Analysis and Optimization Design of Internal Flow Evolution of Large Centrifugal Fans Under Inlet Distortion Effects

Large curvature, high pre-swirl large high-speed centrifugal fans are the preferred choice for industrial gas quenching furnaces, as they need to operate under non-uniform inlet conditions for extended periods. The resulting inlet distortion disrupts the symmetric flow of the gas, leading to reduced fan stability and phenomena such as flow separation and rotational stall. This issue has become a key research focus in the field of large centrifugal fan applications. This paper introduces an eddy viscosity correction method, and compares it with experimental results from U-shaped pipe curved flow. The corrected SST k-ω model shows a maximum error of only 4.7%. Simulation results show that the fan inlet generates a positive pre-swirl inflow with a relative distortion intensity of 3.83°. The flow characteristics within the impeller passage are significantly affected by the swirl angle distribution. At the maximum swirl angle, the leakage flow at the blade tip develops into a stall vortex that spans the entire passage, with an average blockage coefficient of 0.29. At the minimum swirl angle, the downstream leakage flow at the blade tip is suppressed on the suction side by the main flow, leading to a reduced vortex structure within the passage and an average blockage coefficient of 0.21. To address the design challenges of large high-speed centrifugal fans under inlet distortion, a blade design method based on secondary flow suppression is proposed. Eleven impeller flow surfaces are selected as control parameters, and the centrifugal impeller blade profile is redesigned. Numerical simulations and experimental results of the gas quenching furnace’s flow and temperature fields indicate that the modified impeller significantly reduces the blade tip leakage flow strength, with the average blockage coefficient decreasing to 0.07 and 0.04, respectively. The standard deviation of the average flow velocity at the test section is reduced by 42.78% compared to the original, and the temperature fluctuation at the workpiece surface is reduced by 53.09%. Both the flow and temperature field uniformity are significantly improved.