Gas Turbine Combustor: Swirl Flame Stabilization

Swirler & Mixture

Vane angle θ 45°

Equivalence ratio φ 1.00

Inlet velocity U₀ 25 m/s

Flame State

UNLIT

Swirl number S

0.00

Damköhler Da

0.00

Laminar S_L

0.00 m/s

CTRZ length

0.0 D

How it works

A swirler imparts tangential momentum to the incoming air/fuel stream. Above a critical swirl number, vortex breakdown forms a central toroidal recirculation zone (CTRZ) that pulls hot combustion products back upstream — a continuous ignition source that anchors the flame instead of letting it blow downstream.

Swirl number:      S = (2/3)·tan(θ)      (radial-vane swirler, hub/tip ≈ 0.5)
Breakdown onset:   CTRZ forms once S > S_c ≈ 0.6
Stabilization:     Da = τ_res / τ_chem  (Damköhler number)
                   τ_res  = L_CTRZ / U_recirc
                   τ_chem = α / S_L²      (α = thermal diffusivity)
                   Flame stays lit while Da > Da_crit ≈ 1

The laminar flame speed S_L and adiabatic flame temperature both peak near stoichiometric (φ = 1) and fall toward zero at the lean and rich flammability limits (φ ≈ 0.5 and φ ≈ 1.6 for methane–air). Two failure modes bound the operating window:

Lean blowout (LBO) — too lean, or U₀ too high for the CTRZ that forms: τ_res drops below τ_chem, Da falls under 1, and the recirculating gas cools faster than it can re-ignite fresh mixture. The flame extinguishes.
Flashback — at low U₀ with a strong, near-stoichiometric mixture, the turbulent flame speed can exceed the local flow velocity near the swirler throat and the flame propagates upstream into the premixing passage — a hazard real annular combustors are designed to avoid.

Drag the sliders to sweep the vane angle, equivalence ratio and inlet velocity and watch the CTRZ (translucent torus) grow or shrink, and the flame (bright particles) anchor, blow out, or threaten to flash back.

Unburned mixture Burning / hot products Recirculation zone

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