Effects of the vena contracta for perforations on stability enhancement of an axial compressor using the impedance boundary-controlled casing treatment

Casing treatments are extensively utilized in engineering to significantly enhance stability. The impedance boundary-controlled casing treatment (IBCCT), based on a three-dimensional compressible stability model, is one of the examples and has demonstrated a notable stall margin improvement in a series of extensive experiments. However, the impedance model employed to characterize the perforated plates in IBCCT falls short in considering complex geometric parameters, such as dimensionless thickness and perforation edge angle. With an aim to optimize geometric parameters, the impedance of perforated plates with different vena contracta is determined by appropriate boundary conditions within an acoustic resistance model in this study. These impedance values are integrated with previous models to perform sensitivity analysis. The appropriate cross-sectional profiles for perforation are designed to achieve the desired adjustment of different vena contracta. IBCCTs with different vena contracta are subjected to experimental validation to substantiate the predictions. The results of both the experiments and the sensitivity analysis indicate that the stall margin improvement of IBCCTs increases as the vena contracta decreases. In addition, single-passage numerical simulations are performed under casing treatment conditions to determine whether the IBCCT with varying vena contracta intensifies the impact on the steady flow field. By integrating sensitivity analysis, experimental data, and numerical simulations, the impact of vena contracta on the stability enhancement performance of IBCCTs can be elucidated.