Novel measurement of horizontal liquid film thickness and viscosity from acoustic signal of a sphere – wall wet impact

This thesis studies how the acoustic pressure from an impact between a solid sphere and a horizontal wall is modified by the presence of a thin film of Newtonian liquid via systematic precise measurements and integrated theoretical analysis. We first extend an existing acoustic theory describing the pressure radiated from dry impacts between two solid objects according to their acceleration history to incorporate hydrodynamic deceleration via partially – immersed lubrication theory developed herein. We then propose a method to extract acceleration history based on the acoustic signals and determine the model coefficients via systematic experiments. Acceleration predicted by Hertz contact theory fairly matches to the dry impact data but only agrees to the later – time acceleration signal from a wet impact. The early-time acceleration signal from a wet impact, on the other hand, matches to the partially – immersed lubrication theory. Hence, we propose a method to extract film thickness and viscosity from the acoustic signal and evaluate its effectiveness and accuracy via complementary experiment. We also comment on how the accuracy varies with film thickness and viscosity.