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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