THE EFFECT OF PLACING VORTEX GENERATORS ABOVE RIBS IN RIBBED DUCTS ONTHE FLOW, FLOW TEMPERATURE, AND HEAT-TRANSFER BEHAVIOR

Flaw temperature and laser-Doppler velocity measurements are presented to understand better the pow and heat transfer behavior resulting fro m the placement of vortex generators above the first and fifth ribs in a ribbed duct airflow (Re = 3450) and as a benchmark for comparing mo del predictions. Because the generator-rib spacing, at the smallest sp acing (s/h = 0.25), was too small for the flow to pass through it, the generator-rib pair functioned as a single element with an increased e ffective height, comprising the rib height, the generator-rib space, a nd the generator proper which resulted in a downstream shift in the fl ow reattachment and peak Nusselt number locations. At s/h = 0.75, the pow expanded as it passed through the generator-rib space. Dictated by the upstream flow conditions, the expansion resulted in a vertical do wnward pow behind the first generator-rib configuration and no vertica l downward pow behind the fifth. The vertical downward pow compensated for generator-induced reductions in the near-wall streamwise velociti es behind the first generator-rib configuration, resulting in increase d local Nusselt numbers, whereas the generator-induced seductions in t he streamwise velocities in the absence of the vertical downward flow gave way to reduced Nusselt numbers behind the fifth generator-rib con figuration.