Flow visualization and local mass transfer studies for turbulent flow in a wind tunnel with chamfered ribs |
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Authors: | Rajendra Karwa B K Maheshwari Nitin Karwa |
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Institution: | (1) Mechanical Engineering Department, Indian Institute of Technology, Delhi, New Delhi, -110016, India; |
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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 ϕ of
-15°, 0°, and 15°; relative roughness pitchp/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 atp/e <- 7.5. The performance of negatively chamfered ribs is found to be poor compared to other ribs irrespective of the relative
roughness pitch. |
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