Compact and rapid heat transfer technology can, within ultra-confined spaces and on the order of milliseconds, efficiently capture and transport large amounts of heat from the intake or internal components. It is the core determinant of both performance and technical success for a precooled engine. Conventional civil use heat exchanger analysis, design procedures, and experimental testing approaches are insufficient for validation due to the harsh operating environment and demanding performance requirements inside such systems. Therefore, conducting highly targeted, application oriented research on compact and rapid heat transfer technology specifically for precooled engines carries significant academic and engineering value. In this paper, the research progress of compact and rapid heat transfer technology from multiple dimensions, including underlying mechanisms, technical approaches, and experimental methods, is systematically reviewed, and the principal challenges it faces when applied to precooled engines are analyzed. Existing studies have yielded extensive and in-depth results in several areas: the mechanisms of rapid and intensive heat transfer of supercritical working fluids in microscale channels and cross-flow tube bundles; rapid simulation and similarity analysis methods for fluids with sharply varying properties; refined and uncertainty quantification based design methodologies; and experimental testing techniques tailored for extreme thermal environments in confined spaces, etc. Overall, in terms of fundamental research, it is urgent to deepen our understanding of the coupled flow heat transfer mechanisms under complex thermal conditions at micro scales and to further enrich high accuracy empirical correlation databases for compact and rapid heat transfer. From an analysis and design perspective, attention should be paid to integrating emerging techniques into analysis and design methods to enhance overall performance across broad operating ranges. In terms of experimental validation, more sophisticated flow-field measurement techniques appropriate for intricate structures in confined spaces must be developed, and complete temperature and full pressure testing must be conducted under actual engine installation circumstances. These research efforts will provide a solid foundation for improving the maturity of compact and rapid heat transfer technology and for advancing and validating precooled engine technology.

Multiscale mixing of the turbine blade tip leakage and mainstream flows causes considerable aerodynamic loss. Understanding it is crucial to correctly estimating the mixing loss and thus improving the turbine’s performance. The multiscale mixing phenomenon in a typical high-pressure turbine rotor flow was studied in this work. The contributions of various scale flows to entropy production and mixing properties were identified. The corresponding physical mechanisms at different scales were explored. It is shown that the large-scale and time-averaged flow contributions to mixing are significant, accounting for approximately 37.1 % and 25 % of the total. Time-averaged and large-scale flows cause the majority of the fluid deformation of the material surface, while meso- and small-scale flows just generate finer deformations. It raises the area stretch coefficient and the virtual concentration gradient. Thus, mixing is enhanced. Furthermore, time-averaged and large-scale flows account for the majority of the losses in the upstream and downstream regions of the blade tip respectively, accounting for approximately 53.8 % and 33.5 % of the total. The sheet-like structures—rather than the tip leaking vortex—are the primary source of the loss. High-dissipation regions are produced by the sheet-like structures via the pressure Hessian term and the self-amplification terms.

The precooler is a distinctive component of precooled air-breathing engines but constitutes a challenge to conventional thermal design methods. The latter are based upon assumptions that often reveal to be limited for precooler design. In this paper, a refined design method considering the variations of fluid thermophysical properties, flow area and thermal parameters distortion, was proposed to remediate their limitations. Firstly, the precooler was discretized into a fixed number of sub-microtubes based on a new discretization criterion. Next, in-house one-dimensional (1D) and two-dimensional (2D) segmented models were established for rapid thermal design and precooler rating with non-uniform airflow, respectively. The heat transfer experimental studies of supercritical hydrocarbon fuel were performed to verify the Jackson correlation for precooler design and the in-house models were validated against the reported data from open literature. On this basis, the proposed method was employed for the design analysis of hydrocarbon fuel precoolers for precooled-Turbine Based Combined Cycle (TBCC) engines. The results show that the local performance of precoolers is intrinsically impacted by the aforementioned three variations. In the case study, the local heat transfer performance is drastically affected by coolant flow transition. While the circumferential temperature distortion of airflow is weakened by heat transfer. With consideration of additional parameter variations, this novel method improves design accuracy and shortens the design time.