Effect of high freestream turbulence with large length scale on blade heat/mass transfer

The naphthalene sublimation technique is used to investigate the influence of high freestream turbulence with large length scale on the heat/mass transfer from a turbine blade in a highly accelerated linear cascade. The experiments are conducted at four exit Reynolds numbers, ranging from 2.4×10⁵ to 7.8×10⁵, with freestream turbulence of 3%, 8.5% and 18% and corresponding integral length scales of 0.9 cm, 2.6 cm and 8 cm, respectively. On the suction surface, the heat/mass transfer rate is significantly enhanced by high freestream turbulence due to an early boundary layer transition. By contrast, the transition occurs very late, and may not occur at very low Reynolds numbers with low freestream turbulence. In the turbulent boundary layer, lower heat/mass transfer rates are found for the highest freestream turbulence level with large length scale than for the moderate turbulence levels with relatively small scales. Similar phenomena also occur at the leading edge. However, the effect of turbulence is not as pronounced in the laminar boundary layer.