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

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 beta = 90 degrees, 120 degrees, 135 degrees and 180 degrees 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 degrees-hole; moreover, the trench could weaken the unsteadiness of effectiveness when beta < 135, and reduce the BR effect on the unsteadiness; however, the flow loss of backward-holes with 90 degrees < beta < 180 degrees 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.

Automated summary

An experimental investigation was conducted on the effect of transverse trench on unsteady film cooling performances of backward cylindrical-holes with various compound angles using time-resolved thermal infrared technique. The results showed that the trench can significantly improve effectiveness, reduce effectiveness unsteadiness, but also increase flow loss.