The influence of convergence ratio on secondary losses in highly-loaded turbine airfoils

The secondary flows of a family of three turbine airfoils have been investigated through numerical study of linear cascades. The airfoils match in Zweifel coefficient and in axial loading distribution, but vary widely in convergence ratio. The baseline airfoil, which has the highest convergence ratio, is representative of highly-loaded turbine hub profiles. All airfoil profiles were designed using a novel methodology developed for this research.;Simulations were carried out with experimentally determined inlet conditions that match the low-speed cascade at the National Research Council Canada. The inlet Reynolds number was 150,000 based on axial chord, and the midspan turbulence intensity was 4%. The downstream total pressure and streamwise vorticity fields were investigated. The airfoils produced secondary flows that were similar in structure and peak intensity, but varied in cross-stream extent. Lower convergence ratios produced broader secondary flow structures resulting in higher total losses. Local entropy production due to viscous dissipation was used to understand the sources of loss both within and downstream of the airfoil passage.;Numerical results were compared against one legacy and one more recent loss correlation. All cases indicated an increase in loss at lower convergence ratios. The relative disagreement between the numerically calculated and statistically correlated loss levels was larger for lower convergence ratios. A new airfoil loading parameter was proposed based on convergence ratio.;Keywords: Gas Turbines, Computational Fluid Dynamics, Secondary Flows, Convergence Ratio...