Experimental and numerical investigation on stability enhancement mechanisms of self-recirculating casing treatment

The stall induced by tip leakage flow (TLF) seriously restricts the stable operating range of the compressor. This study investigates the stability enhancement mechanism of the radially inclined self-circulating casing treatment (SCT) through experiments and unsteady numerical simulations, with a focus on analyzing the influences of the number and bleed position of the SCT structures on the stall margin. The results indicate that the negative pre-swirl provided by the radially inclined SCT increases the rotor tip loading and the total pressure ratio. Compared with the non-radially inclined SCT, a higher stall margin improvement (SMI) is obtained. The N20B70 scheme with 20 SCT structures and the bleed position at 70% Ca (Ca represents the rotor tip axial chord length) has the strongest stability enhancement capability, achieving an SMI of 15.5%. The more SCT structures there are, the stronger the compressor stability. The reason is that the increase in the number of SCT structures raises the frequency of the bleed effect, and the time is shorter than the time it takes for the TLF to recover to a low-speed state, keeping the TLF at a relatively high speed all the time. The upstream TLF is blocked by the downstream TLF with fully circumferential development, which is the fundamental cause of the low-speed region. For the SCT schemes with different bleed positions, precisely controlling the TLF with fully circumferential development is the key factor affecting the stability enhancement capability.