Windmills of Sistan is known as the oldest type of windmills in Persia as well as the World, that has been built facing the 120-day winds of Sistan plains, usually seen singularly or plurally in suburbs of the Zabol city. This article would focus on physical analysis of singular windmills in Sistan. A literature review in history of windmills shows lack of laboratory simulation studies on the way these windmills used to function as well they may in the future. According to historical resources, this particular structure passes a physical evolution in utilizing wind energy in a sustainable manner. Evolution through of time and constructional trials and errors, has deployed architectural components and structural details in an integrated design. This article aims to survey the impact of windmill's superstructure and wind receiving facade affecting the efficiency of utilizing wind energy. The research method includes lab experiments in wind tunnel and computer simulation as well as source materials and documentary evidence. In order to achieve the goal, a physical model was built in a small scale based on existing windmills of Sistan, (windmill 2: Machi). Initial and secondary experiments scrutinized reasons for the displacement of blade space (Par-Khaneh) and axis space (Ath-Khaneh) in Sistan windmills.
Whereas the wind-catching face in these windmills have three parts: 1- main wind entrance port, 2- small wind entrance port, 3-Guiding fins, therefore in second, third and fourth experiments with extra equipment in physical structure, the rotational value in different speeds were calculated. Then, the simulation of windmills in COMSOL Multi-physics software was conducted to confirm the experimental results. The findings show that the main factor in displacement of the blade space (Par-Khaneh) and the single-axis space millstone (Ath-Khaneh) in old Sistan windmills utilizes wind energy more efficiently. For this purpose, Persian architects, while making windmills in uphill, transferred the blade space to the upper floor. This improves functional properties and prevents possible disorders in windmills operation arising from accumulation of sand and shavings or animals kenneling in blade space. It also facilitates the construction process and preventing structural damages arising from millstone vibrations.
Testing models 2, 3 and 4 in wind tunnel and their simulations indicated that in model 2 with one wind entrance port and without guiding fins, wind power on the blades compared to models 3 and 4 is at the lowest state. Additionally, the upgraded model 2 as a result of adding guiding fins of wind, has reduced the number of whirlwinds. Similarly, wind convergence and flow rate of entrance port and on blades increases compared to speed of free wind stream. As a result, the power of windmill is improved as well as its efficiency in the windmill function. In model 4, with two entrance-wind port and guiding fins of wind, concentration in wind speed flow lines shows an improved structural function of windmill.
The results of this experiment suggest profound traditional understanding of Persian architects of climatic conditions and architectural efficiency. This is particularly evident in the implementation of a peripheral small wind port entrance next to main one in Sistan windmills, which improves the windmills efficiency, in addition to ensuring its optimal performance in the fluctuations of the famous adverse 120-day winds.