### 7.20.3. Turbulence Effects

The above reaction rates are applicable to laminar flow. In turbulent systems, fluctuations can have a significant impact on nuclei and soot formation because of the nonlinearity of the respective source terms. To account for the effect of turbulence on soot formation, the Eddy Dissipation Concept (EDC) developed by Magnussen [44] is applied.

The Eddy Dissipation Concept (EDC) is a reactor concept that identifies a reactor, where the combustion of fuel takes place, related to the fine structures in turbulence. This reactor is treated as a homogeneous reactor exchanging mass and energy with the surrounding fluid. The fraction of mass that is contained in the fine structures is determined from the turbulence quantities.

Local balance equations are solved to compute the temperature and the concentrations of nuclei and soot particles in the fine structures and in the surrounding fluid, respectively. The mean source terms are then computed assuming a bimodal distribution of the fluid between the fine structures and the surrounding. For a detailed explanation of the Eddy Dissipation Concept, see (Magnussen, 1989).

The EDC procedure need not be applied to the soot combustion terms, because turbulence is already accounted for in the computation of the fuel reaction rate. For details, see Soot Combustion.

Release 18.2 - © ANSYS, Inc. All rights reserved.