An investigation of the effect of the pulse width and amplitude on sand bed scouring by a vertical submerged pulsed jet

Abstract

This paper investigates the effects of the pulse width and amplitude on the scouring of sand beds by vertical submerged pulsed jets using a combination of experimental and numerical calculations. The reliability of the numerical calculations is verified through a comparison between the numerical simulations with the sedimentation scour model and the experimental data at a low pulse width T2 of 0, with the result that the various errors are within 5%. The results show that the scour hole depth |hmin| grows with the relative low pulse width T3 throughout three intervals: a slowly increasing zone I, a rapidly increasing zone II, and a decreasing zone III, producing a unique extreme value of |hmin|. The optimal scouring effect equation was obtained by analytically fitting the relationship curve between the pulse amplitude V and the relatively low pulse width T3. Including the optimal T3 and optimal duty cycle ƞ. The difference in the scour hole depth |hmin| under different pulse amplitudes is reflected in the initial period F of the jet. With an increasing pulse amplitude, |hmin| goes through three intervals: an increasing zone M, decreasing zone N, and rebound zone R. It is found that the scouring effect in the pulse jet is not necessarily always stronger with a larger amplitude. The results of the research in this paper can provide guidance for optimizing low-frequency pulsed jets for related engineering practices, such as dredging and rock-breaking projects.