Session: 31-12 Inlet Distortion

Paper Number: 128983

128983 - Experimental Investigation of Stall Mechanism and Warning Method in a Two-Stage Transonic Fan Under Inlet Distortion With Axial Slot Casing Treatment 

The instability warning method has been used to predict the level of disturbances in active control systems. In recent times, attention has focused on the irregularity of blade passing signatures with the aim of detecting the pre-stall disturbances. For uniform inflow conditions, the onset of disturbances at different circumferential positions is almost at the same moment, regardless of the circumferential propagation. When the fan suffers from inlet distortion, one of the most external destabilizing factors of aero-engines, the disturbances might disappear in the undistorted region. The changes between the distorted and undistorted regions make the accurate and robust instability warning method challenging. Revealing the mode characteristics of pre-stall disturbances under the distorted inflow condition is a key to realizing engineering applications. For this purpose, modal analysis based on proper orthogonal decomposition and stall warning are implemented in a 2-stage transonic fan. Work on this project has concluded that the pre-stall disturbances first appear in the downstream of the distorted region, decay in the process of circumferential propagation, and finally disappear in the upstream of the distortion region. The detailed time and frequency domain analysis reveals that the stalling process of the fan corresponds to a characteristic frequency. Then, the proper orthogonal decomposition is conducted to study the dynamic physics of the stalling process. This characteristic frequency is closely related to the self-induced unsteadiness in the tip leakage flow. In the downstream position of the distorted region, the incidence is largest due to the low axial momentum of main flow, and the fluctuation of tip leakage flow is strongest. In order to achieve stall warning under inlet distortion condition, a novel warning parameter characterizing the energy of pre-stall disturbances is proposed. This parameter can more clearly reflect the change in disturbances during the throttling process. It is found that the increase in disturbances can only be detected downstream of the distorted region, which corresponds to the optimal position of sensor installation for stall warning. From these findings, it is clear that the position of the stability warning should be carefully considered under distorted inflow. Considering the uncertainty of the distortion during the flight cycle, it is difficult to achieve instability prediction by using a single sensor.

Presenting Author: Zhonggang Fan Institute of Engineering thermophysics, Chinese Academic of Science

Presenting Author Biography: Mr. Fan's main research interests include compressor instability, casing treatment design, stall warning method, etc. The stall warning method has been widely used in active control method. In this paper, the stall mechanism and warning method in a 2-stage transonic fan on the inlet distortion have been investigated.

Authors:

Zhonggang Fan Institute of Engineering thermophysics, Chinese Academic of Science
Juan Du Institute of Engineering thermophysics, Chinese Academic of Science
Yang Liu Institute of Engineering thermophysics, Chinese Academic of Science
Dun Ba Institute of Engineering thermophysics, Chinese Academic of Science
Min Zhang Institute of Engineering thermophysics, Chinese Academic of Science
Guofeng Ji AVIC Guizhou Engine Design Institute