Flow field and scouring effects of steady and pulsating jets impinging on a movable bed : Abschlußbericht B 2

Abstract

Jets impinging on a movable bed of particles can lead to strong local scouring effects. Submerged jets, which in practice frequently show periodical velocity fluctuations, can either lead to dangerous scouring near hydraulic structures, or be put to technical use due to their strong erosion capacity. Unwanted effects are found, for example, in the erosion of the bottom of navigable waterways by ship propellers, whereas in dredging high velocity jets are successfully used for loosening hardpacked sandy soils, or also for submarine underground-laying of pipes. Furthermore, the flow field of impinging jets is of interest for hovercrafts end for vertical takeoffs, and also for numerous applications in chemical engineering. In order to control the wanted or unwanted scouring effects of impinging jets, it is necessary to know in detail both the flow field and the scouring effect of this flow configuration. Therefore, on experimental investigation of an axi-symetrical, vertical, submerged jet impinging on a horizontal sand bed of uniform grain size was studied. Particular attention was paid to the quantification of the influence of a pulsation of the jet velocity, which under certain geometrical and flow conditions causes en increase of the scouring rates.