Sensitivity of Isothermal Swirl Combustor Flow to Inlet Reynolds Number

TL;DR

This study uses numerical simulations to analyze how inlet Reynolds number affects flow patterns in a swirl combustor, revealing increased recirculation strength but stable recirculation zone location, which supports flame stability.

Contribution

It introduces a velocity profile inlet method for swirl generation and validates RANS simulations against experimental data, extending analysis to higher Reynolds numbers.

Findings

Increased Reynolds number intensifies recirculation zones.

Recirculation zone location remains stable despite flow changes.

Flow features are robust under varying inertial conditions.

Abstract

Numerical simulations were conducted to investigate the influence of inlet Reynolds number on the isothermal flow field in a lab-scale swirl combustor while keeping a fixed inlet swirl number of 0.67. The combustor geometry and baseline conditions were adopted from Taamallah et al. [1]. Unlike the experimental setup, which used axial vane swirlers to generate rotation, this study imposed a velocity profile at the inlet to introduce swirl. The simulations employed the Reynolds averaged Navier Stokes (RANS) approach with the shear stress transport k omega turbulence model, using ANSYS Fluent 2024R2. A grid independence study was performed using meshes of approximately 0.4, 0.5, and 0.6 million elements. The turbulent kinetic energy varied by less than 2 percent between the 0.5M and 0.6M grids, confirming adequate mesh resolution. The solver was validated against experimental data from Taamallah et al. [1], showing good agreement in axial velocity distribution. The validated model was then used to simulate a higher Reynolds number of about 30000. Contours and centerline profiles of axial velocity were analyzed. An inner recirculation zone (IRZ), identified by negative axial velocity in the core, formed in both cases and plays a key role in flame stabilization. An outer recirculation zone (ORZ) was observed near the expansion plane. Increasing Reynolds number raised the peak forward axial velocity by about 46 percent and intensified reverse velocity at x = 0.10 m by nearly 68 percent, indicating stronger recirculation. However, the axial location of the IRZ remained nearly unchanged. These results suggest robust flame anchoring under varying inertial conditions. Reacting flow simulations are planned as future work.