Investigation of heat transfer and fluid flow in fractal truncated ribbed channels for the internal cooling of turbine blades

Ribs are widely employed in internal cooling passages of turbine blades to enhance heat transfer. From the mathematics, a fractal is an abstract object used to describe naturally occurring objects which exhibits similar properties with increased smaller scales. In a ribbed channel, originating from two sides truncated ribs, fractal truncated ribs are built and the evolving process contains three sides truncated ribs, five sides truncated ribs, nine sides truncated ribs and seventeen sides truncated ribs. Steady Liquid Crystal Thermography (LCT) is employed to measure surface temperature and derive heat transfer coefficients over the ribbed surfaces in the tested channels. Turbulent flow details are presented by numerical calculations with an established turbulence model, i.e. the k-ω SST model. From the study, truncated ribs can enhance the heat transfer at the truncated gap regions. With the scale of fractal truncated ribs becoming smaller, the low heat transfer regions downstream the ribs are effectively reduced. With the evolving of the fractal truncated ribs, the shape of high heat transfer region behind single truncated part keeps similar. The truncated ribs change cause enhancement vortices in the spanwise direction and enlarge local heat transfer. The truncated ribs enhance heat transfer by reducing the recirculating flows and the cases with smaller scales have more uniform heat transfer distributions. With the scale of the fractal truncated ribs becoming smaller, the flow related terms, such as, pressure field, turbulent kinetic energy and vorticity magnitude, also become more uniform.