Conjugate heat transfer on full-coverage film cooling with array jet impingements with various Biot numbers

Total cooling effectiveness was determined on a film cooled surface with staggered array jet impingement cooling at various Biot numbers. Heat transfer experiments were conducted using infra-red thermography for materials of three thermal conductivities: stainless steel (k = 13.4 W/m K), Corian (k = 1 W/m K), and polycarbonate (k = 0.2 W/m K). Conjugated heat transfer was analyzed with the combined effects of conduction through the test plates and convective heat transfer due to the arrayed jet impingement. The inclination angle of the film cooling holes was 35° and that of the jet impingement holes was 90°. The film and jet impingement holes on each plate were arranged in staggered patterns, and the film cooling holes and jet impingement holes were also positioned in a staggered pattern. The jet Reynolds number, based on hole diameter, was 3000 and the equivalent blowing ratio was 0.3. The diameter of the film cooling holes and the jet impingement holes was 5 mm. The distance between jet and film hole plates was varied in the range 1 ⩽ H/d ⩽ 5. Total cooling effectiveness was measured with and without jet impingement. When jet impingement was added to the internal cooling, the averaged total cooling effectiveness was enhanced about 8.4%. At low Biot numbers, meaning that cooling performance dominated over the conduction effect, the temperature distribution became more uniform due to higher conductive heat transfer. The total cooling effectiveness was strongly related to the Biot number of the plate, and the correlation between total cooling effectiveness at various Biot numbers was determined to predict the total cooling effectiveness in an actual gas turbine engine. The effect of H/d ratio was limited, to within 2.7%.