Abstract
This work focuses its attention on possibilities to enhance the stability of an axial compressor using a casing treatment technique. Circumferential grooves machined into the case are considered and their performances evaluated using three-dimensional steady state computational simulations. The effects of rectangular and new T-shape grooves on NASA Rotor 37 performances are investigated, resolving in detail the flow field near the blade tip in order to understand the stall inception delay mechanism produced by the casing treatment. First, a validation of the computational model was carried out analysing a smooth wall case without grooves. The comparisons of the total pressure ratio, total temperature ratio and adiabatic efficiency profiles with experimental data highlighted the accuracy and validity of the model. Then, the results for a rectangular groove chosen as the baseline case demonstrated that the groove interacts with the tip leakage flow, weakening the vortex breakdown and reducing the separation at the blade suction side. These effects delay stall inception, improving compressor stability. New T-shape grooves were designed keeping the volume as a constant parameter and their performances were evaluated in terms of stall margin improvement and efficiency variation. All the configurations showed a common efficiency loss near the peak condition and some of them revealed a stall margin improvement with respect to the baseline. Due to their reduced depth, these new configurations are interesting because they enable the use of a thinner light-weight compressor case as is desirable in aerospace applications.
Highlights
The stall of an axial compressor is characterized by an abrupt change in the flow pattern passing through the compressor, altering its pressure rise capability and leading to flow reversal
The results demonstrated two optimal axial positions where the stall margin is maximized: one near the leading edge (10% chord), the other near 50% chord
Results of all configurations are presented in terms of compressor characteristic curve, stall margin improvement, and adiabatic efficiency variation, and compared to the smooth wall case
Summary
The stall of an axial compressor is characterized by an abrupt change in the flow pattern passing through the compressor, altering its pressure rise capability and leading to flow reversal This phenomenon, appearing at low mass flow rates, is very dangerous and it has to be avoided as it reduces the engine thrust and can severely damage the compressor. Several methods to avoid and delay stall inception have been developed in order to increase compressor stall margin. These techniques can be active or passive and their main purpose is to improve the machine stability without affecting the performance at the design point. The system is managed by an algorithm which determines the magnitude and phase of the first mode of rotating stall and controls the injection of air in the front of the rotor face [1]
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