A study on unsteady flow phenomena at near-stall in a multi-stage axial flow compressor by large-scale DES with K computer

Abstract

The paper presents the results of large-scale numerical simulations which were conducted for better understanding of unsteady flow phenomena in a multi-stage axial flow compressor at near-stall condition. The compressor is a test rig compressor which was used for development of the industrial gas turbine, Kawasaki L30A. The compressor consists of 14 stages, the front two stages and the front half stages of which were investigated in the present study. According to the test data, it is considered that the 2nd stage and the 5th or 6th stage are suspected of leading to the stall. The final goal of this study is to elucidate the flow mechanism of the rotating stall inception in the multi-stage axial compressor for actual gas turbines. In order to capture precise flow physics in the compressor, a computational mesh for the simulation was generated to have at least several million cells per passage, which amounted to 650 million cells for the front 2-stage simulation and two billion cells for the front 7-stage simulation (three hundred million cells for each stage). Since these were still not enough for the large-eddy simulation (LES), the detached-eddy simulation (DES) was employed, which can calculate flow fields except near-wall region by LES. The required computational resources were quite large for such simulations, so the computations were conducted on the K computer (RIKEN AICS in Japan). Unsteady flow phenomena in the present compressor at near-stall condition were analyzed by using data mining techniques such as vortex identification and limiting streamline drawing with the LIC (line integral convolution) method. The simulation showed that the stall in the present compressor could be related to the corner separation on the hub side.