Settling Length for Turbulent Flow of Air in Smooth Annuli With Square-Edged or Bellmouth Entrances

Abstract

Settling or hydrodynamic entrance lengths have been determined for turbulent flow of air in three smooth concentric annuli of diameter ratios 0.306, 0.527, and 0.842. Both square-edged and bellmouth entrances were investigated for Reynolds number ranging from 7000–47,500. Flow separation caused by the abrupt change in area of the square-edged entrance resulted in skewed (distorted) velocity profiles near the entrance. This skewness was modified further downstream and finally fully developed velocity profiles were established. The settling lengths for the annuli with the square-edged entrances were between 25 and 35 dia. With the bellmouth entrance, the velocity profile developed conventionally from the nearly flat profile at the inlet. The settling lengths for the bellmouth entrances were about 10–15 equivalent diameters more than those for the square-edged entrances.

Developing turbulent flow in concentric annuli: An analytical and experimental study

“…17 shows that the local turbulent intensity distribution reached its limiting value at the values of (x/De) somewhere between those based on (Umax)x/(U~ax) ~--t.00 and (/x//d) = 1.00. The agreement between the present results and those of Sm~II)HA]~ et al [11] based on (U~a~)~/(Uma~) = 1.00 is good. In this paper, the results in a circular pipe have not been compared with those of the present study as the wall boundary conditions are different.…”

“…The flow in this region of a duet or channel is obviously dependent on the shape of the inlet section. The flow in an entrance with a rounded inlet section is not the same as the flow existing in an entrance with a square-edged inlet section, as shown by experiments [9,10,11]. For a rounded entrance, a reasonably uniform velocity exists at the entrance and one can expect that the boundary-layer will progress from laminar to turbulent.…”

“…On the contrary, very few works on developing turbulent flow in concentric annuli of constant cross-sectionM area can be found in the literature. The experiments regarding the momentum entrance region in annuli appear to be confined to those of RoT~Pus et al [8], OLSO~ and SPARROW [9], O~IISm and SEROVu [10], and S?aID~A~ et al [11]. The analytical results on the subject is even more scarce.…”