Aerothermal Model for Real-Time Digital Simulation of a Mixed-Flow Turbofan Engine

Abstract

Thispaperpresents awayto simplifyanexplicitly time-integrated,aerothermodynamictransientmodelofa twinspool,mixed- ow turbofan engine based on state variables and control volumesapproach such that computational performance becomes suitable for real-time digital simulation. The key simpliŽ cation lies in the modeling of main mixer, in which the mixing of core and bypass streams takes place. The number of state variables in an existing thermodynamicmodel has been reduced to six from nine by assuming that, instead of a uniform rate of static pressure rise, the static pressure is uniform across the main mixer. Computational time decreases primarily because the model is now less sensitive to pressure dynamics, thus allowing a larger integration time step. The accuracy of transient simulationsis also less affected by artiŽ cial increases in actual physical size of controlvolumes, permitting further increase in integration time step. Numerical experiments show that simpliŽ ed mixer modeling together with an increase in control volumes size by a factor of three resulted in an integration time step of 1.2 ms. It enables the model to run in real time on a stateof-the-art personal computer type of digital platform, without loosing the accuracy and numerical stability of the analysis. The formulation,validation,and real-time capabilities of the proposed methodology are discussed.