| Natural ventilation is a passive building technology,which can reduce the energy consumption for mechanical cooling of indoor environment,improve the indoor thermal environment and promote indoor air quality.Therefore,based on the requirements of energy conservation,environmental protection,health and comfort,natural ventilation technology has been paid attention to by researchers again.In the single-sided ventilation problem,when there are multiple openings on the leeward of the building,a form of pumping flow may occur,and the indoor airflow direction will change periodically.Taking the building with two openings on the leeward side as the analysis object,this paper makes a qualitative and quantitative analysis of the pumping flow driven by wind and wind coupling with stack.Firstly,this paper expounds on the research status of natural ventilation all domestic and overseas,carries out literature clustering analysis through a visualization software Cite Space based on bibliometrics,to excavate the research hotspots of unsteady natural ventilation,at the same time,summarizes the calculation models of unsteady natural ventilation driven by different forces.Secondly,based on the introduction of numerical simulation theory,this paper completes the establishment of the physical model,meshing and independence verification,FLUENT parameter setting,experimental and simulation verification of turbulence model and so on.Comparing the steady-state and unsteady-state calculation results,it is found that for the periodic flow,the steady-state calculation underestimates the calculated value of flow rate,and the unsteady-state calculation method can better capture the microstructure in the flow.The periodic change of the flow field of the pumping flow under the unsteady state calculation is in good agreement with the existing experimental results.The building wake vortices are generated and fall off alternately,which drives the outdoor airflow in and out of the opening in turn,and the indoor airflow direction changes periodically.Then,pumping ventilation of single-zone and multi-zone buildings induced by wind is simulated and analyzed.For single-zone buildings,the characteristics of airflow shedding frequency around buildings are analyzed.It is found that this property can be expressed by Ro number,which has a good linear relationship with Re number and is directly proportional to the shedding frequency.The indoor flow oscillation frequency is consistent with the flow shedding frequency around buildings,which increases with the increase of wind speed.By fitting the simulation data,the calculation formula of pumping ventilation rate of single-zone buildings and the formula related to the opening separation are derived;For rooms at different locations in multi-zone buildings,it is found that the flow rate of rooms in the middle of the building is greater than that of side rooms,and the flow rate in any location of the multi-zone buildings is greater than that that in the single-zone buildings.Finally,the variation of indoor flow field,temperature distribution and ventilation rate are simulated and analyzed for the pumping ventilation driven by wind and stack.It reveals that the ventilation rate caused by wind and stack is less than that driven by wind alone,and the value can be estimated by De GIDS and Phaff model.Compared with t the wind-driven alone,the oscillation frequency of indoor air also decreased,but the change of heat source parameters did not affect the frequency characteristics.The research conclusion of this paper has a certain guiding significance for the design and evaluation of natural ventilation. |
