Investigation of aerodynamic performance and noise of tip shape clearance in a diagonal flow fan

Unlike centrifugal fans, diagonal flow fans have an air inflow direction at a certain angle to the axis, with tip clearance (TC) significantly affecting aerodynamic performance and noise. This study focuses on investigating the effects of four different TC shapes based on blade height (BH) ratios. Large Eddy Simulation (LES) was used to capture the structure and development of tip leakage flow (TLF) and tip leakage vortex (TLV) accurately. Diagonal flow fan casings with different TC shapes were 3D-printed for aerodynamic performance experiments. The results from both numerical simulations and experiments show that diagonal flow fans with Tapering or Parallel TC shapes achieve superior aerodynamic performance compared to other geometries, with a 24.1% variance in flow rate. The study further indicates that different TC shapes significantly influence the flow field, altering the mechanisms governing turbulence transition on the suction side. Compared to the Diverging shape, reducing the TC width decreases the amplitude of the TLV, which in turn reduces the turbulence-affected area while increasing dominant mode frequencies. Experimental results also confirm that the Tapering-Diverging TC shape yields the lowest noise levels, with a 3.6 dB reduction in Sound Pressure Level (SPL).