Geometry of intensive scalar dissipation events in turbulence.

Geometry of intensive scalar mixing events in turbulence

Maxima of the scalar dissipation rate in turbulence appear in form of sheets and correspond with potentially most intensive scalar mixing events. Their cross-section thickness determines a local diffusion scale. The distribution of this scale is analysed with a fast multiscale clustering algorithm which is applied to very high-resolution simulation data. The thickness is found to be distributed...

Analysis of scalar dissipation in terms of vorticity geometry in isotropic turbulence

Stochastic modeling of scalar dissipation rate fluctuations in non-premixed turbulent combustion

where DZ is the diffusion coefficient of the mixture fraction. The scalar dissipation rate appears in many models for turbulent non-premixed combustion as, for instance, the flamelet model (Peters (1984), Peters (1987)), the Conditional Moment Closure (CMC) model (Klimenko & Bilger (1999)), or the compositional pdf model (O’Brien (1980), Pope (1985)). In common technical applications, it has be...

Statistics and geometry of passive scalars in turbulence

We present direct numerical simulations of the mixing of the passive scalar at modest Taylor microscale 10 R 42 and Schmidt numbers larger than unity 2 Sc 32 . The simulations resolve below the Batchelor scale up to a factor of 4. The advecting turbulence is homogeneous and isotropic, and is maintained stationary by stochastic forcing at low wave numbers. The passive scalar is rendered stationa...

Statistics and geometry in high-Schmidt number scalar mixing

The mixing of substances is present in various turbulent systems. Examples arise in reacting flows and combustion, mixing of salt and plankton in oceans and of chemical pollutants in the stratosphere [1]. The physics of scalar mixing depends strongly on the ratio of the kinematic viscosity ν of the fluid to the diffusivity κ of the scalar. It is given by the Schmidt number Sc = ν/κ. For the fol...