A NEW TEST RIG FOR FILM COOLING EXPERIMENTS ON TURBINE ENDWALLS

摘要

Endwall film cooling has been subject to many investigations over the past years. Since the coolant is injected into the wall boundary layer, it is primarily affected by the complex three-dimensional flow structure which is developed near the endwall inside turbine bladings. Little information can be found in the literature about how load variation affects endwall film cooling. As the secondary flow, driven by the circumferential and radial pressure gradient, is intensified with higher cascade load, strong interaction of the coolant injected in the near-wall cross flow is expected. Therefore, an airfoil cascade rig has been designed with an endwall cooling configuration containing multiple rows of expanded film holes. The film rows are combined to groups which can be supplied with different types of coolant gas through individual plenum cavities.Additionally, basic film cooling experiments have been conducted on a flat surface to validate the temperature measurement technique on results available in the literature. Film cooling injection is established through a row of 7 cylindrical holes inclined streamwise at 35° for a blowing rate ranging from 0.35 to 1.5. Experiments are conducted at constant main flow conditions at Re_D = 4200 and at low turbulence level Tu = 1.5% with CO_2 (D_R = 1.37) and Air (D_R=0.9) used as coolant gas. Centerline effectiveness for selected blowing rates is compared to results available from previous literature.