= Orr mechanism
{c}
The Orr mechanism amplifies a leading two-dimensional shear disturbance as the background flow swings its wavefronts toward alignment. Conserved perturbation <vorticity> implies velocity <amplitude> proportional to the inverse <wavevector> magnitude. This produces algebraic or transient <energy> amplification without an exponentially growing <normal mode>. <Viscosity> limits the benefit of choosing an initially tightly wound disturbance.
// Target: gravitational-instability-of-an-astrophysical-disk.bigb
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