Effects of Round Rib Curvature on Heat Transfer and Friction Characteristics in a Rotating Two-Pass Square Channel

Abstract

In the serpentine internal cooling passages of gas turbine blades, various turbulence-enhancing techniques are employed. In particular, rib turbulators are widely used in the mid-chord region to improve heat transfer performance. This study experimentally investigates the effects of round rib curvature on heat transfer and friction characteristics in a rotating two-pass square channel. Three round ribs with different radii of curvature (r = 20, 15, and 10 mm) were investigated, corresponding to curvature parameters (Cr = l/r) of 1.00, 1.33, and 2.00, based on a straight rib length (l) of 20 mm. Under conditions of rib pitch-to-height ratio (p/e) of 10 and rib height-to-hydraulic diameter ratio (e/Dh) of 0.125, local heat-transfer coefficients and pressure losses were measured to determine the thermal-performance factor. Experiments were conducted under rotating conditions (Ro = 0.00–0.09, Re = 20,000–50,000). The working fluid was compressed air cooled to approximately −47 °C, and the local HTC distributions were measured using the transient liquid crystal technique. Across all rotation conditions, the Cr=1.33 round rib exhibited the highest HTC and greatest friction loss, while the Cr=1.00 round rib achieved the highest TPF. The results demonstrate that thermal performance does not improve monotonically with increasing curvature. Rather, an optimal compromise between heat transfer enhancement and the accompanying frictional penalty, as achieved by the Cr=1.00 round rib, governs overall performance.