Simulation of the transient response of a helicopter turboshaft engine to hot-gas ingestion

Hot-Gas Ingestion (HGI) to the engines can potentially occur when a rotorcraft or a VTOL/STOVL fixed-wing aircraft is operating in close proximity to the ground. Especially for helicopters, due to the rotor downwash hot exhaust gases get recirculated into the engine inlet. Similar conditions may also occur due to the ingestion of hot exhaust gases from rocket launchers or gun fire. In this study, we present the results of a simulation of the transient response of a helicopter turboshaft engine to HGI. Specifically for this study we will present the results for the T800-LHT-800 turboshaft engine. The simulations are performed using an in-house generic simulation code based on an aerothermal model, which consists of the governing equations representing the aero-thermodynamic process of each engine component. The algorithm is composed of a set of differential equations and a set of non-linear algebraic equations which are solved numerically in a sequence. A simple proportional control algorithm is also incorporated into the simulation code, which acts as a simple speed governor. Simulation results show that the code has the potential to correctly capture the transient behaviour of a turboshaft engine under various HGI conditions, such as the reduction in the gas generator speed and the power levels as well as the decrease in the compressor surge margin. The code can also be used for developing engine control algorithms as well as health monitoring systems.