Abstract
An underexpanded jet has typical shock-cell structure and strongly oscillates, its behavior being known to cause many industrial problems. An underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine, a pressure control valve and so on. When a supersonic jet exhausted from a circular nozzle impinges on a flat plate, the wall jet formed on the plate often becomes underexpanded and spreads out radially. Such underexpanded impinging jet is one of models of supersonic jets on laser cutting process and glass tempering process. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two cylinders, was experimentally examined for different nozzle pressure ratios and for different diameters of cylinder. Jet structure was analyzed by means of a visualization e.g. Schlieren method. A noise emitted from the jet was measured and the frequency of screech tone was analyzed. The experimental results were compared with those of a two dimensional jet issuing from a rectangular nozzle. Furthermore, a comparison of visualized sound waves with the screech tone frequency reveals that the sound source measured was in the vicinity of the end of the second cell and that the length of the second or third cell was one of the most important parameters to determine the frequency of the emitted screech tone.
Highlights
When a supersonic jet exhausted from a circular nozzle impinges on a flat plate, the wall jet formed on the plate often becomes underexpanded and spreads out radially
An underexpanded jet radially discharged from a circular slit nozzle, which consists of two cylinders, was experimentally examined for different nozzle pressure ratios and for different diameters of cylinder
A comparison of visualized sound waves with the screech tone frequency reveals that the sound source measured was in the vicinity of the end of the second cell and that the length of the second or third cell was one of the most important parameters to determine the frequency of the emitted screech tone
Summary
The underexpanded radial jet occurs in a flow field around an intake valve in an internal combustion engine and a pressure regulating valve in a piping system. When an underexpanded jet from a circular nozzle or a rectangular nozzle impinges on a plate at a relatively short distance between the nozzle and the plate, the wall jet spreading radially on the flat plate may be underexpanded [1]. Such a flow field is practically formed when an assist gas of a laser cutting machine or a quenching gas of tempered glass impinges on an object [2] [3] [4]. The paper shows that the length of the 1st cell is closely related to the dominant frequency of the broadband noise and that the broadband noise is supposed to radiate from the end of the 1st cell
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