[GTP] TODAY--Reminder- GTP seminar--Sergei Chumakov

[Silvia Gentile]

Sergei Chumakov
Center for Turbulence Research, Stanford University

December 3 2009
Foothills Laboratory 2, Room 1022 (3450 Mitchell Lane, 303 497 8700)
Lecture 3:30pm

Lag-modeling Approach for Dissipation Terms in Large Eddy Simulation
Modeling the rate of scalar mixing in turbulent flow presents an 
important practical challenge. For example, in non-premixed combustion, 
the heat release is almost entirely determined by the mixing rate. Rapid 
mixing of the initially separated fiel and oxidizer is required to 
maximize the heat release rate and overall efficiently of a general 
compact combustor. The rate of mixing in the non-premixed combustion is 
expressed by the dissipation rate of the scalar variance, which is not 
available directly from turbulent simulations that use any kind of 
turbulence modeling. Similar issues arise in any reacting turbulent flow 
where the initial distribution of reacting species is non-uniform. 
Therefore the dissipation has to be modeled.
All present dissipation models use algebraic relations between the 
dissipation and known variables, implying an instantaneous connection 
between the large-scale flow features and the molecular level of mixing, 
represented by the dissipation. In the present work, an a priori study 
shows that the dissipation-rate is instead most highly correlated with 
the large-scale eddies at a previous time. Therefore, our modeling 
approach takes this "lag" into account. The new model is tested in large 
eddy simulation of the Sydney bluff-body flame. We show that in the 
region of the high dissipation latel (the "neck" region of the flame), 
the lag-model gives improved predictions when compared to the state of 
the art algebraic model.