Erosion onset of a cohesionless granular medium by an immersed impinging round jet

Abstract

To cite this version: AbstractAmong different devices developed quite recently to quantify the resistance to erosion of a natural soil within the broader context of dyke safety, the most commonly used is probably the Jet Erosion Test (JET) in which a scouring crater is induced by impingement of an immersed water jet. A comprehensive experimental investigation on the jet erosion in the specific situation of a cohesionless granular material is presented here. The tests were performed combining special optical techniques allowing for an accurate measurement of the scouring onset and evolution inside an artificially translucent granular sample. The impinging jet hydrodynamics are also analyzed empirically validating the use of a self-similar theoretical framework for the laminar round jet. The critical conditions at the onset of erosion appear to be best described by a dimensionless Shields number based on the inertial drag force created by the fluid flow on the eroded particles rather than on the pressure gradients around them. To conclude, a tentative empirical model for the maximal flow velocity initiating erosion at the bottom of the scoured crater is put forward and discussed in the light of some preliminary results.

Generalized Shields criterion for weakly cohesive granular materials

“…The remainder of this paper is organized as follows: Sec. II revisits previous results by the authors [48] in the light of recent numerical results [49] for an accurate estimate of fluid shear stress for an impinging jet. Next, Sec.…”

“…In the light of these recent findings, the previous experimental results by Badr et al [53] on the erosion onset of a granular bed by a plane-impinging jet have been revisited, leading to more 034308-4 realistic values of the critical Shields number [49]. The following section follows a similar approach in the present 3D situation and compares it with the recently published results carried out with cohesionless materials using the same experimental device [48].…”

“…In almost all previous studies on soil erosion by an impinging jet, this issue is circumvented by using empirical expressions derived from experiments of solid wall impingements [38,50,51]. In some instances this approach is improved to account for the flow confinement [52] or coupled with even stronger assumptions such as directly neglecting the presence of the soil surface to permit the use of well-known self-similar free jet models [48,53,54]. In the related literature, several numerical analyses of the impinging jet flow have been proposed for both laminar and turbulent flow regimes, while the actual coupling to soil erosion may also be included either explicitly or implicitly with different strategies.…”

“…The resulting cohesive granular materials were then subjected to mechanical tests at both local and sample scales for the assessment of their cohesive strength. Finally, the erodibility of the samples was evaluated quantitatively by means of JET tests (i.e., an immersed impinging jet as the fluid flow configuration) and ultimately compared to a previous analysis by the authors in the limit of the cohesionless case [48]. Special attention was devoted to the choices of materials and methods, which in this case permits the use of a nonintrusive optical probe in order to investigate not only the erosion threshold but also the subsequent crater scouring and its kinetics.…”

Fluid density effects in supersonic jet-induced cratering in a granular bed on a planetary body having an atmosphere in the continuum regime

“…The results reported two types of crater morphologies: a shallow parabolic crater (type I) occurring for a weakly deflected jet and deep conical craters (type II) for a strongly deflected jet. The significance of the Shields number was additionally highlighted by Brunier-Coulin, Cuellar & Philippe (2017), who have experimentally investigated a water jet impinging on a granular bed under low-speed conditions and constructed an empirical model for quantifying erosion of the bed. For laminar flows, Ouriemi et al.…”