Comparison of Laminar and Linear Eddy Model Closures for Combustion Instability Simulations

摘要

Unstable liquid rocket engines can produce highly complex dynamic flowfields with features such as rapid changes in temperature and pressure, increased heat transfer, local flame extinction and reignition, and local partially-premixed and non-premixed combustion. This type of flowfield represents a challenge for turbulent combustion models, which are typically associated with a number of assumptions that limit regime applicability. In the present study, the linear eddy model (LEM) is applied to an unstable single element liquid rocket engine to assess its performance and to contrast it with simple laminar combustion model (LCM). Two distinct operating conditions showing different dynamic behavior are used; the first is marginally stable and has peak-to-peak amplitudes of 12% of the mean, while the second is strongly unstable and has pressure amplitudes in excess of 40% of the mean. Results show that while the LEM is able to capture the general dynamics behavior, the trends are in the wrong direction when compared with the experimental results. In other words, the stable case becomes more unstable and the unstable case becomes more stable. The paper also examines the underlying assumptions of the LEM and suggests reasons for the observed behavior.