Abstract
An underexpanded jet is utilized in industries as well as aviation field, e.g. to cool a body by the jet impingement, to remove molten metal in laser cutting, etc. One of the biggest problems is noise radiating from the jet which has high frequency, or screech tone. It is pointed out that the noise is closely related to the structure of the jet. In this paper, the underexpanded jets on a plate and hemispheres of different radii are visualized using the shadowgraph method so as to analyze the jet structure, especially a plate shock formed above the body. As a result, the radius of the hemisphere is found to have an effect not on the shape greatly, but on location of the plate shock.
