NS is "Navier-Stokes"?
In cylindrical coordinates, r= (x^2+ y^2)^{1/2} and \theta= arctan(y/x).
\frac{\partial r}{\partial x}= (1/2)(x^2+ y^2)^{-1/2}(2x)= \frac{x}{\sqrt{x^2+ y^2}}= \frac{x}{r}
= \frac{r cos(\theta)}{r}= cos(\theta)
\frac{\partial r}{\partial y}= sin(\theta)
\frac{\partial \theta}{\partial x}= \frac{1}{1+ (y/x)^2}(-y/x^2)=\frac{-y}{x^2+ y^2}
= \frac{-r sin(\theta)}{r^2}= -\frac{sin(\theta)}{r}
\frac{\partial \theta}{\partial y}= \frac{1}{1+ (y/x)^2}(1/x)= \frac{x}{x^2+ y^2}
= \frac{r cos(\theta)}{r^2}= \frac{cos(\theta)}{r}
Using the chain rule
\frac{\partial \phi}{\partial x}= \frac{\partial \phi}{\partial r}\frac{\partial r}{\partial x}+ \frac{\partial \phi}{\partial \theta}\frac{\partial \theta}{\partial x}
You should be able to finish that, and then the second derivatives yourself. It's tedious but requires no deep mathematics.
