Numerical Simulation of Effects of Building Tip on Atmospheric Electric Field Distortion

The effects of building tip on atmospheric electric field distortion are an important part of atmospheric electricity, especially in the research of corona layer above the inhomogeneous underlying surface, upward lightning leader and even upward lightning initiated from tall building, and also an influencing factor in lightning protection. For the account that the existing measurements are ineffectual in measuring the electric intensity above the tip, numerical simulation becomes very helpful.Assuming the building to be an ideal conductor and fully connected with earth and the potential is 0, which satisfies the Dirichlet boundary condition; three other air boundaries all satisfying Numann boundary condition and the electric potential gradient on these boundaries are constants. A two-dimensional finite difference method of calculation is used to obtain the potential distribution around the building and electric intensity near the tip in further. What's more, the two-dimensional finite difference equation is solved by successive over-relaxation method.The effects on the atmospheric electric field distortion by the height, width and location of building's tip are discussed, respectively. The result shows that λ_i (maximum distort coefficient of electric field) is linearly increasing with height and the slope of linear equation is decreasing with width. λ_i shows symmetrical increasing trend when the tip is located from the center to the each edge on the roof of a structure. It grows evidently with the increasing height of structure. Furthermore, λ_i is declined exponentially with the tip width, particularly when less than five meters, λ_i has a sensitive response to width, and the effect on λ_i by width is more obviously presented with the increasing height. Taking no account of the extinction effect of corona layer, electric field intensification shows much greater on the top when the structure is taller and thinner. In actual problems, the effects on electric field distortion mainly depend on the structure height when the top is flat. But when there is an obvious tip such as lightning conductor and so on, the height, width and location of tip should be taken into consideration.