الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 147 |  |  |
| | | from | 147 | | |
Abstract
otted Blades are known to reduce noise and improve flow behavior and
teadiness in centrifugal fans. Slot creates a jet of fluid that passes from the blade
pressure side to the suction side. The benefit of the slot jet is to increase the main flow
momentum and postpone the flow separation at the blade suction side. In addition, the
slot with optimum geometry makes the fluid movement smoother and more efficient in
impeller passages.
The present work utilities an unsteady Computational Fluid Dynamic (CFD) study to
investigate the effectiveness of slot location, width, and inclination angle on the fan
performance and flow steadiness inside the fan impeller. 3D flow through ten-backward
curved centrifugal fan model is numerically simulated by a commercial CFD (ANSYS
FLUENT.19) program. The fan performance and flow characteristics inside the
impeller-volute interaction are validated by comparing their results with measurements
on the same fan by earlier researchers. The CFD simulations results allowed for a more
detailed analysis of the flow field, including the identification of regions of high
turbulence stresses and recirculation inside the fan impeller.
The objective of the present study is to find the best slot location and appropriate slot
width at that location followed by finding the optimum slot jet direction. The flow
pattern is firstly analyzed and simulated without slot and then simulated with slot at six
different radial locations, namely S1, S2, S3, S4, S5, and S6 at a distance from the leading
edge with respect to the blade cord equal to (x/c = 15, 30, 40, 50, 65, and 80%) with a
fixed slot width of 2.5 mm (w/c= 0.8%) and a fixed slot jet inclination angle of θS=-60°
directed outward towards the blade trailing edge. The computationally generated
characteristics of unsteady flow at the fan outlet duct demonstrated that they improve
flow steadiness and reduce noise levels. The slots added at S3 i.e. near the midpoint of
the blade span (at 40% from the leading edge), showed a 2.6 % increase in efficiency
as compared to fans with slot at S1 (near the leading edge) and 3.6 % increase in static
pressure rise coefficient as compared to fan with slot at S6 (near the trailing edge).
However, span wise slots at all locations on the fan blade from the hub to the shroud
have an adverse influence on the centrifugal fan efficiency as well as the static pressure
rise compared with the fan without slots.
S Computations width different slot widths; namely W1.5, W2.5, W3.5, and W5, as a
percentage with respect to the blade cord equal to (w/c = 0.5, 0.8, 1.1, and 1.6%), are
carried out to find the best slot width at the best slot location S3. The results revealed
that the optimum width was found to be W2.5 (w/c = 0.8%) with 2.1 % increase in
efficiency as compared with W5.
Finally, the flow at the blade sides was examined and simulated for six distinct slot
inclination angles, designated θS1, θS2, θS3, θS4, θS5 and θS6. These angles ranged from
an inward slot direction of θS1= +60° to an outward direction of θS6 = -80° located at
the optimum slot location S3 and width of W2.5 (w/c = 0.8%). The CFD results have
proven the benefits of the outward slots ranged from (θS = -60 ° to -80°) on stall control
of the fluid on the blade suction side compared to inward slots. At the BEP, the
computed performance of the simulated fan with an outward slot inclination angles θS5
and θS6 showed a 2.6 percent efficiency improvement compared to fans with inward
slot of θS1.