Novel Low-y⁺ Roughness Correlation for Hydrogen-Fired Jet Burners Validated Under Isothermal and Reacting Conditions

Surface roughness has a critical influence on the aerothermal and combustion behavior of gas turbine burners, particularly with the growing use of additively manufactured (AM) components that exhibit inherently rougher surfaces than conventionally machined parts. This study investigates the impact of surface roughness on flow and flame dynamics in a premixed jet burner (PJB) operating under both isothermal-air and reacting hydrogen-fired conditions. Experimental measurements using Laser Doppler Anemometry (LDA) and OH* chemiluminescence were complemented by Computational Fluid Dynamics (CFD) simulations employing Reynolds-Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) frameworks. Building upon existing equivalent sand-grain roughness (kₛ) models, a novel correlation incorporating both measured roughness parameters and bulk flow velocity was developed to improve predictive accuracy for resolved boundary layers (y⁺ ≈ 1), a regime in which k_s ⁺ > y⁺ is common and standard roughness-function formulations lose validity. The new correlation demonstrated strong agreement with experimental data in isothermal simulations. When extended to reacting hydrogen-air flames, RANS simulations successfully reproduced roughness-induced flow redistribution and flame shortening, although DES tended to overpredict bluff-body effects and underperform under lean conditions. Overall, the proposed k_s correlation, validated under isothermal conditions, provides a computationally efficient framework for modelling surface-roughness effects, and its extension to reacting hydrogen flames, particularly under RANS, offers a promising basis for future development toward additively manufactured gas turbine components.

The online version contains supplementary material available at https://doi.org/10.1007/s10494-026-00799-z.