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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER IN THE SEPARATION ZONE BEHIND A BACK-FACING STEP IN THE PRESENCE OF TABS

Get access (open in a dialog) DOI: 10.1615/IHTC16.hte.022580
pages 4985-4992

Resumo

Control of the transfer of heat and mass between separated flows exerted using tabs is an important area in the field of reliability and efficiency enhancement of heat-andpower apparatuses and gas-turbine plants. This work was aimed at experimental investigation of the heat transfer in the recirculation region behind the back-facing step with placed tabs. The experiments were performed at Reynolds number Re = 4 000 based on the average velocity U and step height H=10 mm. Tabs height Δ and distance to the back-facing step S were varied (Δ from 3 to 6 mm and S from 0 to 40 mm). The spanwise spacing between two adjacent tabs P was varied (P from 12.5 to 75 mm) in multiply tabs. Measurements were carried out by the thermal imager. Thermographic visualization of the flow behind the step in the presence of a solid mini rib or tabs installed upstream of the step was performed. The thermograms show that the tab produces a pair of counter rotating streamwise vortices and the nominally two-dimensional separating flow becomes the fully three-dimensional one behind the step. Despite the decrease in the temperature the back-facing step with placed tabs, it was increased in a downstream region from the interaction of streamwise vortices. The coordinate of the heat transfer peak was reduced at all the spanwise locations through the increased entrainment of high momentum fluids into the recirculation region. The most significant shift of the peak to the base of the step (Xmax /H ~ 3.6) was observed in the case where the flow separated from the tabs reattaches in the vicinity of the step edge (Δ = 6 mm, P= 25 mm). It was shown that reattachment of the flow disturbed by the tabs intensifies the heat transfer on the surface behind the backward-facing step. An increase in the height of the tabs also leads to an increase in the maximum heat transfer coefficient. The data on the average heat transfer coefficient allow estimating the intensity of the heat transfer process, depending on the intensity of interaction of the separated flows.