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Research Article

The Role of Flame–flow Interactions on Lean Premixed Lifted Flame Stabilization in a Low Swirl Flow

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Pages 897-922 | Received 11 May 2021, Accepted 01 Sep 2021, Published online: 30 Sep 2021
 

ABSTRACT

Swirling flows have been widely used to stabilize lean premixed combustion in various gas turbines and furnaces. In such flows, understanding and characterizing the flame stabilization are of both practical and fundamental interests. It is known that the swirling motion decreases the flow velocity at the burner outlet, which contributes to flame stabilization. In low swirl flows, such a deceleration stabilizes a premixed flame aerodynamically. The present investigations, using large eddy simulations, study flame–flow interactions in lean premixed lifted flame stabilized in a low swirl flow. The results show that in addition to the swirling motion, combustion heat release reduces axial velocity in the reactant stream by reducing dilatation, vortex stretching, and baroclinic vorticity production terms. The analyses of vorticity production source terms show that besides the flow deceleration induced by the swirling motion, the dominant mechanism for the flow deceleration upstream of the low swirl lifted flame is the baroclinic torque. However, unlike the dilatation term, the effects of the vortex stretching and baroclinic diminish further upstream of the flame front.

Nomenclature

ω˙=0.01ω˙maxρ=density

U=velocity

P=pressure

τij=stress tensor

Y=mass fraction

hs=sensible enthalpy

Sc=Schmidt number

Pr=Prandtl number

Sij=strain rate tensor

μ=viscosity

k=kinetic energy

δ=Kronecker delta

Ck, β, Cms,a=Costants

Δ=grid size

ω˙h=source term in conservation of sensible enthalpy equation

ω˙k=source term in conservation of mass equation

SL=laminar flame speed

δL=laminar flame thickness

Dm=molecular diffusivity

ω˙=reaction rate

F=thickening factor

E=efficiency function

u=velocity fluctuation

Re=Reynolds number

RR=heat release rate

A=pre-exponential factor

T=temperature

q˙s=spark source term

Es=total spark energy

σs=size of the spark kernel

σt=duration of spark discharge

t=time

r,θ,Z=cylindrical coordinate

Δs=spatial characteristic length of the spark

Δt=temporal characteristic length of the spark

Cp=heat capacity at constant pressure

D=burner diameter

φ=root-mean-square velocity fluctuation

u=equivalence ratio

ω=vorticity

Subscripts/Superscripts

Subscripts

T=turbulent

sgs=Subgrid-scale

max=Maximum

is=instant sparking

un=unburnt mixture

rms=root-mean-square fluctuation

Superscripts

sgs=Subgrid-scale

0=non-thickened flame

1=thickened flame

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

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