Optimization of heat transfer and friction characteristics of a rotating U-channel with a combination of variable size connecting bridges

Abstract

Gas turbine blades typically feature a U-shaped or multi-flow snake channel in their mid-chord region, both incorporating a 180° turn. However, the addition of fins and dimple or protrusion turbulent flow structures can result in excessive pressure losses within the flow channel. This study aims to reduce pressure loss and improve flow uniformity by inserting one to three connecting bridges of varying sizes in the gap between the two channels. The suitability of various connecting bridges with different angles and sizes is assessed in both stationary and rotating states through simulations. Subsequently, the cooling efficiency and reduction in resistance performance of different-sized connecting bridge combinations are evaluated. A layout scheme for optimal connecting bridge placement within the U-shaped channel is proposed. Results indicate that the incorporation of a single minimum-size connecting bridge leads to an average 22.6 % decrease in overall flow resistance within the U-shaped channel, and simultaneously yields a 3.5 % increase in the overall thermal performance. When using the recommended connecting bridge angle and layout combinations, the incorporation of connecting bridges leads to an average 46 % and 49.7 % reduction in overall flow resistance within the U-shaped channel in order to counterbalance pressure losses generated by turbulent structures. This effect consequently results in a 6.5 % and 6.6 % increase of the overall thermal performance. This study offers new insights and data-backed evidence that can potentially facilitate the design of high-efficiency and low-resistance cooling methods in the mid-chord region of high-temperature turbine blades.