| For fire protection,security and privacy,natural ventilation through a single opening is common in the daily life and engineering applications.Firstly the research status of natural ventilation through a single opening at home and abroad was introduced,and it was pointed out that the uncertainty and complexity of airflow in natural ventilation through a single opening brought about the difficulties of research.Theoretical deductive,experimental and numerical simulation methods were all used to research natural ventilation through a single opening.Both small opening and large opening were considered,mainly from four aspects of the opening,building,heat source and meteorological parameters,The influence of 10 parameters on natural ventilation through a single opening,such as the width and height of opening,ground height of opening,wall thickness,building depth,ground height of heat source,heat intensity,difference of indoor and outdoor temperature,the speed and direction of outdoor wind,were the main focus of the research,and characteristics of natural ventilation through a single opening were more fully analyzed and researched.A model was deduced for the calculation of natural ventilation,and according to the flow and heat transfer mechanism of natural ventilation through a single opening,two new types of windows were designed,made and installed,and compared the effect of natural ventilation with side-hung window and sliding window of these two common types of windows.The definition and physical model of natural ventilation through a single opening was first introduced,then characteristics of natural ventilation through a single small opening and a single large opening were both analyzed.According to the difference of flow characteristics between small opening and large opening,firstly opening needed to be judged small or large opening in the design and calculation of natural ventilation through a single opening,then calculation model of corresponding single openings was used.Three calculation models of natural ventilation through a single opening forced respectively by thermal pressure,wind pressure and both of them were introduced.On the basis of previous studies,according to the principles of natural ventilation through a single small opening and a single large opening,reasonable assumptions were set to simplify their physical models,the two-dimensional calculation models of natural ventilation through a single opening were deduced and built.Especially for complex natural ventilation through a single large opening,two new models were proposed: "the control volume model with opening boundary" and "the pipe flow model with outdoor space boundary",and characteristics,usage and working condition of these two models were analyzed,which provided a theoretical basis for experimental and numerical simulation of the following chapters.Based on "the control volume model with opening boundary",spot test and CFD numerical study were carried out to research on the characteristics of natural ventilation through a single opening.Through the experimental study,the width of opening and the difference between indoor and outdoor temperature were mainly analyzed,and a simple calculation formula of natural ventilation through a single opening on the experimental conditions was deduced.Entered on the four aspects of the opening,building,heat source and meteorological parameters,according to the basic data in engineering practice,10 parameters,such as the width and height of opening,ground height of opening,wall thickness,building depth,ground height of heat source,heat intensity,difference of indoor and outdoor temperature,the speed and direction of outdoor wind,were changed respectively,and they were all simulated and calculated.Temperature fields,pressure fields and streamlines were analyzed and compared on all conditions,and the flow and heat transfer mechanisms of natural ventilation through a single opening were illustrated.Natural ventilation rates were calculated,compared and analyzed to get the influence of above 10 changed parameters on natural ventilation through a single opening.Due to little indoor wind speed with a single opening,it was proposed that according to the indoor air velocity the chamber was divided into two regions: "the breeze region" and "the calm region",indoor air velocity on different working conditions were analyzed and compared.The new concept of "effective ventilation depth" was put forward,and carries on the definition.Focus on the analysis of six parameters,such as the width and height of opening,ground height of opening,wall thickness,the speed and direction of outdoor wind,their effects on "effective ventilation depth" were analyzed.Combined the influence law of the above parameters,the formula for calculating the effective ventilation depth was derived.Comprehensive experimental and simulated data and research results,according to the development and changes of eddies in streamlines on every condition,the temperature and pressure distribution,as well as the influence of every changed parameter on natural ventilation rates,indoor partition,the effective ventilation depth,the judgment condition of large opening and small opening was specific proposed.Based on "the pipe flow model with outdoor space boundary" in the study,"the pipe flow model with computational region boundary" was established in numerical simulation.It was proposed that the building with a single opening was considered as a whole with local resistance component,and the difference between the inlet and outlet total pressure in the model without building was the on-way resistance of pipe flow with a single opening,the local resistance was concentrated on the building with a single opening.The formula for calculating the Coefficient of local resistance was derived and used to calculate on various working conditions.It was found that for the width and height of opening,ground height of opening,wall thickness,ground height of heat source,heat intensity,difference of indoor and outdoor temperature,the speed of outdoor wind,there were little influence on the Coefficient of local resistance,while building depth and the direction of outdoor wind greatly influenced on the Coefficient of local resistance.Finally,according to experimental and simulated results of natural ventilation through a single opening,taking the improvement of the opening device into consideration,two new types of windows were designed,made and installed: "a dual level ‘up-down folio' window" and "a multi-sash mid-pivoted window with vertical deflectors".By spot tests and CFD,compared two new types of windows with the traditional side-hung window and sliding window,the effect of natural ventilation were analyzed.The results showed that the two types of windows took better effects on natural ventilation than the two types of traditional windows,especially to improve the sensitivity of the wind direction for the two types of traditional windows,and there was stronger adaptability to the outdoor wind direction.The study also found that it was necessary to set a horizontal splitter plate in "the dual level ‘up-down folio' window" and a vertical guide plate diversion baffle in "the multi-sash mid-pivoted window with vertical deflectors".By numerical simulation,the relevant suggestions and opinions to different outdoor wind direction were given in the practical application of the two new types of windows,which provided guidance for the design and application of the two new types of windows. |
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