Experimental flow visulization study in a trapezoidal duct with impingement jets and cross flow near the leading edge

An enlarged model of trapezoidal duct in leading-edge with impingement jets, swirl, cross flow and effusion was built up. Experiments were performed to measure flow fields in the confined passage and exit holes on one of its side walls. A row of staggered circular impingement holes were arranged on the opposite side wall. Cross flow and effusion flow was induced in the channel by the outflow of exit hole and film cooling hole, which were oriented on one end wall and bottom wall of the passage. Detailed flow structures were measured for two impingement angles of 350 and 450 with 6 combinations of out flow ratios. Results showed that the small jets impinged the target wall effectively while the large jets contributed to inducing and impelling a strong counter-clockwise vortex in the upper part of the passage. Cross flow had significant effect on the flow structures in the passage and exit holes. It deflected the jets, enhanced swirl and deteriorated side exit conditions. Impingement angle also had important influence on flow fields and its effect revealed more evidently with cross flow. Within the present test conditions, the mass flow rates and outflow positions of film cooling holes had no distinct effect on the main flow structures. These data were helpful for the design and optimization of internal cooling structures in gas turbine airfoils.