Study on flow and heat transfer characteristics in rectangular channels with lantern-shaped pin fin array: Part I- effect of sphere diameter

Featuring high heat transfer capacity and low pressure loss, pin fin arrays have become one of the important cooling methods for the trailing edge cooling channel of modern gas turbines. To improve the heat transfer efficiency of the channel, a lantern-shaped pin consisting of a cylinder and a sphere is proposed in Part I of this study. The flow and heat transfer characteristics in rectangular channels containing eight rows of staggered lantern-shaped pins with different sphere-to-pin diameter ratios, R/D, are investigated and compared by numerical simulations in the Re range of 3,000 to 30,000. The calculations indicate that the spheres trigger a pair of counter-rotating vortices behind the pins, which significantly enhance the Nusselt number and pressure loss. The pair of vortices also change the distributions of the endwall and pin Nusselt number. The endwall Nusselt numbers behind the fins and the pin Nusselt numbers at the leading edge and trailing edge of the pins are substantially enhanced. After the third row, the endwall Nusselt number augmentation Nue/Nu0 of the lantern-shaped pin with R/D = 1.0 decreases with the increased Re. However, the result of a slight increase in the Nue/Nu0 with the increased Re for R/D = 1.7 is diametrically opposite to that for R/D = 1.0. Meanwhile, with the increasing R/D, the separation and transition points are closer to the trailing edge. The increased Re makes the separation point moves closer to the leading edge while the transition point remains near 130 degrees. The endwall, pin, total area-averaged Nusselt numbers, and pressure loss rapidly boost with the increased R/D. The thermal performance index of the lantern-shaped pin with R/D = 1.7 ranges from 1.72 to 1.21. At Re = 10,000, the lantern-shaped pin with R/D = 1.7 shows the most significant percentage increase in thermal performance index of 4.39% compared to R/D = 1.0.