Abstract
Investigating internal-injector cavitating flow dynamics is difficult but important. The interaction of nozzle cavitation with the moving needle valve dictates the fuel mass flow rate and therefore spray combustion performance and emissions. In the present study, a two-dimensional low-Reynolds-number cavitating contracting-nozzle flow interacting with a moving valve is simulated using the lattice Boltzmann (LB) method. The Bhatnagar–Gross–Krook algorithm coupled with the immersed boundary method and an improved pseudo-potential multiphase flow model are employed and further developed based on the open-source LB code PALABOS. The performance of the immersed boundary method is first verified in a case where an oscillating cylinder moves according to a sine function in water. In order to improve the pseudo-potential model on its limitation of the density ratio, so to be used in engineering multiphase flow, the Carnahan–Starling equation of state is incorporated together with the exact difference method force scheme and an upgraded interaction force term. The upgraded pseudo-potential model proves via validations to be effective in improving numerical stability at large density ratios. With a seamless cooperation of the improved Shan–Chen model and the immersed boundary method achieved in PALABOS, cavitation in a contracting nozzle is simulated for a whole cycle of the valve motion. Cavitation dynamics under different fuel mass flow rates is investigated. It is found that cavitation dynamics, including interface conditions, cavitation bubble distributions, and inside-bubble vapor-phase flow fields, is distinctly different when the flow path is widely open and completely shut by the valve.
Highlights
Gas–liquid two-phase flow interacting with a moving geometry is a ubiquitous phenomenon in a multitude of important industrial applications, including rotating propellers in ship propulsion systems,1 cavitation impact on pump blades,2 lubricant cavitation in rotating bearings,3 the water entry or exit problem of missiles,4 and so on
A 2D low-Reynolds-number cavitating flow interacting with a moving valve has been investigated using lattice Boltzmann methods based on the further developed opensource code PALABOS
In order to enhance the density ratio in a two-phase flow that can be coped by lattice Boltzmann (LB) methods, the original pseudo-potential model was further developed by incorporating the Carnahan–Starling equation of state, the exact-difference force scheme, and an upgraded interaction force term
Summary
Gas–liquid two-phase flow interacting with a moving geometry is a ubiquitous phenomenon in a multitude of important industrial applications, including rotating propellers in ship propulsion systems, cavitation impact on pump blades, lubricant cavitation in rotating bearings, the water entry or exit problem of missiles, and so on. It is a rather attractive characteristic as the phase interface is no longer a mathematical boundary and no explicit interface tracking or capturing techniques are needed.46 Due to this feature, a great number of studies on cavitation or phase transition along with heat transfer have been conducted, including the exploration of its applicability toward simulating idealized internal fuel-injector flow.. Since there has been little research on interactions of cavitation with a moving geometry due to the difficulty of dealing with valve-motion-impacted cavitation using conventional computational approaches, we believe we have made a further important step in the area by using a more realistic configuration with a gas/liquid density ratio O(103). Understanding the transient cavitation dynamics is important for controlling fuel spray processes and alleviating injector-nozzle erosion These direct LB simulation data will be useful for validation, development, and calibration of LES/RANS models, especially as the measurement is still difficult and Navier–Stokes-based direct simulation would be too expensive to conduct. Our future research interests in the LBM will be developing methodologies to simulate a high-Reynoldsnumber internal gas–liquid flow interacting with complex moving geometries
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