Effects of Wake Passing on Stagnation Region Heat Transfer

An experimental study is described in which both time-averaged and time-resolved effects of wake passing were measured in a cylinder stagnation region. The experiments were carried out in an annular-flow wind tunnel, which was fitted with a spoked-wheel wake generator. The cylindrical spokes produce wakes that simulate those shed from a turbine inlet guide vane. Time-averaged heat transfer results indicate an asymmetric distribution of heat transfer coefficient about the stagnation line, with higher heat transfer coefficients on the windward side (with respect to the bar-passing direction), which corresponds to the suction side of a turbine blade. This asymmetry is also reflected in the time-resolved heat transfer results, which were obtained using a test cylinder instrumented with platinum thin-film gages. Unsteady heat flux records reveal very large positive excursions (as much as a factor of three) in instantaneous heat flux during wake passing on the windward side of the cylinder and much smaller effects on the leeward side. Hot-film records in the cylinder stagnation region were also obtained by operating the thin-film gages in the constant-temperature mode. Spectra of these hot-film records indicate that vortex shedding is a major contributor to the unsteady buffeting of the test-cylinder boundary layer at circumferential stations located at both + 60 deg and − 60 deg from the stagnation line, but makes a very small contribution on the stagnation line itself.