Mass transfer from a circular cylinder: Effects of flow unsteadiness and ""slight" nonuniformities

The effect of periodic variations in the angle of the flow incident to a turbine blade on its leading edge heat load was investigated measuring a circular cylinder oscillating rotationally in a uniform steady flow A stationary cylinder was used and the transfer rate was measured for Re = 75,000 to 110,000 and turbulence levels from .34% to 4.9%. The accuracy and repeatability of the developed mass transfer technique is about + or - 2%, a large improvement over similar methods. Identical flow conditions were used when the cylinder was oscillated. A Strouhal number range from .0071 to .1406 was covered. Comparisons of the unsteady results indicate that the magnitude of the effect of oscillation is small and dependent on the incident turbulence conditions. Experiments were conducted in which a small amplitude periodic perturbation was superimposed on the mean flow by a woven wire grid. Spanwise traverses of the mean velocity and turbulence quantities and spanwise and circumferential traverses of the mass transfer rate on the cylinder were made. Although the perturbation was measured to be only .25% of the mean velocity and was buried in the stream's turbulence, disproportionately larger 15% variations in the spanwise transfer rate were observed.