Numerical investigation on the cross-stage self-recirculating casing treatment for a counter-rotating axial compressor

Although the counter-rotating axial compressor (CRAC) can promote the thrust-to-weight ratio of aero-engines, the “stall transposition” phenomenon poses a huge technology challenge in controlling the flow due to the speed ratio effect. Traditional flow control technology hardly operates under off-design conditions, posing an urgent need to develop a new flow control approach suitable for CRAC's variable speed ratio conditions. Hence, based on the conventional rear-jet self-recirculating casing treatment (SRCT), this work designs two cross-stage SRCT cases (front-jet SRCT and dual-jet SRCT) to resolve the “stall transposition” issue in a two-stage CRAC. The results demonstrate that although all SRCT cases improve the stall margin of the CRAC at the design condition, both front-jet SRCT and dual-jet SRCT cases have a significant stabilization capacity without changing the first stall stage, opposing the rear-jet SRCT case, which changes the first stall stage. The dual-jet and front-jet SRCT cases have a significant stabilization capacity under the off-design speed ratio conditions; since they can simultaneously act on the tip clearance flow of both the upstream and the downstream rotors and increase the stall margin by about 6.23%∼10.78% and 6.66%∼10.42%, respectively. Variations in speed ratio may shift the location of the first stall stage, forcing the rear-jet SRCT case to fail in expanding the stall margin at the partial speed ratio conditions. Moreover, the suppression of SRCT on the flow instability of the tip leakage flow decreases the unsteady pressure fluctuation intensity near the rotor tip.