Velocity measurements and turbulence statistics of a confined isothermal swirling flow

Abstract

A two-component laser Doppler velocimeter was employed to measure the flow properties of a confined, isothermal, swirling flowfield in an axisymmetric sudden expansion research combustor. A free vortex swirler was used to stir the flow at the inlet of the combustor. Measurements of mean velocities, Reynolds normal and shear stresses, and triple products were carried out at axial distances ranging from 0.38 H (step height) to 18 H downstream of the swirler. Detailed experimental data are provided to help in the understanding of the behavior of swirling, recirculating, axisymmetric, and turbulent flows inside dump combustors. A balance of the turbulence energy equation has been performed in order to get a detailed insight into the turbulent shear layer behavior. The turbulent kinetic energy terms: production, diffusion, and convection terms were computed directly from the experimental data using central differences. The viscous dissipation term was obtained from the balance of the kinetic energy equation. The analysis of the data was successful in identifying the various areas of interest in the flowfield where different turbulent transport mechanisms dominate. In addition, the data from this study will be available for upgrading advanced numerical codes. The swirling flow streamlines data are compared with the simple dump flow and it is shown that swirl reduces the size of the corner recirculation region in addition to creating a central toroidial recirculation region. In summary, swirling enhances the production and distribution of turbulence energy in the combustor which, in turn, indicates thorough flow mixing and earlier flow recovery.