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Impact of fuel supply impedance and fuel staging on gas turbine ...

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4 Modeling <str<strong>on</strong>g>of</str<strong>on</strong>g> turbulent reactive flows<br />

using CFD<br />

In the present work transient Computati<strong>on</strong>al Fluid Dynamics simulati<strong>on</strong>s are<br />

used to analyze quantitatively the resp<strong>on</strong>se <str<strong>on</strong>g>of</str<strong>on</strong>g> a practical premixed flame to<br />

acoustic fluctuati<strong>on</strong>s at the flame holder <str<strong>on</strong>g>and</str<strong>on</strong>g> in the vicinity <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>fuel</str<strong>on</strong>g> injecti<strong>on</strong>.<br />

The dynamics <str<strong>on</strong>g>of</str<strong>on</strong>g> the flame is determined in a post-processing step<br />

using the exported transient CFD data <str<strong>on</strong>g>and</str<strong>on</strong>g> the system identificati<strong>on</strong> method<br />

presented in chapter 5. This secti<strong>on</strong> describes the basic c<strong>on</strong>cepts <str<strong>on</strong>g>of</str<strong>on</strong>g> the numerical<br />

methods used in this work to model the turbulent reactive flow. For a<br />

more detailed informati<strong>on</strong> the reader is referred to Pope [104], Friedrich [33]<br />

or Tennekes <str<strong>on</strong>g>and</str<strong>on</strong>g> Lumley [126] regarding the descripti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> turbulence <str<strong>on</strong>g>and</str<strong>on</strong>g> to<br />

Poinsot <str<strong>on</strong>g>and</str<strong>on</strong>g> Veynante [94], Turns [128], Peters [92], Fox [32] <str<strong>on</strong>g>and</str<strong>on</strong>g> Williams [132]<br />

in terms <str<strong>on</strong>g>of</str<strong>on</strong>g> turbulent reacting flows. As the CFD simulati<strong>on</strong>s are performed<br />

using the commercial s<str<strong>on</strong>g>of</str<strong>on</strong>g>tware package ANSYS CFX, the equati<strong>on</strong>s presented<br />

below are similar to those described in [5].<br />

4.1 Theory <str<strong>on</strong>g>and</str<strong>on</strong>g> numerical modeling <str<strong>on</strong>g>of</str<strong>on</strong>g> turbulence<br />

4.1.1 Basic equati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> turbulent flows<br />

The numerical simulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> a turbulent reacting flow is based <strong>on</strong> the c<strong>on</strong>servati<strong>on</strong><br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> mass, momentum <str<strong>on</strong>g>and</str<strong>on</strong>g> energy. As the c<strong>on</strong>servati<strong>on</strong> equati<strong>on</strong>s c<strong>on</strong>tain<br />

more unknowns than equati<strong>on</strong>s, further simplificati<strong>on</strong>s have to be made<br />

to obtain a closed system <str<strong>on</strong>g>of</str<strong>on</strong>g> equati<strong>on</strong>s. These simplificati<strong>on</strong>s include the introducti<strong>on</strong><br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> the equati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> state for an ideal <strong>gas</strong> (Eqn. (3.7)), the caloric c<strong>on</strong>stitutive<br />

equati<strong>on</strong> d e= c v d T <str<strong>on</strong>g>and</str<strong>on</strong>g> a relati<strong>on</strong> for the stress tensor. The resulting<br />

system <str<strong>on</strong>g>of</str<strong>on</strong>g> equati<strong>on</strong>s is called the unsteady Navier-Stokes equati<strong>on</strong>s, which can<br />

69

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