- #1
MichielM
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Homework Statement
A flow field is considered to be steady two-dimensional and can be described by the following
velocity components in the xy- or r[tex]\theta[/tex]-plane at the front half of the cylinder:
[tex]
u_r=V\cos\theta\left(1-\frac{a^2}{r^2}\right)
[/tex]
[tex]
u_{\theta}=-V\sin\theta\left(1+\frac{a^2}{r^2}\right)
[/tex]
Question: Transform this system from cylindrical coordinates into cartesian coordinates and give [tex]u_x[/tex], [tex]u_y[/tex] and [tex]u_z[/tex]
Homework Equations
The link between cartesian and cylindrical coordinates is:
[tex] x = x [/tex]
[tex]y = r \cos \theta[/tex]
[tex]z = r \sin \theta[/tex]
or the other way around:
[tex] x = x [/tex]
[tex]r^2 = x^2+y^2[/tex]
[tex]\theta =tan^{-1}(y/x)[/tex]
The Attempt at a Solution
For [tex]u_r[/tex] I take 1 term r outside the brackets and then transform to get:
[tex]
u_r=V y \left(\frac{1}{x^2+y^2}-\frac{a^2}{\left(x^2+y^2\right)^3}\right)
[/tex]
And similarly for [tex]u_{\theta}[/tex] I get:
[tex]
u_{\theta}=-V x \left(\frac{1}{x^2+y^2}+\frac{a^2}{\left(x^2+y^2\right)^3}\right)
[/tex]
This is where I get stuck, because I don't know how to separate the x and y parts of [tex]u_{\theta}[/tex] and [tex]u_{r}[/tex] to find the velocities in cartesian coordinates. Does anyone have any hints?!
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