diff --git a/src/particlesTransport.f90 b/src/particlesTransport.f90
index b8428d4d4dc7c84ddb5a6e4001f6f5de810cb744..6cdcfe6ed5b831b0789e0d325d1c3bd14aa659f2 100755
--- a/src/particlesTransport.f90
+++ b/src/particlesTransport.f90
@@ -81,7 +81,7 @@
       do 1 n=1,np
         urel= sqrt((uf(n)-up(n))**2+(vf(n)-vp(n))**2+(wf(n)-wp(n))**2)
         Reyp= max(1.e-10_pr,2._pr*radp(n)*urel/nuf)
-        Reyf= radp(n)**2/nuf*sqrt(dufdy(n)**2+dufdz(n)**2)
+        Reyf= 4._pr*radp(n)**2/nuf*sqrt(dufdy(n)**2+dufdz(n)**2)
         beta= Reyf/Reyp/2._pr
   
         if (Reyp.le.40._pr) then