EFFECTS OF HIGH FREE-STREAM TURBULENCE ON THE NEAR-WALL FLOW AND HEAT/MASS TRANSFER ON THE ENDWALL OF A LINEAR TURBINE ROTOR CASCADE

摘要

Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer in the endwall region of a linear high-turning turbine rotor cascade. The endwall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a turbulent boundary layer flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80 mm, respectively, at the entrance of the turbine cascade. The surface flow visualization shows that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides at a shallower angle with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the endwall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the endwall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. The endwall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.