Affiliations: Department of Mechanical Engineering, Faculty of
Engineering, Jai Narain Vyas University, Jodhpur 342011, India. E-mail:
karwa_r@yahoo.com, and bkmaheshwari@hotmail.com | Department of Mechanical Engineering, Technical
University Darmstadt, Darmstadt 64287 Germany. E-mail:
nitinkarwa@gmail.com
Abstract: The paper presents results of flow visualization and mass transfer
studies for fully developed turbulent flow of air in a square section wind
tunnel with repeated chamfered rib roughness on the bottom of the tunnel (rib
head chamfer angles � of −15°, 0°, and 15°; relative
roughness pitch p/ e = 3, 5, 7.5, and 10). Direct video recordings of flow
patterns were made using a simple technique of particles visualization. For the
positively chamfered closely spaced ribs (p/ e ⩽ 5) vigorous vortex
shedding has been seen compared to the square or negatively chamfered ribs,
which is found to be a function of the Reynolds number. For the widely spaced
ribs, the study shows flow separation at the ribs and reattachment in the
inter-rib region. Local mass transfer studies, based on the variation in colour
of cobaltous chloride solution impregnated paper due to evaporation of water,
showed a significant improvement in mass transfer rate in the recirculating
region in the wake of ribs with the change in the chamfer angle from −15° to
15°. The positively chamfered 15° ribs are found to be better than square
section ribs at p/ e ⩽ 7.5. The performance of negatively chamfered ribs is
found to be poor compared to other ribs irrespective of the relative roughness
pitch.
Keywords: Rib roughness, Chamfer, Flow Structure, Mass Transfer Study
