Detailed validation of LES for H2/CH4/Air deflagrations in an obstructed tube using PIV measurements

Abstract

This study offers a detailed validation of Large Eddy Simulation (LES) for lean H${}_2$/CH${}_4$/Air deflagrations in an obstructed tube. An exhaustive validation is conducted against detailed measurements from Li et al. (2019), which include pressure traces, flame speeds, and especially, Particle Image Velocimetry measurements of the deflagration-induced flow field. The exercise is performed without adjusting any model parameters, so that all simulations are executed using a unique numerical setup across all test cases. This approach provides a robust and unbiased assessment of LES capabilities in capturing the complex interactions between flame propagation, turbulence, and obstacles in explosion scenarios. Results demonstrate that LES accurately predicts the detailed evolution of the flow field in the recirculation zone behind the second obstacle, and the resulting over-pressure as well as flame speed and flame qualitative shape for various deflagration severities. Such results highlight the potential of LES for improving Safety Computational Fluid Dynamics predictive capabilities in industrial applications involving explosive environments. Once validated, LES is analyzed to unravel flame propagation dynamics: It is demonstrated that the flame remains laminar-like up to the second obstacle and then transitions to the turbulent combustion regime. Independently from the mixture blend, the maximum over-pressure is correlated to flame-turbulence interactions occurring in the wake of the second obstacle. While LES effectively captures these dynamics, it is noted that usual methods to quantify flows in pipes are inadequate for fully characterizing the transition to turbulence: Developing more refined indicators to detect this transition are required.

Novelty and significance statement

This study presents a significant advancement in the validation of Large Eddy Simulation (LES) for complex deflagration scenarios within obstructed geometries. Unlike previous works that typically rely on pressure data, flame speeds, and basic visualizations, this research integrates comparisons to Particle Image Velocimetry measurements for a quantitative validation of LES deflagrations in obstructed channels. By leveraging the detailed experimental dataset from Li et al. (2019), this paper establishes a new benchmark for simulation accuracy, demonstrating LES ability to capture complex flame-turbulence interactions in confined spaces. This work not only addresses the critical gap in the literature but also opens the way for advancements in Safety Computational Dynamics, setting a higher standard for future simulation studies.