Session: 01-11 Modelling, Simulation and Validation III

Paper Number: 124058

124058 - The Effect of Flight Speed and Altitude on Windmilling Restart Operation of Turbofan Engine System 

The windmilling restart performance is of great significance for the turbofan engine, as flame-out can occur due to various factors such as weather conditions, bird strikes, or crew actions. In the event of flame-out, the engine can operate in a stable state known as “free windmilling” sustained by the ram effect of the incoming airflow, depending on the flight speed and altitude. Failure to restart the engine from free windmilling can cause catastrophic consequences for the aircraft. Therefore, the prediction of turbofan performance in windmilling restart operation is essential in the design process.

In the present study, a thermodynamic model is constructed in a modular scheme, with respect to the windmilling restart operation of the turbofan engine system. An improved compressor modeling method is proposed for the cycle matching in the low shaft speed region. The equations combining the corrected torque and the polynomial of temperature are added to the traditional compressor model, so that the stirrer state and the turbine state of the compressor can be clearly expressed. Using the proposed compressor model to the cycle matching, the analysis of the overall and local performance of the turbofan engine is possible during the windmilling restart process. In addition, the shaft acceleration control loop, which has been used in many advanced aero-engine is applied to the control system with limit protection controller. The shaft acceleration is tightly controlled, which secure the restart operation can be effectively performed within an acceptable time.

The windmilling restart operation is successfully simulated through the constructed thermodynamic model, and then the modal transition analysis is performed through the operating line using the output pressure ratio and the corrected torque of the compressor model. The results indicate that the fan acts successive as a turbine, stirrer, and compressor during the windmilling restart process, as the pressure ratio rises from one and the corrected torque rises from zero. In contrast, the high-pressure compressor is hard to act as a turbine because of the expansion of airflow in the fan under free windmilling condition. Additionally, the effect of Mach number and height on the restart operation is studied. Increasing height and decreasing Mach number result in a decrease in shaft speed in free windmilling process, so that the turbofan engine fails to stabilize in windmilling state under certain conditions, such as Mach number is 0.5 and height is 4 km. Higher height and Mach number shorten the start-up time of the turbofan engine with the same control logic. For instance, with a height of 3 km, the start-up time decreases by 5.56s as Mach number increases from 0.70 to 0.75. Similarly, as Mach number is 0.7, an increase in height from 3 km to 5 km leads to a decrease in start-up time by 9.41s. However, the results show that higher height causes higher combustor exit temperature, which means the turbine operates under more extreme condition when the restart operation is performed at high altitude. The research findings contribute not only to the design of windmilling restart strategies for turbofan engines but also to determining the reliable restart range for aircraft.

Presenting Author: Jingkai Zhang Harbin Engineering University

Presenting Author Biography: Jingkai Zhang (1999), male, PhD. His research interests cover aero-engine performance analysis and optimization, engine control, diagnostics and prognostics, etc.

Authors:

Jingkai Zhang Harbin Engineering University
Zhitao Wang Harbin Engineering University
Shuying Li Harbin Engineering University
Pengfei Wei Harbin Engineering University