Numerical analysis and experiments on heat transfer and flow structures in rotating three-pass serpentine channels with ribs, guide vanes and trailing bleed holes

Numerical and experimental studies are conducted on heat transfer and pressure loss in a three-pass serpentine channel with trailing bleed holes. The guide vanes' effects in the smooth and ribbed channels are studied comparatively. Based on the hydraulic diameter and inlet velocity, the Reynolds number ranges from Re = 14,000 to Re = 100,000, and the rotation number ranges from Ro = 0 to Ro = 0.1. Through the numerical simulations, the rib configuration in serpentine channels influences the guide vane's flow control effects. Applying the guide vanes in the ribbed serpentine channel's tip bend region enhances the flow impingement and advection, increasing the total Nusselt number in the blade-tip region by about 25%, and this region's heat transfer uniformity is improved as well under non-rotating and rotating conditions without additional pressure loss penalty in the channel. Moreover, it is a promising method to improve the turning flow structures and enhance heat transfer further in the ribbed serpentine channel by applying the tandem guide vane in the tip bend region. Both the numerical computations and experiments show only slightly higher and more uniform heat transfer in the second and third passages after applying the guide vanes in the bend regions under non-rotating and rotating conditions. The experiments indicate that the rotation effects show a more appreciable influence on the heat transfer enhancement values along the serpentine channel than the channel Reynolds numbers. The heat transfer differences between the leading and trailing sides are 15.4%, 14.0%, and 21.3% in the three passages, respectively, at Re = 14,000 and Ro = 0.1, referring to the averaged Nusselt number in each passage. The CFD results demonstrate that the rotation significantly improves the heat transfer in the third passage by promoting more radial outflow through the tip hole, reducing the flow rates through the lateral bleed holes by about 13.2%.