An isothermal analysis of curved-vane and flat-vane swirlers for burners

Abstract

.

This paper focuses on assessing the accuracy of different swirl generators in the context of achieving high efficiency and low NOx emissions in burner technology. The aim is to maintain a compact flame with a fixed position through swirling flow, necessitating efficient swirler design. The study considers two axial-swirlers: one with curve-vanes featuring a straight line and a trailing edge in the shape of an arc of a circle, and the other with common flat vanes. The evaluation uses a well-known benchmark test case. Two approaches are used to model the swirler: the general-purpose Computational Fluid Dynamics (CFD) solver Ansys-Fluent® and the OpenFOAM® library suite to solve the Reynolds Averaged Navier Stokes equations. Slight deviations between these approaches are observed. The assessment includes the Swirl number and the size of recirculation zones in the test chamber, with a focus on segregation intensity as an indicator of mixing quality. The findings indicate that CFD models are valuable for predicting flow characteristics. Numerical results show a reduction in the radial size of the inner recirculation zone (IRZ), with a higher swirl number leading to a larger IRZ and a smaller outer recirculation zone (ORZ). The curved swirler exhibits better axi-symmetric behavior than flat vanes, with minimal influence of chord vanes on the swirl number. The number of vanes represents a compromise between head losses and flow guidance. This paper provides two distinct approaches for solving turbulent swirling flows: one using a commercial tool (Ansys-Fluent®) and the other employing open-source code (OpenFOAM®). Both approaches yield similar results. Additionally, the paper introduces an innovative setup for an axial swirler, departing from conventional flat vanes, which adds to its originality and value.