Yu Rao

Compared to traditional film cooling, effusion cooling provides stronger internal convection and better external film attachment. However, the poor mechanical properties of conventional cylindrical hole arrays limit their widespread application. Triply periodic minimal surface (TPMS) lattices exhibit isotropic mechanical properties without stress concentrations, making them highly suitable for advanced effusion cooling designs. In this study, steady-state infrared thermography was employed to evaluate the thermal performance of uniform and gradient-porosity TPMS topologies (Diamond, Gyroid, and Koch) while numerical simulations revealed the underlying mechanisms. Results indicate that the Diamond lattice maintains a low pressure loss alongside high cooling effectiveness, while the Koch lattice yields the highest overall cooling effectiveness. To address upstream lattice “coolant starvation” and hot gas ingestion caused by mainstream backpressure, a gradient porosity design was introduced. This design significantly improves spatial uniformity: the uniformity index increased by up to 12.7%, the standard deviation decreased by up to 61.4%, and the area-averaged overall cooling effectiveness improved by a maximum of 6.1% compared to the uniform baselines. At a low injection ratio, the uniform configurations channel nearly 50% of the coolant through the trailing row. In contrast, the gradient lattice increases the central coolant mass flow ratio by up to 154.4%. Flow analysis demonstrates that the gradient design shifts the high wall-normal velocity region upstream to resist mainstream ingestion, thereby reducing the scale of downstream counter-rotating vortex pairs to sustain a well-attached protective film. Finally, empirical correlations were developed to provide valuable design guidelines for advanced turbine cooling systems.

Triply periodic minimal surface (TPMS) lattices provide a promising architecture for transpiration cooling by promoting uniform near-wall coolant coverage. Although their time-averaged cooling performance has been investigated, the unsteady organization of the wall thermal response and the associated flow structures remains insufficiently understood. In this study, wall-resolved large eddy simulations were performed for diamond and gyroid TPMS transpiration cooling at coolant injection ratios of 9.0% and 18.0%. Proper orthogonal decomposition (POD) was applied to the fluctuating wall cooling effectiveness and wall-normal velocity fields to quantify modal energy distributions and identify leading unsteady structures. Results show that, for both lattices, the coolant coverage extended farther downstream at F = 18.0% than at F = 9.0%, while the area-averaged standard deviation of cooling effectiveness differed only slightly between the two conditions. The diamond lattice produced around 20% higher area-averaged cooling effectiveness and a 5% lower relative fluctuation level than the gyroid lattice, indicating more effective and temporally stable wall protection under the present conditions. The POD energy spectra of both TPMS lattices were broadly distributed across multiple modes, with each leading mode accounting for only a limited fraction of the total fluctuation energy. The leading thermal modes were concentrated near the local jet exits of the TPMS lattices, reflecting unsteady coolant discharge and variations in near-wall coverage in the exit region. Their broadband spectra demonstrated that the leading wall thermal response spanned multiple time scales. The instantaneous fields and velocity POD modes further revealed multiscale flow disturbances with streamwise convective organization, and several velocity modes exhibited preferred-frequency peaks.

The supercritical carbon dioxide (SCO₂) Brayton cycle presents a promising alternative to the traditional steam Rankine cycle, owing to its superior thermal efficiency, high power density, and compact design. As a key component governing system performance, the heat exchanger requires a highly compact and efficient design. This study proposes a novel additively manufactured (AM) wavy microchannel heat exchanger that achieves a compactness of 1670 m²/m³. The design incorporates adaptive flow channels to accommodate SCO₂’s density variation, along with wavy patterns and ribs to enhance thermal performance. A comprehensive fluid–thermal–mechanical coupling numerical analysis was conducted to evaluate its thermal–hydraulic and mechanical performance. Within the Reynolds number range of about 900–6000, the wavy structures improve the heat transfer rate by 21–58%, compared with the straight channel. The maximum effectiveness (ε = 0.66) occurs at a Reynolds number of 900. Compared with other heat exchangers used in the SCO₂ cycle, the overall performance of the hot and cold channels has improved by 12–44% and 3–89%, respectively. Structural analysis confirms that the average total stress under operating conditions remains below the yield strength of the Inconel 617 material, with thermal stress being the dominant contributor. This work underscores the potential of the proposed AM heat exchanger to deliver a superior combination of compactness, thermal–hydraulic performance, and structural integrity for advanced SCO₂ power cycles.

This research numerically investigates the cooling performance of Diamond-type triply periodic minimal surface (TPMS) networks as a gas turbine effusion cooling layer, augmented with various jet impingement configurations. The study analyzes the internal and external flow characteristics, pressure loss, and overall cooling effectiveness using conjugate heat transfer simulations. The Diamond design is compared to conventional film cooling and micro-hole models within a blowing ratio range of 0.5 to 2.0. The jet hole diameter and jet-to-plate distance are varied to identify an optimal double-wall cooling configuration. The results reveal that the Diamond hole mitigates the strong discharge of coolant, resulting in a more adherent cooling film, which provides excellent surface coverage. While jet impingement enhances internal heat transfer, its contribution to cooling effectiveness is minor compared to the benefit of film coverage. At an equivalent total pressure loss coefficient, the Diamond with impinging jets demonstrates 101% higher cooling effectiveness than the film hole. The thermal-mechanical analysis indicates that the Diamond model exhibits a more uniform distribution of thermal stress and displacement. The average stress is reduced by 44.7% compared to the film hole. This work confirms the TPMS-based effusion as an advanced cooling solution for next-generation gas turbines.

Integrated additional cooling channels offer precise thermal management for solid-oxide fuel cells (SOFCs), mitigating temperature gradients. This research studies the thermal–hydraulic performance of cooling channels integrated between SOFC interconnectors, including a Diamond-type triply periodic minimal surface (TPMS), a conventional topology-optimized structure, and a topology-optimized lattice-filled structure. A conjugate heat transfer analysis is employed to investigate the influences of flow rate within the range of Reynolds numbers from 300 to 5000, and the effects of coolant type, including air and liquid metals, as well as the impacts of structural material. The results demonstrate that the topology-optimized lattice-filled structure, generating high turbulence mixing, achieves superior temperature uniformity, especially at high flow rates, despite having higher thermal resistance and pressure loss than the conventional topology-optimized design. The coolant types show the largest influence on thermal–hydraulic performance, and the use of liquid gallium in the conventional optimized design obtains the best temperature uniformity, yielding differences between the maximum and minimum temperatures of less than 5 K. Moreover, the higher-thermal-conductivity material improves temperature uniformity, even at low flow rates. Overall, the optimized-baffle designs in the conventional topology-optimized model, utilizing high-conductivity coolant and structural materials, could be the most suitable for thermal management of the SOFC.