Air-cushioning effect and Kelvin-Helmholtz instability before the slamming of a disk on water

Jain, Utkarsh; Gauthier, Anaïs; Lohse, Detlef; Meer, Devaraj van der

doi:10.1103/physrevfluids.6.l042001

Cited by 14 publications

(10 citation statements)

References 43 publications

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“…For flatter impact (), we see the trapped gas layer expected with disk impact ( ms) (Jain et al. 2021 a ). The layer breaks down as water contacts the impacting face in concentric rings ( ms), leaving a shrinking air pocket in the middle of the face ( ms).…”

Section: Disk Water Impactmentioning

confidence: 62%

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Water entry of cups and disks

et al. 2023

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It is known that the water entry of a body with a recessed, cupped nose can suppress the splash and air cavity typically observed for solid body entry (Mathai, Govardhan & Arakeri, Appl. Phys. Lett., vol. 106, 2015, 064101). However, the interplay between the captive gas in the cup, the cavity and the splash is quite subtle and has not been thoroughly explored. Here we study the cavity and splash dynamics associated with the vertical water entry of cups and find a variety of regimes over a range of Weber numbers ( $We_D$ ) and dimensionless cup depths. Our parameter space spans a transition between slow-developing cavities with long closure times (low $We_D$ ) to fast-sealing cavities (high $We_D$ ). An important dynamic event is the evacuation of trapped gas from within the cup, which drives the ensuing cavity and splash behaviour. Through modelling, we predict the conditions for which the evacuating gas inflates a cavity that opens to the atmosphere versus inflating a submerged cavity that suppresses air entrainment from above the surface. We also compare our cup water entry findings to the impact phenomena observed for flat disks, which entrap gas on the front surface similar to cups. In doing so, we reveal the sensitivity of disk splash and cavity behaviour to impact angle, and show that disks share a common regime with cups, in which a thin splash quickly seals on the body. We deduce the mechanisms by which increasing cup depth delays the cavity seal time in this regime. These findings reveal that cups may in fact promote or suppress cavity growth, depending on the cup depth and impact conditions.

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Section: Disk Water Impactmentioning

confidence: 62%

“…Typically, past studies on the vertical water entry of disks have either actively enforced that the disk face impacts truly flat to the surface (Peters, van der Meer & Gordillo 2013; Jain et al. 2021 a , b ) or have explicitly varied the inclination angle, but for values of (Bodily et al. 2014; Sun et al.…”

Section: Disk Water Impactmentioning

confidence: 99%

Water entry of cups and disks

et al. 2023

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“…To the authors' knowledge, this is the first study to compare the performance of multiple optical techniques for surface reconstruction. The TIR-D and M-G techniques, due to their recency, are featured in limited studies other than the original work (Jain et al, 2022;Jain, Gauthier, Lohse, et al, 2021;Jain, Vega-Martínez, et al, 2021;Kochkin et al, 2022;Mungalov & Derevyannikov, 2021;Rudenko et al, 2022). These techniques have also gone unnoticed in reviews of optical techniques for surface measurements such as a recent comprehensive review by Gomit et al (2022).…”

Section: Introductionmentioning

confidence: 99%

Comparison of Schlieren-based techniques for measurements of a turbulent and wavy free surface

Bheeroo

Mandel

2023

Preprint

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The free surface at an air-water interface can provide information regarding bathymetric complexities, as well as the subsurface flow. We present a comparison of the performance of two recent advances in light-based optical techniques for free surface measurements, Total Internal Reflection-Deflectometry and Moon-Glade Background Oriented Schlieren, with the more established method of Free-Surface Synthetic Schlieren. We make use of an optical flow algorithm over the more traditional Digital Image Correlation, in order to obtain higher spatial resolution data across the imaged free surface domain. The Optical flow algorithm presents additional benefits, such as computational efficiency and robustness in capturing large displacements and straining of tracked features. The three optical techniques are assembled in synchronization to image two free surface conditions: (1) a free surface being impinged upon by an underlying turbulent, free-shear flow and (2) a random and irregular wave field induced by a free jet. Using the high-resolution measurements, we provide insight on the emergence of multiple free surface dynamics for a turbulent free surface and dissect the local hydrodynamics of the free surface for several wave forcings. We present a comprehensive discussion on the benefits and drawbacks of each technique, including suggestions on the suitability of each technique for several experimental constraints.

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“…The effect of the air cushion is especially important for phenomena at the very initial stage, when the instantaneous Froude number is tremendously large. The detailed behaviour of the air cushion and its effect on various aspects of the impact, such as splash, pressure and force, are studied in, for example, Bouwhuis et al (2015), Jain et al (2021), Moore (2021), Hicks et al (2012).…”

Section: Introductionmentioning

confidence: 99%

“…These studies largely confirm the theoretical findings discussed above. Experiments performed by Judge, Troesch & Perlin (2004) on the vertical/oblique impact of a tilted wedge on a water surface illustrated the effects of the wedge's initial velocity ratio and the level of asymmetry from the vertical axis at its vertex on the symmetry of the spray root propagation as well as on the flow separation from the wedge's surface. Mathematical models for the water entry of an asymmetric wedge are developed in studies such as Semenov & Iafrati (2006) and Semenov & Wu (2018).…”

Section: Introductionmentioning

confidence: 99%

The controlled impact of elastic plates on a quiescent water surface

Wang

Wong

et al. 2022

J. Fluid Mech.

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The impact of flexible rectangular aluminum plates on a quiescent water surface is studied experimentally. The plates are mounted via pinned supports at the leading and trailing edges to an instrument carriage that drives the plates at constant velocity and various angles relative to horizontal into the water surface. Time-resolved measurements of the hydrodynamic normal force ( $F_n$ ) and transverse moment ( $M_{to}$ ), the spray root position ( $\xi _r$ ) and the plate deflection ( $\delta$ ) are collected during plate impacts at 25 experimental conditions for each plate. These conditions comprise a matrix of impact Froude numbers ${Fr} = V_n(gL)^{-0.5}$ , plate stiffness ratios $R_D= \rho _w V_n^2 L^3D^{-1}$ and submergence time ratios $R_T= T_sT_{1w}^{-1}$ . It is found that $R_D$ is the primary dimensionless ratio controlling the role of flexibility during the impact. At conditions with low $R_D$ , maximum plate deflections on the order of $1$ mm occur and the records of the dimensionless form of $F_n$ , $M_{to}$ , $\xi _r$ and $\delta _c$ are nearly identical when plotted vs $tT_s^{-1}$ . In these cases, the impact occurs over time scales substantially greater than the plate's natural period, and a quasi-static response ensues with the maximum deflection occurring approximately midway through the impact. For conditions with higher $R_D$ ( $\gtrsim 1.0$ ), the above-mentioned dimensionless quantities depend strongly on $R_D$ . These response features indicate a dynamic plate response and a two-way fluid–structure interaction in which the deformation of the plate causes significant changes in the hydrodynamic force and moment.

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Air-cushioning effect and Kelvin-Helmholtz instability before the slamming of a disk on water

Cited by 14 publications

References 43 publications

Water entry of cups and disks

Water entry of cups and disks

Comparison of Schlieren-based techniques for measurements of a turbulent and wavy free surface

The controlled impact of elastic plates on a quiescent water surface

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