Potential-flow streamlines · pressure & lift · separation and stall
The flow is built by superposition of elementary potential-flow solutions — a uniform stream plus a doublet (which makes a cylinder) and a vortex of strength Γ (which adds circulation). For the aerofoil the cylinder solution is mapped to a wing-like shape. Wherever the streamlines crowd together the local speed v rises, and Bernoulli's equation p + ½ρv² = const says the pressure must fall there. The colour shows the pressure coefficient Cp = 1 − (v/U)²: blue is suction (fast flow, low pressure) and red is high pressure near the stagnation points where the flow divides.
Lift comes from circulation. The Kutta–Joukowski theorem gives L = ρ·U·Γ per unit span, so more circulation (more camber or angle of attack) means more lift. The low pressure on the upper surface and higher pressure below add up to a net upward force.
Potential flow alone never stalls, so this model adds a simple boundary-layer cue: past a critical angle of attack the adverse pressure gradient on the upper surface separates the flow, the smoke breaks into a turbulent wake, lift collapses and drag jumps — a stall. For the cylinder you can see hints of the alternating Kármán vortex street in the wake. The Reynolds number Re = ρUL/μ sets how thin the boundary layer is and when transition to turbulence occurs.