Abstract
Film cooling is a cooling technique in which a protective layer is generated by the coolant along the wall to shield the wall surface against high temperature flow. When the fluids of the coolant and high-temperature gas are of different qualities, it is often accompanied by the mass and energy transfer. During the film cooling process, the lower-temperature gas is transported to the surface through the tangential gap on the wall which requires thermal protection. And then the film is formed along the direction of the high-temperature flow, causing the solid wall isolated from the high temperature gas, thereby it can prevent the wall surface from being touched and damaged by hot stream. Since the film cooling sets high standards for hole shape, the structure of injection, the length of the coolant supply tube, the angle of incidence, the blowing ratio, the thickness of the boundary layer, ribs and the Reynolds number, etc., the analysis and optimization of these factors have been particular significance on improving cooling efficiency. This paper introduces the dominant factors which influence film cooling effectiveness, besides, analyzes the methods to achieve the best cooling results. The impact of the vortex structures on enhancing film cooling performance is explored. Moreover, a new train of thought is proposed to improve the cooling efficiency under the joint action of the vortex generator and the synthetic jet.
Highlights
The advance of turbine engine technology has led to higher turbine inlet temperature
The flow field of Jet in crossflow (JICF), as indicated by McClintic,7 is well fit for being applied in film cooling, since the crossflow leads to an asymmetry in the counter-rotating vortex pair, which results in more spanwise spreading of the coolant, thereby the cooling efficiency can be radically improved
The results indicate that these two domains are interconnected and both greatly influence film cooling performance
Summary
The advance of turbine engine technology has led to higher turbine inlet temperature. Under the action of several large-scale coherent vortex structures, the rapid mixing between the jet and the crossflow forms a highly three-dimensional flow field. The flow field of JICF, as indicated by McClintic, is well fit for being applied in film cooling, since the crossflow leads to an asymmetry in the counter-rotating vortex pair, which results in more spanwise spreading of the coolant, thereby the cooling efficiency can be radically improved. The fast mixing between the jet and the crossflow in the flow filed of JIFC is through several largescale coherent vortex structures, and an instantaneous or average three-dimensional flow field is generated therefrom. The factors determining the film cooling efficiency are investigated, and how the vortex structures affected the flow field are analyzed. The third aspect deals with another frontier of synthetic jet and the relation with film cooling as well as the uncertainties and insufficiency that may exist in open literature
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