This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance. Some combined-hole designs with swirling coolant flow entering the delivery hole are proposed and analyzed. Adiabatic film cooling effectiveness values for cases with various blowing ratios are compared. Detailed flow structures and underlying mechanisms are discussed. The results show that film cooling effectiveness is improved with jet swirl at high blowing ratios, and that swirl strength has significant influence on film cooling performance. Combined-hole designs can further improve film cooling performance using swirling jets due to mixing of coolant flows and interaction of vortices. The largest improvements of area-averaged film cooling effectiveness for a single-hole swirl case and a combined-hole swirl case over corresponding non-swirling case results are 157% and 173%, respectively.

Attempts for higher output power and thermal efficiency of gas turbines make the inlet temperature of turbine to be far beyond the material melting temperature. Therefore, to protect the airfoil in gas turbine from hot gas and eventually prolong the lifetime of the blade, internal and film cooling structures with better thermal performance and cooling effectiveness are urgently needed. However, the traditional way of proceeding involves numerous simulations, additional experiments, and separate trials. Optimization of turbine cooling structures is an effective way to achieve better structures with higher overall performances while considering the multiple objectives, disciplines or subsystems. In this context, this paper reviews optimization research works on film cooling structures and internal cooling structures in gas turbines by means of various optimization methods. This review covers the following aspects: (A) optimization of film cooling conducted on flat plates and on turbine blades or vanes; (B) optimization of jet impingement cooling structures; (C) optimization of rib shapes, dimple shapes, pin–fin arrays in the cooling channels; (D) optimization of U-bend shaped cooling channels, and internal cooling systems of turbine blades or vanes. The review shows that through a reliable and accurate optimization procedure combined with conjugate heat transfer analysis, higher overall thermal performance can be acquired for single-objective or multi-objectives balanced by other constrained conditions. Future ways forward are pointed out in this review.

Supercritical fluids (e.g., hydrocarbon fuels, water, carbon dioxide, and organic working medium, etc) have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion, and have been used or selected as the working fluids in engineering fields such as aerospace, nuclear power, solar energy, refrigeration, geothermal energy, chemical technology, and so on. To better understand the interesting characteristic or abnormal behaviors of supercritical fluids, most valuable research works (including experimental results and numerical studies) from domestic and abroad have been documented. As such, this paper presents a comprehensive review on heat transfer behaviors of some supercritical fluids in engineering applications. This review focuses on recently available articles published mainly from 2016 up to the present time. The common problems (i.e., heat transfer enhancement and heat transfer deterioration particularly for the supercritical hydrocarbon fuels) in the supercritical field are summarized and some perspectives on future prospects are also included.