Physics of Deep Surge in an Automotive Turbocharger Centrifugal Compression System

Abstract

Deep surge is a violent fluid instability that occurs within turbomachinery compression systems and limits the low-flow operating range. It is characterized by large amplitude pressure and flow rate fluctuations, where the cross-sectional averaged flow direction alternates between forward and reverse. The present study includes both measurements and predictions from a turbocharger centrifugal compressor installed on a gas stand. A three-dimensional (3D) computational fluid dynamics (CFD) model of the compression system was constructed to carry out unsteady surge predictions. The results included here capture the transition from mild to deep surge, as the flow rate at the outlet boundary (valve) is reduced. During this transition, the amplitude of pressure and flow rate fluctuations greatly increase until they reach a repeating cyclic structure characteristic of deep surge. During the deep surge portion of the prediction, pressure fluctuations are compared with measurements at the corresponding compressor inlet and outlet transducer locations, where the amplitudes and frequencies exhibit excellent agreement. The predicted flow field throughout the compression system is studied in detail during operation in deep surge, in order to characterize the unsteady and highly 3D structures present within the impeller, diffuser, and compressor inlet duct. Key observations include a core flow region near the axis of the inlet duct, where the flow remains in the forward direction throughout the deep surge cycle. The dominant noise generation occurs at the fundamental surge frequency, which is near the Helmholtz resonance of the compression system, along with harmonics at integer multiples of this fundamental frequency.

Modelo matemático de un plenum para obtener las características dinámicas del flujo másico de un turbocargador

“…Esta máquina térmica debe reducir su tamaño de sus componentes (turbina-compresor) para aportar eficientemente en su función específica, pero al reducir su tamaño en su turbina, se afecta considerablemente la potencia que entrega al compresor a bajas revoluciones, produciéndose así una relación de compresión de manera significante que perjudica su rendimiento de operación [18]. Para estabilizar este efecto, se debe mantener el margen del flujo que genera el compresor para no caer en vibraciones y acarrear problemas constructivos, este fenómeno es comúnmente llamado bombeo o surge [19,20].…”