The Numerical Simulation Effect Of Surface Roughness To Tornado Load

A tornado is a strong whirlwind, which has a great destructive power. Since the probability of tornado is very small, our country's "load code for the design of building structures" has not contained tornado design of structure terms. However, When design the some important facilities such as the nuclear power plant, which you must explicitly consider the factor of structure by tornado. Surface roughness is not only an important parameter of the meteorology, but also is important parameter to decide to the tornado wind field structure. So in this paper, the author studies on surface roughness of the surface of a tornado wind field characteristics and construction load impact,which could provide some useful information for follow-up study tornado and also be used for giving some reference to design and site selection to the nuclear power plant such as extremely important structural resistance tornado.First of all, the paper is based on CFD numerical simulation method, and under the action of the different swirl ratio of tornado wind field characteristics were studied. To study the characteristics of vortex field structure tornado more, which using the fluid software FLUENT14.5'S SSTk —?turbulence model to simulate three typical swirl ratio of 0.28,0.5 and 1.0 of the tornado, what is obtained the structure of the quasi-static tornadoes form figure by discrete phase simulation technology. Different swirl ratio is analyzed under the action of a tornado tangential velocity curve variation and distribution characteristics of the velocity vector diagram. And the different building surface wind pressure coefficient of vortex than a tornado field are simulated. The results show that the multi-vortex tornado structure has more surface wind pressure coefficient absolute value is smaller. This article main research content is as follows:Secondly, the paper also based on the CFD numerical simulation method, studied the class B surface roughness of terrain (yo is 0,0.1 and 0.25) in tornado near wind field fluctuations and the impact of load on the surface of a building. According to the result of the above, when selected the swirl ratio is 0.5and the uniform sand model as the equivalent roughness on the ground, the ground roughness is analyzed in detail under the action of tornado wind field structure features and building surface wind pressure coefficient distribution. Results show that surface roughness plays the core within the radius of the tangential velocity and decrease the tornado enhanced cyclone tangential velocity outside the core radius, and cause tornado core radius is larger; Building surface wind pressure coefficient absolute value with the increase of roughness is bigger.Finally, to the study of the more real tornado on the principle of structural load, surface roughness effects on translational tornado structure load. CFD numerical simulation was used to study the translation the difference between the tornado and static field characteristics of the tornado, which include translational tornado core radius is bigger than the maximum tangential velocity static cyclone; And analyzes the translation tornado structure under the effect of surface roughness and surface wind pressure coefficient variation law. The results showed that the building surface distribution of wind pressure coefficient is negative, it indicates that the tornado center produced on the surface wind suction; Circumstances, the greater the roughness length in building near the left side of the location of the wind pressure coefficient absolute value, the greater the increase the absolute value of the other location is local; The left and right sides of the center location of the wind pressure coefficient of the absolute value as the roughness length gets bigger and bigger.