A Passive Control Method of Hub Corner Stall in a 1.5-Stage Axial Compressor under Low-Speed Conditions

Wenfeng Zhao,Aqiang Lin,Qun Zheng,Bin Jiang

doi:10.3390/en13112691

Abstract

Since the use of the compressor of a ship gas turbine is unavoidable at a low-speed operation, the flow field characteristics and stall mechanism at off-design speeds are important aspects for compressor designers. In this study, the first 1.5 stages of an eight-stage compressor are numerically simulated. The mechanism of compressor rotor instability at lower speeds is identified. The characteristic lines of compressors with various partial clearance are calculated at low speed (0.6 N). The flow field of the same outlet pressure (near stall point of the original compressor without clearance) is compared and analyzed. The results show that, at the near stall point, the suction surface separation and backflow occur in the main flow of the rotor top. It develops along the blade span and finally blocks the flow passage of the rotor, which results in the compressor stall. At the same time, the stall also occurs at the corner of the stator hub. In this paper, the characteristics of partial clearance in four different positions of the stator hub are analyzed. The near stall point and the working point are selected for the flow field analysis. It is concluded that the radial development of the stall vortex on the suction surface of the stator can be restrained by the partial clearance at the stator. In this paper, a passive control method by partial clearance is used in the real compressors, which is different from previous studies on cascades. The margin increases at low speeds.

Highlights

The off-design performance of a compressor is an important parameter in order to measure the design constrains of the compressor, which is used to ensure the safety of the gas turbine [1]
In order to prevent the compressor from losing stability and deteriorating its performance, inter-stage air-bleed is considered necessary for a marine gas turbine
Many control methods have been applied to the compressor stabilization, but there are few studies on the instability mechanism of the ship compressor under low operating conditions

Summary

Introduction

The off-design performance of a compressor is an important parameter in order to measure the design constrains of the compressor, which is used to ensure the safety of the gas turbine [1]. In order to prevent the compressor from losing stability and deteriorating its performance, inter-stage air-bleed is considered necessary for a marine gas turbine. During ship navigation engine frequent acceleration, deceleration, and switching to different operational modes is a necessity that cannot be neglected. In this process of changing speeds, the load change will cause the engine operating line to shift. The world’s most advanced marine gas turbine (MT30, LM2500+) has good design performance as it maintains a stable working margin under low operating conditions. Many control methods have been applied to the compressor stabilization, but there are few studies on the instability mechanism of the ship compressor under low operating conditions. Researchers need to understand the instability mechanism and put forward reasonable methods to improve it

Methods

Results

Conclusion