Heat Transfer in an Asymmetric Trapezoidal Duct with Angled Rib Turbulators

Abstract Heat transfer characteristics in a turbine-representative trapezoidal duct with angled rib turbulators were investigated over Reynolds numbers of 20,000–60,000. Previous studies have examined non-rectangular ribbed passages, however, simultaneous two-wall, wall-resolved heat transfer datasets that enable direct wall-to-wall comparison in an asymmetric cross-section remain relatively limited. To address this gap, wall-resolved Sherwood number contours were obtained using the naphthalene sublimation method on two ribbed walls, referred to as the vertical and lean walls, which serve as pressure side and suction side analogs. The measured contours show typical angled rib behavior, including rib-imposed streamwise periodicity and pronounced spanwise non-uniformity in Sherwood number. Despite the geometrically asymmetric trapezoidal cross-section, the vertical and lean walls exhibit nearly identical heat transfer levels within experimental uncertainty, with a maximum difference of 3.4 % in area-averaged Sherwood number. Complementary simulations were used to relate the spanwise redistribution to cross-sectional secondary flow structures and to explain the observed wall-to-wall behavior through comparable secondary flow intensity near the two ribbed walls. The present results also provide a direct comparison showing that the area-averaged heat transfer enhancement in asymmetric trapezoidal ribbed passage is slightly lower to that reported for symmetric rectangular ribbed channels under matched Reynolds number and aspect ratio. Overall, the simultaneous two-wall dataset and the flow structure interpretation provide a practical reference for angled rib heat transfer behavior in non-rectangular passages relevant to trailing edge cooling design.