Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway:The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents.An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system.We investigated the release characteristics of main energy sources in coal seam,and obtained the dynamic characteristics of outburst two-phase flow in a roadway.Additionally,we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure.The results indicate that the outburst process exhibits pulse characteristics,and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon.The outburst energy is released in stages,and the elastic potential energy is released in the vertical direction before the horizontal direction.In a straight roadway,the impact force oscillates along the roadway.With an increase in the solid–gas ratio,the two-phase flow impact force gradually increases,and the disaster range extends from the middle of the roadway to the coal seam.In the area near the coal seam,the disaster caused by the two-phase flow impact is characterized by intermittent recovery.In a bifurcated roadway,the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow,and the impact force tends to weaken with increasing solid-gas ratio.The impact force is asymmetrically distributed;it is higher on the left of the bifurcated roadway.With an increase in the solid-gas ratio,the static pressure rapidly decreases,and the bifurcated structure accelerates the attenuation of static pressure.Moreover,secondary acceleration is observed when the shock wave moves along the T-shaped roadway,indicating that the bifurcated structure increases the shock wave velocity.

Numerical simulation of airflow distribution in mine tunnels

Based on 3D modelling of typical tunnels in mines, the airflow distribution in a three-center arch-section tunnel is investigated and the influence of air velocity and cross section on airflow distribution in tunnels is studied. The average velocity points were analyzed quantitatively. The results show that the airflow pattern is similar for the three-center arch section under different ventilation velocities and cross sectional areas. The shape of the tunnel cross section and wall are the critical factors influencing the airflow pattern. The average velocity points are mainly close to the tunnel wall. Characteristic equations are developed to describe the average velocity distribution, and provide a theoretical basis for accurately measuring the average velocity in mine tunnels.

Influence of gas ventilation pressure on the stability of airways airflow

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.

The spring Yellow Sea fog：synoptic and air–sea characteristics associated with different airflow paths

The fog occurs frequently over the Yellow Sea in spring(April–May), a climatical period of Asian monsoon transition. A comprehensive survey of the characteristic weather pattern and the air-sea condition is provided associated with the fog for the period of 1960–2006. The sea fog is categorized by airflow pathways of backward trajectory cluster analysis with the surface observations derived from international comprehensive oceanatmosphere dataset(I_COADS) I_COADS datasets and contemporaneous wind fields from the National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research(NCAR) reanalysis. On the basis of the airflow paths, the large-scale lower-tropospheric circulation patterns and the associated surface divergence,the distribution of a vertical humidity, the horizontal water vapor transportation and the air-sea temperature difference are investigated and the major findings are summarized as follows.(1) Four primary clusters of the airflow paths that lead to spring sea fog formation are identified. They are originated from the northwest, east,southeast and southwest of the Yellow Sea, respectively.(2) Springtime Yellow Sea fog occurs under two typical weather patterns: the Yellow Sea high(YSH) and cyclone and anticyclone couplet(CAC). Each pattern appears by about equal chance in April but the YSH occurrence drops to around one third and the CAC rises to around two third of chance in May.(3) The common feature in the two types of synoptic conditions is that surface divergence center is located over the Yellow Sea.(4) For the YSH type of fog, water vapor comes mainly from local evaporation with a well-defined dry layer present in the lower atmosphere; for the CAC type of fog, however, water vapor comes mainly from areas outside the Yellow Sea with a thick surface layer of high humidity.(5) With the differences in weather patterns and its associated vertical distribution of the humidity and the transportation of water vapor, there are two types of sea fogs. Most fogs of the CAC types are "warm" fog, while fogs of YSH type have nearly equal chance to be "warm" and "cold" fog.

Subsurface Airflow Induced by Natural Forcings

Subsurface air flow can be induced by natural processes, such as atmospheric or barometric pressure changes, water table fluctuations, topographic effects, and rainfall infiltration. Barometric pressure fluctuations are the most common cause of subsurface air flow, which can be significant under favourable geological conditions. This process has been studied most extensively because of its application to passive soil vapor extraction. Soil air flow induced by water table fluctuations can be significant, particularly where the fluctuations are of high frequency, for example, in tidal-influenced coastal areas. Topographic effects can lead to strong subsoil air flow in areas with great elevation differences. Rainfall infiltration usually produces only weak airflow. Air flow induced by these natural processes has important environmental and engineering implications. Among the different processes, air flow induced by tidal fluctuations has been studied the least, although it has exciting applications to coastal engineering projects and environmental remediation.

Effects of the transverse electric field on nanosecond pulsed dielectric barrier discharge in atmospheric airflow

In this paper,an asymmetric electrode geometry(the misalignment between the ends of highvoltage and grounded electrodes)is proposed in order to investigate the effects of the transverse electric field on nanosecond pulsed dielectric barrier discharge(DBD).The results show that diffuse discharge manifests in the misaligned region and the micro-discharge channel in the aligned region moves directionally.Moreover,the diffuse discharge area increases with the decrease of the discharge gap and pulse repetition frequency,which is consistent with the variation of the moving velocity of the micro-discharge channel.When airflow is introduced into the discharge gap in the same direction as the transverse electric field,the dense filamentary discharge region at the airflow inlet of asymmetric electrode geometry is larger than that of symmetric electrode geometry.However,when the direction of the airflow is opposite to that of the transverse electric field,the dense filamentary discharge region of asymmetric electrode geometry is reduced.The above phenomena are mainly attributed to the redistribution of the space charges induced by the transverse electric field.

Research and Application of Airflow Recirculation System in Working Faces with Leaking Airflow

In order to develop the technology of the controlled recircuIation of airflow in the world, some formulas about the airflow recirculation system in the working face with leaking airflow are deduced,which reduces the error between calculating and real values. on the base of the application of the formulas mentioned above, the problem about lack of airflow in the working face 2712 was solved successfully in Xiandewang Coal Mine.

STUDY OF AIRFLOW HOMOGENEITY STANDARD IN REGENERATIVE CHAMBER OF TANK FURNACE

The authers compared six used criterions ofinflucencing homogeneity of moving airflow in virtue of er-rors such as variance Q,average square deviation T,homoge-neous indices H,inhomogeneous degree W,range R and non-uniform index S.The auther think that the effects of the er-rors will be magnified when all these old stnadards were cal-culated,especially for higher airflow homogeneity,thus,thereliability of these norms would be reduced.The authers putforward two new standards to lower influence of error.

FIRE-EXTINGUISHING MECHANISM AND ENERGY PROCEDURE BY HIGH VELOCITY AIRFLOW

Based on the testing restult of character of forest fire, with the aid mold of flameextinguishing and mathematical method, the combustion of the forest fuels and the energy transtfer under the convention condition were studied and the mechanism and interrelated elements of flameextinguishing with high velocity airflow were given. The energy formulae is given:Nz =Ka0 L0 (15)GH/102η through combustion calculation and test revision This formula was checked through simulated testing for extinguishing low, medial and high intensity fires with high velocity airflow.

THE ANALYSIS FOR THE AIRFLOW EXCITING-VIBRATION FORCE OF CONTROL STAGE OF STEAM TURBINE

Based on the hydrodynamics, the airflow exciting_vibration force of control stage of steam turbine is studied by using the momentum theorem. A formulation for calculating the air exciting_vibration force of the control stage of steam turbine is deduced first by using theoretical analysis method and taking all the design factors of vane and nozzles into consideration. Moreover, the exciting_vibration forces in different load cases are discussed respectively.

Model of Airflow Field on the Deck for Shipborne Helicopter Flight Dynamics Analysis

For the research of helicopter/ship dynamic interface,the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter.The steady flow is calculated by computational fluid dynamics(CFD)method,while the stochastic flow is composed of the compensation velocity derived from ship motion and turbulence above the deck.The accuracy of the proposed flow field model is verified by comparing the helicopter response in the proposed flow field with the results calculated by US Army′s Military Specifications(MIL)model which is commonly used in engineering.Meanwhile,it also shows the proposed flow field model is more appliable to flight dynamics analysis of shipborne helicopter.On that the basis,ship deck flow field is simulated at different sea conditions by adjusting the wind speed on the deck,mother ship movement and shipboard turbulence,etc.And helicopter angular rate response is calculated.The results show that the difference of dynamic stability between helicopter′s roll and pitch leads to the facts that the influence of above factors on the helicopter′s roll angular rate response is greater than that of pitch angular rate,that the frequency and amplitude of mother ship roll motion are much greater than those of pitch motion,and that the disturbance caused by roll motion on the air has greater influence on the helicopter response.The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.

Novel assisted cough system based on simulating cough airflow dynamics

Cough is a defensive behavior that protects the respiratory system from infection and clears airway secretions.Cough airflow dynamics have been analyzed by a variety of mathematical and experimental tools.In this paper,the cough airflow dynamics of 42 subjects were obtained and analyzed.An identification model based on piecewise Gauss function for cough airflow dynamics is proposed through the dimensionless method,which could achieve over 90%identification accuracy.Meanwhile,an assisted cough system based on pneumatic flow servo system is presented.The vacuum situation and feedback control are used to increase the simulated peak cough flow rate,which are important for airway secretion clearance and to avoid airway collapse,respectively.The simulated cough peak flow could reach 5 L/s without the external assistance such as manual pressing,patient cooperation and other means.Finally,the backstepping control is developed to generate a simulated cough airflow that closely mimics the natural cough airflow of humans.The assisted cough system opens up wide opportunities of practical application in airway secretion clearance for critically ill patients with COVID 2019 and other pulmonary diseases.

Numerical Simulation of the Airflow within a Canopy Using a 3D Canopy Structure

Canopy architecture of windbreaks is vital in agriculture,meteorological and ecological applications.In this study,computational fluid dynamics(CFD) and field experiments were used to investigate the flow characteristics and flow resistance through vegetation canopies with several different leaf area densities(L_(ad)).Compared with traditional modelling approaches,the present model introduced 3D architecture of the tree that contained a hard trunk,branches and artificial leaves to model the effect of leaves and the other parts of the canopy on airflow.Visual basic application(VBA) produced the 3D architecture of canopy.Simulations were made with the full closure model(FCM) and microcosmic model(MM).Canopies L_(ad),used in the simulations were7.76,18.12 and 25.89 m^(-1).The objectives of this paper are to analyze the contour of velocity(U) and turbulent kinetic energy(k)of two models in different leaf area densities,comparing the simulation results with experimental data/other works and investigate the real effects of the canopy on the airflow distribution.Results are encouraging,compared with the FCM,V and k of MM profiles qualitatively agree better with other works.Therefore,the model and method are recommended for future use in simulating turbulent flows in forest canopies.

Diagnosis Analysis of One Cold Airflow Snowfall in Shandong Peninsula

[Objective]One cold airflow snowfall in Shandong Peninsula was analyzed.[Method] Using conventional weather observation data,the NCEP /NCAR 1°×1° grid point by 6 h in data analysis,the synoptic weather dynamics principle and diagnosis analysis method,the cold airflow snowfall in Shandong Peninsula on December 4,2008 to 6 th was analyzed and summarized.[Result]The results showed that the cold deep groove of large scale circulation form caused the cold airflow snowfall in Shandong Peninsula.While the 850 hPa mistral wind strengthened,cold airflow snow in Shandong Peninsula will be strengthened.During the eruption of snowstorm,the relative humidity from 925 to 750 hPa was larger than 90%.The area formed by 90% relative humidity line corresponded with the period of heavy snowfall.The changes of relative humidity line reflected the changes of warm and wet air transmitting to the higher place.The more warm and wet air being sent to the upper air,the more conductive to the formation of cold airflow snowfall in Shandong Peninsula.The cold airflow snowfall had distinct temporal and spatial distribution characteristics and corresponded with the vertical increasing movement zone.[Conclusion]The study provided reference for the preciseness of short term and incoming report of cold airflow snowfall in Shandong Peninsula.

CFD-Based Evaluation of Flowand Temperature Characteristics of Airflow in an Aircraft Cockpit

The rational design of airflow distribution is of great importance for comfort and energy conservation.Several numerical investigations of flow and temperature characteristics in cockpits have been performed to study the distinct airflow distribution.This study developed the coupled heat transfer model of radiation,convection,and heat conduction for the cockpit flight environment.A three-dimensional physical model was created and a shear stress transfer(SST)k-w turbulence model was well verified with a high prediction accuracy of 91%for the experimental data.The strong inhomogeneous flow and temperature distribution were captured for various initial operating conditions(inlet temperature,inlet pressure,and gravitational acceleration).The results indicated that the common feature of the flow field was stable in the middle part of the cockpit,while the temperature field showed a large temperature gradient near the cockpit’s top region.It was also found that there was remarkable consistency in the distributed features,regardless of the applied initial operating conditions.Additionally,the mass flux and the top heat source greatly affected the flow and temperature characteristics.This study suggests that an optimized operating condition does exist and that this condition makes the flow and temperature field more stable in the cockpit.The corresponding results can provide necessary theoretical guidance for the further design of the cockpit structure.

Nasal airflow of patient with septal deviation and allergy rhinitis

A numerical simulation of a patient’s nasal airflow was developed via computational fluid dynamics.Accordingly,computerized tomography scans of a patient with septal deviation and allergic rhinitis were obtained.The three-dimensional(3D)nasal model was designed using InVesalius 3.0,which was then imported to(computer aided 3D interactive application)CATIA V5 for modification,and finally to analysis system(ANSYS)flow oriented logistics upgrade for enterprise networks(FLUENT)to obtain the numerical solution.The velocity contours of the cross-sectional area were analyzed on four main surfaces:the vestibule,nasal valve,middle turbinate,and nasopharynx.The pressure and velocity characteristics were assessed at both laminar and turbulent mass flow rates for both the standardized and the patient’s model nasal cavity.The developed model of the patient is approximately half the size of the standardized model;hence,its velocity was approximately two times more than that of the standardized model.

Effect of Laryngopharyngeal Anatomy on Expiratory Airflow and Submicrometer Particle Deposition in Human Extrathoracic Airways

The objective of this study is to systematically assess the influences of the larynopharyneal anatomical details on airflow and particle behaviors during exhalation by means of image-based modeling. A physiologically realistic nose-throat airway was developed with medical images. Individual airway anatomy such as uvula, pharynx, and larynx were then isolated for examination by progressively simplifying this image-based model geometry. Low Reynolds number (LRN) k-w model and Langrangian tracking model were used to simulate the dynamics of airflow and particle transport for a wide range of exhalation conditions (4-45 L/min) and particle sizes (1 nm-1 μm). Results showed that pharyngeal anatomical details exerted a significant impact on breathing resistance and particle profiles. Abrupt pressure drop resulting from the uvula-related airway obstruction was observed. Even though the total deposition rate in the nasal airway is largely unaffected by the upstream effect, the local deposition patterns vary notably. Results of this study also indicate that the pressure drop appears to be an appropriate parameter to characterize the geometric variations for diffusive depositions. Inclusion of pressure drop (D0.5Q-0.62dp0.07) gives an improved correlation than using the conventional diffusion factor (D0.5Q﹣0.28).

A new geometrical and mechanical relation in the respiratory system with airflow limitation—From the perspective of analytical respiratory mechanics

Classic respiratory mechanics is a branch of vectorial mechanics, which aims to recognize all forces acting on the respiratory system. Another branch of mechanics, analytical mechanics, has been used for analyzing the motions of complicated systems with constraints through equilibrium among scalar quantities such as kinetic energy and potential energy. However, until now, there have not been any studies concerning about analytical respiratory mechanics. In this paper, the author has obtained two types of motion equations (linear and nonlinear) for the airflow limitation from formulation of the analytical respiratory mechanics. Reconstructed flow-volume trajectories of the linear equation revealed a new relationship among the slope of the linear portion of trajectory, the coefficient of the dissipation function and the coefficient of the potential function. Reconstructed trajectories of the nonlinear equation suggested that a curved flow-volume trajectory would be caused by the emergence of regional hypoventilated clusters with airtrapped lobules. In conclusion, analytical respiratory mechanics will provide the basis for analyzing the mechanical properties of the respiratory system con cerning pulmonary functional images made by newly developed technologies.

Airflow Distribution Measurements around the Human Body Using a Thermal Manikin by Particle Image Velocimetry

The human body is a heat source in a room. As the human body has a complex shape, it is difficult to accurately measure the airflow distribution around the human body using a conventional anemometer. This study measured the airflow distribution around a thermal manikin acting as a human body by visualization and particle image velocimetry (PIV). The thermal manikin was 1700 mm in height, and its surface temperature was set to 30oC. The experiments were performed in the conditions when the manikin was seated on a chair. The ambient air temperature and wind velocity were experimental variables. The airflow distribution around the manikin was reported by considering the relationships between convection and ambient wind velocity. There were no differences in the airflow distribution around the manikin due to the ambient air temperature when the wind velocity in the chamber was set as 1.0 m/s. Hence, it was assumed that the ambient wind velocity was dominant in this condition. Various airflow distributions were formed around the manikin due to the difference between the body surface temperature and the ambient air temperature in the case where the wind velocity in the chamber was set to approximately equal to 0.0 m/s.

Active Absorption of Perforated Plate Based on Airflow

The theory of active absorption of the perforated plate is proposed in this paper.The perforated plate is used as the material of active absorption and the depth of the cavity behind the perforated plate is changed according to the resonant frequency of the perforated plate.The rigid wall is moved to produce resonance so that the absorption coefficient can reach the maximal level.It is shown from the numerical calculation that when the perforated plate resonates,the moving distance is large at low frequencies,and the absorption coefficient is low under certain conditions.Perforated plate resonance is effective for single frequency of incident sound wave,which is difficult for the wide frequency,so active absorption based on airflow is posed,and the numerical calculation and experiment are carried out.The results denote that this method of active absorption is practical.