Abstract: The organ-pipe nozzle is widely used because of its generation of self-resonating cavitating jets which combines the advantages of cavitating jets and pulsed jets. In order to improve the working efficiency of organ-pipe nozzle by studying the influence of internal surface roughness on the characteristics of high pressure jet under high Reynolds numbers, the relations between turbulent boundary layer and surface roughness are theoretically analyzed, and the laws of the axial pressure fluctuation and the diffusion angle of the jet are investigated by experiment. The results show that, the peak pressure, the rage of pressure fluctuation and the diffusion angle are influenced more greatly by the surface roughness when the inlet pressure is greater. There exists a minimum roughness number, above which the diffusion angle starts to increase while the peak pressure and the rage of pressure fluctuation starts to decrease greatly. For a certain inlet pressure, there exists a critical roughness number, below which the axial pressure fluctuation increases at first and then decreases with the increase of stand-off distance, while above which the axis pressure fluctuation only decreases when the stand-off distance increases. Based on the experimental data, a preliminary mathematical model of the axial peak pressure relating to inlet pressure, internal surface roughness and stand-off distance was established by utilizing the principle of conservation of energy.

Key words: diffusion angle, organ-pipe nozzle, pressure fluctuation, surface roughness