Film cooling characteristics of serrated trenched-hole on curved surfaces

Abstract

A numerical investigation is performed to study the serrated trenched-hole film cooling performance on the convex and the concave surfaces, with the use of a plenum coolant-fed mode. In current study, the relevant curvature of curved surface is varied as 2r1/d = 30, 60 and 90 at the convex side, 2r2/d = 90, 120 and 180 at the concave side. In addition, three coolant injection angles (such as θ = 30°, 35° and 45°) are considered in a specific curved channel. The blowing ratio defined in terms of the local primary flow velocity is ranged from 0.25 to 1.5. From the present study, a critical parameter (I0), in the form of Icos2θ, is preliminarily identified to be around 0.5 for the serrated trenched-hole film cooling. When Icos2θ<I0, the film cooling effectiveness on the convex surface is better than that on the flat surface and concave surfaces. The situation is opposite when Icos2θ>I0. In particular, this critical value for the serrated trenched-hole film cooling is obviously less than the unity that previously identified in the cylindrical-hole film cooling situation. The relevant curvature shows nearly rare influence on the film cooling effectiveness under small blowing ratios, either on the convex surface or the concave surface. However, under high blowing ratios, it has a pronounced impact on the film cooling effectiveness, in particular at the concave side. Under M = 1.5, the area-averaged adiabatic film cooling effectiveness in the region between s/d = 10 and s/d = 20 is increased up to 33% by the smallest relevant curvature case with respect to the biggest relevant curvature case. The coolant injection angle plays an important role on the mutual interaction of jet-in-corssflow of the serrated trenched-hole film cooling. The reduction in the coolant injection angle leads to an obvious film cooling enhancement, either on the convex surface or the concave surface. Moreover, the enhancing effect led by the reduction of coolant injection angle behaves more pronouncedly as the blowing ratio increases.