A computational study on compressor inlet restriction to suppress surge instabilities in turbochargers

Operation of centrifugal compression systems below their stability limit causes surge to occur, resulting in large amplitude pressure fluctuations near the natural frequency of the system. Deep surge in the compression system of turbocharged internal combustion engines degrades performance and drastically increases noise. The current computational work demonstrates elimination of surge instabilities by incorporating sufficient restriction at the inlet of a turbocharger compressor. Both one-dimensional (1D) gas dynamics and three-dimensional (3D) computational fluid dynamics (CFD) models were developed to study the impact of a flow restriction on the amplitude of pressure and mass flow rate fluctuations and, therefore, system stability. The analyses were performed at a fixed operating point with a (time-averaged) mass flow rate below the deep surge boundary. As the inlet restriction was partially closed with the 1D model, the compression system remained in deep surge over a majority of the area ratio (of restriction to adjacent duct) range, and the amplitude of mass flow rate fluctuations gradually reduced with decreasing area of restriction. With sufficient inlet restriction, pressure and flow rate fluctuations were eliminated and the system was stabilized. In order to gain further insight into the importance ofmulti-dimensional physics, a simulation with the 3D model was carried out. Qualitatively, the 1D and 3D modeling results at equal pressure drop across the restriction were found to be similar. These unsteady predictions highlight the role of mass balance in the intermediate volume (between the restriction and compressor) toward reducing the amplitude of mass flow rate fluctuations.