2D Axisymmetric Modelling of Single Liquid Droplet Impingement at High Speeds on Thin Liquid Films in Compressible Regime

Abstract

High-speed droplet impact is of great interest to power generation and aerospace industries due to the accrued cost of maintenance in steam and gas turbines. The repetitive impacts of liquid droplets onto rotor blades, at high relative velocities, result in the blade erosion, which is known as Liquid Impingement Erosion (LIE). Experimental and analytical studies in this field are limited due to the complexity of the droplet impact at such conditions. Hence, numerical analysis is a very powerful and affordable tool to investigate LIE phenomenon. In this regard, it is crucial to understand the hydrodynamics of the impact in order to identify the consequent solid response before addressing the LIE problem. The numerical study of the droplet impingement provides the transient pressure history generated in the liquid. Knowing the transient behavior of the substrate, in response to pressure force exerted due to the impact, would facilitate engineering new types of surface coatings that are more resistant to LIE. In LIE problem, a scenario may occur where the previously impinged droplet has spread over the surface and the subsequent impinged droplet impacts a thin liquid film that was formed on the substrate. For this reason, the droplet impingement is simulated with compressible VOF solver for the impact of a 500-µm droplet impinged at 350 m/s onto a liquid film with a thickness of 100 µm and the results obtained from the compressible fluid modeling are compared with the case of a dry substrate under the same impact condition.

Liquid–Solid Impact Mechanism, Liquid Impingement Erosion, and Erosion-Resistant Surface Engineering: A Review

“…Thus, in simulations of the compressible droplet impact, it is important to consider the variations in the sound speed, via the changes in liquid density, with an appropriate equation of state. Recently, Marzbali and Dolatabadi [170] and [171] used a compressible volume-of-fluid (VOF) model together with proper equations of state to determine the interfacial gas-liquid flow in high-speed droplet impingements. In [170], they studied the impact of a 200 µm droplet at a velocity of 500 m/s on a dry rigid surface, and in [171] they focused on the impingement of a 500 µm droplet at a velocity of 350 m/s on a 100 µm thick liquid film.…”

“…Recently, Marzbali and Dolatabadi [170] and [171] used a compressible volume-of-fluid (VOF) model together with proper equations of state to determine the interfacial gas-liquid flow in high-speed droplet impingements. In [170], they studied the impact of a 200 µm droplet at a velocity of 500 m/s on a dry rigid surface, and in [171] they focused on the impingement of a 500 µm droplet at a velocity of 350 m/s on a 100 µm thick liquid film. They compared their numerical results for lateral jet speed, liquid density, and maximum pressure with the data obtained by Haller [167] for the droplet impingement on a rigid surface [172].…”

“…Since the solid deformation, even under high impact velocities, is negligible for metals [202], it is possible to decouple the fluid and solid domains in order to reduce the computational cost in the simulations. To that end, a 2D axisymmetric geometry for spherical droplets with a compressible VOF model [170,171] (in which the ideal gas assumption for the air and Tait's equation of state (EOS) for water were used [203]) was employed parametrically for a wide range of impingement scenarios on both dry and wetted substrates [172] to obtain a correlation for the maximum impact pressure.…”