  In Navier-Stokes turbulence, energy and helicity injected at large scales are
subject to a joint direct cascade, with both quantities exhibiting a spectral
scaling $\propto k^{-5/3}$. We demonstrate via direct numerical simulations
that the two cascades are compatible due to the existence of a strong
scale-dependent phase alignment between velocity and vorticity fluctuations,
with the phase alignment angle scaling as $\cos\alpha_k\propto k^{-1}$.
