Analysis of thermodiffusive instabilities in hydrogen/air premixed flames using a tabulated flamelet model

Abstract

In this work, a comprehensive formulation including detailed transport effects through mixture-averaged molecular diffusion in the context of tabulated chemistry is applied to the study of the propagation and structure of freely propagating hydrogen flames where intrinsic instabilities play an important role. The performance of the tabulated approach is evaluated by comparing its predictions with those from detailed chemistry calculations. The analysis focuses on two key aspects: the model’s behaviour in both linear and non-linear regimes, and its sensitivity to pressure and temperature variations. Additionally, the impact of mesh resolution on the flame response is examined to assess the capabilities of the proposed method to recover the fundamental aspects of the flames. The analysis begins by examining the linear regime through the dispersion relation. The results indicate that thermodynamic conditions significantly influence the wavenumber range predicted by the tabulated model. Specifically, increasing temperature or pressure extends the model’s predictive capability—either by reducing flame instability (at higher temperature) or by producing a thinner flame front (at higher pressure). However, some discrepancies in the dispersion relation within the linear regime, particularly for the stable range, are observed, revealing a slight tendency of the tabulated model to overpredict flame wrinkling. Subsequently, the non-linear regime is analysed by computing global flame parameters and comparing the flame structure with the reference solutions. The results show that the model accurately captures global flame descriptors for the three conditions investigated with relative errors of less than 10%. Considering the complexity of the physical and chemical phenomena involved, it can be concluded that the model successfully reproduces the most relevant effects governing flames exhibiting thermodiffusive instabilities and offers a reliable alternative to detailed chemistry with notably lower computational cost.

Novelty and significance statement

This research work contributes to delimiting the capabilities of a new formulation for a flamelet tabulated method that includes preferential diffusion through mixture-averaged diffusion to predict intrinsic instabilities in premixed hydrogen flames. To this end, several operating conditions are simulated to understand the influence of pressure and temperature on the accuracy of the model’s response. The linear and non-linear regimes are studied and compared with the detailed chemistry solutions to provide an integral description. The novelty of this investigation lies in the demonstration that such formulation can recover significant characteristics of the flame that exhibits thermodiffusive instabilities for representative operating conditions.