We present results on the computational fluid dynamics (CFD) numerical simulations as well as the wind tunnel experiments for the observation facilities of the University of Tokyo Atacama Observatory 6.5m Telescope being constructed at the summit of Co. Chajnantor in northern Chile. Main purpose of this study starting with the baseline design reported in 2014 is to analyze topographic effect on the wind behavior, and to evaluate the wind pressure, the air turbulence, and the air change (ventilation) efficiency in the enclosure. The wind velocity is found to be accelerated by a factor of ~ 1.2 to reach the summit (78 m sec-1 expected at a maximum), and the resulting wind pressure (3,750 N m-2) is used for the framework design of the facilities. The CFD data reveals that the open space below the floor of the facilities works efficiently to drift away the air turbulence near the ground level which could significantly affect the dome seeing. From comparisons of the wind velocity field obtained from the CFD simulation for three configurations of the ventilation windows, we find that the windows at a level of the telescope secondary mirror have less efficiency of the air change than those at lower levels. Considering the construction and maintenance costs, and operation procedures, we finally decide to allocate 13 windows at a level of the observing floor, 12 at a level of the primary mirror, and 2 at the level of the secondary mirror. The opening area by those windows accounts for about 14% of the total interior surface of the enclosure. Typical air change rate of 20-30 per hour is expected at the wind velocity of 1 m sec-1.