Film cooling is a method of cooling a surface by maintaining a thin layer of cooling fluid adjacent to the surface, which separates a hot gas flow from the surface. Gas turbine engines use film cooling on components such as combustors, turbine shrouds, and turbine vanes and blades. Such components have walls with a first surface in a hot gas flow path and an opposite second surface not exposed to the hot gas. A cooling fluid such as air is supplied to the second surface at a pressure greater than the hot gas. Holes in the component walls cause the cooling fluid to pass through the holes to the first surface, and spread over it generally along streamlines of the hot gas flow. This forms a cool boundary layer or “film” on the first surface.
Optimizing the effectiveness of cooling film has been a long-standing concern in gas turbine design. The more evenly the film spreads over the heated surface, and the closer it can be kept to the surface, the more efficient and effective it is.
Dielectric barrier plasma generators have been used to control gas flows in boundary layers for various reasons. Such generators induce a directed flow in a neutral gas via momentum transfer from plasma moving between an exposed electrode and an insulated electrode. US patent publication 2008/0131265 describes modifying a film cooling flow downstream of film cooling holes using plasma generators. The present inventors devised improvements to this technique as described herein.
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