Gelatine cavity dynamics of high-speed sphere impact

Abstract

We investigate the impact and penetration of a solid sphere passing through gelatine at various impact speeds up to 143.2 m s −1 . Tests were performed with several concentrations of gelatine. Impacts for low elastic Froude number Fr e , a ratio between inertia and gelatine elasticity, resulted in rebound. Higher Fr e values resulted in penetration, forming cavities with prominent surface textures. The overall shape of the cavities resembles those observed in water-entry experiments, yet they appear in a different order with respect to increasing inertia: rebound, quasi-seal, deep-seal, shallow-seal and surface-seal. Remarkably, similar to the We-Bo phase diagram in water-entry experiments, the elastic Froude number Fr e and elastic Grashof number Gr e (a ratio between gravity and gelatine elasticity) classify all five different phenomena into distinguishable regimes. We find that Fr e can be a good indicator to describe the cavity length H, particularly in the shallow-seal regime. Finally, the evolution of cavity shape, pinch-off depth, and lower cavity radius are investigated for different Fr e values.

Impact of a microfluidic jet on a pendant droplet

“…However, as De increases, i.e., when the viscoelastic timescales become increasingly comparable to the capillary time, the jet needs larger speeds to traverse the droplet. This is in line with previous experiments where by increasing the elastic modulus of gelatin the cavity depth of an impacting sphere would decrease, keeping the impact velocity constant 35 . These results show that viscoelastic properties as described by De significantly change the traversing dynamics.…”

“…This is in line with previous experiments where by increasing the elastic modulus of gelatin the cavity depth of an impacting sphere would decrease, keeping the impact velocity constant. 35 These results show that viscoelastic properties as described by De significantly change the traversing dynamics. This is crucial information when trying to understand needle-free injections on skin, as it has been shown that skin has viscoelastic properties.…”

Microfluidic jet impact: spreading, splashing, soft substrate deformation and injection

“…Within the reported cavity types our observations can be best compared to the shallow seal regime, which we found for G = 3.5 kPa and W e jet > 3500, F r e > 1200; G = 0.8 kPa and W e jet > 650, F r e > 1000; G = 0.2 kPa and W e jet = 125-215, F r e > 700-1300. Our results are in agreement with Kiyama et al, where they found shallow seals starting from F r e 200 -400 and transitioning to surface seal at F r e > 10 4 [67]. We did not observe a transition to a surface seal as for our experiments F r e < 10 4 .…”

“…We can compare our results by looking at studies where high-speed projectiles were impacted on various concentrations of gelatin gels, and cavity regimes were defined based on projectile elastic Froude number (F r) as function of substrate G [67]. Within the reported cavity types our observations can be best compared to the shallow seal regime, which we found for G = 3.5 kPa and W e jet > 3500, F r e > 1200; G = 0.8 kPa and W e jet > 650, F r e > 1000; G = 0.2 kPa and W e jet = 125-215, F r e > 700-1300.…”

Dynamics of pulsed laser-induced cavities on a liquid–gas interface: from a conical splash to a ‘bullet’ jet

“…a few tens of microns below the surface). Similar to the fluid mechanics created by an object impacting on a free surface (Kiyama et al 2019), laser focusing gives origin to an explosive expansion of a cavity front into the liquid and a recoil induced material expulsion (or splash) into the air (Vogel & Venugopalan 2003;Apitz & Vogel 2005;Thoroddsen et al 2009). While typical impact velocities of objects result in cavity front velocities of tens of metres per second, and splashes rising in opposite direction with similar velocities, laser induced splashes are considerably faster.…”