A comparison of pre-impact gas cushioning and Wagner theory for liquid-solid impacts

Snizhana Ross, Peter D. Hicks (Corresponding Author)

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Abstract

The normal impact of a symmetric rigid body with an initially quiescent liquid half-space is considered using both Wagner theory and a model of viscous gas pre-impact cushioning. The predictions of these two theories are compared for a range of different body shapes. Both theories assume the impactor has small deadrise angle. Novel solutions of the Wagner normal impact problem for a symmetric body with a power-law shape are presented, which generalize the well-known results for a parabola and a wedge. For gas cushioned preimpacts, it is shown that a pocket of gas is entrained even for body shapes with a cusp at the body minimum. A scaling law is developed that relates the dimensions of the trapped gas pocket to the slope of the body. For pre-impact gas cushioning, surface tension is shown to smooth the liquid free-surface and delay the instant of touchdown for a smooth parabolic body, while for a wedge, increasing surface tension initially delays touchdown, before hastening touchdown as the importance of surface tension is increased further. For a flat-bottomed wedge, gas entrainment is again predicted in the gas-cushioning model, although the location of initial touchdown, either on the transition between the wedge and the flat bottom or along the side of the wedge, now depends upon the parameters of the body shape.
Original languageEnglish
Article number042101
JournalPhysics of Fluids
Volume31
Issue number4
Early online date2 Apr 2019
DOIs
Publication statusPublished - Apr 2019

Keywords

  • WATER-ENTRY
  • BUBBLE ENTRAPMENT
  • DROPLET IMPACT
  • INITIAL-STAGE
  • SURFACE
  • SPHERE
  • LOADS

ASJC Scopus subject areas

  • Condensed Matter Physics

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