= Solution
The normalization denominator vanishes when $\sin2\alpha-2\alpha\cos2\alpha=0$, namely $\boxed{\tan2\alpha_c=2\alpha_c}$. The relevant first root above $\pi/2$ is $\alpha_c\simeq2.24670$ radians. The zero root is not the critical angle of interest.
For $\pi/2<\alpha<\alpha_c$ the denominator is positive. The profile is even, with outward flow near the bisector and reverse flow adjacent to each wall:
$$
G_0>0\quad(|\theta|<\pi-\alpha),\qquad G_0<0\quad(\pi-\alpha<|\theta|<\alpha).
$$
It vanishes at the walls and at $\theta=\pm(\pi-\alpha)$; its minima are at $\theta=\pm\pi/2$. The following sketch shows the leading approximation to $G$ for small $\epsilon$.
\Image[/past-exam-of-the-theoretical-mechanics-course-of-the-university-of-oxford/2008-wedge-flow.png]
{title=Leading radial wedge-flow profiles: outward central flux and reverse wall layers grow near the critical angle}
As $\alpha$ approaches $\alpha_c$ from below, the large positive central and negative wall contributions nearly cancel while the prescribed net <flux> remains one. The leading Stokes solution diverges, so the supposedly small nonlinear inertial term can no longer be treated as a <perturbation>. This is the <critical angle of a flux-normalized Stokes wedge flow>. It demonstrates breakdown of this <regular perturbation>[regular expansion]; it does not establish that the exact viscous flow must have infinite speed or that a global steady branch continues through the critical angle.
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