Session: 04-24 Combustion - Modeling II

Submission Number: 177644

Assessment of RANS-Based Turbulence Models for Predicting Isothermal Swirling Flows in a Model RQL Combustor 

This study evaluates the predictive capability of several Reynolds-Averaged Navier-Stokes (RANS) turbulence models by simulating non-reacting (isothermal) flow in a laboratory-scale Rich-Quench-Lean (RQL) combustor. The combustor consists of three flow streams: primary air through the swirler, fuel injector flow, and quench air through five staggered quench holes at a downstream location. The swirler provides a nominal swirl number of 0.69. Five two-equation turbulence models, namely standard 𝑘-𝜖, realizable 𝑘-𝜖, RNG 𝑘-𝜖, SST 𝑘-𝜔, and GEKO 𝑘-𝜔 are assessed against Particle Image Velocimetry (PIV) measurements. A seven-equation model (LPS-RSM) is also evaluated. Most of these models do not accurately capture the swirl flow field. The standard 𝑘-𝜖 model shows the best agreement with the measurements. The model evaluation is based on predictions of velocity profiles, coherent structures, and the inner recirculation zone (IRZ) topology. RANS models are initially assessed for the baseline case with only primary air flow through the swirler at a Reynolds number of 10,000. After the assessment of models for the baseline flow case, the standard 𝑘-𝜖 model is used to predict the flow field with the primary air and fuel stream flows. The fuel stream flow rate corresponds to an equivalence ratio of 1.6 based on the butane equivalent volumetric flow rate. The simulations reveal a reduction in swirl intensity with fuel injection. Air-fuel mixing occurs primarily within the inner shear layer within a short distance of 30 mm from the swirler. Finally, the selected RANS model is applied to simulate the complete RQL configuration, including the primary air, fuel stream, and quench air flows. Two quench air flow rates are considered. The upstream entrainment of quench air is captured by the RANS simulations. Analysis shows that fuel-rich mixtures from the primary region may escape the quench zone when the quench air jet momentum is insufficient, while increasing the quench air flow reduces this escape. The standard 𝑘-𝜖 model provides the overall agreement with the experimental measurements for the examined RQL configuration. The discrepancies in simulated flow field are primarily attributed to the inherent limitations of steady-state RANS in representing anisotropic and unsteady swirling flow structures.

Presenting Author: Irfan A. Mulla Indian Institute of Science, Bangalore

Presenting Author Biography: Dr. Irfan Mulla is an Assistant Professor in the Department of Aerospace Engineering at the Indian Institute of Science, Bangalore. He received his Ph.D. in experimental combustion from the Indian Institute of Technology Madras. Following his doctoral studies, he conducted postdoctoral research in the UK and France. He was awarded the prestigious Marie-Curie Postdoctoral Fellowship. His current focus is on soot, NOx, and CO formation in both canonical laminar burners and in gas turbine combustors. The emissions are studied using the laser-based measurements and chemical kinetics simulations. His research group has expertise in the quantification of laser-based measurements through spectroscopic modelling.

Authors:

Kundan Kumar Indian institute of Science, Bangalore
Irfan A. Mulla Indian Institute of Science, Bangalore