Numerical Investigation of the Effect of Flow Turbulence on Heterogeneous Reaction Rates

Abstract

In this thesis, the effect of turbulence on heterogeneous reactions is investigated. After a short introduction into the state-of-the-art of turbulent combustion modelling, an overview over the numerical methods and models used to simulate homogeneous and heterogeneous combustion in turbulent flows is given. Then, a brief introduction into the most important features of the numerical implementation is provided. Simulations featuring a simple heterogeneous reaction system involving a passive reactant are performed with a compressible Direct Numerical Simulation (DNS) Computational Fluid Dynamics (CFD) code, called ”The Pencil Code”. Different particle numbers, sizes and flow properties are investigated, and an inhibiting effect of the turbulence on the reaction rates for high particle numbers is found. In further studies using the simplified model, the inhibiting effect is quantified for a range of particle numbers, and a model predicting the inhibiting effect from flow and particle properties is proposed. A sub model for the detailed modelling of particles burning in a cloud of gas, the ”Stanford Code” is extended and implemented into ”The Pencil Code”. The proposed model to predict the inhibiting effect is compared against data from simulations that use real chemistry represented by a simple reaction mechanism. Agreement between the proposed model obtained from the simplified reaction systems and the data from the more complex combustion system is found to be good. The performance of the proposed model is discussed and recommendations for further work to increase the predictive capabilities of the model are given.