Study On The Natural Ventilation Characteristics Of Maiji Mountain Grottoes

Maiji Mountain grottoes are located in Maiji District,Tianshui City,Gansu Province.It has preserved 221 niches,10632 statues and 1300m~2 murals.It is one of the representative Grottoes in the Northern Dynasties and one of the largest Grottoes in China.Most of the caves are in the form of half open,only the south side is connected with the outside world through the cave gate,the other three sides are inside the mountain,can be regarded as a single-sided ventilation building Natural ventilation promotes the exchange of heat-mass inside and outside the cave,which is one of the reasons for the change of heat and humidity in the cave.According to the disease mechanism of Maijishan grottoes,frequent changes of thermal and humid environment are not conducive to the protection of cultural relics in the caves.Therefore,it is of great significance to study the natural ventilation of the cave to maintain the environmental stability of the cave and the protection of the cultural relics in the cave.Firstly,this paper systematically introduces the basic principle of building unilateral ventilation,and qualitatively analyzes the influence of temperature and humidity,natural wind,cave shape and cave opening on the natural ventilation of Maijishan grottoes.Combined with the particularity of cultural relics protection and evaluation index of natural ventilation of buildings,the evaluation index of natural ventilation in Maijishan Grottoes is put forward.In the field study,the small-medium-sized caves and large caves represented by cave126 and cave 30 were selected as the research objects.In the winter and summer,the air temperature and wind speed inside and outside the two caves were measured on the spot,providing first-hand data for the next simulation study.Through the comparative analysis of the measured data,the basic law of air exchange inside and outside the cave is summarized,which points out the direction for quantitative analysis in simulation study.In the simulation study,after verifying the validity of FLUENT to predict the wind environment inside the grottoes,the numerical simulation was carried out on the natural ventilation of cave 126 and cave 30 from the two sides of the cave external wind and cave gate form.The influence of the wind speed and wind direction outside the cave on the wind environment inside the two caves was analyzed.The differences of the wind environment in cave 126 and cave 30 were further compared among different cave gate forms.In order to reduce the disturbance of wind outside the grottoes,the optimal form of cave gate is selected.Finally,on the basis of the optimal shape of the cave door,the one-sided ventilation of the cave126 and cave 30 is calculated numerically from the position of the door frame and the width of the door frame.Comparing the results of the analysis and simulation,some suggestions are provided for the design of the door size of the cave in Maiji Mountain Grottoes,and it is hoped that these suggestions can provide some basis for environmental regulation and preventive protection in the cave.