Study On The Influence Of The Cave Doors Of Dunhuang Mogao Grottoes On The Thermal And Humid Environment In The Grottoes

Mogao Grottoes are located 25 kilometers southeast of Dunhuang City,with a length of more than 1600 meters from north to south.There are 492 existing grottoes with murals and statues,which are the largest Buddhist art sites.Mogao Grottoes are carved on the cliff body,and the direction of the depth of the grottoes is east-west.The three sides of the grottoes are connected with the cliff body.Only in the east side is the cave doors adjacent to the atmosphere outside the grottoes,and the grottoes are all in the form of one side openings.The cave door is the only way of air exchange inside and outside the grottoes.The cave doors play an important role in regulating the changes of the thermal and humid environment inside the grottoes.There is a direct relationship between the thermal and humid environment in the grottoes and the diseases of the murals in the grottoes.Therefore,it is of great significance to study the influence of cave door on the thermal and humid environment in the grottoes.First of all,this paper systematically studies the basic situation of the cave doors,introduces in detail the different classification forms of the existing cave doors,the dimensional drawings of the common types of the cave doors and the functions of the cave doors.This paper analyzes the influence factors of the cave door on the hot and humid environment in the grottoes,and expounds the principle of the influence of the cave doors on the thermal and humid environment in the grottoes from three aspects of heat transfer coefficient,natural ventilation and air infiltration.In the field investigation and test,the cave 206 and cave 209 with different door materials and air tightness were selected.In autumn and winter,the thermal and humidity environment parameters inside and outside the two cave were tested on site.Through the analysis of the test data,the change rule of temperature and humidity inside the two cave and the fluctuation degree of temperature and humidity inside the cave were studied under the effect of the atmospheric environment outside the cave.The results show that the temperature and humidity in the caves with aluminum alloy doors fluctuate greatly.Then take the cave 206 with aluminum alloy doors as the research object,after verifying the validity of CFD simulation method in predicting the thermal environment of Mogao Grottoes.Fluent software is used to simulate the influence of the atmosphere outside the cave on the distribution and depth of the thermal environment inside the cave 206 under the action of heat pressure and the action of heat wind pressure when the cave doors are opened and closed.Furthermore,the influence of the atmosphere outside the cave on the effective depth of the temperature inside the cave is compared when the area of the shutters changes.Finally,according to the test and simulation results,aiming at the stability of the thermal and humidity environment in the cave,combined with the reasons of the great fluctuation of the temperature and humidity in the cave with aluminum alloy doors,the optimization measures of the aluminum alloy doors are studied,and some suggestions are put forward in the aspects of the selection of the outer surface color,the size of the heat transfer coefficient,the setting of the ventilation louvers,and the treatment of the door seams.It is hoped that these measures can provide some reference and basis for the optimization of grottoes.