A technique is described for visualizing the air flow over a surface by means of an oil film. The technique is used in conjunction with experimentally determined flapper-plate pressure profiles to examine the flow characteristics of a flapper-nozzle valve used to control air at 425 kPa (4.25 bar). The oil film shows clearly the points of separation and reattachment of the air boundary layer resulting from shock wave and boundary layer interaction.
Possible applications of the technique are discussed and attention is focused on the use of the oil-film technique in conjunction with interferometry as a tool for the rapid determination of the effects caused by changes in nozzle geometry.
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