Affiliations: Department of Mechanical Engineering, University of
Alberta, Edmonton, Alberta, Canada
Abstract: Flow visualization results for secondary flow phenomena at the exit
of 90° and 180° bends and helically coiled pipes (1, 2 and 5 turns),
(radius of curvature R_c = 381 mm, inside pipe diameter d=37.5 mm, curvature
ratio d/2R_c = 0.049) and in the downstream straight pipe ( l/d = 30 ) are
presented to study the stabilizing (relaminarization) effect in curved pipes
with fully developed entry turbulent air flow and the destabilizing
(re-transition from laminar to turbulent flow) effect in the downstream
straight region. The entry Reynolds numbers are Re = 2200, 3200, 4300 and
5300). The related measurement results using a hot-film anemometer are
presented for developing profiles of the time-mean streamwise velocity
distribution and the axial turbulence intensity field in the 180° return
bend and in the downstream straight pipe for Reynolds numbers Re = 3200, 4300,
6300 and 8200. The time traces showing the output of the hot-film sensor are
also presented for developing fluctuating velocity field in the 180° bend
and in the downstream straight pipe for the same Reynolds number range. Some
aspects of the relaminarization phenomena in curved pipes and the re-transition
phenomena from laminar to turbulent flow in the downstream straight pipe are
clarified by the present experimental investigation.