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Impact of different human walking patterns on flow and contaminant dispersion in residential kitchens:Dynamic simulation study

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Building Simulation 2022年第6期15卷 1051-1066页

作者： Lipeng Lv Yuhang Wu Changsheng Cao Lingjie Zeng Jun Gao Wuhao Xie Jing Zhang Institute of HVAC Engineering School of Mechanical EngineeringTongji UniversityShanghai200092China College of Environmental Science and Engineering Tongji UniversityShanghai200092China

The effects of different human walking patterns on contaminant dispersion in residential kitchens were investigated through computational fluid dynamics simulation with the dynamic mesh method.A tracer gas experiment was performed to verify the feasibility and accuracy of the simulation method.flow characteristics induced by human walking were minutely described,and the transient capture efficiency of the range hood was adopted to assess the impact of human walking quantitatively.Human walking parallel to a counter,human walking parallel to a counter manned by another human,and human walking toward a counter were studied.Results showed that the mutual effect of the wake and thermal plume caused contaminant dispersion and decreased the performance of the range hood as the human subject walked beside the counter.Even a standing person operated ahead the counter,the wake would affect the thermal plume in a certain extent.The decrement of capture efficiency approached 0.5 in the most unfavorable situation.Moreover,the coaction of the positive/negative pressure zone and impinging air jet drew the thermal plume to the human body.The fluctuation of capture efficiency in this condition was moderate relative to that for the human walking pattern beside the counter.This research could provide a comprehensive overview of different human walking patterns and their impact on residential kitchens and thereby facilitate the maintenance of kitchen air quality.

关键词： human walking overset mesh method dynamic simulation flow characteristics residential kitchen

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Investigation into gas lubrication performance of porous gas bearing considering velocity slip boundary condition

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Friction 2022年第6期10卷 891-910页

作者： Xiangbo ZHANG Shuiting DING Farong DU Fenzhu JI Zheng XU Jiang LIU Qi ZHANG Yu ZHOU School of Energy and Power Engineering Beihang UniversityBeijing 100191China Aircraft/Engine Integrated System Safety Beijing Key Laboratory Beihang UniversityBeijing 100191China Research Institute of Aero-Engine Beihang UniversityBeijing 100191China School of Transportation Science and Engineering Beihang UniversityBeijing 100191China

Porous gas bearings(PGBs)have a proactive application in aerospace and turbomachinery.This study investigates the gas lubrication performance of a PGB with the condition of velocity slip boundary(VSB)owing to the high Knudsen number in the gas film.The Darcy-Forchheimer laws and modified Navier-Stokes equations were adopted to describe the gas flow in the porous layer and gas film region,respectively.An improved bearing experimental platform was established to verify the accuracy of the derived theory and the reliability of the numerical analysis.The effects of various parameters on the pressure distribution,flow cycle,load capacity,mass flow rate,and velocity profile are demonstrated and discussed.The results show that the gas can flow in both directions,from the porous layer to the gas film region,or in reverse.The load capacity of the PGB increases with an increase in speed and inlet pressure and decreases with an increase in permeability.The mass flow rate increases as the inlet pressure and permeability increase.Furthermore,the simulation results using VSB are in agreement with the experimental results,with an average error of 3.4%,which indicates that the model using VSB achieves a high accuracy.The simulation results ignoring the VSB overrate the load capacity by 16.42%and undervalue the mass flow rate by 11.29%.This study may aid in understanding the gas lubrication mechanism in PGBs and the development of novel gas lubricants.

关键词： porous gas bearing(PGB) velocity slip boundary(VSB) numerical simulation gas lubrication flow characteristics

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Migration characteristics and profile control capabilities of preformed particle gel in porous media

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Petroleum 2022年第4期8卷 483-498页

作者： Nanjun Lai Shufang Chen Lei Tang Yuaojie Huang Hongwei Xu School of Chemistry and Chemical Engineering Southwest Petroleum UniversityChengdu610500China

Inspired by the viscoelastic displacement theory,a product called preformed particle gel(PPG)is developed as conformance control agent to enhance oil recovery and control excess water production.The migration law of PPG suspension in porous media is related to its deep profile control and displacement capability.Laboratory experiments indicate that PPG suspension has good viscosity increasing,and the apparent viscosity decreases with the increase of shear rate.PPG suspension is mainly elastic,and its network structure makes it have certain shear stability.PPG particles realize migration in porous media in the way of“accumulation and blockage/pressure increase/deformation and migration”.When the ratio of the PPG particle size to the pore throat diameter d ranges from 35.52 to 53.38,the particles can match through the porous medium.When the permeability difference of the parallel model is 5,PPG suspension has the highest profile improvement rate,69.10%.PPG suspension can adjust the planar heterogeneity,and increase the oil recovery rate by 20.75%.The PPG suspension can effectively start“cluster"、“film”and“blind end residual oil”,and has a high oil washing efficiency.The core NMR T2 spectrum shows that PPG suspension mainly reduces oil saturation in mesopores and macropores.After PPG flooding,the EOR capacity of small pores is the highest,39.11%.

关键词： Preformed particle gel(PPG) Migration law Profile control flow characteristics Microscopic oil displacement

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CFD Analysis of Fluid-Dynamic and Heat Transfer Effects Generated by a Fixed Electricity Transmission Line Interacting with an External Wind

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Fluid Dynamics & Materials Processing 2022年第2期18卷 329-344页

作者： Yajuan Jia Lisha Shang Jiangping Nan Guangping Hu Zhigang Fang Xi’an Traffic Engineering Institute Xi’anChina Xi’an Yuanai Electronic Technology Co. Ltd.Xi’anChina School of Automotive Engineering Wuhan University of TechnologyWuhanChina Hubei Key Laboratory of Advanced Technology of Automotive Components Wuhan University of TechnologyWuhanChina

The flow past a fixed single transmission conductor and the related heat transfer characteristics are investigated using computational fluid dynamics and a relevant turbulence model.After validating the method through comparison with relevant results in the literature,this thermofluid-dynamic problem is addressed considering different working conditions.It is shown that the resistance coefficient depends on the Reynolds number.As expected,the Nusselt number is also affected by Reynolds number.In particular,the Nusselt number under constant heat flux is always greater than that under a constant wall temperature.

关键词： flow characteristics heat transfer characteristics fluid mechanics Reynolds number

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CFD-Based Evaluation of flowand Temperature characteristics of Airflow in an Aircraft Cockpit

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Computer Modeling in Engineering & Sciences 2022年第2期130卷 701-721页

作者： Xiaosai Duan Suihuai Yu Jianjie Chu Dengkai Chen Zhaojing Su Key Laboratory of Industrial Design and Ergonomics Ministry of Industry and Information TechnologyNorthwestern Polytechnical UniversityXi’an710072China

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.

关键词： Aircraft cockpit airflow distribution flow characteristics temperature characteristics inhomogeneous behaviors

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Development of a static test apparatus for evaluating the performance of three PM2.5 separators commonly used in China

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Journal of Environmental Sciences 2020年第1期32卷 238-249页

作者： Peng Du Jianguo Liu Huaqiao Gui Jiaoshi Zhang Tongzhu Yu Jie Wang Yin Cheng Yihuai Lu Yawei Yao Qiang Fu ChihChieh Chen Key Laboratory of Environmental Optics and Technology AnhuiInstitute of Optics and Fine MechanicsChinese Academy of SciencesHefei 230031China University of Chinese Academy of Sciences Beijing 100049China Center for Excellence in Regional Atmospheric Environment Institute of Urban EnvironmentChinese Academy cf SciencesXiamen 361021China China National Environment Monitoring Centre Beijing 100012China Institute of Occupational Medicine and Industrial Hygiene "National"Taituan UniversityChinese TaipeiTaiiuan

PM2.5 separator directly affects the accuracy of PM2.5 sampling.The specification testing and evaluation for PM2.5 separator is particularly important,especially under China’s wide variation of terrain and climate.In this study,first a static test apparatus based on polydisperse aerosol was established and calibrated to evaluate the performance of the PM2.5 separators.A uniform mixing chamber was developed to make particles mix completely.The aerosol concentration relative standard deviations of three test points at the same horizontal chamber position were less than 0.57%,and the particle size distribution obeyed logarithmic normal distribution with an R2 of 0.996.The flow rate deviation between the measurement and the set point flow rate agreed to within±1.0%in the range of-40 to 50℃.Secondly,the separation,flow and loading characteristics of three cyclone separators(VSCC-A,SCC-A and SCC112)were evaluated using this system.The results showed that the 50%cutoff sizes(D50)of the three cyclones were 2.48,2.47 and 2.44μm when worked at the manufacturer’s recommended flow rates,respectively.The geometric standard deviation(GSD)of the capture efficiency of VSCCA was 1.23,showed a slightly sharper than SCC-A(GSD=1.27),while the SCC112 did not meet the relevant indicator(GSD=1.2±0.1)with a GSD=1.44.The flow rate and loading test had a great effect on D50,while the GSD remained almost the same as before.In addition,the maintenance frequency under different air pollution conditions of the cyclones was summarized according to the loading test.

关键词： PM2.5 separator Performance assessment Separation characteristics flow characteristics Loading test

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Simulation of the load rejection transient process of a francis turbine by using a 1-D-3-D coupling approach

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Journal of Hydrodynamics 2014年第5期26卷 715-724页

作者：张晓曦程永光杨建东夏林生赖旭 State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University

This paper presents the simulation and the analysis of the transient process of a Francis turbine during the load rejection by employing a one-dimensional and three-dimensional （1-D-3-D） coupling approach. The coupling is realized by partly overlapping the I-D and 3-D parts, the water hammer wave is modeled by defining the pressure dependent density, and the guide vane closure is treated by a dynamic mesh method. To verify the results of the coupling approach, the transient parameters for both typical models and a real power station are compared with the data obtained by the 1-D approach, and good agreements are found. To investigate the differences between the transient and steady states at the corresponding operating parameters, the flow characteristics inside a turbine of the real power station are simulated by both transient and steady methods, and the results are analyzed in details. Our analysis suggests that there are just a little differences in the turbine outer characteristics, thus the traditional 1-D method is in general acceptable. However, the flow patterns in the spiral casing, the draft tube, and the runner passages are quite different： the transient situation has obvious water hammer waves, the water inertia, and some other effects. These may be crucial for the draft tube pul- sation and need further studies.

关键词： Francis turbine hydraulic transients CFD simulation flow characteristics

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Investigation of hypersonic flows through a cavity with sweepback angle in near space using the DSMC method

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Chinese Physics B 2021年第7期30卷 311-323页

作者：郭广明陈浩朱林边义祥 College of Mechanical Engineering Yangzhou UniversityYangzhou 225127China

Near space has been paid more and more attentionin recent years due to its military application value.However,flow characteristics of some fundamental configurations(e.g.,the cavity)in near space have rarely been investigated due to rarefied gas effects,which make the numerical simulation methods based on continuous flow hypothesis lose validity.In this work,the direct simulation Monte Carlo(DSMC),one of the most successful particle simulation methods in treating rarefied gas dynamics,is employed to explore flow characteristics of a hypersonic cavity with sweepback angle in near space by considering a variety of cases,such as the cavity at a wide range of altitudes 20-60 km,the cavity at freestream Mach numbers of 6-20,and the cavity with a sweepback angle of 30°-90°.By analyzing the simulation results,flow characteristics are obtained and meanwhile some interesting phenomena are also found.The primary recirculation region,which occupies the most area of the cavity,causes pressure and temperature stratification due to rotational motion of fluid inside it,whereas the pressure and temperature in the secondary recirculation region,which is a small vortex and locates at the lower left corner of the cavity,change slightly due to low-speed movement of fluid inside it.With the increase of altitude,both the primary and secondary recirculation regions contract greatly and it causes them to separate.A notable finding is that rotation direction of the secondary recirculation region would be reversed at a higher altitude.The overall effect of increasing the Mach number is that the velocity,pressure,and temperature within the cavity increase uniformly.The maximum pressure nearby the trailing edge of the cavity decreases rapidly as the sweepback angle increases,whereas the influence of sweepback angle on velocity distribution and maximum temperature within the cavity is slight.

关键词： flow characteristics cavity with sweepback angle hypersonic flow near space DSMC

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Experimental investigation of hypersonic flight-duplicated shock tunnel characteristics

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Acta Mechanica Sinica 2021年第3期37卷 422-433,I0002页

作者： C K.Yuan Z.L.Jiang Institute of Mechanics Chinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100190China

Hypersonic air-breathing propulsion is one of the key techniques for future aviation and the ground aerodynamic testing for full scale test models with sufficient test time at flight conditions is of fundamental importance for verifying hypersonic air-breathing engines.Based on the backward detonation-driven concept,the hypersonic flight-duplicated shock tunnel(or JF-12 shock tunnel)has been successfully constructed and calibrated.This facility is capable of reproducing airflow for Mach numbers ranging from 5 to 9 at an altitude of 25-50 km,with a test duration of more than 100 ms.To quantify the performance of the shock tunnel,experiments were conducted to investigate the aerodynamic characteristics of the test flows and the effects of several critical techniques that play important roles in the operation of the shock tunnel.The stagnation pressure was constant within士5%and the average stagnation pressure varied by less than 0.048%/ms.The variation of the stagnation pressure in repeated experiments is less than 2.0%,indicating the good repeatability of the wind tunnel.The non-uniformity of the Mach number in the core flow field at the nozzle exit was within士2.5%.Additional,a uniform flow field is established upstream of the nozzle exit.The axial gradients of the flow field are small since the Mach number varies less than 1.7%/m.Findings regarding the ignition technology,diaphragm ruptures,detonation driver capacity,incident shock-wave decay,and tunnel operation mode are also presented.The findings of this study are not only helpful for operating the shock tunnel,but can also assist the future development of hypersonic wind tunnels.

关键词： Hypersonics Shock tunnels flow characteristics

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Numerical investigation on flow mechanism in a supersonic fluidic oscillator

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Chinese Journal of Aeronautics 2021年第5期34卷 214-223页

作者： Yongjun SANG Yong SHAN Jingzhou ZHANG Xiaoming TAN Yuanwei LYU College of Energy and Power Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China

A type of supersonic fluidic oscillator is proposed and its ability to generate pulsating supersonic jet is proved in this paper.Unsteady two-dimensional numerical simulations reveal that the fluid transforms from subsonic to supersonic condition in the mixing chamber of oscillator after the supplied flow pressure increases from 1.1×105 Pa to 5.0×105 Pa.When the supersonic flow is formed inside the oscillator,the wall-attached flow represents expansion wave and compression wave alternately.The oscillating frequency will saturate to a certain value with the increase of supplied pressure.Examination of the internal fluid dynamics indicates that the flow direction inside the FeedBack Channel(FBC)is related to the change of the local pressure at the inlet and the outlet of the feedback channel.The vortices produced in the mixing chamber present different distribution characteristics with the change of the fluid’s direction in the FBC.The sweeping jet is divided into two jets with varying flow rate over time by the splitter.In the end of two channels,two jets are accelerated above sound speed by convergent-divergent nozzle.Therefore,pulsating supersonic jets are produced at two outlets for this type of fluidic oscillator.

关键词： Convergent-divergent nozzle Feedback channel flow characteristics Supersonic flow Supersonic fluidic oscillator

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