Numerical flow and experimental heat transfer of S-shaped two-pass square channel with cooling applications to gas turbine blade

This study experimentally detected the endwall Nusselt numbers (Nu) distributions, Fanning friction factors (f) and thermal performance factors (TPF) for a stationary S-shaped two-pass square channel with the associated turbulent flow fields analyzed by ANSYS Fluent code to disclose the flow mechanisms responsive to the measured thermal performances. The full-field Nu distributions over the endwalls of present S-shaped inlet/outlet legs and 180° sharp bend at Reynolds numbers (Re) of 5000, 7500, 10,000, 12,500, 15,000, 20,000 and 30,000 were measured using the steady-state infrared thermography method; while the validated RNG k-ε turbulence model was adopted to reveal the fields of time-mean fluid velocity, turbulent kinetic energy and cross-plane secondary flow. Acting by sectional vortices induced along the inlet/outlet S-pathways and 180° sharp bend, the core-to-wall momentum/heat exchanges are boosted to elevate both Nu and f values. Accompanying with the f augmentations from 10.19-8.27 times of Balssius f∞ levels, the area-averaged Nusselt numbers (Nu‾A) over the entire S-shaped endwall were elevated to 3.21-3.09 times of Dittus-Boelter Nusselt number (Nu∞) values at 5000 ⩽ Re ⩽ 30,000, resulting in the TPF between 1.4 and 1.44. To assist relevant engineering applications, two sets of empirical correlations evaluating the regionally averaged endwall Nusselt numbers and f factors are devised.