Flow and heat transfer characteristics in rotating two-pass channels cooled by superheated steam

In a modern gas turbine, using superheated steam to cool the vane and blade for internal convection cooling is a promising alternative to traditional compressor air. However, further investigations of steam cooling need to be performed. In this paper, the three-dimensional flow and heat transfer characteristics of steam are numerically investigated in two-pass square channels with 45° ribbed walls under stationary and rotating conditions. The investigated rotation numbers are 0 and 0.24. The simulation is carried out by solving the Reynolds averaged Navier-Stokes equations employing the Reynolds stress turbulence model, especially considering two additional terms for Coriolis and rotational buoyancy forces caused by the rotating effect. For comparison, calculations for the air-cooled channels are done first at a Reynolds number of 25 000 and inlet coolant-to-wall density ratio of 0.13. The results are compared with the experiment data. Then the flow and heat transfer in steam-cooled channels are analyzed under the same operating conditions. The results indicate that the superheated steam has better heat transfer performance than air. Due to the combined effect of rotation, skewed ribs and 180° sharp turn, the secondary flow pattern in steam-cooled rotating two-pass channels is quite complex. This complex secondary flow pattern leads to strong anisotropic turbulence and high level of anisotropy of Reynolds stresses, which have a significant impact on the local heat transfer coefficient distributions.