A Computational and Experimental Study of the Internal Flow in a Scaled Pressure- Swirl Atomizer

Abstract

The internal flow in a scaled p ressure-swirl atomizer has been studied bo th numerically and experimentally. The atomizer is a scale-up of a Danfoss pressure-swirl atomizer designed for domestic boilers. The atomizer is operated with water. The main objective of the work is to investigate whether it is possible to model the internal gas-liquid flow of an atomizer by use of the commercial code CFX-4.3. Special emphasis is given to the flow of the liquid p hase. Laser Doppler Anemometry (LDA) measurements have been performed in the a tomizer at a flow rate of 15 and 50 L/min respectively. Profiles of axial and tangential mean and RMS velocities are obtained. Furthermore, pressure measurements are c onducted and p ictures of the a ir-core a nd spray-cone a re taken for qualitative comparison. The tangential velocity profile resembles a Rankine vortex as reported by [1] and [2]. Transient computational fluid dynamics, CFD, simulations have been performed in a three-dimensional curvilinear grid representing the swirl chamber of the atomizer. The gas-liquid flow is modelled with the homogeneous multi-phase model i n CFX-4.3. Two approaches are used in the simulations: A Large Eddy Simulation, LES, based on the work of [3] and a simulation where the flow is modelled as being laminar. The simulations manage to capture the overall flow characteristics of a pressure-swirl atomizer with the formation of an air-core and a thin liquid film in the exit region of the swirl chamber. The numerical grid is able to resolve vortices in the liquid in the upper part of the swirl chamber. The trends in mean and RMS tangential velocity are captured, but the magnitude of the velocity is underestimated. With a modified inlet velocity in the laminar case, the magnitude of the tangential velocity shows better agreement with measurements demonstrating the importance of having representative inlet boundary conditions