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 that 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 pre-impacts, 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.
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April 2019
Research Article|
April 02 2019
A comparison of pre-impact gas cushioning and Wagner theory for liquid-solid impacts
Snizhana Ross
;
Snizhana Ross
School of Engineering, University of Aberdeen, King’s College, Fraser Noble Building
, Aberdeen AB24 3UE, United Kingdom
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Peter D. Hicks
Peter D. Hicks
a)
School of Engineering, University of Aberdeen, King’s College, Fraser Noble Building
, Aberdeen AB24 3UE, United Kingdom
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Physics of Fluids 31, 042101 (2019)
Article history
Received:
December 21 2018
Accepted:
March 11 2019
Citation
Snizhana Ross, Peter D. Hicks; A comparison of pre-impact gas cushioning and Wagner theory for liquid-solid impacts. Physics of Fluids 1 April 2019; 31 (4): 042101. https://doi.org/10.1063/1.5086510
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