Evaluation of the performance of an analytical-numerical coupled method for droplet impacts on soft material surfaces

TL;DR

This study evaluates the effectiveness of an analytical-numerical coupled model for droplet impacts on soft surfaces, comparing it with experiments and SPH simulations, and identifies its applicability limits based on material softness.

Contribution

The paper assesses the performance of the ANCM model on soft materials, extending its validation beyond rigid surfaces and identifying its limitations at low Young's modulus.

Findings

ANCM performs well for materials with Young's modulus above 47,400 Pa.

SPH simulations show impact mitigation due to surface deformation in soft materials.

ANCM's impact load estimates are independent of surface geometry, leading to non-physical conservation of impact impulse.

Abstract

Impacts between droplets and solid surfaces can commonly cause erosion problem in Engineering applications, including aircraft surface erosion, wind blade leading-edge erosion and steam turbine blade erosion. In practice, the impacted solid surfaces have varied material softness, ranging from stiff metallic coatings to soft materials. An analytical-numerical coupled model (ANCM) for simulating droplet impacts on surfaces, and corresponding material analysis, has been developed in the literature. However, the analytical impact pressure solution of the ANCM model has been derived assuming rigid solid surface. In the current study, we investigate the performance of the ANCM model for droplet impacts on soft materials made of urethane gel phantom, by comparing the ANCM computations to lab-based experiments and numerical simulations based on Smoothed Particle Hydrodynamics (SPH). Parametric studies explore the applicability limit of the ANCM model for droplet impacts on very soft materials at low Young's modulus. It was found that for materials at Young's modulus of $47,400$ Pa or stiffer, which covers most engineering applications, the developed ANCM model performs as expected for an assumed rigid surface. For softer solid materials, the SPH-modeled liquid interacts with the evolving surface geometry and mitigates impact intensity as deformation occurs. The analytical impact loads estimated by ANCM are independent of surface geometry, and hence provide conserved impact impulse in a non-physical way. Results show a critical value of Young's modulus at $E=10,000$ pa for the ANCM model, below which the model exhibits overshoot in total contact force and surface deformation, leading to the formation of steep wall craters.