Session: 04-42 Combustion dynamics - flow instabilities

Paper Number: 121890

121890 - Global Stability and Forced Response Analysis of Swirling Flows in Aviation Combustors 

Swirling jets are canonical flow fields used to stabilized flames in many gas turbine combustion systems.  The vortex dynamics of these flows amplifies background acoustic disturbances and perturb the flame, producing combustion noise and potentially combustion instabilities. Thus, hydrodynamic flow response to acoustic excitations in reacting flows is an important modeling task for understanding combustion noise and combustion instabilities. 

In this study, a global hydrodynamic stability analysis in a bi-global and tri-global framework is used to model the unsteady structures and vortical hydrodynamic modes of a harmonically forced, reacting swirling flow. The base state of this study is a swirling and reacting mean flow computed with LES, based upon a commercial nozzle. First, the unforced, natural bi-global solutions are analyzed to study unstable eigenmodes using the linearized momentum and continuity equations around the base state with an unstructured, tetrahedral finite element mesh. An empirical velocity transfer function is constructed by determining the flow response to a harmonically varying 150-1500 Hz u' velocity disturbance at the inflow boundary.

A prominent result of this study is that the 1050 Hz inlet-forced disturbance is dominant in amplification of axial velocity disturbances. Excitations around the corresponding St = 0.375 mode lead to axial velocity disturbances with amplification factors varying between 20 and 50 times at axial locations 0.24d_Sw < z < 1.5d_Sw  and over 60 times at downstream axial locations  z > 1.5d_Sw. 

A comparison study with a cartesian, three-dimensional reacting base flow is also conducted. The companion study utilizes a stable, high accuracy, but computationally effective centered finite difference scheme based on a three-dimensional structured mesh. Comparisons of computational cost, qualitative modes, and quantitative transfer functions between bi-global and tri-global stability analyses are illustrated in this study. 

Presenting Author: Parth Patki Georgia Institute of Technology

Presenting Author Biography: Parth Patki is a 4th year PhD student in the George W. Woodruff School of Mechanical Engineering at Georgia Institute of Technology and Graduate Research Assistant in the Ben T. Zinn Combustion Laboratory. He received his B.S. in Mechanical Engineering (2019) and M.S. in Mechanical Engineering (2021) from Georgia Insitute of Technology. Parth’s research focuses on hydrodynamic stability analysis of reacting swirling flows in combustion systems using an analytical and computational framework. He has also done research to identify mechanisms of entropy generation in a premixed flame. The research was primarily motivated by the topic of indirect combustion noise, where entropy fluctuations due to chemical reactions are generated during the combustion process and are convected downstream to interact with the accelerating mean flow.

Authors:

Parth Patki Georgia Institute of Technology
Benjamin Emerson Georgia Institute of Technology
Timothy Lieuwen Georgia Institute of Technology