Numerical decoupling of the effect of internal cooling and external film cooling on overall cooling effectiveness

Abstract

In modern aero-engine turbine blades, the coolant flows from the internal cooling channel and out through the film hole, forming a coolant coverage over the blade surface to isolate the high-temperature gas. Essentially, the cooling system can be divided into parts with internal cooling and external film cooling; in particular, external film cooling includes coolant coverage (film cooling) and bore cooling (cooling within the film hole). Accordingly, it is important to quantitatively analyze the effects of these three cooling parts (internal, bore, and film cooling) on the overall cooling effectiveness, which can help improve the design of turbine blades. To this end, in this study, the numerical decoupling method was used to investigate the relationship between the overall cooling effectiveness of two plate cooling structures and three cooling parts. Considering blowing ratios of 0.25, 0.5, 1, and 1.5, it was found that the blowing ratio and film hole position have considerable impacts on the overall cooling effectiveness of a smooth model; however, the overall cooling effectiveness of an impingement-effusion model was deemed insensitive to the film hole position. Furthermore, in the case of a small blowing ratio (M = 0.25), the internal heat transfer enhancement caused by impinging jets was less than that due to increased coolant flow rates. In the regions located upstream of each film hole exit, bore cooling had significant effects on the overall cooling effectiveness; particularly, these effects were more pronounced in the smooth model. Moreover, for a blowing ratio of 0.25, film cooling was dominant across all the cooling parts. With an increase in the blowing ratio, the influence of bore cooling grew rapidly, gradually replacing film cooling. Additionally, as the blowing ratio increased to 1.5, the effect of internal cooling exceeded that of film cooling. This work and its results are expected to serve as guidance for the design of turbine blade cooling structures.