A Possible Strategy for the Performance Enhancement of Turbine Blade Internal Cooling With Inclined Ribs

Ribbing the internal passages of turbine blades with 45 deg inclined ribs is a common practice to achieve a good compromise between high heat transfer coefficients and not too large pressure drop penalties. Literature studies demonstrated that, for channels having a large aspect ratio, the effect of the secondary vortices induced by angled ribs is reduced and the heat transfer performance is degraded. In order to enhance the performance, a possible strategy consists in introducing one or more longitudinal ribs (intersecting ribs) aligned to the main direction of flow. The intersecting ribs cut the ribbed channel into separate sub-channels and markedly affect the secondary flows with consequent increases in heat transfer performance. Experiments were performed for a rectangular channel with a large aspect ratio (equal to five) and 45 deg inclined ribs, regularly spaced on one of the principal walls of the channel. The effect of one and two intersecting ribs on friction and heat transfer characteristics has been investigated. The ribbed surface of the channel has been electrically heated to provide a uniform heat flux condition over each inter-rib region. The convective fluid was air. Heat transfer experiments have been conducted by using the liquid crystal thermography. Results obtained for the ribbed channel without intersecting rib and with one/two intersecting ribs are compared in terms of dimensionless groups.