Abstract
With the increase of temperature requirement, the application of metal matrix materials is gradually reduced due to its poor temperature resistance. In order to improve the application of traditional metal based materials, new cooling technology must be developed to meet the application of metal based materials. In this paper, the cooling flow field of cylindrical hole and two kinds of stepped film holes based on metal materials is simulated by large eddy method(LES), the development of vortex structure and flow characteristics in the mixing area of coolant flow and mainstream are analyzed and studied. The distribution is strongly effected by stronger thermal convection compared with the new temperature resistant material. The results show that four kinds of vortices form downstream the film hole, namely, horseshoes vortex, shear layer vortex, hairpin vortex and the counter rotate vortex pair (CVP). The CVRP formed on the stepped plane which strongly influences the flow and heat transfer of downstream, which is more evident in metal based materials, especially resulted by its isotropic features. Compared with the cylindrical film hole, the structure of step plane efficiently decreases the coolant flow velocity which results in a decrease of the CVP intensity so that the cooling film is adherent to the wall. The thermal conductivity of metal base material is strong, which has a great influence on the temperature distribution inside the wall. Velocity pulsation tightly influenced by CVP, in where the CVP intensity is strong, velocity pulsation is also strong so that the coolant flow strongly mixes with the mainstream. The flow velocity and velocity pulsation decrease with the increasing of the area ratio of stepped hole. The influence of geometric parameters on the heat transfer performance is mainly due to the high heat transfer performance of the metal matrix material.
Highlights
Film cooling is a kind of cooling technology widely used in gas turbine combustion chamber, turbine blade and other high temperature components
Tyagi and Acharya 16 performed LES for a row of inclined round film hole. They reported that the hairpin-vortex dominates the flow field and the leg of hairpin structure is the origination of counter rotate vortex pair (CVP) while the head is associated with roller vortex
Sakai et al 21 concluded that the hanging vortex and hairpin vortex are the origins of CVP at low density ratio while the hanging vortex and the shear jet vortex are the source of CVP at high density ratio
Summary
Film cooling is a kind of cooling technology widely used in gas turbine combustion chamber, turbine blade and other high temperature components. Sarkar studied the behavior of wake and evaluated film-cooling effect and discussed the evolution of vortex structures by LES. Tyagi and Acharya performed LES for a row of inclined round film hole They reported that the hairpin-vortex dominates the flow field and the leg of hairpin structure is the origination of CVP while the head is associated with roller vortex. Kalghatgi and Acharya 20 performed LES for a single round inclined cooling jet of 35 deg and discussed the evolution of Kelvin-Helmholtz (K-H) vortex, hairpin vortex and CVP structures. The cooling flow field of stepped film holes with different aperture ratio are studied by using the large eddy simulation method, and the jet trace, large-scale coherent structures and velocity pulsation characteristics of the three models are analyzed
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