<p>This study investigates the influence of injector flare angle (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\beta$</EquationSource> <EquationSource Format="MATHML"><math> <mi>β</mi> </math></EquationSource> </InlineEquation>) on the flow dynamics and dynamic stability of a counter-rotating dual-radial swirl injector. The objective is to elucidate how geometric variation modifies both hydrodynamic and thermo-acoustic instability characteristics, thereby shaping flame topology and global stability limits in swirl-stabilized combustors. A series of non-reacting and reacting experiments were conducted for flare angles <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\beta$</EquationSource> <EquationSource Format="MATHML"><math> <mi>β</mi> </math></EquationSource> </InlineEquation> = <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$0^{\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>0</mn> <mo>∘</mo> </msup> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$30^{\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>30</mn> <mo>∘</mo> </msup> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$50^{\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>50</mn> <mo>∘</mo> </msup> </math></EquationSource> </InlineEquation>. High-speed <InlineEquation ID="IEq6"> <EquationSource Format="TEX">$OH^*$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>O</mi> <msup> <mi>H</mi> <mo>∗</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> chemiluminescence, stereo-PIV, and dynamic pressure measurements were acquired simultaneously to resolve unsteady flow--flame interactions. Time-resolved and spectral analyses–including spectral POD–were employed to extract coherent structures, instability modes, and coupling mechanisms between pressure and velocity oscillations. Under non-reacting conditions, increasing the flare angle enhances the interaction between primary and secondary swirl streams, leading to stronger recirculation, a larger central recirculation zone (CRZ), and intensified precessing vortex core (PVC) activity. In reacting flows, <InlineEquation ID="IEq7"> <EquationSource Format="TEX">$\beta$</EquationSource> <EquationSource Format="MATHML"><math> <mi>β</mi> </math></EquationSource> </InlineEquation>profoundly affects both static and dynamic stability. The <InlineEquation ID="IEq8"> <EquationSource Format="TEX">$\beta = {0}^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>β</mi> <mo>=</mo> <msup> <mrow> <mn>0</mn> </mrow> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq9"> <EquationSource Format="TEX">$\beta = {30}^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>β</mi> <mo>=</mo> <msup> <mrow> <mn>30</mn> </mrow> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> cases sustain attached V-flames dominated by longitudinal thermo-acoustic oscillations, whereas <InlineEquation ID="IEq10"> <EquationSource Format="TEX">$\beta = {50}^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>β</mi> <mo>=</mo> <msup> <mrow> <mn>50</mn> </mrow> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> exhibits a transition from bubble-type to conical vortex breakdown (BVB <InlineEquation ID="IEq11"> <EquationSource Format="TEX">$\rightarrow$</EquationSource> <EquationSource Format="MATHML"><math> <mo stretchy="false">→</mo> </math></EquationSource> </InlineEquation> CVB), yielding lifted flames and intermittent low-frequency oscillations. This transition weakens acoustic coupling and produces a dynamically quieter yet stable flame. The flare angle is identified as a critical geometric control parameter dictating the balance between hydrodynamic and thermo-acoustic dominance. Optimizing <InlineEquation ID="IEq12"> <EquationSource Format="TEX">$\beta$</EquationSource> <EquationSource Format="MATHML"><math> <mi>β</mi> </math></EquationSource> </InlineEquation> improves fuel–air mixing, extends the rich blow-off limit, and mitigates high-amplitude oscillations. These findings provide fundamental guidance for designing high-shear swirl injectors in next-generation low-emission gas turbine combustors with enhanced stability and reduced acoustic sensitivity.</p>

Dynamic stability of a swirl-stabilized flame in a counter-rotating dual-radial swirler

期刊论文
发表日期：

2026年1月19日

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Darshan Rathod,
Thirumalaikumaran S K,
Saptarshi Basu,
Pratikash Panda

摘要

This study investigates the influence of injector flare angle ( $\beta$ $β$ ) on the flow dynamics and dynamic stability of a counter-rotating dual-radial swirl injector. The objective is to elucidate how geometric variation modifies both hydrodynamic and thermo-acoustic instability characteristics, thereby shaping flame topology and global stability limits in swirl-stabilized combustors. A series of non-reacting and reacting experiments were conducted for flare angles $\beta$ $β$ = $0^{\circ }$ $0^{\circ}$ , $30^{\circ }$ $30^{\circ}$ , and $50^{\circ }$ $50^{\circ}$ . High-speed $OH^*$ $O H^{*}$ chemiluminescence, stereo-PIV, and dynamic pressure measurements were acquired simultaneously to resolve unsteady flow--flame interactions. Time-resolved and spectral analyses–including spectral POD–were employed to extract coherent structures, instability modes, and coupling mechanisms between pressure and velocity oscillations. Under non-reacting conditions, increasing the flare angle enhances the interaction between primary and secondary swirl streams, leading to stronger recirculation, a larger central recirculation zone (CRZ), and intensified precessing vortex core (PVC) activity. In reacting flows, $\beta$ $β$ profoundly affects both static and dynamic stability. The $\beta = {0}^\circ$ $β = 0^{\circ}$ and $\beta = {30}^\circ$ $β = 30^{\circ}$ cases sustain attached V-flames dominated by longitudinal thermo-acoustic oscillations, whereas $\beta = {50}^\circ$ $β = 50^{\circ}$ exhibits a transition from bubble-type to conical vortex breakdown (BVB $\rightarrow$ $\to$ CVB), yielding lifted flames and intermittent low-frequency oscillations. This transition weakens acoustic coupling and produces a dynamically quieter yet stable flame. The flare angle is identified as a critical geometric control parameter dictating the balance between hydrodynamic and thermo-acoustic dominance. Optimizing $\beta$ $β$ improves fuel–air mixing, extends the rich blow-off limit, and mitigates high-amplitude oscillations. These findings provide fundamental guidance for designing high-shear swirl injectors in next-generation low-emission gas turbine combustors with enhanced stability and reduced acoustic sensitivity.