Numerical optimization study for the geometry of film cooling nozzle

Abstract

Film cooling is one of the essential approaches developed to protect gas turbine blades and vanes from high temperature gases. It does so by covering the surface with a film of coolant air. Experimental and numerical studies have identified the parameters affecting film cooling aerodynamic and thermal behaviours; one of the most important is the coolant nozzle geometry. In this study, the nozzle geometry is optimized to enhance film effectiveness and heat transfer while keeping the inlet area and pitch-to-hole-width ratio fixed. A Reynolds-Averaged Navier Stokes (RANS) model, developed and validated against experimental data, served as the baseline for further optimization. The model was used to design a “racetrack slot” which is rectangular slot with semi-circular lateral edges. The aspect ratio of the slot was varied and an aspect ratio of seven was found to have the best cooling performance. As such, it served as the starting point for further, irregular, shape optimization of the coolant nozzle utilizing the ANSYS Fluent Adjoint solver. This solver allows mesh morphing within specified constraints and yielded a highly irregular coolant hole which taps into the potential of using additive manufacturing to produce cooled parts. The irregular shape optimization increased adiabatic film effectiveness over the test surface from 0.24 (for optimum racetrack coolant hole) to 0.34 (for optimum, irregular, coolant nozzle geometry). The enhancement is remarkable, especially when compared to 0.1; the value for the round coolant hole under the same conditions.