Entropy-based evaluation and optimization of double-wall cooling structures: Design and experimental validation

The design of double-wall structures must minimize the impact on engine performance while simultaneously ensuring effective cooling. Current research on cooling efficiency, which considers parameters such as blowing ratio, as well as studies on aerodynamic flow losses, do not adequately meet the design requirements for double-wall structures in engine environments. This paper presents an entropy-based cooling effectiveness (ECE) metric that integrates the cooling performance of double-wall structures with the associated system losses in the engine. This metric serves as an effective tool for comparing the design levels of various cooling structures under engine operating conditions. Simulation results indicate that external cooling structures with a small blowing ratio and internal cooling structures characterized by weak impingement and a high heat transfer area are pivotal in enhancing the low-entropy generation design of double-wall structures. A novel double-wall structure is proposed, which features V-shaped fins and small-blowing-ratio film-cooling holes (VF-SF). Experimental tests were conducted in a high-temperature wind tunnel, comparing the conventional 121 structure with the newly proposed VF-SF structure. The research findings revealed significant improvements in both overall cooling efficiency (ϕ) and ECE with the VF-SF design. Under comparable engine conditions, specifically with a bleed air ratio of 3.8 %, the VF-SF structure exhibited a 76 % increase in ϕ and an 84 % enhancement in ECE, marking a substantial advancement in low entropy generation design. These results offer critical insights for optimizing the design of double-wall structures within engine system environments and highlight the considerable potential for enhanced thermal management in aircraft engines.