Center line turning angle effect on the flow and performance characteristics of
long S-shaped circular diffusers (length/inlet diameter ratio, L/Di =11:4) having an area
ratio of 1.9 and centre-line length of 600mm has been established. The numerical
investigation using three dimensional large eddy simulation model has been performed
for three S-shaped circular diffusers having angles of turn of 15o/ 15o, 22.5o /22.5o and
30o /30o. The simulations were performed at Re=105 based on S-duct inlet diameter, using
1.87 million grid nodes and using Smagorinsky-lilly as a subgrid turbulence model
Cs=0.1. Code validation and grid independence study have been done to examine whether
the physical models used in computer simulations agree with real world observations.
Velocity, total pressure and turbulence intensity distributions at different planes along
the length of the diffusers are obtained and compared with experimental work.
For S-diffusing ducts with different center line turning angle, the magnitudes of counter
rotating vortices being higher for the higher angle of turn. The losses in recovery at
separation region through S-diffusing ducts are increased by the increase of turning
angle. The static pressure recovery coefficient is found to equal (0.516, 0.49, and 0.4551)
for diffusing S-ducts with center line turning angle of (15°/15°, 22.5°/22.5°and 30°/30°)
respectively. The velocity distribution at S-duct outlet station is more uniform, with the
increase of center line turning angle. |
