Quantifying the Scale Effect in Hydrogen/Air Explosions Using High-Fidelity Simulations with Detailed Chemistry

Abstract This study investigates the scale effect in hydrogen-air explosions using high-fidelity 2D and 3D numerical simulations with detailed chemistry. Simulations are conducted in an obstacle-laden channel, varying the geometric scaling factor, hydrogen mole fraction and dimensionality. Results show that flame acceleration increases significantly with geometric scale, primarily due to the enhanced growth of the turbulent flame surface area. Additionally, the local burning rate per unit flame area exhibits a complex dependency on scale and mixture composition, characterized by flame stretch and Markstein numbers, particularly in lean mixtures. It is found that the normalized critical distance to reach a specific velocity decreases as a power-law with increasing scale, confirming that explosions accelerate more effectively over shorter relative distances in larger facilities. While 2D simulations suggest that the corresponding power-law exponents are consistent across a wide range of equivalence ratios, 3D results reveal a critical deviation. The scale effect is significantly more pronounced in 3D than in 2D, where the flame acceleration is found to be significantly stronger and this holds particularly for lean mixtures. The findings are consistent with scale-dependent experimental results obtained in the laboratory-scale MiniRUT and the industrial-scale RUT facilities. They further demonstrate that two-dimensional approximations may substantially underpredict the scale sensitivity of lean hydrogen explosions. In this case, 3D effects are identified as crucial for accurately predicting the severity of hydrogen explosions.