Numerical Investigation of Transient Flow Characteristics in a Centrifugal Compressor Stage with Variable Inlet Guide Vanes at Low Mass Flow Rates

Shuai Li,Hongkun Li,Chuang Zhang,Yan Liu,Mohammad Omidi

doi:10.3390/en14237906

Abstract

This study numerically investigates the beneficial effects of positive pre-swirl on the aerodynamic performance and internal flow field in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) at low mass flow rates. Four positions of VIGV are considered, including 0°, 30°, 45°, and 60° angle. The latter three positions of VIGV induce positive pre-swirl. Numerical results show that as positive pre-swirl increases, the aerodynamic performance curve of the stage moves in the low mass flow rate direction. In the three cases of positive pre-swirl, there was an improvement of approximately 9.95% of stall/surge margin greater than in conditions with no pre-swirl. The regulation of IGV can effectively improve the unstable flow of the compressor stage at low mass flow rates. A low frequency that has a great influence on the internal flow of the compressor stage is found, and the unstable flow caused by low frequency is analyzed by the combination of streamline distribution, spectrum analysis, vector, entropy increase, and modal decomposition method. Meanwhile, the modal decomposition method and flow field reconstruction techniques are used to investigate the coherent flow structures caused by low frequency under different guide vane openings.

Highlights

The results showed that the evolution of jet and wake downstream of the Variable inlet guide vanes (VIGVs) was related to the VIGV solidity
The results show that the compressed dynamic modal decomposition (DMD) approach can save 88.4% of the calculation time, and it is found that the origin of the diffuser stall lies at the hub surface with a fixed circumferential position
Steady and unsteady numerical calculations have been applied to study the internal flow of a compressor stage with VIGVs

Summary

Introduction

The mass flow rate of centrifugal compressors needs to be regularly adjusted in actual operation to adapt to operational requirements and density change caused by temperature changes. VIGVs can change the impeller inflow pre-swirl for a variable mass flow rate at a constant rotational speed. According to the Euler work calculation formula, the aerodynamic performance of a compressor is determined by the flow state at the impeller inlet and changes of input work. When the inflow at the impeller inlet changes from negative pre-swirl to positive pre-swirl, the incidence angle of the impeller blade increases, and the operation curve of the compressor moves in the low mass flow rate direction, which further changes the aerodynamic performance and operating range of the compressor [2,3]

Methods

Results

Conclusion