Experimental investigation of hole-geometry effect on unsteady characteristics of film cooling at turbine vane leading edge

In present work, the hole-geometry effect on the unsteady characteristics of film cooling at leading-edge of a turbine vane was experimentally studied under blowing ratios (BRs) from 0.5 to 3.0. The typical double-row staggered layout was applied in the stagnation zone. Selected hole-geometries include the cylindrical-hole and fan-shaped-hole, as well as the cylindrical-holes in a transverse trench and an individual crater. Through employing the infrared thermography and planar quantitative light sheet techniques, the unsteadiness of surface film effectiveness and in-plane jet-concentration were analyzed. The level of cooling unsteadiness was estimated by the standard deviations of these scalar parameters. A comparison of both techniques revealed that the flow unsteadiness at the interface of mainstream and cooling air jet is the essence of surface film effectiveness fluctuation. Under small BRs, the fan-shaped-hole displays the best film coverages; however, adding the transverse trench can generate the highest film effectiveness under large BRs. Relative to the cylindrical-hole, the maximum increments in area-averaged effectiveness can be above 10% for both the new designs. The transverse trench design can generate the lowest-level cooling unsteadiness, and improve evidently the uniformity of film effectiveness over entire leading-edge. However, two challenges for trench design should be concerned. The first was the faster decay in film effectiveness, in comparison with the fan-shaped-hole jets. The second was the high-level cooling unsteadiness on the sidewalls of trench.

Automated summary

This study experimentally investigated the effect of hole geometry on the unsteady characteristics of film cooling at the leading edge of a turbine vane. Infrared thermography and planar quantitative light sheet techniques were used to analyze the unsteadiness of surface film effectiveness and in-plane jet concentration. The results showed that the flow unsteadiness at the interface of mainstream and cooling air jet is the main cause of surface film effectiveness fluctuation. The fan-shaped hole and the design with a transverse trench displayed better film coverage and effectiveness improvement under different blowing ratios. However, the transverse trench design had lower cooling unsteadiness but challenges in terms of effectiveness decay rate and sidewall cooling unsteadiness.