Numerically assessing aerodynamic stability of compression component running in turbofan engine

After a decade or so of research, we have come to the point at which we are confident that we can assess by calculation the aerodynamic stability of compression component running in turbofan engine. Such assessment, though highly desirable, was generally avoided because of its complexity. The occurrence of surge of aero-engine is disastrous for fighter aircraft, so ensuring its stability margin to be sufficient is important. Traditional method for aerodynamic stability assessment of compression component is not in engine environment. For accurately analyzing effect of other components of turbofan engine on aerodynamic stability of compression component, a new model is presented for predicting aerodynamic stability limit of compression component in turbofan engine. Firstly, according to the actuator-lag-volume model and parallel compressor model, a quasi one-dimensional and time dependent compression system model is given to model the dynamic flow in compressor. Secondly, Lyapunov stability theory is used to identify the aerodynamic stability of compression component. Finally, this aerodynamic stability numerical model is coupled with steady state thermodynamic-cycle model of turbofan for predicting aerodynamic stability limit of compression component in turbofan engine environment. A turbofan engine with 3 stage fan and 5 stage compressor as an example was simulated. Fig.5 in the full paper gives fan surge lines for clean inflow in different stability assessment environments and similarly, Table 1 in the full paper gives fan surge lines for distortion inflow. The analysis of Fig.5 shows that for clean inflow, the effect of different stability assessment environments on surge line is negligible. For distortion inflow, the effect of different stability assessment environments on surge line is considerable; for example, at 100% speed and 8% distortion index, in turbofan engine environment, the loss of surge margin is 6.67%, but in isolated component environment, under the same conditions, the loss of surge margin is 11.13%, or 4.46% higher.