Film cooling on a flat plate: investigating density

Abstract

This study is an investigation of two specific effects on turbine blade film cooling. The effect of coolant to mainstream density ratio and upstream steps was studied. The studies were conducted on two flat plates with 4mm cylindrical film cooling holes, one with simple angle and the other with compound angle, in a low-speed suction type wind tunnel. Density effect was studied at ratios of 0.93 and 1.47 by using air and CO2 as coolant. An IR camera was used to record the temperature on the plate and T-type thermocouples were used to record the coolant and mainstream temperatures. During the study the nature of the conduction effect from the heated coolant was studied and found to be most prevalent along the plate surface not through the plate from the plenum. A methodology was presented by which conduction error free results were obtained. The results showed an increased effectiveness at higher density ratios, particularly near the holes and for the simple angle plate. Upstream step effect was studied using pressure sensitive paint and a coupled strobe light and camera. Steps of 0.5, 1 and 1.5mm were placed at the upstream edge of the holes. The steps were found to increase effectiveness significantly more than previous studies have shown when placing the step slightly upstream of the holes.