| dc.description.abstract | A computational fluid dynamics (CFD) analysis was performed on developing turbulent flow of air in straight ducts. A uniform inlet velocity was assumed for two different scenarios, namely at the straight duct inlet and at the inlet of a right-angle elbow located immediately upstream of the straight duct. Using STAR CCM+ commercial software, velocity gradient profiles and pressure gradient profiles were obtained for different flow rats and duct sizes representing a range used in engineering practice including round and rectangular duct geometries with the latter having aspect ratios of 1, 1.5, and 2.
The results show that the velocity and pressure developing lengths in round ducts were shorter than those in corresponding square ducts by around 13% and 19%, respectively. Also, the velocity and pressure developing lengths in round ducts were shorter than the corresponded rectangular ducts with a 1.5 aspect ratio by around 25% and 30% respectively. Similarly, the developing length in the round ducts were shorter than the corresponding rectangular ducts with an aspect ratio of 2 by around 36% based on the velocity profiles and 40% based on the pressure profiles. All of the above results indicate that the developing length of the flow is geometry dependent in addition to being Reynolds number dependent.
Comparing the CFD results for the square and rectangular ducts shows that the velocity developing length of the square duct was 15 % and 27 % less than the developing length for the 1.5 and 2 aspect ratio ducts, respectively. Similarly, the pressure drop developing length in the square duct was 16% and 27 % less than those for the 1.5 and 2 aspect ratio ducts, respectively.
Last but not least, comparing the CFD entrance length of a round duct with a well-known experimental entrance length correlation, the results of the CFD approach used in this study were within 10% of the experimental results. | en |
