Modeling of a Turbofan Engine Start Using a High Fidelity Aero-Thermodynamic Simulation

Abstract

Simulating the thermodynamics of a multi-spool turbofan engine during engine start can present challenges to the conventional high fidelity aero-thermodynamic simulation. The conventional high fidelity aero-thermodynamic simulation uses an iterative solver technique to preserve flow continuity and conservation of energy based on component maps and subsystem characteristics. Traditionally, operation of such simulations have been limited to regions from self-sustaining idle to maximum power, where component and subsystem representation has been well defined and engine operating pressures are sufficient to ensure one-directional flow. However, simulating transient operation which initiates from engine “off” condition followed by starter engagement and fuel introduction, presents a new set of challenges. These include the modeling of the engine “off” state itself, as well as two aspects of the starting process particular to a multi-spool turbofan: the modeling of the flow passing through the entire core stream even though only the high pressure shaft is rotating, and the modeling of the flow split into the bypass stream when the fan is not rotating. This paper discusses the modeling techniques that have been developed to overcome these challenges in order to ensure the smooth operation starting with engine off and continuing through the regions of starter engagement, fuel addition, and starter disengagement leading to normal engine operating regime.