Wing —

Pressure along the chord Cp · upper amber · lower blue

Lift curve dashed = 2π(α − α₀)

Wind Tunnel close

Model

domain

4.4 × 2.4 chords · 400 × 220 cells · walls 2.4 chords apart

method

lattice Boltzmann D2Q9 · BGK collision · bounce-back body · fixed inlet · sponge at the walls and outlet

speed

U∞ = 0.1 cells / step (Mach 0.17) · Re = U∞ c / ν set by the slider

forces

momentum exchange at the wall · C_L C_D on the chord · mean of the last 600 steps

C_p

(p − p∞) / ½ρU∞² · p = ρ/3 · first fluid cell off the surface

separation

first upper-surface station with reversed flow, 3 cells out, two stations in a row

thin airfoil

C_L = 2π(α − α₀) · α₀ from the camber line, flap included

caveats

2-D: no tip vortices, no induced drag · Re ≤ 3,000 (a trainer wing at 60 kt is ~3,000,000: thinner boundary layer, later stall) · blockage inflates lift · laminar only

Controls

sliders

reshape the wing in the running flow

↑ ↓

α ± 1°

space · R · S

pause · reset flow · smoke

1 2 3 0

pressure · speed · vorticity · none

hover

local speed and C_p

sweep α

−6° → 22°, 2,400 steps each, the last 1,200 averaged onto the lift curve

mark

one point at the current α

Reading it

smoke

streaklines from 15 rakes at the inlet

pressure

blue = below freestream (suction) · red = above

vorticity

red = counter-clockwise · blue = clockwise · the wake sheds when the wing stalls

C_p plot

negative up, as charted · area between the curves ≈ lift