Effect of axial spacing on rotating stall performance of FBCDZ-10-No20 contra-rotating fan

Mining contra-rotating fan are prone to rotational stall when it operates at low flow rates, which seriously affects the operational stability. The unsteady flow in the full flow passage of a FBCDZ-10-No20 contra-rotating fan at five axial spacings was numerically simulated by using the SST k-ω turbulence model. The effect of axial spacing on the stall process of contra-rotating fan was studied, and the mechanism of stall inception and development at different axial spacings was revealed. The results shown that the axial spacing had a significant influence on the initial position, type and development of stall inception. For the axial spacings of 70 mm and 100 mm, the stall inception first occurred at the tip of the front stage, and subsequently appeared at the tip of the rear stage due to the rotor-rotor interaction between the two stages. However, compared with the axial spacing of 70 mm, the rotor-rotor interaction at the axial spacing of 100 mm was relatively weak, making it take longer for a stall inception to occur in the rear stage. For all three axial spacings of 140 mm, 170 mm and 225 mm, the stall inception occurred first in the root of rear stage. The difference was that for the axial spacing of 140 mm, the leakage flow at the tip of the front stage cannot completely flow out of the channel with the main flow, and a localized tip blockage area was formed. However, for both spacings of 170 mm and 225 mm, there was almost no blockage area at the tip of the front stage, and eventually only mature stall vortices formed in the rear stage. With the increase of the axial spacing, the blockage area formed by both the leading edge overflow and the trailing edge reverse flow those originated from the leakage flow at the tip of the front stage gradually reduced. In contrast, the blockage area formed by the radial vortex on the suction surface near the root of the rear stage gradually increased. When the leakage flow at the tip of the front stage failed to form blockage area, the stall type changed from the “spike type” induced by the tip leakage flow at the front stage to the “localized surge type” induced by the radial vortex flow at the root of the rear stage.