Influence of Surface Roughness on Turbine Nozzle Profile Loss and Secondary Loss

Abstract

The effects of surface roughness of both nozzle and end-wall on a turbine nozzle performance were investigated experimentally using liner cascade wind tunnel facility under the Reynolds number (Re) condition of Re = 0.3∼1.0 × 106. With buffing, milling, sand blasting and shot blasting, the total of seven levels of the model surface roughness were realized. In order to clarify the effect of the nozzle surface roughness on the profile loss, total pressure losses were measured using three-hole probe for different levels of the surface roughness. It became clear the nozzle profile loss increases as Reynolds number increases for larger roughness group. In addition, it appeared the profile loss depends on not only maximum value of the surface roughness but also roughness conditions. In order to examine the effect of surface roughness on the secondary flow loss, spatial total pressure field of the secondary flow region was measured using three-hole probe for the cases of smooth or rough nozzle surface with smooth or rough end-wall. The secondary flow structures were recognized at the 5∼10% span-wise height region of the suction surface of the nozzle for all cases. With increasing the nozzle surface roughness, not only the profile loss but also net secondary flow loss increases, which is defined as the difference between the total pressure loss and the profile loss in the secondary flow region. However, increase of the end-wall roughness has higher effect on the net secondary flow loss increase. Difference of the effect between the nozzle surface roughness and the end-wall roughness on the nozzle secondary flow loss was discussed.