PASSIVE SCALARS

Passive scalars do not affect the flow.  They are transported by
advection and diffusion, and they can be created/destroyed as a result
of reaction.
 
In the code, the scalars are identified by "scalar type".

Scalars of type < 100 are non-reactive.

Scalars of type > 100 have a reaction rate of type R(T), where T is
the scalar.  For reactive scalars, the first digit of scalar type
(hundreds) determines the particular kind of reaction rate:

  1 - KPP reaction rate, R(T) = 1 - T^2;
  2 - symmetric bistable (spinodal) reaction rate, R(T) = (1-T^2)*T;
  3 - self-adjusting bistable reaction rate, R(T) = (1-T^2)*(T-Tavg).

The last two digits of scalar type determines the initial distribution
of scalar:

  0 - Plain Kolmogorov spectrum
  1 - Exponential spectrum
  2 - Von Karman spectrum
  3 - double-delta PDF

 11 - scalar is spatially distributed: T = 1 for z/2pi = [1/4:3/4],
      and T = -1 elsewhere.

Scalars' properties are specified in the *.in file in the table: 

  type, Sc, infrared exponent, peak wavenumber, reaction rate