Evaluation of the effectiveness of typical casing treatments for a low-speed compressor by an integral method

Abstract

A novel integral method is proposed to quickly assess the effectiveness on stability improvement with end-wall casing treatments. With this low-cost method, efficacies for various casing treatment configurations can be evaluated instead of calculating the entire performance curves, which can be used in place of expensive and costly experiments. The underlying mechanism for this approach is based on the hypothesis that the spike stall precursors can be triggered by the forward spillage of the rotor tip leakage flow, and the onset condition of such a spillage is determined by the axial momentum balance within the rotor tip region. Based on the simulation, a series of control volumes are set at the rotor tip region in order to catch the axial momentum balance between the incoming main flow and the reversed tip leakage flow. Cumulative axial momentum distributions for these control volumes named as “bell-shaped curves” are presented to evaluate the effectiveness of different configurations. The axial location of the bell curve peak indicates the time- and spatial-averaged interface position between the main flow and tip leakage flow, which moves upstream during throttling. Three types of typical casing treatments: multiple circumferential grooves, skewed axial slots and self-injection configurations for a low-speed in-house compressor are evaluated by their bell-shaped curves. Among these configurations, the skewed axial slots has the most downstream of the peak, followed by the multiple-grooves, while the self-injection configuration shows the least. Based on an existed experimental result for a double-groove configuration, the effectiveness of the three studied casing treatments are predicted by their locations of the bell-shape curve's peak without simulating the entire performance curves. The assessments are then validated by experiments.