Merge pull request #14754 from rmcdermo/master

FDS Source: change default TAU_CHEM to 1E-4 s

I found that providing a reasonably physical value for this parameter helped avoid instabilities.

Author: rmcdermo

Source/cons.f90

@@ -340,7 +340,7 @@ MODULE GLOBAL_CONSTANTS
 REAL(EB) :: LIMITING_DT_RATIO=1.E-4_EB         !< Ratio of current to initial time step when code is stopped
 REAL(EB) :: NOISE_VELOCITY=0.005_EB            !< Velocity of random noise vectors (m/s)
 REAL(EB) :: TAU_DEFAULT=1._EB                  !< Default ramp-up time (s)
-REAL(EB) :: TAU_CHEM=1.E-10_EB                 !< Smallest reaction mixing time scale (s)
+REAL(EB) :: TAU_CHEM=1.E-4_EB                  !< Smallest reaction mixing time scale (s)
 REAL(EB) :: TAU_FLAME=1.E10_EB                 !< Largest reaction mixing time scale (s)
 REAL(EB) :: SMOKE_ALBEDO=0.3_EB                !< Parmeter used by Smokeview
 REAL(EB) :: Y_WERNER_WENGLE=11.81_EB           !< Limit of y+ in Werner-Wengle model