Upgrading Only the Viscous Term to Second Order Made the Error 1.82x Worse — Why the Semi-Implicit Gear Scheme Extrapolates Convection
·8 min read
Pairing BDF2 with convection at N^n drops the scheme to first order and inflates the error. The extrapolation 2N^n − N^(n−1) restores second order.
The Man Who Erased Pressure — Chorin's Projection Method and Fractional Step
·6 min read
After the predictor the divergence sits near 1e-2. One FFT projection drops it to 1e-13, and the pressure Poisson still takes most of the step.