Zhao Liu

With the increase in turbine inlet temperatures, effective cooling is essential for all regions of the turbine. However, most previous studies have focused on the thermal protection of individual components, often neglecting marginal areas. From the perspective of multi-zone interactions within the cascades, this study numerically investigates the combined cooling effects between mid-passage gap (MPG) leakage and blade coolant, with a focus on the suction side (SS) and corner cooling. An interesting corner cooling phenomenon is observed, involving interactions among the blade film coolant, leakage flow, and secondary flow. Results show that corner cooling is enhanced when the coolant is either guided by a counter leakage vortex or when the vortex is weakened by leakage. The combined effects of MPG leakage and blade coolant expand the cooling coverage on the suction side and contribute to achieving full surface thermal protection. Additionally, while a compound angle improves blade cooling, its effect is limited and mainly improves the peak value of laterally-averaged cooling effectiveness (ηl). When the blowing ratio of blade coolant (Mb) increases from 0.5 to 1.5 at leakage mass flow rate (MFRg) = 1%, the peak value of ηl on the blade suction side increases by 51%. Under this condition, when film holes are with a compound angle (β) value of 30°, the peak value of ηl further increases by 17.9%. These findings highlight the importance of considering the synergistic effects of passage vortices and leakage flows in future blade cooling designs to achieve more comprehensive and effective suction-side coverage.

For the design of modern gas turbine, cooling sources such as middle passage gap leakage flow, upstream slot leakage flow, and discrete film holes are designed to protect the blade. This research included middle passage gap leakage flow and two shapes of film holes (cylindrical holes and fan-shaped holes). First, experiment was carried out to verify the turbulence model at an inlet mainstream Reynolds number of 340,000, blowing ratio (M) of 1.0, and middle passage gap leakage mass flow ratio of 0.5%. Then, the circumferential positions of the endwall discrete film holes were optimized, and 100 samples were generated through Latin hypercube sampling (LHS) method, among which 80 samples were selected as the training data and 20 samples were selected as the verification set of radial basis function (RBF) neural network. Then particle swarm optimization (PSO) algorithm was adopted for the optimization. Finally, the flow structure, adiabatic film cooling effectiveness, and aerodynamic losses of four surrogate models were analyzed to achieve the most effective film hole arrangement on endwall. The results draw a conclusion that compared with the baseline and the best sample model, the area-averaged film cooling effectiveness of the endwall for most effective case increased by 188% and 9.6%, respectively. The area-averaged aerodynamic loss along the blade height at the endwall outlet decreased by 1.7% and 0.96%. Finally, the staggered arrangement of film holes shows the best film cooling performance.

Mortise and tenon are very important parts of gas turbine dealing operation safety. Additionally, the temperature distribution of the turbine blade and disk is affected by the heat transfer characteristics in its gap. Then, the S-shaped mortise and tenon gap were numerically studied under rotating conditions, and the flow and heat transfer characteristics were analyzed. First, the heat transfer coefficient (HTC) of the mortise and tenon surfaces was measured with thermochromic liquid crystal. Then, the numerical method was verified using the test results, and the grid independence analysis was conducted. Finally, the flow and heat transfer characteristics of the gap under static and rotating conditions were numerically studied, five different Reynolds numbers (Re = 15,000, 20,000, 25,000, 30,000, 35,000) and five gap widths (d = 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm) were conducted and analyzed in detail. The results show that, under the rotating condition, the pressure distribution in the gap is different from that of the static condition; the pressure increases along the radial direction due to the action of centrifugal force and reaches its maximum value at the corner of the “S” shaped structure. With the increase in Re, the heat transfer intensity of the gap increases gradually. Additionally, the heat transfer intensity of the gap increases with an increase in its width.

A liquid carbon dioxide energy storage (LCES) system has the characteristic of compact structure and easy liquefaction. As a component of heat recovery in the LCES system, the recuperator plays a crucial role in influencing the round trip efficiency (RTE) of the energy storage system, but very little attention has been paid to it even though its operation conditions are quite different from other thermal systems. In this case, the thermal and hydraulic design of the recuperator in the LCES system was completed. The flow characteristics and thermal performance of the recuperator under design conditions were analyzed, and the effects of operating at various loads on the flow characteristics and thermal performance of the recuperator were investigated. It was found that from the inlet to the outlet, the resistance coefficient of CO₂ on the cold side increased gradually while decreasing gradually on the hot side. Down the flow direction, the average temperature of CO₂ on the cold side increased sharply, while decreasing slowly in the hot side. When the systems discharged with varying loads, the pressure drop increased along both channels, but the resistance coefficient decreased gradually on both channels. The heat transfer coefficient (HTC) increased gradually on both sides too. The Nusselt number (Nu) in the first half of the cold side did not change much, while increasing gradually in the second half, but it continued to increase on the hot side.

During the practical operation of gas turbines, relatively cooled air from the compressor and the rim seal is applied in order to prevent mainstream ingestion into the space between the rotor and stator disc cavities, which can prolong the service life of hot components. On the one hand, the purge flow from the rim seal will inevitably interact with the mainstream and result in secondary flow on the endwall. On the other hand, it can also provide an additional cooling effect. In this paper, four rim seal structures, including an original single-tooth seal (ORI), a double-tooth seal (DS), a single-tooth seal with an adverse direction of the coolant purge flow and mainstream (AS) and a double-tooth seal with an adverse direction of the coolant purge flow and mainstream (ASDS), are experimentally and numerically investigated with mass flow ratios of 0.5%, 1.0% and 1.5%. The flow orientation of the coolant from the rim seal is considered as one of the main factors. The pressure-sensitive paint technique is used to experimentally measure the film cooling effectiveness on the endwall, and flow field analysis is conducted via numerical simulations. The results show that the cooling effect decreases in the cases of DS and ASDS. AS and ASDS can achieve a better film cooling performance, especially under a higher mass flow ratio. Furthermore, the structural changes in the rim seal have little impact on the aerodynamic performance. AS and ASDS can both achieve a better aerodynamic and film cooling performance.

A novel modification method, the ‘micro-scale’ rib, is proposed to expand cooling coverage for turbine endwalls. However, the introduction of the rib will inevitably affect the flow in the near-wall region. Therefore, the variation in the flow pattern for the traditional model of secondary flow needs further exploration. In this paper, to gain a clearer understanding of the micro-scale rib, the original endwall and three types of ribbed endwalls were adopted to numerically present the detailed flow, film cooling, and heat transfer information for the endwall surface and phantom cooling on the suction side (SS) of the blade. The Ansys code CFX was utilized to solve the 3D Reynolds-averaged Navier–Stokes (RANS) equations, and the SST k-ω was selected as the turbulence model after the verification. The results show that the rib-like vortex changed the flow of the coolant and had various impacts on the cooling characteristics. Although the cooling performance of the ribbed endwall improved, it also had a negative impact on heat transfer in most cases. Compared with the original, the vertical rib cases provided optimal film cooling, with increases of 26.9% and 17.4% for rib spacing values of 8 mm and 10 mm, respectively, with little difference in heat transfer (less than 1%). In addition, the horizontal rib cases presented the worse performance for both film cooling and heat transfer, which indicates that the rib layout should consider a mainstream flow direction for future designs.