Effect of array jet on cooling effectiveness on full-coverage film cooled surface

In this study, the cooling effectiveness (φ) was measured on full-coverage film cooled surface with and without array jet impingement cooing using an infra-red thermographic technique. Measurements were conducted with two test plates of different thermal conductivities. One was made of stainless steel (k=16.3 W/m·K) and the other was made of polycarbonate (k=0.2 W/m·K). The measured cooling effectiveness comprises the adiabatic film cooling effectiveness on the film cooled surfaces, the heat conduction through the test plates and convective heat transfer of array jet impingement underneath the test plates. The inclination angles of film cooling holes and impingement jet holes were 35° and 90°, respectively. The diameters of both film cooling and impingement jet cooling holes were 5 mm. The streamwise and spanwise hole spacing-to-hole diameter ratios (p/d) are 3 for both the effusion plate (film cooled plate) and the injection plate (impingement nozzle plate. The holes on each plate were arranged in an inline pattern, while the film cooling holes and jet holes were positioned in a staggered manner. The jet Reynolds number based on the hole diameter was 3,000 and the equivalent blowing ratio (M) was 0.3. The gap distance between the jet plate and the film cooling plate was varied from 1 to 5 times of the hole diameter. In addition, the cooling effectiveness without impingement was tested, too. The stainless steel plate shows relatively higher and uniform cooling effectiveness than the polycarbonate plate. The effect of H/d was not significant for both test plates. However, the cooling effectiveness without the impingement jets decreases significantly for the stainless steel plate, while it changed a little for the cooling effectiveness of the polycarbonate plate.