Adjoint-Based Sensitivity Analysis of Steady Char Burnout

TL;DR

This paper develops and compares adjoint-based sensitivity analysis methods for steady char burnout in pulverised coal combustion, offering an efficient way to analyze large parameter spaces and quantify uncertainties.

Contribution

It introduces an adjoint framework for sensitivity analysis in coal combustion models, comparing discrete and continuous adjoints with traditional methods, and provides a benchmark for future unsteady and turbulent studies.

Findings

Adjoint methods efficiently analyze sensitivities in complex combustion models.

Discrete and continuous adjoints are compared to finite differences and forward analysis.

Sensitivity results vary with different combustion atmospheres and parameters.

Abstract

Simulations of pulverised coal combustion rely on various models, required in order to correctly approximate the flow, chemical reactions, and behavior of solid particles. These models, in turn, rely on multiple model parameters, which are determined through experiments or small-scale simulations and contain a certain level of uncertainty. The competing effects of transport, particle physics, and chemistry give rise to various scales and disparate dynamics, making it a very challenging problem to analyse. Therefore, the steady combustion process of a single solid particle is considered as a starting point for this study. As an added complication, the large number of parameters present in such simulations makes a purely forward approach to sensitivity analysis very expensive and almost infeasible. Therefore, the use of adjoint-based algorithms, to identify and quantify the underlying sensitivities and uncertainties, is proposed. This adjoint framework bears a great advantage in this case, where a large input space is analysed, since a single forward and backward sweep provides sensitivity information with respect to all parameters of interest. In order to investigate the applicability of such methods, both discrete and continuous adjoints are considered, and compared to the conventional approaches, such as finite differences, and forward sensitivity analysis. Various quantities of interest are considered, and sensitivities with respect to the relevant combustion parameters are reported for two different freestream compositions, describing air and oxy-atmospheres. This study serves as a benchmark for future research, where unsteady and finally turbulent cases will be considered.