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

수직 수중 펄스 제트에 의한 모래층 정련에 대한 펄스 폭과 진폭의 영향 조사

Chuan Wang abc, Hao Yu b, Yang Yang b, Zhenjun Gao c, Bin Xi b, Hui Wang b, Yulong Yao b

aInternational Shipping Research Institute, GongQing Institute of Science and Technology, Jiujiang, 332020, ChinabCollege of Hydraulic Science and Engineering, Yangzhou University, Yangzhou, 225009, ChinacCollege of Mechanical and Power Engineering, China Three Gorges University, Yichang, 443002, China

https://doi.org/10.1016/j.oceaneng.2024.117324

Highlights

  • Numerical simulations and experiments were combined to investigate pulsed jet scour.
  • The effect mechanism of pulse amplitude on the variation of scour hole depth was analyzed.
  • Models for the prediction of relative low pulse width with the inlet pulse amplitude have been developed.

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.

Introduction

Submerged jet scouring technology is widely used in marine engineering and dredging projects due to its high efficiency and low cost, and a wide range of research exists on the topic (Zhang et al., 2017; Thaha et al., 2018; Lourenço et al., 2020). Numerous scholars studied the scouring caused by different forms of jets, such as propeller jets (Curulli et al., 2023; Wei et al., 2020), plane jets (Sharafati et al., 2020; Mostaani and Azimi, 2022), free-fall jets (Salmasi and Abraham, 2022; Salmasi et al., 2023), and moving jets (Wang et al., 2021). Among them, vertical jets were more popular than inclined jets due to theirs simple equipment and good silt-scouring performance (Chen et al., 2023; Wang et al., 2017). So, a large number of scholars have proposed relevant static and dynamic empirical equations for the scour depth of submerged jets. Among them, Chen et al. (2022) and Mao et al. (2023) investigated the influence of jet diameters, jet angles, exit velocities, and impinging distances on scouring effects. Finally, based on a large amount of experimental data and theoretical analysis, a semi-empirical equation for the dynamic scour depth in equilibrium was established. Amin et al. (2021) developed semi-empirical prediction equations for asymptotic lengths and empirical equations for the temporal development of lengths. Shakya et al. (2021, 2022) found that the ANN model in dimensionless form performs better than the ANN model in dimensioned form and proposed an equation for predicting the depth of static scour under submerged vertical jets using MNLR. Kartal and Emiroglu (2021) proposed an empirical equation for predicting the maximum dynamic scour depth for a submerged vertical jet with a plate at the nozzle. The effect of soil properties on jet scour has also been studied by numerous scholars. Among them, Nguyen et al. (2017) investigated the effects of compaction dry density and water content on the scour volume, critical shear stress, linear scour coefficient, and volumetric scour coefficient using a new jet-scour test device. Dong et al. (2020) investigated the effect of water content on scour hole size through experiments with a vertical submerged jet scouring a cohesive sediment bed. It was found that the depth and width of the scour holes increased with the increasing water content of the cohesive sediments, and equations for the scour depth and width in the initial stage of scouring and the calculation of the scouring rate were proposed. Kartal and Emiroglu (2023) studied the scouring characteristics of different nozzle types produced in non-cohesive sands. The results of the study found that the air entrainment rate of venturi nozzles was 2–6.5 times higher than that of circular nozzles. Cihan et al. (2022) investigated the effect of different proportions of clay and sand on propeller water jet scouring. And finally, he proposed an estimation equation for the maximum depth and length of the scour hole under equilibrium conditions. From the above summary, it is clear that a great deal of research has been carried out on submerged jet scouring under continuous jet flows.

Pulsed jets have advantages such as higher erosion rates and entrainment rates compared to continuous jets and have therefore received more attention in the development of engineering fields such as cleaning and rock breaking (Raj et al., 2019; Zhu et al., 2019; Kang et al., 2022; Y. Zhang et al., 2023). In the study of jet structure, Li et al. (2018, 2019a, 2019b, 2023) investigated the effects of the jet hole diameter, the number of jet holes, the jet distance, and the tank pressure on pulse jet cleaning. It was found that the transient pressure below the injection hole gradually increased along the airflow direction of the injection pipe, and the peak positive pressure at the inner surface of the injection pipe also increased. Liu and Shen (2019) investigated the effect of a new venturi structure on the performance of pulse jet dust removal. It was found that the longer the length of the venturi or the shorter the throat diameter of the venturi, the greater the energy loss. Zhang et al. (2023b) studied jet scouring at different angles based on FLOW-3D. It was found that counter flow scouring is better than down flow scouring. In the study of pulsed structure, Li et al. (2020) investigated the effects of different pulse amplitudes, pulse frequencies, and circumferential pressures on the rock-breaking performance. It was found that the rock-breaking performance of the jet increased with increasing pulse amplitude. However, due to the variation in pulse frequency, the rock-breaking performance does not show a clear pattern. The effect of Reynolds number on pulsating jets impinging on a plane was systematically investigated by H. H Medina et al. (2013) It was found that pulsation leads to a shorter core region of the jet, a faster decrease in the centerline axial velocity component, and a wider axial velocity distribution. Bi and Zhu (2021) investigated the effect of nozzle geometry on jet performance at low Reynolds numbers, while Luo et al. (2020) studied pulse jet propulsion at high Reynolds numbers and finally found that higher Reynolds numbers accelerate the formation of irregular vortices and symmetry-breaking instabilities. Cao et al. (2019) investigated the effect of four different pulse flushing methods on diamond core drilling efficiency. It was found that the use of intermittent rinsing methods not only increases penetration rates but also reduces rinse fluid flow and saves power.

Previous research on vertical submerged jet scouring has primarily focused on the effect of jet structure on scouring under continuous jet conditions. However, there have been fewer studies conducted on scouring under pulsed jet conditions. We found that the pulsed jet has a high erosion rate and entrainment rate, which can significantly enhance the scouring effect of the jet. Therefore, to address the research gap, this paper utilizes a combination of numerical calculations and experiments to investigate the effects of high pulse width, low pulse width, and amplitude on the scouring of vertically submerged jets. The study includes analyzing the structure of the pulsed jet flow field, studying the evolution of the scouring effect over time, and examining the relationship between the optimal pulse width, duty cycle, and amplitude. The study’s conclusions of the study can provide a reference for optimizing the performance of pulse jets in the fields of jet scouring applications, such as dredger dredging and pulse rock breaking, as well as a theoretical basis for the development of submerged pulse jets.

Section snippets

Model and calculation settings

Fig. 1 shows the geometric model of the submerged vertical jet impinging on the sand bed, which was built in Flow-3D on a 1:1 dimensional scale corresponding to the experiment. The jet scour simulation was set up between four baffles, where the top baffle was used to ensure that the jet entered only from the brass tube, and the remaining three tank baffles were used to fix the sediment and water body. The computational domain consisted of only solid and liquid components, with the specific

The effects of the pulse width on submerged jet scouring

The blocking pulsed jet, indicated as A and C in Fig. 8(a)–is discontinuous and divided into a water section and a pulse interval section. The water section in region A is not a regular shape, due to part of the water section near the side wall being affected by the wall friction and the falling speed being lower, but this also shows that the wall plays a certain buffer role. Region B of Fig. 8(a) shows the symmetrical vortex generation that occurs below the nozzle as the water section is

conclusions

In this paper, the effects of the pulse width and pulse amplitude on jet scour under submerged low-frequency pulse conditions are discussed and investigated, and the following conclusions have been reached.

  • (1)The errors of between the Flow-3D simulation and the experimental measurements were within 5%, which proves that the sedimentation scouring model of Flow-3D can reliably perform numerical calculation of the type considered in this paper.
  • (2)The change in the high pulse width T1 in the pulse cycle 

CRediT authorship contribution statement

Chuan Wang: Data curation, Conceptualization. Hao Yu: Writing – original draft. Yang Yang: Writing – review & editing, Supervision. Zhenjun Gao: Supervision, Writing – review & editing. Bin Xi: Resources, Project administration. Hui Wang: Software, Data curation. Yulong Yao: Validation, Software.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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