Effect of Suction Slot Location and Width on the Performance of Centrifugal Fan

Abstract

: Blade slots are known to reduce the noise and improve flow behavior and steadiness in centrifugal fans. The present work considers an unsteady Computational Fluid Dynamic (CFD) study to investigate the effectiveness of slot location and width on the performance and flow field inside the centrifugal fan blade passages. The computer program, Fluent 19, is used and the 3D fan model is validated by comparing its results with those of earlier researchers. The aim of the present study is to find the best slot location and appropriate slot width at that location. The flow pattern is then analyzed and simulated with no slot and with a slot at six different radial locations; namely S1, S2, S3, S4, S5, and S6 with fixed slot width W of 2.5 mm. The computationally generated characteristics of unsteady flow demonstrated that although cut slots at all locations on the fan blade from the hub to the shroud has a negative influence on the centrifugal fan efficiency as well as the static pressure rise compared with the fan without slot, the slots added at S3 i.e. near the midpoint of the blade span gives the highest fan efficiency and largest increase in static pressure. Slots at S3 suppress secondary flow at the blade passages and push it to the blade tip. Additionally, streamlines and velocity distributions in impeller passages and over the blade surfaces (pressure and suction sides) validated the slots' benefits. Computations width different slot width; namely 1.5 mm, 3.5 mm, and 5 mm are carried out to find the best slot location and width at the best slot location S3. At the optimal efficiency point, the calculated performance of the employed fan with slot location S3 and 2.5 mm width, showed a 2.7 % increase of efficiency and 1.5% increase in static pressure rise as compared to fans with slot at S1 with same width of 2.5 mm. However, it showed a positive impact on the boundary layer buildup and flow separation over the blade suction side for the impeller studied .