Stability analysis of a gas turbine exhaust stack

Stability analysis, based on finite element method, was carried out on a gas turbine exhaust stack following obvious appearances of significant gaps between its silencer casings and embracing rings. The finite element model was developed by referring to the corresponding technical drawing of the exhaust stack and the information obtained during the site inspection. In the case of axial constraint at both ends of the exhaust stack, the original design was found incapable of withstanding the thermal loading experienced during operation of the gas turbine, leading to instability of the structure. A design modification of the exhaust stack was proposed to rectify this problem. The outcome of the finite element analysis indicated that the modified design of the exhaust stack had improved stability as compared to the original design when subjected to typical thermal loading of the gas turbine operation.