Timescaling Control Volumes During Real Time Digital Simulation of a Military Turbofan

The real-time digital simulation of the dynamic response of an aircraft gas turbine engine is achieved when the cycle time, that is, computation time for one pass through the engine dynamic model, is shorter than the integration time-step size (or frame time D(T)). The engine considered is a twin-spool, military turbofan with mixed exhausts. An explicitly time-integrated, real-time aerothermodynamic model of this engine based on state variables and control volumes is described. It is concluded that the smallest volume in a twin-spool, mixed-flow military turbofan is between the high-pressure turbine (HPT) and the low-pressure turbine (LPT) and is used to update Ps. Ps, therefore, has the highest frequency dynamics, and as such, use of a large D(T) causes a cyclic variation in its update. This cyclic variation is more pronounced when LPT is not choked and, therefore, occurs at a much lower D(T). Because of the presence of cyclic variations in Ps, the response prediction deviates from the baseline. (CSA)