Experimental Investigation of Rotating Instability in an Axial Compressor with a Steady Swirl Distortion Inlet

Rong Xu,Jun Hu,Chao Jiang,Xuegao Wang,Jiajia Ji

doi:10.3390/en14238057

Abstract

In this paper, an experimental study was carried out on the rotating instability in an axial compressor subjected to inlet steady paired swirl distortion. In order to deepen the understanding of the rotating stall mechanism under inlet steady paired swirl distortion, the dynamic-wall static pressure near the rotor tip was monitored to characterize the flow in the rotor tip region at different circumferential stations. In the experiment, the dynamic characteristics of the rotor tip flow field at a stable operating point and during the process from the stable point to complete stall were measured. The results indicated that for the compressor with a 2 mm rotor tip clearance, the inlet paired swirl distortion induced rotating instability (RI) near the stall point, causing the compressor to enter stall in advance. Compared with the RI intensity of the clean inlet, the distortion with a swirling blade stagger angle (αst) of ±20° increased the RI intensity up to 69.8%, while for αst equal to ±40°, the RI intensity increased at most by 135.8%. As the rotor tip clearance increased to 3 mm, the co-rotating swirl in the paired swirl distortion inhibited the appearance of RI, while the counter-rotating part aggravated the development of RI. At the beginning, the process of the compressor rotating stall involved the alternation of short-scale disturbance and long-scale disturbance. The co-rotating swirl weakened the perturbation propagated from the counter-rotating swirl sector. Once the inhibition was no longer present, the short-scale disturbance rapidly developed into a long-scale disturbance and then entered the rotating stall.

Highlights

With the development of aero engines, the performance demand of compressors is becoming higher, which brings more severe challenges to the stability of compressors
März [16] found through experiments and numerical simulations that rotating instability (RI) only exists in the blade tip area during the stable operation of the compressor and it is especially obvious in the presence of a large stagger angle and a large tip clearance
Two intensities of steady paired swirl distortion were considered in the experiment, and the stagger angles of the swirl blades were αst = ±20◦and ±40◦

Summary

Introduction

With the development of aero engines, the performance demand of compressors is becoming higher, which brings more severe challenges to the stability of compressors. Studies have found that there is a close connection between the tip clearance flow and an unstable flow pattern of compressors This has inspired scholars to conduct experimental and numerical studies on the formation and development of the tip clearance flow and its relationship with stall [1,2,3,4,5,6]. Vo [10] proposed two necessary conditions for the formation of stall inception of the spike-type: the interface between the tip clearance flow and the incoming flow is parallel to the blade leading edge plane and a backflow is triggered. Further research discovered an instability phenomenon in the stable operating point, which is called rotating instability (RI) [11,12] This phenomenon precedes the classical stall inception signal and may become an earlier stall warning. Li et al [24] carried out a full annulus unsteady simulation for a low-speed axial compressor with and without clearance and found that when there was clearance, the transverse vortex in each passage and the shedding vortex at the rear of the blade suction side every two passages were related to RI

Methods

Results

Conclusion