Simulation of Transient Load Behaviour of Gas Turbines in High Speed Marine Applications

This paper describes a model simulation of the transient behaviour of a twin spool gas turbine which could be used to drive a water jet propulsion system in a high speed vessel. The transient loading is considered to be due to torque variations that can occur due to the effect of air entrainment in the propulsor in a heavy sea. For the simulation, measured shaft torque from a diesel engined vessel operating in waves of height 2.0–2.5 meters were scaled to fit with the design output power of the studied gas turbine. This transient variation of torque was applied to the power turbine shaft in the mathematical model. The objective was to study the behaviour and thermal loading on the turbine under such conditions. Results from simulating the influence of heavy sea conditions show that very large shaft power drops can occur due to wave loading, and that for short periods of time higher gas temperatures can occur than the corresponding steady state values. In conclusion, this type of operation may increase the risk of damage due to cyclic variation of load and temperature, and lead to shorter component lifetimes compared with expected design values.