Abstract
This paper compares 2D axisymmetric and 3D numerical models used to predict the internal flow of a pressure-swirl atomizer using a commercial software Ansys Fluent 18.1. The computed results are compared with experimental data in terms of spray cone angle (SCA), discharge coefficient (CD), internal air-core dimensions and swirl velocity profile. The swirl velocity was experimentally studied using a Laser Doppler Anemometry in a scaled transparent model of the atomizer. The internal air-core was visualized at high temporal and spatial resolution by a high-speed camera with backlit illumination. The internal flow was numerically treated as transient two-phase flow. The gas-liquid interface was captured with Volume of Fluid scheme. The numerical solver used both laminar and turbulent approach. Turbulence was modelled using k-ε, k-ω, Reynolds Stress model (RSM) and coarse Large Eddy Simulation (LES). The laminar solver was capable to predict all the parameters with an error less than 5% compared with the experimental results in both 2D and 3D simulation. However, it overpredicted the velocity of the discharged liquid sheet. The LES model performed similarly to the laminar solver, but the liquid sheet velocity was 10% lower. The two-equation models k-ε and k-ω overpredicted the turbulence viscosity and the internal air-core was not predicted.
Highlights
The Pressure swirl atomizers (PS) have an irreplaceable role in many industrial applications including combustion, spray cooling, spray drying etc
The CFD simulations are compared with the experimental data in terms of the discharge parameters such as the discharge coefficient CD, spray cone angle (SCA) and atomizer efficiency, the air-core dimensions and the velocity profiles inside the swirl chamber
The dimensionless air-core diameters, dimensionless velocity profiles, SCA and CD were identical for both atomizers, in this paper, the results are shown here in a dimensionless form and they are based on the CFD simulations of the originally sized atomizer
Summary
The Pressure swirl atomizers (PS) have an irreplaceable role in many industrial applications including combustion, spray cooling, spray drying etc. In a typical PS atomizer, the pumped liquid is fed via tangential ports into a swirl chamber where it gains high angular velocity and creates a low-pressure zone along a centre line of the swirl chamber. The air is pulled inside the low-pressure zone, so an air-core is formed. The swirling liquid is discharged from the exit orifice in a form of a conical liquid sheet at a certain spray cone angle (SCA) and disintegrates due to aerodynamical forces into filaments and ligaments. The internal flow behaviour is complex, mainly due to the dominant swirling velocity component and the induced internal aircore which blocks a portion of the exit orifice. Secondary flow effect as Görtler vortices could be presented in a boundary layer inside the swirl chamber [2, 3]
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