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Numerical investigation of the cavitation noise around a marine propeller focusing on the influence of Ventilation

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Journal of Hydrodynamics 2023年第4期35卷 630-648页

作者： Shu-jian Lyu Bin Ji Xin-cheng Wang Zhi-wen Zhan Da-hai Zhang State Key Laboratory of Water Resources Engineering and Management Wuhan UniversityWuhan430072China China Ship Development and Design Center National key laboratory on ship Vibration and NoiseWuhan430064China

Cavitation noise around propellers has many adverse effects.It is still very limited nowadays to inhibit propeller cavitation noise in engineering.In this study,the cavitation noise around a PPTC propeller is simulated using the large eddy simulation(LES)coupled with the porous Ffowcs Williams-Hawkings(PFW-H)equation.The investigation aims to find a strategy to suppress cavitation noise and analyze the noise suppression mechanism.The predicted hydrodynamic results agree well with the experimental data and are utilized in the hydroacoustic analysis.The hydroacoustic results indicate that the pseudo-thickness noise dominates the dominant frequency component of the total cavitation noise due to the effect of cavity evolution,which is one of the reasons why the pseudo-thickness noise dominates the total cavitation noise.A method is found to weaken the cavitation noise through Ventilation at the generation location of the sheet cavity(SC).It is worth noting that Ventilation inhibits the generation and development of SC by changing the pressure distribution on the suction surface of the blade and pushing away the cavities around the Ventilation holes.Moreover,cavity evolution noise dominates the fluid volume evolution noise under the ventilated cavitating condition.Ventilation significantly attenuates the vapor volume pulsation and thus the cavity evolution noise,which leads to a reduction in pseudo-thickness noise and total cavitation noise.The Ventilation mainly reduces noises at the dominant frequency of the pseudo-thickness noise and the total cavitation noise.

关键词： Cavitation noise Ventilation porous Ffowcs Williams-Hawkings(PFW-H)equation large eddy simulation(LES) PPTC propeller

An improved wall-mounted displacement Ventilation system in a large-span machining workshop

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Building Simulation 2022年第11期15卷 1943-1953页

作者： Fei Liu Tengfei(Tim)Zhang Liqiang Yang Zhengwei Long Tianjin Key Laboratory of Indoor Air Environmental Quality Control School of Environmental Science and EngineeringTianjin University92 Weijin RoadTianjin 300072China School of Civil Engineering Dalian University of Technology(DUT)2 Linggong RoadDalian 116024China Tianjin Fengjin Auto Parts Co. Ltd.8 1 Xianfeng East RoadTianjin 300310China

A machining workshop requires Ventilation that removes oil mist particles efficiently and conditions air to a comfortable temperature.Displacement Ventilation has been reported to be highly efficient in removing airborne pollutants in a workshop.However,the traditional wall-mounted displacement Ventilation system may be inadequate for delivering conditioned,clean air to the internal zone of a large-span workshop.This investigation proposed an improved wall-mounted displacement Ventilation system in which machining equipment is elevated,relay fans are operated in corridors in the cooling season,and ceiling air exhausts are lowered.The proposed Ventilation system was compared with the traditional wall-mounted displacement Ventilation system and a displacement Ventilation system with multiple local diffusers in the corridors,separately.A validated computational fluid dynamics(CFD)software program was used to investigate the three Ventilation systems in both the cooling and heating seasons.The airflow,oil mist particle concentration,and air temperature under the three Ventilation systems were evaluated.The results revealed that the traditional wall-mounted displacement Ventilation system is inappropriate for use in a large-span workshop,particularly in the cooling season.The proposed improved wall-mounted displacement Ventilation provided the lowest oil mist particle concentration in the breathing zone and an appropriate air temperature in the occupied zone in both the cooling and heating seasons.Notably in the cooling season,the proposed system reduced the oil mist particle concentration by 48.5%in the breathing zone as compared with the traditional system.Such an improved Ventilation system is highly recommended for use in large-span workshops.

关键词： Ventilation workshop oil mist particle temperature CFD

On the optimisation of age of the air in the breathing zone of floor heating systems:The role of Ventilation design

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Energy and Built Environment

Energy and Built Environment 2024年第1期5卷 130-142页

作者： Aminhossein Jahanbin Giovanni Semprini Department of Industrial Engineering(DIN) Alma Mater Studiorum-University of BolognaViale Risorgimento 240136 BolognaItaly CIRI-Centro Interdipartimentale di Ricerca Industriale Edilizia e Costruzioni Alma Mater Studiorum-University of BolognaVia del Lazzaretto 15/540131 BolognaItaly

For a mechanically ventilated space,the nominal age of the air can be obtained by the reciprocal of the air change rate.However,values of the local mean age of the air in practice may differ to some extent from the nominal one since the nominal time constant employs as reference the theoretical optimum model.This discrepancy could become more prominent in spaces conditioning with both Ventilation and heating system where the indoor air pattern is affected by turbulent mixed convection flow.Given importance of knowledge on the distribution of age of the air in these spaces,the present study provides insights on how Ventilation design in floor heating systems can optimise the delivery of fresh air into the breathing zone.In this context,by establishing a computational fluid dynamic(CFD)model validated against experimental data,the local mean age of the air as well as the indoor air quality(IAQ)indices in the breathing zone of the floor heating system are examined under different Ventilation modes.Six different Ventilation scenarios are regarded in order to find the optimal Ventilation design in terms of the delivery of the fresh air and Ventilation effectiveness in occupied space.Furthermore,the integrated effects of the floor temperature and inlet supply temperature along with the Ventilation design on the distribution of local age of the air are addressed.The obtained results indicate that the up-supply Ventilation strategy is more efficient than down-supply one in the Ventilation effectiveness and delivery of fresh air into the breathing zone.Moreover,it is shown that the mean age of the air in the breathing zone of the up-supply Ventilation increases with increment of the Ri(Richardson number),whereas an increase in Ri improves the delivery of fresh air in down-supply mode.For a given floor temperature,the similar trend is also observed in the variation of age of the air with the characteristic temperature of supply inlet,namely the temperature difference between inlet supply and surrounding walls.

关键词： Age of the air Indoor air quality Ventilation Floor heating CFD

Prevention of surgical site infection under different Ventilation systems in operating room environment

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Frontiers of Environmental Science & Engineering 2021年第3期15卷 63-76页

作者： Zhijian Liu Haiyang Liu Hang Yin Rui Rong Guoqing Cao Qihong Deng Department of Power Engineering North China Electric Power UniversityBaoding 071003China Department of Civil Engineering Technical University of DenmarkCopenhagenDK-2800 KgsDenmark Institute of Building Environment and Energy China Academy of Building ResearchBeijing 100013China School of Energy Science and Engineering Central South UniversityChangsha 410083China

Biological particles in the operating room(OR)air environment can cause surgical site infections(SSIs).Various Ventilation systems have been employed in ORs to ensure an ultraclean environment.However,the effect of different Ventilation systems on the control of bacteria-carrying particles(BCPs)released from the surgical staff during surgery is unclear.In this study,the performance of four different Ventilation systems(vertical laminar airflow Ventilation(VLAF),horizontal laminar airflow Ventilation(HLAP),differential vertical airflow Ventilation(DVAF),and temperature-controlled airflow Ventilation(TAF))used in an OR was evaluated and compared based on the spatial BCP concentration.The airflow field in the OR was solved by the Renormalization Group(RNG)k-e turbulence model,and the BCP phase was calculated by Lagrangian particle tracking(LPT)and the discrete random walk(DRW)model.It was found that the TAF system was the most effective Ventilation system among the four Ventilation systems for ensuring air cleanliness in the operating area.This study also indicated that air cleanliness in the operating area depended not only on the airflow rate of the Ventilation system but also on the airflow distribution,which was greatly affected by obstacles such as surgical lamps and surgical staff.

关键词： Operating room(OR) Bacteria-carrying particles(BCPs) Surgical site infections(SSIs) Ventilation

Evaluating the impact of auxiliary fan practices on localised subsurface Ventilation

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International Journal of Mining Science and Technology 2019年第6期29卷 933-941页

作者： David J.de Villiers Marc J.Mathews Philip Maré Marius Kleingeld Deon Arndt Centre for Research and Continued Engineering Development North-West University

Mines are continually expanding in size and depth,leading to an increased reliance on localised subsurface Ventilation systems.The use of underground auxiliary fans is a favoured method to increase and control airflow in working areas.However,the effectiveness of auxiliary fans in this regard is not clear.This paper evaluated the performance of these underground fan systems in four different South African deeplevel gold mines.A total auxiliary fan system efficiency of 5%was found across six systems,with the average fan efficiency of 33 fans at 38%.The results showed that these fans deviate significantly from their design operating points.Therefore,there are significant shortcomings in current underground fan practices.Our detailed investigations led to the conclusion that the assemblage of underground auxiliary fan systems results in significant energy inefficiencies.Therefore,maintaining good underground fan practice such as optimal fan selection,ducting design and maintenance is crucial for the efficacy of a mine Ventilation network.

关键词： Mine Ventilation Underground fan assemblage Fan system performance

Spatial-temporal variation features and law of gas concentration in the fully mechanized working face under the condition of intermittent Ventilation

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International Journal of Mining Science and Technology 2019年第6期29卷 963-969页

作者： Yinpin Cao Yimin Li Zhongning Zhou School of Electrical and Power Engineering China University of Mining & Technology

Based on the fluid mechanics and mass transfer theory,a mathematical model of the spatial-temporal variation of gas was derived to avoid the gas accident caused by the main fan stopping Ventilation under the condition of intermittent Ventilation in the tunnel.According to the actual parameters of the tunnel,a numerical calculation model was established.The spatial-temporal variation of gas concentration in the fully mechanized working face under the condition of intermittent Ventilation was calculated by using the commercial package Fluent,and the correctness of the calculated results was verified by the actual monitoring data of the mine.Firstly,the gas concentration was calculated under different wind velocities at driving face in coal tunnel,and the result showed that the gas can be carried effectively by the wind when the wind velocity is about 1.8 m/s.Secondly,the distributions of wind velocity and gas concentration at driving face were studied at 1.8 m/s,and the result showed the gas concentration increased gradually with the distance close to the outlet,but the gas concentration almost kept constant at the height of driving face.Thirdly,the distribution of gas concentration was investigated with time after the Ventilation was stopped and restarted,respectively.The gas concentration of test point gradually increased with the increment of downtime,when the downtime was 40 min,the gas concentration of test point 3 reached the maximum value.The gas concentration increased gradually and reached the maximum after10 min of restart,then sharply decreased and kept constant.

关键词： Fully mechanized working face Intermittent Ventilation Gas concentration

Influence of longwall gateroad convergence on the process of mine Ventilation network-model tests

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International Journal of Mining Science and Technology 2019年第4期29卷 585-590页

作者： Andrzej Walentek Tomasz Janoszek Stanis?aw Prusek Aleksander Wrana Department of Extraction Technologies Rockburst and Mining Support Central Mining Institute

Hard coal mines are required to constantly ventilate mine workings to ensure that the air composition is at a certain humidity and temperature level that is comfortable for underground mine workers,especially in deep deposits.All underground workings,which are part of the mine Ventilation network,should be ventilated in a way that allows maintaining proper oxygen concentration not lower than 19%(by volume),and limits concentration of gases in the air such as methane,carbon monoxide or carbon dioxide.The air flow in the mine Ventilation network may be disturbed due to the natural convergence(deformation)and lead to change in its original cross-section.Reducing the cross-sectional area of the mining excavation causes local resistances in the air flow and changes in aerodynamic potentials,which leads to emergency states in the mine Ventilation network.This paper presents the results of numerical simulations of the influence of gateroad convergence on the Ventilation process of a selected part of the mine Ventilation network.The gateroad convergence was modelled with the finite element software PHASE 2.The influence of changes in the cross-sectional area of the gateroad on the Ventilation process was carried out using the computational fluid dynamics software Ansys-Fluent.

关键词： Geomechanics Convergence Numerical modelling Ventilation process Support

A survey of Ventilation strategies during cardiopulmonary resuscitation

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World Journal of Emergency Medicine 2019年第4期10卷 222-227页

作者： Ye-cheng Liu Yan-meng Qi Hui Zhang Joseph Walline Hua-dong Zhu Department of Emergency Medicine Peking Union Medical College HospitalBeijingChina Accident and Emergency Medicine Academic Unit Prince of Wales HospitalThe Chinese University of Hong KongHong KongChina

BACKGROUND:Many controversies still exist regarding ventilator parameters during cardiopulmonary resuscitation(CPR).This study aimed to investigate the CPR Ventilation strategies currently being used among physicians in Chinese tertiary hospitals.METHODS:A survey was conducted among the cardiac arrest team physicians of 500 tertiary hospitals in China in August,2018.Surveyed data included physician and hospital information,and preferred Ventilation strategy during CPR.RESULTS:A total of 438(88%)hospitals completed the survey,including hospitals from all 31 Chinese mainland provinces.About 41.1%of respondents chose delayed or no Ventilation during CPR,with delayed Ventilations all starting within 12 minutes.Of all the respondents who provided Ventilation,83.0%chose to strictly follow the 30:2 strategy,while 17.0%chose Ventilations concurrently with uninterrupted compressions.Only 38.3%respondents chose to intubate after initiating CPR,while 61.7%chose to intubate immediately when resuscitation began.During bagvalve-mask Ventilation,only 51.4%of respondents delivered a frequency of 10 breaths per minute.In terms of ventilator settings,the majority of respondents chose volume control(VC)mode(75.2%),tidal volume of 6–7 mL/kg(72.1%),PEEP of 0–5 cmH2O(69.9%),and an FiO2 of 100%(66.9%).However,62.0%of respondents had mistriggers after setting the ventilator,and 51.8%had high pressure alarms.CONCLUSION:There is a great amount of variability in CPR Ventilation strategies among cardiac arrest team physicians in Chinese tertiary hospitals.Guidelines are needed with specific recommendations on Ventilation during CPR.

关键词： Cardiopulmonary resuscitation Ventilation strategy Questionnaire survey Cardiac arrest team

High-Density Block Transformation to Increase Natural Ventilation Based on CFD Simulation

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Fluid Dynamics & Materials Processing 2021年第1期17卷 141-157页

作者： Siqi Liu Guanqi Huang Shaanxi Provincial Land Engineering Construction Group Co. Ltd.Xi’an710075China Institute of Land Engineering and Technology Shaanxi Provincial Land Engineering Construction Group Co.Ltd.Xi’an710075China Center for Housing Innovations Chinese University of Hong KongHong Kong Guangzhou Urban Planning&Design Survey Research Institute Guangzhou510060China

Many countries in the world have experienced extremely rapid urbanization during recent decades. The rapiddevelopment of densely populated areas has produced many urban environmental problems. This researchexplores the relationship between urban morphology and Ventilation conditions. Through 3D modeling andComputational Fluid Dynamics (CFD) simulation, we focus on the large scale Ventilation of an extended area withseveral buildings. As a testbed, in particular, the core part of Kwun Tong industrial park in Hong Kong is examined, and in order to validate the approach, 10 measurement points are used to get experimental values to be usedfor comparison (such points are located in different positions involving traffic road, pedestrian path and openspace). The error range (±0.7 m/s) indicates that the agreement between field measurement and CFD calculationis good. On the basis of design guidelines and earlier studies, the effective configuration (in terms of building) ofthis area is partially transformed (virtually, i.e., in the numerical simulations) in order to assess the ensuingchanges in terms of wind speed in different locations. This results in a general design and analysis methodologypotentially applicable to other areas.

关键词： CFD thermal comfort Ventilation open space