Session: 04-09 Combustion Experiments
Paper Number: 127060
127060 - Schlieren Image Velocimetry and Modal Decomposition Study of Preheated Isothermal Flow From a Generic Multi-Swirl Burner
Modern gas turbine technology relies on lean premixed combustion to minimize NOx emissions. However, this approach introduces challenges such as thermoacoustic instabilities, flame blowout, and flashback. These combustion systems often utilize swirling flows for flame stabilization within combustors. Swirling flow induces vortex breakdown, creating a central recirculation zone that sustains the flame by supplying heat and active species. This promotes efficient mixing of air-fuel mixtures and temperature control, reducing NOx emissions and enhancing safety against auto-ignition and flashback. Nonetheless, intense swirling flows are susceptible to a self-excited global hydrodynamic instability known as the precessing vortex core (PVC), resulting in significant flame fluctuations. These instabilities can interact with fluctuations from turbulent flow or random changes in operational parameters (noise), resulting in a complex flow environment. Understanding the dynamics of these interactions, including swirl intensity, equivalence ratio, vorticity, heat release, and pressure fluctuations, is crucial.
The primary objective of this study is to employ optical measurement techniques and advanced data analysis tools to gain insights into swirling flow instabilities. In this work, we conduct experiments on an unconfined preheated isothermal (non-reactive) flow subjected to stochastic turbulent perturbations (colored noise forcing) from a multi-swirl burner. This burner consists of three concentric air-swirling passages: an outer radial swirler, an intermediate swirler, and an inner axial swirler. The isothermal flow is investigated at a constant airflow rate of 50kg/h under three preheat conditions: 20oC, 40oC and 60oC. We employ Schlieren image velocimetry (SIV) to capture the velocity field of the swirling jets. Since the multi-swirl burner features multiple shear layers, multiple recirculation zones, boundary layer detachments, and a wide range of structures, we utilize spectral proper orthogonal decomposition (SPOD) to identify and characterize large-scale coherent structures from the SIV data. This allows us to analyze the energy-based spatial structures at different characteristic frequencies. In this work, we show the impact of preheat temperature variations on instability mode dynamics, including their shape, energy, and oscillation frequency shifts, particularly when the flow is subjected to stochastic forcing.
Presenting Author: Neha Vishnoi Indian Institute of Technology Ropar
Presenting Author Biography: Neha Vishnoi is a 5th year PhD student in the department of Mechanical Engineering at Indian Institute of Technology Ropar, India.
Her research area includes thermoacoustic instability and control, nonlinear dynamics, combustion diagnostics and flow instability in gas turbine combustors.
Authors:
Neha Vishnoi Indian Institute of Technology RoparAditya Saurabh Indian Institute of Technology Kanpur
Lipika Kabiraj Indian Institute of Technology Ropar
Schlieren Image Velocimetry and Modal Decomposition Study of Preheated Isothermal Flow From a Generic Multi-Swirl Burner
Paper Type
Technical Paper Publication