An experimental investigation on streamwise distance and density ratio effects on double-jet film-cooling

In the present study, flow field and film-cooling effectiveness of several double-jet film-cooling geometries on a flat plate are measured. The streamwise distance varies as s/d = 3.0, 4.0, 5.0, and 6.0, while three spanwise distance conditions (p/d) are considered. The density ratio varies as DR = 1.0, 1.5, and 2.5. Both effects of the streamwise distance and the density ratio are focused. Results show, though the streamwise distance effect is not monotonic for all the cases, a general trend is witnessed when comparing with the baseline of s/d = 3.0. For p/d = 0, with an increased streamwise distance, the lateral coverage widens and the laterally averaged effectiveness rises. However, for p/d = 0.5 and 1.0, increasing the s/d may weaken the interaction between the two jets, and reduce the film coverage and effectiveness. With an increased density ratio, the jet momentum decreases, therefore better attachment and higher film-cooling effectiveness are obtained. However, in most cases, the range of lateral coverage is mainly dominated by the spanwise distance, rather than the streamwise distance or the density ratio. By comparing the area averaged effectiveness, an optimal DJFC configuration (among the geometries in this study) is identified for each operation condition.