A Refined Model to Predict Boundary of Instability of Axial Compressors

A quantitative model to predict the boundary of instability of axial compressors based on their maximum loading capability is proposed in this paper, which is an improved version of the classic method of stalling pressure rise. The original model correlates the maximum pressure rise of a compressor to a characteristic geometric parameter, which is an analogue of the normalized length of diffusion in two-dimensional diffusers. However, the influence of the aspect ratio of the passage is overlooked in this analogy, which leads to significant discrepancies in its predictions for compressors, especially those with varying blade aspect ratios. Our model contains two improvements to address this issue. The first involves refining in the definition of the normalized length of diffusion, whereas the second introduces a supplementary correction factor for the aspect ratio of the blades. Nearly 20 low-speed compressor configurations, with variations in solidity, aspect ratio, tip clearance, and axial spacing, were tested to develop the proposed model. It can reduce error in the predicted stalling static pressure rise from 10% to 5%. Experimental data robustly verify the accuracy of our model, making it a more reliable predictive tool of instability boundary in the preliminary design of axial compressors.