The thermal efficiency and power output of gas turbine is highly dependent on the turbine inlet temperature, which is continuously raised and has exceeded the temperature limitation of advanced materials, making advanced cooling technique necessary and important. Internal cooling and film cooling are two main cooling methods in modern gas turbines. They work together to protect the high-temperature components. This paper presents the results of a computational study on cooling performance for a flat plate with both film cooling and internal cooling using conjugate heat transfer analysis. Three internal delivery channel geometries, smooth channel, channel roughened by square ribs, and channel roughened by crescent ribs, are studied with cylindrical film cooling holes. Cases with three blowing ratios for film cooling and two Reynolds numbers for internal cooling are computed. The respective conjugate cooling performances are compared. To help understand the interaction between film cooling and internal cooling, detailed flow and heat transfer characteristics are presented and discussed. Results show how overall cooling effectiveness is controlled by conjugate heat transfer of the two cooling schemes. For the internal cooling, adding straight ribs and crescent ribs both enhance the overall cooling effectiveness greatly, as the ribs broken the boundary layer and create vortices between the ribs, which enhances the mixing in the delivery passages and thus improves the heat transfer efficiency. Crescent ribs can further enhance the heat transfer near the ribs by creating longitude vortices, compared to the straight rib cases. The film cooling effectiveness decreases with increasing blowing ratio, as the coolant film tends to blow off from the plate at large blowing ratios. The internal cooling effectiveness also decreases with increasing blowing ratio, because less coolant goes through the internal channel after the film cooling hole. At larger Reynolds number, the internal heat transfer is enhanced, and takes the dominating position in the conjugate heat transfer. The film cooling effectiveness is affected by the internal channel geometry near the hole inlet, because the vortices created by the ribs will change the flow inside the film cooling hole, and then influence the interaction between the film cooling jet and the mainflow. The internal cooling performance is also influenced by the sucking effect of film cooling, which enhances the heat transfer near the hole inlets. Overall, film cooling and internal cooling are influenced by each other, making conjugate heat transfer analysis important in the design of cooling system in gas turbines. KEYWORDS: Film cooling; Internal cooling; Rib-roughened channel; Conjugate heat transfer.

Conjugate Heat Transfer Analysis of Film Cooling With a Rib-Roughened Delivery Passage

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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