Impacts of tip clearance size variation in different rotors on the overall performance and unsteady flow fields in a counter-rotating axial flow compressor

The objective of current investigation is to study how the change of tip clearance size (TCS) in each of the two different rotors affects the compressor performance and the unsteady flow fields inside. It is found that the compressor stage performance is mainly dominated by the rear rotor. An increase of TCS in one rotor has no significant influence on the other rotor's performance within a limited range of TCS. The pressure fluctuations in front rotor are dominated by the potential effects from downstream, while the oscillations in rear rotor are mainly caused by the unsteadiness of local tip leakage flow. Additionally, the pressure oscillating strength in one rotor is reduced obviously by the increased TCS in the other rotor. Frequency analysis indicates that the happening of periodical fluctuation in rear rotor is easier than that in front rotor and the frequency component of the strongest oscillation in rear rotor always appears in front rotor due to the potential effects. The pressure fluctuating components with lower frequency begin to happen in the corresponding rotor with TCS change when the TCS is increased to a large enough value for both rotors.