This paper proposed an alternating elliptical U-shaped internal cooling channel and investigated the flow and heat transfer characteristics, based on the optimal flow field structure deduced from the Field Synergy Principle. The channel consisted of the straight sections and the transition sections. In the straight sections, the cross section of the channel is ellipse, and in the transition sections, the long axis gradually shortened into the short axis, and the short axis gradually expanded to the long axis. However, the cross-section area of the channel remained unchanged.

Numerical simulations were performed to solve 3D steady Reynolds-averaged Navier-Stokes equations (RANS) with the standard k-ε turbulence model. The influence of alternating of the cross section on heat transfer and pressure drop of the channel was studied by comparing with the smooth elliptical U-shaped channel, and all the cases were conducted with the Re numbers from 10,000 to 40,000. On this basis, the investigation on alternating elliptical U-shaped internal cooling channel performance was made mainly into two parts. One was the effect of aspect ratio which was set as from 1.1 to 2.0, while the other was the effect of alternating angle θ which was set as from 10° to 90°.

The results showed that for the flow field, there was no vortex in the first pass of the smooth elliptical U-shaped channel. On the contrary, in the first pass of the alternating elliptical U-shaped channel, after the transition section, for different Re numbers, four or eight longitudinal vortices were generated. In the second pass, the flow separation in smooth elliptical U-shaped channel was serious because of the centrifugal force at the elbow, while the alternating elliptical channel restrained the flow separation to a certain extent and formed a double-vortex structure just like the vortex cooling. The average Nusselt number of the alternating elliptical U-shaped channel was significantly higher than that of the straight channel, but the pressure loss increased slightly. In addition, with the increase of aspect ratio, the thermal performance of the channel increased in the study range, and when the alternating angle is between 40° to 90°, the thermal performance nearly kept constant and the best.

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