling tower under crosswinds

Crosswind affects the airflow fields of the natural draft dry cooling towers (NDDCTs), thus the spray zones for pre-cooling the inlet air of the NDDCT might be different from no crosswind. Therefore, a 3-D model of pre-cooled NDDCT under crosswind was established by Fluent 16.2 to investigate the feasible zone of nozzle spray of a 120 m high NDDCT based on the behavior of the droplets. Six nozzle heights, nine nozzle radiuses and four spray angles were simulated for the NDDCT application within the crosswind speeds of 0∼10 m/s. The evaporation percentage of droplets higher than 99% and the maximum effective evaporation ratio are selected as the criterion for the feasible zone of nozzle arrangement. Simulation finds that: (1) the nozzle arrangement height should be set at 7 m when the crosswind speed is 0 m/s, and it should be set at 9 m when the crosswind speeds are 2 m/s, 4 m/s,6 m/s, 8 m/s and 10 m/s, respectively. (2) The feasible spray angles of nozzles are 0°and 90° at the crosswind speeds of 0∼4 m/s and 6∼10 m/s, respectively. (3) The nozzle radiuses are 0∼41.5 m at crosswind speed of 0 m/s, they are 0∼21.5 m at the crosswind speed of 2 m/s, and they are 0∼16.5 m when the crosswind speeds are 4 m/s, 6 m/s, 8 m/s and 10 m/s, respectively based on the above feasible heights and spray angles. The results will provide a guidance for nozzle design of spray pre-cooled NDDCT under crosswinds.

Spatial Identification, Prevention and Control of Epidemics in High-Rise Residential Areas Based on Wind Environments

The wind environment in residential areas can exert a direct or indirect influence on the spread of epidemics, with some scholars paying particular attention to the epidemic prevention and control of residential areas from the perspective of wind environments. As a result, it is urgent to re-examine the epidemic prevention response of residential spaces. Taking high-rise residential areas in Xi’an as an example, the article defines the air flow field area based on on-site wind environment measurements, crowd behavior annotation, and CFD simulation. Using the double-effect superposition of crowd behavior and risk space, the paper undertook a multiple identification strategy of epidemic prevention space. The identification methods and management and control strategies of epidemic prevention in high-rise residential areas are proposed. Additionally, the living environment of residential areas is optimized, and a healthy residential space is created. The transformation from concept and calls for action to space implementation is made to provide a reference for improving the space management and control capabilities in high-rise residential areas in China. The results of this study can be used as a guideline for future residential planning and design from the perspective of preventing airborne diseases.

Comparing airborne infectious aerosol exposures in sparsely occupied large spaces utilizing large-diameter ceiling fans

In sparsely occupied large industrial and commercial buildings, large-diameter ceiling fans1 (LDCFs) are commonly utilized for comfort cooling and destratification; however, a limited number of studies were conducted to guide the operation of these devices during the COVID-19 pandemic. This study conducted 223 parametrical computational-fluid-dynamics (CFD) simulations of LDCFs in the U.S. Department of Energy warehouse reference building to compare the impacts of fan operations, index-person, and worker-packing-line locations on airborne exposures to infectious aerosols under both summer and winter conditions. The steady-state airflow fields were modeled while transient exposures to particles of varying sizes (0.5–10 μm) were evaluated over an 8-h period. Both the airflow and aerosol models were validated by measurement data from the literature. It was found that it is preferable to create a breeze from LDCFs for increased airborne dilution into a sparsely occupied large warehouse, which is more similar to an outdoor scenario than a typical indoor scenario. Operation of fans at the highest feasible speed while maintaining thermal-comfort requirements consistently outperformed the other options in terms of airborne exposures. There is no substantial evidence that fan reversal is beneficial in the current large space of interest. Reversal flow direction to create upward flows at higher fan speeds generally reduced performance compared with downward flows, as there was less airflow through the fan blades at the same rotational speed. Reversing flow at lower fan speeds decreased airflow speeds and dilution in the space and, thus, increased whole-warehouse concentrations.

Study on the coal dust deposition fraction and site in the upper respiratory tract under different particle sizes and labor intensities

In order to study the dust exposure amount and coal dust deposition rule of coal miners under different labor intensity in coal mine environment, an airflow-particle two-phase coupling calculation model of human upper respiratory tract was established based on Euler-Lagrange framework, and the airflow field in the upper respiratory tract and the characteristics of coal dust deposition were simulated and studied. By comparing the experimental data, the relative error of simulation is in the range of 1.5 %–11.2 %. The results showed that the total deposition fraction of 1 μm dust was the smallest (0.61–1.20 %), and was relatively less affected by respiratory intensity, and the overall distribution was uniform. When the dust particle size increased to 7.07 μm, the total dust deposition fraction in the nasal cavity, pharynx and larynx was in the range of 11.10 %–20.91 %, and increased with the respiratory intensity. When the dust particle size was large, the dust particles of 20 μm and 80 μm were mostly concentrated in the front of the nasal cavity, and the deposition amount of 80 μm dust was about 99.52 %. It was found that with the increase of dust particle size or the increase of labor intensity, the possibility of dust being transported into lungs became smaller. The fitting function of 7.07 μm dust escape rate and labor intensity was obtained, for example, Y7.07μm = 91.73–0.22n (n is labor intensity), and the escape rate of dust with 7.07 μm particle size was up to 88.90 %. Most of them escape from the upper respiratory tract and enter the lungs, which provides theoretical guidance for quantifying the accumulated dust exposure amount in the lungs and monitoring respiratory dust concentration.

CFD Simulation and Uniformity Optimization of the Airflow Field in Chinese Solar Greenhouses Using the Multifunctional Fan–Coil Unit System

Supplying homogenous and suitable airflow schemes were explored in Chinese solar greenhouses, which had a positive impact on the crop yield and quality. This paper provided a multifunctional fan–coil unit system (FCU) to assist in circulating air. This system could collect the surplus heat of daytime air and release it to heat the greenhouse at nighttime. However, the main problem to be faced was the nonuniform airflow distributions. Thus, this paper aimed to optimize and analyze the placement strategy of the FCU system for a Chinese solar greenhouse using the numerical methodology. The computational fluid dynamics model was constructed to evaluate the effect of the FCU system on the airflow field and to uphold its validation. The complex structure of the FCU system was simplified to a fan model by fitting the pressure jump and the air velocity to enhance the practicality of the simulation model. Finally, the coefficient of variation was used to optimize four parameters: the tilt angle, swing angle, height above the ground, and shape of the outlet baffle. The effective disturbance velocity percentage was proposed as the evaluation index to improve the turbulence characteristics. The mean absolute error (MAE) between the measured and simulated values of the air velocity for the two planes was 0.06 m/s and 0.09 m/s, and the root mean square error (RMSE) was 0.08 m/s and 0.11 m/s. The simulated results showed that the coefficient of variation before optimization was 0.76, and the effective disturbance velocity percentages of the planes at 0.7 m and 1.0 m from the ground were 42.73% and 41.02%, respectively. After optimization, the coefficient of variation was reduced to 0.33, and the effective disturbance velocity percentages of the two planes increased to 58.68% and 43.73%, respectively. These results significantly improved the uniformity of the interior airflow field. This paper provides a reference for the design and installation of the FCU system.

Enhanced Effect of Mining Dust Diffusion on Melting of the Adjacent Glacier: A Case Study in Xinjiang, China

Given the typical disturbances in the aqueous environment in the alpine area because of mining activities in Northwest China, a case study highlighting the enhanced effect of mining dust diffusion on the melting of the adjacent glacier is presented here. Initially, a three-dimensional numerical model of the local airflow field was established by considering the effects of both mines and glaciers using the FLUENT software. Then, the diffusion path and size range of dust particles from the mines were simulated by feeding the mining dust parameters into the above numerical model. Finally, a physical simulation experiment was performed to evaluate the influence of mining dust coverage on the glaciers. The major conclusions of this study were as follows: (1) The local airflow field in the target alpine area is controlled by the ‘heat and cold double-island effects’ formed by the mine and the glacier, and the wind circulation always takes place in a clockwise direction between the mining pit on the left and the glacier on the right. (2) In a given airflow field, there is a spread of mining dust from the mine to the glacier along the upper airflow. The arrival rates of the dust are 16.9% and 13.3% in winter and summer, respectively, and the horizontal distance of dust diffusion is inversely proportional to its particle size. (3) For an ice sample with a sectional area of 225 cm2 and a volume of 1000 mL, the melting rate increased by 4.5 mL/h with an increase of dust coverage by 10%. Furthermore, when compared with a control group without dust cover, the effect of a 28% increase in dust coverage is approximately equivalent to the effect of a 1 °C increase in temperature on the ablation speed of the glacier. The study results can provide a useful reference for the selection of mining sites and the control of mining dust diffusion in alpine regions with glaciers, thereby facilitating environmentally friendly mining in alpine regions.

Effect mechanism of wind shields on the thermal performance for mechanical draft wet cooling towers

Environmental crosswind is demonstrated to be disadvantageous for the thermal characteristics of mechanical draft cooling towers. To mitigate the adverse effect of crosswind, this study proposes an innovative structural retrofit by adding wind shields with simple structure for both single and double air inlet cooling towers. Numerical investigations are conducted to clarify the effect mechanism of wind shields on tower thermal performance under different crosswinds, through assessing the ventilation rate, the water temperature drop, the air flow field and water temperature field, etc. Results demonstrate that wind shields can eliminate transverse vortices to improve the distribution homogeneity of airflow velocity and water temperature, of which the effects are greatly affected by crosswind velocity and angle. Based on this mechanism, the thermal performance of these cooling towers is prominently strengthened by wind shields when crosswind angle exceeds 45°. The positive effect of wind shields is the most noticeable under a crosswind angle of 90° and a crosswind velocity of 10 m/s, which recovers 17.2 % and 9.4 % of the water temperature drop, and 33.1 % and 19.5 % of the ventilation rate, respectively for the single and double air inlet cooling tower. Present findings can promote applications of wind shields in practical engineering.

The study on influencing factors of airflow in laboratory fume hood

This study investigates the influence of the side wind flowing directly from different indoor environments on the airflow of the laboratory fume hood (LFH). When an LFH is used to discharge the harmful from the laboratory, the side wind can affect the airflow of the LFH, which is likely to cause the leakage of harmful fumes. In this study, incense was used to simulate harmful fumes, sampling and analysis of the total suspended particulate concentrations were performed in an LFH under different side wind conditions with or without air conditioning, operator, laboratory door open, and electric fan when the fume hood sash (FHS) is at the top, middle, and bottom positions, respectively. A laser pen and hot-wire anemometer are employed to demonstrate the airflow of the smoke and wind speed in different indoor environmental conditions. The experimental results reveal that the airflow field and distribution of harmful fumes in the LFH can be changed according to the different heights of the FHS and changes in the external airflow. Therefore, when using the LFH, the influence of the external airflow should be reduced, and the LFH should be operated for a few minutes before switching it off.

Air Change and Transfer Efficiencies within a Cross-Ventilated Room Model Sheltered by Urban-Like Block Arrays using RANS simulations

Natural and cross ventilation is recognized as an important measure for introducing outdoor fresh air to indoor without the use of mechanical equipment. Plenty of fruitful studies for elucidating natural and cross ventilation mechanisms have been reported adopting experimental and computational methods. Field and wind tunnel experiments could provide substantial flow information on indoor-outdoor interaction in actual or reduced model conditions. However, these approaches were relatively costly and time-consuming and limited in terms of spatial and temporal resolutions. Computational fluid dynamics approaches are promising complementary technique to these methods. In this study, we performed isothermal CFD simulations for both airflow and concentration fields for cross-ventilation conditions sheltered by surrounding buildings with two different opening conditions. ANSYS/Fluent was utilized to perform CFD using RANS simulation. Heterogeneity of ventilation efficiencies determined by concentration distributions in cross-ventilated room model were quantitatively analyzed using ventilation efficiencies, e.g., age of air. The results showed that the location of the openings had a significant impact on the cross-ventilation rate, creating completely different concentration fields, and ventilation efficiencies indices could quantitatively demonstrate the formation mechanisms of scalar concentration distributions in an indoor space.

Mixing Characteristics and Flow Fields Optimization of Primary Air for Coal Mill

This paper mainly focuses on the problems of inaccurate measurement of the primary air flow rate in a coal-fired power plant. The feasibility of improving the uniformity of flow fields and temperature fields by installing double-layer arch cool air distributor and mixed flow matrix was analyzed by the method of numerical simulation. The results show that, the relative standard deviation of the wind speed measurement section of optimization model decreased from 18.7%~18.4% to 9%~9.1%, compared with the original model. Similarly, the relative standard deviation of temperature measurement section also decreased from 15%~14.6% to 1.3%~1.4%. The study suggests that this mixed flow fields equalization solution can effectively enhance the mixing of cool and hot primary air, and can improve the uniformity of the mixed air flow fields, thereby improving the accuracy and reliability of primary air measurement.

CFD Simulation of Circulating-Airflow Distribution Inside Canopy From Novel Air-Assisted Sprayer in Orchard

HIGHLIGHTS A CFD model was developed to simulate airflow movements from circulating air-assisted sprayer. The CFD model can simulate airflow distribution inside the pear canopy with good accuracy. Simulation identifies the preferred parameters for circulating air-assisted spraying. An excessive adjustment of the airflow angle resulted in the formation of an eddy. ABSTRACT. Circulating air-assisted (CAA) spraying involves a negative pressure suction (NPS) created by a fan placed over the top of a canopy to change the airflow direction twice, i.e., first from the outside of the canopy to its inside and then from the bottom up, which can increase the airflow velocity inside the canopy. However, this new pesticide application technology has not been adequately investigated. In particular, the effects of the inlet and outlet airflow parameters of CAA spraying technology on the airflow distribution inside a canopy are yet to be determined. In this study, a computational fluid dynamics (CFD) model is developed and validated to simulate the interactions between the airflow ejected by a CAA sprayer and the canopy of a fruit tree. In the computational domain, the fruit tree is considered a porous medium. The model is validated based on three fruit trees of different sizes, leaf-area densities (LAD). The root mean square error and the mean relative square error are 1.44, 1.43, 2.22 m/s, and 24.9%, 24.7%, and 36.4%, respectively. This suggests that the CFD model can predict the interactions between the airflow field generated by a CAA sprayer and the canopy of a fruit tree. The validated CFD model is employed to analyze the airflow distribution patterns inside a canopy under different combinations of inlet and outlet airflow parameters. A reasonable combination of inlet and airflow parameters is obtained for CAA spraying technology. For example, the suitable outlet airflow velocity, top NPS, and bottom outlet angle for seven-year-old crown pear trees (average height: 2.0 m; average canopy diameter: 1.2 m; average trunk height: 0.62 m; average LAD: 2.96) selected in this study from a farm in southern China are 15 m/s, 200 Pa, and 10°, respectively. The results of this study can facilitate the parametric adjustment of CAA sprayers and enhance plant protection in orchards. Keywords: Circulating air-assisted spraying, Fruit-tree canopy, Inlet and outlet airflow parameters, Simulation.

Downwash airflow field distribution characteristics and their effect on the spray field distribution of the DJI T30 six-rotor plant protection UAV

Downwash airflow field distribution characteristics and their effect on the spray field distribution of the DJI T30 six-rotor plant protection UAV

Reconstruction of Pressure Distribution in High-Velocity Airflow Fields by Schlieren Decoupling of Velocity and Density Fields

Reconstruction of Pressure Distribution in High-Velocity Airflow Fields by Schlieren Decoupling of Velocity and Density Fields

气力输送式排种器流场模拟与气流分配室结构设计

The pneumatic conveying metering technology is used to enhance the filling and clearing capacity of the seed metering device by forming a rotary air flow field inside the airflow distribution. The simulation test results show that the increase of the number of fan blades, the velocity of flow field at different outlets of the seed cleaning area decreases linearly, but the average velocity basically remains unchanged. The flow field velocity in the seed filling area decreased significantly with the increase of fan angle, and the difference between seed filling area and clearing area remains unchanged. When the blade angles in the filling area are the same, the fan blades size has no effect in flow field velocity.

Atmospheric dustfall exhibits consistent sedimentary sorting with height evidenced by grain size characteristics

The grain size of aeolian deposits is a key property to understanding their sedimentary sorting characteristics, which determine the sedimentary dynamics of an airflow field. Although atmospheric dust sedimentary sorting processes are understood well in the horizontal direction, those in the vertical direction and their influencing factors remain unclear. Herein, modern atmospheric dustfall was collected using dust traps at heights of 1, 2, 4, 6, and 8 m to reveal its sedimentary sorting characteristics. The analysis demonstrated that atmospheric dustfall exhibits a bimodal grain size distribution, and the bimodal grain size distribution curves change within a height of 8 m. However, either peak 1 or peak 2 exhibits consistent grain size characteristics with height; hence, each sub-peak indicates consistent sedimentary sorting within a height of 8 m. The modification of grain size distribution curves with height is mainly driven by different sedimentary fluxes for peak 1 at different heights. Dustfall grain size characteristics are also potentially affected by the settling height, concentration of the atmospheric dust, and dust sedimentary flux. However, the sedimentary sorting of sub-peak components is mainly governed by the near-surface airflow field. Thus, this reveals the process of formation and grain size distribution of aeolian deposits. Overall, atmospheric dustfall with mixed multi-peak components conceals information on the sedimentary environment.

Design and Test of Stripping and Impurity Removal Device for Spring-Tooth Residual Plastic Film Collector

The residual agricultural plastic film in China is not easily recovered due to the thinness and poor mechanical properties of domestic films, and a large amount of plastic film remaining in farmland soil poses a great threat to soil quality and crop production. A spring-tooth residual plastic film collector (SRPFC) is widely used in domestic residual plastic film (RPF) recycling operations. However, there are two major problems in the current SRPFC: the low recovery rate of the residual film (RRRF) caused by the difficulty of film-stripping and the high impurity rate in the film (IRF). In this paper, a stripping and impurity removal device (SIRD) is designed to address the existing problems of SRPFC, which is mainly composed of film-stripping tooth plates (FTP), two wind-collecting hoods, and two centrifugal fans. The motion and force analysis of the RPF in the film-stripping process was carried out, and the arc FTP was determined to be used for film-stripping. The size parameters of the FTP were obtained by establishing the coordinate system to solve the differential equation. By comparing and analyzing the force of RPF in the airflow field of the test bench for suspension speed and the airflow field of the wind-collecting hood, the RPF equivalent particle was established. The discrete phase model (DPM) in Fluent software was used to simulate the movement of the RPF equivalent particle, and the calculated air volume range of the centrifugal fan was 5501.88~6829.92 m3/h. The effects of forward speed, rotating speed of film conveying chain harrow (FCCH), and rotating speed of the centrifugal fan on RRRF and IRF were studied by orthogonal rotary combination experiment. The test results showed that the best combination of machine operation parameters was when the forward speed was 5 km/h, the rotating speed of the FCCH was 235 r/min, and the rotating speed of the centrifugal fan was 1978 r/min. Under these conditions, the RRRF was 92.53%, and the IRF was 9.31%. Field experiments were carried out with the rounded parameters, and the average RRRF was 92.07%, and the average IRF was 9.56% under the parameter combination, indicating that the optimization scheme of the device was feasible.