02 / Eulerian · constraint solve

Watch pressure repair a velocity field

Click or drag to move the forcing region. Increase the solve budget and compare the same field before and after projection.

Both panels use the same color scale. Coral and mint show opposite signs of divergence; arrows show face velocities averaged to cells. Pressure transports the correction across the domain, so a low iteration budget leaves a visible residual.
—RMS divergence · before
—RMS divergence · after
—Residual / initial
Computed explanation · native implementation in Physics2D
Equations and model boundary
∇²π = ∇·u*
u = u* − ∇π

A computed 32 × 20 MAC-grid projection with closed, no-through-flow walls and Jacobi pressure iterations. The pressure potential uses the native velocity-correction convention. This isolates projection: advection, buoyancy, SDF obstacles, combustion and nonzero expansion sources are separate stages.