Abstract
A casing treatment using inclined oblique slots (INOS) is proposed to improve the stability of the single-stage transonic axial compressor, NASA Stage 37, during operation. The slots are installed on the casing of the rotor blades. The aerodynamic performance was estimated using three-dimensional steady Reynolds-Averaged Navier-Stokes analysis. The results showed that the slots effectively increased the stall margin of the compressor with slight reductions in the pressure ratio and adiabatic efficiency. Three geometric parameters were tested in a parametric study. A single-objective optimization to maximize the stall margin was carried out using a Genetic Algorithm coupled with a surrogate model created by a radial basis neural network. The optimized design increased the stall margin by 37.1% compared to that of the smooth casing with little impacts on the efficiency and pressure ratio.
Highlights
The aerodynamic performance and stability of a compressor are affected by various factors
The stall margin of the compressor is increased from 9.95% of the smooth casing to 11.16% by installing the reference inclined oblique slots (INOS)
Since the impact of INOS is more pronounced at near-stall condition, the flow field at the low mass flow rate condition is analyzed comparatively, in Figure 6, which presents the relative Mach number contours of smooth casing and reference INOS at 98% blade span
Summary
The aerodynamic performance and stability of a compressor are affected by various factors. Tip leakage vortex is a notable source of instability and loss, which greatly limits the machine’s safety and performance. This mainly resulted from its interaction with the in-passage shock. As the compressor becomes throttled toward the stall condition, the pressure ratio significantly increases, the shock moves forward, and the vortex experiences a severe deceleration across the passage shock barrier. This results in a vortex breakdown and formation of low momentum regions, which act as blockages to the main flow. As the compressor moves closer to the stall condition, the blockages expand until a limit is reached, and stall occurs, causing severe instability and degradation of aerodynamic performance
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