Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experiment...Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experimentally. A critical frequency of 1 kHz was found. With the frequency above 1 kHz, when a fast airflow was introduced into the discharge gap, the discharge patterns varied from filaments to curved stripes and the curvature degree rose with an increase in the airflow speed. At the same time, the discharge intensity decreased. However with the discharge frequency below 1 kHz, the discharge intensity would get greater with an increase in the airflow speed.展开更多
Dielectric barrier discharge has widely used in airflow control, ignition and combustion, and other applications; the influence of airflow on dielectric barrier discharge is of extensive concern. Previous studies demo...Dielectric barrier discharge has widely used in airflow control, ignition and combustion, and other applications; the influence of airflow on dielectric barrier discharge is of extensive concern. Previous studies demonstrate that the discharge becomes more uniform and the discharge intensity decreases with increasing of airflow velocity. In this study, we adopt a discharge cell construction with upstream and downstream structure and study the discharge states and intensities. The experimental results demonstrate that within a specific range of airflow speed, the upstream discharge intensity is decreased, and the downstream discharge intensity is enhanced. The physical basis for this phenomenon is proposed as follows： Within a pulse interval time, some particles, such as charged and metastable particles produced by the upstream discharge, could be transported to the downstream region. The concentration of particles in the downstream region is increased, and these particles play a pre-ionization role in the downstream discharge, the intensity of the downstream discharge is enhanced. Further, factors such as the pulse frequency and the distance between electrodes are discussed in detail, along with the conditions for enhancing downstream discharge intensity.展开更多
Atmospheric pressure discharges excited by repetitive nanosecond pulses have at- tracted significant attention for various applications. In this paper, a plate-plate discharge with airflows is excited by a repetitive ...Atmospheric pressure discharges excited by repetitive nanosecond pulses have at- tracted significant attention for various applications. In this paper, a plate-plate discharge with airflows is excited by a repetitive nanosecond pulse generator. Under different experiment con- ditions, the applied voltages, discharge currents, and discharge images are recorded. The plasma images presented here indicate that the volume discharge modes vary with airflow speeds, anda diffuse and homogeneous volume discharge occurs at the speed of more than 35 m/s. The role of airflows provides different effects on the 2-stage pulse discharges. The 1st pulse currents nearly maintain consistency for different airflow speeds. However, the 2nd pulse current has a change trend of first decreasing and then rapidly increasing, and the value difference for 2nd pulse cur- rents is about 20 A under different airflows. In addition, the experimental results are discussed according to the electrical parameters and discharge images.展开更多
Objective Post tuberculosis lung disease(PTLD)manifests in various forms,including tuberculosisassociated chronic obstructive pulmonary disease(TB-COPD),yet the clinical features of PTLD remain undercharacterized.This...Objective Post tuberculosis lung disease(PTLD)manifests in various forms,including tuberculosisassociated chronic obstructive pulmonary disease(TB-COPD),yet the clinical features of PTLD remain undercharacterized.This study aimed to assess longitudinal changes in lung function over a 5-year period and to identify predictors of airflow obstruction in a cohort of patients treated for active pulmonary TB.Methods Patients with active pulmonary TB were enrolled in this study and were followed during treatment,at treatment completion and five years post-treatment.Assessments included lung function and chest CT,analyzing longitudinal trends and airflow obstruction risk factors.Results Among 53 patients(mean age 36.9±13.9 years;64.2%male),7 patients(13.2%)exhibited airflow obstruction.At the 5-year follow-up,the mean FEV_(1)/FVC declined significantly(76.27%±12.04%vs.80.23%±11.02%,P<0.001)and 9 patients(17.0%)exhibited airflow obstruction.Seven of these patients predominantly showed air trapping consistent with small airway disease on chest CT,aligning with TB-COPD phenotype.Notably,four young-to-middle-aged patients(<60 years old)had persistent obstruction over the five years.Conclusion The initial test revealed that 13.2%of patients presented with airflow obstruction.By the 5-year follow-up,this proportion had increased to 17.0%,with most cases demonstrating imaging findings aligning with TB-COPD,even among younger,non-smoking individuals.These findings emphasize the importance of long-term follow-up and routine lung function assessments in TB survivors.展开更多
Increasing air movement by utilizing electric fans is among the common approaches for comfort and energy savings in buildings in summer;however,the use of electric fans is usually the forced constant airflow.This stud...Increasing air movement by utilizing electric fans is among the common approaches for comfort and energy savings in buildings in summer;however,the use of electric fans is usually the forced constant airflow.This study reformed the one-chip computer program of a floor fan motor and simulated dynamic airflow through controlling the rotating frequency only.The flow field characteristics of constant,oscillated,sinusoidal airflows with periods of 10 s,30 s,60 s,100 s were measured.The comfort performance was evaluated by chamber experiments,with 20 subjects exposed to six airflow patterns under 30℃,70%RH.The results showed that the simulated sinusoidal airflows had relatively higher turbulence intensity(32%–37%)andβvalues(>0.4).While subjects’thermal sensations were not statistically significant among six airflows,their reported discomfort symptoms during 60 min exposure were reduced under sinusoidal airflows.The calculated convective heat transfer shared similar variations to instantaneous air velocity and skin temperature.A large fluctuation of 10–50 W/m^(2)and higher total convective heat loss(3000–3500 W/m^(2))were found for sinusoidal period 30 s.This study develops a new method to simulate varying air velocities through conveniently controlling the fan motor amplitude and frequency,and verifies the comfortable feelings to dynamic sinusoidal airflows.The work benefits to improve the performance of the current electric fans with lower costs and promote the applications of personal ventilation devices in buildings,thus optimizing human thermal comfort,reducing dependences on air conditionings and achieving building energy efficiency.展开更多
The dynamic characteristics of different airflows on micro-scales have been explored from many perspectives since the late 1970s.On the one hand,most analytical tools and research subjects in previous contributions va...The dynamic characteristics of different airflows on micro-scales have been explored from many perspectives since the late 1970s.On the one hand,most analytical tools and research subjects in previous contributions vary significantly:some only focus on fluctuant velocity features,while others pay attention to directional features.On the other hand,despite the wide variety of existing analytical methods,they are not systematically classified and organized.This paper aims to establish a system including state-of-the-art tools for airflow analysis and to further design a holistic toolkit named Airflow Analytical Toolkit(AAT).The AAT contains two tools,responsible for analyzing the velocity and direction characteristics of airflows,each of which is integrated with multiple analytical modules.To assess the performance of the developed toolkit,we further take typical natural and mechanical winds as cases to show its excellent analytical capability.With the help of this toolkit,the great differences in velocity and directional characteristics among different airflows are identified.The comparative results reveal that not only is the velocity of natural wind more fluctuating than that of mechanical wind,but its incoming flow direction is also more varying.The AAT,serving as a powerful and user-friendly instrument,will hopefully offer great convenience in data analysis and guidance for a deeper understanding of the dynamic characteristics of airflows,and further remedy the gap in airflow analytical tools.展开更多
Carbon Carbon(C/C)composites in thermal-protection system are exposed to severe thermochemical ablation and mechanical erosion,and their thermal-protection performance is of vital importance to the structural safety a...Carbon Carbon(C/C)composites in thermal-protection system are exposed to severe thermochemical ablation and mechanical erosion,and their thermal-protection performance is of vital importance to the structural safety and flight status of hypersonic vehicles.We numerically analyzes the mesoscopic ablation-erosion of C/C Composites with Inclined Fibers(CCIF).First,a thermochemical ablation model describing the reaction-diffusion coupled problem of C/C composites on mesoscale is employed to analyze ablative process,and the corresponding surface ablation morphology is obtained.Then,the ablation morphology of CCIF is taken as the geometrical model for mechanical erosion analysis,and their damage and failure behavior under high-speed airflow shear is analyzed by using progressive damage method.Moreover,the effects of fiber inclined angle and airflow direction on the mechanical erosion of CCIF are investigated,and the ablationerosion behavior is analyzed and discussed.The results show that the failure modes of mechanical erosion in inner and edge regions are obviously different,showing granular and block erosion phenomena respectively.The mechanical erosion of CCIF in the direction of reverse flow is easier than that in the direction of forward flow.These results can provide a theoretical basis for the design and optimization of thermal protection system materials.展开更多
Aiming at reducing the dust pollution during the tunneling process and improving the application efficiency of air curtain dust prevention technology,according to the changes of radial jet velocity(v_(r)),axial extrac...Aiming at reducing the dust pollution during the tunneling process and improving the application efficiency of air curtain dust prevention technology,according to the changes of radial jet velocity(v_(r)),axial extraction velocity(v_(e))and extraction distance(L)in the formation process of air curtain,the numerical simulation method was used to analyze the rules of airflow structure evolution and the diffusion characteristics of dust particles in fully mechanized excavation tunnel.The results indicate that as v_(r) and v_(e) increase,the migration path of the wall jet of the air curtain changes into an axial direction;as L decreases,the migration distance increases accordingly.These phenomena make the airflow distribution in the working face tends to be uniform.The dust diffusion distance reduces as well,wherein,the range of the discrete area of dust particles decreases sharply,until all dust particles are concentrated in the accumulation area.On this basis,the v_(r),v_(e) and L were optimized and applied in the 63_(up) 08 fully mechanized working face.By the application of the optimal parameters,the average dust removal efficiency at the driver’s position increased by 71%.The dust concentration was reduced and the working environment had been improved effectively.展开更多
https://www.sciencedirect.com/journal/energy-and-buildings/vol/342/suppl/C Volume 342,1 September 2025[OA](1)Experimental validation of neural network-based prediction of natural ventilation bulk airflow rate by Jo ao...https://www.sciencedirect.com/journal/energy-and-buildings/vol/342/suppl/C Volume 342,1 September 2025[OA](1)Experimental validation of neural network-based prediction of natural ventilation bulk airflow rate by Jo ao Carlos Sim oes,Guilherme Carrilho da Graca,Article115871Abstract:To fully exploit natural ventilation(NV)as an energysaving strategy in mixed-mode buildings,accurate real-time prediction of NV airflow rates is essential.Current approaches for NV airflow rates prediction often rely heavily on expertise knowledge and computationally demanding methods such as Computational Fluid Dynamics(CFD)as well as expensive and complex direct airflow measurements.展开更多
The embankment and bridge are the basic forms of railway lines.To date,no reports have addressed the optimal form to adopt when passing through sandy areas.Therefore,models of railway embankment and bridge were create...The embankment and bridge are the basic forms of railway lines.To date,no reports have addressed the optimal form to adopt when passing through sandy areas.Therefore,models of railway embankment and bridge were created,and wind tunnel experiments were conducted to compare the differences in wind speed,flow field,sand transport rate,and other wind–sand environmental effects of railway embankment and bridge.Results show that wind speed reduction areas in the upwind and downwind directions were observed for the railway embankment and bridge.In these areas,the extent and degree of wind speed reduction on the embankment were greater than those on the bridge.At the top of the embankment,especially on the windward slope shoulder,an obvious area of wind speed increase was observed.Similarly,a distinct area of wind speed increase was found between the top of the windward side slope shoulder and 3H downwind of the bridge.Within these regions,the range of wind speed increase on the embankment was smaller than that on the bridge,but the degree of increase was greater than that on the bridge.The range of variation in wind speed on the embankment was generally greater than that on the bridge.The wind–sand flow field around the embankment exhibited greater variability than that around the bridge.Moreover,higher wind–sand flow passage rates on the embankment than on the bridge.This study aims to offer recommendations to assist in the route selection,surveying,and design of railways in sandy regions.展开更多
The process of riming significantly impacts the microphysical characteristics of clouds.This study uses aircraft and radar observation data in stratiform clouds with convection embedded that occurred in the central an...The process of riming significantly impacts the microphysical characteristics of clouds.This study uses aircraft and radar observation data in stratiform clouds with convection embedded that occurred in the central and southern regions of North China on 22 May 2017.The microphysical structural characteristics and processes near the embedded convection core and in the stratiform cloud are analyzed comparatively.Particular attention is given to the effect of riming on the microphysical properties near the upper boundary of the melting layer and to the factors influencing riming efficiency.The collaborative observations reveal that the particle size distributions observed near the convection core and in the stratiform region are close,while the particle properties like habit and riming degree are quite different.Above the melting layer,larger plate-like ice particles and supercooled water droplets(D>50μm)are more abundant near the convective core,leading to higher collision efficiencies between ice particles and supercooled water droplets.Larger fluctuation amplitudes of vertical airflow near the convective core also contribute to the increased riming activity and the formation of more heavily rimed particles,such as graupel.Furthermore,in situ measurements from airborne probes also revealed that above the melting layer,the riming process involves two stages:the mass of snow crystals grows as supercooled droplets merge internally without changing size,followed by external freezing that significantly enlarges the crystals.展开更多
Governing airflow poses challenges under numerous conditions,particularly for the superposition of aerodynamic behaviors induced by multiple moving boundaries,mainly because of the uncertainty of the aerodynamic mecha...Governing airflow poses challenges under numerous conditions,particularly for the superposition of aerodynamic behaviors induced by multiple moving boundaries,mainly because of the uncertainty of the aerodynamic mechanism.Taking the airflow disturbance in the glass fiber transport process as an example,a numerical method for multidomain coupling is proposed considering dynamic meshing boundaries.Specifically,two-and three-dimensional modeling approaches were utilized to investigate the aerodynamic behavior around a fiber thrower(including a finger wheel and pull wheel)and its axial distribution characteristics,respectively.Some aerodynamic data were obtained through the proposed numerical approach,which is difficult to monitor using experimental strategies.The computational results showed that the flow structure in the external flow field of the fiber thrower was mainly regulated by the pull wheel rather than the finger wheel.The average airflow velocity in a specific region of the fiber thrower was decreased by 25%(from 2 m/s to 1.5 m/s)by improving the cross-sectional shape of the pull wheel.The spatial scale of the vortex clusters around the fiber thrower configured with the improved pull wheel was reduced,providing a novel perspective for understanding the improvement in the aerodynamic behavior.This study on the suppression of multiple-motion boundary-induced airflow is representative of the chemical industry.展开更多
This study explores the impact of winter sea surface temperature(SST)anomalies in the Southern Indian Ocean on summer precipitation patterns in China,utilizing data from reanalysis sources and Coupled Model Intercompa...This study explores the impact of winter sea surface temperature(SST)anomalies in the Southern Indian Ocean on summer precipitation patterns in China,utilizing data from reanalysis sources and Coupled Model Intercomparison Project Phase 6(CMIP6)models.The results reveal that the Southern Indian Ocean Dipole(SIOD),characterized by contrasting SST anomalies in the northeast and southwest regions,acts as a predictor for Chinese summer precipitation patterns,namely floods in the south and drought in the north.In a positive SIOD event,the southwestern Indian Ocean exhibits warmer SSTs,while the northeastern region remains cooler.A negative SIOD event shows the opposite pattern.During the positive phase of the SIOD,the winter SST distribution strengthens the 850-hPa cross-equatorial airflow,generating a robust low-level westerly jet that enhances water vapor transport to the Bay of Bengal(BoB).These air-sea interactions maintain lower SSTs in the northeastern region,which significantly increase the land-sea temperature contrast in the Northern Hemisphere during spring and summer.This strengthened thermal gradient intensifies the southwest monsoon,establishing a strong convergence zone near the South China Sea and amplifying monsoon-driven precipitation in South China.Additionally,CMIP6 models,such as NorESM2-LM and NorCPM1,which accurately simulate the SIOD pattern,effectively capture the seasonal response of cross-equatorial airflow driven by SST anomalies of Southern Indian Ocean.The result highlights the essential role of cross-equatorial airflow generated by the SIOD in forecasting crossseasonal precipitation patterns.展开更多
The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk dur...The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk during emergency braking at a speed of 300 km/h considering airflow cooling were investigated using finite element （FE） and computational fluid dynamics （CFD） methods. All three modes of heat transfer （conduction, convection and radiation） were analyzed along with the design features of the brake assembly and their interfaces. The results suggested that the higher convection coefficients achieved with airflow cooling will not only reduce the maximum temperature in the braking but also reduce the thermal gradients, since heat will be removed faster from hotter parts of the disk. Airflow cooling should be effective to reduce the risk of hot spot formation and disc thermal distortion. The highest temperature after emergency braking was 461 °C and 359 °C without and with considering airflow cooling, respectively. The equivalent stress could reach 269 MPa and 164 MPa without and with considering airflow cooling, respectively. However, the maximum surface stress may exceed the material yield strength during an emergency braking, which may cause a plastic damage accumulation in a brake disk without cooling. The simulation results are consistent with the experimental results well.展开更多
The structure, separation principle and feasibility research for a new type of vehicle air filter called the high speed rotary positive air filter were described. The analysis of the experimental data showed that the ...The structure, separation principle and feasibility research for a new type of vehicle air filter called the high speed rotary positive air filter were described. The analysis of the experimental data showed that the principle and structure of it were feasible and it possessed high separation efficiency and great self cleaning ability. Compared with the conventional air filter it also has lower air intake loss. So it is worth further practical research.展开更多
The association between chronic obstructive pulmonary disease(COPD) and lung cancer has long been a subject of intense debate. The high prevalence of COPD in elderly smokers inevitably strengthens their coincidence. I...The association between chronic obstructive pulmonary disease(COPD) and lung cancer has long been a subject of intense debate. The high prevalence of COPD in elderly smokers inevitably strengthens their coincidence. In addition to this contingent coincidence, recent studies have revealed a close association between the two diseases that is independent of the smoking history; that is, the existence of COPD is an independent risk factor for the development of lung cancer. Molecular-based evidence has been accumulating as a result of the efforts to explain the underlying mechanisms of this association. These mechanisms may include the following: the retention of airborne carcinogens followed by the activation of oncogenes and the suppression of tumor suppressor genes; the complex molecular mechanism associated with chronic inflammation in the distal airways of patients with COPD; the possible in-volvement of putative distal airway stem cells; and gel netic factors that are common to both COPD and lung cancer. The existence of COPD in patients with lung l cancer may potentially affect the process of diagnosis, surgical resection, radiotherapy, chemotherapy, and end-of-life care. The comprehensive management of COPD is extremely important for the appropriate treatment of lung cancer. Surgical resections with the aid of early interventions for COPD are often possible, even for patients with mild-to-moderate COPD. New challenges, such as lung cancer CT screening for individuals t at high risk, are now in the process of being implemented. Evaluating the risk of lung cancer in patients with COPD may be warranted in community-based lung cancer screening.展开更多
Coal mine ventilation is an extremely complicated system that can be affected by many factors. Gas ventilation pressure is one of important factors that can disturb the stabilization of airflow in airways.The formatio...Coal mine ventilation is an extremely complicated system that can be affected by many factors. Gas ventilation pressure is one of important factors that can disturb the stabilization of airflow in airways.The formation and characteristics of gas ventilation pressure were further elaborated, and numerical simulations were conducted to verify the role of gas ventilation pressure in the stability of airway airflow.Then a case study of airflow stagnation accident that occurred in the Tangshan Coal Mine was performed.The results show that under the condition of upward ventilation, the direction of gas ventilation pressure in the branch is the same to that of the main fan, airflow of the branches beside the branch may be reversed. The greater the gas ventilation pressure is, the more obvious the reversion is. Moreover, reversion sequence of paralleled branches is related to the airflow velocity and length of the branch. Under the condition of downward ventilation, the airflow in the branch filled with gas may be reversed. Methane in downward ventilation is hard to discharge; therefore, accumulation in downward ventilation is more harmful than that in upward ventilation.展开更多
基金supported by National Natural Science Foundation of China (Nos. 50537020, 50528707 and 10775027)
文摘Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experimentally. A critical frequency of 1 kHz was found. With the frequency above 1 kHz, when a fast airflow was introduced into the discharge gap, the discharge patterns varied from filaments to curved stripes and the curvature degree rose with an increase in the airflow speed. At the same time, the discharge intensity decreased. However with the discharge frequency below 1 kHz, the discharge intensity would get greater with an increase in the airflow speed.
基金supported by National Natural Science Foundation of China(Grant Nos.51437002,51676053)
文摘Dielectric barrier discharge has widely used in airflow control, ignition and combustion, and other applications; the influence of airflow on dielectric barrier discharge is of extensive concern. Previous studies demonstrate that the discharge becomes more uniform and the discharge intensity decreases with increasing of airflow velocity. In this study, we adopt a discharge cell construction with upstream and downstream structure and study the discharge states and intensities. The experimental results demonstrate that within a specific range of airflow speed, the upstream discharge intensity is decreased, and the downstream discharge intensity is enhanced. The physical basis for this phenomenon is proposed as follows： Within a pulse interval time, some particles, such as charged and metastable particles produced by the upstream discharge, could be transported to the downstream region. The concentration of particles in the downstream region is increased, and these particles play a pre-ionization role in the downstream discharge, the intensity of the downstream discharge is enhanced. Further, factors such as the pulse frequency and the distance between electrodes are discussed in detail, along with the conditions for enhancing downstream discharge intensity.
基金supported by National Natural Science Foundation of China (Nos.51006027,51437002,and 51477035)
文摘Atmospheric pressure discharges excited by repetitive nanosecond pulses have at- tracted significant attention for various applications. In this paper, a plate-plate discharge with airflows is excited by a repetitive nanosecond pulse generator. Under different experiment con- ditions, the applied voltages, discharge currents, and discharge images are recorded. The plasma images presented here indicate that the volume discharge modes vary with airflow speeds, anda diffuse and homogeneous volume discharge occurs at the speed of more than 35 m/s. The role of airflows provides different effects on the 2-stage pulse discharges. The 1st pulse currents nearly maintain consistency for different airflow speeds. However, the 2nd pulse current has a change trend of first decreasing and then rapidly increasing, and the value difference for 2nd pulse cur- rents is about 20 A under different airflows. In addition, the experimental results are discussed according to the electrical parameters and discharge images.
基金supported by the National Science and Technology Major Project for the Prevention and Control of Emerging and Major Infectious Diseases[2025ZD01908702]Peking University Medicine Fund of Fostering Young Scholars’Scientific&Technological innovation[BMU2024YFJHP014]supported by Fundamental Research Funds for the Central Universities+1 种基金Key Clinical Projects of Peking University Third Hospital[BYSYZD2022014]Peking University Third Hospital[2025024].
文摘Objective Post tuberculosis lung disease(PTLD)manifests in various forms,including tuberculosisassociated chronic obstructive pulmonary disease(TB-COPD),yet the clinical features of PTLD remain undercharacterized.This study aimed to assess longitudinal changes in lung function over a 5-year period and to identify predictors of airflow obstruction in a cohort of patients treated for active pulmonary TB.Methods Patients with active pulmonary TB were enrolled in this study and were followed during treatment,at treatment completion and five years post-treatment.Assessments included lung function and chest CT,analyzing longitudinal trends and airflow obstruction risk factors.Results Among 53 patients(mean age 36.9±13.9 years;64.2%male),7 patients(13.2%)exhibited airflow obstruction.At the 5-year follow-up,the mean FEV_(1)/FVC declined significantly(76.27%±12.04%vs.80.23%±11.02%,P<0.001)and 9 patients(17.0%)exhibited airflow obstruction.Seven of these patients predominantly showed air trapping consistent with small airway disease on chest CT,aligning with TB-COPD phenotype.Notably,four young-to-middle-aged patients(<60 years old)had persistent obstruction over the five years.Conclusion The initial test revealed that 13.2%of patients presented with airflow obstruction.By the 5-year follow-up,this proportion had increased to 17.0%,with most cases demonstrating imaging findings aligning with TB-COPD,even among younger,non-smoking individuals.These findings emphasize the importance of long-term follow-up and routine lung function assessments in TB survivors.
基金supported by the National Natural Science Foundation of China(No.51908079)associated with the projects supported by the Fundamental Research Funds for the Central Universities(No.2021CDJCGJ015)。
文摘Increasing air movement by utilizing electric fans is among the common approaches for comfort and energy savings in buildings in summer;however,the use of electric fans is usually the forced constant airflow.This study reformed the one-chip computer program of a floor fan motor and simulated dynamic airflow through controlling the rotating frequency only.The flow field characteristics of constant,oscillated,sinusoidal airflows with periods of 10 s,30 s,60 s,100 s were measured.The comfort performance was evaluated by chamber experiments,with 20 subjects exposed to six airflow patterns under 30℃,70%RH.The results showed that the simulated sinusoidal airflows had relatively higher turbulence intensity(32%–37%)andβvalues(>0.4).While subjects’thermal sensations were not statistically significant among six airflows,their reported discomfort symptoms during 60 min exposure were reduced under sinusoidal airflows.The calculated convective heat transfer shared similar variations to instantaneous air velocity and skin temperature.A large fluctuation of 10–50 W/m^(2)and higher total convective heat loss(3000–3500 W/m^(2))were found for sinusoidal period 30 s.This study develops a new method to simulate varying air velocities through conveniently controlling the fan motor amplitude and frequency,and verifies the comfortable feelings to dynamic sinusoidal airflows.The work benefits to improve the performance of the current electric fans with lower costs and promote the applications of personal ventilation devices in buildings,thus optimizing human thermal comfort,reducing dependences on air conditionings and achieving building energy efficiency.
基金supported by the China National Key R&D Program(No.2022YFC3801500)the National Natural Science Foundation of China(No.52078270 and No.52130803).
文摘The dynamic characteristics of different airflows on micro-scales have been explored from many perspectives since the late 1970s.On the one hand,most analytical tools and research subjects in previous contributions vary significantly:some only focus on fluctuant velocity features,while others pay attention to directional features.On the other hand,despite the wide variety of existing analytical methods,they are not systematically classified and organized.This paper aims to establish a system including state-of-the-art tools for airflow analysis and to further design a holistic toolkit named Airflow Analytical Toolkit(AAT).The AAT contains two tools,responsible for analyzing the velocity and direction characteristics of airflows,each of which is integrated with multiple analytical modules.To assess the performance of the developed toolkit,we further take typical natural and mechanical winds as cases to show its excellent analytical capability.With the help of this toolkit,the great differences in velocity and directional characteristics among different airflows are identified.The comparative results reveal that not only is the velocity of natural wind more fluctuating than that of mechanical wind,but its incoming flow direction is also more varying.The AAT,serving as a powerful and user-friendly instrument,will hopefully offer great convenience in data analysis and guidance for a deeper understanding of the dynamic characteristics of airflows,and further remedy the gap in airflow analytical tools.
基金supported by the National Natural Science Foundation of China(Nos.U2241240,12172045 and 12221002)the Opening Fund of State Key Laboratory of Explosion Science and Technology of Beijing Institute of Technology,China(No.ZDKT23-02)。
文摘Carbon Carbon(C/C)composites in thermal-protection system are exposed to severe thermochemical ablation and mechanical erosion,and their thermal-protection performance is of vital importance to the structural safety and flight status of hypersonic vehicles.We numerically analyzes the mesoscopic ablation-erosion of C/C Composites with Inclined Fibers(CCIF).First,a thermochemical ablation model describing the reaction-diffusion coupled problem of C/C composites on mesoscale is employed to analyze ablative process,and the corresponding surface ablation morphology is obtained.Then,the ablation morphology of CCIF is taken as the geometrical model for mechanical erosion analysis,and their damage and failure behavior under high-speed airflow shear is analyzed by using progressive damage method.Moreover,the effects of fiber inclined angle and airflow direction on the mechanical erosion of CCIF are investigated,and the ablationerosion behavior is analyzed and discussed.The results show that the failure modes of mechanical erosion in inner and edge regions are obviously different,showing granular and block erosion phenomena respectively.The mechanical erosion of CCIF in the direction of reverse flow is easier than that in the direction of forward flow.These results can provide a theoretical basis for the design and optimization of thermal protection system materials.
基金financially supported by the Natural Science Foundation of Shandong Province(ZR2020QE124,ZR2023ME031 and ZR2023ME012)Innovation Achievement Cultivation Project of Qingdao University of Technology(CLZ2022-002)National Natural Science Foundation of China(52404222 and 52374209).
文摘Aiming at reducing the dust pollution during the tunneling process and improving the application efficiency of air curtain dust prevention technology,according to the changes of radial jet velocity(v_(r)),axial extraction velocity(v_(e))and extraction distance(L)in the formation process of air curtain,the numerical simulation method was used to analyze the rules of airflow structure evolution and the diffusion characteristics of dust particles in fully mechanized excavation tunnel.The results indicate that as v_(r) and v_(e) increase,the migration path of the wall jet of the air curtain changes into an axial direction;as L decreases,the migration distance increases accordingly.These phenomena make the airflow distribution in the working face tends to be uniform.The dust diffusion distance reduces as well,wherein,the range of the discrete area of dust particles decreases sharply,until all dust particles are concentrated in the accumulation area.On this basis,the v_(r),v_(e) and L were optimized and applied in the 63_(up) 08 fully mechanized working face.By the application of the optimal parameters,the average dust removal efficiency at the driver’s position increased by 71%.The dust concentration was reduced and the working environment had been improved effectively.
文摘https://www.sciencedirect.com/journal/energy-and-buildings/vol/342/suppl/C Volume 342,1 September 2025[OA](1)Experimental validation of neural network-based prediction of natural ventilation bulk airflow rate by Jo ao Carlos Sim oes,Guilherme Carrilho da Graca,Article115871Abstract:To fully exploit natural ventilation(NV)as an energysaving strategy in mixed-mode buildings,accurate real-time prediction of NV airflow rates is essential.Current approaches for NV airflow rates prediction often rely heavily on expertise knowledge and computationally demanding methods such as Computational Fluid Dynamics(CFD)as well as expensive and complex direct airflow measurements.
基金supported by the National Natural Science Foundation of China(Grant Nos.42077448 and 42477505)the Western Young Scholars project of the Chinese Academy of Sciences of China(Grant No.xbzglzb2022024)+2 种基金the Natural Science Foundation of Gansu Province for Distinguished Young Scholars(Grant No.22JR5RA049)the Ordos Science and Technology Plan(Grant No.2021EEDSCXQDFZ013)the Longyuan Youth Talent Project of Gansu Province(Grant No.E339020101)。
文摘The embankment and bridge are the basic forms of railway lines.To date,no reports have addressed the optimal form to adopt when passing through sandy areas.Therefore,models of railway embankment and bridge were created,and wind tunnel experiments were conducted to compare the differences in wind speed,flow field,sand transport rate,and other wind–sand environmental effects of railway embankment and bridge.Results show that wind speed reduction areas in the upwind and downwind directions were observed for the railway embankment and bridge.In these areas,the extent and degree of wind speed reduction on the embankment were greater than those on the bridge.At the top of the embankment,especially on the windward slope shoulder,an obvious area of wind speed increase was observed.Similarly,a distinct area of wind speed increase was found between the top of the windward side slope shoulder and 3H downwind of the bridge.Within these regions,the range of wind speed increase on the embankment was smaller than that on the bridge,but the degree of increase was greater than that on the bridge.The range of variation in wind speed on the embankment was generally greater than that on the bridge.The wind–sand flow field around the embankment exhibited greater variability than that around the bridge.Moreover,higher wind–sand flow passage rates on the embankment than on the bridge.This study aims to offer recommendations to assist in the route selection,surveying,and design of railways in sandy regions.
基金supported by the National Natural Science Foundation of China(Grant No.42025501)the Natural Science Foundation of Hebei Province(Grant No.D2024304015)+4 种基金the Fundamental Research Funds for the Central Universities,including Grant No.020714380217the Cemac“GeoX”Interdisciplinary Program(Grant No.020714380210)the Open Grants of the Key Laboratory of Radar Meteorology,China Meteorological Administration(Grant No.2023LRM-B05)the Hebei Meteorological Service Scientific Research and Development Project(Grant No.23ky08)the Open Research Program of the State Key Laboratory of Severe Weather(Grant No.2023LASW-A01)。
文摘The process of riming significantly impacts the microphysical characteristics of clouds.This study uses aircraft and radar observation data in stratiform clouds with convection embedded that occurred in the central and southern regions of North China on 22 May 2017.The microphysical structural characteristics and processes near the embedded convection core and in the stratiform cloud are analyzed comparatively.Particular attention is given to the effect of riming on the microphysical properties near the upper boundary of the melting layer and to the factors influencing riming efficiency.The collaborative observations reveal that the particle size distributions observed near the convection core and in the stratiform region are close,while the particle properties like habit and riming degree are quite different.Above the melting layer,larger plate-like ice particles and supercooled water droplets(D>50μm)are more abundant near the convective core,leading to higher collision efficiencies between ice particles and supercooled water droplets.Larger fluctuation amplitudes of vertical airflow near the convective core also contribute to the increased riming activity and the formation of more heavily rimed particles,such as graupel.Furthermore,in situ measurements from airborne probes also revealed that above the melting layer,the riming process involves two stages:the mass of snow crystals grows as supercooled droplets merge internally without changing size,followed by external freezing that significantly enlarges the crystals.
基金Supported by Jilin Provincial Youth and Middle-Aged Scientific and Technological Innovation and Entrepreneurship Excellence Talents(Grant No.20210509007RQ)Jilin Provincial Key Scientific and Technological Projects(Grant No.20220201026GX)Jilin Provincial Fundamental Research Funds for the Central Universities(Grant No.2022-JCXK-15).
文摘Governing airflow poses challenges under numerous conditions,particularly for the superposition of aerodynamic behaviors induced by multiple moving boundaries,mainly because of the uncertainty of the aerodynamic mechanism.Taking the airflow disturbance in the glass fiber transport process as an example,a numerical method for multidomain coupling is proposed considering dynamic meshing boundaries.Specifically,two-and three-dimensional modeling approaches were utilized to investigate the aerodynamic behavior around a fiber thrower(including a finger wheel and pull wheel)and its axial distribution characteristics,respectively.Some aerodynamic data were obtained through the proposed numerical approach,which is difficult to monitor using experimental strategies.The computational results showed that the flow structure in the external flow field of the fiber thrower was mainly regulated by the pull wheel rather than the finger wheel.The average airflow velocity in a specific region of the fiber thrower was decreased by 25%(from 2 m/s to 1.5 m/s)by improving the cross-sectional shape of the pull wheel.The spatial scale of the vortex clusters around the fiber thrower configured with the improved pull wheel was reduced,providing a novel perspective for understanding the improvement in the aerodynamic behavior.This study on the suppression of multiple-motion boundary-induced airflow is representative of the chemical industry.
基金Guangdong Major Project of Basic and Applied Basic Research(2020B0301030004)National Natural Science Foundation of China(U2442202)+1 种基金Key Innovation Team of China Meteorological Administration“Climate Change Detection and Response”(CMA2022ZD03)National Key Research and Development Program of China(2023YFF0805104)。
文摘This study explores the impact of winter sea surface temperature(SST)anomalies in the Southern Indian Ocean on summer precipitation patterns in China,utilizing data from reanalysis sources and Coupled Model Intercomparison Project Phase 6(CMIP6)models.The results reveal that the Southern Indian Ocean Dipole(SIOD),characterized by contrasting SST anomalies in the northeast and southwest regions,acts as a predictor for Chinese summer precipitation patterns,namely floods in the south and drought in the north.In a positive SIOD event,the southwestern Indian Ocean exhibits warmer SSTs,while the northeastern region remains cooler.A negative SIOD event shows the opposite pattern.During the positive phase of the SIOD,the winter SST distribution strengthens the 850-hPa cross-equatorial airflow,generating a robust low-level westerly jet that enhances water vapor transport to the Bay of Bengal(BoB).These air-sea interactions maintain lower SSTs in the northeastern region,which significantly increase the land-sea temperature contrast in the Northern Hemisphere during spring and summer.This strengthened thermal gradient intensifies the southwest monsoon,establishing a strong convergence zone near the South China Sea and amplifying monsoon-driven precipitation in South China.Additionally,CMIP6 models,such as NorESM2-LM and NorCPM1,which accurately simulate the SIOD pattern,effectively capture the seasonal response of cross-equatorial airflow driven by SST anomalies of Southern Indian Ocean.The result highlights the essential role of cross-equatorial airflow generated by the SIOD in forecasting crossseasonal precipitation patterns.
基金Projects (50872018, 50902018) supported by the National Natural Science Foundation of ChinaProject (1099043) supported by the Science and Technology in Guangxi Province, ChinaProject (090302005) supported by the Basic Research Fund for Northeastern University, China
文摘The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk during emergency braking at a speed of 300 km/h considering airflow cooling were investigated using finite element （FE） and computational fluid dynamics （CFD） methods. All three modes of heat transfer （conduction, convection and radiation） were analyzed along with the design features of the brake assembly and their interfaces. The results suggested that the higher convection coefficients achieved with airflow cooling will not only reduce the maximum temperature in the braking but also reduce the thermal gradients, since heat will be removed faster from hotter parts of the disk. Airflow cooling should be effective to reduce the risk of hot spot formation and disc thermal distortion. The highest temperature after emergency braking was 461 °C and 359 °C without and with considering airflow cooling, respectively. The equivalent stress could reach 269 MPa and 164 MPa without and with considering airflow cooling, respectively. However, the maximum surface stress may exceed the material yield strength during an emergency braking, which may cause a plastic damage accumulation in a brake disk without cooling. The simulation results are consistent with the experimental results well.
文摘The structure, separation principle and feasibility research for a new type of vehicle air filter called the high speed rotary positive air filter were described. The analysis of the experimental data showed that the principle and structure of it were feasible and it possessed high separation efficiency and great self cleaning ability. Compared with the conventional air filter it also has lower air intake loss. So it is worth further practical research.
基金Supported by The Ministry of Education,Culture,Sports,Science and Technology of Japan
文摘The association between chronic obstructive pulmonary disease(COPD) and lung cancer has long been a subject of intense debate. The high prevalence of COPD in elderly smokers inevitably strengthens their coincidence. In addition to this contingent coincidence, recent studies have revealed a close association between the two diseases that is independent of the smoking history; that is, the existence of COPD is an independent risk factor for the development of lung cancer. Molecular-based evidence has been accumulating as a result of the efforts to explain the underlying mechanisms of this association. These mechanisms may include the following: the retention of airborne carcinogens followed by the activation of oncogenes and the suppression of tumor suppressor genes; the complex molecular mechanism associated with chronic inflammation in the distal airways of patients with COPD; the possible in-volvement of putative distal airway stem cells; and gel netic factors that are common to both COPD and lung cancer. The existence of COPD in patients with lung l cancer may potentially affect the process of diagnosis, surgical resection, radiotherapy, chemotherapy, and end-of-life care. The comprehensive management of COPD is extremely important for the appropriate treatment of lung cancer. Surgical resections with the aid of early interventions for COPD are often possible, even for patients with mild-to-moderate COPD. New challenges, such as lung cancer CT screening for individuals t at high risk, are now in the process of being implemented. Evaluating the risk of lung cancer in patients with COPD may be warranted in community-based lung cancer screening.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51774292, 51474219, 51604278)the State Key Research Development Program of China (Grant Nos. 2016YFC0801402, 2016YFC0600708)
文摘Coal mine ventilation is an extremely complicated system that can be affected by many factors. Gas ventilation pressure is one of important factors that can disturb the stabilization of airflow in airways.The formation and characteristics of gas ventilation pressure were further elaborated, and numerical simulations were conducted to verify the role of gas ventilation pressure in the stability of airway airflow.Then a case study of airflow stagnation accident that occurred in the Tangshan Coal Mine was performed.The results show that under the condition of upward ventilation, the direction of gas ventilation pressure in the branch is the same to that of the main fan, airflow of the branches beside the branch may be reversed. The greater the gas ventilation pressure is, the more obvious the reversion is. Moreover, reversion sequence of paralleled branches is related to the airflow velocity and length of the branch. Under the condition of downward ventilation, the airflow in the branch filled with gas may be reversed. Methane in downward ventilation is hard to discharge; therefore, accumulation in downward ventilation is more harmful than that in upward ventilation.
