Calculating acceleration along the streamwise direction (dU/ds) in CFD post
 

my case is modeling flow around an airfoil using the Gamma-Retheta model
I'm trying to integrate these equations into the CFD post as expressions:

U=(u^2+v^2+w^2)^0.5

dU/dx=0.5((u^2+v^2+w^2)^-0.5)*(2u(du/dx)+2v(dv/dx)+2w(dw/dx))
dU/dy=0.5((u^2+v^2+w^2)^-0.5)*(2u(du/dy)+2v(dv/dy)+2w(dw/dy))
dU/dx=0.5((u^2+v^2+w^2)^-0.5)*(2u(du/dz)+2v(dv/dz)+2w(dw/dz))

but the problem arises due to the zero velocity near the airfoil, because of this the " DIVIDE BY ZERO" error is showing, so the expression can't be evaluated globally in the flow field.

any tips or tricks would be most helpful.

these are the expressions I wrote in CFD post:

Dutodx=0.5*(((Velocity u^2)+(Velocity v^2)+(Velocity w^2))^-0.5)*((2*Velocity u*Velocity u.Gradient X)+(2*Velocity v*Velocity v.Gradient X)+(2*Velocity w*Velocity w.Gradient X))

Dutody=0.5*(((Velocity u^2)+(Velocity v^2)+(Velocity w^2))^-0.5)*((2*Velocity u*Velocity u.Gradient Y)+(2*Velocity v*Velocity v.Gradient Y)+(2*Velocity w*Velocity w.Gradient Y))

Dutodz=0.5*(((Velocity u^2)+(Velocity v^2)+(Velocity w^2))^-0.5)*((2*Velocity u*Velocity u.Gradient Z)+(2*Velocity v*Velocity v.Gradient Z)+(2*Velocity w*Velocity w.Gradient Z))

Dutods=((Velocity u/Velocity)*dutodx)+((Velocity v/Velocity)*dutody)+((Velocity w/Velocity)*dutodz)