Impact of non-uniform incoming flow from intermediate cooling systems on second-stage centrifugal compressors: Insights from three-dimensional spatiotemporal coupled simulation

Abstract

In this paper, the impact of the intermediate cooling system on the second-stage compressor is investigated through three-dimensional spatiotemporal coupled simulation of a two-stage centrifugal compressor. Specifically, the study predominantly focuses on the pressure loss coefficients and temperature drop coefficients of the cooling system, as well as the pressure ratio and the polytropic efficiency of the second-stage centrifugal compressor. The internal flow fields of both the cooling system and the compressor are meticulously explored under steady and unsteady conditions. The results distinctly suggest that the internal flow field of the second-stage compressor becomes more turbulent due to the non-uniform incoming flow from the intercooling system. Consequently, more complex flow structures are generated within the impeller channel, which causes more energy dissipation. This inevitably leads to a reduction in the thermal and aerodynamic performance of the second-stage compressor. At the design point (Q_n), the pressure ratio and polytropic efficiency of the second-stage compressor are decreased by 0.49% and 0.32%, respectively. Notably, as the mass flow rate increases from 0.9 Q_n to 1.1 Q_n, the reduction in polytropic efficiency becomes progressively more pronounced, a decrease of 0.63% is obtained at 1.1 Q_n. Despite this trend, the polytropic efficiency at 1.1 Q_n remains superior to that of 0.9 Q_n due to the inherent flow characteristics of the centrifugal compressor. Additionally, the midstream and downstream regions of the impeller channel are more substantially affected by the cooling system than the upstream region. The analysis of the complex flow in the impeller at the design point has revealed the spatiotemporal evolution of one rotation. Coupled simulations have provided comprehensive qualitative and quantitative analyses for multi-stage compressors with intercooling systems, clarified the mechanisms underlying performance degradation, and offered practical operational/optimization recommendations to enhance efficiency and save energy.