Numerical Simulation of Cold Flow Field of Aero-Engine Combustors for Lean Blow Off Analysis

Lean blow off (LBO) performance is critical to the operational performance of combustion system in propulsion and power generation. Current predictive tools for LBO are based on decades-old empirical correlations that have limited applicability for modern combustor designs. Recent advances in computational fluids dynamics (CFD) have provided new insight into the fundamental processes that occur in these flows. In this paper, it is envisaged a new methodology for the LBO predictions that is predicting the LBO fuel/air ratio based on the cold flow field of the combustor. Comparing to the traditional tools, this methodology has the lower prediction cost, especially in the designing stage of the combustor. The study presented here is the preliminary study of this method. According to the Lefebvre’s LBO model, a new load parameter (mr ·Vf ) extracted from the cold flow field is obtained for LBO analysis. Commercial software FLUENT is used to simulate the velocity and concentration field without combustion in different combustors. LBO fuel/air ratios are obtained from the model combustor experiments. Flammable zone volume (Vf ) is used instead of Vc (as defined in Lefebvre’s model: combustor volume ahead of the dilution holes) in this LBO analysis. Vf is defined according to the lean/rich limits and increased with the increase of φLBO . In addition, the mass flow rate of back-flow air which enters the flammable zone (mr ) is used to account for the combustion air. φLBO is increased in a parabolic way with the increase of mr . The load parameter (mr ·Vf ) could represent the actual combustion load of the combustor near LBO and relates φLBO to the cold flow field of the combustor. It will be encouraging and beneficial to the study of LBO prediction in the future.Copyright © 2011 by ASME