Mechanism of stall margin improvement of two stages transonic fan with two-portion axial slot casing treatment

The mechanism of stall margin improvement is investigated on a high rotating speed and high load two-stage transonic compressor with two-portion axial slot casing treatment by 3D numerical simulation. The calculated overall performance curves good agree well with the experiments. The results show that the stable operating range is extended with two-portion axial slot casing treatment in the subsonic condition. The detailed analysis of the calculated flow-filed at the blade tip shows that the separation of the rotor blade suction boundary of the first stage cause blockage in the blade tip passage, which is the primary reason for compressor stall in the subsonic condition. Back flow come into being in the slots by pressure difference, which makes low energy air mass of blade tip enter slot or transport the low energy of slot downstream to slot upstream. The low energy air mass is accelerated by pressure difference during transportation and it turns into mainstream again at the slot upstream. This kind of flow manner can inspirit the low energy air mass of blade tip near end wall and extend the stable operating range of transonic compressor in the subsonic condition effectively.