Abstract
The present paper focuses on the effect of swirl on important parameters of conical diffusers flows such as static pressure evolution, recirculation zones and wall shear stress. Governing equations are solved using a software based on the finite volume method. Moreover, turbulence effects are taken into account employing the k-e RNG model with an ennhaced wall treatment. The Reynolds number has been kept constant at 105, and various diffuser geometries were simulated, maintaining a high area ratio of 7 and varying the total divergence angle (16°, 24°, 40°, and 60°). Results showed that the swirl velocity component develops into a Rankine-vortex type or a forced-vortex type. In the former, swirl is not effective to prevent boundary layer separation, and a tailpipe is recommended to allow a large-scale mixing to enhance the pressure recovery process. In the latter case, boundary layer separation is prevented but an intermediary recirculation zone appears. Higher pressure recovery is attained at the exit of the diffuser with swirl addition, without the need of a tailpipe. Results also suggest that there is exists an imposed swirl intensity where the energy losses are minimum thus leading pressure recovery to an optimum level.
Highlights
Diffusers are widely used in many industrial devices and applications in order to convert kinetic energy into static pressure
The present study aims at the analysis of the effect of swirl addition to the conical diffuser flow pattern, including the regime when vortex breakdown occurs and its relation to static pressure evolution, boundary layer separation and radial pressure gradient
The present study analyzed the influence of swirl addition in the streamline pattern, pressure recovery, pressure gradient, and wall shear stress in a conical diffuser flow
Summary
Diffusers are widely used in many industrial devices and applications in order to convert kinetic energy into static pressure. The present study aims at the analysis of the effect of swirl addition to the conical diffuser flow pattern, including the regime when vortex breakdown occurs and its relation to static pressure evolution, boundary layer separation and radial pressure gradient. The density was constant and known, with a value corresponding to 1 atm and temperature of 500 K, i.e. ρ = 0.71 kg/m3 These conditions were chosen to better simulate the environment of a diffuser in a gas turbine, which is the main motivation for this study, it could be extended to any swirling flow in conical diffuser since the non-dimensional parameters match has been satisfied. This can be confirmed by noting that the recirculating bubble appears further downstream for those cases
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