Ventilation is one of the most vital measures to create a healthy and comfortable indoor environment, significantly influencing indoor air quality and building energy consumption. The conventional ...steady-state airflow field of a ventilated room, if not reasonably configured, is prone to cause air stagnation in certain regions, whereas the unsteady airflow improves the mixing effect, which favors the dispersion and purging of indoor air pollutants. This paper proposes a method to induce an unstable air flow field utilizing the spontaneous Karman vortex street effect on the air-supply jet and swinging modulation. The quasi-periodicity of the airflow field and its influence on the indoor pollutant purging effect were investigated. The effects of air velocity oscillation and pollutant concentration decay in a ventilated room were studied through experimental measurements and computational fluid dynamics analysis. The results show that the transverse oscillation jet has a dominant period of 1.6 s and the longitudinal oscillation jet has a dominant period of 2.987 s, and both jets have a width about twice that of the free jet. The airborne pollutant discharge efficiency of the oscillating jet was higher than that of the free jet at the occupancy level, and the longitudinal oscillating jet purged pollutants faster than the transverse oscillating jet. This study reveals that oscillating jets can provide an option to create periodic flow fields and improve the efficiency of ventilation.
•Oscillating jets show better efficiency than steady ventilation in purging pollutants.•The actively modulated swinging jet has more prominent periodicity than spontaneous one.•The longitudinal oscillating jet purged pollutants faster than the transverse oscillating jet.
Airplane cabin ventilation is essential to ensure passengers' well‐being. The conventional ventilation method is mixing ventilation with a statistically steady supply, which, according to former ...studies, has reached its limits regarding, for example, the ventilation efficiency. However, the effect of a statistically unsteady (time‐periodic) supply on the mixing ventilation efficiency has remained largely unexplored. This research uses computational fluid dynamics (CFD) with the large eddy simulation (LES) approach to study isothermal time‐periodic mixing ventilation in a section of a single‐aisle airplane cabin model, in which the air exhaled by the passengers functions as (passive) contaminants. Two time‐periodic supply strategies are evaluated. The induced time‐periodic airflow patterns promote an efficient delivery of fresh air to the passenger zone and affect the passengers' expiratory plumes. This results in increased mean contaminant mass fluxes, causing a strong reduction of the mean contaminant concentrations in the passenger zone (up to 23%) and an increased contaminant extraction from the cabin. Mean velocities increase with up to 55% but remain within the comfortable range. It is shown that the ventilation efficiency improves; that is, the contaminant removal effectiveness and air change efficiency (in the full cabin volume) increase with up to 20% and 7%, respectively.
A novel vortex ring personalized ventilation system (VRPV) is proposed for efficiently supplying fresh air to room occupants. A vortex ring generator with a piston‐cylinder is developed for an ...experimental study of the formation, transportation, and ventilation characteristics of the VRPV. The translational velocity, volume, and fresh air ratio of the vortex rings are studied using high‐speed cameras and tracer gas experiments. According to the results, the categories of the vortex ring volume in the formation stage are studied. It is observed that the velocity of the piston determines the initial translational velocity of the vortex ring, and a fitting equation is proposed to predict the evolution of the translational velocity. The deviation range of the VRPV over different distances is studied, and it is shown to be affected by interference from both the generator and the environment. Finally, the total volumes, fresh air volumes, and fresh air ratios of the VRPV are studied at different distances. The results indicate that, as a personalized ventilation system, the fresh air ratio of the VRPV is up to 159.3% higher than that of a symmetrical round jet within a 0‐4 m range. This shows the excellent application potential of the VRPV for providing high‐efficiency personalized ventilation with lower fresh airflow rates.
This study presents extensive experimental measurements in a modern Finnish ice rink arena including temperature, relative humidity, carbon dioxide, air speed, air flow and pressure difference ...measurements in addition to smoke tests. Furthermore, the air exchange rate (ACH), air-exchange efficiency, and mixing factor were calculated. The main aim was to determine ventilation effectiveness, vertical stratification of the air and how commonly re-circulation can be used in a modern ice rink arena representing common practice. Results show that re-circulation of return air was virtually continuous and in normal operating conditions the outdoor air fraction of the supply air was only 3.7% corresponding to ACH of 0.03 1/h. The ceiling distributed mixing ventilation was not able to mix the whole volume sufficiently, leading to two imperfectly mixed zones with an average air-exchange efficiency of 39% in the lower zone, corresponding to a mixing factor of 1.7.
This scientific article delves into the intricacies of wind flow's impact on multi-storey buildings, presenting results from a series of experimental investigations. The research encompasses an ...examination of wind interactions with buildings of varying heights and geometric profiles. Furthermore, it unveils the effects of tall structures on the natural ventilation and smoke evacuation systems of shorter edifices, considering different wind flow directions. The study leverages specialized wind tunnel and measurement techniques for a comprehensive analysis of wind-induced loads on buildings. The acquired insights furnish crucial input for the design of single-story temporary modular constructions within densely populated urban areas, subject to wind-induced stresses. Additionally, they hold potential applicability in the advancement of energy-efficient technologies and strategies within the realm of construction. The acquired dataset underscores the criticality of scrutinizing wind flow's impact on structures of varied typologies and dimensions and will allow to significantly improve the quality and efficiency of modern buildings in the future.
•Implementing LES to predict the flow and pollutant fields.•Detailed evaluation of the impact of opening shape on cross-ventilation.•Increasing the height to width ratio of openings leads to better ...ventilation performance.•The convective flux is the major one in pollutant transportation.
Natural ventilation, a useful mechanism to moderate the indoor temperature and to disperse pollutants, is a complex engineering problem to analyze due to a large number of influential factors such as wind direction, size, and location of openings, etc. The present paper investigates the effect of different shapes of openings, with a constant wall porosity, namely, horizontally long, squared and vertically long, on cross-ventilation in a generic isolated building. Flow and passive pollutant concentration fields are the performance indicators. The large eddy simulation (LES) approach together with the wall-adapting local eddy-viscosity (WALE) sub-grid scale (SGS) model is employed for the simulations. Validation results, based on available wind-tunnel measurements, of time-averaged velocity and pollutant concentration for the reference case are reported. Results display that the performance of cross-ventilation in reducing the pollutant concentration enhances as the height to width ratio of the openings increases and the building with horizontally long openings is the most contaminated case. The ventilation performance in the case of vertically long openings is shown to be the most effective one. Furthermore, present findings show that the participation of the turbulent diffusion flux in the passive pollutant transportation becomes smaller as the flow makes progress toward the downstream.
•The ventilation characteristics of the cabin of the Jack-up offshore platform were studied by establishing a scaled model.•The factors that affect the ventilation characteristics were analyzed ...through experiments.•This paper analyzes the influence of optimal shutdown choice, the position of the air outlet and the air volume on the temperature field of the engine room, which can provide a certain basis for related research
This paper aims to investigate the ventilation characteristics of a main cabin in a JU2000E jack-up offshore platform. A scaled model of the ventilation system was built based on the similarity theory, and the factors (such as the engine shutdown choice, the layout of the air outlets, and the supply air volume) that affect the ventilation characteristics were analyzed. The results showed that the reasonable choice of engine shutdown is able to reduce average temperature in certain locations of the engine room as well as decreasing the maximum temperature of the engine room. Suitable layout of the air outlets can accelerate the heat dissipation and reduce the temperature variance. When the air supply volume is 600 m3/h, it is the most economic to meet the heat dissipation requirement of the engine room. As a result, the findings provide important guidance for the ventilation system design of jack-up offshore platforms.
•Explores an urban form indicator associated with local outdoor ventilation potentials.•Provides a method for the correlation study between urban space form and regional spatial ventilation condition ...based on spatial partition.•Space partition method is an important factor that affects the degree of correlation between the SVF and ventilation index.•SVF could be an urban form parameter related to urban spatial ventilation for urban space.
Urban ventilation conditions, which are significantly influenced by urban space forms, are essential for healthy and livable urban environments. In urban design practice, morphological indicators related to urban ventilation could be improved for the effective assessment of ventilation quality and timely adjustment of the design. This study attempted to explore local spatial morphological indicators related to ventilation performance. Considering the sky view factor (SVF) as a quantitative parameter of urban local spaces, this study investigated the correlation between the SVF and outdoor ventilation performance. The SVF was calculated using single and multipoint methods, and a wind velocity ratio <V*> was adopted as the spatial ventilation performance indicator. In addition, local spaces were defined using three different partition methods (GSP1, GSP2, and CSP), as the urban space is continuous and complex. A typical urban centre space in Nanjing, China, was adopted as the research subject. The wind flows were calculated using the computational fluid dynamics (CFD) method for two wind directions. The results showed a positive correlation between the SVF and ventilation indices. Different partitioning methods had a considerable impact on the correlation, as the value of R2 between SVF and <V*> could reach around 0.3 in GSP1 and CSP but only 0.05 in GSP2.
▶ Ventilation is a key factor for controlling the climate inside greenhouses. ▶ Airflow pattern and climatic parameter distribution depend on the greenhouse design. ▶ The vent combination strongly ...impacts the ventilation characteristics. ▶ CFD offers a powerful tool to investigate the distributed climate.
Ventilation processes inside the greenhouse strongly affect air renewal and internal climatic conditions, which themselves interact with the growth and homogeneity of the crop. Natural ventilation is often chosen since it is the most economic method available.
Studies of internal distributed climate induced by ventilation have been taking place for the past 25 years. Experimental studies have pointed out the impact of vent configurations on airflow pattern, particularly when the wind is the main driving force. However, the development of computational fluid dynamics (CFDs) has only recently provided the opportunity to simulate the climate inside greenhouses for known vent configurations, and to test a wide range of geometries with different vent combinations under different climatic conditions.
In this article, the main factors governing air movements inside the greenhouse are first analysed. The characteristics of the laboratory scale models and field experiments are reviewed, with particular focus on the technologies implemented. The principles of CFD, the main modelling approach, together with its adaptations to greenhouse climate simulation, are then described in detail. Conclusions of studies concerning ventilation efficiency inside greenhouses are reviewed with respect to greenhouse geometry and opening arrangements. Other parameters affecting ventilation, such as wind speed and direction, the addition of insect-proof or shading screens, and interactions with the crop, are also discussed.
The purpose of ventilation management systems is to ensure the health and safety of underground workers by creating and incorporating structured plans, procedures and processes on the day-to-day ...operations of the mine ventilation system. The application of ventilation management programs consists of audit, verification, and corrective action procedures to：（1） ensure adherence to regulatory standards,or to（2） return to compliance and safety standards when an upset condition arises. This paper describes how a ventilation management program can be developed and implemented to ensure regulation compliance, to increase safety, to improve operational efficiency and to reduce the operating costs of an operating mine. Two case applications are presented in this paper. The first case is presented to demonstrate use of a ventilation management program in response to a site inspection and audit, with follow-up application of corrective actions. The second case application describes how air quality conditions has been substantially improved with the development and implementation of a ventilation management program for an operating underground hard rock mine.
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