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Title: Large Eddy Simulation of liquid jet primary breakup
Authors: Xiao, Feng
Issue Date: 2012
Publisher: © F. Xiao
Abstract: Atomisation of liquid fuel jets is an important determinant of combustion performance in gas turbine engines, and thus is the prime research driver here. Since the first stage of the atomisation process primary breakup has not been well understood due to its complexity, the objective of the current project is to develop a robust algorithm for Large Eddy Simulation (LES) to predict primary breakup. In order to provide realistic turbulent inflows for LES of liquid jet primary breakup, a rescaling/recycling method has been developed and validated. Three interface capturing ethods, namely Level Set (LS), Volume of Fluid (VOF), and coupled Level Set and VOF (CLSVOF), have been implemented and evaluated. The CLSVOF technique is adopted as the interface-tracking method in order to combine the advantages of LS and VOF methods. Due to the discontinuity of density and viscosity across the interface, simulations can become unstable due to numerical errors when a conventional discretisation approach is applied. Therefore, the governing equations are discretised here by introducing an extrapolated liquid velocity to minimise the interface momentum error, showing significant improvement in accuracy and robustness for simulations of primary breakup. For several reasons, single drop breakup in a uniform air flow is chosen as a benchmark test case for validation of the developed methodology for modelling atomisation. It is shown that the predicted drop breakup agrees quantitatively well with experiments for different Weber numbers. The solver is then applied to simulate primary breakup of liquid jets, which are more relevant to industrial applications. By simulating single round water jet atomisation in high-speed coaxial air flow, it is found that the predicted liquid core breakup lengths at different air/liquid velocities agree closely with measured data, but only when appropriate turbulent inflow conditions are specified. In simulations of liquid jet breakup in air crossflow, the penetration of the liquid jet is also well reproduced when turbulent inflows are used. In both simulations, it is found that the turbulence convected downstream from the injection nozzles affects significantly the primary breakup process, and the liquid turbulence rather than the gas turbulence plays a dominant role in initial disturbance of the liquid jet surface.
Description: A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/10148
Appears in Collections:PhD Theses (Aeronautical and Automotive Engineering)

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