The use of slotted blades for centrifugal fan impellers improves fluid flow steadiness and reduces fan noise. The slots create a jet of fluid from the pressure side to the suction side that increases the momentum of the main flow and postpones the flow separation. In addition, these slots make the fluid movement smoother and more efficient in impeller passages. In previous research, the optimum slot location was determined at 40% from the leading edge (at diameter Ds=0.65 DImpeller) with a 2.5 mm width. The present research concentrates on determining the optimum slot jet angle of a ten-blade backward curved centrifugal fan at the best efficiency point (BEP). Six values of slot inclination angles, namely θS1, θS2, θS3, θS4, θS5 and θS6, ranging from an inward slot direction of (+60°) to an outward direction of (-80°), are simulated numerically using an unsteady Computational Fluid Dynamics (CFD) model. The CFD results have proven the benefits of the outward slots that ranged from (θS= -60° to -80°) on stall control of the fluid on the blade suction side compared with the inward slots. At the BEP, the computed performance of the tested fan with an outward slot inclination angle θS6 =-80° showed a 2.6 percent efficiency improvement compared to fans with an inward slot of θS1=+60°. Generally, the outward slot direction has a positive effect on the boundary layer attachment on the suction side of the blade. |
