Boundary-Layer Flashback Prediction in Nonswirling and Swirling Hydrogen-Enriched Flames

Boundary-layer flashback (BLF) is a major challenge in hydrogen-fueled nozzles design. This work aims at improving the BLF criterion based on the critical velocity gradient (CVG) theory and developing a method that performs better than existing methods and can rapidly predict the global flashback limit and local flashback risk. First, the turbulent-flame-speed-based CVG (T-CVG) criterion was improved to formulate an enhanced T-CVG (ET-CVG) criterion, which better accounts for the characteristics of the lean premixed hydrogen/air mixture. Then, the performance of the T-CVG, ET-CVG, and critically strained flame (CSF) criteria as the global BLF criteria were evaluated, and the feasibility of the BLF criteria to evaluate the local flashback risk was analyzed. Results show that, compared to the T-CVG criterion, the ET-CVG criterion improves the accuracy of global flashback limits. The relative error is less than 15 and 10% in nonswirling pipe flows and bluff-body swirling flows, respectively. With its optimal [Formula: see text] being less sensitive to the calibration process compared to that of the CSF criterion, the ET-CVG criterion combined with the nonreacting Reynolds-averaged Navier–Stokes flowfield enables the rapid prediction of local flashback risk in bluff-body swirling flows with broad universality, illustrating its potential for the design of hydrogen-fueled injectors.