不足膨張状態の放射状自由噴流の構造に関する研究

抄録

This paper focuses on structure of an underexpanded jet spreading radially. The underexpanded radial jet can be seen in various industrial fields, such as intake process of an internal combustion engine, flow rate control by a pressure control valve, molten metal removal in laser cutting process, cooling process of thermal tempering glass and so on. In some of these processes, gas goes through a small gap and radially spreads out at supersonic velocity. In this paper, the underexpanded radial jet is modeled by air discharged from small space between the ends of two circular tubes, which are installed face to face, like a slit-shaped nozzle. Using visualization and acoustic measurement, the underexpanded radial jet from the slit nozzle is examined at different supply pressures. Pictures by shadowgraphy are analyzed to measure cell lengths of the jet, and noises emitted from the jet are analyzed by FFT analyzer to obtain screech tone frequencies. Furthermore, the cellular structure of the radial jet is theoretically analyzed to estimate the cell length. As a result, the cell lengths obtained theoretically agree well with those by the experiment. Furthermore, relation between the jet structure and the screech tone emitted from the jet is discussed based on Strouhal number. It was found that the 3rd cell length plays an important role in the screech noise radiation.