Abstract: To evaluate the air tightness of lined cavern for compressed air energy storage, a kind of unsteady seepage equation considering the influence of air leakage and porosity of concrete lining in the cavern is derived based on seepage flow theory of porous media, and an approximate analytical solution for approximate calculation of air pressure in the cavern is given. To solve this kind of nonlinear parabolic equation accurately, an unconditional stable implicit difference scheme with second order accuracy is constructed by using finite difference method. The results show that, compared with the traditional air leakage estimation formula based on the steady seepage theory, the air leakage calculated considering unsteady flow process of air is slightly smaller. When the permeability of concrete lining with a thickness of 0.5 m is less than 6×10?20 m2, the percentage of air leakage within 24 hours in a compressed air energy storage cycle is less than 1%, ordinary impermeable concrete cannot meet the requirements of air leakage control, and special sealing measures are thus needed. The air leakage percentage of compressed air energy storage cavern is related to lining permeability, air storage pressure, lining thickness. The lower the permeability is, the larger the gas storage pressure is, the larger the lining thickness is, the smaller the air leakage percentage is, and the control effect of lining thickness on gas leakage decreases with the increase of lining thickness.

Key words: compressed air energy storage, unsteady seepage, finite difference method, air leakage