NICOP - DMHS computer simulations of cavitation-induced pressure waves and erosion of nearby solid surfaces
Abstract
Cavitation erosion is the process of surface deterioration and surface material loss due to the generation of vapour pockets inside the flow of liquids. These pockets are formed when, as a result of underwater objects moving at high speed, local pressure drops below saturation levels creating vapour cavities in the liquid. Subsequently, higher pressure causes rapid collapse of the voids and generates intense shock waves. If the implosion of the bubbles cavities occurs near to metal surfaces such as propellers or impellers, it causes high local stresses and, with time, fatigue and wear.In this project, a computational method called the Discrete Multi-Hybrid System (DMHS) is employed to perform computer simulations of cavitation erosion. This methodology has been recently developed at the University of Birmingham and it is based on the idea of linking together various particle-based modelling techniques to achieve a realistic simulation of complex phenomena.The philosophy behind the DMHS is to ~model-by-models~, i.e. the ability to link the most suitable mathematical models together in order to realize a complete representation of complex solid-fluid interactions. This method has been so far successfully tested for a variety of systems (biological flows, lava flows, cleaning processes), with various types of solids (non- spherical, elastic, breakable, melting, solidifying, swelling, dissolving), flow conditions (confined, free-surface, microscopic) and length scales (from microns to meters) and, within this project, it will be further developed to tackle the complex phenomenology of cavitation erosion.Various phenomena, in fact, are determinant in the process of cavitation erosion: (i) nucleation and growth of the cavities, (ii) collapse and wave propagation, (iii) impact on the metal surface and indentation. At the moment, modelling and simulation of these phenomena rely on distinct and separate approaches such as (i) thermodynamics, (ii) fluid dynamics, and molecular dynamics. No single modelling technique can cover alone the full spectrum of the phenomena involved and, therefore, a unified approach that goes from the formation of the cavity to the erosion on the metal is still missing.In this project, a unified framework will be achieved by combining together a modelling technique called smoothed-particle hydrodynamics (SPH) for the simulation of the fluid dynamics and a second technique called coarse-grained molecular dynamics (CGMD) for the simulation of the erosion. The SPH method, in fact, is particularly effective in modelling shock waves such as those generated during cavitation, while CGMD is very accurate in the calculation of shock-induced damage in metals. By combining these two techniques in a hybrid fashion, therefore, we can reach a very sophisticated level of simulation.We will also extend the DMHS to include heat transfer and heat generation. In this way, we will be able to include in our simulation the effect of temperature both inside and outside of the vapor bubbles, and on the erosion process. In this project, therefore, we also expect to improve the current understanding of the role that heat generated during cavitation can play in the wearing process. Recent experimental and theoretical studies, in fact, highlight the importance of local high temperatures in the erosion mechanism, but the actual connection among localized high temperatures, the shock impact at the solid surface and the erosion mechanism is not fully understood yet.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2017
- Source ID
- N629091712051
Entities
People
- Alessio Alexiadis
Organizations
- Office of Naval Research
- United States Navy
- University of Birmingham