Fixes to enable stable single-phase runs.

src/chkdt.f90

@@ -77,7 +77,8 @@ subroutine chkdt(n,dl,dzci,dzfi,is_solve_ns,mu12,rho12,sigma,gacc,u,v,w,dtmax,ga
       dtik = sqrt(sigma/(minval(rho12(:)))/dlmin**3)
       dtig = maxval(abs(gacc))/dlmin
       dti = 2.*(dti+dtiv+sqrt((dti+dtiv)**2+4.*(dtig**2+dtik**2))) !TODO: follow Kang's paper to include dtipsi in the single dti formula, if is_solve_ns = .true.
-      if(dti == 0.) dti = 1.
+      if(dti    == 0.) dti    = 1.
+      if(dtipsi == 0.) dtipsi = 1.
       dtmax = min(dti**(-1),dtipsi**(-1))
     end if
 #if defined(_SCALAR)

src/rk.f90

@@ -169,7 +169,8 @@ subroutine rk_scal(rkpar,n,dli,dzci,dzfi,dt, &
   end subroutine rk_scal
   !
   subroutine rk_2fl(rkpar,n,dli,dzci,dzfi,dt,gam,seps,u,v,w,psi)
-    use mod_acdi, only: acdi_transport_pf
+    use mod_acdi     , only: acdi_transport_pf
+    use mod_two_fluid, only: clip_field
     !
     ! low-storage 3rd-order Runge-Kutta scheme
     ! for time integration of the phase field (actually Adams-Bashforth).
@@ -214,6 +215,7 @@ subroutine rk_2fl(rkpar,n,dli,dzci,dzfi,dt,gam,seps,u,v,w,psi)
         end do
       end do
     end do
+    call clip_field([1,1,1],[0._rp,1._rp],psi)
     !
     ! swap d?dtrk <-> d?dtrko
     !

src/two_fluid.f90

@@ -10,7 +10,7 @@ module mod_two_fluid
   use mod_types
   implicit none
   private
-  public init2fl,cmpt_norm_curv
+  public init2fl,clip_field,cmpt_norm_curv
   type sphere
     real(rp) :: xyz(3),r
   end type sphere