Effects of varied bend turning vanes on flow control and heat transfer performance in a smooth two-pass channel

Turbine blades are always withstanding high temperature and thermal stress from hot gas. Serpentine passages with 180-deg turns are widely used within the turbine blade so as to guide cooling flow and enhance heat transfer. However, there is always a large pressure drop when cooling airflow passes the 180-deg bend. Turning vanes are usually arranged in the bend of two-pass channel to reduce the flow separation and pressure loss, and improve mainstream uniformity in the second passage. In this study, the heat transfer performance and flow field features of six two-pass channels with / without varied turning vanes are investigated by using Computational Fluid Dynamics numerical methods. The studies on effects of shape lines and curvature of the turning vane are conducted by commercial software Fluent based on realizable k - ε turbulent model. The influences of Reynolds number are also included. Numerical results indicate that the friction loss factors of channels with turning vane are decreased by 10.5%–31.4% compared to smooth channel without turning vane. However, the Nusselt number in the second passage is reduced greatly by 12.6%–22.1%. Considering the heat transfer and pressure loss, semicircular turning vane yields the highest thermal performance factor with an improvement by 5.2%. Moreover, turning vane with big curvature shows the best ability to suppress the flow separation and recirculation around the divider in the second passage. Among all the turning vanes studied, the novel airfoil-shaped turning vane produces the highest transfer augmentation at the region downstream the bend.