Session: 04-27 Combustion Dynamics - Modeling

Paper Number: 153212

Impact of a Central Pilot Jet on the Stability of a Swirling Flow 

Swirling flows are a preferred flame stabilization mechanism for many lean premixed combustors, particularly used in gas turbines for both power-generation and aircraft applications. The vortex breakdown zone of a swirling jet produces a large central recirculation zone and regions of high shear to support flame stabilization. While these flows are successful at stabilizing flames over a large operating condition, issues related to engine turndown and thermoacoustic instability can lead to loss of both static and dynamic stability of the flame. The presence of pilot flames in the vicinity of the main flame often help improve static stability near lean blowoff and suppress combustion instabilities. Prior work showed how a central pilot flame enhances both static and dynamic stability through thermochemical back-support of the main flame. However, the impact of the central jet on the hydrodynamic stability of the flow, and hence its receptivity to velocity-coupled instability, was not considered. This study investigates the impact of the central pilot jet on the hydrodynamic stability of a swirling flow in a configuration relevant to power-generation and industrial gas turbine engines. Large-eddy simulations are done at a range of flow rates of the central pilot jet and results are first analyzed using spectral proper orthogonal decomposition, which shows significant shear layer oscillations at all pilot flow rates. Linear hydrodynamic stability analysis and companion adjoint analysis is used to identify instability modes and their sensitivities at these different flow rates; these results align with the results from the SPOD. Finally, resolvent analysis is performed at known instability frequencies in the companion experimental facility to understand how changes to the structure of the flow with the pilot jet alters the response of the flow to external perturbations.

Presenting Author: Pratikshya Mohanty Pennsylvania State University

Presenting Author Biography: Pratikshya Mohanty is a PhD candidate in the Department of Mechanical Engineering at the Pennsylvania State University and a graduate research assistant in both the Reacting Flow Dynamics Laboratory and the Computational Reacting Flows Laboratory.

Authors:

Pratikshya Mohanty Pennsylvania State University
Saarthak Gupta Indian Institute of Science - Bengaluru
Santosh Hemchandra Indian Institute of Science - Bengaluru
Yuan Xuan Pennsylvania State University
Jacqueline O'Connor Pennsylvania State University