Experimental study of transverse trench effect on unsteady film cooling effectiveness of backward cylindrical-holes with various compound angles

Abstract

By means of time-resolved thermal infrared technique, an experimental investigation of the effect of transverse trench on unsteady film cooling performances of backward cylindrical-holes with various compound angles was carried out under typical coolant-to-mainstream blowing ratios (BRs) from 0.2 to 2.0. The main feature of this work was that the time-averaged film cooling effectiveness and the unsteadiness of effectiveness caused by fluid-interaction were evaluated simultaneously. A row of backward-holes with orientation angles of β = 90°, 120°, 135° and 180° were designed as the specimens, and the corresponding forward injections were also chosen. The effect of transverse trench on the coverage and loss performances of film cooling flow of backward-holes under different BRs was analyzed, and the effects of compound angle and jet orientation on the film cooling performances of common- and trenched-holes were compared. The conclusions revealed that the trench could improve obviously the effectiveness and the maximum increment was 46% for 135°-hole; moreover, the trench could weaken the unsteadiness of effectiveness when β < 135°, and reduce the BR effect on the unsteadiness; however, the flow loss of backward-holes with 90° < β < 180° was increased by the trench. In comparison with the forward injections, the backward injections increased the flow loss but eliminated the jet entrainment effect between two adjacent film-holes. The effect of jet orientation on effectiveness was eliminated by the trench to generate a similar area-averaged effectiveness, and that on unsteadiness of film cooling was weakened.