Computational investigation of unsteady effect of axial spacing on the performance in a contra-rotating axial compressor

Unsteady numerical simulations are conducted to investigate the unsteady effects of axial spacing on the performance of a contra-rotating axial compressor. The results show that the adiabatic efficiency decreases with increasing axial gaps, and the stage efficiency is dominant by rotor2. The variation of aerodynamic force is different for the two rotors. In addition, the variation of the fluctuating phenomenon also shows the different behavior for the two rotors as the axial spacing increased. The perturbation form in the tip region varies for different axial gaps. For the axial gap of 60% a spiral focus is generated, and the perturbation form turns to be a star node at the axial spacing of 40%. The impact of the stable spiral focus on the flow field results in the reduction of the efficiency for a larger axial spacing.